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Arduino IRremote

A library enabling the sending & receiving of infra-red signals.

Badge License: MIT     Badge Version     Badge Commits since latest     Badge LibraryBuild

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Available as Arduino library "IRremote".

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If you find this program useful, please give it a star.

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Table of content

Supported IR Protocols

NEC / Onkyo / Apple     Denon / Sharp     Panasonic / Kaseikyo

JVC     LG     RC5     RC6     Samsung     Sony

Universal Pulse Distance     Universal Pulse Width     Universal Pulse Distance Width

Hash     Pronto

BoseWave     Bang & Olufsen     Lego     FAST     Whynter     MagiQuest

Protocols can be switched off and on by defining macros before the line #include <IRremote.hpp> like here:

#define DECODE_NEC
//#define DECODE_DENON
#include <IRremote.hpp>


  • Lots of tutorials and examples.
  • Actively maintained.
  • Allows receiving and sending of raw timing data.

New features with version 4.x

  • Since 4.3 IrSender.begin(DISABLE_LED_FEEDBACK) will no longer work, use IrSender.begin(DISABLE_LED_FEEDBACK, 0) instead.
  • New universal Pulse Distance / Pulse Width / Pulse Distance Width decoder added, which covers many previous unknown protocols.
  • Printout of code how to send received command by IrReceiver.printIRSendUsage(&Serial).
  • RawData type is now 64 bit for 32 bit platforms and therefore decodedIRData.decodedRawData can contain complete frame information for more protocols than with 32 bit as before.
  • Callback after receiving a command - It calls your code as soon as a message was received.
  • Improved handling of PULSE_DISTANCE + PULSE_WIDTH protocols.
  • New FAST protocol.
  • Automatic printout of the corresponding send function with printIRSendUsage().

Converting your 3.x program to the 4.x version

  • You must replace #define DECODE_DISTANCE by #define DECODE_DISTANCE_WIDTH (only if you explicitly enabled this decoder).
  • The parameter bool hasStopBit is not longer required and removed e.g. for function sendPulseDistanceWidth().

New features with version 3.x

  • Any pin can be used for receiving and if SEND_PWM_BY_TIMER is not defined also for sending.
  • Feedback LED can be activated for sending / receiving.
  • An 8/16 bit **command value as well as an 16 bit address and a protocol number is provided for decoding (instead of the old 32 bit value).
  • Protocol values comply to protocol standards.
    NEC, Panasonic, Sony, Samsung and JVC decode & send LSB first.
  • Supports Universal Distance protocol, which covers a lot of previous unknown protocols.
  • Compatible with tone() library. See the ReceiveDemo example.
  • Simultaneous sending and receiving. See the SendAndReceive example.
  • Supports more platforms.
  • Allows for the generation of non PWM signal to just simulate an active low receiver signal for direct connect to existent receiving devices without using IR.
  • Easy protocol configuration, directly in your source code.
    Reduces memory footprint and decreases decoding time.
  • Contains a very small NEC only decoder, which does not require any timer resource.

-> Feature comparison of 5 Arduino IR libraries.

Converting your 2.x program to the 4.x version

Starting with the 3.1 version, the generation of PWM for sending is done by software, thus saving the hardware timer and enabling arbitrary output pins for sending.
If you use an (old) Arduino core that does not use the -flto flag for compile, you can activate the line #define SUPPRESS_ERROR_MESSAGE_FOR_BEGIN in IRRemote.h, if you get false error messages regarding begin() during compilation.

  • IRreceiver and IRsender object have been added and can be used without defining them, like the well known Arduino Serial object.

  • Just remove the line IRrecv IrReceiver(IR_RECEIVE_PIN); and/or IRsend IrSender; in your program, and replace all occurrences of IRrecv. or irrecv. with IrReceiver and replace all IRsend or irsend with IrSender.

  • Since the decoded values are now in IrReceiver.decodedIRData and not in results any more, remove the line decode_results results or similar.

