texts: AC-coupled RF Microstrip routing over power plane

texts:
If I route a 433 MHz AC-coupled RF microstrip trace out of an MMIC such that it's referenced to a Power plane rather than a Ground plane, will that have a significant effect on the impedance of the trace?

I'm designing a 4-layer PCB with a Signal-Ground-Power-Signal stackup which has MMICs on both sides (this amplifier being one example). This makes me want to run microstrip on the bottom such that it's referenced to Power rather than to Ground. I'm aware that this is OK for digital signals (this page from Henry Ott being what finally convinced me of that), and I've read through Microstrip over power plane, but there are a few things that make me leery of blindly applying those conclusions to this situation.

1) This isn't a push-pull driver like the ones in the paper, it's a Class C amplifier (some of the others are Class A). This means it's not symmetric and if I understand right there's likely to be significant inductance from power to collector when compared to emitter to ground.

2) MMICs have a nice big flat low-inductance ground connection through their thermal pad, but typically only a few pins for power. I can only assume any microstrip on-die will be referenced to that ground plane, which I'd imagine would create a discontinuity when transitioning to the PCB microstrip.

3) Eventually this all runs into a coaxial connector whose shield is connected to ground. Unless I connected shield to power (which seems like a terrible idea), wouldn't that create a pretty significant discontinuity as well?

Can someone clarify this for me, ideally with a level of specificity comparable to that Henry Ott paper? I'd really appreciate it!


texts: Appropriate resistor values for 5V LNK low-power supply in CC mode

texts:
UPDATE: QUESTION SOLVED/CLARIFIED. PLEASE REFER TO THE LAST "HAND MADE" SCHEMATIC IN THE SERIES OF PICTURES BELOW, AND READ MY FINAL "SOLUTION".
Original question:
*
I wonder what would be the R27 value for this Power Supply (non-isolated, LNK IC-based, 5V dc 80mA nominal output in CC mode), given that original SMD resistor got off and lost, and I’m not much used to this kind of PS. Please feel free to comment on my scratched schematic and also to visit my other thread in which I post about a problem related to insufficient “fuel” from this in a ESP01+AtMega Tiny85 coffee machine control project...
Thanks So much in advance folks!
*
PS1- Please notice I had an errata for the R2 value, see my comments below.
PS2- Adding datasheet for the AC-DC chip.
PS3- Adding corrected schematic.

DATASHEET


texts: Options to control (fast switch) a 12V LED DC with MCU - mosfets vs. relays vs. SSR vs. mosfet relays vs. something else?

texts:
(Newbie alert) I have a 12V 3A light that I want to control in a ~12V DC circuit (lead acid battery, stator coil). The light shares a common ground with every other light unit in the circuit. I was looking into options how to control it with Arduino or similar microcontroller. I found few options and I have few doubts.

nMOS: most examples and cases have them connected between the load and ground. Since all the light loads in my circuit are sharing the same ground, this looks problematic - would wiring a separate ground for that one controlled light with nMOS be a safe practice?

relays: I'm aware that these are the simplest solution, but since I'm doing this as a practice project, I would prefer a device that bit more "new tech" so to speak

solid state relays: I've looked on few catalogues and it seems most of SSRs are for controlling AC loads, and few of DC variants I've found are limited to 1A or some low number.

mosfet relays: I found this on Omron website (link) but my level of understanding finds it too convoluted and there seems to be lack of youtube videos about these devices, can anyone enlighten me how do these devices work?


texts: ESP32 AND CP2102 Serial data reading issue

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I have a PCB on which i am taking a 5v - 1A DC power supply , and again providing 3.3v to ESP32 through AMS-1117 3.3v.
Basically things are not working on when i solder the esp32 on my pcb but things are working when i check it with NodeMCU version of ESP32 ( development board with USB connection ).
My question here is , for a dubugging purpose ( to check the flow of my program ) can i connect the CP2102( USB to TTL converter ) to the esp32 ( RX,TX connections ) and a common Ground ( CP2102 Ground with PCB's Ground ) and get the data on the Serial Monitor on the laptop where CP2102 is connected.

I am attaching the image which will describe my idea more.
Please guide me.


texts:
I have a Kinera Idun. It's an IEM with multiple drivers (2 balanced armatures for highs, 1 dynamic driver for lows).

I was listening to some Lo-fi music when right side bass simply disappeared. I can't think of a reason why. It still works great, except without any bass on the right side. During a sine sweep, it's silent below 40 Hz, with volume slowly ramping up until it's equally loud ≥1.7 kHz.

I've verified that the dynamic driver itself was bust, not the wires and solder joints.

Due to budget constraints, I've decided to go the repair route.

How do I look for a replacement speaker? Specifically, what parameters are commonly considered? I tried my best at filtering results, but there's so many. An example below from Digikey:

More photos on this Imgur album: https://imgur.com/a/MBFcfav


texts: How is the cut-off frequency is set relatively to the signal of interest in a simple RC filter?

texts:
My question is simple. If I have a signal of interest max 30Hz and below what cutoff frequency should the RC low pass filter be set to?
Similarly, if I have a signal of interest min 30Hz and above what cutoff frequency should the RC high pass filter be set to?

I don't think the answer is fc must be set to exactly 30Hz, thats why I asked. Is there a rule of thumb and logic behind setting fc versus max/min signal of interest?


texts: Regulate brightness over video composite signal

texts:
I have a b/w camera that outputs a video composite signal. At night it works very well, but during the day it's so bright everything just turns white. Is it possible to add a potentiometer to be able to dim the brightness?

If so, what resistance value should I use and how should I connect it, in series with the video signal or a to-ground from video signal setup?


texts: Unusually clean 5 kHz noise from BLDC motor

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The noise does seem to pulsate but I'm not sure how I'd go about measuring the beat frequency.
I'm driving this thing with 2 L293D (works fine with just one, heats up a bit though,) and feeding a sinewave in the form of a PWM (with frequency 32k hertz) phased 120 degrees apart.
The code I'm using is this:
https://github.com/juanpablocanguro/BRUSHLESS-MOTORS/blob/master/open_loop_youtube.ino
This user seems to have hit a similar problem:
Noise in BLDC motor with 32kHz PWM
I have two questions now:

Where's the noise coming from?
What can I do to get rid of it?

Since the frequency is so consistent I thought of using a simple passive filter, but I'm not sure of the coil inductance and I have no means of measuring it. Is knowing the coil resistance enough to make some kind of filter? I wonder if I can impliment some LR high pass filter.
I also checked my power supply, it seems to be droning around 1.5kHz, nothing around 5kHz.
Changing PWM frequency seems to add more harmonics but the peak is still 5khz, perhaps this is a hardware related?


texts: Implementation of complementary filter and output of sensor while stationary

texts:
The code for a complementary filtered angle is not outputting the expected angle.

I can get close to 90° using arctan formula from the accelerometer sensor data. Whereas, the complementary filter angle output is just around 1.717.

Also, I am not able to get 90° on the integrated gyroscope data.
So, can anyone help and check to see if I did implemented the complementary filter correctly or not?

def read_GyroscopeScaled (try_xAccelRotation, try_yAccelRotation):
    start_time = timeit.default_timer()
    data = bus.read_i2c_block_data(0x68, 0x43, 6)
    xGyro = data[0] * 256 + data[1]
    if xGyro > 32767 :
        xGyro -= 65536

    yGyro = data[2] * 256 + data[3]
    if yGyro > 32767 :
        yGyro -= 65536

    zGyro = data[4] * 256 + data[5]
    if zGyro > 32767 :
        zGyro -= 65536

    xGyroDPS = (xGyro - GyroxOff) / Gyro_scale
    yGyroDPS = (yGyro - GyroyOff) / Gyro_scale
    zGyroDPS = (zGyro - GyrozOff) / Gyro_scale
    end_time = timeit.default_timer()
    current_time = end_time - start_time
    dt = current_time - previous_time
    xGyroAngle = xGyroAngle + xGyroDPS * dt
    yGyroAngle = yGyroAngle + yGyroDPS  * dt
    previous_time = current_time
    cfXangle2 = 0.98 * (cfXangle2 + xGyroAngle) + 0.02 * (xAccelRotation)
    cfYangle2 = 0.98 * (cfYangle2 + yGyroAngle) + 0.02 * (yAccelRotation)
    print ("X-Axis Degree per second : %.2f" %xGyroDPS)
    print ("Y-Axis Degree per second : %.2f" %yGyroDPS)
    print ("Z-Axis Degree per second : %.2f" %zGyroDPS)

n = 0
while n!=1:
    try_xAccelRotation, try_yAccelRotation, NetAcceleration = ADXL_read_AccelerometerScaled()
    read_GyroscopeScaled(try_xAccelRotation, try_yAccelRotation)


texts: What is necessary to drive two op amps (tl071 for instance) from one piezo guitar pickup, which of course is a very high impedance source? Result being, one very high impedance source creating two identical low impedance outputs that are isolated from each other. I have looked at a great number of buffer circuits, but none address the issue of using one source to drive two op amps. Thanks so much, for any help. Jon


texts: Will current flow through both loops of the 2nd circuit?

texts:
I have following two circuits. In 1st circuit(figure 1.a), I can join ground terminal of R2 with node D,so that current can flow as in loop A-B-D-E-A and loop B-C-D-B.

But I am confused with figure 1.b. In this circuit, current can flow in loop as M-N-S-T-M but I don't understand can there be current flow in the loop O-P-Q-R-O or not?


texts: Transmit a signal using RF transmitter/reciever without using microcontrol or a decoder/encoder

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Objective: I am trying to build a transmitter that transmit an on signal when a button is push. The transmitter will need to be small enough to wear or hold in a pocket. I prefer not to use any microprocessor or encoder for the transmitter. For the receiver, it have to be able to receive the signal from the transmitter and play an alarm.

433Mhz RF transmitter and receiver: https://www.amazon.com/UCEC-XY-MK-5V-Transmitter-Receiver-Raspberry/dp/B017AYH5G0/ref=sr_1_1/163-3850928-5773553?ie=UTF8&qid=1470685976&sr=8-1&keywords=rf+transmitter+module

Question: I am planning to use a 433Mhz RF transmitter and receiver. Since I am only sending an on signal, I wonder if I can just send a voltage as a signal or data through the data pin on the transmitter chip. Would that be possible for the transmitter to transmit such data and for the receive to interpret it as a 1 or an on signal?


texts: Does a PID provide any benefit if there are no time and mass constants?

texts:
I have a 120V PID with an internal relay (output rating of 5A) using a K type TC. The plant is a 275W  band heater wrapping a cup, attempting to maintain a set temperature.
A substance is added to the cup at varying time intervals and is boiled off. Then the heater brings the cup back to the set temperature, but because the cup is empty during this process there is a lot of overshoot.
Is a PID of any value in this situation or would an on/off function provide the same service?
Everyone reading this is smarter than I am in this subject, so please help me out. It appears to me that though this product is traditionally using a PID, since there is no time constant to filling the cup and no constant as to what is in the cup, that a PID is of no use. Am I thinking correctly?


texts: Make larger capacitance using multiple capacitors?

texts: Can I connect five 100μF capacitors in series or parallel to form 500μF in total that I can use like a regular 500μF capacitor? (Apologies for noob question.)


texts: Does the quartz crystal in the standard clock vibrate the same frequency as the sweep motion one?

texts:
In the standard quartz clocks/watches,the quartz crystal vibrates 32768 times
per seconds(32768HZ),while this frequency is divided by an electronic counter(15 bit binary digital counter)to derive one second pulse,which drives a step-motor.
Most of the quartz clocks have a second hand which ticks once per seconds,due to the explain above,but there are,also,quartz clocks which their second hand ticks several times per seconds and they called"quartz sweep clock movements".
Do on those quartz sweep clocks,the quartz crystal vibrates at the same frequency(32768 HZ)as the standard ones?while the counter is,actually,just divided the  32768 frequency to a request frequency value?I mean,if the second hand ticks 4 time per second,Does it,actually,use a 13 bit binary digital counter,which produced 4Hz?

