I bought a new multimeter recently (good reviews)

I have a basic transistor circuit on breadboard. Whenever I measure voltage across different resistors the multimeter always give a different value , the difference in value is 0.2 to 0.3 V.

Hello,
Is this power supply circuit correct? Are there any changes I should make?

Unfortunately, I started working on it several months ago, and I don’t really remember why I made some choices.. there are actually a lot of ceramic capacitors on it. For some of the capacitor and resistor values, I just used whatever I had on hand.

The 9V supply will power an OPA1622 op-amp, and the 5V supply will power a QCC5125-based Bluetooth module. The goal is to upgrade the KRC-86B that’s currently in my car’s stereo, it only outputs sound through one speaker at a time (I haven’t found the cause) and this will finally let me take calls via Bluetooth.

Hello!

Been dipping my toes into PCB design recently as a complete novice. I've been playing with shift registers as a way to get more switches on my microcontroller.

The shift register pins are set up in a way that I don't understand. But I'm sure that there's a reason for it, and I'd love to know what it is in hopes that it'll illuminate some design considerations that I'm unaware of.

I've been trying to break out this shift register in KiCAD in such a way that it's easy to daisy chain them and easy to connect to buttons, but I'm finding it unnecessarily complicated. It seems as though it's actually impossible to do on one layer (not that it's necessary to do it on one! But I think that's an illustration of the complexity!)

I quickly doodled up how I'd naively expect it to be laid out for ease of use. I'm absolutely sure there are very good reasons that they picked the layout they did.

Thanks in advance for helping me learn :)

Pic attached.

The rice cooker is being used for the heating element as it’s a convenient shape, I’m trying to use it to make yoghurt. There is a possibility of a larger rice cooker being used in future but I don’t think it would ever exceed 5A.
Prefer to ask for certainty.

I do have another 10A 250VAC relay module that will be controlled by an SBC so I could use the W1209 to control that but that results in extra wires if it’s not necessary.

After finishing Dr Stone, I got a lil inspired and wanna make my own computer. Then ironically an electroboom vid showed up about switches so I got the relay he used in that vid. I didn't realize I would have to bend the pins in order to get them to fit properly. I got a bunch of these things in and bending the pins to make them fit barely works.

Are there better relays for my application? I kinda like how small these things are and the very low current draw is nice.

Turning them 90° makes them fit without bending the pins but then that binds the NC / NO with the coil pins which kinda defeats the simplicity of logic gates with relays. Maybe I can spend an afternoon extending the legs with some wire.

Relays are J1031C5VDC.15

Hello friends, I need help with this issue which is way beyond me.

The setup uses a pico with cheap no-name GY-ADS1115 breakout boards from AliExpress. The ADS1115 boards have 10 kΩ pull-up resistors on SDA and SCL. Everything so far has been powered solely through the 3.3v pin of the pico.

The original setup used two ADS1115 boards connected to the pico in a star topology. ADDR was wired to VCC and GND. Each board had 4 SS49E hall effect sensors attached. The VCC and GND pins of the sensors were wired directly to the pico's 3.3v and GND pins. That setup worked successfully for an extended time with no sign of failure.

As soon as a third ADS1115 board (ADDR to SDA) was added with a single hall effect sensor, the two pico GPIO pins used for SDA and SCL got fried. I did not get it to work for a single second. As far as I could tell, they fried instantly.

I now know that TI recommends wiring ADDR to SCL for the 3rd board. But surely this wouldn't cause it to fry GPIO pins?

Anyway. The wiring was then changed from a star topology to a daisy-chain topology, with the third ADS1115 board placed first after the pico. Two new GPIOs were used for SDA and SCL.

That setup initially worked and read nominal hall effect sensor values from all 9 sensors, but after roughly 10 minutes, SCL began intermittently getting stuck low. The problem was initially transient: unplugging the pico and leaving it unpowered for several minutes could make the problem disappear temporarily. Eventually the two GPIOs used for SDA/SCL became permanently damaged.

I checked for solder bridges and miswiring, and I reflowed the SDA and SCL lines in case it was a cold joint which would explain why it got better after being unplugged for a bit. I kept the 2 known working boards and replaced the 3rd I had just added with a new one in case the 3rd board was defective. The same problem happened again. This time only SCL failed; SDA remained functional. So right now I'm standing at 5 burnt pins on this pico. I have no desire to risk a brand new pico or healthy pins until I have narrowed down the issue and have a way to guard against it.