  • Like for the Serial object, call IrReceiver.begin(IR_RECEIVE_PIN, ENABLE_LED_FEEDBACK) or IrReceiver.begin(IR_RECEIVE_PIN, DISABLE_LED_FEEDBACK) instead of the IrReceiver.enableIRIn() or irrecv.enableIRIn() in setup().
    For sending, call IrSender.begin(); in setup().
    If IR_SEND_PIN is not defined (before the line #include <IRremote.hpp>) you must use e.g. IrSender.begin(3, ENABLE_LED_FEEDBACK, USE_DEFAULT_FEEDBACK_LED_PIN);

  • Old decode(decode_results *aResults) function is replaced by simple decode(). So if you have a statement if(irrecv.decode(&results)) replace it with if (IrReceiver.decode()).

  • The decoded result is now in in IrReceiver.decodedIRData and not in results any more, therefore replace any occurrences of results.value and results.decode_type (and similar) to IrReceiver.decodedIRData.decodedRawData and IrReceiver.decodedIRData.protocol.

  • Overflow, Repeat and other flags are now in IrReceiver.receivedIRData.flags.

  • Seldom used: results.rawbuf and results.rawlen must be replaced by IrReceiver.decodedIRData.rawDataPtr->rawbuf and IrReceiver.decodedIRData.rawDataPtr->rawlen.

  • The 5 protocols NEC, Panasonic, Sony, Samsung and JVC have been converted to LSB first. Send functions for sending old MSB data were renamed to sendNECMSB, sendSamsungMSB(), sendSonyMSB() and sendJVCMSB(). The old sendSAMSUNG() and sendSony() MSB functions are still available. The old MSB version of sendPanasonic() function was deleted, since it had bugs nobody recognized and therfore was assumed to be never used.
    For converting MSB codes to LSB see below.


Old 2.x program:

#include <IRremote.h>
#define RECV_PIN 2

IRrecv irrecv(RECV_PIN);
decode_results results;

void setup()
  irrecv.enableIRIn(); // Start the receiver

void loop() {
  if (irrecv.decode(&results)) {
      Serial.println(results.value, HEX);
      irrecv.resume(); // Receive the next value

New 4.x program:

#include <IRremote.hpp>
#define IR_RECEIVE_PIN 2

void setup()
  IrReceiver.begin(IR_RECEIVE_PIN, ENABLE_LED_FEEDBACK); // Start the receiver

void loop() {
  if (IrReceiver.decode()) {
      Serial.println(IrReceiver.decodedIRData.decodedRawData, HEX); // Print "old" raw data
      IrReceiver.printIRResultShort(&Serial); // Print complete received data in one line
      IrReceiver.printIRSendUsage(&Serial);   // Print the statement required to send this data
      IrReceiver.resume(); // Enable receiving of the next value

How to convert old MSB first 32 bit IR data codes to new LSB first 32 bit IR data codes

For the new decoders for NEC, Panasonic, Sony, Samsung and JVC, the result IrReceiver.decodedIRData.decodedRawData is now LSB-first, as the definition of these protocols suggests!

To convert one into the other, you must reverse the byte/nibble positions and then reverse all bit positions of each byte/nibble or write it as one binary string and reverse/mirror it.

Example: 0xCB 34 01 02
0x20 10 43 BC after nibble reverse
0x40 80 2C D3 after bit reverse of each nibble

Nibble reverse map:

 0->0   1->8   2->4   3->C
 4->2   5->A   6->6   7->E
 8->1   9->9   A->5   B->D
 C->3   D->B   E->7   F->F

0xCB340102 is binary 1100 1011 0011 0100 0000 0001 0000 0010.
0x40802CD3 is binary 0100 0000 1000 0000 0010 1100 1101 0011.
If you read the first binary sequence backwards (right to left), you get the second sequence. You may use bitreverseOneByte() or bitreverse32Bit() for this.

Sending old MSB codes without conversion can be done by using sendNECMSB(), sendSonyMSB(), sendSamsungMSB(), sendJVCMSB().

Errors with using the 4.x versions for old tutorials

If you suffer from errors with old tutorial code including IRremote.h instead of IRremote.hpp, just try to rollback to Version 2.4.0.
Most likely your code will run and you will not miss the new features.

Staying on 2.x

Consider using the original 2.4 release form 2017 or the last backwards compatible 2.8 version for you project.
It may be sufficient and deals flawlessly with 32 bit IR codes.
If this doesn't fit your case, be assured that 4.x is at least trying to be backwards compatible, so your old examples should still work fine.

