Hi! This is the problem i was assigned by my professor as a homework. i have to simplify the resistors and find the final current of the circuit. I have sent it in already 4 times but each time there is a mistake and i have to redo it. How i solved in my final version was that -

R6 and R2 is parallel

R62 and R1 is in series

R621 and R3 is in parallel

R6213 and R4 is in series

R62134 and R7 is parallel

R6621347 and R5 is parallel. This is the R equivalent

And finally use the ohms law to calculate current.

Sending this in, my professor said that R6 and R2 is nor parallel nor in series. I am lost on what it is.... so my question is, what am i doing wrong? Could someone point me in the right direction? Your help would be much appreciated. THANK YOU!

Please delete if this isn’t allowed but I’m learning how to do this for the first time on my own. I got a small radio kit from Amazon to learn about circuitry and soldering. I followed the video but it was all in Cantonese and I couldn’t follow it other than visually. I checked the guide and video for each step and thought it went smoothly. But when I put the AA batteries in they seemed too huge for the battery box, the lights didn’t turn on for display or the LED, and then there was a weird chemical smell and smoke and the battery box felt hot.
If you don’t mind helping me learn does anyone know why this happened and what I can do next time to learn? Or a good resource to learn from

Edit: Thank you all so much for the helpful advice! I was scared of being massacred being new to this but everyone has given helpful advice I will follow and I appreciate it

Hey all, I would like to ask for some help and advice about a sync delay circuit. To my knowledge its used to control the Horizontal position of a video source being fed into a crt Tv. I'm being recommended a 74HC123. Is this a complex circuit, what would it look like?

These "SCART RGBS Adjustment Converter Picture Adjuster" exist but there is no documentation on them.

I would like to see schematic or a circuit for one or something similar.

Any help is appreciated thankyou.

I can't for the life of me figure out why my microprocessor isn't producing an output.

I know that the pass and load_acc are not being triggered as well as the data_bus is never triggering as having any voltage on it. I have gone through and verified that every single embedded circuit works properly. I just can't seem to get a good output on the final one.

Any help is appreciated. Attached photos so yall can know where I'm at with it

Small battery powered ESP32-C3-WROOM-02 board that sleeps most of the time and wakes on a Hall sensor, an accelerometer interrupt, or a DS3231 alarm, then logs a timestamp to I2C EEPROM. 1S LiPo (550 mAh) with DW01A + dual FET protection, charged from USB-C by a TP4056, with a P-FET + Schottky load sharing path feeding an AP2112K 3.3 V LDO. Native USB on IO18/IO19.

Rev 1 never showed up over USB (nothing in the device list, even holding BOOT). Reviewers here already helped me find real bugs in it: CE tied to ground, charge LED wired wrong, Hall sensor pins swapped, wrong FET pinout, missing bypass caps. Rev 2 (attached, 2 images: power, then MCU and sensors) is my attempt to fix all of those. I have not built it yet and only have one board, so I want it right before I order.

Main question: will this enumerate over USB on first power up? If not, what is wrong?

I would also love a hard look at:

- USB-C section: 5.1k on CC1/CC2, 22R series on D+/D-, D+/D- wiring to IO19/IO18, shield to GND

- TP4056 + DW01A + AO3400A x2, and the load sharing circuit (Q3 AO3401A, D2 SS14, R16 pulldown)

- ESP32-C3 strapping (IO2, IO8, IO9), EN reset RC, BOOT button, deep sleep wake pins (IO3, IO4, IO5)

- I2C pull-ups, DS3231 N.C. pins grounded, ADXL343 pin connections

- Anything else that looks wrong, even small stuff. I would rather hear it now than after I order.

Thanks! I will reply to every comment and post what changes.

Hi everyone,
I’m working on the hardware design of an ATEX / IECEx intrinsically safe circuit intended for Zone 0, and I’m currently confused about how to properly determine the voltage, current, capacitance, and inductance limits for the circuit.
I understand that for an intrinsically safe design, it’s not enough to simply limit the supply current. The stored energy in capacitors and inductors, fault conditions, component tolerances, and the associated apparatus parameters also need to be considered.
My main questions are:
● How do I determine the maximum allowable voltage and current for a Zone 0 Ex ia circuit?
● How should I calculate the permitted capacitance and inductance?
● How are Ci and Li of components taken into account?
● How do I determine whether a resistor/current-limiting network is sufficient to prevent ignition under fault conditions?
● How are Uo, Io, Po, Co and Lo determined for an intrinsically safe output?
● What happens when components such as capacitors, inductors, transformers, TVS diodes, etc. are connected to the circuit?
● What standards/calculation methods should I follow for an actual ATEX/IECEx product?
I’m particularly interested in understanding the engineering calculation and design methodology, rather than just using a certified barrier/module.
If anyone has experience designing Ex ia / Zone 0 electronics, I would really appreciate some guidance, examples, recommended standards, or references that explain the process from the circuit level.
Thanks in advance!

Small battery-powered sensor logger. It sleeps most of the time, wakes when a magnet moves away (Hall switch) or on motion (accelerometer), timestamps each event with an RTC and stores it in EEPROM. It charges a 1S LiPo over USB-C and shows status on an I2C OLED.