Thanks


texts:
I've followed advice on the web on how to use "bandgap" voltage reference to measure supply voltage, however, the measurements are not as accurate as the ADC can be on an Arduino Mega.

On the one hand, I've measured the 1.1V ref to actually be 1.087V using a DMM to measure the voltage across a capacitor from AREF to GND with the appropriate code.

On the other hand, measuring the BG internally with the ADC using the attached code returns an ADC average reading of 226.5 which is 1.107V with a 5V supply (measured using a DMM from the 5V pin). This is a 20mV error. I've being getting about 5mV accuracy when using the ADC to measure an external voltage source.

The Arduino Mega is powered via USB.

An external supply of 1.087V was simultaneously (alternately) measured with the analog pin yielded a different reading. What is the difference between the two passes?

#define N 128
#define ND 128.0D

int analogReadBG(){
  uint8_t low, high;
  ADMUX = 0;
  bitClear(ADCSRB,MUX5); // Set ADC input as BG (1.1V)
  bitSet(ADMUX,MUX4);
  bitSet(ADMUX,MUX3);
  bitSet(ADMUX,MUX2);
  bitSet(ADMUX,MUX1);
  bitSet(ADMUX,REFS0);  // Set 5V as ADC reference voltage

  for (int i=0;i<7;i++){ // Perform several converstions for reading to settle
    bitSet(ADCSRA, ADSC);
    while (bit_is_set(ADCSRA, ADSC));
  }
  low  = ADCL;
  high = ADCH;
  return (high << 8) | low;
}

void setup() {
  Serial.begin(115200);
}
long movingSum;
double movingAverage;
void loop() {
  movingSum = 0;
  for (int i=0;i<N;i++){
    movingSum += analogReadBG();
  }
  movingAverage = movingSum/ND;
  Serial.println(movingAverage);
  delay(1000);
}


texts:
I have to create an adapter that will take a pot(it is a piano pedal) to 3 states, full, half, and off. That is, the piano only supports what is called half-damper and not continuous control so I have to modify the pedal so it works. The issue is I do not want to have to supply a battery nor design a complex circuit.
Here is the specs:
The paino has 3 inputs, F, H, and Gnd. F and H are pulled up to 3.3V by 10k. The pot on the pedal is 10k but only ranges from 9k to 2k. I replaced the pot so it goes from 135k to 93k. Clearly half way between these ranges is the half damper setting.
Normally the pedal would simply act as a voltage divider and the piano would read the voltage from 0 to V and that would correspond to the damper value. In this case F must "float" and H is grounded gives half damper. For full dampening F and H must be grounded. When F and H are floating no dampening takes place.
Hence this is just converting the high resistance to F = H = 1, the in between to F = 1, H = 0, and the low resistance to F = H = 0. Clearly though the pot can be reversed(and ideally a simple switch can do this because sometimes the effects are different).
I feel that there is some way to rig up a simple circuit so it works but since the pots do not go all the way to 0 and the pullup resistors are so high it seems to make it difficult. I can't really change the pot range as the actuator arm mechanics is fixed.
It doesn't have to be perfect although I think some hysteresis like effect would be required because unlike a real piano you can't "recover" the dampening. This means that if you enter H or F mode and then back off quickly then renter you get nothing. Hence any jitter around these values could cause problems. I'm not sure how the piano handles it though. It doesn't have to be all that robust beyond these issues. As long as it works then it works.
Although I guess I could try to modify the pullups to provide more drive.... that might be the way to go but might cause problems with the uC. I might be able to add a VCC pin that gives more drive directly too so two comparators could be run. I'd ideally like to just use a few transistors though.
Any ideas?


texts:
I'm trying to wire a CVBS-to-RGB converter into my car's monitor that only supports Navigation Maps with an old-fashioned technology of displaying picture via RGB signal. All the wiring is done via a 14-pin relay to switch between either the camera signal (r,g,b,s) or the navigation signal (r,g,b,s).

Now, which wire gauge I should use here to display the video signal? Also, copper or aluminum? to avoid as much distortion as I can.


texts:
My next robotics project is a "1 cubic inch robot" and I am planning to add a 2 way wireless communication between my robot and a computer. Since for that size Power is a big bottleneck the best I could come up is a IR transceiver. So how can I achieve this ?

If I use a 38khz receiver then I might end up receiving the same transmit signal ? what Is the best option I can use in my application ??


texts: I want to print a breakout board for CH201 sensor on EAGLE

texts:
I am completely new to the world of printed circuit board design.
I want to connect this CH201 ultrasonic sensor to a breadboard, but the sensor is extremey small and the pins are the width of wires. I need to make a breakout board on EAGLE so it becomes slightly easier to solder it and use it on the breadboard. The problem is I don't know how to even get started on creating the EAGLE design.
What components I need?
I have created a model for the CH201 sensor, but what kind of holes do I need on the PCB? Do I need thru holes on the sides which extends inwards to connect to the CH201 pins (something like this?)
Just a general overview of what I should be doing would be extremely helpful as I can research on my own once I get the basic understanding.


texts: Driving a Fan using TIP120 to PWM from Arduino

texts:
So I have recently started my first group project, which is to design an autonomous hovercraft. We decided to drive the propulsion fans (which are rated at ~7 V and our battery runs at 12 V) using a TIP120 transistor.

We found the design online and it seemed to match our situation, so we used it. The problem is that when we connect the battery, the fans do not turn on. I made a quick picture of our circuit:

The original circuit that based ours on is found here.

Is there a problem with the wiring, or did we pick out the wrong transistor?


texts: Driving an LED from a uC pin with the Anode above uC's Vcc rail

texts:
I am using a 3.3V uC (ATMega 328p in Arduino Pro Mini) running from 3 alkalines (nominal 4.5V).  So Vin=4.5V, Vcc=3.3V

I'd like to drive LEDs from some pins, say at 20ma each.  And I was thinking to connect the LED anodes to Vin (4.5v) with the cathode going to the uC pin, rather than putting all the LED currents through the 3.3v onboard regulator.  (Also, while I'll use Red LEDs in the example here, I may want to use Blue as well, which would be more comfortable with a bit more driving voltage).

I figure a red LED at about 2v Vfwd, so the resistor would need to drop 2.5v @ 20ma, say 1K2 ohms.

The issue: this connect a uC pin to a source 1.2V about its Vcc rail (through an LED).

I think we are fine when the LED is on (pin low).  But what about turning the LED off?

simulate this circuit – Schematic created using CircuitLab

Approach 1: Pull uC pin high (3.3v) to turn off the LED.  The LED is between 4.5V and 3.3V, and the 1.2v difference will not be enough to light it - and I THINK it also won't bring the pin too high above its rail.  But LEDs are not ideal devices, hence this question.

Approach 2: tristate uC pin (make it an input) to turn off the LED.  The LED is between 4.5V and the high impedance input (along with it's static protection diode to Vcc).  Again, I hope the LED's Vfwd would be enough protection for the uC pin.

Is either or both of these approaches workable and safe for the uC?

EDIT: substitute 120 ohm resistor above, oops.


texts: What is the most efficient way to power a solar computer (5V) from a 12V lead acid battery?

texts:
My project: Power a Beaglebone Black (BBB) entirely from solar energy. Obviously energy efficiency is crucial here. My setup so far: PV panel connected to a deep-cycle lead acid battery. Now I need to get from the battery's 12V to 5V (2A) for the BBB.

Most similar projects suggest the use of a UBEC (Universal Battery Elimination Circuit), like this one. However, I am not sure if this is the right thing for me. The efficiency curve of a typical UBEC drops pretty badly for low currents. I expect the BBB to spent most of the time idle, i.e. draw around 150 mA, which means that efficiency would be pretty low.

Is an UBEC the best solution or are there more efficient ways to supply 5V/2A(max) for my purpose? Since my soldering arts are rather limited, I would prefer a ready-made solution.


texts: how is the 1PPS signal generated in GPS receivers?

texts:
The question might seem stupid, but the time of flight from the satellite is unknown and moving, the doppler effect is skewing the frequency (and is not constant due to the relative trajectory) and satellites are constantly coming and going to view, forcing a constant change of the reference clock.

Moreover, the 1pps is meant to have low jitter but also be in phase with the UTC clock (but I don't think it is claimed to be accurate in this aspect, it's mostly famous for low jitter).

Here is a secondary question: is the 1PPS phase connected to the carrier wave or to the demodulated signal?


texts: Design a P-Controller given the root locus ?

texts:
I used to have the transfer function given but here the root locus instead ...

Can one help with the start...


texts:
I found this component lying about, anybody have any idea what it is? I found a few people selling them on ebay but no description.
The label says, "NEC 208 D4164D"

Thanks,


texts:
I have a solar system on a boat.
12v  8amp max
The wiring is 12 ga
The digital amp gauge I have has 20ga wire 2”long  ea total is 4”
This wire seems to small. Should I shorten the  gauge wires ??
Is it OK ?? Safe ??
Thanks. Nick


texts:
I want to design a block of combinational logic using VHDL, but occasionally the synthesized result contains an unintentional latch.

What coding guidelines do I need to follow in order to avoid the synthesizer from inferring latches?

Example : in small segment of code, should I use if-else statements?


texts: Modern alternative to TRIAC for switching alternating current?

texts: The only alternative I know is a high power MOSFET wrapped with diode bridge.


texts: How much current can these diodes handle in real world?

texts:
I came across these diodes on ebay today and was very surprised! So surprised that I probably have read something wrong. So I'm asking you guys just to make sure.

