Reddit:Electronics

My simple lab in my dungeon. Recently picked up the Kepco Programmable Power Supply and Agilent 54622D oscilloscope from work. We’re moving buildings and they’re tossing a lot of stuff. I’m running an Intel NUC with Win11, HP Slice with Fedora, RPi 4b (in the 3D printed green and black Fractal case) with RPi OS, and a Dogbone running Debian. It’s a very simple setup compared to a lot of yours but I love it. A nice place to escape.

Fantastic!!! STM32-based project with an LCD display and a PIR + temp module.
Simple, cheap, and surprisingly effective — perfect for those hot nights when you’re too lazy to turn the knob manually 😎

im k

I just parts-salvaged a Metz camera flash with a burnt-out charging transformer, and found this vintage beauty on the inside.

Tell me what you think!

This bloody LM2576-33 (new) gave out 10V instead of 3,3V. Killed two STM32 before I figured out WTH was going on.

I am, of course, going to widlarize it, as it it written in the ancient scrolls.

After addressing the issue with the shorted Kelvin Leads this instrument a FNIRSI LC2010E, it has so far proven to be a handy tool to have going above and beyond my Fluke DMM.
Symptoms were erroneous readings and it would fail the lead calibration check on the short setting. FNIRSI support has also has responded well sending a replacement.

Today I milled another working pcb (for practice) and its turned out great! In the basic TP4056 chip, only replaced the leds with bigger ones.

Qualcomm acquired Arduino. This is a result of that acquisition. That was quick!

Link to official page

- Qualcomm QRB2210 (- 0.4mm pitch BGA package)

- STMicroelectronics STM32U585

- 8 layer board

As you can see it's a green little toroid with a "secondary" made using green metal wire used for flowers etc 3 windings. Gave the coil some 19MHz 24VPP Sinus wich gave me a result of 5.89VPP 19MHz on osciloscope but with multimeter i got 149.9V in both AC and DC.

Not to sure if this belongs here but i aquired these with an order of vintage NOS. I am trying to find a way to scan these and digitize them correctly. Ill post or link the scans once i can get them done.

DigiKey is known for comically over-packing their orders. A regular $50 order usually leaves you with a lifetime supply in ESD bags and packing material. But today they really went "hold my beer!".

I wanted to start a small side project to 'calm down' from my last big one. And because we need something to replace the old FM radio in our dining room, I started building this, an active smart speaker.

Currently, I have what you can see on the pictures. I pulled all the parts out of an old multimedia system my mother gave to me. The donor-board can be seen on one of the pictures. It was to big to fit in the speakers I am planing to use, so I decided to split it up by transferring the components onto a self soldered PCB and throwing out unnecessary parts out in the process. The amplifier board was quite easy and done in a few hours, but the power supply took quite long as I paid careful attention while building it because you know, things plugged into the mains.

The PSU originally put out multiple voltages for not only the Amp itself(24V) but also the Vacuum fluorescent display and other shenanigans I don't need. I threw out everything except the 24V for the amplifier and the 5V rail to power the RPI and micro-controller that I will put into the device for the 'smart' part. I still have to isolate the bottom of the Power supply and build a small shielding for it to eliminate noise as it will be sitting directly behind the amplifier part.

Like I said, apart from these two PCBs I will also be putting a RPI1 and a STM32 with a LCD screen and rotary encoder into this thing to give it streaming capabilities.

I will keep you up to date on the progress!

I wanted to share a common issue with the LM358 that might help others troubleshooting similar problems.

Built a simple non-inverting amplifier (gain ≈ 4.9) using an LM358 with ±9V rails. The output showed significant crossover distortion around zero-crossing - you can see the characteristic "flattening" in the waveform.

Root Cause

The LM358 uses an NPN output stage that pulls high well but relies on an internal current source to pull low. When driving high-impedance loads (like a scope probe directly), there's insufficient sink current to rapidly transition through zero, creating a dead zone.

Adding a 1kΩ pull-down resistor (RL) from output to the negative rail (-9V) completely fixed it:

• Provides a continuous current path to the negative supply
• Enables smooth zero-crossing transitions
• Result: much cleaner waveform with minimal distortion

1. LM358/LM324 require careful output loading considerations in bipolar configurations
2. Pull-down resistor to negative rail (typically 1kΩ-10kΩ) enables proper operation
3. This is in the datasheets but easily overlooked in practice
4. For true rail-to-rail with minimal distortion, consider CMOS op-amps (TLV274, MCP6004, etc.)

Hope this helps someone debugging similar issues! The LM358 is a low cost and accessible op-amp great for general or educational/hobby use, but understanding its output stage limitations is key for clean signals. This came up while documenting some lab exercises, and I thought it was worth sharing since it's such a common gotcha.

Its a Wayne Kerr 6425 LCR meter.