How to generate an IR beacon frequency with a microprocessor

Received by email from JL Blankenship

// F_CPU tells util/delay.h our clock frequency

//#define F_CPU 8000000UL // Orangutan frequency (8MHz)

#define F_CPU 20000000UL // Baby Orangutan frequency (20MHz)

#include 

#include 

uint16_t i;

void delayms( uint16_t millis ) {

 while ( millis ) {

  _delay_ms( 1 );

  millis--;

 }

}



int main( void ) {

 DDRD |= 1 << DDD0;    // set LED pin PD1 to output

 DDRD &= ~(1 << DDD2);           // set D2 to input

 while ( 1 )

   {

     for(i=1;i<556;i++)              // 10ms of 56K signal

    {

    PORTD &= ~( 1 << PORTD0 ); // LED off

    _delay_us(9);        // delay 9 microsec

    PORTD |= 1 << PORTD0;   // LED on

    _delay_us(9);        // delay 9 microsec

    }

    if (PIND & (1<          _delay_us(100);               // beacon 1

       else

       _delay_us(200);               // beacon 2

   }

 return 0;

}