Split (1)

train · 1.46M rows

text stringlengths 83 79.5k
H: Converting 3 seperate 4.5V battery operated devices to one AC power supply I'm wanting to convert 3 battery operated marquee signs to AC power by following one of the many tutorials out there on sites like instructables.com. I'm more than capable of doing each one on its own and having 3 wall warts for each sign. My question is can I power all 3 signs off 1 AC power supply? Each sign takes 3 C batteries so I know to do each one would require a 4.5v power supply on its own. Could I do 1 13.5v power supply and wire it to all 3 signs? Thank you. AI: If each sign requires 4.5 volts, then you need to connect all the signs in parallel, to a 4.5 volt DC power supply You should determine the maximum current required by each sign, and get a power supply that can deliver at least the total current required by all signs.
H: DC to AC converter I know there are lots of circuits that do this, but I need to design a circuit that has a DC input and a square wave output by using any of these components: capacitors, inductors, OpAmps, resistors, diodes, and a dc power supply To be more specific, the square wave should have a duty cycle of 20% Any ideas? AI: I think the easiest solution to understand, given those components, would be an RC oscillator, followed by a comparator. Design your RC oscillator to give the frequency you want. See, for example, http://www.electronics-tutorials.ws/oscillator/rc_oscillator.html Feed the oscillator output into the input of a comparator, with the threshold voltage proportional to the duty. See, for example, http://www.electronics-tutorials.ws/opamp/op-amp-comparator.html Note this solution doesn't require the diode - not sure if there's a more elegant solution that involves diodes.
H: Why is XNOR gate not referred to as an "Equality" gate? I am a programmer and I was thinking about some logic I was just writing and the logical statement started out as a negated exclusive or, but this simplifies to a logical equality check, e.g. var x = a == b. That is to say, we can express this as x <- a XNOR b. Since I was looking at the XOR page i found that there is an XNOR gate which is just an XOR gate negated. It got me to wondering because XNOR seems like such a convoluted way to refer to the concept of what this gate does. I wonder if this is just how history played out, or if there is something subtle that I'm missing. AI: I think that's a valid observation. The reason it's called an XNOR is that all logic gates are based on boolean algebra. The boolean operations of conjunction, disjunction and negation map isometrically to AND, OR and NOT. Combining negation with conjunction and disjunction gives you NAND and NOR and exclusive disjunction gives you XOR. Naturally then, when you add negation, you get XNOR (which is simply easier to say than NXOR). The fact that XOR performs an inequality operation and XNOR performs equality operation is a by-product, but a valid one nonetheless. Note that it is no more remarkable then the fact that AND is modulo two multiplication and XOR is modulo two addition. You're free to use the representation that is most convenient to the task at hand. If you're programming, then converting your result into arithmetic operators makes sense.
H: Making my own Breakout board for a GPS I am prototyping a few things and wanted to make my own breakout for something that I haven't done before: GPS. (link to page) I know that high-freq. PCB are usually different compared to regular PCB. My question to you guys are as follows: Is the ground plane nessecary? Should I put decoupling caps on the PCB or leave them to the prototype? What should I change to acomodate to the 5GHz frequency /antenna? How can I put power protection on this aside from a fuse? Is this a viable setup for prototyping? Schematic: refrence: red: fill black:nofill small white text: solder pad large white text: silk layer AI: Is the ground plane nessecary? Yes, only to control the characteristic impedance of the antenna trace. Without a ground plane it is very difficult to ensure 50&ohm;. For such a short trace, you may get away with it, but you might find that depending on where you place your prototyping board, or how close you hand comes to it, has a big effect on the reception performance of the antenna. To save yourself the trouble of adding a ground plane, for the sake of prototyping I'd just move the connector closer to the pin and live with the possible degradation to reception. Should I put decoupling caps on the PCB or leave them to the prototype? Put them on. The inductance of the pin headers will make external caps pretty useless. What should I change to acomodate to the 5GHz frequency /antenna? Make that antenna trace as short as possible. How can I put power protection on this aside from a fuse? I don't see power protection as necessary. You're likely to kill the chip due to over voltage before you manage to blow a fuse. If you're concerned about that, add some Zeners and a fuse. Is this a viable setup for prototyping? Don't see why not. PS. That gnd traces on pins 18 and 20 look painfully thin. PPS. Nice schematic symbol for the antenna!
H: Are these PCB , and if so can it be repaired? I'm very new to soldering, and I think I have irreversibly damaged the circuit I was trying to fix. The joints are pretty burnt, but I read that in some cases you can scrape the carbon off and get a workable joint. I'd very much like to know if I can save my circuit by doing so to these joints. Thanks. AI: Looks like the copper pads have been ripped off. It may be possible to salvage, but you're going to have to be really careful to prevent any further damage. This looks like it might be a USB connector footprint. Fortunately, it also looks like most of the traces connect to the pads on the bottom layer. If this wasn't the case, it may not be possible to fix. What I would do is install the new connector and glue it to the board. Solder a nice thick wire between the two large pads for mechanical support. Then scrape the solder mask off of the two thin data traces, the thicker power trace, and the ground plane around the last pin. Use some 30 gauge wire wrap wire to connect the data pins to the traces and use a short piece of thicker wire to connect the power pin. Also, you really should invest in the proper tools for rework if you haven't already. Don't use a $5 soldering iron - you need a real temperature-controlled iron with a fine point. You won't be able to rescue this board without decent tools.
H: Finding the correct wire I am trying to connect my apartment door bell system to my raspberry pi; I am not too good with the wiring, and hope someone can help. What I have: 3 wires from the door bell system: red wire, black wire, white wire. 1 digital multimeter 1 AC/DC to DC Power Supply Converter Step Down The AC/DC to DC Power Supply has the following specs listed: Input: DC 0V ~ 30V or AC 0V ~ 20V Output: DC 1.25V ~ 28V (continuously adjustable) Output current: 2A Max. What I am trying to do: connect the wires from door bell system to the power supply, then output a 3.3v DC logic input to the raspberry pi. What I need: the transformer needs a ground and a live wire, I need to find out from that three colored wires from the apt door bell system what's my problem: my multimeter showed me some frustrated digits, I'm out of clues to define the correct wires, and here I am... My multimeter result with the button not pushed: black and red: 10v AC; white and red: 12v AC; black and white: 1.5v AC; If I press the door bell button outside black and red = 0v AC; white and red = 12v AC; white and black = 0v AC; So how do I connect wires to the power supply? AI: Seems like a standard doorbell, though your "pressed button" status seems like a probable measurement error. For detecting the doorbell button, connect to black and white - if that does not work, connect to black and red. The reason I'm pretty sure you have a measurement error is that if black and red are 0V and red and white are 12V, black and white should be 12V, not 0V. simulate this circuit – Schematic created using CircuitLab Or, if black and white are 0V, and white and red are 12V then black and red should be 12V - Same circuit as above, swap labels for white and red. So one of your measurements is probably not what you've said.
H: How can I make a linearly tunable 50% duty astable multivibrator? I want to make an astable multivibrator with a 50% duty cycle that can be tuned with a potentiometer for generating sound, so accuracy is desired. My first thought was to build the standard one with transistors, but that requires 2 resistors that control the mark and space separately. Second thought was to use a 555 timer. I made the below circuit with a pot for R3. The circuit claims to have a 50% duty cycle and a frequency of 1.4/RC. Except it satisfies neither of those claims. It only has 50% when Vout=Vcc, which is not the case. This thing does not go rail-to-rail. It's also not linear. If I halve the resistance, the frequency is less than doubled. So the question is if there is such a circuit that truly has a 50% duty cycle and where the frequency is linearly dependant on the RC time? where frequency closely matches \$f=\frac{k}{RC}\$ [edit] To clarify what I meant by linear. Any sort of sensible/relevant/simple relation between resistance and frequency will do. But I was thinking of something that actually does \$f=\frac{1}{RC}\$. The point is that I want to connect multiple potmeters with buttons to make sort of a keyboard. Now if you press 2 buttons you get parallel resistance. I'm hoping that those parallel resistances will turn out to be nice harmonics. This is why I mentioned that 2 buttons of the same resistance don't quite make an octave(double frequency) with the 555 circuit. [edit2] I'll put some values for the relaxation oscillator here, which is expected to do \$f=\frac{k}{RC}\$, but just like the above 555 circuit this does not seem to be the case. \$C=10^{-6}\$ R=4.01k, f=136 R=3.13k, f=191 R=2.05k, f=290 R=1.30k, f=452 R=0.95k, f=602 R=0.56k, f=915 R=0.26k, f=1547 [edit3] The Schmitt trigger + integrator circuit proposed by Andy Aka displays similar behaviour to all the others, where 2 resistances tuned to 400Hz in parallel only give 754Hz, two times 200Hz gives 392Hz. this was the main issue with the 555 circuit AI: The OP says this regarding his 555 circuit: - If I halve the resistance, the frequency is less than doubled. I take this to mean that the frequency the OP wants is proportional to the inverse of resistance. Furthermore I'm assuming that when the OP talks about a potentiometer, he wants in fact to use it as a rheostat i.e. wiper and one end of the pot aka "a variable resistor". The use of the term "linear" in the question is possibly misleading. So, consider using an integrator and a schmitt trigger like this: - Basically it relies on the integrator capacitor being charged and then discharged from the output of the schmitt trigger. Because it's an integrator you will have a very linear ramp-up and ramp-down due to the current in and out of the capacitor being set by the square wave amplitude and R3. There are plenty of designs based on this type of circuit and here's another one: - Here's the article that describes it in more detail. For tuning it you can turn R3 into a pot like the one below: - Or you can use a pot in series with the positive feedback resistor on the schmitt trigger. You can even put the pot in place of R2. There are variations of this circuit that allow pulse width modulation i.e. you can make the triangle wave more saw-like. NEW SECTION about choice of op-amp. The biggest problem area in this design is the comparator. Ideally you want it to switch its output from positive to negative in zero time but that won't happen. For instance the 741 is a bad choise because it has a large delay in dragging its output transistors out of saturation. This will likely be tens of microseconds added to the more normal propagation delay of about a micro second. Then the 741 is slew rate limited on its output to 0.5 volts per micro second. If you have a +/-15V supply the typical output voltage levels will be at +/-14V (loaded with a 10k resistor). To change the output all the way from +14 volts to -14 volts takes 56 micro seconds and it needs to do this twice per oscillation cycle - that's 112 micro seconds. For most of the time while it's doing this, the integrator isn't really moving its triangle wave output but I reckon you could bank on at least 60 microseconds added to the oscillation cycle. Also when you load the output the p-p voltage level drops - the data sheet says the 741 output level will drop from +/-14V with a 10k load to +/-13V with a 2k load. So what does 60 us mean in this design? The op says that he halved the resistance and expected 800 Hz but only got 756 Hz. The time difference between one cycle of 800 Hz and one cycle of 756 Hz is 73 us i.e. probably everything can be put down to slew rate limiting. To improve this get a much better op-amp circa 10V/us slew rate. Then run it from +/- 5V rails. A typical op-amp of this type might produce +/-4V output i.e. a delta of 8V and, due to the improvement in slew rate the "delay" would be about 0.8 us but what does this mean? Compare this to a 1Hz error in 800 Hz - this is a time delay per cycle of 1.6 us so now, using a 10V/us slew rate op-amp, gives a 1 Hz error at 1600 Hz. To avoid the extra propagation delay (common to a lot of op-amps) when their outputs saturate, negative feedback can be used to limit the comparator output to maybe +/-2.5V. Use of series back-to-back precision shunt zeners may be able to do this but, as always, the devil is in the data sheet's details so I'm not going to propose anything hard and fast for this feature - I'd just look for an op-amp that is quick at coming out of saturation or go for a fast comparator with push-pull output.
H: How can an active rectifier block current? This is a 2 part question for my understand about how an MOSFET/IGBT based active rectifier controls current. 1) Assuming a 3 phase active front end to a DC bus, and some huge load on the DC bus attempted drawn below. (Only 1 phase drawn, ignore exact values) simulate this circuit – Schematic created using CircuitLab Once the short/big load makes the DC bus voltage drop, won`t this effectively become a passive rectifier through its diodes? Which in turn would give it no way of blocking its current? 2) In normal operation I assume its diodes also works as passive rectifiers. With its transistors are only used for boosting input voltage...? AI: You are correct, the active rectifier has no way of blocking current. A safety device needs to be provided separately to protect against short circuit. Passive rectifiers have the same problem. The MOSFETs are there not to boost voltage but to get better efficiency. MOSFETs can have a very low on resistance sometimes as low as tens of miliohms. An average diode has a forward operating voltage 0.6v to 0.7v and if passing 10A the power dissipation is 6W. If the MOSFET has a RDSon of 20mOhm then the power dissapated is 2W.
H: Does the 802.3 Ethernet standard provide a recommended circuit design? I have a project I am designing whose fundamental parts consist of sensors connected to a micro-controller. the micro-controller will then send the data out over an ethernet port using standard tcp/ip protocols. I have already created the a proof of concept for the project using an Arduino Yun, but ran into several issues when the libraries and apis that make the Arduino easy to use seem to have prevented me from directly manipulating the registers that control the Arduino's ADC. Additionally, designing the physical ethernet circuitry would allow me to be more flexible with the board layout and housing design and allow me to choose micro-controllers without built in ethernet circuitry if I wish. However, I am having trouble designing the ethernet hardware due to my limited experience. It would help me greatly if there were circuit designs I could use as a reference when designing my circuit. Therefore my question is does the 802.3 Ethernet standard have a set of recommended circuit designs in schematic and/or block diagram form or does it solely lay out the features and functions for the standard? It would also be a helpful if someone could point out some surface mount ICs commonly used in mass manufacture Ethernet socket designs. AI: IEEE802.3 is thousands of pages covering everything from 1 Mb/s to 100 Gb/s systems. You can download and read the standard for yourself here. IEEE provides little in the way of reference implementations. However the chipmakers who provide the PHY devices will typically provide reference designs. These designs will, however, depend on you to provide a uC implementing all the higher layers of the ethernet stack (from the MAC on up).
H: What is the pin to light up colon in Basys 2? I am trying to make a clock in a Basys2 board but I can't find in documentation the pin to light up the colon of the 7segment display. Where is it? AI: I don't think the colon lights up. From reading the schematic, in page 2 you can see that there are 12 wires, none of which seem to drive the colon (there are wires CA..CG for the segments, DP for the decimal point and AN0..AN3 for multiplexing the displays). Looking at the datasheet of the 7-segment display, does not have a way to light up the colon, either. I worked once with a similar board (Nexys3) and I don't remember the colon lighting up.
H: Why can't I measure resistance when there is current on the potentiometer? Probably a very basic question but I have no idea why this happens. I have a 1K potentiometer. When I measure the resistance over its legs when it is not connected to anything, the results are as expected and alter expectedly when I move the knob. However, when I connect the pot to a 9V battery and try to measure the pot's resistance, I don't get any readings. What is the reason for this behavior? AI: Because your multimeter can't measure resistance. So it applies a known current, measures the resulting voltage, and computes the resistance from that. 1 So when you're applying an external current to the potentiometer you are upsetting the meter's procedure, and the resulting voltage is probably outside the measurement range. 1 Unless it's really old. In which case it applies a fixed voltage, measures the current, and lets you read the resistance off an inverse scale.
H: what i have to use to only allow voltages above certin value to pass? I have a school project which it requires me to design a logical circuit that tests a 12v battery if it is full or not or half-full and light the corresponding LED, but, I am having a trouble because I want a component that only allow a voltage to pass if it is above 12v in first branch and 6v in second branch and 0.5v in third branch, but, I don't know what to component to use to achieve my goal. I am thinking to use resistors but I do not know what are the values to assign to it to achieve my goal. NOTE: I am using Proutuse isis AI: This is a possible solution. As Passerby stated comparators (or op amps) could be used. If the voltage (from the battery) is more than the voltage at the minus-pin on the comparator then there is positive output from the comparator (i.e the voltage "passes"). The voltage at the minus-pin of the comparators can be constructed with simple voltage dividers. The XORs at the end makes sure that only one lights up at a time. This solution needs an external voltage source of at least 12V to power the comparators, XORs and also create the voltage dividers connected to the minus-pins of the comparators.
H: Why can sticking fingers in an electric outlet kill you? I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing through your body be 0.0022 amps? AI: In Europe the rule is generally 60V DC is safe for casual contact with live conductors. Read what the IEC says: - The International Electrotechnical Commission (IEC) has issued several reports on electrical safety. The IEC “Electrical installations of buildings” report (IEC 60634-4-41:2001) specifies that for unearthed circuits “if the nominal voltage does not exceed 25 V a.c. r.m.s. [35 VPEAK] or 60 V ripple-free d.c., protection against direct contact is generally unnecessary; however, it may be necessary under certain conditions of external influences (under consideration).” For earthed circuits the IEC considers protection unnecessary when “nominal voltage does not exceed 25 V a.c. r.m.s or 60 V ripple-free d.c., when the equipment is normally used in dry locations only and large-area contact of live parts with the human body is not expected; 6 V a.c. r.m.s. [8.5 VPEAK] or 15 V ripple-free d.c. in all other cases.” Extract taken from this document. The sort of voltage level talked about in the extract isn't generally believed to sufficiently break down the skin's "high surface resistance" BUT, mains voltages are lethal because they DO break down the surface resistance and then you just have the body's internal resistance and this is only a few hundred ohms. With (say) 220V AC applied, the current can be greater than 100mA and this is really problematic: - NEW SECTION: An interesting and related spin off subject is the well-known effect of a human body damaging electronic circuits by static discharge. The human body is modelled as a capacitance to earth of about 100 pF. This capacitance is charged up to several kV and the discharge path into the electronics under test is via a current limiting resistor. An important thing to note is that unless the human body directly connects to earth (a rarer situation than normal), the current flow due to touching a live wire is somewhat limited by this capacitance. This document entitled "Measurements upon Human Body Capacitance: Theory and Experimental Setup" concludes that about 160 pF is a the human body capacitance in the following experiment: - So if we connect to 220V 60Hz, 160 pF has an impedance of 16.6 Mohms (reactive) and would cause a reactive current of about 13.3 uA. I don't think capacitive effects are going to be very significant.
