Attiny 45 38khz flash

Using Arduino Microcontrollers
4

To generate 38KHz it's better to use one of the timer/counters. I use timer 1 so that timer 0 is still available for supporting the micros() function. This is the code I use:

void setup()
{
  PORTB = 0;
  DDRB =  0b00000010;		// set PB1 (= OCR1A) to be an output
}

// Set the frequency that we will get on pin OCR1A but don't turn it on
void setFrequency(uint16_t freq)
{
  uint32_t requiredDivisor = (F_CPU/2)/(uint32_t)freq;

  uint16_t prescalerVal = 1;
  uint8_t prescalerBits = 1;
  while ((requiredDivisor + prescalerVal/2)/prescalerVal > 256)
  {
    ++prescalerBits;
    prescalerVal <<= 1;
  }
  
  uint8_t top = ((requiredDivisor + (prescalerVal/2))/prescalerVal) - 1;
  TCCR1 = (1 << CTC1) | prescalerBits;
  GTCCR = 0;
  OCR1C = top;
}

// Turn the frequency on
void on()
{
  TCNT1 = 0;
  TCCR1 |= (1 << COM1A0);
}

// Turn the frequency off and turn off the IR LED.
// We let the counter continue running, we just turn off the OCR1A pin.
void off()
{
  TCCR1 &= ~(1 << COM1A0);
}