int sTx = 2;
int sRx = 3;

long base = 800;
long rst = base*10; // reset
boolean bt = false;
long dif = 0;
long lt = 0;
long now = 0;
char rcv = 0;
int idx = 0;
String message;
void setup(){
  pinMode(sRx,INPUT);
  pinMode(sTx,OUTPUT);
  attachInterrupt(digitalPinToInterrupt(sRx),change,CHANGE);
  Serial.begin(115200);  
  Serial.println("Receiver ready");
}

void reset(long dif){
    rcv = 0;
    idx = -1;
    message.reserve(32);
}
void change(){
  bool bt = digitalRead(sRx);
  now = micros();
  dif = now - lt;
  lt = now;
  if (dif > rst){
    reset(dif);
  } else {
    handle(!bt,dif);
  }
}

void handle(boolean bt, long dif){
  long count = dif/base;
  for (int i=0; i<count; i++) push(bt);
}

void push(boolean bt){
  if (idx>=0) rcv |= bt<<idx;
  idx++;
  
  if (idx == 8){
    if (rcv == 13) {
      Serial.println(message);
      message = "";
    } else {
      message+=rcv;
    } 
    idx =0;
    rcv =0;
  }
}

void loop(){}