Drawbacks of using 2.x

  • Only the following decoders are available:
    NEC     Denon     Panasonic     JVC     LG
    RC5     RC6     Samsung     Sony
  • The call of irrecv.decode(&results) uses the old MSB first decoders like in 2.x and sets the 32 bit codes in results.value.
  • No decoding to a more meaningful (constant) 8/16 bit address and 8 bit command.

Why *.hpp instead of *.cpp?

Every *.cpp file is compiled separately by a call of the compiler exclusively for this cpp file. These calls are managed by the IDE / make system. In the Arduino IDE the calls are executed when you click on Verify or Upload.

And now our problem with Arduino is:
How to set compile options for all *.cpp files, especially for libraries used?
IDE's like Sloeber or PlatformIO support this by allowing to specify a set of options per project. They add these options at each compiler call e.g. -DTRACE.

But Arduino lacks this feature. So the workaround is not to compile all sources separately, but to concatenate them to one huge source file by including them in your source.
This is done by e.g. #include "IRremote.hpp".

But why not #include "IRremote.cpp"?
Try it and you will see tons of errors, because each function of the *.cpp file is now compiled twice, first by compiling the huge file and second by compiling the *.cpp file separately, like described above.
So using the extension cpp is not longer possible, and one solution is to use hpp as extension, to show that it is an included *.cpp file.
Every other extension e.g. cinclude would do, but hpp seems to be common sense.

Using the new *.hpp files

In order to support compile options more easily, you must use the statement #include <IRremote.hpp> instead of #include <IRremote.h> in your main program (aka *.ino file with setup() and loop()).

In all other files you must use the following, to prevent multiple definitions linker errors:

#include <IRremote.hpp>

Ensure that all macros in your main program are defined before any #include <IRremote.hpp>.
The following macros will definitely be overridden with default values otherwise:


3 ways to specify an IR code

There are 3 different ways of specifying a particular IR code.

1. Timing

The timing of each mark/pulse and space/distance_between_pulses is specified in a list or array. This enables specifying all IR codes, but requires a lot of memory and is not readable at all. One formal definition of such a timing array, including specification of frequency and repeats is the Pronto format.
Memory can be saved by using a lower time resolution. For IRremote you can use a 50 µs resolution which halves the memory requirement by using byte values instead of int16 values. For receiving purposes you can use the hash of the timing provided by the decodeHash() decoder.

2. Encoding schemes

There are 3 main encoding schemes which encodes a binary bitstream / hex value:

  1. PULSE_DISTANCE. The distance between pulses determines the bit value. This requires always a stop bit! Examples are NEC and KASEIKYO protocols. The pulse width is constant for most protocols.
  2. PULSE_WIDTH. The width of a pulse determines the bit value, pulse distance is constant. This requires no stop bit! The only known example is the SONY protocol.
  3. Phase / Manchester encoding. The time of the pulse/pause transition (phase) relative to the clock determines the bit value. Examples are RC5 and RC6 protocols.

Phase encoding has a constant bit length, PULSE_DISTANCE with constant pulse width and PULSE_WIDTH have no constant bit length!

A well known example for PULSE_DISTANCE with non constant pulse width encoding is the RS232 serial encoding. Here the non constant pulse width is used to enable a constant bit length.

Most IR signals have a special header to help in setting the automatic gain of the receiver circuit. This header is not part of the encoding, but is often significant for a special protocol and therefore must be reproducible.

Be aware that there are codes using a PULSE_DISTANCE encoding where more than a binary 0/1 is put into a pulse/pause combination. This requires more than 2 different pulse or pause length combinations. The HobToHood protocol uses such an encoding.

Using encoding schemes reduces the specification of an IR code to a bitstream / hex value, which is LSB by default and pulse / pause timings of header, 0, and 1. The hex value is quite readable. These schemes can not put any semantics like address, command or checksum on this bitstream.

3. Protocols

There are a few common protocols that are implemented directly in IRremote. They specify the frequency, the timings of header, 0, and 1 as well as other values like checksum, repeat distance, repeat coding, bit toggling etc. The semantics of the hex value is also specified, allowing the usage of only 2 parameters address and command to specify an IR code. This saves memory and is highly readable. Often the address is also constant, which further reduces memory requirements.

