Arduino Pro Micro – DMX Relay
An Arduino Pro Micro (ATmega32U4) firmware that listens for DMX512 packets and drives up to 8 relays based on configurable channel values. A 16×2 I²C LCD and four push-buttons provide an on-device menu for address selection, manual relay override, and settings.
Wiring Diagram
Full-resolution SVG: wiring-diagram.svg
Hardware Components
| Component |
Details |
| Microcontroller |
Arduino Pro Micro (ATmega32U4, 5 V / 16 MHz) |
| Relay module |
8-channel, active-LOW inputs, opto-isolated (e.g. SainSmart) |
| Display |
16×2 LCD with I²C backpack (PCF8574, default address MDINLINECODEaa76020f08df99247dc3344d129bee54ENDMDINLINECODE) |
| DMX interface |
MAX485 (or equivalent RS-485 transceiver) |
| DMX connector |
XLR-5 female panel socket |
| Buttons |
4 × momentary push-buttons (NO) |
Pin Connections
Relay Module
| Pro Micro Pin |
Relay Module Pin |
Relay |
| D4 |
IN1 |
Relay 1 |
| D5 |
IN2 |
Relay 2 |
| D6 |
IN3 |
Relay 3 |
| D7 |
IN4 |
Relay 4 |
| D8 |
IN5 |
Relay 5 |
| D9 |
IN6 |
Relay 6 |
| D10 |
IN7 |
Relay 7 |
| D16 (MOSI) |
IN8 |
Relay 8 |
| VCC |
VCC |
Logic power |
| GND |
GND |
Ground |
| Ext. 5 V |
JD-VCC |
Relay-coil power (see note) |
JD-VCC note: Power the relay coils from a separate 5 V supply connected to JD-VCC (remove the VCC–JD-VCC jumper). This isolates the MCU from relay-switching noise.
I²C LCD (16×2)
| Pro Micro Pin |
LCD Backpack Pin |
| D2 (SDA) |
SDA |
| D3 (SCL) |
SCL |
| VCC |
VCC |
| GND |
GND |
If your LCD does not illuminate after upload, try changing the I²C address from 0x27 to 0x3F in the sketch.
Push-Buttons
Each button connects between the listed pin and GND. The firmware enables internal pull-ups, so no external resistor is needed.
| Button |
Pro Micro Pin |
| UP |
A0 |
| DOWN |
A1 |
| ENTER |
A2 |
| BACK |
A3 |
DMX512 Input (via MAX485)
XLR-5 Pin 1 (Shield/GND) ──► GND
XLR-5 Pin 2 (Data −) ──► MAX485 A
XLR-5 Pin 3 (Data +) ──► MAX485 B
MAX485 RO ──► Pro Micro D0 (RX)
MAX485 RE ──► GND (tie to GND – permanent receive)
MAX485 DE ──► GND (tie to GND – permanent receive)
MAX485 DI ── not connected
MAX485 VCC ──► 5 V
MAX485 GND ──► GND
Use shielded twisted-pair DMX cable; connect the shield to XLR pin 1.
Recommended Wire Gauges
| Wire type |
Gauge |
| Signal (relay IN, buttons, I²C, DMX) |
22 AWG |
| Power / GND rails |
18 AWG |
| Relay load (switched circuit) |
Size to load current |
Software
Dependencies
Install the following libraries via the Arduino Library Manager before compiling:
| Library |
Purpose |
| DMXSerial |
DMX512 receive |
| LiquidCrystal_I2C |
I²C LCD driver |
| Wire (built-in) |
I²C bus |
| EEPROM (built-in) |
Persistent settings |
Upload Settings
| Setting |
Value |
| Board |
Arduino Leonardo (or "Pro Micro" via SparkFun board package) |
| Processor |
ATmega32U4 (5 V, 16 MHz) |
| Port |
The COM/tty port that appears when the Pro Micro is plugged in |
Operation
Home Screen
Addr:001 DMX
----1234----
- Addr – current DMX start channel (1–505).
- DMX / MAN – current source (DMX input or manual override).
- Bottom row – relay states; digits 1–8 = ON, dash = OFF.
Buttons on the Home Screen
| Button |
Action |
| UP / DOWN |
Increment / decrement DMX start address |
| ENTER |
Open the menu |
| BACK |
Toggle manual-override mode |
Menu
| Item |
Description |
| Manual Control |
Individually toggle each relay on/off |
| Settings |
Adjust DMX thresholds, timeout, and failsafe mode |
Settings
| Parameter |
Default |
Description |
| ON threshold |
128 |
DMX value that turns a relay ON |
| OFF threshold |
120 |
DMX value that turns a relay OFF (hysteresis) |
| RX wait (ms) |
30 |
How long each DMX probe waits for a packet |
| Timeout (ms) |
1000 |
Declare "no DMX" after this many ms without a packet |
| Failsafe |
All OFF |
Behaviour when DMX is lost: **All OFF** or **Hold last** |
All settings are saved to EEPROM automatically 1.5 s after the last change.
Wire Colour Convention (diagram)
| Colour |
Signal |
| Red |
5 V / VCC |
| Black |
GND |
| Dark red |
Relay control (D4–D10, D16) |
| Purple |
I²C bus (SDA / SCL) |
| Green |
DMX RX (D0) |
| Blue |
RS-485 differential pair (A−, B+) |
| Amber/yellow |
Button inputs (A0–A3) |
| Orange |
TX (D1) – unused / future |
License
This project is released under the MIT License. See LICENSE for details.
