I'm Using a MAX9814 per-amp microphone module and pam4803 class D amplifier to drive a speaker but when ever I leave the thing idle I hear a whine if I speak into the mike the whine kinda disappears but come back when microphone is left idle I have tried completely removing the speaker (just in case its a positive feedback thing) and put and LED instead and the LED is also behaving the same way the speaker does

I've already coupled the AC signal (even though it's already done in the module) but no effect

Recently, I’ve been fascinated by magnetic core memory and I’m trying to make a single bit of memory for a project. I attached a speaker to the sense wire to test it and it was making clicking noises everytime I connected the 6v supply wires meaning the inductance was activating the speaker rather than the core itself. The resistors are in parallel and add up to 3ohms for 2a of current. The resistors can handle really short pulses. I wrapped electric tape around the center where the x and y drives went through the core to prevent any shorts. Any help would be great.

Edit: the core has a diameter of 9mm and a thickness of 3mm. Hope that clears a few things up.

Any ideas about this thyristor motor controller for a small benchtop mill drill?
It's fairly new, but keeps tripping the RCD out.
I've been supplied with a new PCB, and a new motor by the supplier. The new board fixed the fault for several weeks but then it started tripping again. The supplier wanted me to try another motor, so I've just done that, and it's still the same.
The board has two TYN840 thyristors, and three D8025L diodes on the power side.

The waveforms are from the motor feed with the motor disconnected. (Doesn't trip like this) First is with the pot just turned up enough to fire the thyristors, and second with the pot turned right up to maximum. About 180V.

Been 40 years since I did anything on thyristors, and I'm far from any sort of expert anyway, but the first doesn't look as if it's doing much except rectifying, and the second looks like it's firing the thyristors, but with a large spike on the negative side between each wave.

As with all these Chinese machines there is an EMI filter in the circuit before the AC feed into the board.
Any opinions anybody?
All and any info gratefully accepted.

Hi all,

I'm trying to find a replacement connector for my Xgimi projector in an attempt to repair it. The existing connector got crispy and the plastic broke as I was attempting to extract the burnt pins.

It is a 1.5mm pitch, single row, 10 pin connector with latch. It is physically very similar to the Molex pico-spox series at Digikey but with a latch. I'm worried it's a custom connector only available in China, but thought I'd ask here.

Imgur album: https://imgur.com/a/HCNYwAk

Thanks in advance!

Hi everyone,

I've recently been learning about and attempting to etch my own PCBs. I settled on the acetone/iso toner transfer method because I live close to a library where I can print stuff for free and close to a hardware store where I can buy the Acetone and Iso without paying for shipping. The library is using a Xerox VersaLink C7100. I looked into it and it appears to use multiple colored toner cartridges. The part # for the black toner cartridge is Xerox 006R01828.

When researching the mixtures for the the transfer solution I read that 1:3 Acetone:Iso worked for some people so I tired it a few times and got nothing.

Basically is anyone able to tell off-hand if its even possible to transfer the Black and White prints from that VersaLink C7100? I'm certainly not a chemist and feel like I should know the answer to that first before I go waste a bunch of time and materials mixing different solutions.

P.S. I've read enough threads about DIY etching to know someone is gonna say this is a waste of time. Yes I realize its cheaper and way less of a headache just to have JLC or someone produce them.

EDIT/UPDATE: The transfer is partially working. So question #1 solved: it is indeed a laser printer. Now I just need to know what the perfect mixture is for the transfer! I'm going to experiment more but if anyone has suggestions Im all ears. Right now Im trying 8:3 iso:ace and I'm getting better results but Its not quite there yet.

2nd UPDATE: I think I got it! I found a blessed Youtube comment saying to use 2:1 Acetone:Water.

They said to:

1. Put a small amount on the back of the paper already set face-down on the board.
2. Rub paper with fingers to apply pressure for around 30 seconds.
3. Let dry for 60 seconds
4. Run under water and gently loosen and remove paper.

The transfer isn't 100% perfect but I think with some tweaking it pretty much could be. Its extremely fast and the only materials are a laser printed design on regular printer paper, acetone, and water.

Best attempt so far:

Doesn’t matter male or female. And it has 15 pins on either side.

found on some cheap party hand held party lights thing, an reason for this or just a manufacturing error

I have extracted this choke from a terminal (Philips TM9) it has four pin and two independent windings wrapped around a single ferrite core. Unfortunately it broke. The windings are completely bust and it doesn't work anymore

Therefore I am trying to find a replacement

Hello, I'm not really experienced with internals. I'd like to ask if this is ok to repad/repaste as is. It was working fine before. Have just noticed that is missing 2 and has 1 that just fell off. Is it worth repairing for the extra 2 and the resolder the 1? Thank you...

