texts: Is it possible to measure inductance without LCR Meter/OSC/FG

texts:
Like the question, i don't have an oscilliscope/Function Generator/LCR Meter. I do have a multimeter and a lot of "scrap inductors" that i would like to measure.

I have searched a lot on the web and everyone seems to include OSC or a Function Generator. I also have a lot of parts laying around so that i can build my own circuit if needed.

I don't really have any requirments, It doesn't have to be a 100% accurate reading, around 70% works fine for me.
Thanks.


texts: Two secondary flyback transformer coils in parallel

texts:
This feels like a simple question, but my google game is letting me down:

The below flyback transformer has two secondary coils that are meant to be connected in parallel, as per the below image, and a turns ratio of 1:1:1:0.5 (pri:sec:sec:aux). If I link the two coils in parallel, is the turns ratio still 1:1? Has it changed to 1:0.5 as though adding inductors in parallel? Is it 1:2 as though you doubled the output of a single coil? What would happen if I connected them in series instead? I'm new to designing any kind of power supply and am struggling with some of these concepts, although I'm familiar with the general idea of how a flyback converter works.


texts: STM32L011 temperature sensor - almost constant output

texts:
I am trying to use the internal temperature sensor of STM32L011 (Nucleo-32 board), but I get almost a constant reading (ADC code) in the 100-120 (decimal) range that changes little to none with temperature (I've tried pressing a soldering iron against the chip and freezer spray). On the other hand - measurement of internal Vcc works fine.

My TS_CAL2 is 928 (decimal), though I am not using it yet for anything.

My code:

void adc_init(void){
RCC_APB2ENR |= BIT9; // Turn on ADC
ADC_CFGR2 = BIT31/*CKMODE1*/ | BIT30/*CKMODE0*/; //ADC clock is PCLK/1

ADC_CCR = BIT25/*LFMEN*/; //low frequency mode (ADC is clocked from APB 2MHz)
ADC_CCR |= BIT22/*VREFEN*/; //enable reference voltage

ADC_IER |= BIT11 /*EOCALIE*/ | BIT2 /*EOCIE*/; //enable interrupts for end of calibration and end of conversion
ISER = BIT12; //enable ADC interrupt vector in NVIC

ADC_CR = BIT31; //start ADC calibration
cpu_sleep(); //ISR should wake up the CPU when calibration is done
while ((ADC_CR & BIT31)); //wait for calibration complete (in case something else woke up the CPU)

ADC_CR |= BIT0; //enable ADC
}

uint32_t adc_get_temperature(void){
ADC_CCR |= BIT23/*TSEN*/; //enable internal temperature sensor
ADC_CCR |= BIT22/*VREFEN*/; //enable internal voltage reference
ADC_CHSELR = BIT18; //select channel 18 (internal voltage sensor)
ADC_CR |=  BIT2/*ADSTART*/; //trigger a conversion

cpu_sleep(); //ISR should wake up the CPU

while ( (ADC_CR & BIT2) ); //wait for end of conversion (in case something else woke up the CPU)
uint32_t conversion_result = ADC_DR;

return conversion_result;
}


texts: Why is 4.096V so often used as a voltage reference?

texts: I get that each mV is equivalent to a bit in a 12-bit ADC, but why is 4.096V used so often? I've heard of this being from a "bridge". What does this mean and what is the historical significance?


texts: I want maximum 5V output from an Op-Amp. Is it a good idea to use a supply voltage for the Op-Amp of more than 5V?

texts:
I have the following circuit.
An Op-Amp (currently TLC2272CP) as a buffer (voltage follower). The non-inverted input of the op-amp comes from a DAC (MCP4922). I measure with an ADC (MCP3202) the input voltage of the Op-Amp and I measure with the same ADC the output voltage.
Currently I use 5.0V supply voltage.
For testing I set the DAC to a fixed voltage for a few seconds.
My goal is to have exactly the output voltage at the Op-Amp output which I set with the DAC independent of the load (max a few mA).
The desired output voltage will change slowly (less than 1Hz)

My testing shows: If there is no load on the Op-Amp output then the output voltage is equal to the input voltage almost for the full range from 0V up to 5V. This is what I expected.

But with a load (initial test with a 2.2kOhm resistor to V+ or GND) the output of the Op-Amp goes only to a maximum of about 4.1V.

I looked at the data sheet of the Op-Amp and it shows a High-Level output of minimum 4.25V with a load of 1mA.

I want to be able to get nearer to 5V. Probably something like 4.8V is good enough.

The ADC and DAC allow max 5.5V supply voltage. That Op-Amp allows up to 8V supply voltage.

I guess I won't be able to do this with these parts and conditions. My idea is to use 6V or 7V supply voltage for the Op-Amp and continue with 5V supply voltage for the ADC and DAC. I guess with the higher supply voltage for the Op-Amp it should be no problem to reach 5V output, even if the output current is a few mA.

My question is: Is this the proper way to do this? Or what should I do to have output voltage, with load, of at least 4.8V?

And when I use a higher supply voltage for the Op-Amp I have to make sure that the output voltage is never higher than 5V. Because I don't want anything higher and a higher output might destroy the ADC which measures the output voltage.
Currently my idea is to use a Zener diode to make sure the output is never higher than 5V (also not when the circuit is just switched on). Is that a good way to do this?


texts: RLC circuit, at what frequencies is the current 0.8A

texts:
So I want to know at what frequencies the current is 0.8A.
I've calculated the resonance freq to =1006.6 Hz and the current is at that point 1A.

So if I understand this correctly there will be 2 frequencies on each side of the resonance and at the same distance that will have the 0.8A current.

Is my understanding correct? if so, how do I calculate these frequencies?


texts: How Is Intensity of Blue Light Measured?

texts:
As a hobby project and to help solve issues getting up early in the morning (specially given that it's winter and the sun isn't up until long after I am) I'm trying to find a bright blue light that I can put on a dimmer. I've read that the eye (even closed) detects blue light as a cue that it's time to wake up, so by placing a bright blue light on a dimmer to turn on gradually 30 minutes before waking up, this will allow me to feel more rested.

There are presently alarm clocks that do what I'm looking for, however only a couple models and they price a lot higher than it seems like they should. I'd also much rather do it myself and gain knowledge in the process. Based on my general research, I've determined that LEDs are substantially more efficient than incandescent bulbs, however the vast majority of LEDs I find online are incredibly weak.

I'm having a lot of trouble comparing different bulbs, in terms of the perceived brightness in the blue spectrum. The best I've been able to find is the lumens or lux unit, however those are largely centered around green output. (Because the human eye perceives green light the most.) It's a pretty big impact - blue LEDs rate incredibly poorly and a green LED would be 10 times as many lumens for the same output. But if I understand correctly, green light makes little/no difference in waking someone up.

I've been searching for many hours trying to find some way to compare various bulbs on the blue output, and I haven't found much of anything. Surely in the vast world of the internet there is someone who's taken it upon themselves to compare the output of various blue LEDs including ones powerful enough for my purpose. Does anyone know how or where I could find a comparison of bulbs based on perceived brightness in the blue spectrum? Is there another technical term for brightness of light in the blue spectrum?


texts: Transfer function using signal flow graph problem

texts:
Determine the system transfer function for the following signal-flow diagram of figure

I have shown my attempt of solving this problem. Can anyone tell me whether I did this problem properly?


texts:
I am new to electronics and just getting started with a project to make a BT speaker. I bought some quality protected 18650 Li-ion cells from Orbtronic. I would like to build a charger myself for these batteries using a 5V,3A wall adapter that I have.
Most people use the TP4056 to charge unprotected cells, which is fine, but

Do I need a TP4056 to charge my cells (one TP4056 per cell)?

If I don't need them, am I okay to hook up the 5V,3A wall adapter directly to the 18650 cells and rely on their protection circuit to charge them? Is this okay? It seems like the more dangerous of the 2 options.

I would appreciate any help or, better yet, any links you can provide.


texts:
im using xl6009 dc to dc  converter , in page no 7 of datasheet the sepic inverting topology is show which generates  12 and -12v .my doubt is what component is used, is it a transformer or coupled inductor my hunch is it is a coupled inductor but those have only four terminals please help

link for datasheet

https://e-radionica.com/productdata/XL6009.pdf


texts:
So this isn't really a big question, but I really need to get something clarified from the derivation of the RC step response equation, which goes like this: $$V(t)=V_S+(V_0-V_S)e^{-\frac{t}{RC}}$$

Given an RC circuit, one can, using KVL, deduce the following: $$V_S-V_R-V(t)=0$$ Where \$V_S\$ - the supply voltage; \$V_R\$ - the resistor voltage and \$V(t)\$ - capacitor voltage.

Using Ohm's Law and capacitor i-v characteristics, \$V_R=RC\frac{dV}{dt}\$ $$V_S-RC\frac{dV}{dt}-V(t)=0$$ $$\frac{1}{V(t)-V_S}\frac{dV}{dt}=-\frac{1}{RC}$$

And then, we take the integral of both sides with respect to \$t\$ from \$0\$ to another independent time variable \$t\$.

$$\int_0^t{\frac{1}{V(t)-V_S}\frac{dV}{dt}dt}=\int_0^t{-\frac{1}{RC}dt}$$ Until you end up with $$V(t)=V_S+(V_0-V_S)e^{-\frac{t}{RC}}$$ Where \$V_0=V(0)\$.

But, what wasn't clear to me was why we integrated from zero to \$t\$? I mean you can do this too: $$\int{\frac{1}{V(t)-V_S}\frac{dV}{dt}dt}=\int{-\frac{1}{RC}dt}$$

Then end up with $$V(t)=V_S+e^{-\frac{t}{RC}}$$ But we know that this cannot be the step response. It is a solution for the differential equation shown above (I'm familiar with differential equations having multiple solutions), but how did we know that only one actually works as the step response?


texts:
I'm currently trying to connect my wifi obd2 dongle directly to a VW ecu that is powered by a bench power supply.

I followed the guide here:

http://www.nefariousmotorsports.com/wiki/index.php/ECU_Bench_Flashing

And it looks like the dongle is getting power as the led is lit up and I can see the obd wifi ssid, but when I try to connect I am given the error "Unable to connect"

What am I missing?

(the dongle works when I use it in the car)


texts: Having different voltage potentials as power planes on the same inner layer of a PCB

texts:
I am working on a 6 layer job which placement of the given components in the rather limited area that I have to work with...is driving me a bit crazy.

I have no option but to have 2 different voltage levels on the same inner-layer (layer 5 in this case). I have never done this way before because I always considered it to be "safer" not to put different potentials on the same layer as a copper pour (but I have done this as normal tracks e.g. 10mil/15mil).

Consider the image below from my CAD software. As you can see I have created two pours almost next to each other with one being 28V and the other 12V (with a 200mil gap). To make it worse, I have to route 5V digital signals (with a max speed of 100KH - the green traces) on the layer above this.

