Reading IR Commands

For our final project, we will use a remote control to send messages to a microcontroller. For example, this might be useful for a robot that can be directed with an IR remote. It can also be good for projects that you want to control from far away, without wires.

For a remote in this example we'll be using an Apple clicker remote. You can use any kind of remote you wish, or you can steal one of these from an unsuspecting hipster.

We'll use the code from our previous sketch for raw IR reading but this time we'll edit our printer-outer to have it give us the pulses in a C array, this will make it easier for us to use for pattern matching.
Download: file
void printpulses(void) {
  Serial.println("\n\r\n\rReceived: \n\rOFF \tON");
  for (uint8_t i = 0; i < currentpulse; i++) {
    Serial.print(pulses[i][0] * RESOLUTION, DEC);
    Serial.print(" usec, ");
    Serial.print(pulses[i][1] * RESOLUTION, DEC);
    Serial.println(" usec");
  }
 
  // print it in a 'array' format
  Serial.println("int IRsignal[] = {");
  Serial.println("// ON, OFF (in 10's of microseconds)");
  for (uint8_t i = 0; i < currentpulse-1; i++) {
    Serial.print("\t"); // tab
    Serial.print(pulses[i][1] * RESOLUTION / 10, DEC);
    Serial.print(", ");
    Serial.print(pulses[i+1][0] * RESOLUTION / 10, DEC);
    Serial.println(",");
  }
  Serial.print("\t"); // tab
  Serial.print(pulses[currentpulse-1][1] * RESOLUTION / 10, DEC);
  Serial.print(", 0};");
}
I uploaded the new sketch and pressed the Play button on the Apple remote and got the following:
Download: file
int IRsignal[] = { // ON, OFF (in 10's of microseconds) 
912, 438, 
68, 48, 
68, 158, 
68, 158, 
68, 158, 
68, 48, 
68, 158,  
68, 158,  
68, 158,  
70, 156,  
70, 158,  
68, 158,  
68, 48, 
68, 46,  
70, 46,  
68, 46,  
68, 160,  
68, 158,  
70, 46,  
68, 158,  
68, 46,  
70, 46,
68, 48,  
68, 46,  
68, 48,  
66, 48,  
68, 48,  
66, 160,  
66, 50,  
66, 160,  
66, 52,  
64, 160, 
66, 48,  
66, 3950,  
908, 214, 
66, 3012, 
908, 212, 
68, 0};

We'll try to detect that code.

Let's start a new sketch called IR Commander (you can download the final code from GitHub at the green button below or click Download Project Zip in the complete code listing). 

/* Raw IR commander
 
 This sketch/program uses the Arduno and a PNA4602 to 
 decode IR received.  It then attempts to match it to a previously
 recorded IR signal.  Limor Fried, Adafruit Industries
 
 MIT License, please attribute
 check out learn.adafruit.com  for more tutorials! 
 */

// We need to use the 'raw' pin reading methods
// because timing is very important here and the digitalRead()
// procedure is slower!
//uint8_t IRpin = 2;
// Digital pin #2 is the same as Pin D2 see
// http://arduino.cc/en/Hacking/PinMapping168 for the 'raw' pin mapping
#define IRpin_PIN      PIND
#define IRpin          2

// the maximum pulse we'll listen for - 65 milliseconds is a long time
#define MAXPULSE 65000
#define NUMPULSES 50

// what our timing resolution should be, larger is better
// as its more 'precise' - but too large and you wont get
// accurate timing
#define RESOLUTION 20 

// What percent we will allow in variation to match the same code
#define FUZZINESS 20

// we will store up to 100 pulse pairs (this is -a lot-)
uint16_t pulses[NUMPULSES][2];  // pair is high and low pulse 
uint8_t currentpulse = 0; // index for pulses we're storing

#include "ircommander.h"

void setup(void) {
  Serial.begin(9600);
  Serial.println("Ready to decode IR!");
}

void loop(void) {
  int numberpulses;
  
  numberpulses = listenForIR();
  
  Serial.print("Heard ");
  Serial.print(numberpulses);
  Serial.println("-pulse long IR signal");
  if (IRcompare(numberpulses, ApplePlaySignal,sizeof(ApplePlaySignal)/4)) {
    Serial.println("PLAY");
  }
    if (IRcompare(numberpulses, AppleRewindSignal,sizeof(AppleRewindSignal)/4)) {
    Serial.println("REWIND");
  }
    if (IRcompare(numberpulses, AppleForwardSignal,sizeof(AppleForwardSignal)/4)) {
    Serial.println("FORWARD");
  }
  delay(500);
}

