gistfile1.h

// RADIO
#define RADIO_SPACE 10
#define RADIO_MARK  11
#define ASCII_BIT 8

void rtty_txstring (char * string) {
  char c;
  c = *string++;
  while ( c != '\0') {
    rtty_txbyte (c);
    c = *string++;
  }
}

void rtty_txbyte (char c) {
  int i;
  rtty_txbit (0); // Start bit
  // Send bits for for char LSB first	
  for (i=0; i<ASCII_BIT; i++) {
    if (c & 1) 
      rtty_txbit(1); 
    else
      rtty_txbit(0);	
    c = c >> 1;
  }
  rtty_txbit (1); // Stop bit
  rtty_txbit (1); // Stop bit 2
}

void rtty_txbit (int bit) {
  if (bit) {
    digitalWrite(RADIO_SPACE, LOW);
    digitalWrite(RADIO_MARK,  HIGH);
  } else {    
    digitalWrite(RADIO_SPACE, HIGH);
    digitalWrite(RADIO_MARK,  LOW);
  }
  // This works out to a baud rate of 50 bps. Somehow.
  delay(19);
  delayMicroseconds(250);
}


void setup() {
  pinMode(RADIO_SPACE, OUTPUT);
  pinMode(RADIO_MARK, OUTPUT);
}

void loop() {
  rtty_txstring("Hello World!");
  delay(1000);
}