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Q&A

General Q&A about the design and function of electronic systems, electric power systems and infrastructure, their theory, and tools specific to those fields. Read these guidelines before posting.

Filters (None)
71%
+3 −0
Isolated Digital Input - Overvoltage protection

I am trying to build an active-low digital isolated switch capable of withstanding 32VDC voltage without creating any damage to the system. This is the snapshot of the circuit not fulfilling the r...

3 answers  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Olin Lathrop‭

71%
+3 −0
Measuring Input/Output Impedance with a VNA

On paper you can measure the input impedance of an amplifier circuit by attaching a voltage source to the input, shorting the output, and calculating the resulting impedance from the voltage and cu...

1 answer  ·  posted 2y ago by jm567‭  ·  last activity 2y ago by coquelicot‭

60%
+1 −0
Is it possible to design an n-bit full adder using SystemVerilog?

I am trying to design a full adder in SystemVerilog. I searched on Wikipedia and I found this https://en.wikibooks.org/w/index.php?title=Microprocessor_Design/Add_and_Subtract_Blocks module full_...

1 answer  ·  posted 2y ago by System‭  ·  last activity 2y ago by System‭

50%
+0 −0
My grid dip: how does this electron tube technology work?

Here is a video of the AN/PRM10, and here is a schematic (I believe the image can be zoomed): As most commercial grid dip meters produced in the past, this one possesses several functions in ad...

1 answer  ·  posted 2y ago by coquelicot‭  ·  last activity 2y ago by coquelicot‭

57%
+2 −1
What is causing this massive discharge traveling down a power line?

What is causing this [ABC-news video via Twitter] spectacular power-line phenomenon? [image: still from ABC News]

1 answer  ·  posted 2y ago by Pete W‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+2 −0
Name of this current limiting device

I'm trying to modify a LED torch, and there is a DC-DC booster (1.5 V to 3.3 V) and after that some SOT-23 device which (I assume) keeps constant 90 mA current through LED. I know I could remove th...

2 answers  ·  posted 2y ago by Chupacabras‭  ·  edited 2y ago by Chupacabras‭

71%
+3 −0
Is it always necessary to use the ground terminal of the oscilloscope probe?

Assume my oscilloscope is grounded, and the DUT is grounded as well (earth ground). I am using a standard 10 Mohm impedance 1:10 passive probe. So, the ground terminal of the probe is in fact con...

2 answers  ·  posted 2y ago by coquelicot‭  ·  last activity 2y ago by Andy aka‭

66%
+2 −0
BLDC motor - initial rotor position

Sensorless BLDC motor controller are becoming more and more popular, especially with rising of the drone industry. Being able to detect where the rotor is at 0rpm or no load seems intuitive if we ...

2 answers  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by KalleMP‭

71%
+3 −0
Is a BJT 3-transistor Wilson mirror faster than a simple mirror?

My question is trying to understand if there is an effect on the switching time, on both turn-on and turn-off, between the following configurations. A mirror set up to switch a current, and there ...

1 answer  ·  posted 2y ago by Pete W‭  ·  last activity 2y ago by Olin Lathrop‭

60%
+1 −0
Why are two identical filters required for each signal, if the signals can be multiplexed into a single filter?

In the block diagram of this pulse oximeter design guide , in page 6, I see that the system utilizes two analog filters, one for filtering the PPG signal generated while the RED light/wavelength is...

1 answer  ·  posted 2y ago by Georgian‭  ·  edited 2y ago by Georgian‭

50%
+2 −2
Why does AC frequency affect my microwave's RPM?

I used to live in the United States, and my microwave ovens' turntables turned at six rotations per minute (RPM). I now live in Israel, and my microwave oven's turntable rotates at five RPM. Annoye...

1 answer  ·  posted 2y ago by msh210‭  ·  last activity 2y ago by Olin Lathrop‭

44%
+2 −3
Why isn't voltage of electric chair higher?

I recall vividly a story told by my grandfather who worked with high voltage power lines. A worker drove heavy machinery into 700kV line and then jumped out of the truck, instantly combusting upon ...

2 answers  ·  posted 2y ago by Kranulis‭  ·  last activity 2y ago by manassehkatz‭

75%
+4 −0
MOV vs TVS diode

Simple thing that I realized I should know but do not -- when is an MOV preferable to a TVS diode (with some associated network to really make it work, in both cases)? Is it even something to routi...