Is it electrically safe to do such a thing? what kind of problems can arise in terms of electrical performance (e.g. creepage) and/or manufacturability?


texts: I2C Overshoot with Teensy 4.1 and TCA9406 Level Shifter

texts:
I'm trying to communicate between several MCUs with I2C using a Teensy as the master and a TCA9406DCTR as a level shifter. I'm currently testing the I2C signals from the Teensy without any other MCUs connected.
I seem to be getting quite a lot of overshoot on both the clock and signal lines on the Teensy, over 500mV which concerns me that it may damage it and comms is unstable.

The 5V side of the TCA9406DCTR is even worse, about 1.8V overshoot and -1V undershoot.

My current thinking is that I probably need to revise my PCB layout a bit and make sure the traces between the Teensy and the TCA9406DCTR are as short as possible although they aren't that long (approx. 120mm). Possibly I need to find a better alternative to the TCA9406DCTR.
What can I do to reduce the overshoot and make a more stable I2C signal?
EDIT:
The issue is there with no other MCUs connected.
Here is the schematic in question:

The layout of the PCB in that area:

I2C Clock signal directly from a stand-alone Teensy as measured using the same method as before just to confirm that the scope ground should be adequate (I'm just using the spring clip on the probe directly to ground on the Teensy board):


texts: Overheating when 4 laser diodes in parallel with 2xAA battery

texts:
I bought 10 red laser diodes from ebay for cheap and I wanted to create some art sculptures.
The diodes work fine. I connected 2 lasers together in parallel with 2xAA batteries, and it worked alright.
When I connected another 2 lasers, the wires started to overheat (and I smelled something burning.)
I couldn't explain this to myself with my "basic" knowledge of electrical circuitry.
I would expect the lasers not to light up, or the battery to overheat, but how come the individual wires heated up? How could it be that when an  individual laser diode is connected it is somehow different when others are connected in parallel. The voltage on each diode is the same, as is the current in the wires.
What am I missing here?


texts: Why is the negative rail oscillating in this TPS65130 based design?

texts:
I designed a board with +-10V dual rail supply that are generated by a TPS65130. The design is loosely based on the reference schematic and layout. I had to move some components around due to board dimensions.

 When supply power is applied the positive output is stable at +10V, but the negative oscilates between -26V and -10V. It seems the feedback pin experiences a spike as soon as the output reaches -10V.

Scope screen capture shows the output of the negative rail(Yellow) and the voltage at FBN(Feedback negative) pin. After assembling the board I realized the trace for FBN is too long and goes under the switching diode and I bypassed this with a short piece of wire, but this didn't seem to make a difference in the behavior.


texts:
I have read the manual, but I am not sure how the omron safety PLC works.

I guess this safety PLC use Output Power Supply Output (21,22) to drive the output circuit, but why does it need (1,2) the power supply for input device and test output.

Also what is test output? Why is it useful?


texts:
I need to sequentially power some coils with 10 milliseconds of delay between stages. I'll demonstrate it with 1s and 0s because it is the easiest way for me. 1 = On, 0 = Off. Each coil is powered for 20ms. I will be using 2 of these batteries: http://www.all-battery.com/li-ion1865074v2200mahrechargeablebatterymodulewithpcb.aspx?utm_source=GoogleShopping&utm_medium=GDF&gdffi=fb520bc42d4e46cbab702234d35f7d38&gdfms=84C089F27C604843AE94F6D58759BF54&gclid=Cj0KEQjwjK--BRCzv-Wyu4OTosEBEiQAgFp5OHAsNGKWYNXVuPJ-seUqnTcQIQYEQvtMRQt3g-JGD1kaAkvo8P8HAQ

Battery Stats: Amps: 4, Volts: 7.4, OHMs: 1.85.

Coils: Each is supposed to be provided with 0.5 Volts of DC power, Application: move a 3 inch metal rod as fast as possible, Each coil is on for 20ms, Intercoil delay should be 10ms

~Stage One:
Coil 1: 1
Coil 2: 0
Coil 3: 0

Delay 10ms

~Stage two:
Coil 1: 0
Coil 2: 1
Coil 3: 0

Delay 10ms

~Stage three:
Coil 1: 0
Coil 2: 0
Coil 3: 1

Code proposed: http://pastebin.com/jBQqZWjR


texts: Relative FPGA Footprint of ARM Cortex M3 vs. MicroBlaze

texts: I may have missed it, but does anyone have experience with the relative resource consumption of a MicroBlaze versus the core for an ARM Cortex M3 IP?  It seems like there should be a ballpark comparison of CLBs, BRAMs, and DSP48Es consumed.  Thanks.


texts: Altium hide component designators in fabrication ourput gerber

texts:
As the title says, is there a way to hide the component designators in the fabrication ourput in Altium AD15?

I have a very tight board with 0402 parts very close, so there is no room for the designators in the gerber silkscreen. But I want them to be visible when editing my layout in Altium. So they must be hidden only in the fabrication ourput.

Can this be done in Altium AD15?

Or is there an option to remove silkscreen from solder pads in fabrication gerber output. ?


texts: Troubleshooting a PWM-field effect transistor driver board

texts:
I'm an untrained hobbyist trying to fix this motor driver circuit and was looking for some guidance or help with troubleshooting, or reconstruction. The circuit is from a handheld vacuum cleaner that stopped working.

The device itself isn't very old, the battery pack and charging function seem to be working fine: the batteries measure at 19.00 V and are keeping their charge steadily after days.  The charging indicator LED (on the other side) lights up to indicate charging when plugged in.  The mechanical switch works fine (verified by continuity test and proper voltage measurement when switched) and the motor itself works fine when the circuit is bypassed and is directly powered.

My understanding of the circuit is that it's a MC96P0202 microcontroller-based PWM driver (8051 clone?), using the CED83A3G N-channel field effect transistor.

My best theory is that the C6 capacitor (top, near the FET) exploded. There is what looks like debris all around where C6 should probably have a surface-mounted capacitor.  There are no schematics of the proprietary board and I can't see any traces on the other side that would provide additional information.

R23 measured at 99.4 Kiloohms, R24 at 0.478 Megaohms, R25 at 0.465 Megaohms. There was continuity between the upper FET lead (source?) and bottom of R25.  I'm assuming this board uses a common FET-PWM circuit that I'm obviously not familiar with but had hoped someone would recognize.

My question is both specific and yet open-ended.  First, whether this is possibly the right cause of malfunction (a missing C6)?  If so, how would I estimate values for a suitable replacement candidate?

And of course, if not, what should I be looking into to determine cause of the problem?   Any pointers, help or knowledge are very much appreciated.


texts:
Here is my program, I want to:

The microcontroller, Arduino UNO R3 sends 3.3V to the sensor, Accelerometer, MMA7361
The sensor turns on and send signal to the microcontroller.
When I move the sensor and if the voltage becomes more than 2V, the microcontroller sends 1.5V to the Transistor. Otherwise send 0V.

int outputPin1 = 3;   // Pin D3
int outputPin2 = 5;  // Pin D5
int analogPin = 0;  // Input Pin A0

void setup()
{
  pinMode (outputPin1, OUTPUT);
  pinMode (outputPin2, OUTPUT);
  Serial.begin(9600);
}

void loop()
{
    int volts = 170; // send signals of 3.3v
    analogWrite(outputPin1, volts);  // to Accelerometer

    int reading = analogRead(analogPin);  //  receive signal
    delay(1000);    // delay 5sec.

    if (volts >= 100)    // Input voltage is more than 2.0V
    {
    int volts = 77; // send signals of 1.5V
    analogWrite(outputPin2, volts);  // to Transistor
    }
    else
      {
      int volts = 0;
      analogWrite(outputPin2, volts);  // to Transistor
      }
}

When I measure with Digital Multi Meter, it keeps showing 1.5V even it doesn't change the position of the sensor.

I guess there's some problem in the if, else line.


texts: How do I get a constant current of 2mA; output voltage of 9V dc?

texts:
I need a device that can run on batteries (probably one or two 9V batteries) that will provide an output voltage of about 9V but, more importantly, is constant current of 2mA.  This will be dc output.

Yes, that's a low current.

The output will go to electrodes which then go on a head.  This means the load resistance isn't really known.  Resistance of human skin varies between people and time of day.  It's quite a large variation, between 100kohms and 1kohm.

What words do I need to include in a search to find a suitable circuit? Or what ICs will be suitable as a constant current source for 2mA?  Or does anyone have a handy circuit diagram?


texts: How to diagram power-side and ground-side switches?

texts:
I'm an early-stage self-teaching hobbyist.

Just as a practice exercise I'm diagramming simple circuits (without looking at the instructions) of DIY kits that I've bought on banggood.com (awesome stuff on the cheap, if you can bear to wait a month to get it).

I have here "electronic dice":

Front:

Back (flipped to match):

As you can see the switch is connected to the ground side rather than the power side.

In the schematics I've seen so far power and ground are treated without regard to the physical wiring on the board, like this:

In this case there is a switch to control power, which happens to be ground-side, but there are 2 "V+" inputs and nearly a dozen "ground" lines.

How would I describe that there is a ground-side (or power side) switch to the ground and power rails?

Is this style of diagram that I'm using generally considered "higher level" and not concerned with switches? Or should I should I "simplify" this by having a battery symbol as my start and draw the "V+" more exactly as it is on the board? Or would I have a second diagram showing the "power stage"?

P.S. I realize that my schematic is probably wrong - it wouldn't make a lot of sense for LEDs to go directly from a power gate to ground without a resistor (and so there probably is a directed ground path in this case) - but that's besides the point. Update: After double checking it looks like D3 (which is connected to the ground of all other diodes and therefore U1, U2, and U3) is connected directly to Battery -, so I think I got it right.


texts: Anybody recognize this flat-flex connector?

texts:
Even after a few hours Googling, I'm unable to identify this flat-flex connector, so I'm thinking it's time to turn to the community for help!

The connector in question is this guy:

Of course, I already looked for identifying info such as brand, etc., but was only rewarded with a few generic/informational markings:

"43 2B" in the upper-left-hand corner (on the back retention clip of the connector)
"1A" in the bottom-right-hand corner

Other things I know about the connector:

it has 43 circuits
14.25mm length
3.75mm width (with retention clip closed)
flex cable contacts are all the same size, but staggered into two rows
either 0.5 or 0.3mm pitch (hard to tell, given the staggering)

Here's the same shot of the connector with magnification in each corner (I've verified these markings by viewing/lighting at other angles; not included).

Any help that anyone can offer here would be massively appreciated!


texts: 9v battery to parallel 3v LEDs - burnout

texts:
I'm having an issue in a simple (n00b) LED circuite - ended up burning out a couple of LEDs due to some mistake I'm making, but can't figure out what the error is.

