Clock is built to drive 6 IN+14 nixie tubes display. It shows the time, room temperature and outdoor temperature.
Clock prototype is based on a Raspberry Pi board (yes, I know it is overkill, later version is built on ESP32).
The display is built with 6 IN-14 (ИН-14) soviet-era nixie tubes, driven by 2 soviet-era driver chips K155ID1 (K155ИД1 in Russian). These are analogs of SN74141.
Chips are controlled directly from the Raspberry Pi IO pins. The only reason why we have 2 driver chips is that it can only drive 10 digit pins, the second chip is only used to control 2 dot signs. The display anodes are selected using 6 TLP627 decouplers, controlled via 74HC238. Two more TLP627 control 2 IN-3 bars between the digits.
The clock is powered from a standard micro-USB connector located on the Raspberry Pi board. The tubes require 200-300v voltage to operate, and that voltage is supplied from a charge pump, built on 555 and inductor, pushing from 5v from usb to 300v.
It features a DS18b20 digital thermometer to measure the inside temperature. 6 WS2812 leds are placed under the nixie tubes to backlight them, emulating hot cathodes.
Schematics and PCBs: https://oshwlab.com/alexander.krotov/in14
Wiring between the Raspberry Pi and the board:
| Board header | Board wiring | Raspberry Header | Raspberry pin |
|---|---|---|---|
| Header 1 | 74HC238 A0 | GPIO11 | |
| Header 2 | 74HC238 A1 | GPIO10 | |
| Header 3 | 74HC238 A2 | GPIO9 | |
| Header 4 | 74HC238 E3 | GPIO8 | |
| Header 5 | K155ID1 U4 I1 | GPIO7 | |
| Header 6 | K155ID1 U4 I2 | GPIO6 | |
| Header 7 | WS2812 data | GPIO24 | 18 |
| Header 8 | K155ID1 U3 I1 | GPIO5 | |
| Header 9 | K155ID1 U3 I2 | GPIO4 | |
| Header 10 | K155ID1 U3 I4 | GPIO3 | |
| Header 11 | K155ID1 U3 I8 | GPIO2 | |
| Header 12 | Ground | 6 | |
| Header 13L | +5v | 4 |
References to hardware:
- https://www.raspberrypi.com/
- https://tubehobby.com/datasheets/in14.pdf
- https://eandc.ru/pdf/mikroskhema/k155id1.pdf
- https://neon1.net/nixieclock/sn74141.pdf
- https://www.soemtron.org/downloads/disposals/tlp627.pdf
- https://www.ti.com/product/CD74HC238
- https://www.analog.com/en/products/ds18b20.html
- https://cdn-shop.adafruit.com/datasheets/WS2812.pdf
The clock program source code is clock.c. Written in C, it requires libjson-c, libcurl, libws2811, and should be run as root to have permissions to access to GPIOs.
Clock displays the current system time, that could be set with NTP, for example. The inside temperature is read from the hardware digital thermometer. The outside temperature is read from openweathermap.org (you will need to get your own key and set OWM_KEY to use the service). libjson-c and libcurl are needed to get the outside temperature.
libws2811 is used to control 6 WS2812 leds.
config.txt - example Raspberry Pi config enabling the hardware access.
nixie.service shows how to run the clock program from systemd.
Final clock video: https://www.youtube.com/watch?v=RONzVr5dUMM