The Seemingly Impossible Oscillator

July 14, 2026 by Jenny List 20 Comments

Back in the days when an integrated circuit meant a simple but expensive device such as a 741 or a 555, most electronics enthusiasts made do with discrete transistor circuits. The common emitter amplifier and its variants are the most familiar, but the humble 3-legged device can do so much more. A particularly obtuse circuit is the subject of examination by [lcamtuf], the reverse avalanche oscillator. A 2N2222, a capacitor, an LED, and a resistor, the transistor is the wrong way round, and there’s nothing on its base. Yet the LED flashes, what on earth is up!

The answer lies in avalanche breakdown, the behavior of a reverse biased diode junction as the voltage across it increases. Eventually the electric field reaches the point at which an avalanche of electrons crosses the depletion layer, and the junction conducts. When connected across an RC circuit, the voltage in the capacitor slowly rises to the point at which avalanche breakdown occurs, and the capacitor abruptly discharges. As the voltage falls the avalanche conduction stops, and the cycle repeats itself. It’s a relaxation oscillator.

We’re treated to an explanation of why a transistor behaves this way and why a simple diode doesn’t, due to a “hump” in its I/V curve, and why the emitter-base junction has a lower breakdown voltage than the collector-base. It’s one of those circuits which looks as though it shouldn’t work, but never fails to oscillate.

Want to know more about transistors? Do we have the series for you!

Can’t Find That ISA Sound Card? No Worries!

July 13, 2026 by Jenny List 19 Comments

Many older hackers will have at some point gotten rid of an old piece of hardware that they later ended up regretting. All those ISA cards were next to useless back in 2006, but now their relative rarity plus the popularity of retrocomputing makes them sought-after. But if it’s a sound card you’re after then never fear! [Schlae] has got you covered, with the Beavis Ultrasound. It may have a name reminiscent of a ’90s cartoon series, but it’s a clone of the Gravis Ultrasound from back in the day.

There is of course a snag, to build one you need an AMD AM78C201. Assuming you’ve found one in a surplus supplier though, the rest of the card is analogue, some glue logic, and a ROM for samples. There is also a GAL for driving the IDE CD-ROM interface, from the days when sound cards came with such things.

New ISA cards are cropping up here from time to time, such as this very handy storage and network card.

It’s A Spectrum, With An RP2350 ULA

July 13, 2026 by Jenny List 12 Comments

There was a time in the early 1980s when it was common to see home made keyboards for 8-bit machines that came with membrane or rubber keyboards. Though we’ve seen any numbers of home made modern ‘boards, it’s been decades since we saw one for an 8-bit micro. Until today, that is, when we saw [Vlad]’s Sinclair Spectrum. It’s a Spectrum with all that Sinclair glue logic that was in the ULA replaced in software by an RP2050, and that keyboard with the Spectrum decals.

The machine is a charming mixture of new and old, with a traditional cassette port alongside VGA, gameport joystick, and Sinclair joystick. The aim is to also have HDMI, though it’s not yet implemented. Sadly there is no Spectrum edge connector for period peripherals though. He admits it’s not cycle accurate to the original, but given that it runs all the games he’s given it this seems not to matter. Meanwhile that keyboard which caught our eye is a true period piece, sitting as it does on a piece of phenolic stripboard, and those decals are the perfect finishing touch.

The Spectrum receives quite a bit of love today, and if this one takes too many modern liberties for your liking, you can still make one using proper logic.

The First New WW2 Jeep Since 1945

July 11, 2026 by Jenny List 19 Comments

Online publications sometimes work with sponsors. Over at the Autopian, they landed a sponsorship deal with eBay, but due to an unguarded comment, fulfilling the sponsor’s requirements turned out to be something of a handful. Build a brand-new, completely WW2-spec Jeep using only parts sourced from the auction site, and drive it to Moab for an event. [David Tracy] set to work, and the resulting write-up is a build of epic proportions.

