How does the Irremote.h library work?

Question

Arduino

Does anyone know how the IRRemote library for arduino works?
The search engine did not give anything sensible, I would like to figure out how the signal is received and translated into a set of bits, as well as the principle of radiation by an IR diode.
Links are welcome.

Answer 1

You can open the library and look. By default on Windows in C:\Program Files (x86)\Arduino\libraries\RobotIRremote\srcI\IRremote.cpp
Based on a cursory analysis, then:

// initialization
void IRrecv::enableIRIn() {
  cli();
  // setup pulse clock timer interrupt
  //Prescale /8 (16M/8 = 0.5 microseconds per tick)
  // Therefore, the timer interval can range from 0.5 to 128 microseconds
  // depending on the reset value (255 to 0)
  TIMER_CONFIG_NORMAL();

  //Timer2 Overflow Interrupt Enable
  TIMER_ENABLE_INTR;

  TIMER_RESET;

  sei();  // enable interrupts

  // initialize state machine variables
  irparams.rcvstate = STATE_IDLE;
  irparams.rawlen = 0;

  // set pin modes
  pinMode(irparams.recvpin, INPUT);
}

//само прерывание
ISR(TIMER_INTR_NAME)
{
  TIMER_RESET;

  uint8_t irdata = (uint8_t)digitalRead(irparams.recvpin);

  irparams.timer++; // One more 50us tick
  if (irparams.rawlen >= RAWBUF) {
    // Buffer overflow
    irparams.rcvstate = STATE_STOP;
  }
  switch(irparams.rcvstate) {
  case STATE_IDLE: // In the middle of a gap
    if (irdata == MARK) {
      if (irparams.timer < GAP_TICKS) {
        // Not big enough to be a gap.
        irparams.timer = 0;
      } 
      else {
        // gap just ended, record duration and start recording transmission
        irparams.rawlen = 0;
        irparams.rawbuf[irparams.rawlen++] = irparams.timer;
        irparams.timer = 0;
        irparams.rcvstate = STATE_MARK;
      }
    }
    break;
  case STATE_MARK: // timing MARK
    if (irdata == SPACE) {   // MARK ended, record time
      irparams.rawbuf[irparams.rawlen++] = irparams.timer;
      irparams.timer = 0;
      irparams.rcvstate = STATE_SPACE;
    }
    break;
  case STATE_SPACE: // timing SPACE
    if (irdata == MARK) { // SPACE just ended, record it
      irparams.rawbuf[irparams.rawlen++] = irparams.timer;
      irparams.timer = 0;
      irparams.rcvstate = STATE_MARK;
    } 
    else { // SPACE
      if (irparams.timer > GAP_TICKS) {
        // big SPACE, indicates gap between codes
        // Mark current code as ready for processing
        // Switch to STOP
        // Don't reset timer; keep counting space width
        irparams.rcvstate = STATE_STOP;
      } 
    }
    break;
  case STATE_STOP: // waiting, measuring gap
    if (irdata == MARK) { // reset gap timer
      irparams.timer = 0;
    }
    break;
  }

  if (irparams.blinkflag) {
    if (irdata == MARK) {
      BLINKLED_ON();  // turn pin 13 LED on
    } 
    else {
      BLINKLED_OFF();  // turn pin 13 LED off
    }
  }
}

The timer starts with a period of 0.5 ms and interrupts are enabled +, respectively, reading high / low states. And then the functions of raking the received MARK and SPACE.
Those. to functions, decoding works just like a log. analyzer reading the log. levels every 50µs and storing them.

uint8_t irdata = (uint8_t)digitalRead(irparams.recvpin);

Similarly, you can learn about the work of other libraries.