bit_bending_serial.c

#define TX_PIN 2
#define BAUD_RATE 9600
#define BIT_DURATION_MICROS (1000000 / BAUD_RATE)
//T = 1/f = 1/baudrate seconds = 1000000 / baudrate microseconds
void setup() {
  pinMode(TX_PIN, OUTPUT);
  digitalWrite(TX_PIN, HIGH);  // Idle state
}

void loop() {
  sendByte('H');
  sendByte('e');
  sendByte('l');
  sendByte('l');
  sendByte('o');
  sendByte('\n');
  delay(1000);
}

void sendByte(byte b) {
  // Start bit (LOW)
  digitalWrite(TX_PIN, LOW);
  delayMicroseconds(BIT_DURATION_MICROS);

  // Data bits (LSB first)
  for (int i = 0; i < 8; i++) {
    digitalWrite(TX_PIN, (b >> i) & 1);
    delayMicroseconds(BIT_DURATION_MICROS);
  }

  // Stop bit (HIGH)
  digitalWrite(TX_PIN, HIGH);
  delayMicroseconds(BIT_DURATION_MICROS);
}