Single Numitron Clock

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Numitrons are neat display devices similar to nixie tubes but designed for much lower voltages. Numitrons are basically incandescent displays in which filaments create the segments. I had just one RCA DR2100 Numitron display tube so a single digit clock was the perfect application. The clock operates off a PIC 16F84A using a program written by David Tait (software is further down this page). The crystal oscillator for the clock is a 3.58 MHz color burst crystal salvaged from a VCR. Below is a schematic of the clock:

Four micro-sized yellow LEDs were used below the Numitron to indicate which digit is being displayed (HHMM); I would have used miniature incandescent light bulbs but didn't have any on hand. The clock is pretty small and the board measures approximately 1.25 inches by 1.5 inches. The original purpose of the software and circuit was to drive a single common-anode LED display rather than a numitron, but either way works. I modified the software to flash the digits so the HHMM leds wouldn't be necessary. Also the software was modified so if the tens of hours is 0 then it is not displayed. Moreover, the software does not check the input values so entering the wrong time such as 67:85 would be accepted, but eventually the clock will start resetting the digits correctly.

The .ASM file is the PIC assembly program for the clock. The .HEX file is the assembled program used to program the PIC, but choose the correct HEX file depending on whether you want to use a 3.57Mhz or 4Mhz crystal. Bad timekeeping will result from incorrect matching of the HEX file and crystal speed.

24 Hour Nixie Clock
24hrclock.asm (.ASM file)
24hrclock3.hex (.HEX file) 3.57MHz
24hrclock4.hex (.HEX file) 4MHz

12 Hour Nixie Clock
12hrclock.asm (.ASM file)
12hrclock3.hex (.HEX file) 3.57MHz
12hrclock4.hex (.HEX file) 4MHz

Gallery of other single numitron clocks:


These clocks were made by Terry, a fellow electronics hobbyist who bought 30 IV-6 numitrons off ebay and had to do something with them! I especially like the clock in the clear plastic tube case.

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