2 answers  ·  posted 2y ago by Pete W‭  ·  last activity 2y ago by coquelicot‭

60%
+1 −0
Why is the Linear Time-Invariant System (LTI) dominant in Signal processing?

I just want to know why the Linear time-invariant(LTI) systems are a rich class in Signal Processing. Ofcourse there are different systems but still LTI is stressed a lot in academia. Is there any ...

1 answer  ·  posted 2y ago by aditya98‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+2 −0
recommendation for chip programming connection (pogo?)

Background: I have several microcontroller based projects with custom PCB that have been in very-low-volume production, but the quantities are starting to go up. (batch sizes now ~100 and threateni...

1 answer  ·  posted 2y ago by Pete W‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+2 −0
PCT2075 temperature sensor accuracy

I read datasheet for PCT2075 temperature sensor and there are some contradicting data about accuracy for me. Page 21: accuracy ±1°C (Tamb = -25°C to +100°C) accuracy ±2°C (Tamb = -55°C to +125°C...

1 answer  ·  posted 2y ago by Chupacabras‭  ·  last activity 2y ago by Olin Lathrop‭

75%
+4 −0
What should be considered when picking a flyback diode?

Which are the parameters I should looking for when picking a flyback diode to be placed across a generic coil, such as a relay? That is: a coil with plain on/off functionality, for example a 24VDC ...

2 answers  ·  posted 2y ago by Lundin‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+2 −0
Cable loops between utility poles?

Sometimes cables between utility poles make a loop and do a U-turn. What is the purpose of such loops? The loop I'm asking about is in the lower set of wires towards the left of the picture. The...

0 answers  ·  posted 2y ago by Olin Lathrop‭  ·  edited 2y ago by Olin Lathrop‭

66%
+2 −0
Confused about the amplitude and shape of output voltage pulse

In the circuit below, I am applying a $3.3Vpp$, $63kHz$, 50% Duty Cycle, PWM input signal at the gate of the mosfet and I am expecting to see a similar waveform with different amplitude at the LED...

2 answers  ·  posted 2y ago by Georgian‭  ·  last activity 2y ago by coquelicot‭

66%
+2 −0
CAN Bus - Internal Oscillator

Every time I needed CAN, I had just put external crystal and didn't think about it after that. It worked fine. I am wondering however whether the precisions of MCU internal oscillator is sufficien...

3 answers  ·  posted 2y ago by 2kind‭  ·  edited 2y ago by Lundin‭

66%
+2 −0
Driving ADC with opamp with large rails

In the image below is an opamp buffer with +/- 15v rails connected to a 3.3v ADC. The input to the opamp is limited to 0-3v. There is no protection circuitry for the ADC. Is the risk of the opam...

3 answers  ·  posted 2y ago by z3333‭  ·  last activity 2y ago by coquelicot‭

66%
+2 −0
Transformer - Vsec or Current rating parameter

I am looking at the datasheet of the 7508170315(link) transformer and something seems strange to me. If I connect this to a 12V supply and expose it to 10us pulse: 12V*10us/475uH = 252mA which ...

2 answers  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Olin Lathrop‭

33%
+0 −2
Is it possible for one transistor to switch between two loads?

The output collector-emitter part of a transistor can be thought of as a 2-terminal SPST switch controlled by the input base-emitter voltage or base current. So this transistor switch can control o...

3 answers  ·  posted 2y ago by Circuit fantasist‭  ·  last activity 2y ago by Circuit fantasist‭

71%
+3 −0
Moving average that uses less memory?

My control system gets a signal representing the plant output, but that signal has a lot of noise on it. The control system goes nuts trying to react to the noise. I need to filter out the noise ...

4 answers  ·  posted 3y ago by Olin Lathrop‭  ·  last activity 2y ago by Pete W‭

62%
+3 −1
How to plot the I-V curve of a tunnel diode?

I am trying to understand tunnel diodes by experimenting with them. Research tells me they can have negative resistance, and can be used to build a high frequency oscillator. Tunnel diodes are su...