Can these little guys literally handle 1000 Volts, and 10 Amps, as in 10 kWatts of power on their own? In my opinion they look too small for that.


texts: Reading 4.2v with the ADC on an ESP8266-12E

texts:
The ESP8266-12E is a low power, blazing fast, MCU with WiFi capabilities making it the best option for small robotics projects. I am trying to measure the voltage of a 3.7v lipo in order to determine the battery life of the robot. The battery, when fully charged, is 4.2v but my regulator drops out at less than 1v. I obviously can not pass the 4.2v from the battery directly into the MCU's onboard ADC, and I know I need a resistor in order to drop the voltage to a certain level under 3.6v (it's maximum voltage rating) and generate a percent on that new scale, but to calculate the value of said resistor, I need to know how much current the onboard ADC for the ESP8266-12E draws.

How much current does the ESP8266-12E's onboard ADC draw?

This is what I came up with:

This should allow me to drop the voltage from the maximum possible 4.2v of a fully charged lipo down to solid 3v. I also added a MOSFET to keep the voltage divider from constantly draining the battery. Anyone know if this will work alright? I am using a barebone ESP that I purchased here. @mkeith, I remember seeing somewhere on a datasheet that the ADC can take up to the maximum voltage of the unit itself, which is 3.6v. I could always redo my calculations and drop the voltage down to under 1v to be on the safe side. I just don't want to lose any resolution in my final percentage if I don't have too. I trust this community more than I trust some poorly translated Chinese PDF.


texts: DIN 41612 connectors are rated at 2A per pin.  Is this the absolute maximum current or RMS?  I want to use a DIN connector for power level audio.  Music signal peaks commonly reach 24 dB (16x) above the RMS level.  If the current rating is RMS, what is a safe peak maximum?


texts: How to turn a pulsed signal into a continuous one?

texts: I have a pulse signal at 1 hz which goes high +5V and low 0V. How do i turn it into a continuous one? +5V. i have searched in different places and what i found says that there are different methods such as using an op amp as an integrator, then i also found that it can be used a diode, resistor and a capacitor, others suggest that a sample and hold circuit can also work. However none of these answers seem to be clear to me. i am still a novice in this matter. Would somebody help me with an answer that has a schematic i could test?. I have also found that a retriggerable monostable can work but i am not sure if this is the right approach, as i need the "continuous signal" to go low immediately after the input pulse is interrupted. If possible i would like to do this using logic gates such as the ones found within 4000 cmos series. Thanks for taking your time reading my doubt.


texts: Demodulating a signal generated by IR LED/ phototransistor pair

texts: I am driving an IR LED with a 20kHz square-wave signal (I may/ may not use PWM) and I am trying to demodulate the signal being generated by the corresponding phototransistor. I don't have access to demodulator ICs so that means I have to build a demodulator using an op-amp. My current plan is to subtract the original square-wave signal from the IR LED modulated square-wave signal using a difference amplifier built from an op-amp. My question is this: Is a difference amplifier a sufficient solution to my problem, or is there a better option out there? Any help would be much appreciated.


texts:
I'm working on a Zynq Ultrascale+ MPSoC and trying to play around with the on and off chip memories. In the following program, I'm trying to place only variable 'x' into OCM (on-chip-memory) where everything else is loaded into external DDR.

#include <stdio.h>
#include "platform.h"
#include "xil_printf.h"

volatile u32 x __attribute__ ((section ("psu_ocm_ram_0_MEM_0"))) = 10;
volatile u32 *p = &x;

int main()
{
    init_platform();

    xil_printf("x = %u\r\n", x);
    xil_printf("p = %p\r\n", p);

    cleanup_platform();
    return 0;
}

The output is:

x = 10
p = 2AB0

So it doesn't look like p is pointing to a variable in OCM memory according to the memory map below.

If I change to linker script to put the entire .data section into OCM (and get rid of the gcc attribute), then the output becomes as I expected:

x = 10
p = FFFC0130

The weird thing is that the .map file for the original program does show that the linker is trying to do something with the variable, I'm just not sure what:

                0x0000000000002ab0                __data_end = .

.tm_clone_table
                0x0000000000002ab0        0x0
 .tm_clone_table
                0x0000000000002ab0        0x0
 .tm_clone_table
                0x0000000000002ab0        0x0

.igot.plt       0x0000000000002ab0        0x0
 .igot.plt      0x0000000000002ab0        0x0

psu_ocm_ram_0_MEM_0
                0x0000000000002ab0        0x4
 psu_ocm_ram_0_MEM_0
                0x0000000000002ab0        0x4 ./src/helloworld.o
                0x0000000000002ab0                x

So it looks like the variable is being placed at the end of the .data section, which is in DDR (for the original code), but I want the variable in OCM. Anybody know what's going on here?


texts: Is a twisted pair conductor intrinsically succeptible to thermal noise?

texts:
I am working with a noise sensitive application where the thermal noise is much larger than was anticipated.
There is a resistive sensor (wheatstone bridge) that is subject to various constant temperature conditions served by a constant current feed and twist pair, shielded  sense.

simulate this circuit – Schematic created using CircuitLab
Typically the twist pair is done to minimize noise and EM. Would there be any other obvious unforseen contribution to observed thermal noise from the TP?
The reason that I believe the noise is Johnson-nNquist and not general broadband noise is because the mean amplitude scales as a square of the temperature pretty well. Although other sources are certainly not out of the question


texts: Different isolation when switching port calibration type

texts:
I have designed a directional coupler in ADS, and when simulating it in Momentum, I realized that depending the type of port calibration (checked on Calibration TML and Calibration None) the isolation of the coupler changes. Why is this happening?

Any help is appreciated!


texts:
let's consider a DC power supply of 5V with for instance 1A of maximum output current (i.e. its maximum output power if 5W).

Let's connect a load R = 1 Ohm. Ideally a voltage source of 5V will give to it a current equal to 5V/1Ohm = 5A. But it is out of the maximum current of our power supply.

What does it happen at circuit level? I suppose that our power supply will provide a current of 1A, so the voltage drop on the load will be equal to 1V. Where are the others 4V?


texts: I am usin this http://www.ti.com/lit/ds/symlink/tps68470.pdf and in the schematic they tell us to connect the WLED_SW through an inductor to an input supply. I though the WLED_SW(switching node) is generally driven by the buck itself. Is there any reason why I need to connect it to the input?


texts: Oscilloscope measurement introduces noise to a motor drive system

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How does connecting the oscilloscope ground introduce noise to a board?

We were probing motor terminal waveform with an Agilent scope.  By merely connecting the scope ground to the negative side of the motor terminal (MTR-), the noise level increases when the motor turns.  Removing the ground clip will reduce the noise to a manageable level.

Here is the relevant circuit diagram:

We have a couple of motor drive boards around.  Some are affected and some are not by connecting the scope ground to MTR-.
Our system is switching the low-side, which is where MTR- is connected.
Even though connecting the scope ground to a point where the voltage is constantly changing does not seem to be a good idea (this is how our customer checking the motor terminal waveform), I am wondering how this introduces noise to our system.  Connecting the scope ground to any other points in the system does not seem to have similar effects.

Does it mean that the system does not have good noise immunity?  Is there anything that I can do to lower the noise?

Thanks in advance.

More info on the noise.  Please refer to the two scope captures below:

The first one is measured by Scope #1 with the scope ground and the probe connected to MTR- and MTR+ respectively.  MTR+ is a rectified voltage from 220VAC.
The second one is measured by Scope #2 with the scope ground to the system ground and the probe to the gate of the MOSFET chip.  These two captures are not synchronized.

Please note that in the second picture, there is noise some time after the normal PWM on pulse indicated by the red arrows.  These spikes sometimes get so huge that the MOSFET starts conducting current to the ground.  The first picture shows when the MOSFET gets triggered by the spikes.


texts: It must sound like a really idiotic question but i am just a novice in electronics, i have two 5v phone chargers that i would LOVE to use to feed a 9v project instead of a 9v battery but i want to know if it will... You know... EXPLODE if i mix their output cables in any way, is there a way to do this? Maybe if i rectify them with diodes? Maybe up-step them so they will give a bigger voltage? I DONT KNOW YOU CAN INSULT ME IF YOU REALLY NEED TO, BUT HELP ME, the project is a guitar amplifier


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Why is it that when I see single MOSFET amplifiers or even complementary ones (one NMOS and PMOS), they would use what in single BJT amplifiers would be called "Common Emitter Amplifier". The output is on the Drain side of the MOSFET. This always outputs an inverted signal.

I could see the advantage in BJT as that would provide the highest voltage sourcing, though it will be inverted. This inversion, I've always supposed, does not matter in the application it's usually used for, say working with 1.) frequency or 2.) averaged or RMS amplitudes, etc.

But doing the same with MOSFET (output from Drain or Common Emitter), the signal is also inverted. It would be okay while working with (1) and (2) above, but not for anything else. But if we used the Source side for NMOS and PMOS's, we get a non-inverted output and SHOULD BE the same amount of amplification.

I don't get it... Is it because the tutorials/articles are just following the pattern set up by single BJT Amplifier examples?

EDIT:
I replaced "Common Emitter" with "Common Base", as I thought I had it wrong. Then it was pointed out that it really was "Common Emitter", so it was editted back.

Just to clarify everything I am providing this response so that we are all on the same page. I dunno, I must be the one who's not...

This is what I know to be a NPN Common Emitter:

simulate this circuit – Schematic created using CircuitLab

Sources from V_DD, hence higher voltage amplification, but inverted.

This is it's direct equivalent in NMOS (I just checked and this seems to be a Common Source, though my example lacks a resistor on the source side)

simulate this circuit

This is what meant:

simulate this circuit

or for complementary (and my original intended question):

simulate this circuit

(The Opamp above, for simplicity, does not do any feedback for amplification)

With the last figure above was my original intended question, but I just had to ask what I'm asking here before I go with this.


texts: Can I use thermal paste instead of solder for a SMD heat sink?

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I have some high-power (~5W) SMD LEDs that I will be running for extended periods of time. I would like to use a PCB mill to make breakout boards for these chips for easy prototyping. Ideally I would like to reuse these boards in the final circuit since the chips are expensive.

The chips have legs which I can solder by hand, but the thermal pad on the bottom will be a bit trickier since we don't have access to a good oven or similar equipment. Can I use thermal paste instead of solder, relying on the soldered legs to hold the chip down?


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I make my own PCBs and etch them in a homemade bubble tank.

The tank has failed after a couple of years largely due to the etchant slowly eating it's way through some of the materials (glues, pipes, tubes, sealants etc) that the tank was made out of.

There are a few youtube videos showing etching using rocking tanks to slosh the etchant around (as compared to stirring using bubbles) see this...
rocker tank 1

Has anyone got any experience of both methods and might be able to suggest which is best?

A bit of background might help. I make (on average) one board every 2-3 weeks. I used to use professional tanks, but was fed up of having to mix up 5 litres of liquid every time. (which would eventually need professional disposal). I ended up designing my own vertical bubble tank that would etch a post-card sized board using 250ml of etchant. I found this to be the perfect solution (for me) I would only have to mix up enough etchant for what I wanted, it would last for the couple of boards I might make that day, and then I could dispose of it properly myself and mix up a fresh batch next time needed to make a board.