I have tested the ADS boards with the pico disconnected from SDA and SCL :

For boards 1 and 2:

• VCC to GND: 3.31 V
• VCC to SCL: 0 V
• VCC to SDA: 0 V

For board 3:

• VCC to GND: 3.31 V
• VCC to SCL: 0 V
• VCC to SDA: 1.65 V when ADDR is connected to SDA
• VCC to SDA: 0 V when ADDR is disconnected from SDA
• SCL remained at the expected level regardless of ADDR

With power removed and disconnected from one another (i.e. broke the daisy chain), both board 1 and board 3 measured approximately:

• VCC to GND: 1.5 kΩ
• VCC to SDA: 10 kΩ
• SDA to GND: 11.5 kΩ
• VCC to SCL: 10 kΩ
• SCL to GND: 11.4 kΩ

The ADDR network was also measured:

• ADDR to VCC: 11.5 kΩ
• ADDR to GND: 10 kΩ
• ADDR to SCL: open
• ADDR to SDA: open

Both Board 1 and Board 3 showed essentially identical results.

With the ADS1115 connected as they would be in the setup, but with SCL and SDA disconnected from the pico :

• SDA to GND: 2.48v
• SCL to GND: 3.3v

The system was left in that state for at least 20 minutes and there was no change in the voltages. So no change spontaneously happens on the ADS side that would cause this.

The failed GPIOs were tested independently using code that would output the pin number and whether they read high or low. This was used with nothing connected to the pico for 20 minutes. The fried pins constantly reported being pulled low. No healthy pin started being pulled low for no reason.

The first SDA pin that was fried has approximately 64 Ω resistance to ground while the RP2040 is unpowered. The other fried pins are open.

As for the code, without pasting the whole thing here, this is what I do :

static void setup_i2c() {
  Wire.setSDA(ADS1115_SDA_PIN);   // GPIO12
  Wire.setSCL(ADS1115_SCL_PIN);   // GPIO13
  Wire.begin();
  Wire.setClock(100000);          // 100 kHz
  Wire.setTimeout(25);            // 25 ms bus timeout
  delay(100);
}

The ADS1115 initialization is:

[/code]void initSphereADC() {
  setup_i2c();

  uint8_t addrs[3] = {
    ADS1115_I2C_1_ADDR,
    ADS1115_I2C_2_ADDR,
    ADS1115_I2C_3_ADDR
  };

  Adafruit_ADS1115 *boards[3] = {
    &ads1, &ads2, &ads3
  };

  for (int b = 0; b < 3; b++) {
    if (!boards[b]->begin(addrs[b])) {
      // error reporting
    }

    boards[b]->setGain(ADS1115_GAIN);
    boards[b]->setDataRate(RATE_ADS1115_860SPS);
  }
}

The active firmware reads nine sensor channels. Each conversion uses startADCReading() followed by repeated calls to conversionComplete() for up to 10 ms.

[/code]static int16_t boundedADCRead(
    Adafruit_ADS1115 &ads,
    uint8_t channel,
    int16_t &lastVal)
{
  if (channel > 3) {
    adcTotalReads++;
    adcFaultReads++;
    return lastVal;
  }

  ads.startADCReading(MUX_BY_CHANNEL[channel], false);

  uint32_t t0 = millis();

  while (!ads.conversionComplete() &&
         (uint32_t)(millis() - t0) < ADC_READ_TIMEOUT_MS) {
    // bounded wait
  }

  adcTotalReads++;

  if (!ads.conversionComplete()) {
    adcFaultReads++;
    adcFaultStreak++;

    if (adcFaultStreak > ADC_FAULT_BACKOFF_MAX)
      adcFaultStreak = ADC_FAULT_BACKOFF_MAX;

    delay(ADC_FAULT_BACKOFF_MS);
    return lastVal;
  }

  adcFaultStreak = 0;

  int16_t v = ads.getLastConversionResults();

  if (v <= 0) {
    adcFaultReads++;
    adcFaultStreak++;
    delay(ADC_FAULT_BACKOFF_MS);
    return lastVal;
  }

  lastVal = v;
  return v;
}

The active sensor-reading function accesses the three boards according to a fixed channel mapping:

static Adafruit_ADS1115 *boards[3] = {
  &ads1, &ads2, &ads3
};

for (int i = 0; i < TOTAL_SENSORS; i++) { // TOTAL_SENSORS is 9.
  sensorReads[i] =
      boundedADCRead(
          *boards[board_map[i]],
          chan_map[i],
          lastValid[i]);
}

I don't have a scope or a logic analyzer to test with.