H: How to delay a "not gate oscillator" to make it run at a desired frequency? I want to blink an led(0.75 seconds on and 0.75 seconds off) repeatedly. I was thinking of using an idea from a book called "But How Do It Know" by J. Clark Scott. A part of the book tries to explain how to make an oscillator to use in a computer(The book tries to teach the reader how to make a functioning computer)but doesn't really go into the details about how to change the frequency etc. A schematic to show a square wave generator is provided in the book. Here it is(Diagram 1): simulate this circuit – Schematic created using CircuitLab The author says that the output will be too "fast" to be used for anything. He then says that to slow it down you have to lengthen the wire like so(Diagram 2): simulate this circuit This is obviously over simplified and impractical because you can't extend the wire for a long length without running out of space. How can you "slow down" the output of the circuit in Diagram 1 to produce a desired frequency(0.75 seconds HIGH and 0.75 seconds LOW). Here is a clock digram of what output I want(in hertz I think this would be 0.75 Hz, Correct me if I am wrong): simulate this circuit My question is: How do I slow down the output of the "not gate oscillator" (Diagram 1), to the desired output of(0.75 seconds "on" and 0.75 seconds "off") and is this frequency 0.75 Hz? AI: simulate this circuit – Schematic created using CircuitLab This tends to work better with a Schmitt-trigger NOT gate (one with some hysteresis, or difference between "voltage it changes state on when going down" and "voltage it changes state on going up.") Circuit-lab's logic selection does not appear to have any Schmitt-trigger parts. Incidentally a Schmitt-trigger NAND with the inputs tied together also makes a Schmitt-trigger NOT. It's a crude solution in any case and the R, C values are highly unlikely to give the precise oscillation you want. A 555-timer or 555 timer into a flip-flop is a somewhat less crude approach. The frequency is one over the time for one full cycle. A full cycle is 1.5 seconds, so the frequency is 0.666666666666666666666... Hz (0.66666667 in most calculators due to rounding.)
H: How to work to find the values of the components that should be used in a project My question is somewhat general but I will try to narrow it down. I want to build a project for which I have all the necessary components and the knowledge as to how I should connect them but I don't know what their values should be. In order to make myself clear I will use a simple "project" as a reference. Let's say that I want to build this simple NOT gate: simulate this circuit – Schematic created using CircuitLab How do I find the values of the components that I should use when I only have that schematic? Keep in mind that my question is not focused in that particular "project". I ask generally how should I work in a case when I know the way to connect the components but not their values. AI: There is no general answer other than do the math and figure them out. This of course requires truly understanding how the circuit works. When you do understand it, knowing how to compute component values pretty much falls out naturally. In your specific example, you start by understanding what each component does. R2 sets the current to light the LED when Q1 is off. I'm assuming the bottom of the LED is supposed to be connected to ground. Let's say it's a typical T-1¾ green LED rated for 20 mA and 2.1 V when on. Since 2.1 V will be across the LED and the power supply is 6 V, that leaves 3.9 V across R2. From Ohm's law, (3.9 V)/(20 mA) = 195 Ω. That's the absolute lowest value given the LED specification. The common value of 220 Ω would work if you really want the maximum light. Note that 200 Ω 5% is not OK since it could be as low as 190 Ω. If you don't need every last bit of light, use 300 Ω or higher to save current, get longer lifetime from the LED, and be more tolerant of supply voltage variation. R1 controls how much base current the transistor gets when the switch is on. Figure the B-E junction will drop 700 mV, so that leaves 5.3 V across R1. You didn't specify the transistor, but let's say it has a minimum guaranteed gain of 50 in this application. The collector current needs to be up to 20 mA, so that means the base current must be at least (20 mA)/50 = 400 µA. Using Ohm's law again, (5.3 V)/(400 µA) = 13.3 kΩ. That's the maximum value that is guaranteed to work. The common value of 10 kΩ therefore will be fine. Added I see from the comments it's necessary to dispell some myths about transistors used as switches. There is no place in engineering for blindly following rules of thumb. Conventional wisdom is often not the convention, and rarely wise. There is no substitute for actually understanding what is going on. When you do, you usually don't need the "every knows" rules. Transistors saturate when the external circuit limits the collector current to less than the base current times the gain. At this point, the C-E voltage goes to a few 100 mV and changes little with changing collector current. You can flip this around and calculate the ratio of collector current to base current. Saturation then means that this ratio is less than the actual gain of the transistor. In the example above, I said the gain of the transistor was at least 50. Therefore the transistor is in saturation for any collector to base current ratio less than 50. In the example, I started with the collector current, then made sure the base current was more than 1/50 of that. Same thing. There is no magic C/B current ratio that must always be used for a transistor in saturation, or when it is used as a switch. 10 works for most transistors in most situations, but will also require more base current than necessary in many of those situations. Sometimes you might use a fixed number like that when you don't know anything more about the transistor, but in this case we do know something more, which is that the actual gain is 50. The base current being 1/30, for example, of the collector current is perfectly fine when you know the gain is 50. There are some cases where you might want to deliberately overdrive a transitor way past what the gain tells you. The C-E voltage doesn't change much with collector current or lower C/B current ratio, but it does still change. Sometimes extra low saturation voltage is more important than more base drive current, and you overdrive the transistor to get a 100 mV or whatever lower drop: In this case, a few 100 mV saturation voltage is no issue, so there is no reason to drive the transistor extra deep into saturation. In this case, using 2 mA to drive the base wouldn't be a big deal either, so ending up with a C/B current ratio of 10 is not really wrong, but neither is ending up with 30 or 40.
H: How can a GPIO logic to high amp/voltage logic adapter be built using multiple voltages? (5v, 12v, 24v) I'm working on a project that requires making a fairly universal board (to work on different model machines). I need to hook up many pre existing motors and switches/sensors to the board that all work off of different voltages and have their own unique pin/plug configuration. I figured using fpga would allow programming of the correct configuration, but I need the 3.3v fpga pins to accept input/output from 5vdc, 12vdc, and 24vdc selectively. Is there any simple solution out there? They all need pwm capability, and the ability to drive small motors/devices. I have thought of using load switches for the outputs, which seems correct. As for inputs, I was thinking isolators, but they don't allow such a wide range of input voltages if I am correct. The only other thing I can think of is voltage regulators in series or parallel to convert the voltage to 3.3v logic. However this may pose a problem where pins can not be ground (as in 0v) for high current as well as serve as a logic input. Any help or ideas would be appreciated. AI: For your wide range inputs you could consider a solution that I have used a number of times. Bring your inputs in through a circuit like this: As shown the input threshold for high/low is set at 2.5V by use of the TLV431. The input signal coming through the 2.2K series resistors are clamped to the 5V supply to keep them in safe input range of the AM26LV32. Outputs swing from rail to rail of 0 to 3.3V for input to the FPGA.
H: Paralel charging two Lithium Polymer batteries on a MP3 player Colorfly C4 Is it a good idea to replace a built in lithium polymer battery rated: 3.7 V, 2000 mah with TWO x brand new 3.7 V, 1800 mah (much thinner stacking them together) connected in PARALLEL and place it in my mp3 player model (Colorfly C4)? As it turnes out the built in battery is of very poor quality hence the question. Is this perfectly safe to parallel charge two exactly same brand new lithium poly batteries, or will there be a danger of overheating/fire? Will the capacity truly then be 3600 mah then, meaning longer playbacks as well as longer charging times? What things should I take further into account (aside volume/packaging/fitting etc) AI: 2 1.8Ahr cells in parallel is the same as 1 3.6Ahr. Its called a 1s2p cell. Sometime LiIon chargers stop charging after a fixed time. Something like the capacitry / charge rate * 1.5. So you might not end up with a fully charged pack after a single recharge. Using a single cell LiIon batteries in parallel (with the same specifications and age) is generally acceptable. When they are initially connected though, you need to make sure they're nearly at the same voltage. When connected the current flow will be I = (V1 - V2)/(ESR1 + ESR2). So long as I is less than the peak discharge and charge current you're fine. If the batteries have the same specs, there is nothing more to worry about. If the batteries are different (but operate over the same voltage range) then one just needs to make sure that during charging the current sharing doesn't violate the charge rate of 1 cell. Even have a multicell stack, putting them in parallel is fine. But here it is a bit more tricky as the stack needs to be connected at the cell level, and the parallel capacity of each cell in the stack needs to be nearly identical.
H: Using several microcontrollers as nodes in a neural network I recently read an EETimes article about Google's neural network experiment, where they used several processor cores as nodes in a neural network. That made me wonder: could it be possible to replicate this with off-the-shelf microcontrollers? I was thinking using 15 to 20 ATTinys or picaxe 10f200s and then interconnecting them via their serial communication lines. Is this a viable concept? If not, are there alternate ways of making this kind of neural network? In other words, is this possible and if yes, how would I go about to make it? I'm new to this area of computer science, so I need some help. Thanks! AI: Depending on the application, it would certainly be a possibility. The problem I foresee however, is that for an effective neural network, it needs to be trained via back propogation. Typical ATTiny is something like 20Mhz, whereas a computer is 2Ghz+. Training the neural network would require significantly more time due to the much lower processing speed. Which isn't to say it isn't possible, but you would have to carefully examine the application of your neural network before implementing it. It's also an Idea I've had for a while regarding robotics sensory, localization and path planning. Rather than programming a bunch of rules about how to move in an environment, have sensory input act as the inputs to neurons, which then teach the robot how best to interpret data to get to a destination.
H: How to detect the duty cycle of a laser pointer Our assignment is to design an analog parking lot access system. A laser pointer will represent the car, and an ID detector will check if the laser's duty cycle is 20%. I designed the circuit that will give the laser an input voltage in the square waveform with a duty cycle of 20%, and I was planning to design a detector that will detect the average energy of the laser, but since the laser will be a vehicle (which means it will be moving) the light energy that it will send to the detector will change with time, so the detector MUST check its duty cycle, not the average energy. This is the circuit that will generate a square wave with a duty cycle of 20% The components we are allowed to use are: +/-25 V output of DC power supply, any types of resistors, capacitors, inductors, diodes, LEDs, LDRs, op-amps, transistors So, any ideas on how to make a circuit that will be activated with an input that has a duty cycle of 20%? Update: Just wanted to let you know, thanks to your answers I managed to design something that works perfectly! The LDR detects the laser and causes the first Op-Amp into positive saturation with the same duty cycle as the incoming laser, then it's low-pass filtered (thanks to @transistor and @helloworld922) and since the duty cycle I'm looking for is 20% I compared this value to see if it's lower than 3 Volts and greater than 2 Volts, and then summed the outputs of the comparators to see if both comparators are in positive saturation. I think this one should do quite well. AI: The first component you're going to need is some way to receive the laser signal. You say you have LDR's, so design a circuit which uses one of these and outputs some voltage level corresponding to the input light. As you've stated, variable input signal strength is a problem. That seems to imply that you want something digital, where signals above a certain level are registered as "on", and signals below a certain level are registered as "off". Something like a 1-bit analog to digital converter would do this, so think of how you would design something like this. This will give you a consistent level for "on" and "off". Once you have received the PWM signal from the laser into your circuit as a digital signal with a known level, just low-pass filter it until you get close enough to a DC level. The DC value gives a direct indication of the duty cycle because you've already removed the variable signal strength problem. The last step is to detect if the correct DC value (a.k.a. duty cycle) has been received. Something like a window comparator should do the trick. I'll leave the details of how to design each of these components to you. Feel free to ask questions if you get stuck on any of these.
H: How to wire 3 phase motor to VFD I am trying to wire a new motor to a variable frequency drive (VFD) and having some trouble figuring out how to wire the motor to the VFD. The motor is a 1 HP, 3-phase, 208-230/460 volts, and I'm wiring a 120 VAC supply voltage into the VFD, which steps that up to 3-phase 230 V. I have included a picture of the wiring diagram attached to the motor below. Based on that diagram and the fact that the motor will be operated at 230 V, I gather that wires 9 and 3, 8 and 2, 7 and 1, and 4 and 5 and 6 all need to be wired together - giving me 4 separate wire bundles. The VFD has wire terminals for U, V, and W, so it looks like I have 3 terminals and 4 wires, so I'm not sure which wires go to the U, V, and W terminals on the VFD or what to do with the extra wire bundle. I have included an image of the motor wiring diagram from the VFD manual below. I was thinking that the extra wire bundle would be a ground, but there is also a green screw inside the wiring box on the motor that I'm thinking is where I connect the ground wire (and connect the other end to the protective earth PE terminal on the VFD), but please correct me if I'm wrong. With the extra wire, I'm also left wondering how to differentiate between U, V, W and whatever the 4th wire is. In the VFD motor wiring diagram, I also can't figure out what the Physical Earth Shielding (PES) is - is it just saying to use shielded wires and attach the shield to ground? The model numbers for the items are: Baldor CEM3546 Motor, and Lenze SMVector ACtech ESV751N01SXB. So my specific questions are: What is the 4th wire? Where do I connect the 4th wire? To ground the motor, do I attach a wire between the green nut and the PE (protective earth) terminal on the VFD? By connecting the ground wire on the incoming 120 V single phase to that same PE terminal, is the motor grounded? Is the PES just another way of saying to use shielded wires, with the shielding being attached to ground? Is this really necessary? AI: and 2.: The terminals 4, 5 and 6 are not to be connected to your VFD. This is indicated by the drawing, as there is no wire "leaving" the interconnected terminals. i.e. those are bridging terminals to build the correct wiring of all windings of the motor. probably yes. Normally PE connectors should be designated by green/yellow, but I've seen it often as only green. Depends from your wiring scheme on your premises. If you have combined neutral/protective-earth connect that to your VFD and your motors PE. If you have separate neutral / protective earth you have to connect the PE to your motor's PE terminal. The PES is for EMC-purposes. It starts at your motor's housing and is connected back to the shielding cabling between the motor and the VFD. It will reduce electromagnetic interference. For this purpose you have to use shielded cables. Is it necessary? Probably you won't get any problems with not shielding it. But others may. So in my eyes not applying the appropriate measures for EMC is like letting my dog shit onto the green of my neighbours. So: just do it and use shielded wires. According to the datasheet your motor cable should be low capacitance (<75 pF/m wire-wire, <150 pF/m wire-shield).
H: Conformal Coating Affecting Inductor? Question: Could conformal coating affect the properties of an inductor by adhering to its windings? Context and problem: I have a simple boost regulator circuit based around the TPS61230 IC. It has a handful of SMD resistors and capacitors and one largish SMD inductor (http://www.mouser.com/ProductDetail/Bourns/SRU1028-1R0Y/?qs=%2fha2pyFaduga8qwkov01I2ofW5jqNjYb0PGY4sjOrrG99%2faGtQIpWg%3d%3d). The circuit worked fine when I built it up, but I decided to conformal coat it to protect it before installing in the final product. Since I conformal coated it I'm not longer getting my 5 V on the output and instead when powered there's a -0.5 output voltage which then goes to zero. I can't see how the conformal coating could affect the rest of the circuit, but the inductor has openings on the top which my conformal coating spray probably got into. The question I have is how might the spray have affected the properties of the inductor to cause this behavior? Is this the likely problem? I don't have any extra inductors so am trying to hone in on the issue before ordering more. Picture of circuit board, and yes, I covered my connector pins during conformal coating. AI: Anything intended to be used as a conformal coating should have no effect. If it was electrically conductive it may. This is easily tested. If it was bulk conductive and formed a screen but had very low DC conductivity across terminals it may manage to do something to a circuit but this is unlikely. If it contained a solvent it may have dis-solved something. I have seen IPA dissolve 'expensive stuff' during "cleaning". If power was on during curing it may have been conductive and caused a problem. Did you use heat in the process? Was power on during the application process or during curing? What DC resistance do you see per square cured and "wet" ? Does it contain a conductive filler (eg Nickel or carbon)?
H: Inductance changes in DC relay coils PWM operation of DC relay coils in order to save power while holding is now common. This is at a frequency that is high enough to avoid chattering or audible noise and low enough to not have to worry about switching losses or exotic circuitry. The in circuit coil inductance can be measured by looking at coil current and analyzing the slope. In this case if the PWM frequency is well known like say microprocessor 50% duty cycle at 8KHz and the supply is regulated 24V then you can easily get the coil inductance. What I actually did was a self osc hysteric scheme which gave a change in frequency for a change in relay coil inductance. The Idea is that one can tell the position of the relay coil by its inductance. What I did Vs the orthodox ripple slope approach really comes down to implementation. It is all the same in that you are detecting inductance change to tell if relay armature is in or out. I was expecting big changes like more than 3:1 but that was not the case. Why? Doesn't closing the magnetic circuit raise inductance markedly? Sure the change was totally adequate to make a reliable decision regime for the firmware guy to do. The real odd thing was that the pulled in relay exhibited less inductance. Why would it appear to work back to front? I didn't put this into production because the big relays were not needed after all but I have concerns about the scheme performing differently on different relays. Is the concept flawed due to relay peculiarities? Can it only be used in a specific case? AI: This suggests to me that the relay coil may be saturating its core. Consider this : if you are measuring the inductance in-circuit, while operating the relay, there are two important states : open and closed. In the open state, the inductor is gapped and therefore its reluctance is relatively low. You can apply all the power you like and it won't saturate, therefore your inductance measurements (using the AC component of the PWM signal, right?) reflect the true inductance of the (gapped) coil. However, it will pull in, closing the magnetic circuit. And here I'm speculating. The closed circuit saturates, so the inductance you can measure is a small-signal value on the relatively flat saturated portion of the B-H curve. Then you reduce the PWM duty cycle, but presumably not quite far enough to bring the core out of saturation (or you'd see an increase in inductance). If this is the case, then inductance measurements made unpowered, on an opened relay, operating it with a finger or screwdriver, would show the expected increase in inductance when closed.