I've got a 9v battery, trying to drive two blue LEDs (3.4-3.8v rated, 20mA) in parallel. I calculated necessary resistor as R = (9 - 3.4) / 0.04 = 140 ohms. To be on the safe side, I used a single 180 ohm resistor (brown/gray/brown/gold) in series (battery + to resistor; resistor - to + pole/anode of both LEDs; - pole/cathode of both LEDs back to battery) on a breadboard. Upon briefly connecting the 9V battery the first time, circuit lit; on 2nd connect, it stopped and I smelled distinct LED burnout smell - after which both LEDs would no longer light, even when connected individually to a 3v (2x AA) source.

Would appreciate any advise re: what I'm doing wrong. Thank you!

Thank you for the assistance - so in the circuit I'm considering with 9V battery powering three LEDs (details in my comment above), would the following be the way to go?


texts: How can I use a Integrated IR Receiver IC in a sensor circuit without microprocessors?

texts:
I am asked as a term project to design a circuit that is somewhat similar to a park sensor. Let me first say that I am a 2nd year undergrad student, and we are very newly beginning to get into the circuit design stuff.

As for the project, I roughly have what to do in mind, except I have no idea how to utilize the TK-19 sensor. I have provided the link to the datasheet below, I would be very glad if someone can tell me what happens when this thing detects IR radiation, or does not, that is the main question in my mind.

Here's the link to the datasheet: http://www.datasheetcatalog.org/datasheets/restul/305097_DS.pdf

Edit: Let me note that we are only allowed to use diodes(including LEDs and IR LEDs), capacitors, resistors and opamps.


texts: How to shift signal to baseband using local oscillator frequency?

texts:
If the input to a demodulator is a signal having the spectrum shown below, how would I figure out what local oscillator frequency is required to shift the signal to baseband?

Is there a formula for this? I'm getting no where on google.

Thanks.


texts: I would like to build my own .100 (2.54mm) cables to mate with standard single and double row headers, but the 'rectangular connectors' section of distributors websites is huge. Which ones do you recommend? Can you recommend an IDC system that works with discrete wires (not ribbon cables)?


texts: How to identify JFET terminals with multimeter?

texts: If i have a JFET besides using datasheet , is there any way to use multimeter or ohm meter to find which terminals are gat,e drain, source of the JFET?


texts: Using a step by step relay along with a solid state relay

texts:
I have a step by step relay which is connected to a light bulb and to a manual switch.
In parallel with the manual switch I put a SSR. I command the SSR to be on for 0.5 seconds, however the light would not switch(although the manual switch works).

Is there a problem because the SSR is a zero crossing relay? Or should I look somewhere else? How could I make this assembly to work?

simulate this circuit – Schematic created using CircuitLab


texts:
I understand that typical optoisolators can logically be considered as "normally open". However I have a situation where I'd like the circuit controlled by the opto to be normally closed, mainly for the failure state but also so that the opto's led doesn't have to be activated for 99% of the time.

How can this be done on the transistor side?

Failure states aside, should I be concerned with having the opto activated indefinitely (in a normally open circuit)?


texts: Solving Currents in BiCMOS Darlington Pair

texts:
Using KVL and assuming that the BJT is in forward-active and that the MOSFET is under saturation and using the given, I was able to generate three equations with three unknowns:

1) \$\frac{3V-2V}{1000Ω}=I_D+I_C\$

2) \$I_D=(10^{-3}\frac{A}{V^2})(V_{BE}-0.6V)^2\$

3) \$I_C=(0.1(10^{-15})A)(e^\frac{V_{BE}}{0.026V}-1)\$

. The problem is that, based on my calculations, the above system yields:\$V_{BE}=1.6V, I_D=0.001A, I_C=-4.8658(10^{-17})A\$. Does this really mean that \$I_C\$ is negative and that the npn BJT \$Q_2\$ is actually not in forward active mode or is there something wrong with my method/equations?


texts: Relation between frequency and inductor current

texts: I have a question regarding frequency and inductance. What is the relation between frequency of an applied voltage that is square wave, over an inductor, and the average current that would flow through it? Is there a way to calculate it using analitic equations? I am working on a motor application for university. I applied 5kHz pwm voltage over my motor windings and i couldnt stand the noise, because 5k is in the hearing range. So i applied higher frequency. I noticed that with higher frequency, the average current flowing through windings started to increase. I know we should not try to analyze impedance here as it is a square wave. Why does the current grow with increasing square wave frequency? I would apreciate all help.


texts: How can a common mode choke filter differential noise?

texts:
Consider the following schematic, where there is a 10V offset voltage source with 1V ripple, two selfs mounted in common mode choke and a 100 Ohm resistor. Everything here is "ideal" (no parasitic resistance or capacitance etc.).

Since the current that enters into one winding is equal to the current that enters into the other winding, I would expect that this pair of windings has no effect regarding the AC analysis of the voltage between the two terminals of the resistor. But look at the AC analysis of this voltage in the image below: obviously, the ripple is strongly filtered. How can it be?


texts:
What is the skin effect?
What is meant by the skin effect?


texts: Current source with unlimited cap drive op-amp oscillating

texts:
I've been trying to make a current source, and have finally gotten my hands on some LM8261's which should be an 'unlimited cap drive' op-amp.
The problem is, it is still oscillating.
This is the schematic and PCB layout:

I have tried to route the ground inside the loop area, close to the 5V connection for the opamp, so I could place the bypass capacitors as close as possible. Although the bigger 10uF cap has one of its legs at the groundplane (forgot to include this cap in the schematic picture.)
This is what it looks like when I probe the gate of the MOSFET:

It's all over the place.
I tried adding a 10uF capacitor across the DUT, so from VDD to ground. This removed a lot of the wierd noise and made it look almost like a sinewave:

I've tried with and without the gate resistor R1, it didn't seem to make any difference.
What is going on? Any clues on why this just doesn't work?
EDIT:
Solved it!
With the help from @Andyaka below, I used his solution of inserting a BJT emitter follower in between the op-amp and the MOSFET, together with an integrator and got some great results!
Final circuit:

The simulations can be seen here:
https://imgur.com/a/tBprTjh
The gain/phase bode plots I made on the PCB:

Bandwidth of approximately 350kHz! Very pleased.


texts: RGB LEDs with arduino/transistor won't dim

texts:
Why doesn't this work?  I have fifteen RGB LEDs wired up with this configuration.  The transistor I'm using is the MJE3055T. Are the transistor's voltage ratings (collector-base, collector-emitter) just too high for this low-voltage, high current application?  When I eliminate the arduino and transistor and plug the LEDs directly into the power supply (with resistors of course) they work perfectly...

Does anyone know why this isn't working?  Have suggestions for a different transistor?

Thanks!


texts: duplicate net names wire PA1 - Altium designer

texts:
I have an issue with altium designer

I am trying to connect a pin from my microcontroller to an external pin for gpio via a bus but I get an error: "duplicate net names wire PA1"

this is what I have:

the microcontroller:

the gpio pins:

How can I solve this issue?

A complete view of the entire schematic:

http://imgur.com/a/Zy1nK


texts:
I am currently reading Digital Computer Electronics, and on page 4 of the book (page 7 of the PDF), I am confused by this diagram:

The diagram shows that the transistors with no (or almost no) current being supplied to the base have their outputs on.
The authors even describe the leftmost transistors as being cut off, despite showing 5V output:

The transistors on the left are cut off because
the input base voltages are 0 V. The dark shading symbolizes
the cutoff condition. The two transistors on the right have
base drives of 5 V.
The transistors operate at either saturation or cutoff. A
base voltage of 0 V forces each transistor to cut off, while
a base voltage of 5 V drives it into saturation.

I think this may be a difference between NPN and PNP transistors, but I'm not totally sure because of the way the authors described the left ones as being cut off despite showing 5V.
Any help would be appreciated. Thanks!


texts:
I'm a beginner hobbyist, I'm trying to get to the point where I can look at a basic circuit (physical, not a diagram) and speculate on what it does. Transistors are confusing, because there's so many types and some are visually similar. Obviously I could google whatever I find printed on the side of them, identify the manufacturer, etc. Assuming I don't want to bust out my laptop every time I see a transistor, what I can I determine?

What I'm asking is what I can know by:

Looking. It has 3 pins on one side, it's D shaped, rectangular with through hole, hat shaped, round, Size, notches on the side, Any rules like "If it's D shaped, it's always a BJT" (is that true?)

Testing. Things I can easily determine by poking it with a basic multimeter. Rules like "if there's high/infinite resistance between pins 1 and 2...". Whether or not such tests will work while it's in the circuit or if it needs to be removed to know for sure.

Id numbers. Are there any naming schemes that are in wide enough usage to bother with?

I'm putting together some notes I can keep in the garage with things like resistor color codes, the various things each component is called, their diagram symbol, what each pin does, etc. I hope this isn't too open ended, if I knew more I'd ask something more specific. I've found a lot of resources that explain the types, what they do, and their symbols, which is great for design, but I'm having a rough time finding resources that explain how to identify the type of transistor by examining the actual thing.


texts: Old lead-acid battery inrush charging current

texts:
Can an old lead-acid battery have an usually high inrush charging current, such that the alternator belt squeals for the first 30-90 seconds after the engine is started? It is worse in hot weather.
What would be the reason for this?
Is it because the battery voltage dips too much after turning the motor over?
Or is it because the battery internal resistance is too low? This would be consistent with being influenced by temperature. On the other hand, I would expect an old battery to have higher resistance due to sulfation.
The alternator and the belt are new.
UPDATE:
I forgot to mention. While the belt is squealing, the engine really struggles, almost to the point of dying, like there is a large load on it. I think this rules out a loose belt. Sorry I forgot to mention this important detail.


texts: Does adding thermal relief on PCB increase electrical resistance?

texts: I am just getting started on PCB design (for fun) and came across this term called thermal relief. It increases thermal resistance so the components can be soldered easily. But according to what I have learned, thermal and electrical resistance are always connected. So does thermal relief in any way increase the electrical resistance also? If not, what is the mistake I am making? This may sound silly but I cannot get it out of my mind.


texts: Coupled inductor/pulse transformer for very tiny power supply

texts:
I need an isolated 24V 3mA supply to activate some optocoupler that will be read by some microcontroller. Its power supply will be the microcontroller's 5V. My first instinct was to use a flyback transformer, but these guys seem too start out at 500mA, so they are way too bulky.

I then noticed parts listed as "coupled inductor" or "pulse transformer" seem to have values in the right ballpark. However, I am not sure if these parts are a good fit because the datasheets for inductive parts don't provide much info.