It did a great job of making boards, The only problem with my design was making a tank that could survive the etchant, although most of the materials would survive weeks or months of exposure, after a while something was always getting eaten through and failing.

So rather than making another bubble tank, I though maybe a rocker tank, one advantage (to my thinking) being that a simple take-away container would be about the size I needed, and wouldn't require attempting to join pieces of Plexiglas.

The bubble tank made good boards, is a rocker tank as good?


texts: How to filter noise out from large PWM system

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I have a system that drives 300m of 24V LED strips. The strips are in 25 sections, each controlled by a MOSFET attached to an 328P.

When PWMing the strips (f=500-1000hz depending on the pin), the micros were becoming unresponsive. Suspecting it was a power rail noise problem, I connected the micros to a separate 12V power supply (all grounds are connected) and added a bunch of 100V 2200uF caps to the 24V supplies (as seen in the photo), some 470uF caps to the 12V rail, and some 100uF caps to the 5V rail of each board. This has seemed to help a lot.

However, every now and then, a micro still hangs. How can I further reduce the noise, and avoid a micro hanging?

Extra info:

AC coupled probe of the 12V line

AC coupled probe of the 5V line on the controller boards

AC coupled probe of the 24V line

Controller board

Closer view of the boards. The light gray cable is the 12V line.


texts: Electret microphone into iMac 3.5mm TRRS headphone jack amplification

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I have this electret microphone: http://www.farnell.com/datasheets/1505849.pdf

And I've put it onto a 3.5mm TRRS (4 pole) jack to go into the iMac headphone jack. For the iMac to recognise/accept the mic it needs to be wired with a 10k resistor in parallel and speakers must be 'faked' bz using 33ohm resistors for left/right lines.

It works well but the signal is weak. How can I amplify the signal just a little bit? This is a dirty prototype project and it's not about quality but just about the concept so the easier/quicker/the less parts involved, the better.

I think there is 2V coming out of the headphone jack for the mic but I'm not sure. Is it possible to amplify the mic without using an external battery/energy source?

I tried this circuit but there was just no signal anymore?

Thanks


texts: What is this encoder with micro DC motor in camera auto focus system?

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I recently disassembled an old digital point and shoot camera and found the following micro DC motor (as can be seen in the image)

It is probably part of the auto focus system. Also, there is a  slotted disk connected to the shaft of the motor and this slotted disk sits in a circular cavity with two sensors (looks like light interrupter sensor).

Now, there are five wires that are coming to these sensors one wire is common between the two (the central wire). I think this encoder works by giving pulses when the disk passes through it, but I am not sure if that really happens. I wish to use this circuit but I do not know what are the 5 wires to the encoder. Is anyone here familiar with this encoder and its working?
Kindly help.
Can it be something like this?


texts: Writing to BQ25700A with i2c_smbus_write_block_data

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I'm trying to write to a TI buck boost charger (BQ25700A) using the i2c_smbus_write_block_data command, to try to provide current to a battery.
byte current_reg[2];
current_reg[1] = n & 0xFF;          //LSB       //This is not getting written
current_reg[0] = (n >> 8) & 0xFF;   //MSB
i2c_smbus_write_block_data(deviceDescriptor,0x14,2,current_reg);

n here is the applied current. Can be anything between 0-2000 (in milliamperes). The 0x14 register will discard all the extraneous bits and keep only the 6-12 bits. You can see this in the datasheet images i've attached below.
My issue is that current_reg[0] is written to the charger register, but the LSB
i.e. current_reg1 doesn't seem to go through. Consequently, I get only 256mA of resolution through the charger, instead of the 64mA (since the LSB is what contains that information).
The relevant datasheet excerpt:


texts: Building laser doppler vibrometer for measuring frequency of 1 MHz

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I'm interested in building my own laser doppler vibrometer using laser diodes. The reason I mention laser diodes is because (1) I want it to be cheap and (2) I want to incorporate it into robotics projects. However, I'm unsure if it's possible to build something that satisfies my requirements for reasonably cheap (say, the components of such an LDV would cost < 500 USD). Specifically, I am trying to measure vibrations that have a frequency of 1 MHz – I am not trying to build a general-purpose measurement device, as most commercial LDV devices are. I was thinking of using self-mixing laser interferometry with a laser diode, but the research I've read seems to indicate that such self-mixing laser diode systems don't get anywhere close to 1 MHz. Is it possible to build such a reasonably cheap device? And, if so, how? I would greatly appreciate any references to research papers.
EDIT: I also read this Reddit thread from 8 years ago, where the OP seems to be trying to build their own LDV.
EDIT2: The distance the LDV would have to operate is very short (say, 1 meter or less).


texts: I have collected some samples for a 200Hz sine wave using an AVR microcontroller. I would like to quantify the performance of the ADC using the signal to noise ratio measurement. Theoretically, for an ideal ADC it should be SNR = 6.02N + 1.76 (dB). What could I do in MATLAB to see how this ADC compares to an ideal one?


texts: Why do we use \$s=j\omega\$ in AC analysis instead of \$s=\sigma+j\omega\$?

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In AC analysis, \$s=j\omega\$ when we deal with \$sL\$ or \$1/sC\$. But for a Laplace transform, \$s=\sigma+j\omega\$.

Sorry for being ambiguous but I would like to connect the questions below:

Why is sigma equal to zero?
Is neper frequency connected to this?
Is sigma equal to zero as the input signal is a sinusoid of constant \$\pm V_{max}\$?


texts: Why do 74 series IC's have two ENABLE pins

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I am using 74LS154 4 to 16 decoder Link to *.pdf here. It has two ACTIVE LOW 'ENABLE' pins at the input. What is the use of two ENABLE input pins is the question.

Most of the 74 series IC's used  in the lab has two ENABLE pins..


texts:
Is there a way to find the last address or last page of the program which is stored in an STM32(F1) using a HAL (or LL?) function?

Background: I'm using EEPROM emulation in Flash and this works great. I changed the library from a hardcoded page to be used for EEPROM emulation to a variable one, to be able to implement wear leveling.

However, to know which pages can be used, I need to know where the program 'stops', i.e. the last address or page used by the program being executed, not to overwrite the program itself.

Also I'm a bit confused about the pages used and the size of each page. I'm using this library:

https://github.com/nimaltd/EEPROM/blob/master/eeprom.c (credits to Nima Askari).

Which defines for STM32F103C8T6 (low density F1) 1 KB page sizes and a max page of 31.
Why 31? I would expect 63 as it has 64 KB. Although I noticed when using page 15, it overwrote my program which is around 30 KB in size. (this part is solved, see my answer below).

Of course I can use the size of the program (see below), but this varies while I program, and besides it's too tedious to change/calculate the page number every time, I might forget it too.

arm-none-eabi-size   FuzzTester3.elf
   text    data     bss     dec     hex filename
  26632     236    3104   29972    7514 FuzzTester3.elf


texts:
I am using a comparator (TS3021) as a zero crossing detector (ZCD). The ZCD toggles its output based on the zero crossings of a sine wave generated across a transformer coil. One end of the coil is connected to the +ve input of the comparator via a voltage divider and the other end of the coil is connected to the -ve input of the comparator. The comparator is powered from a 2.5V LDO output supplied by a 3V battery source. The voltage swing of the sine wave is less < (VDD-VSS) of the comparator and doesn't violate the common mode voltage requirements (rail-to-rail) of the comparator. I tested this configuration and I was able to see the comparator output toggle at the zero crossings.

The comparator doesn't have a shut-down/enable pin and consumes around 73 uA of quiescent current. I do not need the ZCD to operate continuously, hence I tried to disable the comparator by inserting an NMOS transistor between the negative supply and the VSS pin of the comparator to cut the tail current. I connected the gate of the MOSFET to VSS to test if it disables the tail current. I noticed that the output of the comparator still toggles, but doesn't go all the way to the negative rail. Also, the VDS voltage is around 0.2V. When I connect the gate of the MOSFET to VDD, I am able to resume normal operation with full rail-to-rail output swing. My question is regarding the case when gate of the MOSFET is tied to VSS. Why  is the output still toggling when I have cut (I assume I have) the tail current? Is there a better way of implementing shut-down functionality?


texts: 220->12 AC voltage transformer into 120 -> 12-20 AC

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I bought a budget headphone amplifier  Objective 2 (Mayflower manufactured), yet just realized that even power supply has a North American plug, it expects  220 V 50Hz (european voltage). I cannot return due Massdrop sales policy. Apparently compatible/recommended power supply ( 120 to 13-20 AC with 2.1 barrel plug) are not so expensive per se (<15$), yet rare and expensive to deliver (about 30 CAN). The amplifier also supposed to work from two 9V rechargeable batteries (I guess about $20), though I do not see where to insert them, probably need disassembly the device. I also have a 220 -> 110 V converter but not wise versa. So is there reasonable way to make it work besides ordering new power supply from Mayflower? For some reason unit is not expected to work with normal AC/DC converter, and requires AC-AC power supply.

The amp designer stresses out "The transformer output can be anywhere from 14 VAC to 20 VAC and at least 200 mA. Don’t use more than 20 VAC or less than 14 VAC (except for the 12 VAC transformers listed in the parts list).Do not try to use a DC adapter. "

Schematics is on:
https://drive.google.com/file/d/0B52Awjeyc5zKMjRlYjlhNGItNGJlNC00ODlmLWIwM2MtNDI4ZWU4YWRjY2Y4/view

2.5 x 5.5 output plugs seems to be more easily available yet I guess it would need some plug adapter or find soldering iron.


texts: How do I specify whether to send a CAN bus message on low-speed or high-speed CAN?

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I'm a student doing an internship and have to send a CAN bus message to a vehicle. I have no experience with the CAN bus, but it's part of my project so I'm trying to learn.

I have to use an i.MX 6 processor that has Linux OpenWrt on it. It has can-utils installed, and I can send commands such as "cansend can0 xxx#xxxxxxx" and see them being received on our in house program.

My problem is that we use the low-speed CAN here and my messages are being sent to the high-speed CAN, so when I try to send a message in a vehicle, it doesn't work. Is there a way I can force the message to be sent on the low-speed so that it will be recognized by the vehicle?

Processor: i.MX 6 application processor

OS: Linux - OpenWrt

CAN utility: canutils


texts:
I have a 12V DC circuit that I want to switch on/off, based on 8V AC signal.

Can I do it with a diode connected to the gate of a transitor?

EDIT: The AC circuit is a door intercom. I'm trying to couple it with a wireless circuit that works with a 12V battery. The DC circuit should stay on only when the the bell (AC) of the intercom is on.


texts:
How do I calculate the frequency of oscillation in this circuit?

I've gathered that I need to obtain the switch threasholds, which I thought I could do, but evidently I can't so a walk through on how to do that too would be great. From the examples in the book, it looks like a little estimation is allowed. The book seems to use Δt≈(CΔV)/(I)Δt≈(CΔV)/(I) and I≈15V/100k.

