Here is my 24H Nixie clock project, the original goal was to construct a six digit nixie clock using only SN74 hard logic, also in my checklist for this project:
Internal (DS32KHZ) / external (1PPS from GPS) time synchronization
On board 3.3V power supply for external GPS receiver (Fastrax UP501 or similar)
5V single supply operation with regular Arduino power jack
LED backlight for nixie tubes
Switchable control of blinking dots
Push button control for time setup
Seconds reset for accurate time setup
Schematic is pretty simple, it consist of four Divide-by-eight counters (SN7493) to get a 1PPS signal from 32768Hz (DS32KHZ oscillator), decade counters (or divide-by-five SN7490) and Divide-by-six (SN7492) counters, BCD-to-Decimal decoders (SN74141) for nixie tubes operation. Time setup is controlled by SN74153 multiplexer, it switches 1PPS signal between minute and hour counters to adjust time. For GPS synchronization Divide-by-eight counters (4x SN7493) are optional as well as DS32KHZ Temperature-Compensated Crystal Oscillator, 1PPS can be applied directly to seconds counter input. Any digital TTL compatible logic from SN54 or SN74 series can be used for this project, including original SN74 and F, LS families, also there are lot of military grade SNJ54 integrated circuits in ceramic DIP available from eBay. In this project I also used Russian cross-references for SN74141 (155ID1) and SN7493(155IE5). Nixie tubes power supply (5V-170V) was purchased off eBay. Time setup sequence:
Press and keep seconds reset button to prevent seconds count
Press minutes setup button and adjust minutes
Press hours setup button and adjust hours
Release seconds button or press it again for precision time setup
And that's it. Lots of vintage electronics and very old nixie tubes from 70’s and I have my finished Nixie clock.