H: Subtract Diff-Signal (Millivolts range) on top of common mode voltage (volts) with opamp - very inaccurate I built a subtractor circuit as shown here with 10k each resistor. Now I want to measure current by using a shunt between the two inputs and letting a current flow through it, see here, figure 4, the only difference is that my reference voltage is not GND but 8V. The voltage on the shunt is in the 10mV region, the common mode voltage swings from GND to about 20V. Ideally this should happen: e.g. (10mA current, shunt resistor 1 Ohm) 10mA x 1 Ohm = 10mV at shunt. Let R_Load be 100 Ohm-> 100 Ohm x 10mA = 1V. So we would have on the lower end of the shunt 1V and on the upper end 1.01V, difference is 10mV. Since all Resistors in the difference amplifier (DA) are equal and reference is 8V we should get at the output 8V+10mV, right? If we changed the load to say 1k, we would have a common mode voltage of 10V at 10mA and still the output of the DA should still be the same, 8.01V, right? But this is not the case, but different CommonModeVoltages (CMVs) result in drastically different output voltages (means, the difference at the shunt is not multiplied by one for all CMVs but alters heavily). Why is that? I suspected, that the common Mode Rejection of the Opamp was not good, but: Using a TL082 we have 80dB CMRR, means 10^4 = 10000, which should mean, that a common mode voltage added to the difference signal should have an effect of 2mV for a CMV-Swing of 20V, right? However the difference at the output is way larger (uselessly large). Does anyone have an explaination for that? When I used a INA122 instrumentational amplifier, the problem was totally solved. Still I don't understand the problem. AI: Consider the effect of a small mismatch between the resistor values (actually the mismatch between two resistor ratios is what is important). If you used 1% resistors, the non-inverting input can be 1% off worst case, and the feedback likewise, so you could see an error of as much as 2% of the common mode voltage. At 20V, that's 400mV, or 40x your entire full-scale signal. Chances are it would be somewhat less in practice, but probably more than 1000% error. While you could buy very expensive 0.01% resistor networks you'd still have a 4% error and even a tiny shift with temperature would cause a huge error in the output. That's why that kind of differential amplifier is generally not used when the signal is small compared to the common-mode voltage- the sensitivity to component tolerances is far too great. You could use the classic three amplifier in-amp configuration and avoid buying a commercial part- the key is to have enough amplification in the first stage (R1/Rgain) that the resistor ratios in the output amplifier are not too critical. Also, watch for saturation. Also, this is not a huge source of error, but note that the amplifier inputs have some current draw. If you put the inverting on the low side of the shunt the load looks like 20K to ground (1mA) so it will measure that current (but not the 1mA the other input draws since it doesn't go through the shunt). The instrumentation amplifiers have high-impedance inputs so that error current will likely be maybe 5-7 orders of magnitude less.
H: Surge protector helped me discover bad wiring at home -- neutral and line swapped; should I be concerned? I purchased two surge protectors and when I plugged them in at two different receptacles in my apartment, I noticed that the 'grounded' light did not illuminate on any of them. To shorten the story, I discovered that at every single receptacle in my apartment, line and neutral were swapped! I rewired the two receptacles (just swapping line and neutral) where I am using the surge protector and it lights up all good now. My question is, given that all the other receptacles are still reversed, should I be concerned? I mean, most devices don't care I would imagine. They just need to see a differential of 120 V. But clearly the surge protector cared, so are there any other devices that do care? Also, another question. I have a dsl modem with a telephone cable that does not go through the surge protector. My Xbox has its Ethernet cable connected to that dsl modem which also functions as a router. Is it possible that a surge could go through the telephone wire, then through the Ethernet all the way to my Xbox and damage it? AI: Yes, you should care. The electric code is generally designed so that it takes two independent failures before you get shocked. In you're apartment, one is already used up by the line and neutral being flipped, so you are closer to a dangerous situation. If all else works correctly, this one error shoudn't matter. As Dirty Harry would say: Do you feel lucky? Well do you, punk? You don't say where this is, but in most jurisdictions this is a serious matter. I would first politely point out the problem you found to the landlord, and give him a chance to fix it. If you need to convince him, point out how this is a serious liability to him if you or anyone else gets hurt, and that his insurance company may refuse to pay in case of electrical fire. If he still refuses or tries to tell you it's OK or something, then you should take further action. Talk to your local electrical inspector, and ask if what you found is OK. It won't be. Then tell him you brought this to the attention of the landlord and he refused to do anything about it. Most likely the electrical inspector will now have steam coming out of his ears. He'll take it from there, and the landlord won't like it. You should absolutely not have changed the wiring yourself. Here in the US, for example, that is illegal for someone who is not a licenced electrician to do, and/or would require a inspection afterwards. You also had no right to do this without the landlord's approval, whether you were fixing something or not. You now own the liability. Don't mention anything about the modifications you made. Only talk to the landord, and electrical inspector if necessary, about the remaining outlets. And don't modify any more wiring.
H: Battery charge times I thought of an idea recently, and I wanted to know if electrical engineers agreed with my theory. I have a smartphone. Recently I bought a power bank because I found my phone's battery not holding up long enough. Now here is what I thought about while charging my power bank and my phone. If both batteries (of my phone and powerbank) could in theory fill up 1 mAh/minute and both my phone and and the power bank are connected to the outlet, and are actively charging, I'm basically charging the two batteries at an effective 2 mAh/minute. If both my phone and my battery pack could hold 1000 mAh, I could charge both half way to 500 mAh and still have an effective 1000 mAh at half the time it would take me to charge the phone alone. So if I bought three banks then together with my phone I could get the same effective 1000 mAh in just a quarter of the time! So if this works in theory: Why not divide the phone's battery into hundreds of separate banks to get hundreds of times the times the charge rate? What prevents this in practice? AI: It doesn't work that way. One of these two issues will get you: You "spilt" the original batteries into smaller batteries, maintaining the overall battery capacity. The smaller batteries now have lower capacity and lower maximum allowed charging current. If a original battery can be charged at 1 mAh/minute, then a battery resulting from a 1:2 split could only be charged at ½ mAh/minute. With the batteries split to conserve overall capacity, a larger fraction of the whole volume would be taken up by interrconnects, so the overall battery pack would now be larger and a little heavier. You use more of the same size batteries. Each can now be charged at the original rate, but the battery pack has become proportionally heavier and larger. The cell phone maker has already picked a tradeoff between size and weight on one side and longevity of charge on the other. For the same battery technology, you can't cheat this tradeoff. By adding more batteries, you increase longevity of charge, but you can't get away from the proportionally larger size and weight of the resulting battery pack. If it were really so simple, they'd be doing it.
H: Solid State Relay not working, am I mis-reading the data sheet? I purchased several IXYS CPC1017NTR SS relays from Mouser. I have 1.2v and .5mA of current running over the control input of this relay and the load side isn't connecting. Here's a diagram of what I'm trying to do roughly (I missed connecting the positive to the load side of the relay in this drawing though) I've confirmed with my multimeter the 1.2v/.5mA, so I must have read the datasheet wrong. Any help would be appreciated. Thanks! Matt AI: You need at least 1 mA to turn o the optoisolatorn. Your 20k on its own would limit the current to 12/20000 = 0.6 mA which isn't enough. R2 is shunting some of the current that does make it through and stealing it from the SSR. Try this (and note convention of + rail at top with current flowing from top to bottom of circuit for readability). simulate this circuit – Schematic created using CircuitLab
H: High frequency signal using low frequency micro-controller How do micro-controllers running at slow clock frequency (under 100 MHz) produce high frequency radio signal (2.4 GHz for example)? For example - ESP8266 runs on a clock speed of 80 MHz but is capable of wifi communication which requires a 2.4 GHz signal. AI: The 2.4 GHz carrier for the radio is generated with a dedicated voltage controlled oscillator. This oscillator will be locked to a low frequency reference with a PLL for stability. The data to be transmitted is not actually sent at 2.4 GHz - it gets generated by a digital to analog converter at several MSa/s. A mixer will be used to translate the output of the DAC up to the required RF channel frequency. There will also be dedicated signal processing logic that translates the actual packet data into baseband modulated samples that get sent to the DAC. The processor only provides the packet data to the beginning of the transmit chain, the rest of it is handled in dedicated digital and analog hardware. The receive chain will be similar to the transmit chain, except operating in the other direction and with a few additional components for tracking the carrier.
H: Why can't I blow a fuse? In the book I am reading, there is an experiment that consists of connecting an automotive style fuse and a 1.5V battery to observe blowing of a fuse. However my fuse does not blow. I have repeated the experiment with a 9V battery but still it doesn't work. After these results, I have tried the experiment using a DC to AC adapter which can output up to 12V. When I tried the experiment with 12V, tiny blue sparks would appear at the connection between the fuse and the adapter's output. Furthermore, the fuse had warmed up but it still did not blow. Why is this the case? I initially thought that the fuse would blow as soon as I connect it to any amount of voltage since there is virtually no resistance. Why my fuse doesn't fuse? AI: Thanks to many commentators, I was finally able to blow my fuse. The main point is, batteries have a significant internal resistance. Hence, they do not provide a "virtually unlimited current". Hence, there weren't enough current to blow the fuse initially. As Respawned Fluff suggested, I have connected 3 AA batteries in parallel and connected them to the fuse. Connecting the batteries in parallel resulted in a lower total resistance while keeping the voltage the same at the same time, which in turn resulted in an increase in the current. Hence, this had produced sufficient current to fuse the fuse.
H: Connect to "gold plate" connectors of existing PCB I got a Bluetooth heating thermostat that I want to modify. The board has an ATmega 169PA, and I identified JTAG and ISP "connectors". They all look like those five round golden plates in the upper right of picture. Their distance is about 2.54 mm (0.1 inch) between each. Is there a name for those gold plates? How do you commonly connect a programmer (e.g. bus pirate) to those "plates"? (Preferably without soldering) AI: The way they are supposed to be used is with "pogo pins" (sharp spring loaded pins) mounted in a test fixture that holds the board in place against the pins. Such a fixture is known as a "bed of nails". Great for production but kinda sucks for development. Building such a fixture for one-off use would be a lot of effort and may make access to the board for test probes difficult. Especially as those pads are nowhere near the mounting holes. Solding wires to the pads is an option and probablly what I would do personally. I would go for 30AWG wirewrap wire, if the wires get accidently stressed you want it to be the wire or the solder joint that fails (as those are easy to replace), not the pad. Depending on the physical constraints an option can be to glue a connector to an empty part of the board with hot glue or silicone rubber and then solder your wires between that connector and the pads.
H: Auto power Arduino I'm working on that cool project that is power efficient . I'm working on a project that auto power the arduino at a given time and keep it on for less than a minute then it should switch off automatically too . I'm using an external circiut for sending a signal for the switching on purpose ( DS3231 board ) http://www.play-zone.ch/en/combo-breakout-mit-ds3231-temperatur-zeit-24c32-memory.html So I am trying to build up a circiut that when it receives a signal from the DS3231 board it latches the signal for a while to autopower the arduino board then it switch off again saving much much battery power . I built up that one but still struggling to make it work.I am worried that it will waste more power than it saves due to the 100 ohm resisters.Would anyone have a proper circuit ? i/p is where I connected to the SQW pin of the DS3231 board and +5v is connected to Vin pin in the arduino and GND to the GND pin as well in the arduino board any help ?? AI: It is probably easier and more efficient to just have the processor on the Arduino sleep when idle rather than building a whole other circuit to disconnect power. The AVR chip on the Arduino is amazingly low power when sleeping, possibly drawing less power than the circuit you are going to build to turn it on and off. You could connect the output of your sensor to an input pin of the Arduino to have trigger the wake up. Note that if you are using a standard Arduino board that you will need to make some changes to get minimum power usage during sleep (primarily disabling the voltage regulator). You will want to do this anyway if you will be running off a battery since the regulator is very inefficient. Try googing "low power sleep arduino" and "arduino wake sleep" for more specific instructions.
H: How many SMD 5630 LEDs can I power with 12V 1A power supply? I am new to this and have what is probably a newbie question. I am using SMD 5630 LEDs from a strip that I am cutting off and wiring each LED individually. They will be wired in parallel and I am trying to understand how many I can power with a 12V 1A power supply. (Edit: The power supply converts to DC current.) From the specifications I found each LED requires 3.6V at 50 mA and using an Ohm's calculator I found I need 22 ohm resistors. I just don't understand how to figure out the maximum number that I can support. Could someone explain, speaking slowly and using small words? :) AI: Adding to Passerby's answer: Replicate what's on the strip. It wastes the least current. The strip is made up of repeating circuits as shown below. simulate this circuit – Schematic created using CircuitLab You should do the same. Polarity of LEDs matters. The resistors can go anywhere in the series circuit - they're probably evenly spaced on the strip to spread the heat.
H: Micro controller programming with bluetooth dongle I have this USB bluetooth dongle . I want to know is it posible to active this dongle with PIC 16F628a micro controller and communicate with PC. I know this micro controller support serial communication, but I don't know is this application is posible. Thanks. AI: The dongle you mentioned has a USB interface. PIC 16F628a doesn't have one. So they can't directly communicate with each other. Better idea will be to use a serial based bluetooth module like HC-05. You can communicate with this modules using serial Tx and Rx. However if you want to use same Tx Rx for uploading code to your micro controller, then you might have to implement software serial on two other pins in order to communicate with the bluetooth. Search for online arduino tutorials for bluetooth module. You will find a lot. You can implement those with your PIC.
H: Power of piecewise defined signal Here is my task: Periodical signal is given (only one period of signal is shown): Calculate value of voltage K so that average power of this signal equals 1.5W. Power of signal can be calculated as $$P=\int_{0}^{T}u^{2}(t)dt$$. My idea is to express u(t) and solve equation $$\int_{0}^{T}u^{2}(t)dt=1.5$$ (after solving integral I will get some function of k, f(k), and solve f(k)=1.5). But u(t) is piecewise defined, it is k+2(1-k)t/T in interval 0 to T/2 and 1 in interval T/2 to T. What to do here? AI: Use piecewise integration - from 0 to T/2 and then the trivial part from T/2 to T.
H: 5w resistor circuit and increasing circuit speakers power I am new to electronics, and I am working on an amplifier circuit that contain LM386. This is the schema of it with bill of materials: Does this circuit give a huge sound ? If not, do I need to increase speakers "W" or I need to make changes with circuits and resistors ? And by the way, can I replace a 5W resistor with a normal 1K resistor ? AI: The item in the photo is a preset potentiometer. 'Preset' means it's adjusted during setup and left alone unlike a regular potentiometer used for a volume control, for example. If you inspect it you might be able to see a circular resistance track going from the bottom left pin the long way around the edge to the other pin. There will also be a wiper connected to a third pin. Adjusting the knob will rotate the wiper allowing adjustment of the voltage or potential (hence potentiometer) anywhere between the values on the two end of track pins. To answer your second question: no. 5 W means 5 watts and is a measure of the power the resistor can dissipate without going up in smoke. 1k is short for 1 kΩ (kilo ohm) - 1000 Ω and is a measure of resistance. You generally need to get the resistance value right for the circuit to work as intended. You need to use a resistor with a power (wattage) rating at least as high as the power it will need to dissipate. [Edit after OP added schematic and question on power.] No. 0.5 W is very low power. This amplifier would be used in a small portable transistor radio.
H: LTSpice Simulation Showing Inaccurate Results and Excessive Current So I'm trying to make the following simulation work properly to verify some hand solving for a circuit. The circuit is an LC tank with some diode clamping, and an initial capacitor voltage of -50V. I tried both with and without a switch to see if that helped...it didn't. Solving for this by hand I expected to see around 300A as the initial surge current, but it's up in the high kA range in the simulation. I know this can occur with LTSpice time base errors, but here's the stranger part I had it working fine, then accidentally didn't save the changes. Now I can't make it work properly for some reason. I've tried: all the integration modes normal/alternate solver Taking the maximum timestep all the way down to 1E-12...took forever but it didn't help. Nothing seems to make this simulation behave properly. Is there anything else I can try? I don't know why it isn't working now as opposed to earlier. Thanks! AI: I actually got the numbers to make a bit more sense, although I don't fully understand why. I set the simulation options to not do an initial operating point solution and suddenly the currents started to match my hand calculations. In addition a total summary of the fixes that were contributed by folks here: @bruce-abbott mentioned that the SI prefixes aren't case sensitive, so my switch off resistance was really low. Several folks reminded me to use actual SI notation for clarity instead of exponential So thanks to all for those tips. I don't yet have a precise understanding of why skipping solving the initial operating point fixed the issue, so for now I guess it's just another thing to try if the numbers don't make sense. DC Operating Point Results: V(n002): 100 voltage V(n003): -49.5131 voltage V(vo): -50 voltage V(n004): -125 voltage V(vcap): -50 voltage V(n001): 0 voltage I(C1): -5e-015 device_current I(D2): -7.501e-011 device_current I(D1): 1.49528e-006 device_current I(L1): 1.49521e-006 device_current I(S1): 1.49528e-006 device_current I(V3): 0 device_current I(V2): 7.50191e-011 device_current I(V1): -1.49528e-006 device_current EDIT: The initial dc solution started the input current at a high value because the operation treats inductors and capacitors in their DC forms as open circuits and shorts.
H: ATMega2560 timer not increasing again after overflow I want to generate waveform with f = 196 Hz using only normal mode. Here is the code I use. Whenever the timer overflows TOV1 is set and PIND0 will toggle. TOV1 is cleared after that and I wait for another overflown to happen so PIND0 will toggle again. I tried my code, with PIND0 connected to the LED. On power up, the LED turned on and off a short time after that but it didn't turn on again. Because it had turned off means that the overflown happened so PIND is toggled but I don't know why it didn't turn on again. I even tried to not clear TOV1 but get the same result as TOV1 is cleared. #include <avr/io.h> #define F_CPU 25690112UL int main(void) { TIFR1 \|= (1<<TOV1); // clear timer 1 overflown flag DDRD = 0xFF; // set port D as output TCCR1B = 0b00000001; // using internal I/O clock with prescaler 1 while(1){ while(TIFR1 & (1<<TOV1)){ PIND ^= (1<<PD0); // toggle bit 0 on port D TIFR1 \|= (1<<TOV1); // clear TOV1 by adding 1 to TOV1 } } } Can anyone see an error in my code? AI: The PIND ^= (1 << PD0) line is off. The PIN register holds the actual physical state pins, and would not normally be written. The PORT register sets the state of the pin drivers. However, as a common read-only register is a waste of I/O address space, Atmel added a neat feature to the pin register: Writing a bit mask to PIN will toggle the corresponding bits in PORT. The line 'PIND ^= mask' is then approximately the same as PORTD XOR PIND XOR mask. Since PIND reads the pins PORTD drives, PIND is usually = PORTD, which results in this being equivalent to 'PORTD = mask'. Try substituting 'PIND' with 'PORTD', -or- '^=' with just '='
H: PWM created from 16-bit timer and 32-bit timer I have a question that does the PWM created from 16-bit timer differ from one created from 32-bit timer. Personally, I deem that they are the same, since by taking the fourier series of the PWM signal I see that the dc level of PWM signal solely depends on the duty cycle. Thanks! AI: X-bit refers to the resolution you can achieve with the timer itself. 32 bit can achieve a higher resolution compared to its 16 bit counterpart. It means you can generate more accurate pwm signals with the 32 bit, but it will act exactly the same if you're using it at 16 bit resolution.