I am at a loss as to why this setup is frying pins and would really like your input. Thank you!

Context: I purchased a Foresight GC3 (golf launch monitor) that was DOA.

Assumption: I assumed it just needed a new battery (consensus online) and set about to make my own 2s3p 18650 battery pack.

In the process I believe I sent my BMS "into protection mode" By dissembling the balance leads in the incorrect order while removing it from the old pack. The output on the BMS reads 0. (it previously read 6v before disassembly and removal from the old battery pack.

Allegedly I need to "wake up the BMS" by supplying 8.4v to P- P+

Ok great, but why doesn't plugging the unit in do the same thing?

The problem?: The unit isn't sending any voltage to the battery pack when plugged in.

First I checked to make sure the power supply is working. The power supply for the unit is 15v @ 2.5A. Voltage on the multi-meter reads 15v when checking the plug for the charger. Presumably this is working, but I don't have the proper resistors to check if it's actually sending the 2.5A.

Should I go though the trouble of replacing, or diagnosing the amperage at this point?

Next I plugged in the Power supply and checked the barrel jack for voltage. The barrel leads show voltage fluctuating between 1.4 and 1.6 volts. I assume this is the power supply protecting the device from a short.

I was unable to identify a short (not saying there isn't one). Checking the barrel adapter and nearby alleged "Transient Voltage Suppression (TVS) diode packaged in a standard surface-mount SMB (DO-214AA) housing". (Image2 in pink).

Problem 2b: Checking voltage through the "TVS"

I measure the voltage around the TVS and one side comes up with the 1.5v and the other is 0.0v

I'm under the impression I can't measure resistance though the TVS to check if it's good without removing it. (I get radically different readings depending on which orientation the probes are in presumably from other downstream components).

Why would I only be getting 1.5v out of of my power adapter once it's plugged in? and why does the current stop once it hits the TVS?

I'm planning on buying a bench-top variable power supply, hot air rework tool, and sourcing and replacing the TVS. But I'm completely stumped why I don't have any voltage to begin with.

Any help would be appreciated.

I have a Casio WQV-1 watch that I bought in non functioning condition. When I took it apart I found a small component that was covered in some kind of white powder. I cleaned it with contact cleaner but it was still caked on there. No other part of the board is dirty. I found a service manual and discovered that this component is a varistor. I’m not sure if there is somewhere to get a replacement or if anyone could help me find an alternative. Any help is appreciated, thanks!

USB4125-GF-A (https://www.digikey.pt/en/products/detail/gct/USB4125-GF-A/13547388).

I'm doing a simple project device and I want to be able to power it with whatever USB-C cable and power brick I have laying around. I know USB-C starts at 5V and tries to negotiate higher voltages. But to do that I'm guessing there needs to be a specific board/logic on my device, and this USB-C female port looks very bare bones so I'm guessing there isn't the logic needed for the negotiation, thus, guaranteeing 5V, but I'm not sure and I don't want to burn my device.

Thanks!

I've noticed that having two PCIe5 connectors with lane sharing (so 1x16 + 0 or 2x 8 lanes) carries high price premium and seriously limits one's choices, especially if it's combined with other requirements, like 2x Gen5 M.2 sticks directly on SoC, powerfull VRM etc.

And those few choices that remain have stratospheric prices.

It seems to me that being able to DIY PCIe Gen5 splitter cable with 2 ( or more connectors) would solve that problem in an elegant way.

Can mini coaxes for such cable, high speed connectors etc be ordered off-the shelves ?

Once one has those and some decent attention to detail and clean, neat solder work, this seem to be doable to me.

What to search for and where would one get those ? Arte there any other showstoppers that I've missed ?

I have bought the above eDP to DP adapter to use a laptop with dead screen with external monitor (yes, I could use hdmi port but it doesn't show Bios/Uefi).

Monitor A (older Dell U2713HM) shows "no cable detected", but laptop shows the screen with supported resolutions etc, so could read Edid. Monitor from other PC/laptop works just fine with the same port and cable etc.

Monitor B (newer Lenovo P27q-20) works just fine with no issues.

My guess based on some searching is missing pull-up/pull-down for hot plug detect, but then why it works with other screen?
Maybe some hand shake problem?

