Electronic – Reducing the brightness of Nixie tubes

nixiepower supply

I have a Nixie tube clock based on IN-12. I assembled the kit, it works great and it was great fun. But the tubes are just too bright in dark conditions.

I would like to modify the clock to be able to change the brightness. I have included the full schematic bellow.

Nixie clock schematic

I feel that a well placed potentiometer on the high-voltage power-supply (lower right of the schematic) could do the job.

UPDATE

I change the voltage, as expected, I got some non-uniform lighting. reprogramming the microcontroller is more work than I was willing to put in this project.

Best Answer

Don't mess with the voltage, that will cause uneven lighting.

Generally for glow discharge tubes like nixies you can get much better control by PWM than by messing with voltage, so I would suggest programming the tiny to PWM the A1-A4 pins. You will want to make the frequency high enough to avoid quench effects (still a thing even in glow discharge regime) and audio frequencies (Actually it looks like 100-500Hz also works because the time constant is really long).

An explanation is given at Wendt's page. He used a 555 to generate the PWM, but the tiny probably can just generate it internally.

As a bonus, you can change the brightnesses on a per tube basis.

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