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2. Controller Board

The dual display configuration uses a custom ESP32 controller board that manages two independent I²C buses (Bus 1 and Bus 2) and coordinates power distribution to support up to 16 split-flap modules. This page covers assembling the perfboard-based design.

ESP32 controller board

The assembled ESP32 controller board

Overview

The controller board is built on perfboard using:

  • ESP32 microcontroller — runs the firmware and manages both I²C buses
  • Perfboard with screw terminals — provides clean connections for power, ground, and I²C signals
  • Wiring and connectors — interface with the 5V power supply and split-flap PCB daisy chains

Notes

A few things to keep in mind before you start — this is one working design, not the only one:

  • You don't have to build this controller board. You can solder wires directly to the ESP32 and skip the perfboard entirely. The controller board exists for easier assembly and disassembly, not because the firmware requires it.
    • The 3d printed enclosure is meant to mount this design. If you choose a different design, you will have to figure out your own mounting setup.
  • The terminal block layout is a personal choice. Separated and different-sized terminal blocks aren't required — I used what I had on hand and like the spacing between connections. A single multi-position block works fine too.
  • Pull-up resistors are not on this board. The 4.7kΩ I²C pull-ups for each bus live on the split-flap PCBs (or DIY boards), not on the controller. See the I²C reference for placement details.

Components

Full list of parts can be found in the BOM. The "Split Flap Display connection" terminals represent the daisy-chain outputs to the first module in each row.

Controller board with labeled components

Labeled components on the controller board — ESP32 and screw terminals for power input and dual I²C bus outputs

Pin Connections

The ESP32 has two dedicated I²C peripherals. The firmware uses these GPIO defaults:

Signal Bus 1 Bus 2
SDA (data) GPIO 21 GPIO 33
SCL (clock) GPIO 22 GPIO 32

These match the SDA_PIN, SCL_PIN, SDA2_PIN, and SCL2_PIN build flags in the firmware.

Assembly Steps

1. Prepare the Perfboard

  • Mount the ESP32 on the perfboard by soldering the pins directly.
  • You can print the "ESPSpacer" part that should be give the correct height between the ESP32 and perfboard when soldering. This will also align the reboot button on the ESP32 with the enclosure side cutout. So you can easily reboot your esp if needed.
  • Make sure you place the EPS32 in the same pins as the pictures, so you won't have any issues installing the board to its mount.

2. Add Screw Terminals

Solder the 4 screw terminal blocks to the perfboard for:

  • +5V Terminal
  • GND Terminal
  • I²C Terminal 1
  • I²C Terminal 2

3. Wire the Internal Connections

Flip the board over:

  • Solder the 3 pins of the 5V terminal block and the ESP32 VIN pin together.
    • I used a solid copper wire, you could solder them all together without a wire if you want.
  • Solder the 3 pins of the GND terminal block and the ESP32 GND pin together, same as 5V.
  • Solder a pair of jumper wires from the ESP32 GPIO pins to the two different I2C screw terminals.
    • I used 24 awg wire.

Internal wiring — front view

Top side internal wiring — wires soldered on the back of the perfboard

Internal wiring — back view

Bottom side solder joints and wiring — keep traces short and well-soldered to avoid intermittent I²C errors

4. Flash the Firmware

Before testing, flash the firmware to the ESP32. The board won't do anything useful without it. Follow the Build & Flash guide for full instructions.

Tip

This is the easiest time to flash — the ESP32 is accessible via USB while it's mounted inside the enclosure, but not once the end caps are in place.

5. Test Before Installation

  • Power on the controller board via USB or 5V supply and verify the ESP32 boots
  • Confirm no shorts between 5V and GND
  • Connect a module or two and verify they respond and home correctly

Completed controller board

Front

Controller board from a different angle

Back

Controller board with bus wires connected

Power and I²C bus wires connected to the screw terminals for testing before assembly

Power Distribution

All power runs through the main 5V supply connected to the controller board's screw terminals. The controller board is responsible for:

  • Receiving 5V from the external PSU
  • Supplying 5V and GND to the split-flap daisy chains via the output terminals
  • The ESP32 itself draws minimal current (~80–100mA); most power goes directly to the motors