Some possible components obliviously missing from the board, only led + current limiting resistor is there.
Link to adapter: https://www.aliexpress.com/item/1005012069631903.html

I am trying to replace this. Can someone help me find an alternative mosfet i can replace this with. I am a novice at most and don't know how to look for alternative replacement. Thanks

I’m doing a project and I need some help. I‘m reusing these laptop speakers but the wires that connect the speakers to the motherboard (the really short 4 wires) is too short for my needs. The speakers will still be connected to the same, original motherboard. I don’t have much wire laying around, but I found some in a soldering iron kit (lower half of the picture)

If I cut those small wires in half, and I put the thicker wire in between the two halves (for all 4 wires), would I be able to splice the wire together with it still working correctly?

I think this is the correct place to post this lol, but if not just tell me where I can get better answers

Thanks!

Hi all! This is my first attempt at embedding an ESP32 module directly into a PCB design. I followed the exact schematic from expressif (https://dl.espressif.com/dl/schematics/esp32_devkitc_v4-sch.pdf), but I can’t connect to the esp through my laptop to program it.

Hey everyone, just a little while now I started my journey on hardware design and I've been doing simple boards and designs on freelancer, but recently some of my designs are pushing for production on more "complex" applications.

I'm about to start a new design requiring voltage and current regulation on the range of 0-10mA while accepting 32VAC input and having a lowest possible output of 5VDC. I've been evaluating between using a linear or a switching regulator for voltage regulation.

Perks on using a linear regulator would be: no swithing noise or ripple in the mA range and easier EMC certification.

On the other hand my biggest concern with using a linear regulator is the efficiency, at 5VDC efficiency could be in the 20% range or less and I'm also concerned about thermals, although not so much as we're talking about 10mA consumption tops.

Right now I'm keen on the Linear regulator option but I was looking to get some advice from some of the more experienced users in here. Thanks in advance!

Does it make sense to put vias around PTH holes to help carry the current through the board to internal layers or is the plated connection enough? I'm talking about the 10-20A range.

Zero luck so far

Header says everything. I have a CRT that relies on this remote to work as it has no buttons, but the remote itself does not work, and opening it up its super sticky for sure and was probably not cared for.

Would just buy a new one bu5 these remotes are harder to come by than I realized

-First picture: the piece that was removed
-Second and third pictures: places where I accidentally unscrewed the pieces
-Fourth picture: entire PSU

Hey everyone!

Yesterday, the fan in the PSU of my 3D printer (Anycubic Mega X) started sputtering and I decided to open it up to take a look. Unfortunately, I accidentally unscrewed a couple of pieces (like the metal rectangular piece in the first picture) instead of the screws holding the casing together. Can anyone identify what these pieces are and if it’s safe to reassemble and use it again, especially now that the glue/seal (?) that was on the screw has been tampered with?

Any help is appreciated!

Two-channel valve microphone preamplifier, takes a mic or instrument on a combo XLR/jack, runs it through an input transformer and three valve stages, and puts it back out balanced through an output transformer — into a screw terminal for the main output plus two JST headers that feed an ADAT converter board and a gain meter. I'd like a second set of eyes on it before I order boards.

**Signal flow (per channel):**

Combo XLR/TRS in → P48 phantom feed (2 × 6.8k, switched) → −20 dB pad (820R / 182R / 820R, switched) → polarity reverse switch

→ input transformer (Neutrik nte10-3) → 12AY7 gain stage (68 k plate, bypassed cathode) → coupling cap → 100 k gain trimmer → 12AY7 second stage (150 k plate) → DC-coupled → 12AU7 White cathode follower → output transformer (off-board) → balanced out ×3

The jack tip is normalled through the connector, so with nothing plugged into the 1/4" side the grid sees the mic transformer, and inserting a plug swaps it over to a high-impedance instrument input. Roughly 60 dB of gain in the valve stages on top of whatever the input transformer contributes. The White cathode follower is there specifically so the output transformer gets driven with real current capability rather than a plain follower.

**Power:**
both rails come in from external supplies on screw terminals, nothing rectifies on this board. B+ is 225 V DC regulated, with 2 × 22 µF / 400 V of bulk on-board and a 4.99 k / 10 µF RC per channel for the gain stages. Heaters run on 50.4 V DC with all four valves in series (4 × 12.6 V @ 150 mA); the chain is ordered so both cathode-follower valves sit at the top of the string, which keeps the worst-case heater-to-cathode voltage around 98 V.

