8-Channel Relay Module

// Canonical example for an 8-channel relay module on Arduino Uno
// The relay inputs are active-low: LOW energizes the relay, HIGH turns it off.

const uint8_t relayPins[8] = {2, 3, 4, 5, 6, 7, 8, 9};

void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ;
  }

  Serial.println("8-Channel Relay Module demo starting...");

  // Set all relay control pins to OFF first.
  for (uint8_t i = 0; i < 8; i++) {
    pinMode(relayPins[i], OUTPUT);
    digitalWrite(relayPins[i], HIGH); // active-low relay OFF
  }

  Serial.println("All relays OFF.");
}

void loop() {
  // Turn each relay on one at a time, then off again.
  for (uint8_t i = 0; i < 8; i++) {
    Serial.print("Turning relay ");
    Serial.print(i + 1);
    Serial.println(" ON");

    digitalWrite(relayPins[i], LOW); // active-low relay ON
    delay(500);

    Serial.print("Turning relay ");
    Serial.print(i + 1);
    Serial.println(" OFF");

    digitalWrite(relayPins[i], HIGH); // active-low relay OFF
    delay(250);
  }

  Serial.println("--- Cycle complete ---");
  delay(1000);
}