Reddit:Electronics

Pictured is the offender, my custom 84V 480A brushed DC motor driver. While testing, I had to make some adjustments to the rev1 routing, since apparently I forgot to run DRC before sending it to the fab. Tried to change the logic power supply to the FET drivers from 12V to 5V, forgot to cut one trace, and ended up bridging 5V to 12V. I used a lead acid battery instead of a current limited power supply for testing, connected it to my laptop without a USB isolator, and... well, I no longer have a laptop.

I wonder how I'll explain to my professors why I won't be able to submit my paper draft that is due tonight.

About Chua's citcut:
https://www2.eecs.berkeley.edu/Pubs/TechRpts/2009/EECS-2009-20.pdf

My implementation:
CHUA custom PCB board (thank you, JLCPCB!), TL082 op amps
signal conditioner board (from +/-6V to 0 - 2V, from +/-1V to 0-2V)
X/Y simple scope - Teensy4.0+ ILI9341 SPI display.

Video: https://imgur.com/a/R0H5TSl

Just some quick soldering in my free time. Wanted to see if its possible to bodge a 50 Ohms dummy load. Its not perfect since it picks up a lot of noise without any EMF shield and the impedance is not exactly 50 Ohms with these resistors.

So the design is ready and working in LTSpice.

The red graph shows the voltage of the L3L4 transformer, that can be seen in the middle of the circuit. The voltage oscillates roughly between +10 and -10 kV.

The blue graph shows the voltage difference between the upper and lower CW circuits output.

Was tinkering this rainy weekend, initially just playing around with assessing noise performance of a couple of amps, which quickly reminded me about input offset at higher gain. Using a pack of 8x fresh AA cells for most of these measurements, in an inverting amp with gain of 101 (5% error possible). The low-voltage amps were tested with 3x fresh AA cells, just under 5V.

The homebrew op amp is made from non-sorted 2N3904/2N3906, circuit from Figure 2 of https://sound-au.com/project07.htm

The vintage part numbers were generally vintage mid-1970s to late-1980s. Only a single amplifier was measured in every case.

Nothing too rigorous but amusing to see how well they general conformed to datasheet typical. Pleasantly surprised how good the modern ST variant of the LM324A is. Just sharing in case anyone else finds it interesting.

I found it cheaper to buy lower amperage power supplies and having them in parallel instead of one with the same specs. I have made a passive balancer using 0.05 ohm resistors and one fuse so that one power supply doesn't works more than the rest. I am going to add ideal diodes to make it diode OR'ing to even further make the balancing better. Using this to drive a flyback transformer. The power supplies are 24V 6A so all four gives me 24V 24A.

Poor little bugger.

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This is my project: ZVS feeding a transformer feeding a symmetrical Cockroft-Walton voltage multiplier. The circuit in the pic is the second part, earlier i posted the CW diagram that i designed with falstad.

I study electrical engineering, and i decided to challenge myself with building this setup. The voltage between the 2 multipliers will be 240kV and produce ~30cm arcs(30cm according to gemini).

I had problems with this ZVS and LTSpice, the simulation was harder to get going than the actual circuit, but today i succeeded with it. I think i'll reward myself with some ice cream later! :)

I’ve been working on a custom CH32V006 dev board for OpenServoCore, which is my attempt to turn cheap servos like the MG90S into smart actuators with Dynamixel-style single-wire UART. PCBWay kindly sponsored the fabrication and assembly for this first spin.

When the boards arrived, I plugged one in over USB-C and immediately noticed the 3.3V rail LED was off. Measuring the rail gave me 0.84V. I checked all 5 boards and got the same result every time, so it was pretty clear this was not a one-off assembly issue. I even injected an external 3.3V supply directly onto the rail and it was still stuck at 0.84V. At that point the evidence was clearly pointing to my design, not the fab.

After staring at the KiCad files and schematics for way too long and finding nothing, I started probing around different test points. At some point I hooked 3.3V up to what was labeled as the +3V3 test point for some reason.

Then I heard a pop, saw magic smoke, and immediately assumed I had just made things worse.

Then I looked down and the green 3.3V LED was on. What???

Measured the rail again: 3.3V.

Turns out the silkscreen test point labels were wrong. That “3V3” test point was actually the EN pin between the MCU and motor driver. So by feeding 3.3V into it, I fried either the DRV or the MCU, and whatever burned open stopped dragging the rail down. In other words, I accidentally failed my way into a debugging success.

From there I started removing parts on a fresh board one at a time. I removed the DRV, still 0.84V. Then I removed MCU, and the LED came back. After another round of staring at the schematic, I finally found the real root cause: I had accidentally swapped VDD and VCC on the MCU. It was staring at my face the entire time. Talk about shame...

I ended up attempted three board surgeries and the third attempt finally worked with trace cuts and magnet wire, and somehow the CH32V006 survived reverse voltage on its power pins and still ran firmware afterwards. This little MCU is tough!

It's not a failure if I never give up, right?

I wrote up the full debugging story with photos and repair details here if anyone wants the whole mess.

The photos are:

1. The finished product! An AT28C256 EEPROM reader/burner on a single-sided PCB
2. A 0.1" dot grid drilling template taped on
3. After drilling and cleaning the surface with sand paper and IPA
4. Traces hand-drawn with an oil-based paint marker (I need one with a finer point...)
5. Etching in cupric chloride
6. After etching and scraping the paint away from solder points
7. Finished soldering
8. A cool view of the traces through the board

Over all I'm very happy with how it turned out. The main thing I'm unsure of at the moment is whether I should leave the paint on the traces or not. I figured it would provide some protection against corrosion, but as you can tell it's pretty fragile and has already been scraped off in several places. I might still just clean it all off.

Hi everyone!

I just finished my new workbench! I extended my existing one(the one facing the desk behind) with the edge-piece facing the wall. Also I sanded the desk surfaces and gave them a new finish. And last but not least, I added the shelf above for all devices.

As you can see it is not completely finished, I am still working on the LED strip that goes below the shelf and some other refinements. But so far I am very pleased with the results!

Rate my setup. I know that the cable management is shit, but I have only one plug.

I discovered that adding a single 1N4004 diode to a Schmitt trigger RC oscillator increases edge jitter by 15x, turning a simple 4-component circuit into a cryptographic-quality hardware RNG for microcontrollers.

I've done (What I think is) a pretty comprehensive write up of the project here:

https://siliconjunction.top/2025/12/04/practical-hardware-entropy-for-arduino-projects/

10eur keyboard from aliexpress, they really wanted to keep the pcb one layer

Someone's gonna start a fire building one of these.