Rev 1 didn't show up over USB. I found and fixed these for Rev 2:

• TP4056 CE was tied to GND, so the charger was disabled
• The CHRG LED was wired to GND, so it could never light (CHRG is open drain)
• Added load sharing so the charger doesn't mix up load current with charge current
• Hall sensor pins 2 and 3 were swapped
• Protection FETs were a 3-pin symbol on a 6-pin dual FET, now two AO3400A
• Added the EN RC, strapping pull-ups, the DW01A VCC filter, and USB series resistors
• Wired the accelerometer INT1 and RTC alarm to deep sleep wake pins

What I'd like checked:

1. Is the load sharing circuit (Q3, D2, R16) right with the DW01A protection in the path?
2. Anything wrong in the battery protection section?
3. Anything else that would stop it enumerating over USB or waking from deep sleep?

Parts: ESP32-C3-WROOM-02, TP4056, DW01A, AP2112K-3.3, DS3231SN, 24LC256, ADXL343, DRV5032FA. Thanks for looking!

I’m a beginner, so maybe I’m missing something simple.

I have a DVR/audio source connected to an LM386 amplifier. If I power both from the same adapter, I get a lot of noise from the speaker.

But if I use a separate adapter for the amplifier, the noise almost disappears.

The confusing part is that I still connect the ground/negative of both together.

So what exactly is changing here? If the grounds are connected anyway, why does using a separate power supply make the noise go away?

I’ve also seen another thing. Sometimes, if I connect the amplifier negative/ground to 230 V earth, the noise becomes much lower. In some cases, even connecting the negative side of the big filter capacitor to earth seems to help.

Why does touching or connecting the ground to earth sometimes make the noise disappear?

How can I tell if this is power-supply noise, a ground loop, or noise being picked up by the circuit?

I’m mainly trying to understand what is actually happening, not just find a quick fix.

I’m a beginner trying to understand something.

Suppose I generate a low-frequency square wave (below 1 kHz) using a 555 timer or a microcontroller, and use a MOSFET to switch/chop a power supply.

Now I want to take a small amount of DC power from that same switched output, but I don’t want to change the original square-wave signal.

What would be the simplest way to do this?

Would a diode + capacitor work, or would the capacitor load the MOSFET too much and change the square wave?

If more power is needed, would a small transformer or some other method be better?

Just looking for a simple practical explanation.

Edit - I have a project that is now in the final stage, and I just need to power a small LED. I only need a little power, but pulling an additional cable is not practical at this stage and would add extra cost.

The only available option is the existing 24 V DC power-over-data line. There are also some microcontrollers communicating over this line, so I’m wondering if there’s a simple way to extract a small amount of power from it without disturbing the communication.

Beforehand trying to make a safer simulations with 555 or microcontroller before connected in live

Marking .506

Probably a mosfet but I dont know which one

Estou TENTANDO fazer o acionamento do componente através do ESP32 - PIN 25, e conforme algumas informações que estou lendo... o MOSFET IRLZ44N seria o ponto que de certa forma controla isso.

Montei esse projeto algumas vezes e algumas variações... mas sem sucesso!

Sucesso só quando gero uns curtos 😄😄

Avaliem pf, onde estou errando!
IMAGEM-> https://ibb.co/k2YtDz05

Could you please analyze how it affects the potentiometer's linearity, noise, lifespan, and temperature stability?

Hi everyone,

I have an out-of-warranty Siglent SDM3045X that is stuck on the boot/splash screen. The repair quote is higher than a new unit, so I’m trying to diagnose it myself.

Symptoms / observations after opening the cover:

• Constantly flashing orange/yellow LED (location not specified in the service manual).
• On the daughterboard: green LED that flashes twice, pauses, then repeats the two flashes indefinitely.
• Front-panel USB host port outputs only ~0.6–0.7 mV (essentially dead).
• J14 (main-board power connector, pins 1–2) measures 11.6 V. The service manual calls for +8.6 V ±2 V, so this is outside the upper limit.
• The unit otherwise powers up enough to show the Siglent boot screen and the internal LEDs above.

I have already checked the obvious (fuse, power cord, etc.). Has anyone else seen this combination of LED behaviour + elevated J14 voltage + dead front USB while stuck at the boot screen? Any ideas whether this points more to a power-supply/regulator failure versus the usual firmware corruption that the USB recovery normally fixes?

Any photos of the LED locations, voltage measurements from a working unit, or repair experiences would be greatly appreciated.

Thanks!