H: What power source and amplifier should I use for high reactive power purpose? I searched the site but most I can find are questions on what reactive power is! I want to know how it affects my decision for the power supply. I have to drive a coil (AC) with a high reactive power (1 kVAR) and little real power (20 W). I plan on using an amplifier and a separate power source otherwise designed for speakers. I can't compensate the reactive power with capacitor banks, because of a varying frequency range (10-100Hz). The amplifier should be able to handle 1kW, right? But what about the power supply to the amplifier, does it to have to be 1kW, or can it be only 20+W? AI: If you have an efficient 4 quadrant (and it's the 4 quadrant that's the important bit) switch mode converter for your 'amplifier', then in principle, your ultimate wall power supply will indeed be the 20w coil losses plus the residual converter losses. What the converter will do is recharge the its input capacitors when the load is delivering power back to the supply. If you have a conventional linear amplifier, that uses dissipation in beefy transistors to power the loudspeaker, then no, it has to be supplied with the full load VA, and then some for losses. A 1kW amplifier will handle it, right? No. As the voltage across its series pass transistors will be much more when handling the reverse power than its designers anticipated for conventional loudspeaker use, it will get much hotter than expected. All that 1kW input is getting lost in the amplifier, practically nothing lost in the load. You may get away with extreme forced cooling, as it's only the power dissipation that is high, the peak volts and current are still OK. You would need an amplifier rated at 3kW output power into a conventional resistive load to handle the 1kW of internal dissipation safely without modification. A good class AB linear amplifier rated at 1kW output will only be dissipating around 300W internally. For a further fly in that ointment, although a 3kW rated amplifier will have the dissipation, it will use a higher internal voltage than you need (to deliver 3 rather than 1kwatt) so will still dissipate excessively. To keep the excess voltage down, look for an amplifier rated for a lower impedance than you apparently need. As a hifi buyer, I'd look at amps rated into 4 or even 2\$\Omega\$ and comment something about specmanship and my speakers are 8\$\Omega\$, but in your case, high power at lower impedance will work to your advantage. We haven't addressed the drive impedance of your load, what are the peak current and peak volts required? This may well affect things like should you use a transformer, or multiple amplifiers in parallel. If you use a full H bridge motor controller, it will almost certainly have 4 quadrant control, it's designed for putting braking power back into the batteries. I doubt that the stock bandwidth will stretch to 100Hz however, but it might, and if it doesn't, it might be hackable with a few timing component changes. A class D switching audio amplifier will have the bandwidth, but will it have 2 or 4 quadrant control? With 2 quadrant control, it may interpret the reverse power from the load as a 'pathological load', and shut down. Different manufacturers may use different control algorithms for their chips, some may use 4 quadrant, it would be worth researching several. 1kW is a lot of power to save! Unfortunately, the standard way that audio amplifiers deal with 'difficult' loads is to add extra resistors, for instance a Zobel network, that make the load 'more' resistive, which is exactly what you don't want. You may be able to speed hack a motor controller, or you may have to brew your own converter from scratch. At 1kW throughput, it's not a job for the faint hearted, though the low 100Hz bandwidth does mean that it should be easy to repurpose components designed for class D audio use. It may be worth tuning your load for 30Hz, it will still help rather than hinder at the frequency extremes, just not very much. Can you switch capacitors with relays or power FETs for better compensation over smaller ranges?
H: How does this string of LEDs work? I bought a cheap string of LEDs in the supermarket (the christmas decorationny type) and just out of curiosity I'm trying to figure out how it works, because I can't understand how it doesn't short itself. It consists of a basic holder for two AA batteries with an on/off switch, and 20 tiny but bright white LEDs on two wires that lead out of the holder. The wires connect to one end of the first LED, and on the other side of the LED two wires lead to the next LED, so each LED has four "legs". The wires on the end of the very last LED simply connect to each other. The wires themselves are not insulated, (only the LEDs are, they appear to be dipped in some kind of transparent silicone), which What's weird to me because the positive and negative wires are touching all along the length of the strip. Also, you can scrunch up the wires and touch each bit of wire to every other bit of wire, and it still works. In fact, the two wires that come out of the battery holder appear to be touching. How is it not immediately shorting out the batteries, or causing a short when you scrunch it up? AI: The LEDs seems to be mounted in parallel with each other. The four legs are the same two wires running across the transparent blob, which is there to give the mounting some physical strength, I believe. simulate this circuit – Schematic created using CircuitLab The wires have to be insulated. But the insulation must be very thin in this case. Or, maybe, it is enameled copper wire. Otherwise, as you said, the circuit would be shorted out. If you want to take the proof, try to scrape the insulation with a sharp knife or blade and test its continuity.
H: Is the laptop's power adapter output negative terminal grounded? Today I find my lenovo laptop power adapter's output negative terminal is not grounded (the input ground terminal is not connected with output negative terminal, measured with DMM). But another old one is just opposite, the output grounded. Why? There is any standard for power adapter? If the laptop is not grounded, is it safe? AI: My experience is that the power supplies for the older laptops in which the backlight was CCFL were usually grounded on the DC side as well. I suspect it was because of the high-voltage inverter needed for the CCFL (approx. 600V DC output), but I'm not entirely certain that was the determining factor. There's a concrete example of an older HP I have that does have minus grounded; details on that in this superuser post. The newer laptops with LED backlight tend not to have the minus pin grounded. There can be static buildup and leakage currents on the non-grounded laptops [the latter particularly on metal cases] which can be irritating to some people. See this discussion on MacBook and this video of an actual measurement; he only measured AC voltage from case to ground as 78V AC with no grounding, which is probably enough to feel a slight tingle on a leakage current. A better test would have been to measure the leakage current as well... but I guess you need to try harder finding EE pros among Mac fans.
H: Can I replace a 27.12MHZ by a 13.56MHZ Xtal on PN532 I have a prototype of NFC reader which is attached to my Board. But it seem it doesn't work ... the only change I made was the Xtal because I don't find 27.12MHZ. Some people told me I can replace it if the hz was a multiple. The fact it don't work as expect. Is it normal ? AI: Some people told me I can replace it if the hz was a multiple. The fact it don't work as expect. Is it normal ? Next time, better take a look at the data-sheet. The PN532 wants to see a 27.12MHZ xtal or external clock of the same frequency. You can't just pick a different clock-frequency. You shouldn't have any problem finding the correct xtal online. They're cheap.
H: Powering multiple white LEDs in parallel Recently the idea struck my mind, that I wanted to build a simple but useful emergency light which can run off of any USB port (the specific use case would be to power it from an USB power bank). For that I wanted to design a simple circuit that drives 25 white LEDs (3.2 V, typ.) in parallel. The question I am facing now is how to achieve a simple design while not using 25 series resistors, as this is just wasteful and not space efficient, for me anyway, I just want to make it more clever somehow. Is it enough to just step the 5 volts (from the USB) down to 3.2 volts using an off-the-shelf linear regulator like the LM317 and then connect all the LEDs to it in parallel or will the non-ideal characteristics of aforementioned spoil my plan? I might be overthinking this, which is why I am asking if there might be a better, simpler or more efficient possibility to achieve what I want? :) AI: You can use a backlight driver IC which steps the 5V up to 20V+ and power several LED strings (perhaps with I2C brightness control from a micro, such as with the Skyworks AAT1236), however I think your best bet is to simply use series resistors and keep it simple. Especially in keeping with the function of the unit.. parallel strings and resistors are more likely to be functional when you need them. The advantage of the switching regulator would be higher efficiency- with resistors you've got 64% efficiency- a switching regulator might be more like 85%, so the battery might last 1/3 longer. A linear regulator would simply gather the heat from the resistors into one place, you should use some resistors anyway, and it would degrade the current regulation, so I think you should forget about that. If you were making a toy light in China, putting the LEDs directly in parallel and using the most horrible smallest-chip white LEDs you could find with a single (or a few with a few parallel banks) series resistor(s) might be an option but I would not stoop to suggest it openly.
H: Need help to design a reverse mosfet/transistor switch I have an accelerometer kind of sensor which gives analog voltage at level of uV-mVs. I want to read voltage values from it with a MCU. I am expecting it will not give more than 0.2 V in normal conditions. So I designed an amplifier where 0.2 V gives 3.3 V at the amplifier output. But there is a minimal chance that it can pass 0.2 V .To eliminate values over 0.2V, V I want to design a reverse mosfet/transistor switch. How can I achieve this? Thank you from now. AI: You can solve this with a simple zener diode voltage limiter, placed after the amplifier stage: simulate this circuit – Schematic created using CircuitLab D1 will start to conduct if the op-amp tries to drive the output voltage above about 3.6 V. R3 will limit the current in to the zener and/or ADC in this situation. Generally the zener voltage might vary by a couple hundred mV, so a 3.6 V zener is needed to ensure the circuit doesn't start to limit below 3.3 V. A 3.6 V limit is generally low enough to prevent damage to the ADC if it's powered by 3.3 V. With an additional capacitor in parallel with the zener, R3 can do double duty as current limiting for the limiter circuit and R3/C can form an antialiasing filter for the ADC.
H: Power an LED strip, power supply or transformer? I'm new to electricity so don't judge me too much. I need to power 5 watts of led strip. Is there a difference between a power supply and a transformer? I found a transformer in my local hardware store and it says: connecting power 10-50 watts, can I use it to power my led strip or do I need to look for suitable power supply? This: Or this: Edit: The led's are 12v 7.2w per meter the power supply shown in picture is 12v 12w, I'm actually building a light pad and searching for a simple way to power led's AI: You haven't provided much info. First white thing is labelled as transformer for "LV Halogen Lamps". Most likely it's just a step down transformer which will fry your christmas LED strip during reverse polarity. Second one is a mystery box without much info. I wouldn't go for that either. Here is what you need to do: Figure out what voltage is required by your LED strip - 3V, 5V, 12V or something else? If the LED strip is 5 watts, then you can calculate the current requirement as follows: Current = Power / Voltage required. Ex- If LED strip needs 5V, then you will need 5W/5V = 1A of current. Go to the market and ask for a 5V 1A(or higher) wall adapter. Modify the voltage and current accordingly. I am just giving an example. Get something less intimidating like this: EDIT after the question was edited: Figure out what length of strip you want to use. I will assume 0.7 meters which will give you total power requirement: Power = Length X Power required per unit length = 0.7 X 7.2 = 5 watts. Voltage = 12 V Current = Power / Voltage = 5/12 = 0.42 A Better to go for 12V 0.5A (or higher) wall adapter or any DC power source. Make sure it's a DC power source and not just a step down transformer. If the power source is DC 12V 12W, then it will do the job without any issues.
H: What is difference between choosing OCRnA and ICRn in timer/counter CTC mode in ATMega2560? I can't find any difference since both function the same role: define the top value so that timer will reset when reach this value. Both have its interrupt flag and interrupt service routine. AI: The difference is that choosing ICRn will allow OCRnA to control the OCnA pin at a value lower than TOP.
H: "error #28: expression must have a constant value" - with nRF51822 app_twi I have been attempting to copy the nRF51822 app_twi example for own application in order to get a better understanding of how the HAL works. However, now I have an error now that I don't understand since my code is basically identical to the example. The error: src\main.c(170): error: #28: expression must have a constant value That function where the error occurs: void LSM303_read(uint8_t m_buffer) { static app_twi_transfer_t const transfers[] = { LSM303_ACC_XYZ_READ(&m_buffer[0]) / <<<<<<<<<<<< ERROR OCCURS HERE */ // Additional transfer go in here }; static app_twi_transaction_t const transaction = { .callback = twi_read_callback, .p_user_data = NULL, .p_transfers = transfers, .number_of_transfers = sizeof(transfers) / sizeof(transfers[0]) }; } That function causing the error, which resides in my LSM303.h header file: extern uint8_t const lsm303_acc_first_reg; #define LSM303_ACC_READ(p_reg_addr, p_buffer, byte_cnt) \ APP_TWI_WRITE(LSM303_ADDRESS_ACCEL, p_reg_addr, 1, APP_TWI_NO_STOP), \ APP_TWI_READ (LSM303_ADDRESS_ACCEL, p_buffer, byte_cnt, 0) #define LSM303_ACC_XYZ_READ(p_buffer) \ LSM303_ACC_READ(&lsm303_acc_first_reg, p_buffer, 6) Not got a clue what the issue is since this is the exact same function used in the app_twi example. Can anyone give some advice here? (I'm using Keil uvision 5 with SDK v10.0.0) Edit: The m_buffer they used (identical to mine) // Buffer for data read from sensors. #define BUFFER_SIZE 11 static uint8_t m_buffer[BUFFER_SIZE]; AI: m_buffer is defined as a global in the main program, therefore there is no need to pass it into the lsm303_read function. Doing this means that the m_buffer pointer is not constant at compile time. Changing the function definition to take no argument resolves the problem: void LSM303_read(void)
H: Inductive reactance: frequency vs current. Why current goes to zero as frequency increases? Suppose I have the circuit below with the frequency of the voltage source as a free parameter. Assuming the inductance is constant, the current flowing through the circuit shoud equal $$I(f) = \frac{V}{j2\pi fL + R}$$ (I'm using phasors). Then by increasing the frequency up to infinity the current goes to zero. Why is this happening? I mean it is probably clear to me from a mathematical point of view and by using the frequency response I guess the absolute value of the trasfer function is going down as f tends to infinity, but what is the physical explanation behind this effect of a high frequency? simulate this circuit – Schematic created using CircuitLab AI: One way to look at this is that the inductor is a frequency-variable resistor (not quite since there's also a phase shift in there, but that's not important for this point). The higher the frequency, the higher the resistance. At the same voltage, the inductor draws less current at higher frequencies. A totally different way to think of this is to visualize what the inductor is doing, going back to how inductors work. If you apply a fixed voltage across a inductor, the current will rise linearly. Put another way, it takes time for the current to build up. Now imagine that you keep switching polarities of the voltage. The current builds up linearly in one direction. When the voltage flips, the current then linearly decreases to 0, then builds up to ever higher magnitude in the other direction as long as the voltage persists. Put yet another way, the maximum current is a function of how long you keep the voltage before flipping. Now consider AC is like the flipping voltage. Higher frequencies means faster flipping, which means the current has less time to change between flips. As the frequency gets higher, the inductor has less time to build up current between flips, and the average magnitude of the current will be less.
H: Through board connector I'm looking for a connector. Ideally it would be a one pin connector mounted on the back side of a board and the pin would come through the board into connector. Here's an illustration: Does such a thing exist? And if so what's its name and where can I buy one (or actually about a hundred). AI: If you don't need the connectors to be 100% flush with the board surface, have a look at the PCB socket range by Harwin. There's also a range produced by Mill-Max, but I've not had experience with them. I believe Digikey is their main distributor. Note that theMill-Max sockets are meant to be pressed in, while Harwin sockets are soldered.
H: How to pick capacitor dimensions What are the tradeoffs and design considerations for capacitor dimensions? Specifically, I need to select 2 electrolytic capacitors (C2 and C3) for a car voltage (noisy 12V) to 5V converter. Here's the circuit: How would I pick a capacitor from this datasheet? http://www.mouser.com/ds/2/420/al-kze-e-140701-514740.pdf AI: The thing that affects capacitor size is energy storage capability and given that energy stored is proportional to voltage squared, THE most important factor that determines size is the voltage rating. So you figure out the necessary voltage rating and from the datasheet you pick the size that has the required capacitance at that voltage rating. If you want to take account of load dumping (battery disconnection and reconnection whilst running) you need to consider this: - Yes, it says 100V so you might wish to consider this circuit from TI: - So, if you are going to choose capacitors that are able to withsatnd a load dump you need to choose types that have a voltage rating greater than 100V and, unfortunately, your linked data sheet does not appear to cover.
H: Triggering BT139 Triac from Microcontroller Using 4n35 Optocoupler This is my first time posting on a forum so please pardon me if i do anything incorrectly. I'm kinda new with using TRIACs, i'm using them as a replacement for a Relay and my sole goal is to switch a light bulb on and off from an arduino. I'm having serious trouble with combining the Optocoupler (4n35) with the TRIAC. When I first prototyped the TRIAC on a breadboard without the optocoupler, using wires, it worked totally fine, would switch ON and OFF when I made contact/removed contact of the GND wire at T2. When I introduced the optocoupler, the Gate on the TRIAC seems to be triggered on all the time and i'm not to switch ON / OFF as expected on a relay. Can somebody please tell me what i'm doing wrong here and provide me with a more accurate explanation on the triggering of a gate on a triac? All i understand is that you need some current flowing between Gate and MT1 (Some say MT2!), which means that you put the gate on 5V, MT2 on GND (or vice versa) and you'll trigger the TRIAC and short MT1 and MT2 allowing AC conductivity between them Thanks and sorry for the long post. AI: Here is a TRIAC circuit using an optocoupler. The AC wave form is broken up into four quadrants. The Triac has different operational needs in each quadrant. A Triac is actually two SCRs back to back. An SCR works like a diode accept it has a trigger pin. When an SCR is forward biased it conducts just like a diode. When an SCR is revers biased it won't conduct util the trigger pin is activated. When the trigger pin is activated the SCR will conduct until the current and voltage across it go down to zero. When talking AC the "zero crossing" happens from Q4 to Q1 and from Q2 to Q3. Because in essence you have to trigger two different SCRs depending what quadrant your in the triggering needed changes. To trigger at the beginning of Q1 you need positive voltage on the pin. Once the Trica is triggered it will continue conducting until the next zero crossing between Q2 and Q3. During the zero crossing the Triac will stop conducting and require triggering again at the beginning of Q3 but now with a negative voltage. It is this positive negative back and forth switch that necessitates the Opto-Triac. Two notes. First, this circuit allows the load to be turned on and off only. If you want to reduce power to the load like a dimmer you need to chop the AC wave form. To do this you need a zero crossing detection circuit. By sensing when the zero crossing occurs you can time and turn on the Triac part way into Q1 and Q3 or even part way into Q2 and Q4. The latter requires a four quadrant Triac. Second, if using this circuit to drive anything other then a resistive load then a snubber is needed. When driving an inductive load like a motor, the current and voltage wave form become shifted compared to each other. This means that the current and voltage can't hit zero at the same time causing the Triac to continue conducting even without triggering. The snubber helps to realign the current and voltage allowing the Trica to shut off during zero crossings.