Any Help is appreciated.


texts: I am planning to design smps power supply that using flyback topology. It will have 12V@5A output values. But it is not clear for me how to estimate input power. It will supply from 220 AC input port. I am trying to find it from my transformer inductance which is 75uH. It is logical to find from V=Lxdi/dt ? My switching frequency is 100kHZ and will work %45 duty cycle. Therefore ramp signal rises to peak current in 4.5us. I have some ideas like this. Can u help me how to find input power and from there eff?


texts: Why does the MCP4241 digital rheostat still work after Vdd is disconnected?

texts:
The MCP4241 digital rheostat still responds to SPI data after Vdd is disconnected. Could someone please shed some light on why that is?

Data sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/22059b.pdf


texts:
I am making a PCB circuit that detects the state of a mains voltage switch. Now since I am dealing with mains voltage a lot can go wrong and a lot can go wrong badly so I would like to ask for some advice on how to properly deal (and might even use standard practices) with mains voltage on my PCB.

My circuit takes advantage of an unused "throw" pin of the switch, which I can use to detect the voltage. I plan on using an AC input optoisolator (could not find an AC input model for the schematics) to fully isolate my electronics from the mains voltage. There will be several of these detector circuits in a single PCB, the number will range from maybe 5-10 depending on how much I can fit in.

So what I would like advice for are:

What would be the thinnest trace I can go for the mains voltage, and also the the distance between traces? (1oz copper)
What would be the best/safest connectors both male and female for this application.
Is it okay to share the neutral line for all the detectors to reduce the wire connecting to the board?


texts:
Is it correct to say that ADC is done in two steps: 1-Sample and Hold 2- Quantization

or it should be done in two steps: 1-Sample and Hold 2- Encoding ?


texts:
I want to buy a 20kW (72V) Air cooled BLDC Motor but how do I to calculate the capacity of the required battery current?
i will use this motor just to start up gas turbine engine , which means it will run for about 50-60 sec


texts:
I want to use a 555 PWM signal to control a motor.

I also want represented the speed of the motor with an LED graph using a  LM3914 led driver.

Can I use a digital signal to control the LM3914 circuit? And if so how do connect the two?


texts:
I have a BU-353, and I am using it in a car. I want to use it to get a more accurate speed reading than RPM/wheel diameter calculation can give me. I am wondering how the incline of a slope, that the car might be going up would impact the GPS reading (specifically NMEA VTG and RMC data). In other words, would the speed out put from the GPS be inaccurate if the altitude of the car is changing, and if so how could I account for that in the software?

The device can also use the following NEMA Protocols: GGA, GKK, GSA, GSV, RMC, VTG, MSS, ZDA


texts: Pigpio control of SG90 servo is imprecise on Raspberry Pi

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I'm in the process of trying to build a laser turret using two SG90 servos, a laser diode and my Raspberry Pi.
I've come to realize that the pigpio library I'm using to control the servo seems a bit imprecise, so I've written a short test program:
import pigpio
import time

pi = pigpio.pi()

def do():
    pi.set_servo_pulsewidth(17, 1500)
    for pulsewidth in range(1600, 1650):
        pi.set_servo_pulsewidth(17, pulsewidth)
        print("pulsewidth: " + str(pulsewidth))
        time.sleep(0.1)

do()

When running the code, I saw that not every new pulsewidth actually changes the position of the servo, the servo rather jumps to a new position every ~5-10 or so steps. Since I'm aiming the laser at a wall 3m away, those jumps are really obvious and it makes it hard, if not impossible, to correctly aim at something.
Is this a problem I can solve by using another library or method or something or is that simply the limit of the SG90 servos?
Also, if there is a better forum to ask this, feel free to give me pointers.


texts: Turning old floor fan into floor floor study light

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I have turned a cheap floor fan into a floor study lamp; i.e. 30cm of 240V 5W a/c LED (under cupboard) strip light facing down on to the desk. These LED strip lights can be easily daisy chained in series to make a long long line of one strip light. The wiring is straightforward using all three live output wires (blue, white and red) from the fan switch to switch one light on. (I have taken the capacitor and resistor out.) I could have used only one wire, but then I would have to press the exact button on the fan switch to turn my light on. The neutral (black wire) and earth wires just pass directly through to the light, as was the case when this was a fan - The fan did not pass the earth to the motor, so I added it.
OK. So, just removed the old fan switch and added 2 on/off a/c switches for 1 or 2 lights on.
Also, as promised, opened up one light to show the rectifier and 24 LEDs. I tried to measure the volt being fed into the LEDs but only shows 1. When switched off and as the large capacitor is discharging I can see a countdown from "20V" down to 0 ish.

No problem. However, I want to use the power buttons (0,1,2,3) of the original fan to turn on 1, 2 or 3 lights, which will be in parallel. But, the problem is how can I use this switch which only has one specific live output for each button 1, 2 and 3.
I thought about (switch at position 2) connecting 2 output wires (blue and white) to two lights respectively and (switch at position 3) all three output wires (blue, white and red) to all three lights respectively - naturally, at switch position 1, only one light would have a live wire (blue); i.e. all lights will have all 3 live outputs connected.
So, the question is, should I use diodes to stop current flowing back to lights 2 and 3 when switch is 1; and diodes to stop current flowing back to light 3 when switch is 2?
Thank you.
proposed:


texts: Examples of schemes for Microcontrollers STM32

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On the Internet a lot of tutorials on AVR microcontrollers, but very few examples for novice developers to STM32.
Who can give a link to educational materials for STM32? Interested in the scheme starting with the simplest of schemes, such as, for example, "traffic light", examples of DAC and ADC.


texts: Increased current consumption of micro-power devices

texts:
I've been working with microwatt and nanowatt power consumption devices for a while and I've mentioned that sometimes, due to unknown reason, current consumption increases in order of magnitude. Currently I've made a few devices that have standby current around few microamps and mentioned this behavior on many chips (some of them: LIS3DH, nRF24L01). I have no idea, maybe it could be some kind of latent electrostatic or thermal damage on chip. The fact is: sometimes chips are getting 10-200 uA increase of current consumption, while still being fully operational. Well, at least before battery goes dead.

Currently I've been just replacing damaged chips with new ones, but now we are increasing amount of devices and such method is no longer appropriate. What is happening and how to avoid this?


texts: What are these fuse-looking cartridge case components on small, battery operated RF tranceivers?

texts:
I have recently opened up 3 dead, battery-operated RF transceivers lying around, both wearable and key-chains. I've noticed that all three had components that looked like fuses (cartridge case), soldered down, that are quite large compared to the size of the circuit. See the pictures below. I'm not posting full circuit pictures because I don't know if I should, I can update if they are necessary.

Device 1:

Device 2:

Device 3:

I can't see why such a device will require a fuse, and I couldn't find any other common components manufactured in cartridge cases, maybe I'm not using the correct name. I don't see them on any applications notes or reference designs for the ICs used either.

I've tried to figure out how they are connected to the circuit, I don't have schematics and PCBs are more than 2 layers so they may not be complete, but see the schematics I've figured below.

Device 1:

Device 2:

Device 3:

Also, when I do a continuity test between the terminals of the components with a multimeter, resistance starts in ~50 Ohms range and goes down to short as I keep the probes on its terminals so my best guess is something for ESD protection, maybe Varistors or Thermistors?

Does anyone know what these components are and why they are there?


texts: Is a HASL surface finish appropriate for edge connector plating?

texts:
I'm working on a daughter board PCB which will plug into a larger board. I'm interested in trying out edge connector plating for the connection type. However, I'm not sure on what surface finish is appropriate for edge connect plating.

Doing a bit of research, I've found that a hard gold finish (gold fingers) is a popular method due to its robustness. However, I'm thinking this is not a cost effective solution.

I know that a lot of board houses use HASL surface finish as default, would it be appropriate to use HASL as edge connect plating? How concerned should I be of ware?


texts:
Is there any classical analog circuit to measure the phase difference between two analog signals ( especially sinusoidal signals )?

I want to measure the phase difference between two sinusoid signals with different amplitudes and same frequency. The frequency range of the signal is from 50kHz to 200 kHz. The purpose of my circuit is to measure the phase component of bio electrical impedance of human body. So one of my input signals will be that from a function generator with fixed amplitude and the other signal will be the voltage developed across the electrodes connected to the body.


texts: Complicated photo-motion-timer switch design?

texts:
Here's my scenario:

I have an array of 120V LED fixtures that need to be turned on for 10 minutes when the following conditions occur:

It's dark out AND Someone walks in front of a motion sensor

OR

Someone toggles a switch inside (this can be a standard light switch or a pushbutton that fits into a standard box and looks professional)

You would think that someone would have already done this and would be marketing it, but I can't find a time-delay dusk-only motion sensor with a switch input.

Basically if someone walks by at night, or if someone hits a switch, then turn on the lights for 10 minutes.

My Question:

I need a schematic that uses common parts (NE555P, discrete components, etc - no microcontrollers) to fulfill this logic.  The total power of the lights is about 50W @ 120VAC.  Normally I would be able to do this myself, but my attempts have ended up as scrap paper.

EDIT: I'm open to using a microcontroller, just make sure to give me very very very detailed instructions, since I'm not very familiar with their quirks.

To clarify: I am 100% open to building something from components/ICs.  In fact, I would prefer that.  I just need to know how to wire up the microcontroller and/or 555-monostable.


texts:
I'd like to reverse-engineer a certain 2-wire digital circuit. I'm looking for the cheapest possible logic analyzer. I don't know the exact frequency of the circuit, but it's sub-1MHz. (Likely in the range of 50kHz-500kHz.)

Obviously, I've heard about Bus Pirate, but I thought - hey, why not just use a serial port on my laptop? I have a UART-to-USB dongle based on a FT232-family chip, which is supposed to work with non-standard baud-rates, up to 1Mbd and beyond (depending which specific model you look up).

There are two challenges I can immediately see:

Voltage. I assume a simple two-resistor voltage divider will suffice?
Clock. Since I don't know the subject baud rate, I won't see the proper signal immediately. Maybe I could oversample initially and figure out the actual frequency from the observed signal?


texts: Re-wiring experimental apparatus: Questions regarding proper ground, DC power supplies, and precision instrumentation

texts:
The apparatus consists of a large metal spherical chamber attached to a metal table. There are two electrical enclosures bolted to the table legs. The chamber is outfitted with multiple servomotors, each driven by an independent servo amplifier. Servo control, along with thermocouple and pressure transducer monitoring, is achieved using LabVIEW via a DAQ chassis with several modules.

One enclosure receives 208 V AC to power the servo drives. It is distributed to a series of breakers and eventually the servo amps. The ground wire is bolted to the enclosure ground lug. Similarly, the second enclosure receives mains 110 V AC to power the instrument control (DC power supplies, relays, stain gauge amp, DAQ chassis, etc.). The ground wire is again bolted to the enclosure ground stud. Essentially the entire apparatus is connected (physically and electrically) to ground via two paths.