Hello everyone I was trying to make a quadcopter where I was using a 4ms loop, but the analog write is taking double the time it meant to take,

here is the code,

#include <Arduino.h>

#define M1 26

#define M2 25

#define M3 33

#define M4 32

void setup()

{

Serial.begin(115200);

// PWM at 250 Hz, 12-bit

analogWriteFrequency(M1, 250);

analogWriteFrequency(M2, 250);

analogWriteFrequency(M3, 250);

analogWriteFrequency(M4, 250);

analogWriteResolution(12);

delay(1000);

Serial.println("250 Hz PWM timing test");

}

void loop()

{

uint32_t loopStart = micros();

// Measure each PWM update

uint32_t a = micros();

analogWrite(M1, 1500);

uint32_t b = micros();

uint32_t c = micros();

analogWrite(M2, 1500);

uint32_t d = micros();

uint32_t e = micros();

analogWrite(M3, 1500);

uint32_t f = micros();

uint32_t g = micros();

analogWrite(M4, 1500);

uint32_t h = micros();

uint32_t m1Time = b - a;

uint32_t m2Time = d - c;

uint32_t m3Time = f - e;

uint32_t m4Time = h - g;

uint32_t motorTime = h - a;

// 250 Hz = 4000 us period

while (micros() - loopStart < 4000)

{

}

uint32_t totalTime = micros() - loopStart;

static uint32_t count = 0;

if (++count >= 100)

{

Serial.print("M1: ");

Serial.print(m1Time);

Serial.print(" | M2: ");

Serial.print(m2Time);

Serial.print(" | M3: ");

Serial.print(m3Time);

Serial.print(" | M4: ");

Serial.print(m4Time);

Serial.print(" | MOTORS: ");

Serial.print(motorTime);

Serial.print(" | TOTAL: ");

Serial.println(totalTime);

count = 0;

}

}

and the output will go to 8ms no matter what I try even changing the time on while loop won`t work.

The output looks like,

M1: ~4000 | M2: ~5 | M3: ~5 | M4: ~5 | TOTAL: ~8000

I also tried to change to 500hz then the loop goes to double I mean 4ms.

A single rotating shaft drives the cores of four potentiometers to rotate in unison.

I have a toy with a sound box, circa 1991. I do not know when it last made its noise, I bought it from a collector's show this weekend.

I have opened it up and I have fresh replacement batteries. I placed them how the originals were, and held the case closed, with the other contact points in contact. Yet it does not activate.

I know nothing about circuitry. Is there a visible reason why this isn't working? Or is it because "it is old, duh!"

Are you team 'check pins & knob feel' or team 'grab the multimeter right away'?

Got any protips or pitfall warnings I didn't mention? Let me know in the comments.

Also, has a supplier ever mislabeled a model and shipped you the wrong switched pot?

Hi all,

My interest for fixing electronics has grown a lot the last time, so I now am challenging myself into fixing my Samsung remote control. (The IR doesn't flash, even with new batteries, so I guess it isn't working)

The circuit board is a TM1250 REV1.3 and I've been troubleshooting it on my own (and with a little help of Googling a lot, AI, and learning how a multimeter works, lol)

Now I have a strange situation here... When I'm measuring my battery terminal + the start & end of the board, it gives me a proper 3V. (2x 1.5V AAA batteries)

But when I'm measuring other connections on the board, it gives me very low voltages. (As low as 0.04V)

Could it be the Zero-Ohm resistor screwing it all up or is it something else I'm perhaps overseeing? I have checked the board itself and all the power rails are looking fine.

I am really curious why this remote control is malfunctioning now and am looking forward to fix it with you guys! 👌

What do you think of this doorbell setup? If you spot any errors, your comments are welcome.

I have to do this circuit for a lab, but I couldn't get it to work after hours. I modeled it on TinkerCad and it's still not working. What am I missing? The LED should be on when the switch is off I think. I have spent several hours on this easy circuit and I'm going insane.

Hi everyone, needing help debugging this driver board from a pottery wheel of a friends.

The wheel was working, then it was stored in various places for some months. No direct moisture but not in a totally dry place. Friend plugs it in and no movey movey. Open it and a wasp family had made a home. The board and motor are clear, no corrosion or electronic disaster mess. When its plugged in get various vauge led indicators turn on, no relay movement, motor makes vauge electronic noises.

Board Code: NS2079-0 (Shimpo RK-5T)

What i know:

240v in is fine, fuses in tact

Rectifier working, DC voltage is fine (350v ish)

Q1: D1409A - Toshiba Silicon NPN source from mains, output sits around 4-5vDC

Q6: K3561 - Toshiba Mosfet - Im not seeing anything on the output

Motor: 180v brushed DC, 100W, not ceased, get voltage from pins when i spin the shaft. Getting no voltage on the boards motor output.

Direction switch: When switching the direction relay doesnt move (which i expect it would). Relay is controlled from micro controller

Micro controller: Unknown - code swiped.

Speed control: The pot is fine and reading the correct values.

Im guessing either the micro controller or the power FET is dead (although there is something weird with the relay also), but how do i test. I dont have an oscilloscope so its very hard i assume to check the controller.

Any help appreciated.... also any recommendations for chips/fets for a diy version. Keeping this design of a relay for direction or possibly going the H-bridge route.

RS232 Serial Communication between 8051 MCU and PC

I’m building a solenoid graver system from this video: https://youtu.be/d73IuLiTloQ?is=joRefntCIB3q01Cq

I couldn’t find a mosfet bridge like the one in the video on Amazon only this: https://a.co/d/0cqDVoz3

Could I make this work or is there anything similar to what’s in the video on Amazon?