So, two questions:

Are the datasheets really bad or am I missing something? I want maximum input voltage, frequency response, LI² values, this sort of stuff. Can I figure out these somehow from the datasheets? How do the people who use these parts know these parameters are ok?
Is there any fundamental difference between parts listed as coupled inductors, pulse transformers and flyback transformers? How about audio transformers and signal transformers?


texts:
Hi I want to make a buzzer for my PC motherboard. Similar things like this:
https://boip.in/home/rajiekart-pc-motherboard-internal-speaker-bios-alarm-buzzer-1-pcs-pack?gclid=CjwKCAjwnK36BRBVEiwAsMT8WNyz6K-LtLk4YecyH2NH6YHbLz0rWyYm8Za_3LTn4GwUSZPk7ViyzhoCFXEQAvD_BwE
My plan is to use a normal speaker with a amplifier like LM386. Is it possible to connect LM386 inputs to PC motherboard buzzer output pin ?


texts: Detect logic signal in a long distance. What type of interface to use?

texts:
My daughter board uses a comparator(LM339) to output logic 1 or 0 under a 3v3 supply. The cable connecting daughter board and main board is at least 1.5m. Luckily, the frequency is not fast but the environment is full of EMI. So I want to use some technologies to improve accuracy of detection. I search the internet and find some solutions from NI:

line driver, open-collector or push-pull

But I do not know the differences among them when used in this application. And any other solutions? like a differential communication (may be too much for this application). Please give me some suggestions.


texts: Non-inverting op-amp amplifier gain as open-loop gain goes to infinity (limit calculation)

texts:
Why is the following true?

I can't seem to understand why. Shouldn't it just be infinity/1+infinity which is approximately 1?

It's comparing the vo/vin of a non-inverting amplifier with finite gain with that of one with infinite gain.


texts:
I am trying to decide on a power source for use in space, and as such they need to have a good operating temperature range.
I can't find any decent source on the web about this particular topic for solar arrays already in use. Hence me being here, does anyone know a typical operating temperature range for a solar array used in space?

The temperatures can vary from extreme highs to extreme lows so I want to include this in my argument to justify a decision being made.


texts: Driving multiple (variable amount of) LEDs with WS2811

texts:
I am trying to control multiple LEDs with the WS8211. According to the specs, RR resistor shall be calculated based on the voltage drop on the red LEDs.

So, my first question is: The formula is RR=(12-3Vledrp)/18.5 K. Is this "3" multiplier mentioned there just because there are 3 LEDs on the schematic example? Or is it whole total voltage drop on all LEDs?
The second question:
I want to make it "universal" to be able to plug different LEDS, so I probably need some kind of constant current source controlled by the WS2811 "R" output. What could I use for that? As simple as it is possible?

Thank you!


texts:
I am planing to build a ROV for underwater use and at this point I am concidering to have some water leak detection system for the electronics enclosure that has to withstand underwater pressures up to 5bar / 70psi / 500kPa.

From my research I found a nice solution from Blue Robotics called the SOS Leak Sensor that goes together with some SOS Probes.

The design and the description of the probes let me think a bit about how they function. In a section of the product description it says:

  Each probe can be re-used a number of times if dried out and re-compressed, but once the tip degrades you can also get replacement SOS Probe Tips.

So the probe tips are made of a sponge material that is probably enriched with some sort of salt (one could simply use NaCl for that I think), that is going to rise the conductivity of any water that is going to touch and get soaked into the tip.

If I am right I think to replicate those probes would not be much of a problem.

Moving on to the circuit board (SOS Leak Sensor):

Here is the circuit diagram from the documentation.

So far I understand that if any probe is going to short out, the circuit is going to switch the signal - that is pulled down by R3 - to high. But what are R1 and R2 doing exactly?

I need to know this because I still didn't get the relation of the conductivity/resistance of the water to where the circuit detects the "short out" and at what threshold.

I got some samples of the water in my local area, where I am planning to bring the ROV in use, and have poorly measured the resistance of them and some tap and distilled water for reference. I've used a multimeter for this and I did not had any rig to hold the two probes at a constant distance to each other but I tried my best holding them with my hand, so my measurements are not so constant. But here are some significant results:

The sample water hat a resistance of something about 500kOhm (+-100kOhm) at a probe distance of about 5mm (tip to tip).
I than added a pinch of salt into a little sample of the same water and measured about 40 to 30 kOhm.

So I am sure that I can get readings with homemade probes with at least 100kOhm resistance. But back to my question, how does these relate to the circuit shown above? do I need to make any adjustments to R1 and/or R2? And if I have to, how are the calculations for that?


texts: What is the Gain, Input and Output Impedence in this circuit?

texts:
So I'm trying to know what the input, output impedence and gain is in this circuit

To begin, I'm kind of confused since I don't know if those two resistors at the right are in series or in parallel.


texts: Repurposing CFL ballast for different bulb (UVC)

texts:
I am attempting to repurpose the (electronic) ballast contained within a CFL lamp to power a UV-C  bulb (mercury discharge, uncoated tube) for disinfection purpose, and out of general interest in fluorescent lamps.

I opted for repurposing a ballast from a CFL due to difficulties in procuring parts (or a whole ballast actually) and because the wattage of CFL is usually a lot lower than common long tubes, which is more appropriate for the small UVC tubes I am hoping to get (<15 watts).

I have opened and extracted the eletronic ballast, which was still functional. It has very short leads hooking it up to the original bulb. Upon replacing those leads with longer (~8 in) and attaching the four leads to a linear 4-watt bulb, nothing happened upon power up. I have removed the linear bulb and re-attached the original coiled bulb, still with the leads, and nothing still attached. (I will now try removing the leads and try again, essentially coming back to the orignal device). Below is the wiring schematics used (~8in leads length).

Could the lead length impact the electronic circuit?
Could there be a polarity to the bulb? (Will try asap, but am under the impression there is no polarity.)

I understand the electronic ballast is a current limiting circuit with an integrated starter. In this case, it is an instant start since when working normally, the bulb striked an arc immediately (there was no apparent heating first and glow before getting the light on).

For the length, I have seen several sketchy videos were much longer length were used (although each pair was twisted) for longer tubes.

Possible follow-up question: Assuming it is a instant start type, why would there be 4 leads (2 for each sides of the bulb)?

Please note that due to the COVID situation I am isolated with absolutely no tools or multimeter (I had to purchase an el-cheapo iron for this project).

My question is similar to this one: Using a CFL ballast to power 9W UV tubes, in the sense that I also want to repurpose a CFL ballast for powering a tube different than the original intended.


texts: How is the antenna return loss measurement impacted by the cable's return loss?

texts:
Say you have an antenna (2.4 GHz) for which you want to know the return loss using a VNA. The connection between your VNA port 1 and the antenna is through a coax cable (e.g., Murata). The cable's own return loss is specified at 14 dB (VSWR \$\approx 1.5\$).
When I measure the return loss with the VNA for the whole setup (cable + antenna), I get about 25 dB, but I am unsure of how the cable's own return loss bias this measurement one way or another. How do I account for the cable's return loss? How would I remove the cable's own return loss such that I know the actual return loss from the antenna on its own?
I am aware the insertion loss (IL) of the cable will bias the measurement by 2*IL (because of the round-trip). So if the cable has an IL = 1dB, the return loss for the whole setup is going to seem better than reality by 2 dB. I'm just curious about the cable's return loss impact on this.


texts: How can I increase senstivity of my emg sensor?

texts:
I have made a emg sensor using ad620 op amp. The problem is it is only working for larger muscles like biceps, but I want to use it for smaller muscles as well.

Can anyone tell me how can I increase its senstivity?

Here is the link from where i make this project.
https://hackaday.io/project/8823-super-simple-muscle-emg-sensor


texts:
I have a device (USB CDC) class that is connected to a host PC via USB. On this device there's a request-response task implemented, meaning I get a message, do some stuff and when I'm done I send a response.
The problem I have is that it takes, from the host perspective, too long until I get a response to a certain request.
My suspicion is that probably the polling of the USB input buffer on the host PC is too slow and therefore causes this delay. But to rule out a problem on my USB device, I thought I can hook up a scope to my data line (D+) and measure the time between the incoming and the outgoing message. Unfortunately there's a lot going on on this line even though no data is transmitted.

Is there some idle communication on the USB line?
Is there a way to distinguish this idle data from real data? Or is there a better way than measuring the data line?

Update
I took a capture (at least I think I did) where the two PPP Unknown messages contain my data. Is this proof that the response time 55.624225 vs 55.625272 is less than 1ms?

As a consequence, this would mean that it's indeed the host application that cannot poll the USB Input Buffer fast enough?


texts:
We have been having problems with pre-made BNC cables. The cause has been narrowed down to the fact that once the BNC is locked in place the cable can still rotate relative to the connector. This can result in the soldered core, or the shield, or both tearing free. The symptoms are a full or partial loss of signal or a major increase in noise.
The question being - how can I specify that the body of the cable is molded to the plug so that this problem is eliminated? I have found a suitable such cable, but as often happens it is apparently going out of production. Any suggestions?


texts: Which 433MHz transmitter module can be used for battery operated wireless communication having vey low current consumption (less than 5mA)

texts: Im designing a wireless water level controller. The WLC detects water between overhead and underground tank. The transmitter will be situated at each of the tanks. After water level sensing , the signal will be fed to encoder IC which transmits data through transmitter. Ive searched many transmitter modules. Most of them has a current consumption ranging from 9 - 40 mA. However such a large current consumption will drain the battery in 5-6 days. Ill be using 2 AA batteries of 1.5V each. Hence it is required to have a current consumption less than 5 mA. Ive researched that OOK modulation can be used for low power consumption. But im unable to understand how to implement it. Please let me know how can i implement the transmission of signal at a distance of 100-200m at 433MHz frequency. Also using arduino is not a feasible option for multiple tanks As it'll require uisng in each transmitter circuit


texts: Fixing 1 failing timing constraint in Xilinx

texts:
In the end of my project I have a timing constraint failure as follows :

clk_in is the 100 Mhz system clock on ML507 I don't know why it is not meeting the criteria, I don't know what the criteria is as well, how can I fix this, any idea what can cause this failure? Although the project is working. How can I debug this?


texts:
Most people know the formula for the total resistance of parallel resistors:

\$ \dfrac{1}{R_t} = \dfrac{1}{R_1} + \dfrac{1}{R_2} + {}...{} + \dfrac{1}{R_n} \$

If there are only 2 resistors, that can be easily rearranged to solve for Rt:

\$ {R_t} = \dfrac{(R_1 \cdot R_2)}{(R_1 + R_2)} \$

Is there a safe way to do that for n resistors?


texts: What is the data register address for GPIO pin 21 Cortex ARM M0?

texts:
I need to find data register address for GPIO pin 21 Cortex ARM M0?

I feel this question can need some background. I am learning embedded MCU programming and most sources mention that I need to find the address for the particular port / pin. It seems like a basic thing to do (so basic, that it is not really covered how to do it)

I studied manuals / architecture reference for Cortex ARM M0 closely, but could not find anything that can point me to the address. All I see is range (in my case, I know the peripheral range is 0x40000000-0x5FFFFFFF).

