Wiring
Check pinout, power supply, common GND and voltage levels before connecting the module.
Full code
const int relayPin = 23;
void setup() {
pinMode(relayPin, OUTPUT);
}
void loop() {
digitalWrite(relayPin, HIGH);
delay(2000);
digitalWrite(relayPin, LOW);
delay(2000);
}How it works
This lesson matches the page title and gives a clean starting point for this exact example.
Common mistakes
Check board selection, wiring, libraries, power supply and serial monitor baud rate.