//KGO: added size of compare sample. Only compare the minimum of the two
boolean IRcompare(int numpulses, int Signal[], int refsize) {
  int count = min(numpulses,refsize);
  Serial.print("count set to: ");
  Serial.println(count);
  for (int i=0; i< count-1; i++) {
    int oncode = pulses[i][1] * RESOLUTION / 10;
    int offcode = pulses[i+1][0] * RESOLUTION / 10;
    
#ifdef DEBUG    
    Serial.print(oncode); // the ON signal we heard
    Serial.print(" - ");
    Serial.print(Signal[i*2 + 0]); // the ON signal we want 
#endif   
    
    // check to make sure the error is less than FUZZINESS percent
    if ( abs(oncode - Signal[i*2 + 0]) <= (Signal[i*2 + 0] * FUZZINESS / 100)) {
#ifdef DEBUG
      Serial.print(" (ok)");
#endif
    } else {
#ifdef DEBUG
      Serial.print(" (x)");
#endif
      // we didn't match perfectly, return a false match
      return false;
    }
    
    
#ifdef DEBUG
    Serial.print("  \t"); // tab
    Serial.print(offcode); // the OFF signal we heard
    Serial.print(" - ");
    Serial.print(Signal[i*2 + 1]); // the OFF signal we want 
#endif    
    
    if ( abs(offcode - Signal[i*2 + 1]) <= (Signal[i*2 + 1] * FUZZINESS / 100)) {
#ifdef DEBUG
      Serial.print(" (ok)");
#endif
    } else {
#ifdef DEBUG
      Serial.print(" (x)");
#endif
      // we didn't match perfectly, return a false match
      return false;
    }
    
#ifdef DEBUG
    Serial.println();
#endif
  }
  // Everything matched!
  return true;
}

int listenForIR(void) {
  currentpulse = 0;
  
  while (1) {
    uint16_t highpulse, lowpulse;  // temporary storage timing
    highpulse = lowpulse = 0; // start out with no pulse length
  
//  while (digitalRead(IRpin)) { // this is too slow!
    while (IRpin_PIN & (1 << IRpin)) {
       // pin is still HIGH

       // count off another few microseconds
       highpulse++;
       delayMicroseconds(RESOLUTION);

       // If the pulse is too long, we 'timed out' - either nothing
       // was received or the code is finished, so print what
       // we've grabbed so far, and then reset
       
       // KGO: Added check for end of receive buffer
       if (((highpulse >= MAXPULSE) && (currentpulse != 0))|| currentpulse == NUMPULSES) {
         return currentpulse;
       }
    }
    // we didn't time out so lets stash the reading
    pulses[currentpulse][0] = highpulse;
  
    // same as above
    while (! (IRpin_PIN & _BV(IRpin))) {
       // pin is still LOW
       lowpulse++;
       delayMicroseconds(RESOLUTION);
        // KGO: Added check for end of receive buffer
        if (((lowpulse >= MAXPULSE)  && (currentpulse != 0))|| currentpulse == NUMPULSES) {
         return currentpulse;
       }
    }
    pulses[currentpulse][1] = lowpulse;

    // we read one high-low pulse successfully, continue!
    currentpulse++;
  }
}
void printpulses(void) {
  Serial.println("\n\r\n\rReceived: \n\rOFF \tON");
  for (uint8_t i = 0; i < currentpulse; i++) {
    Serial.print(pulses[i][0] * RESOLUTION, DEC);
    Serial.print(" usec, ");
    Serial.print(pulses[i][1] * RESOLUTION, DEC);
    Serial.println(" usec");
  }
  
  // print it in a 'array' format
  Serial.println("int IRsignal[] = {");
  Serial.println("// ON, OFF (in 10's of microseconds)");
  for (uint8_t i = 0; i < currentpulse-1; i++) {
    Serial.print("\t"); // tab
    Serial.print(pulses[i][1] * RESOLUTION / 10, DEC);
    Serial.print(", ");
    Serial.print(pulses[i+1][0] * RESOLUTION / 10, DEC);
    Serial.println(",");
  }
  Serial.print("\t"); // tab
  Serial.print(pulses[currentpulse-1][1] * RESOLUTION / 10, DEC);
  Serial.print(", 0};");
}