4 answers  ·  posted 2y ago by tlfong01‭  ·  last activity 2y ago by Circuit fantasist‭

60%
+1 −0
Flyback Converter - Output Ripple

I am eager to create a flyback converter for driving the high side MOSFET. Here is a snapshot of my work so far: 555 timer starts with generating ~100kHz 12V signal on Q1. Q2 is monitoring the v...

1 answer  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Olin Lathrop‭

60%
+1 −0
digital multimeter display count range

The display counts range is one of the digital multimeter characteristics, we know that a DMM is based on an analog/digital converter. And we know too that each ADC has a resolution nBits. A 16 bit...

1 answer  ·  posted 2y ago by Pacifist‭  ·  last activity 2y ago by Olin Lathrop‭

57%
+2 −1
How can I debug, (and eventually fix) this Roomba PCB? [closed]

I've got a broken roomba, I've tried new batteries and a working charger. The charger is supposed to output 20V-24W when the roomba is plugged in. the picture just shows how I'm measuring the pow...

1 answer  ·  posted 2y ago by dustytrash‭  ·  edited 2y ago by dustytrash‭

66%
+2 −0
Cleaning flux out of USB connectors after soldering

When soldering Micro-USB or USB-C connectors by hand, flux is applied generously. This sometimes results in flux getting inside the connector housing, making it sticky and creating high physical re...

1 answer  ·  posted 2y ago by Kranulis‭  ·  edited 2y ago by Lundin‭

50%
+1 −1
High Power Switch - High Side vs. Low Side Switching

Imagine a battery pack with <=60VDC of maximum voltage and a load of up to 10kW of power(the PMSM inverter with the input capacitance of up to 1mF). The load is not always known - could be 100uF...

2 answers  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Olin Lathrop‭

60%
+1 −0
Bit-rate vs Baud-rate

I am really confused how the terms bit-rate are baud-rate are used in electronics. I never bothered thinking about baud-rate being different than bit-rate before. But recently, one of my teachers t...

3 answers  ·  posted 2y ago by Giga-Byte‭  ·  last activity 2y ago by Canina‭

50%
+1 −1
What is the role of the differential amplifier in a delta sigma converter?

A differential amplifier amplifies the difference between the two input voltages but suppresses any voltage common to the two inputs. Based on this scheme the differential amplifier is substrac...

1 answer  ·  posted 2y ago by Pacifist‭  ·  edited 2y ago by Olin Lathrop‭

60%
+1 −0
What is the difference between differential amplifier and differentiator?

Since am interested in how a delta sigma modulator works, I need to know what is the difference between differential amplifier and differentiator if there is a difference of course.

3 answers  ·  posted 2y ago by Pacifist‭  ·  last activity 2y ago by Circuit fantasist‭

66%
+2 −0
How to estimate time of completion while developing an electronic product?

I don't know whether this question is on-topic or not but answering this helps a lot of future electronics entrepreneurs like me understand how the product design and development time estimation ta...

5 answers  ·  posted 2y ago by aditya98‭  ·  last activity 2y ago by TonyStewart‭

66%
+2 −0
Driving LED with NPN transistor from I/O pin

Trying to understand a circuit for driving a LED found on a board I purchased. Below is a circuit driven by an I/O pin (HS2) of a small 3.3V processor. The HS2 pin is driven by the I/O with specs...

3 answers  ·  posted 3y ago by eric‭  ·  last activity 2y ago by coquelicot‭

71%
+3 −0
Using FET based followers and design rules

Usually, voltage followers are built with bipolar transistors (or with opamps if better precision is needed). In this case, the simple rule says that the transistor emitter "follows" the input vol...

5 answers  ·  posted 2y ago by coquelicot‭  ·  last activity 2y ago by TonyStewart‭

66%
+2 −0
Understanding the s11 and s21 coefficients of a microstrip line with resistor to ground

I thought I understood the theory of scattering parameters, smith charts etc. until I tried a practical example. The following stupid example is supposed to be a microstrip line shunted by two 100...

2 answers  ·  posted 2y ago by coquelicot‭  ·  last activity 2y ago by coquelicot‭

57%
+2 −1
ESD Protection - Differential Amplifier

More about the circuit The circuit is sensing (low side sensing for many reasons) current used to power up the lights with 28V(part of the schematics not shown here -> relay with LC filter ...

