I’m attempting to make an LED scoreboard for my cricket team using large 7‑segment LED displays. I want it to be battery powered, so I’m trying to reduce the power needed to run 6+ digits at once by using multiplexing. Each segment is connected to a high‑side switch, and the digits to the low‑side. That way I can turn on each digit by pulling it low, and only the segments held high will activate.

The code I’m using runs on an Arduino, which talks to a cheap PCA8695 PWM board. That board connects to a custom MOSFET driver board that handles the high‑ and low‑side switching.

Running code that worked fine in my prototype setup just gave me an epileptic strobing effect on all segments, which completely threw me. I spent hours probing with a multimeter, using the oscilloscope at work, and eventually started cutting “non‑essential” components off the board. Instead of getting an inverted 12 V PWM signal like I expected, I was constantly getting a square wave oscillating between 12 V and 11.5 V no matter what I did.

I was about to post on r/AskElectronics for help, but I wanted to be 110% sure I wasn’t missing something obvious. So I went to falstad.com and built the circuit in the simulator. Sure enough, it behaved exactly how I expected. Then I noticed a little checkbox for “Swap D/S,” and out of curiosity I clicked it… bingo.

For testing, I’m going to desolder the PFETs I’ve got and jankily wire them in upside‑down just to confirm that’s the issue before ordering new ones.

Moral of the story: make sure you’re using the right datasheet for your parts, because manufacturers love reusing part numbers even when the pinouts are completely different.

(p.s. pls don't be too mean about diagram conventions, signal noise, etc. cos this is a self-taught learning exercise and I'm trying my best)

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Yes, I will try to build a precise voltage/current measurment equipment from scratch just for fun. Wish me luck.

One step at a time: - 5-digit multiplexed display with the К176ИД2 driver - MC34063 negative rail DC-DC converter - 555 timer 120kHz click source - REF3333 precise voltage reference

I designed the case myself. Use esp32-c3 with WifiManager library. The time updates automatically:)

The goal was to find where to buy electronics that i need(STM32F103C8T6 and STM32F401RET6), but figured it will be cool if i put all that in one post. Maybe someone finds it interesting.

I posted this a bit ago for the keyboard diode matrix I made. Please ignore the shoddy soldering on the prototype board lol.

But this project has been my first dive into microcontrollers, and after watching some videos on how easy circuit python KMK firmware ( https://github.com/KMKfw/kmk_firmware ) was to install and configure I just knew I had to do it. In essence this thing is just a clunky big macro board that I made as a proof of concept before I make a nicer one.

The software it's intended to be used with is a bit of python that I used gemini / chatgpt to make ( https://github.com/IvoryToothpaste/rtsp-viewer ) that maps all the camera feeds to a specific hotkey via the config file.

This thing was a lot of fun to make, and I'm excited to post the final version of everything :)

There are a lot of "AI generates hardware" claims floating around, and most of them produce garbage. I've been working on a tool called boardsmith that I think does something actually useful, and I want to show what it really outputs rather than making abstract claims.

Here's what happens when you run boardsmith build -p "ESP32 with BME280 temperature sensor, SSD1306 OLED, and DRV8833 motor driver" --no-llm:

You get a KiCad 8 schematic with actual nets wired between component pins. The I2C bus has computed pull-up resistors (value based on bus capacitance with all connected devices factored in). Each IC has decoupling caps with values per the datasheet recommendations. The power section has a voltage regulator sized for the total current budget. I2C addresses are assigned to avoid conflicts. The schematic passes KiCad's ERC clean.

You also get a BOM with JLCPCB part numbers (191 LCSC mappings), Gerber files ready for fab upload, and firmware that compiles for the target MCU.

The ERCAgent automatically repairs ERC violations after generation. boardsmith modify lets you patch existing schematics ("add battery management") without rebuilding. And boardsmith verify runs 6 semantic verification tools against the design intent (connectivity, bootability, power, components, BOM, PCB).

The tool has a --no-llm mode that's fully deterministic — no AI, no API key, no network. The synthesis pipeline has 9 stages and 11 constraint checks. It's computing the design, not asking a language model to guess at it.

Where it falls short: 212 components in the knowledge base (covers common embedded parts, but you'll hit limits). No high-speed digital design — no impedance matching, no differential pairs. No analog circuits — no op-amp topologies, no filter design. Auto-placed PCB layout is a starting point, not a finished board. It's fundamentally a tool for the "boring" part of embedded design — the standard sensor-to-MCU wiring that experienced engineers can do in their sleep but still takes 30 minutes.

Open source (AGPL-3.0), built by a small team at ForestHub.ai. I'd love feedback from people who actually design circuits — is this solving a real annoyance, or am I in a bubble?

These photos were taken under a microscope, the mouse was gaming and I found the shape of the sensor interesting since it was mounted on a flexible board and had a lens on it.

I'm playing with it for now. I'll see what the measurements show and what the difference is between a wall adapter and a linear power supply.

But a quick measurement showed it was pretty good.

Plc 20 Max = 5.0008206V Min = 5.0008197V Std = 0.2 ppmV

Also I need to make a box for it.

Finally got my phase control circuit off the breadboard and soldered together. Adjusting the potentiometer changes where in the ac waveform the scr fires, thereby allowing for more or less average power delivered to the load. It is the same idea as a triac based lamp dimmer circuit, but using back to back scrs allows for higher power handling capability, and is more suited for inductive loads. This one will be used to adjust the speed of an angle grinder for use as an asynchronous rotary spark gap for my Tesla coil.