H: Timing Issues with Optically Isolated Data Signal I have been working on a system that requires data transmission between two devices powered by separate supplies. I have based my design on the MIDI-hardware Spec, as I'm comfortable working with that configuration and have successfully implemented it in other areas. However, I am experiencing some strange timing issues with this latest design, and can't seem to track down the problem. The screenshot below shows the Data Input (blue) and Isolated output (red). The transmission frequency has been slowed from 200kHz to 30kHz to try and assist debugging: The high(1) and low(0) levels are as I expected, but I can't figure out where the timing issue or 'lag' is coming from. The falling part of the signal is always delayed by around 25uS. I'm using an ACPL-247 opto-isolator. But I think the problem is more likely in the 2N3904 part of the circuit, as I've not encountered this problem in previous uses of the same opto-isolator IC. Example Circuit Below: Thanks for reading, any advice or pointers to relevant literature will be greatly appreciated! AI: Looking at the ACPL-247 datasheet, the off time is typically 40us. So the isolator takes 40us typically to turn off, in your setup it is faster and only taking 25us to trip the BJT. Note you do not see it on the on time because it is specified 2us, although at 200khz I would think it would show up... So you have a 200khz waveform? Try another isolator, I'm 99% confident that a better one will solve your problem. If you really need 200khz, consider something with galvanic isolation or an isolator designed for digital logic signals. See the screen capture below for datasheet summary...
H: multilevel storage elements I've been experimenting with three-valued logic (yeah, I know) and have had quite a bit of success by using voltage comparators to implement the combinatorial logic. All 27 1-input gates and many useful 2-input gates are functioning as expected. The progress is documented at https://hackaday.io/project/6284-tern-physical-implementations-of-ternary-logic The problem comes about when I start getting into sequential logic. Specificly, SR latches, D Flip Flops, etc. Just elementary memory elements. Not only do the circuits become quite complex but they also exhibit behavior I just don't anticipate. I'm not knowlegable enought in analog design to debug them and I don't even own a scope so I'm nearly blind as well. However, I do know that this is a solved problem because Flash chips use anywhere from 2 to 8 (maybe even higher) voltage levels. Because this stuff already exists in the realm of integrated circuits I'm not going to be picky about staying strictly away from binary-digital solutions for storage. What I'm looking for is a relatively simple solution that will fit within these parameters: 1) will accept an input voltage between -5V and 5V 2) will store that voltage until directed otherwise (volatile is okay) 3) will output that voltage while it is stored 4) is available in a dip package My best case scenario (even though it doesn't exist) is a family of dip IC's that are analog equivalents to 8 bit latches, shift registers, etc. My worst case scenario is throwing an arduino into the mix to read analog voltages and PWM them out. I'm looking for a solution that falls inbtween the two. Is there a family of multi-input sample and hold chips that will keep a charge for a reasonable amount of time (at least several minutes). Or maybe an ADC with PWM output that can hold a level until directed and can accept -5 volts. Any other ideas? Thanks much for your help! AI: What I'm looking for is a relatively simple solution that will fit within these parameters: 1) will accept an input voltage between -5V and 5V 2) will store that voltage until directed otherwise (volatile is okay) 3) will output that voltage while it is stored 4) is available in a dip package. Looks like a sample and hold IC is what you're looking for. The LF398 fits your requirements. There are lots of other chips that do the same basic function with different trade-offs. I've seen sample and hold IC's with multiple channels as well. Note that analog sample and hold circuits are never ideal. You will see the output voltage drift over time. You can minimize this effect by doing good pcb layout and picking high quality components, but the effect will always be there.
H: 555 Timer in Bistable Mode - Unexpected Behavior When Removing Power I have a question regarding a 555 timer (TLC555CP) in bistable mode. Here is the schematic for the circuit in question. Now, this circuit works as I expect, when I hit the push button attached to the trigger the led goes on and stays on, and then when I hit the push button attached to the reset the led goes off and stays off. The problem that I have is when I disconnect the 555 timer from power. If I were to open either S1 or S2, and then close it, the 555 timer does not act like it did before. In this situation, when I hit the trigger the led only goes on while the push button is down and goes off when it is up. Therefore the 555 timer does not act as I would expect. Eventually though, I can make it work again by either removing the capacitor, opening and closing S1 or S2, or a combination of both. My question is, what is happening that I am not understanding in regards to why the 555 timer seems to lose its bistable functionality when it is cut off from power? Is there anything wrong with my circuit that would make this not happen? Thanks. AI: The way that I fixed this is just connecting the Threshold pin (THR) to the ground. Leaving it floating caused problems even though I have seen it floating in other examples.
H: Given a transfer function i want an op amp represantation I have a project for my university on the transfer function (where a,b,c are constants): $$G(s)=\frac{(s+a)}{(s^2+bs+c)}$$ and I'm asking how to represent this whole thing with an OPAmp circuit. (The difficult part that got me the most time thinking, is the numerator) I would like some help in order to implement it myself and not an immediate solution. AI: since this is 2nd-order, consider the Sallen-Key circuit and add to it another op-amp circuit that sums (with weighting factors) the voltages at \$V_\text{OUT}\$ and \$V_\text{x}\$. (reference to Figure 1.)
H: convert 5v AC to 3.3 DC I'm working on my raspberry pi door bell and facing the electricity problems that is beyond my knowledge, please help What I have: one AC wire from door bell, it's around 0V when Idle, then when someone press the door bell button, it increases to 5V AC What I want to achieve: My RPi needs the 3.3V DC input to monitor the "Button Press" action, so my first thought was to get a relay or transformer to convert the 5V AC to 3.3V DC. So I brought one from amazon, something called Adjustable Power Module/Regulator, here's the link: http://www.amazon.com/gp/product/B0052YHXOA?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s01 What's my problem: well, it doesn't work, the multimeter shows 0 or a very low voltage (around 0.3V) from the DC output from that Module, so I guess that I was getting the wrong thing I'm asking around to find out any idea or any solutions to convert my 5V AC to 3.3V DC, so I can connect to my RPi to continue the project tks in advance and Merry Christmas to everyone! AI: I think using a full-bridge rectifier is a bit too trusting. I don't like connecting digital pins to mains, even through a transformer. A transient fault could obliterate your RPi. Here's my approach - use an optoisolator to provide an isolation barrier. The diode inside the optoisolator conveniently doubles as a half-wave rectifier. I paralleled a capacitor with the ballast resistor on the optoisolator output. This forms an envelope detector. Here's what the voltage at the output of optoisolator looks like. I had the AC supply on for half a second, then it switched off: This would probably be fine to feed into the Pi but I personally didn't care for the ripple, so I added a comparator midway between 3V3 and ground. This is what the 3V3_BELL_DETECT output looks like alongside the input: LTSpice sim is here if you want it.
H: the voltage resolution for an analog signal with an amplitude say,i have 16-bit DAQ that can read at a rate of 250kSamples/second. What is the voltage resolution for an analog signal with a 2V amplitude? For what value of signal frequency can I safely digitize this signal? How can we relate bit daq and samplas/second with voltage resolution's amplitude to slove the problem?. For second question i think, it wants us to think about Nyquist frequency, but don't know how to relate those value, either. AI: 1) Amplitude has no bearing on the resolution of a waveform. A pure 1KHz wave with a 2V amplitude has the same resolution as a 4V amplitude wave has the same resolution of a 2uV wave. The source wave has "infinite" resolution. I use that in quotes because all real signals have a noise floor which limits their effective resolution. 2) Your DAC (is DAQ a typo?) has a resolution of (Vdd-Vee)/(2^bit depth). That is to say your DAC is limited in how small a change in the signal wave it can actually see. The equation I gave you is the generic form of finding the smallest change in voltage that your DAC can properly distinguish. Your DAC is also limited by the voltage rails it uses. If the signal is larger than the voltage rails than the DAC can't "see" that part of the wave. 3) Nyquist theory states that you must sample MORE THAN two times the frequency of a wave to be able to recover it without aliasing. I.E. using a 1KHz wave as the highest frequency you'd like to recover, you must sample MORE THAN 2000 times per second (>2KHz) to recover the waveform. I'm emphasizing the "MORE THAN" as I see quite a few people who mistakenly think that sampling at exactly twice the rate will recover the signal. If you sample at exactly twice the frequency of the wave you want to capture, you will alias a DC signal. That section of your question confuses me, as DAC's can't READ. They take a digital value and convert it to an analog voltage (or current). However, I've provided and example of how and ADC would react based on sampling rate. Edit 1: In the problem you were given the maximum sampling rate. Using math inequalities you would simply reverse the example to find your answer. I.E. if the ADC could only sample at 2KHz, then you can only "see" frequencies recorded that were LESS THAN 1KHz.
H: Controlling 64 stepper motors with arduino I have seen many post on this site for controlling stepper motor with arduino. And arduino is pretty good at it if provide with good shield/Driver. My query is How can is use to arduino control more than 2 stepper motors i.e(64 stepper motor). It seems to be a huge project for me. Each motor will move at same speed but won't have same steps. More like MIT inForm For now we are just making a prototype. I have attached the internal structure of or device where we will be using full stepping mode and only 2 pins for controlling Stepper motor as rest of the 2 pins are just complement of first 2 pins a b a' b' 1 0 0 1 1 1 0 0 0 1 1 0 0 0 1 1 our basic theory/logic is arduino will generate 2 pulse of each motor pass it to serial to parallel converter and this will further send the pulse to PIC that will generate rest of the 2 pulse and pass it to stepper motor. Each pin on arduino will generate pulse for 4 stepper motor i.e. 8 bit per pin. I will be using 28BYJ-48 stepper and ULN2003 having configuration of stepper motor as 64:1 ratio the thing is at what rate I need to send 128 bits(8 words) of data from arduino to shift register. so the motor should run at decent speed So any one can help us to achieve this and guide us with the project. All reviews are welcome. AI: I will preset a differnet approach that i would use if i where you: 1- Use a SPI or I2C based stepper motor driver like NCV70521 , L6470 , DRV8811 or similar ICs , this will save you from writing the commutation software for the stepper motor ( if micro-stepping is needed ) . These also work in full and half step mode. 2- Focus on the protocol of communication : a- if SPI is choosen (easiest , but you will require 64 pins (chip select) , offcourse you could you decoders / demultiplexer and similar logic ICs to derease the number of needed pins from the microcontroller. b- if I2C is choosen , then 2 pins of the microcontroller are enough to control all these motors ( SDA and SCL ) but you have to configure different address for each driver. the advantage of this mode is that the speed or steps are send serially as commands. In your approach you might face some problems in speed , if want to toggle pins at high speed arduino digitalWrite might not be suffcient.
H: Is this memory card circuit designed properly I'm looking to build a reusable memory card for my SRAM as the cost of the chips can get up there. I'd like to be able to plug this into other projects (mainly with a W65C816S as I work with it) both with a breadboard and other PCBs. Before I go about laying this down on a PCB I'm wondering if there is anything wrong or if there are any other suggestions. I can't really breadboard this as the memory is all surface mounted. I've updated the circuit to add in buffers and bypass caps. For the data buffer to work I needed to add the direction signal to the header so there are some extra pins now. Are there any additional suggestions or comments? Current circuit. I've changed the multiplexer chip to be low active. It's much faster propagation time is nice. The connector has been updates as well, so hopefully it's handling power and ground a little better. Additionally this has CE line suggestion @PeterSmith AI: The Address and CE# pins are quite heavily loaded, as are the data pins during a write. Even though only a single device is active at any time, the capacitive load of the pins is present from all devices at all times. From the datasheet, A0 to A19 will have up to 48pF load plus any track capacitance and the data pins will have up to 64pF during write. CE# has a slightly heavier load (by virtue of driving the '38 decoder as well as all the memory devices). That is a bit hefty (equivalent to about 40 inches of 4 thou track for the address pins and almost 60 inches of track for the data pins), so you may wish to consider Address and Data buffers. The track capacitance assumes a 4 thou PCB core to plane. As noted, you will also need decoupling: a couple of bulk capacitors and two 100nF per device (one for each power pin as they are on opposing sides of the memory devices) would be my starting point. The decoder would probably be ok with a single 100nF part. You may not need all of the decouplers, but if the pad positions are there, you can always choose to simply not fit the parts. You may be ok with a single power pin (only one device will be active at any one time), but I would normally provision at least 2 if I have enough pins available. Update: Use of CE# signal. As the second SRAM CS signal is being gated by CE# already, it seems redundant to take it to the SRAMS as it is doing the same thing and layout can be simplified. I would just tie off that CE# signal low at the SRAMS and use the gated and decoded CS. This has an added benefit: as the capacitive loading on CE# has been significantly reduced, a great deal of timing uncertainty has been removed.
H: How is the solution for \$\alpha\$ and \$\beta\$ current gain of a BJT derived? I'm just an enthusiast, and not too good at maths; I'm exploring constant current source circuits, in doing so I came across two equations for BJT current gain: Could someone help me understand how \$\alpha\$ and \$\beta\$ are derived to the equations below: \$\alpha=\frac{\beta}{\beta+1}\$ and \$\beta=\frac{\alpha}{1-\alpha}\$ I know that: \$I_c=\alpha I_e\$ and \$I_c=\beta I_b\$ Any help would be much appreciated. Thanks Alex AI: Check this out. Found some rich content here electronics-tutorials-transistors α and β Relationship in a NPN Transistor The value of Beta for most standard NPN transistors can be found in the manufactures data sheets.
H: multiple motor h bridge? I see a lot of h bridge diagrams on the internet, more or less like this: If I wanted to connect let's say 4 motors in h bridge configuration while using the same power supply (12v) for all 4 of them and would also like each motor to be able to work independently, what do I need to do? Is this feasible (without a motor driver IC)? Would hooking up more than one h bridge to the same power source affect the current that goes through each motor? If so, how to remedy that? AI: If you want 4 independent motors then you need four independent H-Bridges. If you have a 12V source that can supply current to all 4 simultaneously then there's nothing to worry about. Hook them up in parallel and get a controlling circuit (MCU, timer, etc.) If your 12V supply can't provide enough current to drive all 4 motors then you need to ask more questions: 3a. Do you allow default coasting (non-tracking state)? If yes, you can use that state to save power and then simply apply power to each of the motors out of phase with one and other (i.e. if you can drive two motors at a time, then only drive two at a time and have the other two coasting). 3b. If you don't allow coasting then the solution is get a bigger power supply.
H: How to set SD card clock frequency between 100 kHz - 400 kHz I am interfacing a 32 GB microSD card with PIC32MX795F512L. I am following the examples provided in Lucio de Jasio's book. As the author has described that to set a 250 kHz, they are driving their peripheral clock frequency by 144. Which means 36 MHz when divided by 144 gives 250 kHz. But then why are they setting the SPI1BRG = 71;? (SPI1BRG = SPI baudrate register.) I am using 44 MHz as a peripheral clock frequency. What value should I use? I am really confused in setting the clock frequency for the SD card. AI: They probably set it to 71 as the relationship between the register value and the divider value is probably divider = (BRG register value + 1)2. In this case, (71+1)2=144. You just need to calculate the divider value, divide by two, and subtract 1.
H: Good fan speed for solder fumes I am going to be soldering in an enclosed space, so I am building a fume extractor via ducts. My eventual plan is to have one fan near the vent, and another somewhere near the inlet to help the fumes get to the ducts. So my question is how powerful should the first fan be, preferably in CFM, and if I need the second fan. Thanks in advance. AI: It depends on how much area you want to cover. I generally see under-bench systems with vent hoses in the range of 150-200CFM. The desk top ones can have lower flow rates as they usually sit closer to the work, where as the under bench systems draw more air as they're meant to have the vents sit further away. Keep in mind depending on how aggressive your filter is you may need to get a stronger fan to deal with the resistance presented by your filter. If you want an idea as to what commercially available units use for a sense of scale, look at vendor sites. They usually specify the flow rates for their products. Some suggestions to get you started would be PACE, and Hakko. You should only need one fan.
H: What is the way to detect SD card insertion/removal? I am interfacing a 32 GB Micro SD card with a PIC32MX795F512L. I am following the examples provided in Lucio de Jasio book. In one of their example, they are using while( !getCD()); to check if the card is present or not, but this doesn't seem to work in my case, because when I remove the card, it doesn't give any error and moves forward. Below is its code: // SD card connector presence detection switch int getCD( void) // returns TRUE card present // FALSE card not present { return !SDCD; } In the hardware, SD-CD pin is connected to RA15. So what is the right way of detecting the card's presence? Above is the schematic for SD card connections. SD-CD# pin is the pin for card detect. I am checking the voltage change on R34, but there is no change. When the card is removed, it shows 3.5 V and when the card is inserted, it again shows 3.5 V. Am I doing something wrong or does the hardware have some problem? AI: SD Card detection is typically done by a mechanical switch that is built right into the SD Card socket. It opens and closes when the card is inserted and removed. You will have to investigate how this switch is hooked up in your hardware and test that this works correctly up to the PIC32 pin before you even begin to think about software issues. Testing the hardware should be as simple as looking at the signal going to the PIC32 pin using a scope probe or multi-meter in volts measure mode. With the PIC32 board powered monitor if there are changes of state in the signal as a card is inserted or removed. If you do not see this working then the switch in the socket is not properly connected. It is typical that one side of these switches is connected to GND. The other side has a pullup resistor to +3.3V and also connects to the PIC32 pin. If working correctly you should see it changing between 3.3V and GND. Once you have verified the hardware connection it is time to investigate the PIC32 software aspect. The particular pin connection needs to be a general purpose input port pin on the microprocessor. Then that port pin needs to be properly configured to be acting as a digital input pin. If not properly configured then there will be no joy in reading in the SD Card status signal.
H: Is it possible to pick up noise in an audio circuit through the ground / earth wire? In an audio circuit, such as a guitar's electronics (the only thing I ever dabble with!), I have always thought (probably simplistically) of every point along a continuous earth path being essentially all at the same voltage (a 'zero volt' reference voltage). However, I was wondering - if you extend an earth wire from some point along that path, is it possible for that in itself to introduce noise to the circuit by changing the '0V' of the earth reference? (Possibly I am wondering "What is the difference between a long earth wire and an antenna" - but I don't know enough about antennas to know if that's what I'm asking :) AI: Yes, long ground connections can pick up noise, which means the ground in one place is a different voltage from the ground at another place. For single-ended signals, this ground offset voltage usually appears as part of the signal. There are two common strategies for avoiding this situation: Use differential signals. The actual signal is encoded as the difference between two signals that are driven oppositely from each other. Ground offset then looks like a common mode signal, which can be largely ignored by the receiver. Pay attention to how things are grounded. Make sure all the grounds are tied back to one place without other connections to elsewhere, like the local power outlet ground. This ground net is then connected to real ground in one place only. Also avoid having deliberate current flow thru any ground connection. There should be separate returns for power current. Never use ground as a power return.
