Overview

NOTE: This tutorial has been updated to work with IRLib 2.x which is significantly different from previous versions.

Most consumer electronic devices such as TV, cable box, DVD players and other devices use infrared signals for remote control. Each manufacturer has its own protocols for encoding the data so that signals intended for one device do not interfere with another. In an earlier tutorial by LadyAda she describes the inner working of reading IR signals from a remote and creating your own IR signals using an IR LED. Her tutorial gives you a behind-the-scenes peek at how IR works but it's a bit difficult to wrestle with all those technical details in your project.

If you're like me, you have no idea how NeoPixels work, nor the inner workings of I2C or SPI communications but you don't need to because we have libraries for that. A good code library isolates you, the application programmer, from the hardware details and the inner workings of devices and provide you with an API that makes it easy to use the hardware without knowing or caring what's going on behind the scenes.

In this tutorial we will show you how to use IRLib for receiving, decoding, and sending IR signals in your Arduino based project. We will show you how to change colors on a NeoPixel, control a servo using IR remote and send signals to your TV or cable box from an Arduino. Future tutorials will include an IR control mouse, and Internet of things remote control and controlling a robot arm.

About IR libraries

IR signals consists of a series of modulated pulses called "marks" separated by intervals called "spaces". Typically there is a long mark and space at the beginning of each signal that serves as a header. Then by varying the timing of marks and spaces, a sequence of bits is transmitted. If you had to store the precise timing of the entire signal it would take an array of up to 100 16 bit integers. In order to compare the data received to see if it was what you wanted, you would similarly need to store large arrays of data.

Fortunately the signals are sent according to very specific protocols that allow you to take this received timing data and turn it into a single binary number of up to 32 bits. The IR library collects the timing information in a buffer and then turns it into a single 32 bit value. You can then easily compare that value to the one you want.

Similarly if you want to transmit IR signals, all you need to do is pass 32 bit value to the library and tell it what protocol you want to use. It converts that value into a stream of marks and spaces with the proper headers, bit encodings and timings.

The gold standard of IR libraries is "LIRC" or Linux Infrared Remote Control which can be found at http://www.lirc.org/. It consists of drivers and a large database of information on hundreds of various remote controls. If we are using a Linux based system it's definitely the way to go. We will not be discussing that library here as we intend to focus on Arduino based systems.

In August 2009 Ken Shirrff published "IRremote" on his blog and released it on GitHub. Then in January 2013 I released IRLib based on Ken's earlier work. This revision reorganize the code making it easier to add new protocols using object-oriented programming design in C++.

Detailed information about  IRLib can be found on my blog at http://tech.cyborg5.com/irlib/. It includes an extensive user manual which is also available in the "manuals" folder of the library.. We'll use IRLib in this tutorial to help you get started.

In September 2016 we released a major rewrite of IRLib called IRLib 2.0. It was not fully backward-compatible with the original IRLib. This tutorial has been updated to use IRLib 2.0. The previous IRLib 1.x will no longer be supported. Recently IRLib 2.03 was released which added support for 32-bit SAMD 21 processors such as those used in Arduino Zero, Adafruit Feather M0, and the upcoming Circuit Playground Express.

Receiving and Decoding IR

Software installation

Installation of the IRLib library is as follows:

  1. Visit the IRLib2 page on GitHib.
  2. Select the “Download ZIP” button, or simply click this link to download directly.
  3. Uncompress the ZIP file after it’s finished downloading.
  4. The resulting folder should be named "IRLib2-master" and will contain 5 separate folders. That is because IRLib 2.x is actually a collection of 5 libraries that work together. Sometimes in Windows you’ll get an intermediate-level folder and need to move things around.
  5. Copy all five folders into your Arduino library folderalongside your other Arduino libraries, typically in your (home folder)/Documents/Arduino/Libraries folder. Libraries should not be installed alongside the Arduino application itself.
  6. Re-start the Arduino IDE if it’s currently running

This repository consists of a total of five libraries each of which must be in your arduino/libraries/ folder. So for example it should be installed as follows…

  • arduino/libraries/IRLib2
  • arduino/libraries/IRLibFreq
  • arduino/libraries/IRLibProtocols
  • arduino/libraries/IRLibRecv
  • arduino/libraries/IRLibRecvPCI

Do not install them in a single folder such as this…

  • arduino/libraries/IRLib2_master
    • IRLib2
    • IRLibFreq
    • IRLibProtocols
    • IRLibRecv
    • IRLibRecvPCI

Here’s a tutorial that walks through the process of correctly installing Arduino libraries.