My problem arises when I consider how to wire the DC power supplies. In particular, each servo amp needs +5V DC to enable. So, I split up the positive terminal from my 5 V power supply via terminal blocks and route this to the appropriate point on each amplifier. However, there is no negative terminal on the amplifiers to run return lines to the power supply, the +5 V DC is relative to the amplifiers' common terminal, which is connected to its metal frame, which is connected to the enclosure, which is therefore grounded along with everything else. So, it would appear that I should simply ground my power supply's negative terminal, thus completing the circuit.

I have the same problem with the positive voltage required to control the motor speed. This is output from a digital-to-analog converter but again, the amplifier measures this input voltage relative to its common. So it would once again appear that I need to complete the circuit by connecting ground to the converter's negative terminal.

My question is this:
Can I tie the negative terminals of my 12 V and 5 V power supplies to ground, which basically means they are connected to every piece of the apparatus?

My main concern is that the power supplies also power precision equipment (a 5 V pressure transducer, a 12 V signal conditioner). These items have a positive and negative terminal, and could, in theory, be wired directly to a power supply without involving ground.

Will these be affected by using ground as the negative?

Apologies for the question length, I can add diagrams or detail as required.

Thanks]1

EDIT: Added proposed diagram


texts:
I have a frequency signal range from 25 Khz to 35 Khz. I know that the the minimum signal sampling to assure reconstruction of the signal from the samples is 70 Khz.

Would it be correct to assume that using the Nyquist's sampling criterion, the maximum data rate that the signal can carry for the 10 Khz bandwidth be 700 bits per second?

Do I multiply the samples per second (70) by bandwidth, which yields 700 or by 8 bits per sample?


texts:
Roomba has two bumper sensors (left and right, this is what is mentioned almost everywhere), if pressed it recognizes obstacles.

Then what is the need of the extra array of IR sensors(6 in number).
Also, the way they are placed in front it looks like the Receiver and Transmitter are blocked from each other. How is the signal transmitted?
The IR sensors are covered with this huge bumper panel in front. How is it even detecting obstacles?
Is the IR dead-band range too small? (to detect small bumper press)?


texts: Reverse current protection for a battery-operated circuit

texts:
I'm planning a hobby project with the following characteristics

3.3 V circuit, battery operated (by regulating standard AAA batteries)
Most of the time in "sleep" mode, so I need a very small quiescent current
When operating it will consume 100-350 mA
Linear regulator to avoid noise and ripples

I've chosen the MCP1825 linear LDO regulator because it has enough power (500 mA), very low dropout voltage (less than 210 mV) and reasonable quiescent current (less than 120 µA).

My questions are:

What if I don't put any reverse current protection? Will the PMOS pass element in MCP1825 provide some protection?
Could I avoid adding reverse current protection if I'm careful with batteries' polarity?
If I have to put some sort of reverse current protection, how would you advice designing a simple one with very low (or non-existing) dropout voltage and quiescent current?


texts: CE marking of devices using pre-certified radio modules without antenna, just a 50 ohm RF port

texts:
I'm right now working on a project involving 2 radio modules, a SIM800F and a LoRa1276-C1-868.
The modules are already certified under the radio equipment directive. In the case of the LoRa module it is certified using a wire antenna and helical antenna.  In the case of the SIM800F I couldn't find it specified in any of the documents so I'm assuming it was tested without one, just using a breakout board (as shown in the pictures in the documents.)
In terms of connection this device is intended to have just 2 ports, one for GSM and an other for LoRa. The antenna should be selected according to the location requirements.
Is it possible to certify the device under RED without specifying the antennas used?
The people at the testing lab couldn't answer this very well, and it sounds strange that you would need to do testing for every antenna you could possibly connect to the device.


texts: Write ADC data to memory and back to DAC (without MCU)

texts:
Is there a way that is not too complex way to implement ADC -> SRAM -> DAC data transmission without the usage of the microcontroller?
The application is to implement the audio loop of some sort, to put the audio input chunk to the memory, with an ability to stop the "ADC -> SRAM" process, to keep previously acquired data in the memory.
It does not have to be a high fidelity (I have 8-bit ADC/DAC in mind).
UPD:
I want to do this for the educational purposes, so I'm not looking for the all-rational/optimal solution.


texts: What are the modern day applications of pc 16550 UART, is it still widely used in the industry?

texts:
Just started with learning LINUX serial port driver development and came across pc16550 UART.

Considering the fact that UART is now mostly integrated in SOC or MCU, was just wondering if 16550 is still widely used in the industry.


texts: Current Rating of Stepper Shield Ground Wire

texts:
I have a 2 phase bipolar stepper motor;
https://catalog.orientalmotor.com/item/all-categories/20mm-pkp-series-2-phase-bipolar-stepper-motors/pkp214d06a-2

Its 4 power wires are wrapped in a shielded shroud, for EMC compliance reasons.
The shielded shroud is then grounded to the control board (which provides motor power).
Does it sound sensible and safe to assume the max current rating for the shield grounding wire would be no more than the max current per phase for the motor? If not, what are the key parameters you would consider to determine the current rating of the grounding wire, in terms a mechanical engineer would understand.
Appreciate any advice.


texts:
I'm running an ATMega88A at 8MHz and have the SPI configured to run at Fosc/2 = 4MHz.

In theory, shifting out 5000 bytes over SPI should take 1/4000000 * 8 * 5000 = 10ms. But according to the internal timer, it's taking just over 19ms. This seems like a ton of overhead. Is this typical?

Sample code:

#include <avr/io.h>

#define set_output(portdir,pin) portdir |= (1<<pin)

void init() {
    // Set MOSI, SCK, SS as Output
    set_output(DDRB, DDB5);
    set_output(DDRB, DDB3);
    set_output(DDRB, DDB2);
    // Enable SPI, Set as Master, Set CPOL & CPHA to 1 (SPI mode 3)
    SPCR = (1 << SPE) | (1 << MSTR) | (1 << CPOL) | (1 << CPHA);
    SPSR = (1 << SPI2X); // Enable SPI clock doubler
    DDRD = 0xff; // Set PORTD as output
    TCCR1B |= (1 << CS12) | (1 << CS10); // Setup Timer with 1024 prescaling
}

int main(void) {
    unsigned int i;
    init();
    TCNT1 = 0; //zero the timer
    for (i = 0; i < 5000; i++) {
        SPDR = 0; // Load data into the SPI data reg
        while (!(SPSR & (1 << SPIF))); //Wait until transmission complete
    }
    PORTD = (unsigned char) TCNT1; // Display the timer on PORTD
    for (;;) {}
    return 0;
}


texts: Question about 3/~5 output select pin of a boost IC?

texts:
I want to power up Arduino nano and nRF24l01+ 's Vcc from MAX756 step-up DC-DC convertor (datasheet). I'm using a single AA battery (1.5V)
There is a 3/5(bar) pin to select whether the output would be 3.3 or 5V.
The pin recognizes max 0.4V as low and min 1.6V as high.

Now If I connect that pin to ground, it would produce 5V but what should the pin voltage be if I want 3.3V?
1- How can I select 3.3V OUT if I'm only using 1.5V battery in the input? Should the pin be connected to OUT if I want 3.3V?
2- If so, how does the IC even work? It first wants to know what voltage to produce in OUT therefore it checks 3/~5 pin. But if it is connected to OUT, wouldn't this situation be a paradox?
3- nRF24l01+ is very sensitive in it's VCC. It should never be 5V. Would connecting OUT to 3/~5 pin, create a transient 5V in OUT and burn the RF module?
4- What is meant by this line (bootstrapped?) is the datasheet?

The device is internally bootstrapped, with power derived from the
output voltage (via OUT).

Thank you very much


texts: Zero current switching SMPS with common emitter or source

texts:
Is there any? Is it even possible that such arrangement could exist?
Im interested in SMPS where both, turn ON and turn OFF processes of all switching elements happen at zero current through that switching element. BJT or MOSFET both are ok for the solution. Preferably sunchronous rectification, also with zero current during the switching.
If that is impossible, what can be used to convince that this is truly impossible, some rule?


texts: Steps to ensure greatest success in PCBA production runs?

texts:
We periodically get some boards produced and assembled in small runs of 50 - 200. The PCBA company just makes and loads the boards (SMD reflow), we do the programming and testing after delivery

Sometimes there will be one or two boards with a problem, for example a missing resistor or a solder bridge.

We just received a batch of 200 boards, and in the 26 already tested, 8 have problems such as programming failed or sensors not working properly.

Questions:

What is a typical failure rate for small production runs?
Can we assume all the problems are soldering related? (Assuming components sourced in working condition)
What steps can we take to minimise the failure rate?
What response can we expect from the PCBA manufacturer? Is it reasonable to ask for a refund of assembly costs on the affected boards?

Update:

A particular QFN chip seems to be failing, see an example below. It seems some rework was attempted, which suggests an solder bridge was noticed during a visual inspection. (resistors are 0603 for size reference)


texts: Getting different values while connecting LM35 with PIC16F877A

texts:
I am getting different values while giving LM35 output as input to ADC (Pin RA0/AN0) PIC16F877A.

I am not providing any Reference voltage to the microcontroller. I want to make sure that is the reason for different values.

Also want to know why we need to give reference voltage Vref + & Vref -and how the circuit should me made for reference voltage?

In the datasheet, it was provided only like this,


texts: Series inductor as discontinuity in transmission line

texts:
Dual to this question is the following circuit:

simulate this circuit – Schematic created using CircuitLab

An infinite transmission line (with characteristic impedance \$ Z_0 \$) ends upon a series inductor \$ L \$, then another infinite transmission line (with the same characteristic impedance \$ Z_0 \$) begins.

A step signal of amplitude \$ V^+ \$ is going from left to right: it will come across the inductor and the current will "charge" it.

The following schematic is the equivalent circuit:

simulate this circuit

I followed a procedure similar to the previous one, and wrote the following equation for the charge process of the inductor:

$$I_L (t) = \frac{V^+}{2Z_0}(1 - \exp{(-t/\tau_L)})$$

where \$ \tau_L = L/(2Z_0) \$. But now I would like to obtain the following result:

$$V^{++} (t) = V^+(1 - \exp{(-t/\tau_L)})$$

(exactly the dual of this) where \$ V^{++} \$ is the voltage travelling from the inductor to the right infinite line.

I am supposing that \$ V^{++} \$ is the voltage across the right impedance \$ Z_0 \$. So,

$$I_L(t) = \frac{V^{++}}{Z_0}$$

but anyway

$$\frac{V^{++}}{Z_0} = \frac{V^+}{2Z_0}(1 - \exp{(-t/\tau_L)})$$

$$V^{++} = \frac{V^+}{2}(1 - \exp{(-t/\tau_L)})$$

and there is an undesirable \$ 2 \$ factor. I would like that \$ V^{++} \to V^+ \$ for \$ t \to \infty \$, but when \$ I_L(t) \to V_0 / (2Z_0) \$ there is an unavoidable voltage divider, maybe due to the circuit.