/******************* our codes ************/

int ApplePlaySignal[] = {
// ON, OFF (in 10's of microseconds)
912, 438,
68, 48,
68, 158,
68, 158,
68, 158,
68, 48,
68, 158,
68, 158,
68, 158,
70, 156,
70, 158,
68, 158,
68, 48,
68, 46,
70, 46,
68, 46,
68, 160,
68, 158,
70, 46,
68, 158,
68, 46,
70, 46,
68, 48,
68, 46,
68, 48,
66, 48,
68, 48,
66, 160,
66, 50,
66, 160,
66, 50,
64, 160,
66, 50,
66, 3950,
908, 214,
66, 3012,
908, 212,
68, 0};

int AppleForwardSignal[] = {
// ON, OFF (in 10's of microseconds)
	908, 444,
	64, 50,
	66, 162,
	64, 162,
	64, 162,
	64, 52,
	64, 162,
	64, 162,
	64, 162,
	64, 164,
	62, 164,
	64, 162,
	64, 52,
	62, 52,
	64, 52,
	64, 50,
	64, 164,
	64, 50,
	64, 164,
	64, 162,
	64, 50,
	66, 50,
	66, 50,
	64, 50,
	66, 50,
	64, 52,
	64, 50,
	66, 160,
	66, 50,
	64, 162,
	66, 50,
	64, 162,
	64, 50,
	66, 3938,
	906, 214,
	66, 3014,
	906, 214,
	64, 0};

int AppleRewindSignal[] = {
// ON, OFF (in 10's of microseconds)
	908, 442,
	66, 48,
	66, 162,
	66, 160,
	66, 160,
	66, 50,
	66, 160,
	66, 160,
	66, 160,
	68, 158,
	68, 160,
	66, 160,
	66, 50,
	66, 48,
	66, 50,
	66, 48,
	66, 162,
	66, 160,
	66, 48,
	68, 48,
	66, 160,
	66, 50,
	66, 50,
	66, 48,
	66, 50,
	66, 48,
	68, 48,
	66, 160,
	66, 50,
	66, 160,
	66, 50,
	66, 160,
	66, 48,
	68, 3936,
	906, 214,
	66, 0};

This code uses parts of our previous sketch. The first part we'll do is to create a function that just listens for an IR code an puts the pulse timings into the pulses[] array. It will return the number of pulses it heard as a return-value.

Download: file
int listenForIR(void) {
  currentpulse = 0;
 
  while (1) {
    uint16_t highpulse, lowpulse;  // temporary storage timing
    highpulse = lowpulse = 0; // start out with no pulse length
 
//  while (digitalRead(IRpin)) { // this is too slow!
    while (IRpin_PIN & (1 << IRpin)) {
       // pin is still HIGH
 
       // count off another few microseconds
       highpulse++;
       delayMicroseconds(RESOLUTION);
 
       // If the pulse is too long, we 'timed out' - either nothing
       // was received or the code is finished, so print what
       // we've grabbed so far, and then reset
       if ((highpulse >= MAXPULSE) && (currentpulse != 0)) {
         return currentpulse;
       }
    }
    // we didn't time out so lets stash the reading
    pulses[currentpulse][0] = highpulse;
 
    // same as above
    while (! (IRpin_PIN & _BV(IRpin))) {
       // pin is still LOW
       lowpulse++;
       delayMicroseconds(RESOLUTION);
       if ((lowpulse >= MAXPULSE)  && (currentpulse != 0)) {
         return currentpulse;
       }
    }
    pulses[currentpulse][1] = lowpulse;
 
    // we read one high-low pulse successfully, continue!
    currentpulse++;
  }
}
Our new loop() will start out just listening for pulses
Download: file
void loop(void) {
  int numberpulses;
 
  numberpulses = listenForIR();
 
  Serial.print("Heard ");
  Serial.print(numberpulses);
  Serial.println("-pulse long IR signal");
}
When we run this it will print out something like...
OK time to make the sketch compare what we received to what we have in our stored array:
As you can see, there is some variation. So when we do our comparison we can't look for preciesely the same values, we have to be a little 'fuzzy'. We'll say that the values can vary by 20% - that should be good enough.
Download: file
// What percent we will allow in variation to match the same code \\ #define FUZZINESS 20
 
void loop(void) {
  int numberpulses;
 
  numberpulses = listenForIR();
 
