Nixie clocks are nothing new. But [CuriousMarc] has one with a unique pedigree: the Apollo Program. While restoring the Apollo’s Central Timing Equipment box, [Marc] decided to throw together a nixie-based clock. The avionics unit in question sent timing pulses and a mission elapsed time signal to the rest of the spacecraft. Oddly enough, while it had an internal oscillator, it was only used during failures. It normally synched to the guidance computer’s onboard clock.

There is a detailed explanation of the unit, along with some of the ancillary equipment and panels. Much of what the output from the unit is driving counters to display timers, although some of the clocks drive other pieces of equipment, like the telemetry commutator, which time stamps each telemetry frame.

[Marc] reminds us of an archeologist employing X-rays and other tools to examine the rare hardware. Some of the connectors are very strange these days, too, and require some custom boards. The nixie clock depends on an old HP counter. The counter had an output that sends the BCD digits visible on the display. [Marc] intercepted the connections there and allowed the connector to receive the digits instead of sending them.

The modification involved removing some buffer ICs and replacing them with sockets. If you plug the original ICs in, the counter works as before. If you plug in a special substitute board, you can use the counter as an externally-driven nixie display.

We’ve been following [Marc’s] exploration of the Apollo gear for some time. This isn’t the first time we’ve seen an old counter used in a clock project, either.