• GPIO0 – D3 – Default button (or CLK for APA102)
• GPIO2 – D4 – Default LED out (DI for APA102 strip)
• GPIO14 – D5 – IR receiver or optional button
• GPIO12 – D6 – Relay
• GPIO13 – D7 – Dallas temperature sensor (optional – used to report over MQTT temperature on board)
• GPIO5 – D1 – I2C SCL
• GPIO4 – D2 – I2C SDA
• A0 – Analog input for microphone or another analog device.