// sender + receiver

const int led            = 13;
const int analogPin      = A0;
const int lightThreshold = 100;

const int deltaT = 1000;
const int syncT  = 12*deltaT;

void setup() {
  // put your setup code here, to run once:

}

void writeSignal(bool s, uint16_t time) {
  digitalWrite(led,s);
  delay(time);
}

void sendSync() {
  writeSignal(true,syncT);
  sendBit(false);
}

void sendBit(bool bit) {
  writeSignal(bit,deltaT);
}

void sendByte(byte b) {
  sendSync();
  for( int i = 7; i>=0; i-- ) {
    sendBit(bitRead(b,i));
  }
}

bool readSignal() {
  return analogRead(analogPin) >= lightThreshold;
}

bool receiveBit() {
  delay(deltaT/2);
  bool s = readSignal();
  delay(deltaT);
  return s;
}

bool receiveSync() {
  while(readSignal()==0) {
    delay(syncT/10);
  }
  long int start = millis();
  while(readSignal()==1) {
    delay(syncT/10);
  }
  if ( (millis()-start)>=(12*deltaT) ) {
    delay(deltaT); // low-Signal überspringen ohne Überprüfung
    return true;
  }
  return false;
}

byte receiveByte() {
  byte b = 0;
  if( receiveSync() ) {
    for( int i = 7; i>=0; i-- ) {
      bitWrite(b,i,receiveBit());
    }
  }
  return b;
}

void loop() {
  // put your main code here, to run repeatedly:
  sendByte(0b10101010);
}