Triple Display Rig

Minimal three-board demo for CRUMBS: display_controller issues SEND/REQUEST commands, while each display_peripheral slice drives three LEDs and reports its state.

Rig at a Glance

  • 3Ă— Arduino Nano (ATmega328P)
  • 3Ă— SSD1306 128Ă—64 OLEDs on software I²C pins D7/D8
  • LEDs on D4 (green), D6 (yellow), D5 (red) with 220 Ω resistors
  • Pull-ups present only on the controller; anything in the 2–5 kΩ range works
  • Common SDA/SCL on A4/A5 and a shared ground between all boards
Controller Nano                          Peripheral Nano(s)
--------------                          -------------------
D7 → OLED SDA                             D7 → OLED SDA
D8 → OLED SCL                             D8 → OLED SCL
D4/D6/D5 → LEDs → resistors → GND         D4/D6/D5 → LEDs → resistors → GND
A4 ↔ bus SDA                              A4 ↔ bus SDA
A5 ↔ bus SCL                              A5 ↔ bus SCL
Pull-ups only here                        (no extra pull-ups)

Flashing the Sketches

  1. Install CRUMBS and U8g2.
  2. Set kSliceI2cAddress per slice (e.g. 0x08, 0x09) in display_peripheral.ino.
  3. Upload display_controller to the controller Nano and the slice sketch (with its address) to each peripheral Nano.

Serial Commands (115200 baud) 

SEND <addr> <green> <yellow> <red> <period_ms>
REQUEST <addr>
  • Ratios are 0.0–1.0; period_ms sets the shared blink cycle.
  • Hex addresses (0x08) or decimal (8) are both accepted.
  • Controller OLED lines: status, last TX/RX with CRC, current LED ratios.

Slice Behaviour

  • SEND updates internal LED ratios and immediately applies them without blocking.
  • REQUEST returns the stored ratios, the active period, uptime seconds, and a CRC byte.
  • Slice OLED shows status, last command, LED ratios, and the CRC of the last response.

Quick Sanity Check

  1. Power all boards: both OLEDs should show CRUMBS banners.
  2. SEND 8 0.5 0 0.25 1500 – controller yellow LED blips, slice LEDs match the ratios.
  3. REQUEST 8 – controller prints the reply and shows an RX line; slice logs “response sent”.
  4. Repeat for the second device address.

If a transfer fails, the controller flips to red, prints the Wire error code, and the OLED marks the last exchange as FAIL. Recheck wiring, addresses, or long cable runs introducing noise.

That’s the whole loop: a tiny CRUMBS controller driving slices and asking them how they’re doing. Hack on it from here.