Is it possible to cancel this \$ 2 \$ factor (and obtain exactly \$ V^{++} (t) = V^+(1 - \exp{(-t/\tau_L)}) \$ like in the capacitor)?


texts: Cannot establish serial communication to ESP8266

texts:
I recently designed, had manufactured, and populated my first PCB. As context for the schematic and PCB, the requirements were as follows:

Independent control of seven LEDs
The ability to program into memory specific patterns for the LEDs to turn on/off in
The ability to do this all over wireless (WiFi/BLE)

I am using an ESP8266 as my MCU. For several days I have been investigating a problem: I cannot establish serial communication to the UART. When I run esptool, I get the following error message:

$ esptool chip_id
esptool.py v2.8
Found 1 serial ports
Serial port /dev/ttyUSB0
Connecting........_____....._____....._____....._____....._____....._____....._____
/dev/ttyUSB0 failed to connect: Failed to connect to Espressif device: Timed out waiting for packet header

A fatal error occurred: Could not connect to an Espressif device on any of the 1 available serial ports.

I feel as if I have tried everything I can think of. At this point I am left wondering if I have some massive design flaw in the PCB -- afterall, this is my first.

For your convenience, here are the datasheets for some of the critical components:

ESP8266EX (MCU)
W25X20CL (256 kB flash)

What I've tried:

Flashing software: esptool, the Arduino IDE w/ community ESP8266, Espressif's firmware downloader, nodeMCU-flasher, etc. (I think these are all wrappers of esptool anyway).
Host machine: A desktop and a laptop w/ Arch Linux x64, another laptop w/ Windows 10.
USB: Three different USB cables (including one only a few cm long), several different ports across the three different machines
Power: 12 W USB 5 V to the linear regulator input; 3.3 V rail from a 500 W ATX PSU, bypassing the regulator; adding buffering capacitors to both the input and output sides of the regulator, ranging from 100 nF to 100 uF; power over USB via FTDI USB/tty converter
Serial: FT232 chip; CH340 chip. Added a 510 ohm resistor in series with the ESP_TX line, as per a recommendation (499R) in the datasheet. Different symbolrates (115.2 kBd, ~54 kBd, ~74 kBd, 9.6 kBd, ~250 kBd). Different combinations of bits/symbol (5/6/7/8), parity (none/odd/even/mark/space), stop bits (1/2).
Flash: DIO/DOUT/QIO/QOUT. Tried without a flash chip even populated. Even desoldered an 8 MB chip from an old board and put that in-circuit in place of the 256 kB in my schematic. Also tried telling esptool to use different frequencies (20/40/80 MHz).
Bootstrapping: Tried every combination of MTDO/GPIO0/GPIO2

Additionally, I've monitored the ESP_RX and ESP_TX lines with an oscilloscope. No matter what I do, ESP_TX remains idle (HIGH). However, when esptool displays the dots part of the connecting message I can decode this on ESP_RX:

c0 00 08 24 00 00 00 00
00 07 07 12 20 55 55 55
55 55 55 55 55 55 55 55
55 55 55 55 55 55 55 55
55 55 55 55 55 55 55 55
55 55 55 55 55 c0

Here are photos are the schematics and renders of the PCB:

I apologize if they aren't the greatest quality -- this is my first time doing this.

Does anyone see a glaring issue? Obvious problem in the schematic or PCB? Something I should try in software that I haven't thought of? I'm just at a total loss here. Thanks for your help.


texts: Values of currents in inverting and non-inverting terminal of Op-Amp

texts:
In the given solved example from a textbook on electronic devices, the author has use the voltage divider rule after assuming \$V_{s2}=0\$. Clearly for equation 1 to be true, the current in the non inverting terminal \$i\$ must be 0.
Why is this true? In few other examples current is taken as zero in the inverting input terminal. I wish to know the reason behind this assumption and how to know out of the two which input terminal has zero current? Can the current be ever taken zero in both of them?


texts: Could an aluminum housing and passive cooling interfere with SoC's functioning?

texts:
I took the board out of a broken tablet. The SoC on the board gets hot pretty quickly. I thought about fixing the board to an aluminum plate, so that it touches the SoC and disctributes its heat, and by the way is a simple "one-sided casing".

Would that interfere with the SoC, or the whole computers functioning? (eg: WiFi)


texts: What happens when I use a bigger capacitor?

texts:
I'm using a Adafruit Servo Driver (PCA9685) and I have to solder a capacitor depending of the number of servos.

  We have a spot on the PCB for soldering in an electrolytic capacitor. Based on your usage, you may or may not need a capacitor. If you are driving a lot of servos from a power supply that dips a lot when the servos move, n * 100uF where n is the number of servos is a good place to start - eg 470uF or more for 5 servos. Since its so dependent on servo current draw, the torque on each motor, and what power supply, there is no "one magic capacitor value" we can suggest which is why we don't include a capacitor in the kit.

Right now i'm using only 12 servos (I shoould use a 1200uF capacitor ) but in the future i'm going to use 14 servos (1400uF)

my question is: What happen if I use a bigger capacitor (1400uF) for 12 servos or less?


texts:
This story must be quite familiar:

From the start, I've had a problem with my phone/ADSL line: Cracks, hisses and other noise on the phone - enough to make it occasionally unusable, along with an ADSL connection that is slow and as far from reliable as it can get without failing completely. Naturally, the ISP and phone company insist that the problem is on my end.

My house was renovated about 3 years ago and all indoors wiring was replaced, before we moved in permanently. When my phone went dead three months ago, I finally replaced the last pre-renovation length of cable, the one that went under the garden to connect to the telecom entry point.

Admittedly, that cable was a mess. It was a heavy-duty Cat-3 cable, but it had been in that underground channel for almost 20 years - the insulation had been obviously damaged in some spots, exposing the wires. I think that something may have actually eaten through the cable here and there.

Unfortunately, replacing that cable did get the dial tone back, but it did not solve any of the other issues. I have disconnected and re-connected all accessible joints in the line, and done all the usual tests like disconnecting the house wiring (including the alarm system), to no avail.

Rather than have another bout with the phone company or start going after the newer 3-year old phone cables, I was wondering if there was a way to test the phone line from the telecom entry point to the distribution point inside the house.

Of course, I am talking about something more useful than a simple continuity/resistance test, which does not reflect how the line will behave under an AC signal. I know that there are specialized cable testers, but they are very expensive and very few technicians have them. Ideally I'd use an oscillograph along with a frequency sweep generator to test the frequency response of the line, but I do not have access to any of these instruments at this time.

Is there anything else that I could try, preferably something that does not require a lot of cash, or tearing cables out of the walls?

PS: I don't mind building a circuit or two, as long as I have the schematics - I have not designed a new circuit for quite some time, and I'd rather not do it if I can avoid it.


texts: Programming Pins (PGC/PGD) problem on PIC32mx

texts:
I made a design using PIC32mx and everything is working well. I was trying to debug my first program and for this case instead choosing PGEC1 and PGED1 I am using PGED2 and PGEC2. Problably that's the reason why I am getting the following message while debugging:

The target device is not ready for debugging. Please check your configuration bit settings and program the device before proceeding. The most common causes for this failure are oscillator and/or PGC/PGD settings.

This is the schematic I have done:

Where can I modify the configuration bits to enable the debug mode?


texts: Why do most batteries or circuits use a 12V supply?

texts:
I have seen most of the circuit using 12V supply, is there any reason behind this?

Is there any reason to choose 12V in all systems like battery-powered devices?


texts: Aging LEDs - does their output drop after turn-on?

texts:
Old LEDs tend to have a lower optical ouput than new ones for the same current.
However, are there any other things associated with an old LED? Specifically, does the output remain constant with constant current at constant external temperature over small time intervals eg hours?


texts: In Emitter Follower BJT circuit Why the parallel resistance of the biasing resistors to be 1/10 of the Rin and not their series resistance?

texts:
Well In "Practical Electronics For Inventors" Book P.439 The Below Emitter follower circuit was introduced with the following explanation.

The actual sizes of R2 and R1 should be such that their parallel resistance
is less than or equal to one-tenth the dc (quiescent) input resistance at the base (this prevents the voltage divider’s output voltage from lowering under loading conditions).

Well I know that Keeping their values small will keep that Voltage Divider Output from lowering under the current draw of the load as stated. But what I don't understand is That I see the two Resistors in Series Not parallel as mentioned I.e. Shouldn't I consider their Series resistance to be 1/10 or 1/100 or what ever as a rule of thumb and not their parallel equivalent? Same thing with Rin in case of ac signal Why the total Rin in ac is the parallel resistance of the three Resistors. ( The Top left of the picture )
And one more thing is that The C2 Is supposed to get Back the gain lost from the Re We added to Control The fluctuation effect of the emitter re. ( As I understand ). well this will not effect our bias current but It will just make our gain for ac signal depend on re again so What is the difference it made or what is it I am missing here ?


texts:
This commentator writes:

  if the modem is many years old, the capacitors can leak electrolyte and go out of spec and instead of just blocking the 'low notes' of a telephone conversation, it might also be filtering out some of the carriers used for data transmission so the modem blacklists them as noisy (quieter signal means relatively speaking, the noise becomes louder) which results in a slower connection.

This commentator writes:

  As with older computers, my suspicion would be that a "bulging" capacitor would be the most likely weakest link in hardware such as this.

This repair site shows a method for repairing bulging capacitors. They write:

  Inside, he found some bulging capacitors. Unsheathing his iron and replacing the obviously faulty components, [psgarcha] plugged the router in and had everything work. Great. Until those caps failed again a few months later.

To me it seems that you should choose components that have a lifetime corresponding to the lifetime of the device.

My question is: Why do ADSL router capacitors bulge after a few months?


texts: Why does a Schmitt trigger work in saturation region?

texts:
Given this circuit

simulate this circuit – Schematic created using CircuitLab

I am trying to prove that the opamp works in saturation region as instructed in the first answer to this question : How are positive and negative feedback of opamps so different? How to analyse a circuit where both are present?

So, we have

$$
V^- = V_{in}
$$
$$
V^+ = \dfrac{R_1}{R_1+R_2}V_{out}
$$
$$
V_{out} = A_v(V^+ − V^-)
$$
$$
V_{out} = A_v(\dfrac{R_1}{R_1+R_2} V_{out} − V_{in})
$$
$$
\lim_{A_v\to\infty}\frac{V_{out}}{V_{in}} = \lim_{A_v\to\infty}\dfrac{Av}{Av \frac{R_1}{R_1+R_2} - 1}
$$
$$
\lim_{A_v\to\infty}\frac{V_{out}}{V_{in}} = 1 + \frac{R_2}{R_1}
$$
\$\frac{Vout}{Vin}\$ is finite, even though the feedback is positive! Why is the circuit working in saturation region instead of the linear one?

