Introduction: Simple Nixie Tube Wristwatch
This is a novel nixie tube wristwatch I made a few years ago that uses an MSP430f169 microcontroller and two IN-17 nixie tubes. It has an accelerometer so that you only need to twist your wrist in order to display the time. The power supply consists of three 240 mAh lithium ion batteries in parallel, which makes for about 480 hours (20 days) of stand-by operation at about 1.5 mA current draw (I didn't do much fiddling to try to get the consumption down) if it were to run the batteries dry. Actual operating time may be slightly less since it cannot run the batteries all the way down. I made a few mistakes that, if remedied, could allow for longer operation. One mistake was that I didn't provide a way for the accelerometer to be turned off, so that I could power it only part of the time to decrease power consumption. Another mistake is that I designed in only one button for setting the time. This button only increments the minutes, which makes for a very long time setting procedure. The time itself is kept with a 32.768 kHz crystal, which the microcontroller uses in the conventional method of dividing by 2^15 to get one clock tick per second. The power supply for the tubes, which require a high voltage to operate, is a DC to DC converter made with an LT3580 and a TDK LDT565630T-001 transformer, outputting about 173v DC. The schematic for this power supply can be found in the LT3580 datasheet. Even though the entire watch may look large, it is actually quite small for a nixie tube watch. Of course, this watch was not meant for practical use, so the size doesn't matter much. It is purely a novelty item.
Here are most of the major components I used with quantities in parentheses in case you want to cobble up your own watch:
Microcontroller: (1) MSP430f169
Transistors for driving nixie tubes: (10) MMDTA42
Base resistors for transistors: (2) OSOPTA5001AT1
Accelerometer: (1) ADXL335
Nixie tubes: (2) IN-17
3.3v regulator: (1) MIC5301
DC to DC converter IC: (1) LT3580
Transformer for DC to DC converter: (1) LDT565630T-001 (I had to email TDK to get a sample because the part is only sold in bulk)
Battery: (3) 3.7v 240 mAh Li-Poly batteries in parallel
It has been a while since I made this device, so if I missed anything, feel free to ask! If you could vote for me in the battery powered contest, that would be fantastic!