Zero luck so far

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,

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.

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.

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

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 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

Hopefully someone can help me figure out if I can use one with slightly different specs. I’m looking to replace a cap for a buddy’s 500W car audio amplifier (2023-2024). Somehow I can’t find one. There’s not much room in this and the correct sizes seem to be not manufactured anymore. I’m not sure how much wiggle room there is with the height. I checked digikey and mouser to no avail.

Specs I need: 2200uf, 25v, 12.5mm wide, 18mm height and 2.5mm between the caps. TIA!

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!

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.

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?

Hello all,

I’m trying to repair the backlight on an old fish finder LCD. The northstar explorer 657, I just boat an old boat and the first time I use it the fish finder broke...

The LCD itself appears to be working. If I shine a flashlight very close to the screen, I can see the text/graphics.

The original backlight uses CCFL tubes around the light guide/diffuser, as shown in the photos.

I haven’t diagnosed the exact fault though. I don’t have a CCFL tester, so I don’t know if the problem is:

- the CCFL tubes,

- the inverter/CCFL driver,

- a connector/wiring issue,

- or something else in the backlight circuit.

I’m also not sure how to safely test the inverter.

Instead of troubleshooting the original system, I’m considering bypassing the CCFL backlight completely and installing LEDs around/along the existing light guide.

My idea is to power the LEDs independently from a small USB power bank and route the cable outside through one of the existing screw holes, without modifying the fish finder’s main electronics.

Would there be any problem doing this regardless of whether the original fault is the CCFL tubes, inverter, connector, or something else? Could I simply leave the original CCFL/inverter system disconnected or unused?

I was also thinking about adding a small dimmer in case the LEDs are too bright or create visible hotspots/lines through the diffuser, but dimming is not essential if I can choose the right LEDs and brightness.

What type of LED strip/LEDs would you recommend for something like this?

Photos attached showing the LCD, CCFL tubes and light guide. I am not a professional.

Thank you.

This is an instant water heater. There’s a hall flow sensor, two temperature sensors, and an amp meter. My overall plan is to put an ESP32 in there, reading the data and sending it to home assistant. Maybe also using it to press buttons. Presets for certain users maybe?

I’m also considering intercepting the rx tx stream going to the screen.

If intercepting temp, I could, for example, read the temp directly with an Esp32, and then send the same reading down a different data pin back to the board. Or could I use an optocoupler to read it live? This would mean if the ESP goes down the water heater doesn’t work… but it’s in my house so that’s sort of normal.

I think the flow sensor will be the easiest, with it, I can just tap on the data line. (It has + - and signal) As long as the ground is shared.

i understand how to wire things like sensors up directly, but sharing it with the controller board is the confusing part.

Later I can get better front/back photos of the board.

I spent my summer building a risc v cpu, then verified it using a fpga board and Im currently building a power audio amp on Ltspice however I feel like I've wasted my summer as I didnt complete a really big/rewarding project (I am applying for coop in about two weeks). Apart of this is because of work and other personal things, but I want to complete at least one more hardware project. Projects related to klayout/magic would look nice for the resume however I really like creating pcb's and feel I can actually build something in the time frame I have as I already have experience using kicad and Altium.

Do you guys have any advice and resources for a project I can dedicate myself to? Everything either feels too complicated or not resume worthy (Ik a bad mentality to have) and I feel like Im in a slump . An fpga/analog project sounds really interesting to me but I have no idea where to start. Any advice would be greatly appreciated.

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.

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

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..

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.