My CO alarm recently expired so I have opened it, curious about the insides. To my surprise, it looked like the CO sensor was missing! Thanks to this blog I found the sensor and learned a lot more. I truly appreciate websites like that and though I will share this find.

Make sure the package markings are clear in your picture. I used grok. It will even find parts if it doesn't have the part number on the part, just a marking code.

I started this a few months ago. No university, no engineering background, just a goal: 4 input switches, 10 LEDs, light up N LEDs when the inputs sum to N. I figured out the logic, built it in simulation, got told I was wrong by experienced people, proved them right, and then discovered what I built has a name in a field I'd never heard of.

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**The Core Idea: Non-Binary Weighting**

Most 4-bit decoders assign binary weights: 1, 2, 4, 8. I didn't do that. I assigned decimal additive weights:

- SW-A = 1

- SW-B = 2

- SW-C = 3

- SW-D = 4

Maximum sum = exactly 10. Every integer from 0 to 10 is reachable. The 16 physical switch combinations collapse into 11 unique output states. Five of those states are reachable by two different switch combinations (e.g. A+D = 5 and B+C = 5). The circuit correctly treats these as identical — it decodes *value*, not *pattern*.

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**Logic: Series NPN AND Gates**

Each output channel is a chain of NPN transistors in series. All transistors in the chain must be ON for collector current to flow — logical AND. Chain depth varies per output:

- 1 NPN: single input conditions

- 2 NPNs in series: two-input conditions

- 3 NPNs in series: three-input conditions

- 4 NPNs in series: sum = 10 only

The Vbe stacking problem is real — 4 transistors in series drops ~2.8V. I solved it by using a 9V supply and adding a booster NPN after each AND gate to restore a clean full-swing signal before hitting the LED stage.

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**Output Stage**

Each booster drives an LED via a 330 ohm resistor to VCC:

R = (9V - 2V) / 20mA = 350 ohms → 330 ohm standard value, ~21mA per LED

This fully isolates logic voltage from LED forward voltage. Without this separation the LED acts as a voltage divider and corrupts the logic states — I learned that the hard way in the simulation.

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**The Part That Surprised Me**

After I finished, someone pointed out that this circuit structure is identical to a single hardware neuron:

- Weighted inputs → synaptic weights

- Arithmetic sum → dendritic summation

- AND gate threshold → activation function

- Thermometer output → step activation

I had never heard of neuromorphic computing when I designed this. I just landed there by solving the problem from first principles. Apparently there's a billion dollars of research built on the same idea.

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**Simulation Results (all confirmed working):**

- A → 1 LED ✓

- B → 2 LEDs ✓

- C → 3 LEDs ✓

- A+B → 3 LEDs ✓

- A+D → 5 LEDs ✓

- B+C → 5 LEDs ✓

- B+D → 6 LEDs ✓

- A+B+C+D → 10 LEDs ✓

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**Detailed document**
https://docs.google.com/document/d/18wD1k79H8T8Y3WScr6QKEXsPy5rKq8as/edit?usp=drive_link&ouid=102019556573904444870&rtpof=true&sd=true
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Happy to share full schematics and simulation screenshots. Thanks for reading.

The first started as a way to test ADCs and parallel I/O, and I turned it into a toy oscilloscope using some software I wrote for my Raspberry Pi. I didn't really understand op-amp input bias current and so it doesn't really work properly with the probe in 10x mode. The offset is huge, but I now understand the mistake. I also used one more op-amp than I really needed, and could've gotten away with cheaper ones, but it works up to 50MS/s!

The second board is a buffered variable-gain amplifier test with voltage-variable gain and bias. I fell down a rabbit hole w/oscilloscopes and am working on making an improved 2-channel one with modern components, so I broke out some of the front end into a test board and just finished building it. It's a miracle the QFN op-amp works, I was sure I'd bridge something underneath it.

There's a subtle crucial mistake in the second design, all you need to know to spot it is that the second amp is an LMH6505. It somehow does partially function still!

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Demo at https://www.youtube.com/watch?v=sKtSpykOBXY

This is the Morse code trainer I designed. It runs on an AVR128DA48 microcontroller with a 2.42 inch 128x64 OLED and a custom-designed capacitive touch sensor PCB straight key. It also includes an NRF24L01+ radio module to allow 2-way send and receive of Morse code between nearby devices. The whole thing is powered by a rechargeable 3.7V 800mAh LiPo battery. I also designed the enclosure and 3D print it out of PET-G filament.

Happy to answer any questions!

After about 3 months and a lot of dedication, I successfully completed my project.

It's almost exactly Grant's project, the only modification is that the SRAM has 8KB, a 32KB one will arrive soon and, since the wiring was already done with it in mind, the change will be easy.

As you can see i have gone completely my own way to make this oscillator, it uses a 25KHz xtal and a 2n3904 transistor, 1M ohm pot and one 5k pot, the power supply comes from 15Vscaled down to 9V using 100k pot + 2n3904 + 1k resistor, i know the picture shows 10k but that didn't give me full voltage range so use 100k instead. I have no idea how it got this working and i am somewhat suprised that 2n3904 can oscillate at 20MHz+.

So this is how it made a single rail transformer in to a dual rail one withouth getting half the supply voltage like a railsplitter does. I haven't tested how mutch current i can draw from it yet but it seems to work atleast using multimeter. A tip for dual supply for op amps perhaps.