H: PWM and DC motor speed I'm hoping to try to control the rpm of a DC motor. AFAIK, I'd need to generate PWM for that. How does one find out which frequency is needed for a certain rpm? Is the frequency of the PWM signal supposed to be related to the speed of the motor? Thanks AI: The idea of the PWM speed control of a motor is that you switch the motor on and off between between 0V and its max operating voltage at a fast rate. It is common to use a frequency that is higher than the range of hearing so that this fast switching is not creating an annoying noise in your head. The actual speed of the motor becomes related to the length of time the fast switching time has the voltage attached to the motor versus the length of time the voltage to the motor is switched off. This time relationship is referred to as the duty cycle of the signal. Change the duty cycle and the speed changes.
H: TFT LCD interface I am little confused in basic understanding of LCD interface. Many times datasheet suggest 8/16 bits MPU interfacing. Here, for interface we assign GPIO's of microcontroller to respective data pins of TFT ( DB0 to DB7 or DB0 to DB15 depending upon 8/16 bits interface ) Sometimes in TFT datasheet, RGB interface is mentioned as per below screenshot. Here, RGB pins of LCD are normal GPIO of controller or there is TTL to RGB converter needs to be added then interfaced to LCD? What about HSYNC or VSYNC pins? Are they GPIO's only? Please someone explain. Thanks. AI: The datasheet of the LCD tells you the signals that must be present on the LCD interface pins. How you achive that is up to you, you can bit-bang the signals on GPIOs, use an-on chip or off-chip LCD controller, a custom-programmed FPGA, or even black magic. The LCD doen't care. In most cases, the 8/16 bit interfaces (and for smaller LCDs, SPI or I2C interfaces) talk to some kind of controller on the LCD. The communication is in terms of instructions, like "set these pixels to black". This kind of interface can easily be done by the CPU (using bit-banging) In most cases, interfaces that mention RGB line and SYNC signals interface more directly to the LCD: they specify the full data that must be displayed, and this data (a frame) must be repeated at the frame rate (typically 10..100 Hz). This requires much more attention from the CPU if it would do it all by its own, and for larger LCDs this is totally impractical. (Where the switchover point lies depends on the CPU, programmer skills,a nd CPU time needed for the rest of the application.) These type of LCDs are generally interfaced via an on-chip LCD controller.
H: What happens to a Sine wave in the frequency domain? Say for eg.if we have a sinusoidal signal of f = 1KHZ, VPP = 1V and Voffset = 0V If I change my Offset Voltage from 0v to +5 V, What would be the effects in Time domain and frequency domain? AI: You will see a single peak at 1KHz. In the frequency domain, increasing the offset won't change the peak you see at 1Khz, but will create a new peak at 0 Hz. In time domain, increasing the offset to 5V will simply change the mean voltage of your sine wave to 5V, it won't change the amplitude of the wave. The first part of this answer will help you.
H: How to blink LED with 1.8V? I am experimenting with an Intel Edison mini breakout board with pinout like here: http://fab-lab.eu/wp-content/uploads/2014/10/Edison_IO_LED.jpg Now, I soldered header pins to plug the board into a breadboard. Unfortunately, the GPIO levels are only 1.8V. What should I do to make a LED blink from here (on a breadboard ideally)? What else can be done with 1.8V GPIO levels? UPDATE: It works with a BC547 However, depending on the blink frequency, it seems that LED does not turn ON completely. Might it be because the base resistor is 0 ? AI: 1.8V is enough to drive a transistor which can be used to power all kinds of loads. Example: simulate this circuit – Schematic created using CircuitLab
H: BJT Saturation with small load/ H-bridge I am trying to analyze the operation of a BJT H-bridge configuration. I have searched through these forums and Google and can't seem to find an answer to my question. It is my understanding that it would be desirable to have the "ON" transistors in the saturated state, to provide maximum supply voltage to the motor. This is also a general practice whenever using BJTs as switches. They should operate at cutoff and saturation. I tried to simulate a simpler circuit, ignoring the two "OFF" transistors and only looked at the two "ON" transistors. Suppose I wanted to have my bridge supply 1 amp of current with a 5 volt supply (arbitrarily chosen). I used a 5 ohm resistor as the load to simulate the motor. If both transistors saturate (Vce <= 0.2 V), then the load should receive about 4.6 V. In simulation the load receives only about 1 or 2 volts. If I lower the base resistances to increase base currents, it improves to about a maximum on 2.8 V across the load. If I increase the load resistance to about 50 ohms, then I can get about 4.7 V across the load, but obviously the current is not what I want. I've read for saturation that Vbc should be forward biased, or Vb > Vc. This explains why increasing the load resistance causes the bridge to go into saturation, since the voltage drop across the resistor gets large enough for Vc to become less than Vb. Though, with such a small load resistor it takes a lot of current to make an appreciable voltage drop. If beta is a worst case of 50, then an Ib of 20 mA should be enough to provide 1 A at the collector. However, even when I make the base resistance ridiculously low (10 ohms), I still do not get anywhere near supply voltage across the load. Does this mean that it is not possible to saturate the transistors with such a small load resistor? AI: There are some point to keep in mid when asking a question like this. First there's no guarantee that transistor model that shipped with simulator X matches the datasheet from manufacturer Y, even for the same generic transistor type. If you need to operate in heavy saturation (hfe=10) then you can probably get by with using almost any model. If you want to operate in quasi-saturation (Vb>=Vc but hfe doesn't get close to 10) then you need to be careful what SPICE model you use. Second, 2N3904 or 2N3906 are only good at most 200mA Ic in real life. So don't expect any SPICE model for them to be terribly useful at 1A. Usually some software like MODPEX [or similar] is used to generate the SPICE model by curve fitting from the traced curves; the derived parameters aren't necessarily much good beyond the window in which they were derived because the Gummel equation uses some parameters that pretty difficult to determine accurately. Here are the Gummel plots of two 2N3904 models I happen to have done already; first is the one that comes with LTspice (supposedly from NXP, but God knows where they pulled that data from) and second is the one actually downloaded by me from NXP. There's a big difference between them in terms of how hfe varies and even what the max value is (in the active region) or how low it drops in saturation (Vbc was set to 0 in these plots). So before anyone can answer your question with more than a handwave we need to see the SPICE models that your sim uses for those transistors. To get more to the point of your question, since you apparently using multisim (not exactly my favorite; I find the "virtual instruments" paradigm of having to modify the schematic to measure stuff on it incredibly clunky by design), I just imported their [NatSemi] 2N3904 model in LTspice. Basically you cannot saturate it at 1A collector current (for any base resistor), as you can see from the following sweeps: The green curve is the power dissipation over the transistor. You can see that at 25 ohms load (corresponding to 200mA Ic, max allowed in datasheet), there's a pretty wide region for choosing the base resistor so that the transistor is in saturation. This margin gets smaller as we lower the load resistor. At 5 ohms load (top curve), you basically have nothing left; even with the optimal/minimum value it would dissipate nearly 1W. Never mind that it would burn the transistor in real life by exceeding the collector current alone. I'm not entirely sure what explains the massive difference we see with this model between 10-ohm and 5-ohm load, but it's probably caused by a combination of high-level injection dominating [Ikf, the forward knee current is 66mA] and the built-in collector package resistor (this is 1 ohm); the emitter resistor is not set in this model. If we set the load to 5 ohms but alter the built-in collector resistor to 0 we can see it would saturate to a more reasonable power dissipation level--the lower curve below:
H: Impedance matching resistor for ws2811? I want to design a circuit using ws2811 on page 5 of the datasheet It says "To prevent the reflection and hot-swap protection, we suggest to connect a 33ohm resistor at the data input or output port for impedance." But on modules and boards on the market I don't see these 33ohm resistors, How important is it to add these? In what situations may it be neccessary? AI: But on modules and boards on the market I don't see these 33ohm resistors, How important is it to add these? In what situations may it be neccessary? If the chips/modules/boards (you refer to) cannot be hot swapped AND the data transmission distance between them is small (for 400 kbps) then you can probably avoid using them. When they talk about "reflection" they are referring to transmission line reflections upsetting the digital data passed between them - it's necessary to "quench" reflections or you get corrupted data.
H: Forced beta too small Let's take an example in which the recommended beta for a transistor's(NPN) saturation is 10.If you use a forced beta smaller than 10,will the transistor still be saturated succesfully?Can hFE be small enough to damage the BJT? AI: If you use a forced beta smaller than 10,will the transistor still be saturated succesfully? Yes, if you design for a smaller forced beta than the datasheet recommends the transistor will still be saturated, but you're probably just wasting base current for nothing. As an aside, saturating a power BJT and keeping it saturated is a bit complicated it you want to do it optimally. The initial base current needs to be higher than the maintenance saturation current for optimal results in terms of minimizing power loss on the transistor while entering and staying in saturation. Likewise when you turn it off, you can actively remove the base charge rather than wait for it to disappear by recombination alone. (Image from these slides; you should probably watch the course video [or read the book] for more explanation on that.) If hFE is too small,can the BJT be damaged? I'm not exactly sure what you mean by this... But it you drive it a base current that's too high (which can result by designing for a hfe too small) then yeah, you can burn the transistor. Regarding the BC547C: here's an example of varying the base drive using the BC547C model that comes with LTspice; I chose some 120ohm load (at 12V) since you didn't specify it. The max collector current for BC547 is 100mA, so this is pushing it to the limit. You want to pick R1 (the base resistor) so that the power dissipated on the transistor (green curve) is at a minimum when "ON". That means somewhere between 1K to 3K here. It doesn't matter that the hfe (red curve) is not 10 there. Also note that if chose R1 so that hfe is 10, you may have slightly higher power dissipation; but the variation of power dissipation on the transistor over the entire saturation region isn't all that great. You can see that in a zoomed view of the saturation region: To the left of the curve you can see how you could burn the transistor with a base resistor too small, even though hfe is small there too; the power dissipation is not because the dissipation over the base emitter region starts to dominate. To the far right, the transistor goes in the active region and its collector-emitter voltage drop starts to dominate the power dissipation over it. Do not assume this simulation is necessarily optimal for Fairchild's transistor. They give no SPICE model, so you'd have to create your own from thei datasheet. Also this simulation is for static dissipation while ON, i.e. assuming you don't do fast switching.
H: adjustable IGBT current? Goodmorning all, Here my very first question so I may be asking something that is may be already answerd but I couldn't find, My question is : How is current limiting achieved in modern IGBT based welding equipment? I do have a DC TIG welder myself and I am just curious how to achieve a max current setting from let's say a very wide range between 5-180 Amps? I have googled quite a lot but I can't find anything that is helping me understanding this aspect of power electronics The only thing that gets close to it is the CS8312 that controls the gate of the IGBT for a specific max current through the IGBT. Any help suggestion is appriciated! Cheers AI: With an inductive load and PWM. IGBT's are optimised to be Discrete ON or OFF devices and do not have a linear/active region like MOSFET's and BJT's. The CS8312 shows an example setup with an inductive load and a sense resistor. This particular chip works by increasing the threshold by 45% Changing the CLI pin from a logic low to a logic high increases the FLAG turn on voltage by approximately 45% and the regulation sense voltage by approximately 39% respectively. Other methods are via simple comparator for hysteresis control or PI controller to then generate a PWM signal that is indirectly used to drive the IGBT
H: TVS diode electrical parameters I am using below diode in my design to protect 3V3 lines:- http://www.ibselectronics.com/ibsstore/datasheet/AZ5123-01F_Datasheet.pdf On page 2 they have given :- Also, they have given on same page :- What is the meaning of this!! What is +-16KV & what is the 7V?? AI: They are saying two things. Firstly, if testing the device (on its own) with an ESD gun conforming to IEC 61000-4-2 then it will survive a 16 kV discharge test. It's listed in the absolute maximum ratings section and this is generally what that section defines. It doesn't tell you what it will clamp to but it'll be in the order of tens of volts Further down they are saying that it will clamp a 6kV discharge to typically 7V when used with the same ESD gun. This gives you some confidence about performing in-circuit testing and what sort of voltage levels you may witness when doing ESD testing.
H: Small switch with a button top for gliding over? I wonder if there's a kind of switch for low voltage devices (~3V) that allows small nipples to glide over. For instance, I have a small plastic rod with small nipples (~1-2mm high) and I'd like to count the number of nipples glided over the switch position. I've looked at some microswitches, but they all tend to be rather large (at least 2cm long). I think rounded top switches like this lego one might work, but the lego block itself is fairly big. A ~5mm package would be great. SMD would be even better. Any help will be appreciated. Thanks AI: Would these work mechanically: - If "maybe" then try this link - I googled "4 pin tactile switch pcb mount" and looked at the images.
H: What is the intended use of high current SSRs and triacs? I answered a question recently regarding power dissipation in solid state relays. This is the calculation: Consider this 40 A rated triac - BTA40. Vto = Threshold voltage = 0.85V = Voltage drop across triac. Rd = Dynamic resistance = 10 mohm Assume IT(RMS) = Current through the triac = 25 A Power dissipation = [0.9Vto X IT(RMS)] + [Rd X {IT(RMS)} X {IT(RMS)}] Where 0.9 = 2*sqrt(2) / pi Putting the values, we get P = 25.375 Watts For 1A current, P = 0.775 watts which seems to be a tolerable value without any heat sink. Besides this calculation, I tried testing a few triacs rated 4A to 40A. All of them get pretty hot after 2-3 amps of current. Even after putting a heat sink (approx 5cm X 5cm X 2cm) the condition didn't improve much. As such, I am wondering what might be the intended purpose of these solid state relays? Is it just used for high ampere switching at a very low duty cycle where the triac could get ample time for cooling itself? Because, for continuous currents above 5 amps, I think I will better off with an electromechanical relay rather than going for solids. AI: Yes, they are used for high power switching, and not necessarily at a low duty cycle. I run hundreds of SSR's anywhere from 5A/240VAC up to 100A/460VAC/3P. Past 100A, it is more common to use back to back SCR's and a small firing circuit (and large heat sink). The typical application is for resistance heat control. Contactors/Relays are not a serious option, because of contact wear (the typical 'duty cycle' is 2.5 sec on/2.5 sec off). Basically, a timer is free running for a certain period (I use 5 seconds mostly). The heater is switched on and off for some period out of that 5 seconds to control temperature, based on the output of a PID loop. 10% output is on for 0.5 sec, off for 4.5. 90% output is on for 4.5, off for 0.5. Those duty cycles kill electromechanical devices quickly. There are also hybrids, that use a relatively small SCR to turn on a load, then close an electromechanical contact around it (to prevent closure arcing), and then the SCR is turned on again when opening the contacts. Those are pretty special purpose though, and expensive. Mercury Whetted relays used to be used, which didn't have the contact wear problem, but in the past 15 to 20 years, industry has been trying to eliminate them due to the problems of dealing with heavy metal contamination, and disposal.
H: Multiple Broken Relays -- What About My Circuit Is Making Them Fail? I recently purchased one of these relay boards ... to use along with my Raspberry Pi to switch an AC outlet on/off to control a fountain pump. Since the relay board requires 5V for the control lines and needs to pull more current (IIRC) than the RPi can supply on 5V, I put together this little circuit to test out my system: simulate this circuit – Schematic created using CircuitLab Relay Schematic: I know that my "To Relay Control" line is only going to pull down to ~.3V when the RPi GPIO is high, but it was enough to toggle the relay, so I went with it. I have software that turns the pump on 15 minutes out of every hour, and the system was functioning fine for a few hours. However, after a few (~8) hours of operating the relay is no longer switching -- even if I pull the "To Relay Control" line directly to ground the relay will not flip into the "on" position. I thought this might have just been a random bad part, but I switched to another relay on that board and had the same problem after running fine for a few hours. The LED on the relay board lights up when the line is pulled low, but that's it, I don't hear a "click" out of the relays anymore when I toggle them. Is there something about my test circuit that is causing these relays to fail? In general, what would cause a relay to fail in the manner that I've described? AI: Get rid of the extra AC connection on the relay. This contact set could weld themselves if an inductive load were present and the contacts were shorted like that. For inductive load add a snubber across the relay contacts to help protect the contacts from welding. I took the liberty if showing the AC source correctly and not as + and -.
H: Easiest way to generate 25V speaker signal I have a fire alarm that accepts a 25v line level speaker input at 4w, what is going to be the easiest way to play arbitrary signals over it i.e. from a 3.5mm jack, an amplifier and a transformer? are there small pre built modules for this purpose? Everything I see seems like it is intended for distribution to a large pa system not a signal speaker. Edit: It is a SSPK24-75WR Here are some datasheets I could find, but there is not mutch info beayond "hook it up to our system" http://resource.boschsecurity.us/documents/Datasheet_SSPK_Famil_Data_sheet_enUS_2736837259.pdf https://www.gentex.com/sites/default/files/551-0070%20SSPK24WLP%20Series_0.pdf http://www.thesignalsource.com/documents/sspk.pdf AI: Easiest is to use a 25V or 70V PA (public addressing) amplifier, e.g. first hit google for me. Since you seem to like Bosch, the have plenty of those too. You can surely find low-power cheap Chinese stuff. Your speaker has options for both 25V and 70V. There plenty of youtube tutorials how to hook that up, e.g. https://www.youtube.com/watch?v=M4I9TF4hVLI Or build your own with a regular amplifier and an appropriate audio transformer. For yours, the transformer would be something like this or this (the latter has tap for 25V-5W too and is half-price of dedicated 4W one), assuming you don't want to power more speakers from the same amp/transformer. I have to warn you from my own experience[s] with similar 100V PA transformers that the labeling of the wires tends to be effing confusing and no two manufacturers seem to agree on where to put the ohms where the watts on those taps. So if you go this route, read the [usually skimpy] datasheet carefully and have a [AC] multi-meter handy.
H: Why would a 150 MHz probe work fine for a 100 MHz oscilloscope? I read in many forums that one can use a probe with a higher bandwidth than oscilloscope's bandwidth. If it is right why it is not a problem? What is the theoretical explanation? AI: That is right. Not a problem in doing that. Think of it as a filter between your oscilloscope and the point you are probing. The bandwidth of the oscilloscope will determine the overall bandwidth of your "measuring system", since it is the most restrictive one. For instance, if you are using a 150MHz probe with a 100MHz Oscilloscope, then the probe will attenuate the signals over 150MHz, and that input (with a 150MHz bandwidth) will enter your oscilloscope, which will then attenuate the signals over 100MHz. So your probe will pass the signals between 100MHz and 150MHz, but they will be filtered out by the oscilloscope input circuitry. In the end, you will have filtered the signals over 100MHz anyway, so no big diference with using a 100MHz probe. In the other hand, if you use a probe with lower bandwidth, then it will determine the bandwidth of your input filter, and you will have less bandwidth in your input filter.
