Four Digit IN-12 Nixie Clock

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1

This document describes the design, construction and configuration of a four digit Nixie clock.

The clock uses top facing display Nixie tubes of type IN12 and is multiplexed using two power shift registers to directly drive the tube cathodes and to drive the anodes and neon bulbs via high voltage opto-couplers.

The high voltage (170v) power supply for the tubes uses a simple boost converter design based on a 555 timer. That power supply itself requires a 9v source which is provided by a standard USB Power Delivery (PD) charger, such as is used for recent smartphones, and a USB trigger module to force the charger to deliver 9v. The firmware runs on an ESP32-C3 (super-mini pattern) and uses the ESP32 native time (SNTP) functions, including automatic day light saving time adjustment, but with an optional external RTC backup. Included is also a Captive Portal software module for configuring the clock with data such as WLAN credentials, time zone etc. via a webserver over the ESP32's own access point.

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20260801_1048171920×1440 541 KB

The clock was certainly fun to build and I am quite pleased with the way it turned out and I even have enough tubes left for one or two similar projects. All the design details, schematics and software are included which should allow anyone to either duplicate the project or just see what I did. Anyway, I hope someone finds it useful or interesting.

Schematic: Display Board:
Nixie_4Digit_2026_display_V0_01.pdf (236.5 KB)

Schematic: Logic/Power board:
Nixie_4Digit_2026_logic_power_V0_02.pdf (229.4 KB)

Documentation:
Nixie_4digit_2026_V02.pdf (1.3 MB)

Code:
Nixie_4digit_2026_V1_01.zip (25.5 KB)

EDIT 1
Replaced Schematic: Logic/Power board to correct interchanged MCU pin error.

2

This probably isn't the first question you were expecting, but who does your acrylic cutting? Or is that a standard case of some sort?

3

Great project and fantastic presentation, thanks for sharing this cool device.

4

The case is ready made but comes in a self assembly flat pack.
I've had two of different sizes from here and I am very happy with them:

The other is here:

image
image758×482 85.7 KB

5

If I didn't already know somewhere to get laser cutting done I'd try sign makers and the like.

6

Where did you get the KiCAD symbols/footprints for the tubes?

7

I found the schematic symbol possibly from here: GitHub - judge2005/Eagle-and-KiCAD-Nixie-Libs: Eagle and KiCAD libraries for nixie tubes · GitHub
I made the board footprint myself for a clock I built about 6 years ago.
Anyway, the bits are here (Kicad8)
Nixie_IN12_socketed.zip (4.6 KB)

8

Thanks!