[Today’s run: 1 mile]
Ok, so having trolled the internet for nixie clock designs, multiple times over the last decade, I finally am moving forward.
My source of nixie tubes are a couple of old frequency counters. One, an HP, uses tubes which you view end-wise. The other, a Systron-Donner 6153 uses upright tubes. I like the look of the upright tubes.
I have taken the display board out of the S-D counter, and here it is:
The nixie tubes are in front. Behind them is a line of nixie driver chips (7441). Behind that is a big blue card connector. Behind the connector is a line of buffer chips (one for each nixie) and a line of count-up chips (7490).
A series of pulses comes in on the upper right. The count-up chips are linked together so that the first one counts 0-9 and then trips the next one over. So it works just like the odometer in your car, the first digit goes 0-9 then the next digit get’s a ‘1’ and the first digit goes around again and the second digit increments to ‘2’, etc. They are all linked together that way. The thing just counts the number of pulses that came in.
The counter chips produce their output (the 0-9) in BCD form. That is, they use 4 digits to give the binary code for the decimal number (0000 – 1001). Those four output lines are then sent through the buffer chips and then to the nixie driver chips.
The blue card connector is interesting. It was connected to a rear-panel thing on the back of the counter. It was possible to hook up to that back-panel connector and get the same BCD data that was going to the display driver chips.
Ok, so my goal is to turn this into a 6-digit clock. I have plans for a 1 pulse-per-second thing to drive it.
Plan A:
My first shot is just to rewire the decade counter chips so that they will roll over at the right time. The right-most digit in a clock counts up 0-9 (seconds), but the next one goes 0-5 (60 seconds). And for Minutes it is the same as second. Can I just rewire these chips to make them count that way? If so, this will be pretty easy.
I have noticed that the rightmost digit has some extra circuitry. If I can’t figure that out I could just skip that one and use the next-over nixie as my single-digit-seconds.
Plan B:
If I can’t figure out how to rewire the counters I could just saw off that part of the board and feed the nixie drivers directly from the card connector or from the existing traces.
Plan C:
If that doesn’t work I can remove the nixie drivers and use their sockets to access the nixie pins
and do my own driving, probably with discrete transistors.
Plan D:
Worst option: take these nixies and put them on a homemade circuit board, starting from scratch.
Oh, one other thing. I plan to use this clock for UTC. I need a good UTC clock in my hamshack because I write down the date/time information in my radio log book in UTC. The beauty of that for this project is that I don’t have to worry about daylight savings time.