IN-12 nixie clock: open firmware

Replacement firmware for a RetroModding NixieIN12v2 WiFi nixie clock (the 5 V, USB-C version sold on AliExpress): 4x IN-12 tubes, 2x IN-3 neon dots, 4 WS2812 LEDs, an ESP8266 (ESP-12) and a light sensor. The closed stock firmware (SV1.3) is replaced by ESP_UniClock with a new display driver for this board, WiFi updates and Home Assistant control.

Features

• Time from NTP with time zone and EU summer time, 12/24 h, day/night brightness, auto dimming from the light sensor, digit animations, cathode-poisoning protection, blinking colon
• WS2812 backlight: fixed colour or one of nine animated effects
• UniClock's web page for all settings
• Firmware updates over WiFi (ArduinoOTA)
• Home Assistant over MQTT discovery: tubes on/off, day/night brightness, auto dim, backlight (on/off, brightness, colour), LED effect, cathode protect, light and WiFi-signal sensors

The hardware

The pinout was taken from the stock firmware by disassembly and checked on the clock; details and evidence are in docs/stock-firmware-pins.md.

Function	GPIO
2x 74HC595 (cathodes, anodes, dots) DATA / CLOCK	13 / 14 (hardware SPI)
74HC595 latch	15
WS2812 data	12
Light sensor (LDR)	A0

The two shift registers hold one 16-bit word: bits 0-9 are the cathodes for digits 0-9, bits 11-14 the tube anodes (bit 11 = left tube), bit 10 the neon dots and bit 15 the decimal points. The tubes are multiplexed, one at a time. This board has no RTC chip and no buttons.

Warning: the board makes about 170 V for the tubes whenever USB-C is connected.

Repository layout

Path	Contents
firmware/uniclock/	ESP_UniClock with the board support (PlatformIO project, see its README)
firmware/uniclock/ESP32_UniClock2/nixie595.ino	Display driver for this board
firmware/uniclock/ESP32_UniClock2/clocks.h	Board configuration, CLOCK_90
docs/	Pinout analysis of the stock firmware, schematic of the related 12 V board
tools/	Python helpers used to disassemble the stock firmware

The stock firmware dump is not included: it contains the WiFi password.

Building and flashing

Install PlatformIO, then in firmware/uniclock/:

pio run                                # build
pio run -t upload                      # first flash, over serial
pio run -t uploadfs                    # web page files, over serial
pio run -e nixie_in12_ota -t upload    # later updates, over WiFi

The first flash needs a USB-serial adapter (3.3 V logic) on the programming header (GND, GPIO0, RST, RXD, TXD, 3.3V). The clock stays powered from its own USB-C, so leave the adapter's 3.3V unconnected. There is no auto-reset: before each serial upload, hold GPIO0 to GND, tap RST to GND and release GPIO0. Set the serial port and the clock's IP address in platformio.ini. Back up the stock firmware first (esptool read-flash 0 0x400000 stock.bin); it is the only way back.

On first boot the clock opens a WiFi access point called UNICLOCK. Connect to it and set your WiFi on http://192.168.4.1. For Home Assistant, enter the MQTT broker on the clock's web page and restart the clock; it then shows up under Settings > Devices > MQTT.

Optional passwords for the web page and OTA updates go in firmware/uniclock/ESP32_UniClock2/secrets.h (see secrets.h.example; the file is gitignored).

Changes to ESP_UniClock

Besides the new driver and configuration:

• NeoPixels on any ESP8266 pin, sent only when they change and between tube slots (the bit-banged update blocks interrupts and made the tubes flicker)
• ArduinoOTA; Home Assistant integration rewritten for ArduinoHA 2.1
• EU summer-time rules (upstream ended summer time on the US date); switching DST on no longer shifts the clock by an hour in winter
• Saving the firmware URL no longer starts an HTTP update; optional web password
• Small fixes: PlatformIO build, MQTT message buffer overflow, cathode-protect random start, LED gamma

Credits and license

ESP_UniClock is © Peter Gautier and licensed GPL-3.0-or-later; the modified firmware in firmware/uniclock/ is under the same license. The libraries in firmware/uniclock/lib/ keep their own licenses. The board support, analysis and changes were made with Claude Code.