Relay toggle

example.ino

// This is a global variable
const int relay1 = 7; // let's call pin 7 relay1

// This is the setup function which gets run once, when the MCU gets reset
void setup() {
  pinMode(relay1, OUTPUT); // set pin 7 to an output pin
  digitalWrite(relay1, HIGH); // set pin 7 high
}

// This is the loop function which gets called repeatedly forever
void loop() {
  digitalWrite(relay1, LOW); // set pin 7 low
  delay(500); // wait 500ms
  digitalWrite(relay1, HIGH); // set pin 7 high
  delay(300); // wait 300ms
}