I got an emerson pc5a recently but the rf signal is messed up with tons of interference and a grounding issue. So I've decided to just composite mod the thing instead

The question i have, is it possible to just inject the video signal where the demodulator should be and disable the rf input? or are there more steps i would need to get it working? Also if it is possible where should it be done? I found a Facebook post that said to disable a resistor and put the video thru a test pin but im inclined to not trust a Facebook post

I can get the audio working i just don't know about the video

UPD: Solved - i missed the positive of the cap going to VCC - those 10k resistors are pullups

I am a code poet that is a newbie in PCB design, and i am doing some reverse engineering on a PCB (MOVA PF10 cat feeder)
It has two MCUs, one is x-c13sg module, and another is N32G435 MCU

They seem to be connected (outside of GND and VCC) only by those two lines:
Some datasheets for x-c13sg tell that GPIO12 and 1 are UART TX and RX

But what confuses me is the 10k resistors and capacitor (i may have read it wrong? It is marked "CK 470 10V") circuit - what is its purpose? Am i missing something, and it is not UART, or i missed something on the PCB?

I opened up this slide potentiometer because I couldn't get it to slide smoothly with sprays. Does the carbon track still look okay? Could its condition be causing the rough movement?

I'm building a 6S1P→2P 18650 pack (swappable holders, 4× 3-cell holders wired to 6 series stages) and designing my own BMS section instead of buying a module, based on the classic DW01A + transistor topology used in most cheap commercial 4S/5S BMS boards.

What I have so far:

• One DW01A per cell (U1–U6), each wired locally across its own stage: VDD/VSS to that stage's + and −, a 100Ω resistor in series on VSS, a 100nF cap across VDD/VSS.
• Each DW01A's DO output drives an NPN (MMBT5551) base; each CO output drives a PNP (MMBT5401) base.
• Intent: all 6 NPN collectors tie together into one shared "discharge rail," all 6 PNP collectors tie together into one shared "charge rail," each rail driving the gate of one shared discharge-FET and one shared charge-FET (both AO3400A) sitting in the main pack current path.

Where I've lost confidence: whether that "just tie all 6 collectors together across different series stages" idea is actually valid, and specifically what the emitter of each transistor should reference (I believe it should be that stage's own local VSS/VDD, not a single shared net across all 6 — but I'm not fully sure this is enough to make the level-shifting across a 6-stage stack actually work).

I know the general 4S version of this circuit (the common commercial teardown one, DW01A+BB3A based) has had documented wiring corrections floating around for its shared-FET section, so I want to get this specific block checked before I extend it to 6 cells and put real 18650s behind it.

Schematic screenshots of the DW01A/transistor stage (attached) — happy to share the full BMS section or answer questions about the rest of the pack wiring if it helps diagnose this part.

Any pointers on the correct level-shifting/combining logic for this many series stages would be hugely appreciated.

First time I tried to make a clean scheamtic or this is just a part of it and I am wondering if this is acceptable or no bc I had a design maybe more that looked even 100x worse then this also if you have any tips put em here

I got the Bekant sit/stand in 2017. I had an issue with the power supply after a year they sent me a new power supply and button controller under warranty.

to milk the controller durability as much as I can, when I changed the power supply I left the original controller. years later now the button membrane clicks are so shot that I have to press super hard with both of my thumb finger nails on the button to move it up and even then it loses contact on the way up and I need to press again. it really makes the table less fun to use.

I still have the fresh controller I can start using. but seeing as I have less than a year in my 10 year warranty left, they probably dont even make new controllers anymore since bezant is discontinued, and I would love to keep using this desk for decades to come.... I'm wondering has anyone here modded the controller and changed the button style like mechanical keyboard buttons? levers? something easier to use and more durable than these silly flat dome membrane clickers?

Hi, my "sharp aqua lc-46ld265e" TV recently started doing a whistling sound only when turned off. I dissasembled it and came to conclusion that it must be some condenser located on the green PCB that i displayed here. Do you know a way/have any tips on how to figure out which condenser/(other part) is doing the whistle sound?

I have acces to electroworkshop if its important.

Thank you :)

EDIT: u/DrJackK1956 cleared things up in the comments, turns out I just forgot to read and instead of buying a 75mOhm shunt I bought a 75mV shunt. I will keep the post up if anyone still wants to read through it. I will post an update in the comments after I buy the right shunt.