3 answers  ·  posted 2y ago by 2kind‭  ·  last activity 2y ago by Nick Alexeev‭

71%
+3 −0
Why is the ACK (acknowledge bit) in the CAN bus frames dominant? What could have been the rationale behind that design decision?

[I’m asking this question out of curiosity. I understand that this aspect of the CAN bus specification is what it is, and can not change.] The ACK bit in any CAN data frame is dominant. Each rece...

2 answers  ·  posted 2y ago by Nick Alexeev‭  ·  last activity 2y ago by Olin Lathrop‭

66%
+2 −0
De-bouncing input signals?

I've heard that input signals to digital circuits should be "de-bounced", at least sometimes. What is de-bouncing? Why is it needed? When is it needed? What is bouncing around in the first place?

2 answers  ·  posted 2y ago by Olin Lathrop‭  ·  last activity 2y ago by Circuit fantasist‭

61%
+6 −3
weak WiFi when microwave is running [closed]

Nowadays, that I videoconference over WiFi a lot, I've started to notice some trends in WiFi quality. And it seems my connectivity decreases when my microwave oven is on (I work in the same room a...

1 answer  ·  posted 2y ago by msh210‭  ·  last activity 2y ago by .                                                .‭

71%
+3 −0
Why there is a body diode in mosfets?

In theory (I mean in my engineering curriculum) I never found a diode in a mosfet symbol but in datasheets there is a diode called as body diode in both pmos and nmos.Please explain its significan...

3 answers  ·  posted 2y ago by aditya98‭  ·  last activity 2y ago by Nick Alexeev‭

42%
+1 −2
Usage of modern active building blocks [closed]

In the past, a large number of new active building blocks have been proposed and published by many researchers all over the world. In most cases, these new building blocks were used for realizing n...

0 answers  ·  posted 2y ago by LvW‭  ·  edited 2y ago by LvW‭

71%
+3 −0
Why Ib=const. for BJT output characteristics Ic=f(Vce)

As I have learned, it is allowed to ask a question here to which I already know one of several possible answers. Introduction: In some books and other technical papers (also from universities) it i...

4 answers  ·  posted 2y ago by LvW‭  ·  edited 2y ago by LvW‭

60%
+1 −0
More accuracy from multiple resistors in series or parallel?

What happens to the overall accuracy of a resistor if I implement it as multiple resistors in series or parallel? For example, can I get better than 2 kΩ 5% by putting two 1 kΩ 5% resistors in ser...

2 answers  ·  posted 2y ago by Olin Lathrop‭  ·  last activity 2y ago by coquelicot‭

60%
+1 −0
High pass filter design

Despite there are many filter calculators available on the web, I still have difficulties to translate what I need into calculator design parameters. For my application, I need ideally a high pass ...

3 answers  ·  posted 2y ago by coquelicot‭  ·  last activity 2y ago by a concerned citizen‭

66%
+2 −0
Purpose of emitter resistor in a common collector amplifier

I see a lot of common collector amplifiers with the output taken across an emitter resistor. What is the purpose of doing it this way instead of connecting your load directly to the emitter? I shou...

4 answers  ·  posted 2y ago by jm567‭  ·  last activity 2y ago by LvW‭

85%
+10 −0
How to calculate pullup resistor value for pushbutton?

What value pullup resistor should I use for a pushbutton connected to a microcontroller input? I've seen values from 1 kΩ to over 100 kΩ. Some references just say to use 10 kΩ because it's a "goo...

2 answers  ·  posted 3y ago by Olin Lathrop‭  ·  last activity 2y ago by Circuit fantasist‭

66%
+2 −0
Emitter Bypass Capacitor in a CE Amplifier

How exactly is the emitter capacitor C3 helping to increase the voltage gain in the common emitter amplifier below? Is it because for AC signals the emitter looks like a short to ground and that es...

2 answers  ·  posted 2y ago by jm567‭  ·  last activity 2y ago by Circuit fantasist‭

50%
+0 −0
General Questions Regarding FPGAs [closed]

I'm curious about FPGAs and would eventually like to get into them sometime during the future, so I'd like to ask three broad questions to help orient myself: In what applications are FPGAs the m...

0 answers  ·  posted 2y ago by jm567‭  ·  closed 2y ago by Olin Lathrop‭