IRReceiver pinouts

IRReceiver Pinout

Receiving IR codes

In your program you check for a completely received IR frame with:
if (IrReceiver.decode()) {}
This also decodes the received data.
After successful decoding, the IR data is contained in the IRData structure, available as IrReceiver.decodedIRData.

decodedIRData structure

struct IRData {
    decode_type_t protocol;     // UNKNOWN, NEC, SONY, RC5, PULSE_DISTANCE, ...
    uint16_t address;           // Decoded address
    uint16_t command;           // Decoded command
    uint16_t extra;             // Used for Kaseikyo unknown vendor ID. Ticks used for decoding Distance protocol.
    uint16_t numberOfBits;      // Number of bits received for data (address + command + parity) - to determine protocol length if different length are possible.
    uint8_t flags;              // IRDATA_FLAGS_IS_REPEAT, IRDATA_FLAGS_WAS_OVERFLOW etc. See IRDATA_FLAGS_* definitions
    IRRawDataType decodedRawData;    // Up to 32 (64 bit for 32 bit CPU architectures) bit decoded raw data, used for sendRaw functions.
    uint32_t decodedRawDataArray[RAW_DATA_ARRAY_SIZE]; // 32 bit decoded raw data, to be used for send function.
    irparams_struct *rawDataPtr; // Pointer of the raw timing data to be decoded. Mainly the data buffer filled by receiving ISR.


This is the list of flags contained in the flags field.
Check it with e.g. if(IrReceiver.decodedIRData.flags & IRDATA_FLAGS_IS_REPEAT).

Flag name Description
IRDATA_FLAGS_IS_REPEAT The gap between the preceding frame is as smaller than the maximum gap expected for a repeat. !!!We do not check for changed command or address, because it is almost not possible to press 2 different buttons on the remote within around 100 ms!!!
IRDATA_FLAGS_IS_AUTO_REPEAT The current repeat frame is a repeat, that is always sent after a regular frame and cannot be avoided. Only specified for protocols DENON, and LEGO.
IRDATA_FLAGS_PARITY_FAILED The current (autorepeat) frame violated parity check.
IRDATA_FLAGS_TOGGLE_BIT Is set if RC5 or RC6 toggle bit is set.
IRDATA_FLAGS_EXTRA_INFO There is extra info not contained in address and data (e.g. Kaseikyo unknown vendor ID, or in decodedRawDataArray).
IRDATA_FLAGS_WAS_OVERFLOW Too many marks and spaces for the specified RAW_BUFFER_LENGTH. To avoid endless flagging of overflow, irparams.rawlen is set to 0 in this case.
IRDATA_FLAGS_IS_MSB_FIRST This value is mainly determined by the (known) protocol.

To access the RAW data, use:

auto myRawdata= IrReceiver.decodedIRData.decodedRawData;

The definitions for the IrReceiver.decodedIRData.flags are described here.

Print all fields:


Print the raw timing data received:

IrReceiver.printIRResultRawFormatted(&Serial, true);`

The raw data depends on the internal state of the Arduino timer in relation to the received signal and might therefore be slightly different each time. (resolution problem). The decoded values are the interpreted ones which are tolerant to such slight differences!

Print how to send the received data:


Ambiguous protocols

NEC, Extended NEC, ONKYO

The NEC protocol is defined as 8 bit address and 8 bit command. But the physical address and data fields are each 16 bit wide. The additional 8 bits are used to send the inverted address or command for parity checking.
The extended NEC protocol uses the additional 8 parity bit of address for a 16 bit address, thus disabling the parity check for address.
The ONKYO protocol in turn uses the additional 8 parity bit of address and command for a 16 bit address and command.

The decoder reduces the 16 bit values to 8 bit ones if the parity is correct. If the parity is not correct, it assumes no parity error, but takes the values as 16 bit values without parity assuming extended NEC or extended NEC protocol protocol.

But now we have a problem when we want to receive e.g. the 16 bit address 0x00FF or 0x32CD! The decoder interprets this as a NEC 8 bit address 0x00 / 0x32 with correct parity of 0xFF / 0xCD and reduces it to 0x00 / 0x32.

One way to handle this, is to force the library to always use the ONKYO protocol interpretation by using #define DECODE_ONKYO. Another way is to check if IrReceiver.decodedIRData.protocol is NEC and not ONKYO and to revert the parity reducing manually.


