8-channel relay board on an Arduino Uno

// An eight-channel relay board clicking through its channels, from an Uno.
//
//   relay board IN1 to IN8 -> pins 2 to 9
//   relay board VCC -> 5V    GND -> GND
//
// The board is active low: a channel pulls in while its pin is LOW. Each pin
// is written HIGH before it is made an output, so nothing clicks at power-up.
// Eight channels at about 70 mA each is more than a USB-powered board likes;
// one at a time is fine.

const int FIRST = 2;
const int CHANNELS = 8;

void setup() {
  for (int i = 0; i < CHANNELS; i++) {
    digitalWrite(FIRST + i, HIGH);
    pinMode(FIRST + i, OUTPUT);
  }
  Serial.begin(9600);
  Serial.println("Mokxi Uno: eight relays, one at a time");
}

void loop() {
  for (int i = 0; i < CHANNELS; i++) {
    digitalWrite(FIRST + i, LOW);
    Serial.print("channel ");
    Serial.println(i + 1);
    delay(300);
    digitalWrite(FIRST + i, HIGH);
  }
}