**Main components:**

- U1 / U3 — 12AY7 / 6072A, input and second gain stage (one per channel)

- U2 / U4 — 12AU7 / ECC82, White cathode follower output stage

- J1 / J11 — Neutrik NCJ10FI-H, combo XLR + 6.35 mm switching jack input

- SW1 / SW4 — +48 V phantom, Alps SPUJ190900 latching DPDT

- SW2 / SW5 — −20 dB pad, same switch type

- SW3 / SW6 — polarity reverse, same switch type

- R12 / R31 — PT01-B120D-A104, 100 k gain trimmer

- C17 / C18 — 22 µF / 400 V, B+ reservoir

- J4 / J14 and J3 / J13 — input transformer (NTE 10/3), off-board on JST

- J6 / J16 and J5 / J15 — output transformer (UTM3510), off-board on JST

- J8 / J18 — balanced main output, screw terminal

- J10 / J20 and J17 / J23 — balanced output to ADAT converter and to gain meter

- J21 — B+ 225 V in, screw terminal

- J22 — heater 50.4 V in, screw terminal

**Board:**
180 × 200 mm, 2-layer (top signal + ground pour / bottom signal + ground pour), 1.6 mm FR4, 35 µm copper, through-hole only, single-sided assembly. Ground pour on both layers with 161 stitching vias. Custom clearance rules for the high-voltage nets: 1.25 mm for everything at or above ~167 V, per IPC-2221 table 6-1 case B2. DRC is clean — no errors, no unconnected nets.

Any feedback welcome — layout, grounding, the high-voltage side, component choices, anything I've missed.

Hello,

I know this is a niche question but I am trying to see if there is a way I can test these transducers at work (40kHz units). They are plate style, used for an ultrasonic cleaner.

I have tried using our Fluke 117 multimeter (testing Capacitance) but can not seem to be getting a reading (testing on brand new spare ones so there should be readings).

I could absolutely be doing it wrong but from the videos I have found on similar parts, it seems pretty straight forward to be testing these. I have also seen videos of injecting voltage into them and testing from resistance but they seem to use oscilloscopes which we do not have (I'm just a maintenance tech but love nerding out on these kind of things).

If you have advice or maybe where I can look online for better information on these, I'd appreciate it.

EDIT: I changed the transfo model for a 48V on the secondary.

Hey everyone!

I have a project using PDLC films.
I need a second opinion to confirm I'm choosing the correct transformer (and that I'm not missing something obvious).

They require between 48 and 60V AC and for my dimensions at least 8W (with an included safety margin).
Main's voltage is 220-240V, 50Hz.

I found this
https://www.tme.eu/fr/en/details/tts50_z230_48v/toroidal-transformers/breve-tufvassons/17142-9997/; datasheet: https://www.tme.eu/Document/e6926af030c8ad46ec31ae152e8abbcb/TTS-EN.pdf
Summary:
Primary V: 230V AC
Secondary V: 48V
Secondary current: 1.04A
Power: 50VA

So, it will do the trick right?
Thanks for reading!

Can any1 please give me the model/name of this type c board

I found this board in my cosmic byte cb gk 16 mechanical keyboard actually i snatched the type c wire and in that process the port also got damaged now its rarely working the the angle is right so i opened the keyboard and found this

Please give me the name of this board currently am using a backup keyboard

Hello,

I am currently working on a project based on a PIC16F18323, and I would like to add a user-controllable preset to one of my features. As I am very limited in terms of I/O (it’s a DIP8 and I’m already using 3 of the 5 available inputs/outputs), I thought of using a potentiometer. However, ‘continuous’ rotation is not ideal for the precise selection of preset values 1, 2, …

Basically, I’m looking for the behaviour of a digital encoder using just a single (analogue) input.

Do you have any recommendations for me?

Thanks in advance.

Hi all. I’m trying to repair a Bulldog Gear CT03 gym timer.
The issue started when I needed to fix the remote, the IR sensor had gone, so I opened it up to check internals before finding the issue with the remote.
After the remote was fixed I realised there was something wrong with the beep.
At first the beep was completely gone, but I’ve changed the speaker and now the beep has become very quiet and slightly fuzzy. The timer still works and the beep still triggers at the right moments, but the volume is extremely low.

Here is what I’ve checked so far:

• I’ve replaced the speaker and wires which hasn’t fixed it.
• The connector looks fine and doesn’t cut in or out when moved.
• The PCB shows no obvious burn marks or cracked parts.

I’m looking for help identifying the audio path and understanding what could cause a weak output like this. If anyone recognises this board layout or has ideas for tests I can run, I’d appreciate it.
Also the battery in the photo is back in and isn’t impacting the beep.

Thanks for any guidance.