On a long press, the NEC protocol does not repeat its frame, it sends a special short repeat frame. This enables an easy distinction between long presses and repeated presses and saves a bit of battery energy. This behavior is quite unique for NEC and its derived protocols like LG and Samsung.

But of course there are also remote control systems, that uses the NEC protocol but only repeat the first frame when a long press is made instead of sending the special short repeat frame. We named this the NEC2 protocol and it is sent with sendNEC2().
But be careful, the NEC2 protocol can only be detected by the NEC library decoder after the first frame and if you do a long press!

Samsung, SamsungLG

On a long press, the SamsungLG protocol does not repeat its frame, it sends a special short repeat frame.

Unknown protocol

Use the ReceiveDemo example to print out all informations about your IR protocol.
The ReceiveDump example gives you more information but has bad repeat detection.

If your protocol seems not to be supported by this library, you may try the IRMP library, which especially supports manchester protocols much better.

Sending IR codes

If you have a device at hand which can generate the IR codes you want to work with (aka IR remote), it is recommended to receive the codes with the ReceiveDemo example, which will tell you on the serial output how to send them.

Protocol=LG Address=0x2 Command=0x3434 Raw-Data=0x23434E 28 bits MSB first
Send with: IrSender.sendLG(0x2, 0x3434, <numberOfRepeats>);

You will discover that the address is a constant and the commands sometimes are sensibly grouped.
If you are uncertain about the numbers of repeats to use for sending, 3 is a good starting point. If this works, you can check lower values afterwards.

If you have enabled DECODE_DISTANCE_WIDTH, the code printed by printIRSendUsage() differs between 8 and 32 bit platforms, so it is best to run the receiving program on the same platform as the sending program.

All sending functions support the sending of repeats if sensible. Repeat frames are sent at a fixed period determined by the protocol. e.g. 110 ms from start to start for NEC.
Keep in mind, that there is no delay after the last sent mark. If you handle the sending of repeat frames by your own, you must insert sensible delays before the repeat frames to enable correct decoding.

Sending old MSB codes without conversion can be done by using sendNECMSB(), sendSonyMSB(), sendSamsungMSB(), sendJVCMSB().

Sending IRDB IR codes

The codes found in the Flipper-IRDB database are quite straightforward to convert, because the also use the address / command scheme.
Protocol matching is NECext -> NECext (or Onkyo), Samsung32 -> Samsung, SIRC20 -> Sony with 20 bits etc.

The codes found in the irdb database specify a device, a subdevice and a function. Most of the times, device and subdevice can be taken as upper and lower byte of the address parameter and function is the command parameter for the new structured functions with address, command and repeat-count parameters like e.g. IrSender.sendNEC((device << 8) | subdevice, 0x19, 2).
An exact mapping can be found in the IRP definition files for IR protocols. "D" and "S" denotes device and subdevice and "F" denotes the function.

Send pin

Any pin can be chosen as send pin, because the PWM signal is generated by default with software bit banging, since SEND_PWM_BY_TIMER is not active.
On ESP32 ledc channel 0 is used for generating the IR PWM.
If IR_SEND_PIN is specified (as c macro), it reduces program size and improves send timing for AVR. If you want to use a variable to specify send pin e.g. with setSendPin(uint8_t aSendPinNumber), you must disable this IR_SEND_PIN macro. Then you can change send pin at any time before sending an IR frame. See also Compile options / macros for this library.

List of public IR code databases

Flipper Zero

Flipper IRDB Database

Flipper decoding IRremote decoding
Samsung32 Samsung
<start bit><VendorID:16><VendorID parity:4><Genre1:4><Genre2:4><Command:10><ID:2><Parity:8><stop bit>
and ID is MSB of address.
address: 8A 02 20 00
command: 56 03 00 00
-> IRremote:
Address 0x6A8, sendPanasonic (for 02 20) and Command 0x35
<start bit><VendorID:16><VendorID parity:4><Address:12><Command:8><Parity of VendorID parity, Address and Command:8><stop bit>

Tiny NEC receiver and sender

For applications only requiring NEC, NEC variants or FAST -see below- protocol, there is a special receiver / sender included,
which has very small code size of 500 bytes and does NOT require any timer.