Hardware Needed

IRLib runs on 8-bit AVR based Arduino boards such as Uno, Leonardo, Mega and Micro. It also runs on the Leonardo portion of the Arduino Yun. We have recently added support for 32 bit ARM SAMD 21 processors as used in the Arduino Zero, Feather M0, and Circuit Playground Express. However we do not support the Arduino Due or other Arduino-like systems. Unfortunately at this time it does not run on ATtiny85 base systems such as Adafruit Trinket and Adafruit Gemma but support for that is in the job jar and should be available in a stripped-down version for those platforms in the near future. At this writing, it has not been tested on the Adafruit Trinket Pro however since it is based on the same ATmega328 processor as the Uno, it should work fine. So the first thing you need is Arduino Uno or other compatible board.

You will need an IR receiver. Such as the TSOP38238 shown on the right column under featured products. This device combines an IR sensitive photocell, a 38 kHz bandpass filter, and automatic gain control. It operates on a variety of supply voltages including 3.3v and 5v. It de-modulates the received IR signal and gives you a nice clean square wave of off and on pulses at the voltage level of your power supply. This means it is ideal for feeding its output directly into the digital input pin of our Arduino.

Finally you will need an IR remote such as you use for controlling your TV, cable box, or DVD player. All of our examples will use the Adafruit Mini Remote Control shown on the right however we will show you how to detect what protocol your own TV remote is using and if it is a protocol supported by IRLib you can use it instead.

Connecting the IR receiver is very simple. Connect the left-hand pin to any digital input pin on your Arduino. In our examples we will use pin 2. Connect the center pin to ground and the right-hand pin to +5v.

Note that this device has a bandpass filter tuned to 38 kHz which is the typical frequency for most protocols. However some protocols use frequencies from 36 kHz all the way up to 57 kHz. The filter however is not extremely specific and we have had good success receiving anywhere from 36-40 kHz using a 38 kHz receiver. The Panasonic_Old protocol however uses 56 kHz. The TSOP38238 sold by Adafruit has difficulty decoding that frequency. I have however had good success with the receiver sold by Radio Shack at 56 kHz even though it is a 38 kHz device. Radio Shock did not list a part number but we believe it to be a TSOP4438. Sadly that may not be an option anymore :-(

These devices are made by Vishay and come in a variety of package styles, frequencies, and AGC methods. If the Adafruit device does not work for you and you need 56 kHz you can refer to the following guide.

More information on receivers as well as schematics for using multiple receivers can be found in the IRLib manual section 1.4.3.

Decoding IR Data

Load the following sketch. It is a slightly modified version of "dump" sketch from the examples folder of the library. All of the example sketches are in the folder "IRLib2/examples". 

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#include "IRLibAll.h"

//Create a receiver object to listen on pin 2
IRrecvPCI myReceiver(2);

//Create a decoder object 
IRdecode myDecoder;   

void setup() {
  Serial.begin(9600);
  delay(2000); while (!Serial); //delay for Leonardo
  myReceiver.enableIRIn(); // Start the receiver
  Serial.println(F("Ready to receive IR signals"));
}

void loop() {
  //Continue looping until you get a complete signal received
  if (myReceiver.getResults()) {
    myDecoder.decode();           //Decode it
    myDecoder.dumpResults(true);  //Now print results. Use false for less detail
    myReceiver.enableIRIn();      //Restart receiver
  }
}

After the sketch has loaded, open your serial monitor and make sure it is set to 9600 baud. Aim your IR remote at the receiver and press a button. In this example we press the "Play/Pause" button on the Adafruit Mini Remote. The results were as follows:


Decoded NEC(1): Value:FD807F (32 bits)
Raw samples(68): Gap:40826
Head: m8850 s4450
0:m500 s600 1:m550 s550 2:m500 s600 3:m550 s600
4:m500 s600 5:m500 s600 6:m500 s600 7:m550 s550
8:m500 s1750 9:m500 s1700 10:m500 s1700 11:m550 s1650
12:m550 s1700 13:m500 s1700 14:m500 s600 15:m550 s1700

16:m500 s1700 17:m500 s600 18:m500 s600 19:m500 s600
20:m550 s600 21:m450 s650 22:m500 s600 23:m500 s600
24:m500 s600 25:m500 s1700 26:m550 s1700 27:m500 s1700
28:m500 s1700 29:m550 s1700 30:m500 s1700 31:m500 s1700

32:m500
Extent=65850
Mark min:450 max:550

The important part of this dump is the first line. This tells us that the protocol detected was "NEC" which is protocol number "1" in IRLib's supported protocols. The data value received was the 32-bit hexadecimal value FD807F. The rest of the information is the raw timing data of the actual marks and spaces received. That information is useful in trying to understand and supported protocols.