  Serial.print("Heard ");
  Serial.print(numberpulses);
  Serial.println("-pulse long IR signal");
 
  for (int i=0; i< numberpulses-1; i++) {
    int oncode = pulses[i][1] * RESOLUTION / 10;
    int offcode = pulses[i+1][0] * RESOLUTION / 10;
 
    Serial.print(oncode); // the ON signal we heard
    Serial.print(" - ");
    Serial.print(ApplePlaySignal[i*2 + 0]); // the ON signal we want 
 
    // check to make sure the error is less than FUZZINESS percent
    if ( abs(oncode - ApplePlaySignal[i*2 + 0]) <= (oncode * FUZZINESS / 100)) {
      Serial.print(" (ok)");
    } else {
      Serial.print(" (x)");
    }
    Serial.print("  \t"); // tab
 
    Serial.print(offcode); // the OFF signal we heard
    Serial.print(" - ");
    Serial.print(ApplePlaySignal[i*2 + 1]); // the OFF signal we want 
 
    if ( abs(offcode - ApplePlaySignal[i*2 + 1]) <= (offcode * FUZZINESS / 100)) {
      Serial.print(" (ok)");
    } else {
      Serial.print(" (x)");
    }
 
    Serial.println();
  }
}

This loop, as it goes through each pulse, does a little math. It compares the absolute (abs()) difference between the code we heard and the code we're trying to match abs(oncode - ApplePlaySignal[i*2 + 0]) and then makes sure that the error is less than FUZZINESS percent of the code length (oncode * FUZZINESS / 100)

We found we had to tweak the stored values a little to make them match up 100% each time. IR is not a precision-timed protocol so having to make the FUZZINESS 20% or more is not a bad thing

Finally, we can turn the loop() into its own function which will return true or false depending on whether it matched the code we ask it to. We also commented out the printing functions

Download: file
boolean IRcompare(int numpulses, int Signal[]) {
 
  for (int i=0; i< numpulses-1; i++) {
    int oncode = pulses[i][1] * RESOLUTION / 10;
    int offcode = pulses[i+1][0] * RESOLUTION / 10;
 
    /*
    Serial.print(oncode); // the ON signal we heard
    Serial.print(" - ");
    Serial.print(Signal[i*2 + 0]); // the ON signal we want 
    */
 
    // check to make sure the error is less than FUZZINESS percent
    if ( abs(oncode - Signal[i*2 + 0]) <= (Signal[i*2 + 0] * FUZZINESS / 100)) {
      //Serial.print(" (ok)");
    } else {
      //Serial.print(" (x)");
      // we didn't match perfectly, return a false match
      return false;
    }
 
    /*
    Serial.print("  \t"); // tab
    Serial.print(offcode); // the OFF signal we heard
    Serial.print(" - ");
    Serial.print(Signal[i*2 + 1]); // the OFF signal we want 
    */
 
    if ( abs(offcode - Signal[i*2 + 1]) <= (Signal[i*2 + 1] * FUZZINESS / 100)) {
      //Serial.print(" (ok)");
    } else {
      //Serial.print(" (x)");
      // we didn't match perfectly, return a false match
      return false;
    }
 
    //Serial.println();
  }
  // Everything matched!
  return true;
}

We then took more IR command data for the 'rewind' and 'fastforward' buttons and put all the code array data into ircodes.h to keep the main sketch from being too long and unreadable (you can get all the code from github)

Finally, the main loop looks like this:

Download: file
void loop(void) {
  int numberpulses;
 
  numberpulses = listenForIR();
 
  Serial.print("Heard ");
  Serial.print(numberpulses);
  Serial.println("-pulse long IR signal");
  if (IRcompare(numberpulses, ApplePlaySignal)) {
    Serial.println("PLAY");
  }
    if (IRcompare(numberpulses, AppleRewindSignal)) {
    Serial.println("REWIND");
  }
    if (IRcompare(numberpulses, AppleForwardSignal)) {
    Serial.println("FORWARD");
  }
}

We check against all the codes we know about and print out whenever we get a match. You could now take this code and turn it into something else, like a robot that moves depending on what button is pressed.

After testing, success!

This guide was first published on Jul 29, 2012. It was last updated on Jul 29, 2012. This page (Reading IR Commands) was last updated on Nov 19, 2019.