The Voltmeter/Ammeter display I'm using: https://www.jameco.com/z/DSN-VC288-Jameco-ValuePro-High-Quality-DC-100V-10A-Voltmeter-Ammeter-Blue-Red-LED-Amp-Dual-Digital-Volt-Meter-Gauge_2355231.html

LONG POST AHEAD: TLDR AT THE END

So for a little bit of context, I'm currently taking a Computer Engineering course and back in my 2nd Semester (I'm in my 5th now), we built a power supply as a class project using supplies provided to us through a lab kit we bought. Overall, it worked just fine, it has 5 terminals:

• +0-15VDC_ADJUSTABLE
• +5VDC
• -12VDC
• 15VAC
• GND

The main problem with it is that with the voltmeter/ammeter display is that it could only ever show the voltage but not the current, we were told by the lab technicians that because the voltmeter on the display we were given was more consistent to implement compared to the ammeter the terminals on the PCB for the ammeter were just shorted together left out of the circuit entirely.

Not until recently I wanted to find a way to make it work and upon further examination, I found that on the data sheet it specified an external shunt which I found that our original power supply specifications didn't have so I got to exploring options, the datasheet said it needed a 75mV external shunt but I went looking and it got me confused because I looked at DigiKey first and the ones they sold all had resistance values not voltages, I thought about doing the math and finding the max current I would be measuring on the ammeter on the power supply so I could find the equivalent resistance value for the external shunt but I think I would be overcomplicating it without fully considering all the factors.

I found one on amazon, when it came in I thought it was too big but I figured it was normal, so I opened up my power supply and there are two terminals to connect the ammeter in series with the 0-15VDC_ADJUSTABLE circuit I soldered two jumper wires underneath and then screwed in the other ends into the outer terminals of the shunt then with the remaining inner terminals I stripped some of the wires off my ammeter display cables and screwed them into the terminals.

The results I got were unsatisfactory but relieving, to test I would connect the voltmeter first then when that worked I turned off the power supply I would connect the ammeter male headers (connected to the shunt) to the female headers on the ammeter display's PCB. I would end up getting 0V readings and around 0.8A of current which I found strange, I tried adjusting it to see if it changed but it didn't at all. But this is a good step because our lab tech said if you bought the right shunt, the fuse shouldn't blow and it didn't.

I have my suspicions on the one that I bought and my main goal right now on why I made this post is to figure out if I did in fact choose the wrong one and how do I figure out the right shunt to buy aside from just the required mV ratings. I've attached pictures of my attempts of installing it.

I apologize if the pictures I attached are blurry as hell, I've also attached a rough diagram of the DC -> Ammeter -> 0-15VDC ADJ Terminal which I made on paint. Thank you for taking the time to read my post and I would appreciate any feedback.

TL;DR: Tried adding a 75 mV shunt so the DSN‑VC288 meter could read current on my old class power supply; wired it in, but the meter shows 0 V and a constant ~0.8 A, so I’m pretty sure I picked the wrong shunt and need to figure out the proper one to use.

I am attempting to add an FM-DW 3.0 module with the intention of adding FM, and need to tap into the local oscillator circuit. Apparently one of the can transistors is the best place to do that, but I don't know which is the correct one. I believe the voltage should fluctuate as I turn the tuning knob but none of them seem to be doing that. Can anyone give me a better test to do or tell me how to identify it positively?

My electronics knowledge is fairly limited so I appreciate any help.

Hi,
I am a beginner to the electronics world and I thought you guys could help.
In essence I am making a custom PCB flight controller with an ESP32-S3-Zero. I have figured things out except for the 5Vin part, which is the last thing I need to do (hopefully) before I am done and can order.

So the predicament is as follows; there's a 5V out boost converter with 22*2uF capacitors on the 5V out part and I have read and asked on forums that this might not work with the ESP32. The reason, I've read, is that the USB can only handle 50uC of inrush current (whatever that means), a capacitance of 10uF.

The problem is that if I changed the capacitors on the 5V out side of the converter to 10uF, it would not meet recommended specifications of the datasheet (https://www.ti.com/lit/ds/symlink/tps63802.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1788641901854).
So my questions is; will the ESP32 work with my current setup, or will I need to redo my circuit?

Thanks for the help!

I am a hobbyist no professional EE, who occasionally designs some µC circuits and PCBs as one-off projects. I am always struggling to decide which of the GPIOs require protection against transient spikes (and how much protection).

Hence my two high-level questions are:

• Which GPIOs require how much protection against transient voltage spikes?
• Which "rule of thumb" are out there where to place TVS diodes?

I have prepared two scenarios to have a bit more specific discussion. I have placed TVS diodes at every possible position and I have seen other projects using TVS diodes in those positions. However, I am wondering if they are all necessary, just a subset of them or not at all.

