"special" Nixie Clock


I want to build a “special” Nixie clock and I would like some feedback/advice from the community.

I don’t want a real time clock that would display the time through the day I just want a 4 digits Nixie clock display that I can manually adjust and when a given time is displayed (let’s say 12:34) I would like the arduino to perform an action.

Here is my solution to this day :

  • I would connect 1 rotary switch per nixie tube to be able to display any time on the nixie clock.
  • I would connect Arduino’s D2 to D5 to Nixie tubes in INPUT_PULLUP mode through high Vbreakdown and low enough Vforward diodes (1N4007), connexions are made so that arduino is connected to “special time” 12:34.
  • Diode needs a high Vbreakdown to protect the arduino from high voltage when not connected to ground and low enough Vforward so when the diode is connected to ground the voltage on digital pins is within the tolerance for LOW.

Here is my expected behavior :
Only when 12:34 is displayed on the nixie clock using rotary switched, all D2 to D5 are LOW.
Using if( !(digitalRead(2) || digitalRead(3) || digitalRead(4) || digitalRead(5)) would enable to detect when all D2 to D5 are low.

Do you see any problem with this schematic ?
Do you think it would work ?

Thanks in advance

How much reverse leakage would those diodes allow? You'd need rotary switches rated for that high voltage too.

I'd get 4 digits of SmartNixie or similar nixie tube controllers that integrate control circuitry (I have 4 of the original smart nixie boards from kickstarter, and they work great). Build these. Then build the control completely separately. Not only would you be able to have much more complex behavior (ie, programmable set point, rotary encoders to adjust the time, etc), you won't have your fingers touching a switch with contacts just millimeters from the high voltage.

Hi DrAzzy,

Thanks for your answer. Indeed the smart nixie solution seems a lot better !

I just checked the smart nixie website and there are things I don't understand :
Can the smart nixie modules (1361 - SmartNixie IN18 in my case) be used on their own ?
I mean can I connect it to my tube, 170V and Arduino to be able to display digits with I2C ?
When I check the schematic I see a PIC16F677 that I can't see on the picture.

Or do I need other modules like "1392 - 6 Digit IN18 Clock Backplane" to be able to make my nixie tubes work with an arduino ?


I found my answer :slight_smile:
The Pic must be hidden behind the switches
"The SmartNixie is a sophisticated I2C display module with an onboard uProcessor and high voltage display driver that may be ordered with or without a Nixie display tube"

I don't think that the breakdown voltage is so critical. As soon as any digit fires inside the tube, the other cathodes are almost powered off. But it should not be a real problem to get high voltage diodes (1N400x...) deliverable at acceptable price.

Hi DrDiettrich,

That's what I thougt at first but as shown by Dave Jones from EEVBLOG, the open voltage on other pins is over 100V. I guess the current is very low but still.
Here is the video : Nixie Tube Voltage Drop - YouTube

Thanks for your reply