nixie clock

  
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One of the many random devices I`ve found in my sometimes frightening basement was an HP frequency counter. The thing is built like a rock, still works perfectly and the manual contains full parts list, a complete circuit diagram and a description of the theory of operation. The counter is a 4 digit counter with. 1 or 1 second frequency intervals good to up to several megahertz
nixie clock - schematic

and a nixie tube display. This last bit is what caught my eye. Nixie tube clocks, like binary clocks, are something of a staple of the tinkering community. The nixie tube provides a warm glowing warming glow not present in conventional LED based clocks, and just ooze retro-geek style. The downside of the nixie tube design is that it requires a large number of high voltage components which can be hard to get. The nixie tube counter has the driver circuit built in, and it occurred to me that I could set the clock to an arbitrary time by simply counting up. This also leaves me with a perfectly good (and potentially useful) frequency counter. The idea is simple. The first two digits are the hours, the last two are minutes. Every minute, pulse the timer and it will go up by 1. Every hour (when the time is, for instance, 11:59), send 41 pulses and the timer will count up to the next hour. Every 24 hours, count up from 2400 to 0000 and you roll back to midnight. Some counters have a reset function, so going from 2400 is just a matter of pulsing another port, but this counter would have required modification to be able to do that, and since it only has four digits available the count up method can be used to roll the clock to zero in about 2 minutes at 60hz. The implementation uses my favorite microcontroller, the ATTiny 2313. This uC has 18 general purpose I/O pins (14 more than required) and a "generous" 2k of memory. Complete...



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