This 32-bit number uniquely identifies the button that you pushed. If we push the Volume down and Volume up buttons on this remote we would get the values 0xFD00FF and 0xFD40BF.

Try pressing various buttons on a TV or DVD remote you might have lying around the house. If the top line says:

Decoded Unknown(0): Value:0 (0 bits)

this means that IRLib did not understand the protocol used by your remote. Here are some typical values from other remotes. I got these from the power button on a Sony DVD player, and the play button on my Scientific Atlantic DVR/Cable Box.

Decoded Sony(2): Value:74BCA (20 bits)
Decoded Panasonic Old(5): Value:37990C (22 bits)

This shows that the DVD player used Sony protocol which is protocol number 2 and that it is a 20 bit protocol. The cable box uses Panasonic_Old protocol 5 which is 22 bits. Most protocols always use the same number of bits however some such as Sony have different versions which could use 8, 12, or 15 bits in addition to 20.

How It Works

Let's look at what's going on here. The receiver object listens to the IR sensor and when it sees a signal it starts measuring the timing of the marks and spaces. If a particular amount of time passes with no additional signals, it presumes that the data is complete and when you call My_Receiver.GetResults it returns "true". It passes the data to your decoder object. The decoder uses the timing information and the number of bits to see if it matches one of the supported protocols. If it succeeds, it returns "true" although in this sketch we did not bother to check that first.

You can access the protocol number in My_Decoder.protocolNum, the number of bits in My_Decoder.bits and the the decoded data value in My_Decoder.value.

At the top of the sketch we created the decoder object as type "IRdecode". This is a class which incorporates all 11 of the supported protocols. If you're using the library to control a device such as a servo or turn relays off and on, you probably are going to be using one remote with one protocol. Once you know which protocol you are using, you may wish to use a different decoder class that only works for your particular protocol. It can save valuable program space in your sketch. For example if we were using the Adafruit Mini Remote which uses NEC protocol would change line #7 to read:

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IRdecodeNEC My_Decoder;

Protocol Specific Issues

IRLib supports 11 protocols directly and may include example code on how to implement others. As stated earlier, one of the jobs of a library is to isolate the application programmer from the need to deal with internal issues. However there are some protocol specific things that you may need to deal with.

The protocols are enumerated in IRLibProtocols/IRLibProtocols.h at approximately line 14 as follows.

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#define UNKNOWN 0
#define NEC 1
#define SONY 2
#define RC5 3
#define RC6 4
#define PANASONIC_OLD 5
#define JVC 6
#define NECX 7
#define SAMSUNG36 8
#define GICABLE 9 
#define DIRECTV 10
#define RCMM 11

Here are some protocol specific issues you may have to deal with.

NEC Repeat Codes

The NEC protocol uses a special sequence of marks and spaces that mean "I held down the button so you should repeat whatever I sent you last time". It is up to you to decide do I want to allow repeat codes or do I want to force the operator to push and release the button each time. IRLib returns a value of 0xFFFFFFFF to tell you that the special repeat sequence was received. You can ignore that sequence which forces the user to release and repress the button each time or you can store the previously received code and process it whenever you see the special repeat message.

Sony Triple Messages

The technical specification for Sony protocol says that you should send each code 3 consecutive times per keypress. IRLib takes care of sending three times for you so you don't need to do anything special. However when receiving Sony, be aware that you're going to get three copies of the data each time the user presses a button. If you're busy processing the first sequence you might miss the other two so it won't matter. But you need to be aware of it in case you're counting the number of keypresses or some other application.