Here is the link to technical reference manual:
http://infocenter.arm.com/help/topic/com.arm.doc.ddi0432c/DDI0432C_cortex_m0_r0p0_trm.pdf

Architecture reference:
http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0419b/index.html


texts: Adapt existing usb-2 otg device to usb-c but use usb-2 mode

texts:
there are number of articles out there, like this one: http://www.ti.com/lit/wp/slly017/slly017.pdf

But I'm not super confident in my abilities here so I'm wondering if someone could proof my schematic to make sure it's going to work. Will this schematic work (simply connecting d+ and d- to the microcontroller (samd21) d+ and d- pins and cc1/cc2 to the usbhost pin?

I should explain the reason: I want to be able to not look at the usb when I plug it in, usb-c is a better user experience but I don't need the speed or other things, just the reversible plug and I want it to conform to what is quickly becoming the new standard.

Another link showing the method of adapting usb-c to usb-a: Wiring diagram for USB-C to USB-A cable? As comments have indicated, you can't simply emulate usb2.0 otg with a pull down resister.

http://ww1.microchip.com/downloads/en/AppNotes/00001914B.pdf


texts: How is power affected on a step-up transformer, does it change?

texts:
Ok here is what I have found so far about Step up and step down transformers:

Step down transformers change a high voltage/low current, to low voltage/high current.
Step up transformers change a low voltage/high current, to high voltage/low current.

What about power?

From what I can see, power in a transformer will stay the same based on the power equation power shouldn't change from one side of the coils to the other side.  Does the power stay the same? Can power be increased with a transformer? If not, can power be increased somehow?

If power does not change, then how can an 11W LED light put out 50w of power based on power equation and transformers performance? Or is this something totally different?


texts: Transfer function for this transconductance op-amplifier

texts:
I used the summing-point constraint and KVL to get \$V_{R_1<<}=V_{\text{in}}\$. Followed by a voltage divider for the node left of \$R_L\$; yielding:

$$V_{R_1<<}=V_{\text{in}}=V_o\left(\frac{R_1}{R_1+R_2}\right)^2\iff\frac{V_o}{V_{\text{in}}}=\frac{(R_1+R_2)^2}{R_1^2}=\boxed{1+2\frac{R_2}{R_1}+\frac{R_2^2}{R_1^2}}$$

However, textbook claims it's: $$1+\color{red}{3}\frac{R_2}{R_1}+\frac{R_2^2}{R_1^2}$$


texts:
I want to build a proof of concept implementation of the BB84 algorithm.

I plan on having an Adruino send a pulse across a fiber optic cable, with a polarizer that it controls. On the other end is an Arduino with polarizer for reading. I'm pretty sure I've seen hardware for everything except the detection part. Does something like this exist?


texts: How do we balance an FIR around its center? I was asked this question in an interview. What does this mean? Is the center point the point corresponding to the peak of impulse response?


texts: Best way to turn off P-FET with 3.3V available (P-FET Load Switch Application)?

texts:
honestly I'm drawing a blank.  I am trying to turn on and off a load with a P-CH MOSFET.  I used generic resistor values just to be clear.

Now, in this example the VGS will clearly never go to 0.  It just can't, unless I try to drive the gate with the 24V source.
Is there any way to turn off this PFET without using a second transistor?  Specifically, I was using an N-CH MOSFET to "pull up" to 24V like in this second example.

Is there any advantage to doing it this way?  Am I forgetting something about P-CH FETS?  Is there a better way to do this?  More specifically, is there an easier way to do a load switch that is connected to ground, and the switch connects power?
Thanks :) I appreciate any advice, app note links, etc.


texts: Automatically switching from battery to DC wall adapter on insertion

texts:
I have a project that runs off a 4S LIPO battery and I want to switch to 24V wall power when I plug in an DC wall adapter. I have two designs, an inexpensive one with discretes and one with an expensive LTC4412HV IC.

I simulated both and they seem to work fine. In terms of safety since the battery is a LIPO, is the discrete design okay? Is there anything I should add other than a fuse which I already have?

Edit: The reason I use a PFET instead of a schottky diode is because the diode consumes too much power and I want to maximize battery life.


texts: How to design a keyboard circuit that can use a passive USB-to-PS/2 adapter?

texts:
I'm designing a small device that will act as a USB HID keyboard, but it must also work with PS/2 hosts. I would really want to be able to use it with one of these nifty passive USB-to-PS/2 adapters that used to come with every USB keyboard (not sure if they still do, haven't bought a keyboard in many years!). Problem is, how can I detect if to use USB or PS/2 in my circuit?

Electrical connection

Since I'm using a PIC16F1454 which has a built-in 3.3V LDO, trancievers, and everything for USB my plan was to connect it like this:

I need to connect RA4/5 because D+ and D- can only be used as inputs if they are not used for USB communication. RA4 and RA5 would normally be tri-stated, thus not conflict with the USB, and if the PS/2 mode is enabled, D+ and D- would be disabled in a similar fashion.

I don't foresee any major problems because D+/D- are 3.3V and PS/2 is 5V. Because PS/2 is using an open-collector configuration, any mistake that causes 5V to go out on the USB D+/D- will have a very high impedance, and should not break anything.

Logical

Now, here's the main problem. I'm not sure how I would perform my initialization procedure to detect PS/2 or USB at startup.

One problem is that, from what I understand, there is not a single standard mapping between the USB D+/D- and the PS/2 Clock/Data pins in these passive adapters. Either D+ is connected to Clock and D- to Data, or vice versa. This also leads to the first real question: Is there a standard pin mapping? If not an official standard, perhaps a de facto standard? If there is not, I don't think there will be a problem detecting this in software.

The second question is, well, how do I actually detect if the host is talking to me using USB or PS/2? Preferably in a reliable way. Since every keyboard i have here works with one of those adapters without exception, it can't be that hard. Does the USB standard perhaps discuss this? Few adapters actually carry the USB logo, so I don't think this is something that the USB standard would encourage.


texts: Do I also need a multimeter if I buy a digital oscilloscope?

texts:
This is probably a newbie question, but I am looking to buy some tools and start playing around with more embedded electronics and robotic stuff. The digital oscilloscopes such as the DSO nano http://littlebirdelectronics.com/products/dso-nano-v2-pocketsized-digital-oscilloscope seem to be highly recommended and was thinking of getting one. If I get one of these, would I still need a multimeter? What can a multimeter do that an oscilloscope such as this can't do? ( measuring capacitance for example?)

Is it even worth getting the oscilloscope in these days of prevalent laptops or is there an easier, cheaper, more comprehensive solution, some sort of cheap board or device that plugs directly into the laptop? Or does it not matter and if I am serious, that I should get both a multimeter and a good digital oscilloscope?

Any recommendations/advice would be greatly appreciated


texts:
Here is a transformer where we can see the eddy currents in the core:

I would like to estimate the voltage which induces the eddy currents. I know what voltage is applied to the primary and how much time this voltage is applied. The number of turns on the primary is 1,so I am able to determine what the variation of the flux is.
How can I estimate the voltage into the core as there is no winding, ie no turn?
-------------------------------EDIT--------------------------------


texts: why there is no quad 1-to-4 demultiplexer?

texts:
I have 4 input signals to route on 4x4 outputs. it's not a 1-to-16 demux what i'm looking for. Outputs must be selected 4 by 4.

is there any demultiplexer that can do that on one IC ?

I didn't find quad demultiplexers, I only find dual ones.
like: this


texts:
I've recently taken over a project that has issues with the ACS71020. The values that we get are off, and the software has written to both the EEPROM and the shadow registers with custom values. My understanding is that the default values in register B is factory calibrated, and once overwritten there is no way to restore. The datasheet do not mention any default values for this register.
Is this correct, or have I misunderstood something?
Link to datasheet: https://www.allegromicro.com/-/media/files/datasheets/acs71020-datasheet.ashx


texts:
I've just been introduced to op-amps and am having a little trouble understanding exactly how they work. Take this circuit, for example.

Suppose that there's a 1V source here. Without the op amp there will be a ~0.995V drop across the 10K resistor and then the rest (5mV) is measured by the oscilloscope.

Now that the op amp is introduced, my understanding starts to break down. This op-amp says it has a gain of 10, does this mean that 10V or 50mV should be the measured drop across the oscilloscope? I'm comfortable with the resistors outside the op-amp, but what do I do with the resistors inside? How do I account for those/what do they do?


texts:
Chips like the ESP8266 or ESP32 typically only have a couple of hundred kB of RAM. Alternatively, you can buy boards with chips like the NXP i.MX 6, with which you can have gigabytes, but suddenly you're at the level of "embedded Linux" in terms of complexity, and it also looks fairly hopeless to solder such a board together yourself.
Is there a middle ground which...

is still simple to program (... think "ESP"; maybe a simple RTOS but no MMU and processes and drivers etc etc)
... it also doesn't need high performance (probably not clocked a lot more than 100 MHz
has access to a couple of hundred megabytes of RAM

which doesn't need to be extremely fast, but at least a couple megabytes per second would be nice (... think "streaming out a couple uncompressed audio streams")?


texts:
I have just started learning Verilog, so I tried writing a simple 4-bit binary counter. However, when I run the behavioural simulation, the output stays undetermined. I will really appreciate if someone can tell me where I am going wrong.

module counter(input clk, input rst, output reg [3:0] count);

always@ (posedge clk)
begin

    if(rst)
        count <= 4'b0;
    else
        count <= count + 1'b1;
end

endmodule


texts: Multiplexing 2 digit 7Segment with one Bit

texts:
I want to control a 2 digit 7-segment LED with a MSP430 micro controller. The display has 8 input pins per digit (8th pin is the dot, which I do not need) and two ground pins (common cathode). The idea is to connect the first 7 pins from the µc to the 7 segments of both digits and then use another pin (the control pin) for selecting which digit to display. By switching fast between the two digits I would like to display a two digit number using 8 pins of the µc only.

What I need is the following. We can abstract such that there are only two LEDs.
If the control pin is LOW than LED1 is on and LED2 is off. If the control pin is HIGH then LED2 is on and LED1 is off. I know how to build this with a single PNP transistor (see picture below). However, this is not useful in the common cathode setting, since I want the switching gate "behind" the LEDs.

My question is, how to build such a circuit with one single transistor (and resistors of course). I think it has to be a NPN transistor.

This is my first EE question and I have little experience, so I hope I was able to make my question clear.


texts: Is USB UHCI polling-based or interrupt driven?

texts:
I've had a discussion with some colleagues whether USB is polling-based or interrupt-driven. Some claim USB keyboards involve larger overhead than i.e. PS/2 keyboards due to the requirement of former being polled by the main CPU. Now, with today's typical CPU speeds it would probably be a small amount of CPU-time spent in either case, but it is still interesting to know.

