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.

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 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.

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!

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.

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!

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

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 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.

Hi guys, I want to build a linear PSU and wanted to ask for some advice before I order the PCB.

The plan is to use an LT3081 to control 3x MJ15003. I’m aiming for around 0–20V and 5A.I also added a BC557 for the short-circuit protection.

I’ve made a schematic of what I have in mind, but I’m not 100% sure if everything is correct yet, so I’d really appreciate it if someone could have a look at it and tell me if you see anything wrong or something I should change.

I’m open to any advice or suggestions, so feel free to point out anything you think could be done better.

Sorry for the messy schematic, I know it’s a bit all over the place 😅

Thanks in advance for any help and advice!

h1 h2 h3 mj15004
h5 h9 input
h6 h7 h8 pot.. meter
h4 h10 output connector..

Need to pick some up. They insert into the trigger mechanism. I seen some similar stuff online but just like it to be exactly the same. TIA!

So, the RMB on my rival 650 stopped working consistently and I cannot rma these anymore since the stopped producing them. I have some soldering experience though so I though I'd just replace the switches, but opening it up and desoldering the switches just confused me, as you can see one of the mounting holes does not have a pad (the pin was therefore without any solder) and for some reason the solder mask on the corner is missing completely.

Maybe this is all correct but to me it just looked weird and I have hence decided to ask for help. So guys please help me out, what am I looking at here and how do I fix it?

So, I’ve recently changed my PC case, and it stopped working due to a bad RAM module.

The bad RAM in question comes from a 2-stick DDR4 3600 HZ Kingston FURY Beast kit that I bought when I first built the PC. About a year ago, one of the modules from the kit died, so I stored it. Now the other one has failed as well.

Since I’m not willing to pay the current inflated market prices for RAM, I want to try fixing it myself, using one of the modules as a donor.

My SMD experience goes as far as soldering USB-C ports. I have a soldering station, solder paste, etc., but I’ve never replaced a BGA chip. I’ve seen that stencils are usually used for BGA arrays, but I don’t have any.

I have a few questions for you guys.

First, I’m going to test the resistors and visually inspect the board. But if the problem turns out to be a faulty DRAM chip and the PC won’t POST, how do you determine which chip is failing?

I’ve searched online but haven’t found much discussion about this specific topic. Does anyone have any advice or a direction I could follow?

Is this even feasible? Or are the memory timings and characteristics carefully matched to each individual module?

Any advice would be greatly appreciated.