H: Sony STR DN1030 2nd volume control using a second Vr Encoder First off, I am very, very new to any electronic physics/engineering. Here's my problem: I want a second remote volume control for my receiver that is wired to my desk. (I have already managed to make the standby switch work) There are three pins on the current VR encoder in the unit (Part #: 141872541 on Sears Parts Direct or http://www.searspartsdirect.com/sony-audio-equipment-parts/141872541/0057/528/model-STRDN1030/0996/0311300.html). Is it possible to buy a replacement VR encoder and just solder the second encoder, via a usb 3.0 wire, directly to the current contacts so there are two encoders connected to each terminal on the board? (I'm thinking no) The second solution I was thinking of was having the output of the first encoder be the input of the second encoder, and run the output of the second encoder back into the board. Also would the product below work as a replacement for the encoder, or should I just pay the premium for the genuine part? (I was thinking no because my understanding is that an encoder changes binary code and this changes voltages) "RadioShack® 100K Dual-Ganged Stereo Volume Control"(100K dual-ganged stereo volume control with audio taper. Double potentiometer 40% loudness tap) AI: A dual ganged stereo volume control with audio taper is a potentiometer. That is "a variable resistor". Actually a dual variable resistor! This is an analog component. The other product, VR Encoder, is a low resolution digital encoder that can create two signals that are digital in nature that are 90 degrees out of phase with each other. This is often called a quadrature encoder too. The two components are completely different from each other and can never be used directly in place of each other. You will not be able to parallel up the quadrature contacts of two of the VR Encoders because 75% of the time the one of the internal contacts that create the switch closures to produce the Chan A and Chan B outputs will be closed. The parallel encoder channel to one that was closed would not work. You may be better off making some type of wireless remote robotic mechanism that used a rubber belt to turn the actual knob on the stereo receiver.
H: Do I need special charger for a Lithium-Ion battery? I want to use a Lithium Ion Battery. I saw that there is also a different kind of chargers like Adafruit Micro Lipo/MicroUSB or Adafruit Micro USB Lipo for this kind of battery, do I need it? Can I charge my battery direct from a voltage source? AI: As mkeith mentioned in a comment, the charging starts out as CC (constant current) followed by CV (constant voltage). This is what the charging profile looks like: The charging rate is noted as 1C, which just means the charge current is initially equal to the capacity of the battery for one hour, i.e. 1.5 A for a 1500 mAh battery. If you are buying a stand-alone charger, then you need to buy one specially made for Li-Ion batteries, such as the ones you found. If you are building your own circuit to charge a Li-Ion battery, you need to buy a battery management IC. There are not too many that come in hobbyist friendly through-hole packages. One that does is the BQ2000 which comes in an 8-pin DIP package. It automatically detects the battery chemistry, and will work with nickel cadmium (NiCd), nickel metal-hydride (NiMH), or lithium-ion (Li-Ion). It's available from Digi-Key for $3.46.
H: How to program multiple STM32Fs on same PCB I work in a management roll and only have a very limited electronics knowledge (enough to make simple arduino projects etc). We are working on a product at the moment which has 3 STM32F303s and 2 STM32F103s and the main processor being a AM5718. I was just wondering how you would go about uploading and upgrading the firmware and bootloader one each processor including the AM5718. The 5 STM32s are connected to the AM5718 via UART and all are on the same PCB. I would like to get a good idea about how this would be done after the PCB is produced and the product is in the field. I would obviously ask the electronic engineer working on the project but we have finished for xmas. AI: If hardware design is done correctly and assuming UART is used for programming, the steps would be roughly as follows: The main CPU resets a selected MCU. The CPU then brings the required BOOT pins to an appropriate state and releases the reset. The MCU bootloader starts and waits for data to come in on the appropriate UART line. The CPU send the binary data over the UART and resets the MCU when done. The MCU runs with a new firmware. Here's an image showing bootloader selection for STM32F10xxx parts: The same steps would be repeated for each MCU. The main processor can be updated in numerous ways, but it usually goes like so: Firmware is downloaded into a local storage (FLASH, RAM, SD Card etc.) The CPU reboots and the bootloader discovers the upgrade code. The CPU bootloader reads the data, checks that the binary is valid and programs the appropriate FLASH sectors. The CPU reboots itself again and loads with the new firmware. Update. Based on your current hardware, you'd have to execute the bootloader by jumping to the appropriate memory address (see page 20 of AN2606). I don't know a great deal about this, but your hardware designer should be able to figure it out. Not having the control of the reset line is a bit of an oversight though.
H: Why am I getting very different measurement results on a breadboard? I have an AC to DC multiple output adapter. It has the following output: I set the voltage to 5V. When I measure the supplied current, I get 3.26A. Then I connect an output to it: When I measure the supplied current now, I get 3.23A. Then I try to measure the current on a breadboard: And I get 0.02A! What is going on? Why is this happening? More interestingly, I have discovered that the LED on my adapter gets dim proportional to the current it supplies. However, in all three measurements, although the results differ (especially the last result), the LED gets exactly the same amount dimmer. So this is a curious point as well. Could you explain why the measurement on breadboard differs so much? AI: You are short-circuiting the adapter, first with the ammeter, and then with the breadboard. Both are not good for the adapter. simulate this circuit – Schematic created using CircuitLab The dashed boxes represent the equivalent circuit of your supply and your ammeter; numbers are very approximate. On the right hand side you see the ammeter shorting out your supply and causing it to overheat and probably fail in short order. On the left hand side you see the same thing happening except most of the current is flowing through the solderless breadboard and only a small amount (the voltage drop in the conductors) is getting to the ammeter. If the conductors were perfect the meter would read zero since you've shorted the meter (as well as the adapter). This is bad practice and you will eventually damage something.. putting an ammeter across a voltage source can cause serious injury or death if the source is capable of a lot of current, and certainly can damage the meter or the electronics. Don't ever do it.
H: Energy wastage in wireless charging rotary toothbrushes? I'm not going to change my habits based on the answer, but I did wonder from a theoretical standpoint. I get idea of wireless charging. I still have flashbacks to my power generation & electric motor courses in undergrad (3 phase systems, lossy magnetic field circuits, etc.). So basic intuition, I have a vague sense of. What I don't know is whether today's wireless chargers for rotary toothbrushes are made with enough monitoring and control logic to be aware of when a load (i.e., a toothbrush) is docked and drawing power, so that it dials down the EM field when there is no toothbrush. As a related 2nd question, does the toothbrush switch loads when full charged so that the charger can tell, and dial down the juice? AI: A robust modern product would probably have circuitry to detect the toothbrush load back in the base and turn itself off. Unfortunately the competitive market and cost pressures to keep product prices down means that the products are often designed as simple as possible. So likely no extra special circuitry. Some tooth brushes may have a magnet that activates a reed switch in the base to activate the charge circuit. Other base changers are just going to be a many turns primary winding that exhibits a good amount of inductance. This winding is across the power line when the base is plugged in and will act as a transformer primary when the toothbrush handle is placed in the holder. A coil in the toothbrush handle acts as the transformer secondary and induced current flow occurs and charges the battery. The secondary load characteristics are reflected back to the transformer primary and cause more current to flow from the mains AC connection. With a carefully designed transformer setup like this the primary current could be very low when the secondary in the handle is not in position. Is it low enough to justify the simplest design where it is 100% connected to the power line? In today's world probably not!! In the past? Highly likely.
H: Do buck converters increase the ampere hours of a battery? I've read that they are 90% efficient compared to linear regulators so given the relationship between volts and amperes and that I want to power the project off of a 12V battery that has 18Ah and is charged using a small solar cell. The project itself only needs 5V, so if I buck the voltage down to less than half the required voltage, wouldn't the ampere hours close to double giving me 36+ Ah, or am I missing something about the relationships between volts and ampetes and the mechanism of the buck converter? AI: You are kind of on the right track. The amp-hour rating of the battery specifies how many hours you could pull a certain rated current from the battery. The buck converter to 5V won't change the amp-hour rating of the battery at all. But if you were to only pull half of the current from the battery then the battery will last twice as long. So let's make an example here. As you stated you have a 12V 18AH battery. Let us consider, for sake of example, that your load at the stated 5V required 500mA (i.e. 0.5A) to run. If you were to use a linear regulator to drop the battery 12V down to 5V the linear regulator would pull 0.5A from the battery and radiate (12V-5V)0.5A = 3.5 Watts of energy as heat whilst delivering the 5V to the load. The 12V battery delivering the 0.5A would supply the regulator for 18AH/0.5A = 36 hours. The efficiency of such a system is EnergyOut / EnergyIn = (5V 0.5A)/(12V * 0.5A) = 41.6% efficiency. So if instead you used the buck switching regulator at 90% efficiency we can evaluate the battery life. The buck regulator operates as: Energy Out = 0.9 * Energy In. With a load of 5V @ 0.5A the energy being delivered out of the buck regulator is 5V*0.5A = 2.5W. Applying the 90% efficiency formula the regulator input energy would be 2.5W/0.9 = 2.78W. This wattage at 12V corresponds to 2.78W/12V = 0.231A draw from the battery. At this lower current the battery would last 18AH/0.231A = 77.9 hours. As you can see the battery usage is hugely more efficient.
H: Review my PCB? Mosfet to parallel leds Can someone please review my PCB? Simply, I'm running 24 IR Leds at medium power, from a 5v arduino MCU pin, all pulsing together (38khz). Big fat traces, lots of space, SMD components. The LEDS are in 8 3-serial runs, and I have power/ground traces around. The "leds" on the board are just 2.54 headers, as I'll be running them off-board. But I don't know if I've got my head wrapped around the mosfet circuit correctly. Please be kind (but feel free to talk to me like an idiot, because I am) :) I'll fab at seeedstudio if it's relevant. Edit: I believe this is the schematic for the board as is currently laid out (with the exception of lowering the gate resistor as a commentor suggested). Also, I do believe I'm an idiot with the leds, as I'm bridging their legs, rather than just the leds, so can remove those trace portions (ie on the top left led, 1 and 2 are the +- legs of an led so ought not be 'traced', but 2 and 3 need the trace to connect led1 to led2.): simulate this circuit – Schematic created using CircuitLab AI: Whew, what a color-riffic board! That said, please try to use one color for each layer, such as red and blue. That's the "standard" way of doing it and most others will better understand it represented this way. The AOD510 boasts "Latest Trench Power AlphaMOS (αMOS LV) technology, Very Low RDS(on) at 4.5VGS, Low Gate Charge". Now to extrapolate on that, it is an N-channel power MOSFET. With 4.5V on the gate, it's Source-Drain resistance will be ~4mΩ. Which is really good: when "on", the LED's will be fully on, with minimal loss at the FET. However, not explained, is that these power FETs typically have very large gate capacitances. From the datasheet, \$C_{ISS} = 2719pf\$. What this means is that your CTRL signal, fed through the 10k resistor to the gate, combined with the Ciss of the gate, forms a series RC filter. Ultimately this behaves as a low-pass filter... i.e., as the CTRL switching frequency increases, the resistance and capacitance (RC filtering) will diminish the effective signal. If you do the math at that link, you'll run across \$f_c = \frac{1}{2\pi R C}\$ ... solving for frequency "corner", \$f_c = \frac{1}{2\pi \times 10k \times 2719pF}\$ \$f_c = 5853Hz\$ So at 5.8kHz, using a 10k resistor and device with Ciss of 2719pF, you will have already lost half of the signal due to the R/C combo. Now you can reduce this low-pass filter effect by choosing a smaller value for R. If you re-solve the formula for R = 1kΩ, the cut-off frequency becomes 58kHz. The drawback to this however is, CTRL has to source and sink more current - each time the gate is toggled. This is the drawback to power mosfets - their large gate capacitance makes switching them quickly problematic. You should experiment with this, and don't be surprised if you have to add a "driver" element to make that AOD510 switch as quickly as you'd like.
H: What is the transfer function of an LCL filter? simulate this circuit – Schematic created using CircuitLab I read that for grid-tied inverters it is common to use a LCL filter like above, to turn the PWM output from the H-bridge into a sine. But I'm having trouble designing something like this. If you'd calculate the voltage at the right end without the resistor, L2 doesn't do anything and it's just an LC filter. If you connect it to the grid by placing another voltage source there, the question what the voltage is is moot, because it's always the voltage over the voltage source. So I decided to place a resistive load there and find the voltage over that. But this lead to some horrible mess. $$Z_t=\frac{j\omega L_2 R_1}{1+(j\omega)^2 L_2 C_1 + j\omega R_1 C_1}$$ $$V_{C1}=V_1 \frac{Z_t}{j\omega L_1+Z_t}$$ $$V_{R1}=V_{C1} \frac{R_1}{j\omega L_1+R_l}$$ $$V_{R1}=V_{1} \frac{j\omega L_2 R_1 + R_1^2}{(j\omega L_1)^2+(j\omega)^4 L_1^2 L_2 C_1 +(j\omega)^3 L_1^2 R_1 C_2 + j\omega L_1 R_1 + (j\omega)^3 L_1 L_2 R_1 C_1 + (j\omega)^2 L_1 R_1^2 C_1}$$ I feel like I'm missing something obvious here. Or I made some stupid mistake. Or this stuff is just hard. [edit] I worked out the transfer function for current, as seen below. The transfer function matches the one given in equation 9 in http://inside.mines.edu/~mSimoes/documents/paper_54.pdf and Figure 5 also matches what I get, for some arbitrary values. $$\begin{align} I_2&=\frac{V_s}{j\omega L_1} \cdot \frac{\frac{j\omega L_1}{1+(j\omega)^2 L_1 C_4}}{j\omega L_2 + \frac{j\omega L_1}{1+(j\omega)^2 L_1 C_4}} \\ \frac{I_2}{V_s}&=\frac{1}{j\omega(L_1+L_2) + (j\omega)^3L_1L_2C_4}\\ H(j\omega)&=\frac{1}{\frac{j\omega}{\omega_0}+\left(\frac{j\omega}{\omega_1}\right)^3}\\ \omega_0&=\frac{1}{L_1+L_2}\\ \omega_1&=\frac{1}{\sqrt[3]{L_1L_2C_4}}\\ \left\|H(j\omega)\right\|&=\frac{\|1\|}{\left\|\frac{j\omega}{\omega_0}+\left(\frac{j\omega}{\omega_1}\right)^3\right\|}\\ &=\frac{1}{\frac{\omega}{\omega_0}-\left(\frac{\omega}{\omega_1}\right)^3}\\ arg(H(j\omega))&=arg(1)-arg\left(\frac{j\omega}{\omega_0}+\left(\frac{j\omega}{\omega_1}\right)^3\right) \\ &=0-arctan\left(\frac{\frac{\omega}{\omega_0}-\left(\frac{\omega}{\omega_1}\right)^3}{0}\right)\\ &=\pm \frac{\pi}{2} \end{align}$$ (The omega stuff is wrong, they never taught us to actually rewrite to standard form, but Matlab does't care. It just means I can't find the resonance frequency or draw a straight line approximation, sadly.) AI: For control purposes you need to linearize the system around a single operating point. Considering the synchronous DQ frame, the grid voltage is DC and therefore can be neglected. Do not replace the grid voltage with a resistor. You are mixing the power delivery circuit with the filter circuit. The resistor will cause huge damping where you don't want the damping to be. And your inductances are way too small. First, you need to select the maximum current ripple. This will set your inductance. Then you need to select the shunt capacitor value based on maximum current harmonic distortion that is allowed into the utility. For stability purposes you need to add passive (resistor) or active (measurement + controls) damping into the system. Inductance L2 could be partly physical and partly the inherent grid inductance. So you need to make sure the design and controls are stable for any grid output inductance (which varies based on the grid loading and time of day). So, to answer your question: You need to control the current so calculate the inverter voltage to grid current (L2) transfer function. No reason to calculate voltage to voltage transfer function since the grid voltage is established by the utility. \$ \frac{I_{L2}}{V_{inverter}} = ... \$ Btw. this is a simple sophomore level calculation. But the implications, the control and other dependencies make it a grad-level problem. Good luck!
H: Measurement of negative DC voltage I want to measure -30Vdc up to 0Vdc using a microcontroller. I'm basically measuring a voltage source with an output current of upto 2A. I need to bring the voltage up onto a scale of 0V to 5V so that I can use the ADC of my microcontroller. I found two types of solutions to do this. One with a simple resistive adder as shown below: simulate this circuit – Schematic created using CircuitLab and another with a non inverting summing amplifier: simulate this circuit What I need help with is that I don't understand the specifications for this offset voltage source? Can I use a resistive divider circuit on my 5V power rail to provide this voltage? How do I calculate the current to be provided from this offset voltage source so as to create the divider? Please help. AI: This circuit simulate this circuit – Schematic created using CircuitLab is a resistive level shifter and divider with an output voltage range 2.5V (approximately, see below) to 0V for an input voltage range 0V to -30V respectively. You can solve this circuit using the superposition theorem, for instance. Simply put, it divides the potential between R1 and R2 by 13. When Vin is -30V, Vout is 0V: the voltage difference between R1+R2 is then 32.5V, which if you divide it by thirteen (R1//R2 = 1 over 12+1) yields 2.5V. That voltage is measured over R2 and makes Vout equal to zero volt. However if Vin is 0V, Vout is slightly under 2.5V: 2.5V - (2.5V / 13) ~= 2.5V - 192mV or 2.31V actually. If you need a voltage swing up to 5V you need to replace the 2.5V reference with a 5V reference. When it comes to analogue-to-digital conversion, note that you don't necessarily need to shift voltage levels, for at least two reasons: Many ADCs have differential inputs, which convert a differential voltage between two inputs, plus and minus Vref. This of course makes sense when measuring negative and positive voltages. It also implies a negative supply voltage to your ADC. Depending on how you power your ADC, you may very well use the negative line of your voltage input as the ground line for your ADC (or micro-controller) and its power supply. It is possible if the power supply of the A-D converter can float, i.e. if the voltage to be measured has no galvanic connection with the power supply of your ADC. The latter greatly simplifies the circuitry and keeps the number of input components to a minimum. It also avoids level shifting by performing a relative conversion: just divide the input signal by 6 to have a 0-5V voltage range for your ADC. You will find relevant responses to a similar question, as pointed to by SunnyBoyNY.