Am I missing something here?!!


texts: How to measure cutoff frequency of a low pass audio filter?

texts:
I've built a low pass filter for use in a synthesizer and would like to measure the cutoff frequency compared with various different control voltages to profile its characteristic.

I have access to a digital oscilloscope and a simple multimeter.

How can I measure cutoff frequency?


texts: attiny861 does not want to wake on interrupt but simulation works

texts:
I successful managed to make a software UART without using the USI module and its interrupts.

The AVR code examples on Atmel and avrfreaks just do not work in either simulation or a real device so I got some help and made this soft UART.

Using Proteus I can send messages and receive them on my terminal window on a PC, I can send a character '1' to the Proteus simulation and it turns on an LED pin fine.

When I program the ATTiny861 I can receive messages at 9600bps perfectly but the interrupt procedure never ever fires, it should fire once on startup and then wait while CPU is idle for bit change on PIN.

int main(int argc, char **argv)
{
    USICR   =  0;             // Disable USI.
    MCUCR  |= (0<<ISC00);
    MCUCR  |= (0<<ISC01);
    GIFR    =  (1<<PCIF);     // Clear pin change interrupt flag.
    DDRA    = 0xFE;
    PORTA  |= (1<<PA0);       //int. Pull-up an  PA1
    PINA    = 0x00;
    PCMSK0 |= (1<<PCINT0);
    GIMSK  |= (1<<PCIE0);

    CLKPR = (1 << CLKPCE);
    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);

    MCUCR = (1<<SE) | (0<<SM1) | (0<<SM0);   // Enable Sleepmode: Idle

    while(1){
      //send some startup messages ..

      sei();
      set_sleep_mode(SLEEP_MODE_PWR_DOWN);
      sleep_mode();
    }
}

ISR(PCINT_vect) // interrupt for change in porta0
{
    // pin change interrupt handler
    GIMSK &=  ~(1<<PCIE0);
    if (!( PINA & (1<<PA0) ))
    {
        static char chr;
        get_char(&serial_pins, serial_pin_in, &chr);
        RxData = chr;
    }

    PCMSK0 |= (1<<PCINT0);  //  tell pin change mask to listen to pin0
    GIMSK  |= (1<<PCIE0);   // enable PCINT interrupt in the general interrupt mask of the porta
    GIFR    = (1<<PCIF);    // Clear pin change interrupt flag.

    static char message[] PROGMEM = " INTERRUPTED MESSAGE ";
    put_flash_string(&serial_port, serial_pin_out, (PGM_P) message);
}

I have other libraries and code segments loaded and I know the put_flash_string function works fine. If i take out sleep_mode it will dump messages into the terminal, I can delay it and it also works. But for some unknown reason on my hardware ATTiny861 it just will not interrupt.

I have been looking at this code for two weeks now and I really need some help. Atmel as you might guess is just vague and not really helpful. I'm not sure what to check any more and why the Proteus simulation works and not my hardware.


texts: Can the external power be supplied in one of the ports of the usb hub?

texts: I did a continuity check between all of the ports Vcc and gnd of a usb powered hub including the male end, all are shorted. If I want to make it an external powered hub, instead of connecting the usb female connector of the Vcc to an external supply, can I just connect an external supply on one of the usb female ports? By doing that, I would not have to do a surgery on my usb powered hub.


texts: If I was to use contact cleaner on some connectors, Would this have a better or worst impact then using 100% alcohol?  Does contact cleaner leave Residue?


texts: Is there a sensor capable of measuring distance?

texts:
I'm looking for a simple way to measure the distance between 2 devices, basically 1 device will be placed in each leg and one of them will measure the leg stride, at any moment, by calculating the distance between both mechanisms.
I've read you could measure distance with an ultrasound sensor and an ultrasound transmitter or a magnetic sensor, but are they accurate between 0 and 1 meters, in any direction?
If such a solution is feasible could someone point me to some documentation or a project already made?

The specs are roughly the follow:

distance: 0 to 1m
accuracy: about +/-5cm
type of range: omnidirectional (or at least with a good angle)
size: small enough to fit on someone's heel


texts: How to communicate with 2 devices with 1 UART MCU in AVR

texts:
I am currently looking to integrate GSM SIM900 and GPS Module with Atmega32. As atmega32 has 1 UART option, I was just wondering that can I connect these two devices with single UART. I am making a simple GPS tracker which will send a GPS Lats  Longs to user mobile whenever a user ask for it.

Does anyone have any idea about this problem, pls share. Thanks


texts:
Good day to you all. Am new to RF designs. Presently, am working on a device using RF module for transmitting my signal from TX to RX. Am using the common 315-433MHZ RF module bought from ebay.

My questions are:

Can I use 1/4 whip antenna for this considering a distance of 60m?
Can I place the antenna indoor (for both tx and rx), what is the
maximum distance it can go if placed indoor?
If I can't place the antennas indoors, what is the best cable to use
to extend the antenna outdoor?
the SMA connector of the antenna has the inner pin(antenna) and the
screw(body). Do I need to ground this body to my circuit ground?

I have executed this project before using normal portable radio receiver antenna but I had so much interference issue.


texts:
I need a wireless switch with capability to report current state, so I would like to modify a wireless switche like this, by replacing a current state LED by a trasmitter to get the state of current wirelessly.

it is possible to make such hack? what kind of transmitter could be used ?


texts: Are S/R flip flops still relevent in digital design?

texts:
As I understand it, and please correct me if I'm wrong, one of the main drawbacks of using an S/R flip flop is that it can find itself in an illegal state with both S & R both with a logic value of 1.
The J/K flip flop remedies this by having a clock circuitry prevent the forbidden state.

With this in mind, are there any uses for S/R flip flops in digital design, or have they all been abandoned in favor of J/K and D flip flops?


texts:
Common Emitter Amplifier is used as
A)Current Amplifier
B)Voltage Amplifier
C)Power Amplifier
D)Frequency Modulator

The answer according to key was Voltage Amplifier but I have given Power Amplifier as the CE has moderate Ai and Av hence high Power gain....also it acts as Voltage as well as current Amplifier.....so what's the correct answer? We have to challenge the answers which we feel are wrong with proof!


texts:
I design a module with onboard test-pads. I put ESD protections to all out-world connections like sockets etc.

But I want to ask that; should I put ESD protections to test-pads and ISP socket inputs?


texts: Will a cut or a slot in a PCB change clearance or creepage?

texts:
Does a cut or a slot in a printed circuit board increase clearance, creepage or both?

Some say it will increase clearance, but I don't think clearance will change because, even with a cut in the PCB, distance over the air will be the same. Thus, a cut will only affect the creepage distance.  Please correct me if I'm wrong.

Or does it have nothing to do with either clearance or creepage, and is only for isolation?


texts: Will a servo hold its position without a signal?

texts: A servo interprets a 1ms pulse as far left, a 1.5ms pulse as centre and a 2ms pulse as far right, usually. But what if there is no pulse? Will a servo hold its position if it is just commanded once and never commanded again for a few minutes?


texts: Let's says I have a gate driver and a MOSFET.  I have made the decision to drive my FET using 5V.  The gate driver peak current is 2A.  Do I size my 5 volt power supply at 2A plus my other stuff?  Do I need more or can I get away with less but at the price of, say, max permissible switching frequency?


texts: Question about transformer reflected source

texts:
The following show the idea how a Thevenin equivalent source is used to replace the primary circuit of transformer.

In textbook it is commonly stated that the load impedance sees an equivalent source and the open-circuit voltage is given by \$V_{oc}=N\cdot V_1=N\cdot V_s\$, usually it is said that there is no voltage drop across the source impedance therefore \$V_1=V_s\$ in this equation. However, the primary circuit itself is a closed circuit, there should be some current and voltage drop across impedance of the supply, how V1 can be equals to Vs?

The second question is, the short circuit current is found by \$N\cdot I_{sc}=V_s/Z_s\$. It implies that when the secondary circuit is shorted, the primary current will be \$V_s/Z_s\$. It seems that in this case the impedance of the primary coil is ignored. Why?


texts: Why could the stepper motor be stalling?

texts:
I am trying to run a robot with two wheels using two identical stepper motors and step drives. The motors are Nema 34 and the step drives are RMS R710 Step Drive. The problem I am running into is that while one side works perfectly (or at least without any noticeable issues), the other side starts stalling after running for a while (usually around the 5000 step mark).

I am using an Arduino Uno to send the step and direction signal using the Stepper library, and the drivers are powered by a 24 V battery. The resistor on the drive is appropriate for the current required by the motor.

I have tried everything I can think of to pinpoint the problem, but I ran out of ideas. I have swapped the drivers and the pin connections. I have also used another motor in place of the stalling one, and it still runs into the same problem. It does not make sense for one of the identical sides to be running fine and the other side having issues.

What could the problem be? What else can I try out to see if it solves the issue?


texts: Setup and hold for positive edge flip flop cascaded with negative edge flip flop

texts:
I know the following for two positive edge triggered flip flops in cascade.

Max(combinational logic delay) < Tclk_period + Tskew - Tsetup and
Min(combinational logic delay) > Tskew - Thold

But when I consider positive edge ff followed by negative edge ff how will the equation be modified. Will it be:

Max(combinational logic delay) < Tclk_period + (Tclk_period / 2) + Tskew - Tsetup and
Min(combinational logic delay) > Tskew - Thold

or:

Max(combinational logic delay) < (Tclk_period / 2) + Tskew - Tsetup and
Min(combinational logic delay) > Tskew - Thold


texts:
I'm using Altium Designer 14.2.3 and I have a connector on which are always two pins connected to each other. In my schematic library I have configured the Pins to be hidden and connected to the other. (e.g Pin 7: hide [x] Connect To 6)

In the PCB I want to route to both pins for having a better connection, but altium doesn't let me do this.

As shown in the image I want to connect R4 to pin 1 AND 12. Does anyone have a solution for this?


texts:
First off, this is my first post and I know enough about electronics to get myself in trouble.
I want to build an electric drive for my 25 foot sailboat, but instead of running it on batteries, I want to run it off a 2500watt ac generator To save weight and provide power for coffee maker and such.
I have so far:
130vdc motorrated at 3hp continous
1000volt,50 Amp bridge rectifier
Switch to reverse polarity

My question is, how big of a capacitor do I need to smooth the dirty dc power for the rectifier?


texts: Why use a series resistor between Arduino RX and ESP8266 TX?

texts:
I have seen this in several schematics which i assume are professional since they are for popular open-source products.

But i can't figure out why there is a 470 Ohms resistor in series between the RX pin of the Arduino and the TX pin of the ESP8266? Can someone please explain? Why choose this specific value since i see the same value resistor used in many schematics between the Arduino and the ESP8266?

I was also puzzling over the need for the potential divider but then i did some research and i found that there is a need for a logic-level shifter between the Arduino TX and the ESP8266 RX data line. But i can't find anything on the 470 Ohms series resistor.