I've tried to find out myself. I suspect the answer could be dependent on the USB host controller interface. I looked specifically at UHCI which is one of the original standards and is rather simple to understand (ftp://ftp.netbsd.org/pub/NetBSD/misc/blymn/uhci11d.pdf). Based on my reading of this, it seems it could be argued both ways whether USB devices are polling based or not.

So here some facts I've gathered from reading the UHCI spec:

1) It's true a USB device (at least prior to USB 3.0 which is what applies to most/all keyboards) can't actively send an interrupt. They can only answer a query whether there is a pending interrupt. Hence, this query has to be sent periodically.

So far, point 1 suggests it is indeed polling-based. But then we have:

2) It is not the CPU itself which sends the queries, but rather the host controller.

3) The main CPU does, however, have to program the host controller, by laying out a detailed schedule of what happens in each ms.

4) The UHCI host controller can send interrupts to the main CPU to alert it of completed transfers. Hence, the main CPU doesn't need to poll for completion of transfers.

So now it would seem (and this is what some colleagues argued) that from the point-of-view of the main CPU, USB isn't polling based anyway. It is the host controller that periodically polls, and then delivers the interrupts to the main CPU. This wouldn't be so bad, because the host controller doesn't have other jobs, so it's not a problem it is doing this polling.

But unfortunately, I don't think this is really the case after all, because:

5) According to my reading of UHCI, there is no way the main CPU can configure a UHCI controller and USB keyboard such that once it is configured, the main CPU will not have to do further work until something happens, e.g. the user presses a key and the keyboard sets a pending interrupt which is delivered to the host controller and ultimately host as specified above. According to my reading, the main CPU has to continuously "work" to keep it up and running. There are as I see it two reasons for this:

Transfer descriptors have an Interrupt-on-completion bit that can be set so that the main CPU is interrupted upon completion of the transfer. So far so good, but unfortunately there's no way to differentiate between positive and negative answers to interrupt queries, so this means the main CPU will be interrupted every time a device is queried about interrupt status, no matter whether it has a pending interrupt or not.
The schedule cannot be reused. Each transfer descriptor has an ACTIVE bit that must be set to 1 for the host controller to execute it. The host controller sets it 0 after it has been executed. As a result, the main CPU will have to periodically go through the transfer descriptors and set them back to active, so that they will be executed again.

So even though it seems UHCI has the potential to deliver interrupts "for free" to the main CPU, it seems the above two points ruin it and means that even if the main CPU doesn't have to be engaged in out-right polling of the keyboard, it still has to periodically reschedule the polling, even in the case of no events. Which means it is sort of engaging in polling.

I'm really interested if someone could validate these observations, especially the two bullet points above. Bonus points if someone can point out how OHCI, EHCI, and XHCI differ in these aspects!


texts: How to attenuate a (seemingly) overdriven VGA signal

texts:
I own an 8 port Belkin OmiPro2 KVM switch, which is a device used to connect multiple computers to a single display/mouse/keyboard.  I've owned this KVM for years and it has exhibited the same symptom since I purchased it, so this is not a new behavior.  Basically, when I connect this KVM to a CRT with a standard VGA cable the display looks perfect, but when I connect the KVM to a flat panel display the resulting video looks hot or overdriven.  The colors (especially whites) are so intense they overwhelm surrounding colors/text and severely wash out the display.

I have seen this behavior with multiple flat panels, so I think I can safely rule out a problem with a single flat panel and focus on the Belkin.

My suspicion is that the manufacturer purposefully over-drives the VGA video signal with the assumption that the switch may be rack mounted and have to overcome whatever line loss is introduced when routing the signal 10 or 20 feet to the connected display.

In the past, I placed three 100ohm resistors directly on the Red/Green/Blue lines of the VGA with some reasonable success in my output.  This had the effect of reducing the over-driven video but introduced 'ghosting' into the output.  I suspect this is some sort of impedance matching or frequency-response type problem, but this is definitely outside my normal areas of expertise...

However, feeling like I was on to something, I have googled for how to properly attenuate a VGA signal but with no luck.  Perhaps I am using the wrong terminology, or barking up the wrong tree completely.

Can anyone offer any suggestions or a proper circuit that I could try to achieve a better/cleaner/sharper result?


texts:
I have designed a Control System and don't know how to implement it.

I have modeled the physical system and have designed the control based on the State Space method.

The state space form is as follows: x' = Ax + Bu; y = Cx;

A, B, and C are matrices, x is the state vector, u is the input vector, and y is the output vector.

I designed the A, B, and C matrices in MATLAB, and want to implement it in C onto a micro-controller.

How do I actually implement my system now?

I am wanting to take two readings from a sensor that is measuring the system I attempting to control, send those two readings into my controller, and send one output back to my system.

I have designed the controller based on the dynamics of the system and techniques that are taught in an undergraduate level Automatic Control Systems class. Do the measured values go into the input vector?

And then I send the previously determined output value back into the system, and repeat for each sample?


texts:
I'm interfacing the Nordic nRF52 chip with an FPGA, and sometimes I need MOSI to be at a high impedance state (read "Z" in VHDL). Else the slave won't acknowledge that the data has been transferred completely (see here for the SPI Slave I'm using).

How should I do that properly?


texts: How to wire a 13Amp UK plug for a type 2 electric vehicle charging cable?

texts:
I have a hybrid vehicle that uses a "type 2" charging cable, but the cable is too short. It plugs in to a regular 13Amp UK socket in my garage. The problem is that, in addition to the usual 3 twin and earth cores, the cable also has 2 smaller cores which I believe are used for some charger control / diagnostics.
The plug it was attached to looks like an ordinary UK moulded socket but I can't get into it to see how it is wired.
Can anyone help ? Here are the relevant pics:


texts: Around six months ago, I did some light solder work in my room.  I was pretty reckless with the lead solder, and even ate while soldering on several occasions.  Should I be worried about the lead exposure?  Since soldering in my room, I have vacuumed and wiped down my desk several times.  Could small pieces of lead still be present?


texts: What are these designations on a sensor datasheet?

texts:
I'm working with image sensor Anafocus Lince5M.

In its datasheet there are some designations that I can't understand (underlined).

What are these designations?

And how to calculate threshold sensitivity of this image sensor?


texts: Difference between latches and flip flops in datasheet

texts:
At university and several online searches (Difference between latch and flip-flop) I have been taught that the difference between a latch and a flip flop is that the latch is level triggered while the flip flop is edge triggered.
However, when examining the datasheet of the 74HC595 (8 bit shift register with output latches: https://www.arduino.cc/en/uploads/Tutorial/595datasheet.pdf) I have read that they name the registers forming the shift register Flip Flops and the registers forming the output register latches (SHCP is Shift Clock and STCP is Storage Clock):

However, when observing the function table, both are triggered on rising-edge.

Even the timing diagram portrays the latch as edge-triggered:

What is the difference between a latch and a flip flop then?


texts:
I'm working on piece of software for Raspberry Pi and I'm writing an integration test. One of the cases requires that I'm able to read a state of one pin on another (basically if one output pin is high - another input pin should also be high, and vice-versa).

What's the safest way to connect one pin to another so that:

a) Regardless of software settings (Pin is out/in, high or low), there's never a dangerous short.

b) The state of the IN pin is never "floating" (which is the reason for using pull-downs/pull-ups from what I understood)

simulate this circuit – Schematic created using CircuitLab

Basically is R2 needed?


texts: How to increase data transmission speed between cc2500 and cc2511?

texts:
-I am using cc2500 at target side and cc2511 at host side.

-I want to transmit or receive data of 8Mb between this two chip.

-data rate set to 250 Kbps.

-My communication frequency is 2410.0 Mhz

So is that possible to transmit or receive data of 8 Mb within 10 Min using this cc IC?????
what are the maximum time to take transmit or receive data ???


texts:
I've been trying to find any data sheets for either solderless or solderable breadboards to figure out what voltage/current should be safe to use on them, but either there isn't a single "official" data sheet out there or I'm just extraordinarily bad at googling stuff.
From what I could gather most solderless BBs should have roughly the same characteristics, as they are pretty much the same underneath. As for the solderables, I found many types out there, all without "offical" voltage/amperage ratings.

I need to run 12V DC at ~2A continuously. Is it safe on solderless or solderable BBs?


texts: Instantaneous phase voltages of 3 phase WYE load

texts:
If phase 1 instantaneous voltage is 100 v and decreasing what are the other phase instantaneous voltages if the max voltage of phase 1 is 170 V? Frequency equals 60 HZ. (60 Cps).

I do not understand this question as there is no time given for when it is at 100 V. How would you find the time that the voltage is at 100 V to find the other instantaneous voltage values?


texts: what is the function of a transistor in a microprocessor?

texts: I do not have any in-depth knowledge of electrical engineering, but I would like to understand the purpose of a transistor in a microprocessor. There's usually some talk of Moore's law and that transistors somehow increase computation speed, but it's not clear to me exactly how these transistors are used. I figure it has something to do with pipelining. For example, when a CPU reads some instruction from memory, how are the operations required for that instruction performed with transistors?


texts: How to Design a Closed-loop Controlled Flyback Converter?

texts:
How to design a closed-loop flyback converter based on the figure and requirements given and find the specific values of paramenters?
Find: transformer magnetizing inductance , transformer step-down voltage ratio , and output capacitance . You must specify the voltage and current ratings of the switch and diode, based on the worst-case operating conditions for each device and assuming a safety margin of 20%.
Given:

Switching at a frequency of 40 kHz

Always operating in DCM

With an output voltage regulated at 5 V

With an input voltage ranging from 100 V to 200 V

With a load resistance ranging from 0.77 Ω to 7.7 Ω

With a duty ratio no larger than 35 %

Output voltage peak-to-peak ripple no larger than 5% of the nominal voltage in the worst case.

Closed-loop, controlling the duty ratio based on the output voltage error signal.

Using only a proportional-integral (PI) controller.

For an operating point corresponding to Vdc-max and Rmax
a. With a damping ratio of  = 0.7 for the closed-loop poles.
b. With a natural frequency of  = 519 rad/s for the closed-loop poles.

Question is how do you even begin analyzing and then design this circuit. Will provide the thoery and other relatable information here in 2~3 hours.


texts: How to create an FPGA based Ambilight clone?

texts:
Some quick background:
Ambilight is a system on some Philips TVs that analyzes the color information on the screen and then sets some LEDs on the back of the display to project the screen's color onto the wall. It is a pretty nifty effect. There are clones of this system out there now that use a PC to process the video and control the LEDs. I find this to be a bit overkill - using an entire machine to dance some LEDs...
I'd like to modify bunnie's NeTV to process an unencrypted HDMI video feed and drive some LEDs. I know the NeTV has been designed for other purposes, but I feel that it can be modified to achieve my goal. I don't care for the underlying Linux subsystem, I2C spoofing, video overlay, etc. At this point, I am not concerned with working with HDCP encrypted streams.

