Numitron clock

IV-9 Numitron Clock

A WiFi-connected desk clock built around six IV-9 Numitron tubes — vacuum-tube seven-segment displays, driven by an ESP32-S3 over a chain of TLC5916 constant-current shift registers. Time comes from a battery-backed DS3231 RTC (periodically corrected over NTP), with outdoor temperature/humidity pulled from Open-Meteo and indoor readings from an onboard HDC2010 sensor.

Repo layout

• hardware/ — KiCAD 9.0 board design: ESP32-S3, power (USB-C in, AZ1084-3.3 regulator, USB-C ESD protection), the tube driver chain, buttons, status LED, and the HDC2010 sensor. Hierarchical schematic split across numitron-clock.kicad_sch (main) and tubes.kicad_sch (display).
• firmware/numitron_clock/ — the main ESP32-S3 Arduino sketch: clock display, WiFi setup portal, NTP sync, and weather fetch.
• firmware/set_rtc_serial/ — a small utility sketch for setting the DS3231's time over serial.
• firmware/common/ — the canonical segment bit map shared by the sketches above (each sketch keeps its own copy, since Arduino requires headers to sit alongside the .ino).

Building and flashing the firmware

cd firmware/numitron_clock
arduino-cli compile --fqbn esp32:esp32:esp32s3 .
arduino-cli upload -p /dev/ttyACM0 --fqbn esp32:esp32:esp32s3 .

Requires the esp32:esp32 core and the Adafruit NeoPixel library. There's no serial console on the main sketch, so verification is: compile, flash, and look at the board.

Setup

Hold BOOT (IO0) within a few seconds of power-up to start a WiFi setup portal (SoftAP + captive page) for entering credentials, timezone, display format, and brightness. Settings persist in NVS and survive power loss; the RTC keeps time on battery backup even with no WiFi at all.

See CLAUDE.md for the detailed architecture notes (display/render path, timing constraints, NVS layout, and known caveats).