ATTiny + IR

#define IR_PIN 1
#define LED_PIN 2

int state = 0;

void setup()
{
  pinMode(IR_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
  //Serial.begin(9600);
}

void loop()
{
  int startPulse, startTime, i;
  startPulse = pulseIn(IR_PIN, LOW);
  //Serial.print("startPulse = ");
  //Serial.println(startPulse);
  if(startPulse < 4500 || startPulse > 5500) //Starting pulse is 5ms
    return;
  startTime = millis();
  for(i = 1; i <= 4; i++)
  {
    int pulse = pulseIn(IR_PIN, LOW);
    //Serial.print("Pulse #");
    //Serial.print(i);
    //Serial.print(" = ");
    //Serial.println(pulse);
    if(pulse < 800 || pulse > 1200) //Each subsequent pulse is 1ms
      return;
  }
  //Serial.print("millis() - startTime = ");
  //Serial.println(millis() - startTime);
  if(millis() - startTime < 100)
  {
    state = !state;
    if(state)
      digitalWrite(LED_PIN, HIGH);
    else digitalWrite(LED_PIN, LOW);
  }
}