Millivolt Meter Nixie Clock

Surprisingly, up until a year ago, [Jimmy] hadn’t seen a Nixie tube. Awful we know, but he has come around to the beauty of glowing numbers in a tube. He recently found an old millivolt meter in a junk pile that used Nixie tubes. The wondrous orange glow beckoned him, so [Jimmy] decided to build a clock.

Just about all of the Nixie clocks we’ve seen (including non-clock builds) rely on building a controller for the Nixie tubes. The controllers range from Nixie Arduino shields to the good ‘ol 74141 IC. [Jimmy] realized he didn’t need to bother with controlling the tubes in an already functional millivolt meter – he only needed to send the right voltage.

For his clock build, [Jimmy] used an Arduino to output a voltage through a bunch of resistor dividers. For example, if the time is 12:30, the output voltage will be 12.30mV. Using this technique, the values for the needed resistors don’t exist, so a little bit of PWM means the Arduino keeps fairly good time.

There’s one added bonus of [Jimmy]’s clock – because the voltage varies around 0.01mV, the finished project acts like a digital version of Lord Vetinari’s clock. It may not be perfect, but at least a nice piece of equipment was saved from the trash.

9 thoughts on “Millivolt Meter Nixie Clock

  1. Interesting way to generate the necessary voltage, PWM on a resistor ladder.
    I would have tried a normal R-2R resistor ladder, without the PWM. You would need 12 output pins, but you could stick with resistors of a single value, and then scale it to a max voltage of 40.95mV. This way you could count in discrete steps of 0.01mV up.

    I’ve seen a similar hack done to digital counters, where simply a pulse is sent to the counter once per second, 41 pulses each full minute and 4041 pulses each full hour. Gives a nice effect as the number runs up and then settles.

    1. I actually thought about that, but I decided I wanted to minimize the pins used to both A) leave room for buttons for control, and B) use fewer pins in general for a smaller microcontroller that I could make a PCB for that just bolts on to the terminals.

Leave a Reply to Per Jensen Cancel reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.