NeTV schematics

NeTV source code

FPGA Block Diagram

This is a block diagram from one of bunnie's presentation slides.
The rest of the slide set is here.

This slide seems to imply that video pixels are, in fact, decoded (not necessarily decrypted).

Finally...some of my thoughts and questions:

Can this be done on my desired hardware? If "yes", continue on! If "no", tell me what more I need!
Will I be able to process video information without any external memory? There is no memory that the FPGA can access directly, as far as I can tell. This probably depends on what algorithm I use to process the video data - to use as little FPGA Block RAM as possible, I am guessing I would want to use some kind of 'iterative summing' of the pixels coming in, rather than storing a whole frame of picture data and then averaging the colors. Any hints with regard to implementing this algorithm? How to get started with this is my greatest hurdle.
I have investigated the source code as to where I should 'tap into' the video data. This looks like the appropriate spot:

I know, this image is long - it is the best I could do while making it clear to read. Blame Xilinx's tool for that!
This seems to take in the TMDS data and output 8-bit for each color.
I should have some kind of state machine for the LED driver - every clock cycle, it gets the pixel info from whatever module I create to process the video data.

Sorry if this is wordy or long - I'm trying to be thorough...I just need some help getting off the ground with this. This is my first attempt at an FPGA project - some may say its too difficult for a beginner but I say ... gotta start somewhere :) Thanks for reading.


texts: I'm working with a buck/boost LED driver that uses a 0->10V dimmer input. I would like to use the output of an open-source LED module as a switch for the LED driver. The LED module outputs 0 V in the "off" condition and 6.5 V in the "on" condition. I want to use one of the channels to control a high-power Cree LED using the buck/boost driver. So I would like to boost the 6.5 V output of the LED module to the 10 V required by the LED driver for full brightness. Is an op-amp the best way to do this?


texts: Charge a Lipo battery and power a circuit

texts:
I purchased this LiPo charger and I plan to connect the GND and BAT connections to the battery and an external circuit at the same time.

In the datasheet the reference drawings are for battery charging only but there is a part that says:

  The MCP73831 is designed to operate in conjunction with a host microcontroller or in a stand-alone application

Which makes me believe it's intended to power a microcontroller as well.

My question is about connecting the battery and the external circuit to the BAT input at the same time while charging the battery. How safe is this?

I know the LiPo charging process goes through Constant Current and Constant Voltage, but if there is going to be an external circuit in parallel, I guess this can mess with the Constant Current part, since the Charger will regulate a constant current for both of them, while the current going into the battery might not be constant, since the external circuit current demands might change with time. Is this safe, or can it damage my battery?

To be fair, my circuit will be a low power one, but I rather to read an answer that covers all the cases so I can prevent issues with future projects as well.


texts: Voltage divider output with analog voltmeter

texts: I'm using a voltage divider to bring down 24V to 5V and attaching the output to an analog voltmeter gauge. So my question is should I be counting the resistance of the analog gauge into the value's of the resistors of the voltage divider and vary as needed to get my 5V? (see attached diagram)


texts: Simple method to pulse Blue LEDs from sub-Vf voltage

texts:
I have a design that runs from a lithium coin cell battery with a nominal voltage of 3V but running down to ~2.2V. I'd like to be able to momentarily (~250-500ms) pulse a small Blue LED with a Vf of 3.3V

I am aware of conventional options like voltage converters, the joule thief, etc. but I am looking for a very simple, low cost, and power efficient method to drive this LED with the battery I have. A microcontroller with various peripherals is available on the board.

Any clever suggestions? Is a voltage doubler via microcontroller PWM a reasonable method to drive a few mA?


texts: Does heat affect the magnetic field of an electromagnet?

texts: I know that heat destroys perm magnets, but how about electromagnetics? Does heat affect the strength of an electromagnetic field?


texts: How can RDA5807M get away with very high PLL multiplication?

texts:
An FM radio receiver IC RDA5807M has a VCO local oscillator operating on the order of 100 MHz (implied by "low IF" in the datasheet), yet it can get its reference from a 32768 Hz watch crystal. Because of very high PLL multiplication ratio, there ought to be huge phase noise at the output of the VCO (70 dB increase over reference signal).

How did the chip designers get away with it? Phase noise degrades selectivity. FM stations are packed quite tight, not to mention issues whenever tuned station is weak and adjacent interferer is much stronger (actually a realistic situation).


texts:
I want to select LEDs for a specific application. My requirement is as stated -

I have a beacon. this should be visible to a person at a distance of say 50feet.
Smallest form factor as weight is a criteria.
Visibility is the only criteria. I am not trying to illuminate a surface.

I want to know how can I go about selecting the LEDs for this particular application ? I understand that Lumens is the unit. Say, I select an LED of 500Lumens, how can I calculate the distance at which its visible ? Also, if it is visible, is it enough to be perceived as a legitimate source ? Probably this might require some field tests.
Also, are LED lumens additive ? Say, my requirement is 2000lumens, can I use 4 LEDs of 500LUmens to get the same effect ?


texts: How to add a power-on led in whis circuit?

texts:
I would like to add a power-on led on this circuit (which is part of this project)

I would like the LED to switch off when the SW1 is in OFF position.
I was thinking of adding a LED in series with a 1500 Ohm resistor between pin 14 and pin 11 of DC1, but I am not sure this is a good idea, because DC1 would need to sink current and I think it can't (or at least I wasn't able to get this information from the datasheet).

Adding a LED between Pin 14 of DC1 and GND would cause a load displacement between the two outputs of DC1, or am I wrong?

Also please not that I removed U3 in my design, because I don't need +5V.

EDIT: As correctly pointed,  a LED between pin 14 and pin 11 of DC1 would always be switched on. I would then put it between pin 6 and pin 3 of SW1.


texts:
I am trying to implement a current shunt sensing circuit. This should be automatic and currently i want it to measure uA to around 200mA, and Change to the mA range at around 200uA. This is to profile sleep and active profiles in micro controllers. It will then finally interface with an ADC.

The circuit comprises of the following:

2 x LTC6102 - These are current sense amplifiers and are fed with two different size shunt resistors. 10 ohm for the uA range, 10m ohm for the mA range.
1 x LT1016 Comparator active low - I am using this here for switching to the mA range. With a reference of 3v3.
1 x PMOS - Using this to short the connection of the 10ohm resistor when the current changes to mA.

So the ideal theory of operation is:

Measuring low amount of uA. Micro controller turns on and consumes mA this causes the node uA to saturate, turn on the compartor and thus on the PMOS shorting the 10 ohm resistor and now we use the 10m.

Here is the circuit in LTSpice

Issues

The issue i have with this is it just doesn't work. I don't know if this is due to the fact i would need some kind of delay in the switching and sensing of M2?

I also have an issue with the common mode voltage input. So when using 5V the LTC6102 will output the correct gain when saturated, this is given by Av=R3/R2 which is 1650 in both amplifiers. However when using 3v3 this same gain does not work seems around a 1/4 of the voltage output?

I can provide current/voltage profiles if needed


texts:
Actually, I really wonder that what is the cycle mean? How to count the cycle?
What is the real meaning of cycle life in the curve offered generally by manufacture.


texts: Do microprocessor have any special hardware to do division and multiplicaiton?

texts:
My old school understanding is that multiplication is nothing but successive addition and division is nothing but successive subtraction. So, my question is there any changes being done like do we have a hardware that does the division and multiplication in one machine cycle or go.
For e.g, if I have 2 registers of 64 bits, and if I multiply them, I can get an overflow i.e. I need two 64 registers to store the result. So, when I do multiply do the modern RISC processor does successive addition behind the scene or does it do just multiplication. Is there a hardware that can do just multiplication rather than using full adder?


texts: Signed Addition of two std logic vectors while looking for overflow and carry

texts:
I have what I think to be a working implentation for finding the sum of two signed 32 bit (std_logic_vector) vectors in which I chose to expand the result to always have 33 bits so as to preserve the sign bit while being able to check for carry out with the expanded bit.

My method seems incredibly dirty and I was wondering if there was a cleaner way of accomplishing my goal, for future reference.

sum <= std_logic_vector(resize(signed(std_logic_vector(signed(a_alu32) + signed(b_alu32))), 33));
c_alu32 <= sum(31);
--overflow--
if ((a_alu32(31)='0' and b_alu32(31)='0' and sum(31)='1') or (a_alu32(31)='1' and b_alu32(31)='1' and sum(31)='0')) then
  ov_alu32<='1'; --logic to check for overflow
else
  ov_alu32<='0';
end if;

--removing the extra bit through concatenation to achieve my 32 bit sum
o_alu32 <= sum(32) & sum(30 downto 0);


texts:
Is it possible to make a 16-to-4 encoder using just 4 8-input NAND gates?

Encoders are generally implemented using or gates from my understanding. Can anyone provide any insight into developing an encoder with NANDs?

Tricky! I can't figure this one out.


texts: Measuring a huge resistance on low voltage

texts:
I was thinking on this theoretical experiment for a while, but nothing useful came into my mind.

We have a "resistor" (rather a material like plastic) with a resistance expected to be very high, say 10^5 Mohms. Is it possible to measure the accurate vaule of the resistance with a max. 25V DC power supply (higher voltage damages the resistor) and a multimeter with max. 0.5μA resolution? (This is the main problem: if you connect the resistor and the meter serially to the scource, the meter won't show any current: \$ I = \frac{U}{R} = \frac{25}{10^{11}} = 2.5 \cdot 10^{-4}μA. \$ ) You can use any simple circuit element like resistors, capacitors, diodes etc., maybe really simple ICs like amplifiers at max. The solution does not have to be a circuit: the only aim is to get the accurate vaule of the resistance.


texts: Why can't I see a drop in amplitude on a scope when I induce RF on one side of a toroid compared to the other?

texts:
I put various "clip on" or bead toroids on a single wire and introduced a 7 MHz signal into one side of it.  I looked at the amplitude on a dual trace scope and it is the same.
Should it not have dropped significantly?
I am showing the same RF voltage coming out as going in.


texts:
This circuit

simulate this circuit – Schematic created using CircuitLab

can be regarded as an RC series circuit with a lossy capacitor. The time expression for \$V_C(t)\$ with \$R_2 \to \infty \$ is available here and it is \$V_C(t) = V_0 (1 - e^{-t/\tau})\$.

I would like to obtain the same expression, but in this situation.

\$ V_0 \$ is the DC voltage generator; the switch is closed for \$t \geq 0\$ and \$V_C (t = 0) = 0\$ (capacitor initially discharged).

I can write

$$\frac{V_0 - V_C (t)}{R_1} = I(t)$$

$$\frac{V_0}{R_1} - \frac{1}{R_1 C} \frac{dQ(t)}{dt} = I(t)$$

which is the current across \$R_1\$ and so the total corrent entering \$ C // R_2 \$. \$V_C (t)\$ is variable during the capacitor charge. The fact is that here \$I(t)\$ is not simply \$dQ(t) / dt\$, because not all the charge exiting from \$R_1\$ goes through the capacitor: part of it flows across \$R_2\$ and this amount of "leaked" charge changes (raises) with time. So, how can this be taken into account?