Of course, many Jeeps have been built since the war, not least by Willys and its successors, but also by enthusiasts. You can even buy a modern-day visible derivative of the original made in America by the Indian company Mahindra, which has been licensed to build Jeeps since the 1940s. So his claim of making the first new WW2-spec Jeep since the war may be difficult to substantiate, but it’s certain that his attention to period detail is exceptional. For example, most people would either use a more modern engine or find a second-hand original. Instead, he sources a brand new block from France and builds a new engine from scratch. And is that the infamously flawed early Jeep steering system we spy? The vehicle uses second-hand parts for other major drive train components, but the chassis and body are made in the Philippines.

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Hackaday Podcast Episode Ep 377: Parallel Pixels, Wiggly Consoles, And Seven Segments

July 10, 2026 by Jenny List 1 Comment

This week’s podcast sees Elliot joined by Jenny List, as both suffer silently in the European summer heat because the sound of a desk fan would come over on the recording.

A stand-out hack of the week comes from [Bitluni], whose GPU made from thousands of cheap microcontrollers is on a scale we’ve never seen before. It’s an amazing project in itself, but the manufacturing and power consumption issues of so many processors running at the same time make for a discussion of their own.

Otherwise, we have diecasting on the bench, an impressive achievement by any measure, a Raman spectrometer, and an open source take on something like a Kei truck. In quick hacks there’s a dicussion of soldering versus crimping for high current connectors, and neon tubes used as digital logic in an organ. The recording finishes with a discussion of 7-segment display history, and whether an engineering education teaches design for manufacture.

Or download it yourself, in glorious 192-bit MP3.

Continue reading “Hackaday Podcast Episode Ep 377: Parallel Pixels, Wiggly Consoles, And Seven Segments” →

A Super Cheap Desk Toy Becomes A Hackable Desktop Notifier

July 10, 2026 by Jenny List 14 Comments

The GeekMagic SmallTV is as its name suggests, a tiny, vaguely TV-styled, device with a screen, that’s sold as a desktop notifier. Depending on the firmware running on the device it can display various pieces of information, ranging from the time and weather to the current price of Bitcoin. What makes it interesting is that it supports software updates over WiFi, so [Giovi321] has made a new firmware package for it.

A screenshot of AliExpress showing a range of the devices for sale. — These things are readily available from AliExpress.

It seems there are several versions of this device, something which appears to be reflected in the prices they sell for on AliExpress. The older version runs on the ESP8266, and there’s also a ESP32-C2 variant in the wild. The firmware supports both flavors, providing stock and crypto tickers, an ADS-B tracker, and a Claude AI token usage gauge.

What gives this potential is that the various functions are clearly split out in the code, and there’s nothing to stop you pointing it at a data source of your choosing. This makes it more than a bit of cheap e-waste novelty, and we hope that others will take up the baton and do interesting things with it.

The ESSP8266 is a chip we don’t see too much of these days, having been surpassed by its ESP32 siblings. Still, someone recently gave it a simple OS.

Fixing A Dodgy Cheap Audio DAC

July 9, 2026 by Jenny List 14 Comments

One of the attractions of buying at the bottom end of the electronics market by mail order from China is that you never quite know what will come your way. Sometimes it’s a diamond in the rough, while with others it’s a mess. Occasionally along comes something which should work but doesn’t, and that’s the moment when you wonder if you could fix it. [Nyanpasu64] had just such a device, an HDMI to VGA converter with audio that didn’t work. What could be wrong?

The HDMI to VGA chip has an onboard audio digital-to-analog converter (DAC), and it’s a delta-sigma design. This type of DAC is frequently used in audio applications because it works by shifting its switching frequency many times higher than the input sample rate, thus reducing considerably the distortion. This one wasn’t performing as advertised though, and the problem turned out to be that switching frequency being all over the output. Clearly the filter wasn’t working, which led to the design of a new filter. The write-up is therefore an extensive dive into filter design, and in part also a discovery of the effect of impedance on them.

For a super-cheap module to cause so much work, one might ask why not simply spend a few more dollars and get a better one. But had they done that we wouldn’t have seen this write-up, so we’re sticking with team cheap.

We’ve looked at audio DACs, in the past.