RC5 and RC6 Toggle Bits

The RC5 and RC6 protocols invented by Phillips use a special toggle bit to let you know whether a code was generated by holding down the button or whether this is an independent keypress. For example I have a TV which uses RC5 protocol and the code for Volume Up is 0x1010. If I press and hold that button it sends the same code repeatedly. However if I release the button and press it again I get 0x1810. Every other keypress the single bit 0x0800 will toggle off and on.  You can make sure that you ignore this feature by masking out that particular bit. When you receive a decoded value from this protocol you could do:

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My_Decoder.value &=0xf7ff;

This will make sure that the toggle bit is always off. The RC6 protocol also has a title bit which is 0x10000. Therefore to mask it out you would do:

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My_Decoder.value &=0xfeffff;

Sending IR Codes

Hardware Issues

IRLib not only receives and decodes IR signals but it can transmit them as well using an IR LED and a driver circuit. The library has been used to control TVs, cable boxes, DVDs, VCRs, and IR controlled toys such as helicopters and dinosaur robots.

It could also be used to control some home automation devices. Some users have attempted to control air conditioners and fans however protocols used for air-conditioners are extremely difficult to implement and we have not directly supported such protocols because they are very rare.

Typically the output pin of an Arduino cannot supply sufficient current to drive and IR LED so you will want to implement a simple driver circuit using NPN transistor and a 470 ohm resistor is shown here:

Make sure that you get the polarity of the LED correct. The shorter of the two leads connects to the transistor and the longer one connects to the positive supply. Note that the current passing through the LED will in all likelihood will exceed the maximum continuous current rating. However because the signal is modulated and sending a sequence of pulses that will only last a few milliseconds the circuit will work fine.

More advanced driver circuit schematics are available in the IRLib manual in section 1.4 Hardware Considerations.

While we can connect an IR receiver to any available digital input pin, you can only use very specific pins for output. The library uses PWM pins and modifies the timing parameters to change the default frequency of that pin.

The default timer is TIMER2 on the Arduino Uno and Arduino Mega. On the Leonardo with is TIMER1. The pin numbers are pin 3 for Uno and use pin 9 for the Leonardo and Mega. If you have modified the library to use a different timer such as changing the timer number on a Leonardo to avoid conflicts with the servo library, then you will need to use a different specific pin. See section 1.4.1 Supported Platforms in the IRLib users manual for a table which shows the relationship between hardware timers and pin numbers.

Loading the Software

We presume you have already installed the IRLib library as described earlier in this tutorial. Let's load a simple sketch and see how it works. This is the IRsendDemo sketch from the examples folder.

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#include <IRLibAll.h>

IRsend mySender;

void setup() {
  Serial.begin(9600);
}

void loop() {
  if (Serial.read() != -1) {
    //send a code every time a character is received from the serial port
    //Sony DVD power A8BCA
    mySender.send(SONY,0xa8bca, 20);
  }
}

In this somewhat trivial example we send the code to turn on and off a Sony DVD player every time you type a character into the serial monitor. We create a sending object mySender. There is no set up except to initialize the serial port. In the loop we check for incoming characters and if we've got one we send the code.

The send method has three parameters: the protocol type, the data, and the number of bits.

The IRsend object we created is a generic routine that supports all 11 supported protocols. However in this case since we are only using one protocol we could've created the object using:

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IRsendSony mySender;

Inside the loop the send command would then be:

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mySender.send(0xa8bca, 20);

Some protocols such as NEC always use the same number of bits and so you do not need to specify as an additional parameter. See the the users manual to see if the extra bits parameter is required.

The users manual also gives you information about how to create decoding and sending routines that only use a specific subset of the supported protocols. This is much easier to do in IRLib 2.0 than it was in the original version.

Sending and Receiving in the Same Program

There are special considerations when doing sending and receiving in the same program. Both sending and receiving make use of the building hardware timers. However the timer is used for two different purposes. When you send a code, it reconfigures the timer and disables receiving. So you have to reenable your receiver after each send. For example:

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mySender.send(Protocol, Data, Bits);
myReceiver.enableIRIn(); // Re-enable receiver

Normally you would only need to call  myReceiver.enableIRIn();  once in the setup routine but if you are both sending and receiving you have to call it after each send.

For a complete example of how to send and receive in the same program, look at the record.ino sample sketch in the "IRLib2/examples" folder.  When you load the sketch, open your serial monitor, point a remote at the receiver and push a button. The program will capture that code. Then every time the type of character into the serial monitor it will repeat that code through the LED.

In a separate tutorial we will show you how to use IRLib to create your own universal remote by either sending data through the serial port into the Arduino or by creating a web-based universal remote using Arduino Yun.

All photos, videos and wiring courtesy Kenneth Young
This guide was first published on Feb 26, 2015. It was last updated on Feb 26, 2015.