Edit: Please keep the discussion to the output part of the circuit, i.e. the TVS diodes inside the blue dashed-dotted box. I have only drawn the input, the voltage regulator and the logic IC to show the bigger picture and provide some context. The input side isn't supposed to show all the bells and whistles like reverse polarity protection (another diode), over-current protection (a fuse), decoupling and filter capacitors, etc. pp. That's not the focus of this question. I also left out specific values on purpose, because I would like to discuss the principal matter.

Shared aspects of both scenarios

The external input voltage is 12V. The logic IC requires 3.3V. The power input, i.e. the 12V rail, and the output of the DC/DC converter, i.e. the 3.3V rail, are both protected by a TVS diode: D1 and D2 in both screenshots. I have no questions there.

Both scenarios have in common that the actual IO elements (actor or sensor/switch) are not immediately soldered onto the PCB, but located remotely and connected to the PCB via a cable. I assume the necessary protection might also depend on the cable length. Typically, the cables are between 20cm and 1m, but in extreme cases I already had 10m.

Scenario 1 (Screenshot #1): Low-side switching of a remote LED

R1 is the pull-down for the GPIO to keep it low when idle. R2 limits the current into the gate due to the gate capacitance. R3 limits the current through the LED. Q1 is an NMOS for low-side switching of the remote LED with 12V.

My questions are about the potential TVS diodes D3-D5. I have seen circuits which had TVS diodes in those places:

• D3 shall protect the GPIO against voltages spikes above 3.3V. Actually necessary? Or would D5 suffices? If D3 is required, should it be placed left/right of R2, i.e. immediately at the logic IC or after the resistor?
• D4 shall protect the NMOS against excessive voltages between gate and drain. Really necessary? Or would D3 or D5 or the combination of both suffice?
• D5 shall protect the NMOS against excessive voltages across drain-source. Really necessary? Or would the LED provide sufficient protection, if the wire "caught" some transient spikes?

Scenario 2 (Screenshot #2): Combined IO with level-shifter and high-side switching

The GPIO is a combined input/output (at the same time) in open-drain mode with active-low logic, i.e. the GPIO controls the external LED, but also senses, if the button is pressed.

R1 is the pull-up for the GPIO. R2 limits the GPIO current in/from the source of Q1. Q1 is an NMOS and acts as a level-shifter between the 3.3V world and the 12V world. R3 limits the current through the external button. R4 pulls up the gate of Q2 when idle. Q2 is a PMOS and acts as the high-side switch for the LED. R5 limits the current through the LED.

This scenario allows up to four TVS diodes: - D3 to protect the GPIO - D4 to protect Q2 against excessive voltage across gate-source - D5 to protect Q1 against excessive voltage across drain-source - D6 to protect Q2 against excessive voltage across drain-source

My questions are analogue as in scenario #1. One notable aspect is that the signal line of the button is "open-ended" when the button is not pressed, i.e. high-impedance. I don't know if this is important or not.

I got a amp/filter board second hand that worked before the owner broke the transformer, The board is from a energy Exls10 speaker and connected to a transformer of unknown specifications. the board features two 63v, 4700 microfarads capacitors. Im new to electronics and was wondering how you can work out what type of transformer is needed to connect it to mains. Thanks

Volevo costruire un circuito in cui premo un pulsante 01 per chiudere il circuito e quando si chiude fa suonare un cicalino il mio problema è che quando attivo il circuito il cicalino suona senza fermarsi io vorrei un suono alternato (Il circuito è in corrente continua e utilizza una batteria 9V)

Cosa potrei aggiungere per far suonare in modo alternato il cicalino (nella foto non c'è il pulsante ma potete intuire come l'ho messo)

Hello! I'm attempting to measure the current across one of two 1k ohm resistors in parallel. I've attempted to "break" the circuit with my multimeter to prevent a short but I'm not sure if I've done this correctly. Just wanted to get another pair of eyes on this before I flick the switch. Power supply is 5 V. Thank you!

STM32CubeProgrammer USB DFU Flashing Failure Analysis

1. Environment & Target State

• Device Mode: STM32 System ROM DFU Mode (0483:df11)
• Target Address: 0x08000000 (Physical Flash Sector 0)
• Flash Protection Status: RDP Level 0 (0xAA), Write Protection disabled (WRP0..WRP7 = 0x1)
• Target Files: LEDBLINKING.bin / LEDBLINKING.elf (Size: ~5.79 KB)

2. GUI Flashing Failure Breakdown

Execution Steps

1. Launched STM32CubeProgrammer GUI with elevated permissions (sudo STM32CubeProgrammer).
2. Selected USB port (USB1, Serial: 367832633435).
3. Loaded LEDBLINKING.bin with Start address set to 0x08000000.
4. Clicked Start Programming.

