Counting Without Transistors

The Hackaday Prize is all about Building Hope. We want to see hardware creators change the world with microcontrollers and breadboards. That’s a noble goal, but it also doesn’t mean you can’t have fun. That’s exactly what [Yann] is doing with a pile of surplus Soviet components, a bunch of bodge wire, and exactly zero transistors. He’s building a hexadecimal display module using only relays and diodes. It’s absurd, but still very very cool.

The inspiration for this build comes from homebrew computing. With this, there’s a recurring problem of displaying the status of a bus. Sure, a bank of LEDs will work, but then you have to count to F. The better solution to this is a hexadecimal display. The best solution to this problem is using Numitrons — seven segment Nixies, basically — and doing it all with relays and diode steering.

This module accepts four bits as an input and uses a clever arrangement of diodes to turn those four signals into the digits 0-F. Yes, it’s hexadecimal, but that’s just what you do when you’re building your own computer.

Right now, [Yann] has one module on a slim-profile protoboard that should stack easily enough for an 8 or even a 16-bit wide bus. That’s four tubes and hundreds of diodes for the 16-bit version, but the good news is all of these modules are identical, vastly simplifying the construction of the display panel of a homebrew computer.

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