Are there any hints to obtain a differential equation for the charge or the current of the capacitor?


texts: Benefit of LC tank circuit for signal generation?

texts:
Suppose I want to drive an alternating current (100Hz, 200mApp) across an inductor to generate an electromagnetic field.  What are the benefits, if any, of using a capacitor in parallel to create an 'LC tank circuit'?

The two possible benefits I can think of:

Keeps more of the energy local (via capacitor storage), so that less current has to flow through the earlier part of the circuit.  For example, the output impedance of the current source may be 50 ohms, thus causing additional power dissipation.  However, the inductor resistance is fairly large (~100 ohms) in comparison to the inductance (50-100 mH), so it seems like the coil will dissipate power fairly quickly, and thus heavily 'damp' the LC oscillations.  I do not know how to quantify the damping or capacitive energy storage, though.
In case of a noisy driving signal, the LC filtering can suppress undesirable frequencies.  However, I expect to deliver a fairly clean signal/current to the inductor, so I don't forsee benefits analogous to a receiver LC circuit.

Edit After further consideration, I am going to say that there is negligible benefit of having a parallel capacitor in this case:

With regard to local energy storage, the LC tank can store at most (see here) $$\frac{1}{2}LI_{max}^2 = \frac{1}{2}(.1)(.1)^2 = .0005$$ Joules.  On the other hand, the resistor will be burning power at the rate of $$I_{RMS}^2R = (\frac{.1}{\sqrt2})^2 100 = .5$$ J/s (or Watts).  I am not sure how to interpret the energy storage of the LC tank relative to the inductor's thermal dissipation, but it seems very small by comparison.
Any filtering effects would be largely diminished due to the large inductor resistance (and thus low Q or \$f_r / BW\$).  Specifically, it can be shown for this circuit (see here) that $$Q = \frac{2\pi f_rL}{R} \approx .63 $$  This means that the half power bandwidth is ~160Hz, which extends from 20Hz to 180Hz and therefore is not very selective.


texts: power supply unit for Arduino/solenoid project

texts:
I'm trying to find an off the shelf plug in ac/dc power supply unit to work with my project.
I want to power an Arduino Duemilanove and six 12v 1A solenoids.
Here's the solenoids ->
http://www.rapidonline.com/productinfo.aspx?&tier1=Electronic+Components&tier2=Relays+%26+Solenoids&tier3=Solenoids&tier4=PCB+miniature+solenoids&moduleno=29536&catref=60-3210

I'd like to buy one of the power supply units from this page ->
http://www.rapidonline.com/Electrical-Power/Power-Supplies/Plug-In-PSUs

But I don't know how to work out the right one. Cheers


texts:
I wonder if I can replace a BJT transistor operating in active mode, with its Thevenin Equivalent, like this:

My guess is that I can, because the large signal model of the BJT operating in active mode is made of linear components:

Assuming that it's possible to apply the Thevenin Equivalent, how should I compute Rth? I know that I should set the independent sources to 0, but should I consider  VEB(on) = 0.7V as an independent source?


texts:
I am trying to make a connection between smartphone and Arduino. I found a method which uses an Ethernet shield. Ethernet shield is connected to the router.

I wonder is Wifly shield is also a kind of wireless "Ethernet shield".

Is the only difference between Wifly and Ethernet shield is that one is wired to the router and the other is wireless connected to the router?

Can I use Wifly instead of Ethernet shield?


texts: STM32F103, Having trouble nesting interrupts

texts:
I'm trying to interrupt into a USART handler from inside an RTC_Alarm handler, but it doesn't work.

I have set the NVIC:

void NVIC_Configuration() {
NVIC_InitTypeDef NVIC_InitStructure;

NVIC_SetPriorityGrouping(NVIC_PriorityGroup_4);

/* Configure UART IRQ */
NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

/* Configure RTC Alarm IRQ */
NVIC_InitStructure.NVIC_IRQChannel = RTCAlarm_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 15;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);
}

I have also noticed that my SysTick handler also isn't running while executing code inside the RTC_Alarm handlers.

How do I get the interrupt to nest ?

Here is some of the rest of the code:

So I have this loop waiting for an interrupt from a UART to set the CurrentMode, but the interrupt never occurs. The same interrupt works in the rest of the code.

void RTCAlarm_IRQHandler() {
    /* Reset the Alarm in 24 Hours */
    RTC_Set_Alarm(FALSE, (Get_Alarm_Time() + 3600*24));
    RTC_ClearITPendingBit(RTC_IT_ALR);
    EXTI_ClearITPendingBit(EXTI_Line17);
    RTC_WaitForLastTask();

    Op_Mode_Type SwapTemp = CurrentMode;
    CurrentMode = ModeOnAlarm;
    Alarm_Mode(SwapTemp);
}

void Alarm_Mode(Op_Mode_Type Initial_Mode) {
    /* Enable USART Interrupt */
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    NVIC_EnableIRQ(USART1_IRQn);
    switch (ModeOnAlarm)
    {
        case Op_Mode_Single_Color:
            Set_Color(&Alarm_Color);
            while(CurrentMode == Op_Mode_Single_Color); //TODO - Add Timeout + UART Isn't interrupting here
            break;
//Some more cases here....
    }
    CurrentMode = Initial_Mode;
}

void USART1_IRQHandler() {
    uint8_t data;
    if (USART_GetITStatus(USART1,USART_IT_RXNE)) {
        data = USART_ReceiveData(USART1);
        CurrentMode = (Op_Mode_Type)(data);
        USART_ClearITPendingBit(USART1, USART_IT_RXNE); // Clear interrupt flag
        /* Disable USART Interrupt */
        USART_ITConfig(USART1, USART_IT_RXNE, DISABLE);
        NVIC_DisableIRQ(USART1_IRQn);
    }
}

Functionally I don't really need to use the interrupt in this code, but I want to understand why doesn't it work.


texts:
I need to design a boost converter that outputs ~20 mA DC and  an unloaded voltage of around 68-100 V. The inverter will be part of a Zener diode analyzer.

I built it on the idea of the Joule thief (blocking oscillator). During breadboard experiments at some point the base biasing diode burned.

I suspect it is due to transients from the base winding. Since then I modified the design to try and suppress the transients and not exceed the Veb voltage of the BD139 (is -5 V).

Also the shut-off transistor(BC548) was getting hot. From simulation it looks like it's also from transients(high voltage applied to collector).

My schematic values are different from the actual ones and component annotations.

T1-main switch-----BD139-16
R1-base bias resistor----10k--->~1mA base current for the transistor
D1-base bias diode ----1N4148--->Vf~=0.65V
C1-filter cap for the bias network(release some voltage stress from D1)
R2-main switch base resistor(should help prevent high currents in D2,D1 and keep Vbe>-5V)----10nF
D2-T2 protection diode ( a path for current to flow trough R2 away from the T1 base and T2's  collector)----1N4148
T2---switch off transistor(takes away the T1 base current when the output voltage is too high,the Zenner conducts in the reverse bias and turns on the optocoupler's led)
R3---T2  base current and fototransitor's  current limit resistor.(since BC548 has high hfe can be a larger value ~10k)
D3----T2 base biasing diode--->Vbe T2~=0.65V
D4----T1 collector protection diode(stop the high voltage spikes)
D5----Output diode(any fast rectifier diode i'll use SF 28 G)

Will this design will work and if not what improvements can be made?
Will I need a higher base drive current if the collector inductor will have smaller values (~10-22 uH)?

I'm intrested about other other designs too, but my main focus is to keep the inductor's physical size low.


texts: Is there a generator that injects current into high impedance voltage source?

texts:
For example, having battery with high (few megaohms) series resistance, is it possible to convert mechanical energy to current at that battery's voltage?

Or in other words, if I have low voltage, high current generator like homopolar generator, is it possible to use high impedance voltage source (battery with high resistance or an electret) to increase the generator output voltage?

The question basically is: is there a generator that utilizes external electric field in addition to conventional magnetic field. Conventional generators utilize electromagnetic induction (changing magnetic field) or magnetic field part of Lorentz force (Laplace force). I'm asking about a generator that utilizes both magnetic and electric field.


texts: Does anybody have PCIe (3.0) aka PCI Express module card edge connector technical drawing?

texts:
I was searching through the internet to find PCI Express card edge connector footprints / technical drawings / pin spacing / layout of the module cards that you stick in these connectors you can find on a modern PC/server motherboard.

I wasn't able to find anything so I thought I could maybe ask here? I found some for Altium Designer which I don't have access to and also I am using (Autodesk) Eagle.

If you are wondering, I wanted to create a PCIe 3.0 x8 card that could hold two M.2 NVME SSDs since I could not find this anywhere either. Everyone only sells the type that holds one NVME (PCIe) and one SATA SSD. This is not what I need.

M.2 NVME interface is basically just a PCIe x4 interface, in another form factor. Therefore I don't see a problem with making a x8 standard card for PCs/servers that could hold two of those and properly route their interfaces.

Can anyone help? Thank you!


texts:
I am making a cutoff switch for a SLA battery using the this circuit

V2 is the SLA battery, V5 is 0V or 5V coming from a some other logic circuitry. The simulation comes out fine. I understand that the parameters for the FET's are different (between simulation and my FET), but Rds(on) is low enough that it shouldn't effect it. I am using this P-Ch FET AOD403.

When I put a large load (5A) on the output, I see an output drop(droop) of ~1.0V, so ~11V across the load. Why is that happening, and how do I fix it?

@5A VGS = -11.5V

@5A VDS = 23mV


texts:
I am currently using a KE-25 oxygen sensor which is galvano microcell type oxygen sensor which doesn't require a power supply to sense oxygen level in the environment. Depending on the concentration of oxygen % in the air it gives an equivalent voltage output.

I have to interface this sensor with PLC, but the PLC doesn't sense such mV output so I am trying to convert 0.5-75 mV to  0-10 V which can be read by my PLC.

So please help me to find out which amplifier I should use to boost mV to V.


texts:
I am using a Board with a Cortex M0 to sample signals from force sensors. The sensors have a resistance that corresponds to the force applied, so I am using voltage dividers and read the voltage with the MCUs ADC.

Since the board only has 6 GPIO/ADC ports but I want to connect 10 sensors, I added a 16:1 multiplexer and use 4 GPIOs to select the channel and 1 GPIO ADC to read the signal.

I am designing a little PCB for the multiplexer and the voltage divider resistor. It will get connected to the sensors and the MCU board with cables.

Will I need decoupling capacitors? I guess I should add one between the multiplexers GND and VIN (see C1 in schematic). What is a reasonable value for it, and do I need additional ones?

Datasheet for multiplexer: CD74HC4067