byte relayPin[] = {0, 1, 2, 3, 4};
byte relays = sizeof(relayPin) / sizeof(relayPin[0]);
byte relay;
byte irPin = 5;

void setup() {
  pinMode(irPin, INPUT);
  for (int i = 0; i < relays; i++)
    pinMode(relayPin[i], OUTPUT);
}

void loop() {
  long key = getIrKey();

  switch (key) {
    case 12488: relay = 0; break; // button 0
    case 6368:  relay = 1; break; // button 1
    case 31358: relay = 2; break; // button 2
    case 4328:  relay = 3; break; // button 3
    case 14528: relay = 4; break; // button 4
    case 20408: // button "C" for clear
      for (int i = 0; i < relays; i++) {
        if (digitalRead(relayPin[i])) // if the pin is high
          digitalWrite(relayPin[i], LOW); // make it low
      }
      key = 0; // do not toggle the pin
      break;
    default: key = 0; break; // do not toggle a pin if no key pressed
  }

  if (key) {
    digitalWrite(relayPin[relay], !digitalRead(relayPin[relay]));
  }
}

int getIrKey() {
  int key = 0, temp;
  int len = pulseIn(irPin, LOW);
  if (len > 3500) {
    for (int i = 1; i <= 32; i++) {
      temp = pulseIn(irPin, HIGH);
      if (temp > 1000)
        key = key + (1 << (i - 17));
    }
  }
  if (key < 0 )
    key = -key;
  return key;
}

/*
                                   +-- --+
         PCINT5/-RESET/ADC0/dW/PB5 |1 * 8| VCC
  PCINT3/XTAL1/CLKI/-OC1B/ADC3/PB3 |2   7| PB2/SCK/USCK/SCL/ADC1/T0/INT0/PCINT2
   PCINT4/XTAL2/CLKO/OC1B/ADC2/PB4 |3   6| PB1/MISO/DO/AIN1/OC0B/OC1A/PCINT1
                               GND |4   5| PB0/MOSI/DI/SDA/AIN0/OC0A/-OC1A/AREF/PCINT0
                                   +-----+
*/