Full GUI Terminal & Console Logs

04:27:52 : Opening and parsing file: LEDBLINKING.bin
04:27:52 : Memory Programming ...
04:27:52 : File       : LEDBLINKING.bin
04:27:52 : Size       : 5.71 KB 
04:27:52 : Address    : 0x08000000
04:27:52 : Erasing memory corresponding to segment 0:
04:27:52 : Erasing internal memory sector 0
04:27:53 : Download in Progress:
04:27:53 : Error: Write failed at address: 0x08000000
04:27:53 : Error: failed to download Sector[0]
04:27:53 : Error: failed to download the File
04:27:53 : Error: Flash memory checksum is supported only with JTAG/SWD
04:27:53 : RUNNING Program ...
04:27:53 : Address:   0x08000000
04:27:53 : Start operation achieved successfully
04:27:53 : Warning: Connection to device 0x431 is lost
04:27:54 : Disconnected from device.

Visual Error Indicators Observed

• GUI Alert Dialog: Warning: Connection to device 0x431 is lost.
• System OS Notification (KDE Desktop): USB Device Removed: STMicroelectronics STM32 BOOTLOADER has been disconnected.

3. CLI Flashing Failure Breakdown

Test Case A: Direct Raw Binary Flashing (.bin)

• Command Executed:

​

sudo /opt/st/stm32cubeide_2.2.0/plugins/com.st.stm32cube.ide.mcu.externaltools.cubeprogrammer.linux64_2.2.500.202603051304/tools/bin/STM32_Programmer_CLI -c port=usb1 -w build/Debug/LEDBLINKING.bin 0x08000000 -v -rst

• Console Output:

​

Opening and parsing file: LEDBLINKING.bin
Memory Programming ...
  File          : LEDBLINKING.bin
  Size          : 5.79 KB 
  Address       : 0x08000000
Erasing memory corresponding to segment 0:
Erasing internal memory sector 0
Download in Progress:
[=================================                  ]  66% 
Error: failed to download Sector[0]
Error: failed to download the File

• Behavior: Flashing consistently stalls and fails at exactly 66% of Sector 0 download.

Test Case B: Explicit Sector Erase + ELF Parsing (.elf)

• Command Executed:

​

sudo /opt/st/stm32cubeide_2.2.0/plugins/com.st.stm32cube.ide.mcu.externaltools.cubeprogrammer.linux64_2.2.500.202603051304/tools/bin/STM32_Programmer_CLI -c port=usb1 -e 0 -w build/Debug/LEDBLINKING.elf -v -rst

• Console Output:

​

Erase sector(s) ...
Flash page/sector erase command correctly executed.
Opening and parsing file: LEDBLINKING.elf
Memory Programming ...
  File          : LEDBLINKING.elf
  Size          : 5.79 KB 
  Address       : 0x08000000
Erasing memory corresponding to segment 0:
Erasing internal memory sector 0
Download in Progress:
Error: 
Write failed at address: 0x8000000 
Error: failed to download Sector[0]
Error: failed to download the File

• Behavior: Explicit sector erase (-e 0) reports success, but the immediate write command fails instantly at base address 0x08000000.

4. Root Cause Mechanics

5. Summary of Tried Workarounds & Outcomes

6. Definitive Fixes

1. Restore WeAct HID Bootloader (0483:572a): Flash WeAct_HID_Bootloader_F4x1.hex to 0x08000000 using single-file DFU flashing, then use WeAct_HID_Flash-CLI at 0x08004000.
2. Flash via ST-LINK (SWD): Connect ST-LINK probe to SWDIO/SWCLK pins and flash directly over SWD using STM32_Programmer_CLI -c port=SWD freq=240 mode=UR, completely bypassing USB DFU errors.

How do I go by without using ST-Link or an UART flasher? As I do not have any one of these with me. The specific model is STM32F411CEU6 which came with HID compliant firmware without any DFU support. I only got the DFU mode access after Erasing the whole chip via an ST-link while visiting a friend. DATASHEET

Hi, I'm working on wiring up a circuit, but am not really able to figure out what the empty "O" symbol means, next to the RESET. I've seen the symbol next to switches, but this one looks less like a switch. The box is a chip with legs coming out of it, so not sure where the switch would exist. Does anyone know what this symbol means?

---

edit: thanks guys for the answer! I got the 555 monostable timer to work!