There are probably better nixie clocks out there, but this one is mine. The Concrete Clock uses four IN-1 Nixie tubes and one OG-4 decatron tube. This was one of my first AVR projects. The circuit board, controlling the clock, is based on an AtMega8515. The 8515 controls up to 6 BCD to decimal decoder ICs with high voltage outputs (74141 or K155ID1). Three IRF840 mosfets are used to drive the OG4 dekatron. Adjusting the clock can be done via serial communication over a Bluetooth link.
Schematics, gerber files and example firmware are available via GitHub.
The circuit board requires an external 200V/450V power supply in order to be able to drive both nixies and the decatron.
A decatron is a “three phases glow transfer tube” that require 4-600V in order to operate. It’s basically an analog counter that can count to – wait for it – ten. Decatrons can be daisy chained and they would originally be controlled by analog circuitry, where a correctly shaped pulse would make the glow discharge jump to the next location. A full revolution would trigger the next counter. The necessary (and very analog) circuitry involved in creating a correctly shaped pulse, is relatively archaic. Fortunatetly, we now have cheap high voltage transistors at our disposal.
All you need to do in order to drive such a tube, is to ground triplets of cathodes in the correct sequence. Easy.
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