H: Does my PCB require a 50 ohm impedance trace even if I am using an external antenna? I am using the Quectel M95 GPRS Modem on my PCB. The hardware reference guide says "pin 39 is the RF antenna pad. The RF interface has an impedance of 50Ω." I am using a u.efl connector and connecting a QuadBand PCB antenna to the connector. The antenna spec says impedance: 50 ohm. Now I am confused. My layout designer is saying the manufacturer has to put a 50 ohm trace for the u.efl connector while manufacturing. There is a Pi circuit on the PCB for RF tuning. How do I use that? For now only a 0R is put there, but if tuning is required the values were to be put in accordingly. If the antenna already has 50 Ohm impedance, why does the PCB trace also have be to 50 ohm? AI: When you send a signal along a trace, if the length of the trace is of the same order as the wavelength of the signal, then you have to match impedances or, you will get a "reflection". What this could mean in extremes is that the power actually emitted by the antenna is only a fraction of the power being pumped out by the chip - in other words, you are not efficiently coupling the chip to the antenna and you get "reflections" - this can cause your chip to overheat and maybe it might damage it. So, if you are transmitting 3 GHz (say), it has a wavelength of 100mm and, a rule of thumb is that if your PCB track is longer than 10mm (one tenth the wavelength), you need to ensure its characteristic impedance matches the antenna's impedance. Further reading here and here
H: Is voltage measurement of a battery done in series? This might be a stupid question but I can't find an explanation. Voltage measurement is done in parallel. But when we measure the voltage of a stand alone voltage source, say a battery, it looks like we are doing it in series and yet we get the correct reading. simulate this circuit – Schematic created using CircuitLab So we connect the voltmeter like above to measure the voltage of an isolated voltage source. Although it is connected in series, we get the correct reading. Am I missing something here? AI: This situation is a something of a paradox, yes, but you need to understand that 'series' does not mean 'not parallel', and vice versa. Any components which form a loop in which current is allowed to flow are in series. Any loops which share the same potential difference across them are in parallel. In your example, current flows from the one battery terminal to the other through the voltmeter, which acts like a very large resistance (10M-50M, typically). Current is flowing in a loop, therefore the two components are in series with each other. The voltage across the battery terminals is equal to the voltage across the voltmeter, therefore the two components are also in parallel with each other.
H: Trying to remove distortion of speakers seems impossible I'm working in a project with the goal of make a portable bluetooth speakers without distortion. When I try to turn up the volume, the speakers start to make a distorsion, like when rhe radio can't get the correct frequency.p In the project, I use a 3×2 PAM8403 amplifier in a tiny module, 1× 7805 and a 2N60B transistor (I asked in another forum for this problem, and they answered I have to use the transistor if I want to get more amperes and remove the audio distortion) and two speakers (4Ω, 5-8W). The amp is powered by 5 volts generated by the 7805 from a 9V battery. I searched around the web by 3 months. Different answers and any of them works. I hope some of you could help me removing the distortion definitely, I've been working on this project since the past summer. Schematic AI: If you read the PAM8403 datasheet, it tells you on the first line of the 'Features' section that it promises terrible distortion. 3W Output at 10% THD with a 4 Ω load and 5V power supply It seems that it is working to specification.
H: Correct way to measure a wall wart voltage I got a full drawer of second hand wall warts which I'm planning to use for powering arduino projects (mostly 5V "pro mini" or "nano"). I'm using a voltmeter to check that they are still working, however most of them seem to output a far greater voltage than what is printed on the case. For example the Arduino pro mini accept up to 12V so I've been looking at 9V wall warts, but they often give more than 12V. Example (but typical reading): written specification: 9 V 300 mA Measured voltage: 12.37 V Measured voltage while powering a led (through a 300 ohms resistor): 11.2 V I tried to add a led because I've read that measuring a voltage with no load may give a wrong result, but perhaps that's not enough to get a proper reading... My questions are: Is there a way to measure the correct voltage that will be issued in "normal usage conditions"? Can I safely use a "9V wall wart" to power a "12V max" device if I measure more than 12V? PS: So far I've use 6V wall warts which are giving about 10V, but I don't have any left so I'm trying to use 9V ones AI: It sounds as though you've got some unregulated power supplies. Generally these have a transformer, rectifier and smoothing capacitor. With no load the capacitor will charge up to peak voltage. simulate this circuit – Schematic created using CircuitLab There is always some internal resistance in the transformer, represented by R1, which will cause a voltage drop which increases with current drawn. In addition, C1, which maintains output voltage during troughs in the rectified AC (i.e., between pulses from the rectifier) will droop between cycles causing the average DC value to droop with increasing current. To test you should load them with something simulating the intended load. e.g., for 100 mA load on a 9 V PSU you would use a 9 / 0.1 = 90 Ω test load. Nearest standard values are 82 Ω or 100 Ω. Connect the test load across the terminals / connector and measure the voltage. An alternative is a 12 V, 6 W car tail-light lamp. At 12 V this should pull about 0.5 A. Be aware that the resistance value will change dramatically with temperature which is voltage dependent. To get a good feel for what's happening you would need to measure both the voltage and the current.
H: Adding antenna gain to RX and TX sensitivity Let's say I have a transceiver with 10dBm of TX gain, and an RX sensitivity of -10dBm. If I then attach an antenna with a gain of -2dBi do I then have an RF output power of 8dBm and an RX sensitivity of -8dBm? I'm not clear on if I have to flip the sign when adding to the RX sensitivity but that would seem to make sense. AI: Let's say I have an transceiver with 10dBm of TX gain No, you mean it has a power output of 10 dBm. Gain has got nothing to do with power output capabilities. and an RX sensitivity of -10dBm Yeah that's OK. If I then attach an antenna with a gain of -2dBi do I then have an RF output power of 8dBm Effectively, yes you do and an RX sensitivity of -8dBm If the same antenna is at both ends of the link (or it's a transceiver using the antenna for RX and Tx) then yes. I'm not clear on if I have to flip the sign when adding to the RX sensitivity but that would seem to make sense. Yes it's a bit confusing but an antenna with -2 dB of gain compared to the (i)sotropic "standard" means you need 2 dB more power into your receiver's antenna because you have degraded the signal with the bad antenna. And, because you have degraded the power output by 2 dB, your effective power out is 2 dB lower at 8 dBm In practice, an antenna with loss compared to an isotropic antenna is a pretty crappy antenna and a receiver with a sensitivity of only -10 dBm is also pretty crappy.
H: Mains LED light bulb flickers when switched off We have LED bulbs in our apartment. In the bathroom, the bulb flickers on and off when it's switched off. Same when it was a CFL bulb before I switched to LED cause I hate CFLs. Our mains voltage is 220v. The bulb we have looks like this If I remember correctly, I should add a capacitor in series to the bulb to fix this. But what kind of capacitor? and what rating? Update: The switch is a combined switch and plug in one part. Looks like a normal one line switch. This apartment and the whole building doesn't have grounding. We don't have this in requirement in our building codes. I'm in Lebanon. Only this one bulb in the apartment does this. Other bulbs are also LED and two more CFL not changed yet. Any help appreciated, thanks. Resolution: I fixed it with an incandescent bulb! I'm too lazy to go electrician detective for now. AI: You might find that a different brand of bulb is much less prone to this kind of behavior. The internal circuit varies quite a bit from bulb to bulb. If you have a store with a generous return policy that applies to such products you could simply buy a few different types and try them. In particular, I would expect bulbs based on Microchip's CL8800 to not suffer from this problem. See this excellect article if you are interested in the gory details. Most bulbs have a small switching supply in them, but this type is different.
H: Implementing/using a SATA controller I start by saying that I'm not an electrical engineer, I've got a basic understanding of things from school and from work (I'm a long time computer programmer), but this is not much my field of competence. I'm in the process of evaluating the feasibility of a device that I'd like to try to get designed and produced. But, even before paying a specialist for a feasibility study, I'd like to understand how much I'm far from reality. The focus of the device (90% of its functionality) will be on writing data on an SSD disks connected via a SATA port, so I'll need some kind of chip capable to do that (or, in extrema ratio, to get one designed for it). Is this a realistic thing, can a SATA controller be just bought and used easily on a board, or even designed from scratch? (so to have just one chip that do everything)? AI: A number of ARM SOC chips have provision for a SATA interface, so I don't think that requirement is a particularly huge barrier. For example, the Allwinner and Texas Instruments ARM-based SOCs- SATA and even SATA II are available. Simply make sure that you're using a chip that supports SATA and feed it copious amounts of memory, a real operating system such as Linux, and a lot of cycles to make it happen. If the requirement is written in from the start, I don't think it will be your biggest problem. It does push the required level of hardware sophistication up to around the Raspberry Pi level (GHz-class CPU with lots of memory).
H: Protection of a 1.2V bus I typically put a TVS diode on all of my power rails as standard practice to protect against ESD events. I'm using an FPGA in a design for the first time and I'm finding that I can't get a TVS with a 1.2V reverse standoff voltage to protect the FPGA core voltage. The only close options I could find were these two: 1.0V holdoff (too low?), 1.5V breakdown: https://www.digikey.com/product-detail/en/VESD01-02V-G-08/VESD01-02V-G-08CT-ND/2658775 1.5V holdoff, 4.8V breakdown (probably useless given the 1.32V absolute max voltage on the FPGA?): https://www.digikey.com/product-detail/en/DF2S5.1ASL,L3F/DF2S5.1ASLL3FCT-ND/5415965 Can I get away with using the 1.0V holdoff part? Is there a better way to protect a power rail at this low of a voltage? AI: Here's the device: - On the basis of this table I'd say you will be fine operating it on a 1.2 volt supply - it's only going to take typically 1.5 mA on a 1.5 volt supply so with a 1.2 volt supply, current should be hardly worth bothering about. Unfortunately the data sheet appears to have an omission - figure 1 does not appear to be included. Is there a better way to protect a power rail at this low of a voltage? There probably is and it might be a crowbar protector. You have to consider the effects of distributed capacitance on your power rail and what sort of ESD event your board actually receives. You should be able to make a basic LTSpice model of both the event (human body model) and board capacitance and distributed inductance. Human body model usually falls into to groups: - I can't tell you which to choose as typical for your ESD event, you have to decide that but, when you do you simulate the cap being charged to 4kV or 8kV (your research is needed here), do a simulation of this connecting to your distributed capacitance (seperated by PCB inductance) and see what peak voltage you get. You are looking to either not have a voltage rise that is going to damage anything or, if this is not possible, you are looking for the rate of rise to be slow enough so that a crowbar circuit can begin to work (in conjunction with your TVS). You are likely to have a 3V3 rail or greater so something that monitors the rail and kicks in above 2V to turn on a MOSFET (or SCR) to crowbar the supply is an option worth considering.
H: Why should the output impedance of a current source be much greater than the input impedance of the load? For a voltage source (except RF circuits), the output impedance of the source signal being coupled must be much smaller than the input impedance of the load. This is first of all done to prevent loading. Also even better to set Zin>>Zout to prevent the voltage divider non-linearity effects. But why is that the other way around when it comes to a current source? Why should Zout>>Zin? What is the logic behind it? AI: The output impedance shunts the source in a current source: simulate this circuit – Schematic created using CircuitLab If the source impedance were in series, it would have no effect on the source's behavior, because the current source would simply compensate for its presence to produce the required output current. Since the source impedance is shunting the source, it must have a high value to avoid drawing away source current and reducing the current delivered to the load.
H: Storing images for LCD For TFT LCD, if we want to store images for displaying on screen..can we use flash IC for eg: SST25VF020_2Mbit serial(SPI) flash. Please someone guide since I am newbie to TFT LCD interface. Thanks. AI: You can use any form of storage to recall your images. But define an 'image'. Yes; the end result is probably very clear. But what format do you want to store them in? What size? How many? How fast do they need to be recalled? From a hardware design, the storage device is probably very important. But from a systems design probably very irrelevant; you can also use MCU's internal FLASH (if you got any spare), EEPROMs or SD cards to store them. But defining what data you put on the storage as an "graphic image" is more important. For example: a 480x272x16-bit LCD needs 255kB bytes worth of raw pixel data. This is practically the same size as a BMP file. In 2Mbit, you can store 1 color bitmap. Alternatively you could store the same image in a PNG or JPEG format (much smaller), and use a decoder to get the pixel data back. However this requires extra code, CPU time and RAM. That decision depends completely on the application.
H: MOSFET Circuit Design and Thermal Considerations I'm a newbie at EE, and just I wanted to verify that the design I came up with for a MOSFET circuit that drives a 12V 500mA water pump will work. I'd also like to confirm I can run the N-Channel MOSFET in question (RUR020N02) without a heatsink. P8 is a two-pole terminal block which the pump will be attached to. The MOSFET has a 1.5V Logic Level gate, which will be driven by a 3.3V I/O pin from an Atmega328p. By what research I've done, I've learned that it's good to have a pull-down resistor (R9) in the event the digital I/O pin on the microcontroller (PUMP) is left floating, as well as a limiter resistor (R10) to keep the uC I/O pin within spec (20-40mA). I think this can also act as a voltage divider, but the voltage drop should be negligible in this case and still well over the gate threshold. I've added a flyback diode just in case, though I'm not sure if one is truly needed. The pump is an impeller so I assume it has the same problems as running a DC motor--I'm not sure if the pump has its own internal protection circuitry. So, my main question is whether or not this design is adequate for my needs. However, I'd also like to know if I would need to use a heatsink for this particular SOT-23 MOSFET. Based on the datasheet (linked above), it has a power dissipation of 0.54W at 25°C. Since the MOSFET has a RDS(on) value of around 105mΩ and my pump draws 500mA, I should be OK without a heatsink since it will only need to dissipate 52.5mW, correct? 0.105Ω x 0.500A = 0.0525W Assuming the MOSFET turns on fully in an acceptable timeframe. AI: You have mostly thought this out correctly. One problem I see in your figures is the power dissipation of the FET. You say the gate will be driven by a 3.3 V digital output. The only guaranteed on Rdson is 135 mΩ at 2.5 V gate drive. You can't use the 105 mΩ figure since that's for 4.5 V gate drive. The power dissipation will be (500 mA)2(135 mΩ) = 34 mW. You will have difficulty noticing that get warm. It's not anywhere near any limits. Inrush current will be much larger than the steady 500 mA operating current. However, it won't last long, so it looks like you'll be OK. Note that the maximum pulsed current this FET can handle is 6 A. That sounds sufficient at 12x the operating current. Of course the dissipation will be quite large then, but again, short lived. Without details on the motor, we can's say for sure, but I think you'll probably be OK. It's good that you put R9 there, but I'd make is smaller. 100 kΩ will do a better job against noise that might be picked up, and is still of no consequence to your digital output. If you plan to switch the pump on and off rapidly, I'd use a Schottky diode to get around reverse recovery time issues. If you always leave the pump off for more than a millisecond or so, then this doesn't matter. I would also put a small cap across the pump, especially if you aren't going to switch it rapidly. That will help with RF emissions.
H: How can I mirror a group of components and wires across a line in eagle, without having it switch board sides? I want to design a board that is symmetrical - I have designed the left side, and now I want to copy the components and wires to the right side such that it is "mirrored" across the center line - what is the best way to accomplish this in eagle? here is a screenshot of what I am working with: I want to take the components inside the orange box and mirror them across the teal line, such that I can then re-incorporate them into the PCB on the left AI: You can't do that. At best you could position the components on the right side symmetrically about the cyan line relative to their counterparts on the left. However, the components themselves can't be mirrored. This only works for symmetrical parts, like resistors for example. It's not going to work for whatever the 8-pin chip is since you can't magically mirror its pinout.
H: Transformer VA Ratings, Power factor, and Pulsed current What exactly goes into a transformer's VA rating? At a fundamental level it seems that there has to be a limit to what the VA rating can represent. For example if I draw 2 Amps-RMS from the secondary of a 30VA rated transformer at 15 Vrms this makes sense as the maximum Complex Power I can draw. Still, at a power factor of 1 my maximum current in the transformer would be sqrt(2) * 2 Amps. But what if my power factor is abysmally low (ie in a DC rectifier) due to harmonic distortion and while I still draw 2A-RMS I have brief current spikes of 15 Amps? Surely the transformer's magnetics couldn't handle these spikes as I'd expect the core would saturate. My question is what is the practical limit for VA ratings of transformers? Would brief current spikes that reduce to only 2A-RMS in this case be fine? Obviously the secondary/primary copper losses play a part in the rating but how do the magnetics factor in? I ask this because I am designing a simple bench power supply using a 125VA transformer with a 24Vrms secondary and am trying to figure out how much power I can draw before the current spikes into the inductor are too much for the transformer. I also don't want to have to resort to active PFC as I don't want to risk messing up any HVAC PCB design. Thank you AI: Surely the transformer's magnetics couldn't handle these spikes as I'd expect the core would saturate. Core saturation has nothing to do with load VA rating. It has everything to do with the magnetization current flowing in the primary. This current is largely constant irrespective of secondary load current. In short, the ampere turns on the secondary winding (caused by the load) are exactly equal (but opposite in sign) to the ampere turns on the primary due to that secondary load current. Neither of these currents are the magnetization current that can saturate the core. Imagine a simplified core with a single turn primary: - At the moment it's just a single turn inductor. With V applied, Im flows and inductance, frequency and voltage all determine how much current (Im) flows. OK so far? Now imagine that single turn were replaced by 2 closely coupled parallel turns like this: - You would find that Im/2 flows in each or, in other word,s the same overall current flows. A nice side effect of this is that each individual coil must have twice the inductance of the single coil and, if you happened to make a two turn inductor this way (by wiring them in series) it would have 4x the inductance. Just think about it for a while. Next scenario: - So, you drive one of those closely coupled coils and look at the voltage on the other coil. The driving voltage and the secondary voltage are in phase and of equal amplitude (1:1 turns ratio). Do you see why? If not, consider what would have happened in the 2nd scenario if (say) the voltages were out of phase - you'd get a fire and you wouldn't get the inductance rising with turns squared - you'd get zero inductance. This doesn't happen. Final scenario: - You've applied a load to that 2nd winding and because in the 3rd scenario you (hopefully) recognized that the voltages were in phase, you have to admit that the currents are COMPLETELY antiphase. From here, it's a minor leap of faith to recognize that the ampere.turns on the primary (due to the secondary load) are equal and opposite to the ampere.turns on the secondary. As I said earlier, neither of these currents are the magnetization current that can saturate the core - this is due to Im. It's magnetic field strength that drives the magnetism. It's called "H" and H is measured in ampere.turns per metre. The "per metre" part is irrelevant because it's a core physical dimension and applies equally to primary and secondary. Basically H never alters one bit due to loading effect. In fact that's not quite true; it gets lower with more load because the copper losses lower the actual terminal voltage and reduce the magnetization current a little bit.

Subsets and Splits

No community queries yet

The top public SQL queries from the community will appear here once available.