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Arduino Firmware

Two Arduino Micro boards (ATmega32U4) run the keypad/peripheral I/O:

Board FQBN Sketch Role
Millennium Alpha arduino:avr:millennium_alpha sketches/keypad 4x7 keypad, magstripe reader, hook switch
Millennium Beta arduino:avr:millennium_beta sketches/display VFD display, coin validator, I2C→USB bridge

See PINOUT.md for complete pin assignments, I2C protocol, and serial command reference.

Pre-built Firmware

Pre-built hex files are checked in under build/:

build/keypad/keypad.ino.hex    # Flash to Millennium Alpha
build/display/display.ino.hex  # Flash to Millennium Beta

These can be flashed directly without compiling:

arduino-cli upload -p /dev/serial/by-id/usb-Arduino_LLC_Millennium_Alpha-if00 \
    --fqbn arduino:avr:millennium_alpha --input-dir ./build/keypad

arduino-cli upload -p /dev/serial/by-id/usb-Arduino_LLC_Millennium_Beta-if00 \
    --fqbn arduino:avr:millennium_beta --input-dir ./build/display

Building from Source

Prerequisites

  • arduino-cli in your PATH (or set ARDUINO_CLI=/path/to/arduino-cli)
  • Arduino AVR core: arduino-cli core install arduino:avr
  • The custom board definitions must be appended to the Arduino AVR boards.txt (see Custom Board Definitions below)

Build and Flash

make build              # Compile both sketches → build/
make install            # Flash both to connected Arduinos
make install_keypad     # Flash keypad only
make install_display    # Flash display only
make clean              # Remove build artifacts

Recommended: build on macOS, deploy to Pi via GPIO reset

The Pi has direct GPIO reset connections to both Arduinos:

  • GPIO17/GEN0 (pin 11) → Arduino Alpha RST
  • GPIO27/GEN2 (pin 13) → Arduino Beta RST

The deploy scripts assert reset via GPIO (open-drain: drive low, release to input), wait for the device to disappear then reappear (the bootloader enumerates under the same custom PID as the sketch), then flash with avrdude. No uhubctl or 1200-baud tricks needed. Requires raspi-gpio and avrdude on the Pi. Note: the WDT (4s) limits the bootloader window — flashing completes well within that window.

./Arduino/deploy_display.sh [user@host]   # flash Beta (display)
./Arduino/deploy_keypad.sh  [user@host]   # flash Alpha (keypad)
# Default host: matzen@192.168.86.145

# Or via make:
make deploy_display
make deploy_keypad
make deploy          # flash both (keypad first, then display)

If build fails because arduino-cli.yaml has Linux paths: BUILD_CONFIG=0 make build_display. If hex not pushed: VIA_SCP=1.

If arduino-cli is not in your PATH:

make build ARDUINO_CLI=/home/matzen/bin/arduino-cli

Verifying a Build

The build is reproducible — recompiling from the same source with the same arduino-cli and AVR core version produces identical hex files.

Custom Board Definitions

The two boards are Arduino Micro clones with custom USB product names and PIDs so the Pi can distinguish them via /dev/serial/by-id/. The custom entries must be appended to:

~/.arduino15/packages/arduino/hardware/avr/1.8.6/boards.txt

Key differences from stock Arduino Micro:

Property Stock Micro Millennium Alpha Millennium Beta
USB PID (app) 0x0037 0x0045 0x0046
USB PID (boot) 0x8037 0x8045 0x8046
Product name Arduino Micro Millennium Alpha Millennium Beta

The full board definition entries are documented in PINOUT.md.

Custom Bootloaders

The boards.txt entries reference custom bootloader hex files (Caterina-Micro-Millennium-Alpha.hex, Caterina-Micro-Millennium-Beta.hex) that encode the custom VID/PID. These bootloader hex files were never built — the boards currently run with stock Micro bootloaders that were already flashed at the factory. The custom VID/PID only takes effect when the sketch is running (not during the bootloader's 8-second window).

To build custom bootloaders (requires LUFA library and avr-gcc):

cd ~/.arduino15/packages/arduino/hardware/avr/1.8.6/bootloaders/caterina
make VID=0x2341 PID=0x8045 TARGET=Caterina-Micro-Millennium-Alpha
make VID=0x2341 PID=0x8046 TARGET=Caterina-Micro-Millennium-Beta

This requires the LUFA 111009 library installed at the path referenced in the Makefile (../../../../../../LUFA/LUFA-111009 relative to the bootloader directory).

Directory Structure

Arduino/
├── Makefile                    # Build and flash targets
├── arduino-cli.yaml            # arduino-cli configuration
├── PINOUT.md                   # Pin assignments and protocol reference
├── build/
│   ├── keypad/keypad.ino.hex   # Pre-built keypad firmware
│   └── display/display.ino.hex # Pre-built display firmware
├── sketches/
│   ├── keypad/keypad.ino       # Keypad Arduino source
│   └── display/display.ino     # Display Arduino source
└── libraries/
    ├── Keypad/                 # Keypad matrix library
    └── MagStripe/              # Magnetic stripe reader library