r/electronics

As a follow-up to the toy oscilloscope I designed here, I designed and built something that more closely resembles a real oscilloscope! I included some shots of the build process, all done at home by hand with a hot air station and a preheater.

It has 2 channels, each running an ADC3908 off of a shared clock at anywhere from 1MS/s to 62.5MS/s. I wanted to use the 125MS/s version of the part but since I'm still using the Pi for all of the data acquisition and processing, this is about as fast as you can possibly go.

The front-end was supposed to have ~30MHz of analog bandwidth but since I had to remove the filter caps after assembly, I think theoretically it has whatever the bandwidth is at the ADC inputs. All of the analog components before the ADC have higher bandwidth.

It supports input full-scale ranges from +/-33mV to +/-180V, though I'm hesitant to plug something I made into mains power. It should be isolated as all power comes from the Pi, either through a wall plug or USB powerbank, but I'm still wary. I'll probably try it one day though.

It wound up costing way more than I would have hoped, and I probably chose some components that were more expensive than necessary. For example: the two linear regulators I used for the analog supply rails are pricy because of their very low noise, but my actual noise levels aren't great in the end. I think the total BOM cost was ~$150 if you include the PCB and you can get a way faster real scope for that price. It was still a great learning project though.

I placed order #48116 on 11 February 2026 for a soldering station. As of 19 May 2026, nearly 100 days later, the order has still not shipped. Tracking only shows that a shipping label was created, with no actual carrier movement.

Before receiving any response at all, I sent multiple emails to all listed FNIRSI support addresses and also attempted to contact them through their website chat. I received effectively no responses through chat or email for an extended period.

The only replies I eventually received came after I mentioned escalating the matter through my bank and making the situation public. Over roughly the following 3 weeks, I received only two short replies stating that the issue was being “escalated to manager”, but there were no further updates, no shipment, no refund, and no meaningful communication afterward.

At this point I have neither received the product nor a refund.

Based on my experience, I would strongly caution people against ordering directly from FNIRSI unless they are prepared to risk non-delivery and extremely poor customer support. If you want their products, I would recommend purchasing through a platform with strong buyer protection instead.

i think it is so funny how digikey packages their stuff. i ordered a pnp npn transistor pair and one came in the standard antistatic pin cushion the other came in a make shift package id describe as a chunk of plastic cut with four very intentionally placed rubber stoppers. they are trolls and my favorite company

I built a scientific calculator from scratch: custom PCB, custom FPGA firmware, and a CPU I designed myself in Verilog.

The physical build: a custom main board and keypad PCBs designed in EasyEDA and manufactured by JLCPCB, an Altera Cyclone II FPGA as the brain, an LCD display, battery with charging circuit, and two ROM-flashing connectors on the sides to update the firmware.

Under the hood it runs a nibble-oriented CPU I designed specifically for BCD arithmetic: the way decimal calculators should work internally. I then wrote ~4K of machine code implementing the full set of scientific functions: trig, logarithms, complex numbers, statistics, all verified to 14 significant digits against a dedicated test suite.

The full stack:

• Custom CPU in Verilog: Harvard architecture, 12-bit ISA, 8 registers, hardware fault detection
• Hand-written microcode assembler in Python
• Verilator + Qt simulation framework for development and debugging
• Custom PCB (EasyEDA / JLCPCB), battery, charging circuit, 3D printed case

The finished device is sitting on my desk.

Live WebAssembly demo (runs the actual Verilog + microcode in your browser): https://baltazarstudios.com/files/calculator-d/Calculator.html

Write-up: https://baltazarstudios.com

Source: https://github.com/gdevic/FPGA-Calculator

Hackaday: https://hackaday.com/2026/05/13/build-the-cpu-then-build-the-calculator/

Happy to answer questions about the PCB design, the FPGA setup, or anything else.

For years, devices like the RbPi have been described as “credit-card sized”.

And of course the message is rather the footprint, but at some point I became obsessed with taking that idea one step further:

What would it take to build something that is literally sized like a credit card?

I've got a slight feeling that you really don't seem to like questions here, but I hope this rhetorical one is okay :P

That question slowly escalated into months of experiments to find solutions for things where default methods won't work. I can't use large, rigid components, connectors, and find a way to make my own custom flexPCB.

And after months of tinkering, I made the first prototype. Fragile, but it works within the goal of not exceeding 1 millimeter. Somehow, news pages have picked this up and described it as "revolutionary" which is a bit far fetched, but I feel flattered 🤭

To be fair, 'computer' might be a little overstatement, but it's technically perfectly within the definition of one. If you should have suitable words for it that sounds cool, feel free to suggest ^^

The prototype includes:

• ESP32-C3FH4 w/ WiFi & BLE
• NFC read/write
• 1.54" 200*200 E-Paper display
• ultra-thin LiPo battery including charging circuit and power path management
• accelerometer

Finding small/thin enough components wasn't really the main challenge, mechanical stability was. Solder and general material fatigue, pressure distribution (particularly focused pressure) and other strain related issues were the real problem.

This doesn't even include battery protection and some other things to solve.

At this scale, the project turned into a weird mix of electrical, mechanical and chemical engineering.

A few things that became clear over time:

• preventing strain is much easier than surviving strain
• tiny real-world tolerances start dominating the entire design near the physical limit
• many “thin enough” components stop being thin enough once assembly is considered
• FPC connectors are basically obsolete, forcing me to get creative and solder each single wire for each 0.5mm pitch pad one by one.

The prototype is fully self-powered and running from its internal battery.

I documented a large part of the engineering process, including the process of etching my own flexPCB, on my GitHub repo.

And yes, it's not like this thickness is a necessity, going just 0.5mm thicker would probably have saved me months of engineering. This entire project was probably motivated way too much by the 'disbelief' factor 😄

I am curious on your thoughts on this! :)

Food Ninja turned reflow oven! My first board in 15 years went great other than my bad designs! Attempt at building a 6 channel sonar, dint go so great..... worked in air but not in water.

Finally got a working prototype for my cars instrument panel project. Just running a test script for now to make sure everything works at the same time.

We've got the gauges, warning lights, and LCDs to display the milage.

More updates will come as hardware is added and the actual code is written. GitHub link for anyone interested

I thought this recent project of mine could inspire people on how to reuse the spindle motor on obsolete or crashed hard drives.

After all, it's a shame how these state-of-the-art motors often end up in the bin despite being in full working condition.

I built a so-called "ringing table" for microscopy by creating a drop-in replacement for the original disk controller on a twenty year old WD drive.

My board has a PIC processor, a three-phase spindle motor driver and a simple button-and-led user interface right where the SATA and Power connectors used to be.

It actually worked pretty well. There must be other things one can build from this basic concept! More technical details about the project are laid out on my personal blog.

https://espenandersen.no/ringing-table-from-a-dead-hard-drive/

After some hardware fixes as usual, some glorious resoldering and a few lines of 1's and 0's later...I have data! With my DAC working, both receive antennas are working and able to read the I/Q outputs!

Very pleased and now to turn this into something more understandable!

Started designing a few joystick cap styles for KY-023/Arduino joystick modules and thought they turned out pretty nice.
Made a classic version, textured grip version, tall, wide, and short variants.

if you wan the model:
https://makerworld.com/en/models/2792322-arduino-joystick-cap-pack-5-variants#profileId-3105095

Man the difference between linear and logarithmic pots and faders for volume is pretty interesting.

This is my third TX-6 style mixer that I had time to finally finish. The first used linear faders and pots, and the second had faders that were too high value resistance so it was more on the quiet side.

I built a GPS and temperature data logger equipped with an alarm buzzer and an EEPROM for offline data backup and ESP32S3. I made a mistake with one net name but I was able to solve it.

Pd: How is the market in EE ? Is any opportunity for the new one?

Of course, the process was not completely smooth. I wanted to add reverse polarity protection to V1, which the prototype did not have. In the first design, I built and tested a reverse polarity protection circuit with a single P-Channel MOSFET. However, I had missed one scenario: although a single P-Channel MOSFET can be enough in some cases, it could not block reverse current coming from inside the device. Even when the IRFP260N MOSFETs were off, reverse current could pass through the body diodes and put the connected power supply into a short-circuit condition. To solve this problem, I reworked the PCB to convert the power input block to a back-to-back P-Channel MOSFET structure. I used the banana sockets on the front panel as the protected input, designed to support an 8-30V range. The XT60 connector on the right works as the unprotected input and supports a 0-30V input range. After the rework, the protected power input caused significant heating at 8V and below because it left the protection MOSFETs partially on. For the next PCB revision, I plan to redesign the power input block using an ideal diode controller and two low-RDS(on) N-Channel MOSFETs in a back-to-back structure. Also, because of the two P-Channel back-to-back MOSFETs, the protection MOSFETs heated to unsafe levels at my target 200W test power. For safe operation, I limited the device to 150W. The device can support voltage and current values up to 30V and 10A within this limit. On the software side, with AI assistance, I developed control, protection and monitoring functions such as toggling load draw with the RST button, overcurrent warning, reverse polarity notification, temperature tracking and fan control. For the V2 revision, I aim to improve the device with more functional features and design a structure with higher power capacity. Overall, this project was a very educational and experience-building work for me in power electronics, measurement, PCB design, mechanical design, rework and fault analysis.

https://omerikinci.github.io/projects/electronic-dummy-load.html

maybe it's time to start using PCBs