Check out the TinyReceiver and IRDispatcherDemo examples.
Take care to include TinyIRReceiver.hpp or TinyIRSender.hpp instead of IRremote.hpp.

TinyIRReceiver usage

//#define USE_ONKYO_PROTOCOL    // Like NEC, but take the 16 bit address and command each as one 16 bit value and not as 8 bit normal and 8 bit inverted value.
//#define USE_FAST_PROTOCOL     // Use FAST protocol instead of NEC / ONKYO
#include "TinyIRReceiver.hpp"

void setup() {
  initPCIInterruptForTinyReceiver(); // Enables the interrupt generation on change of IR input signal

void loop() {
    if (TinyIRReceiverData.justWritten) {
        TinyIRReceiverData.justWritten = false;

TinyIRSender usage

#include "TinyIRSender.hpp"

void setup() {
  sendNEC(3, 0, 11, 2); // Send address 0 and command 11 on pin 3 with 2 repeats.

void loop() {}

Another tiny receiver and sender supporting more protocols can be found here.

The FAST protocol

The FAST protocol is a proprietary modified JVC protocol without address, with parity and with a shorter header. It is meant to have a quick response to the event which sent the protocol frame on another board. FAST takes 21 ms for sending and is sent at a 50 ms period. It has full 8 bit parity for error detection.

FAST protocol characteristics:

  • Bit timing is like JVC
  • The header is shorter, 3156 µs vs. 12500 µs
  • No address and 16 bit data, interpreted as 8 bit command and 8 bit inverted command, leading to a fixed protocol length of (6 + (16 * 3) + 1) * 526 = 55 * 526 = 28930 microseconds or 29 ms.
  • Repeats are sent as complete frames but in a 50 ms period / with a 21 ms distance.

Sending FAST protocol with IRremote

#define IR_SEND_PIN 3
#include <IRremote.hpp>

void setup() {
  sendFAST(11, 2); // Send command 11 on pin 3 with 2 repeats.

void loop() {}

Sending FAST protocol with TinyIRSender

#define USE_FAST_PROTOCOL // Use FAST protocol. No address and 16 bit data, interpreted as 8 bit command and 8 bit inverted command
#include "TinyIRSender.hpp"

void setup() {
  sendFAST(3, 11, 2); // Send command 11 on pin 3 with 2 repeats.

void loop() {}

The FAST protocol can be received by IRremote and TinyIRReceiver.

FAQ and hints

Receiving stops after analogWrite() or tone() or after running a motor.

The receiver sample interval of 50 µs is generated by a timer. On many boards this must be a hardware timer. On some boards where a software timer is available, the software timer is used.
Be aware that the hardware timer used for receiving should not be used for analogWrite().
Especially motor control often uses the analogWrite() function and will therefore stop the receiving if used on the pins indicated here.
On the Uno and other AVR boards the receiver timer ist the same as the tone timer. Thus receiving will stop after a tone() command. See ReceiveDemo example how to deal with it, i.e. how to use IrReceiver.restartTimer().

Receiving sets overflow flag.

The flag IRDATA_FLAGS_WAS_OVERFLOW is set, if RAW_BUFFER_LENGTH is too small for all the marks and spaces of the protocol. This can happen on long protocol frames like the ones from air conditioner. It also can happen, if RECORD_GAP_MICROS is smaller than the real gap between a frame and thr repetition frame, thus interpreting both as one consecutive frame. Best is to dump the timing then, to see which reason holds.

Problems with Neopixels, FastLed etc.

IRremote will not work right when you use Neopixels (aka WS2811/WS2812/WS2812B) or other libraries blocking interrupts for a longer time (> 50 µs).
Whether you use the Adafruit Neopixel lib, or FastLED, interrupts get disabled on many lower end CPUs like the basic Arduinos for longer than 50 µs. In turn, this stops the IR interrupt handler from running when it needs to. See also this video.

One workaround is to wait for the IR receiver to be idle before you send the Neopixel data with if (IrReceiver.isIdle()) {;}.
This prevents at least breaking a running IR transmission and -depending of the update rate of the Neopixel- may work quite well.
There are some other solutions to this on more powerful processors, see this page from Marc MERLIN

Does not work/compile with another library

Another library is only working/compiling if you deactivate the line IrReceiver.begin(IR_RECEIVE_PIN, ENABLE_LED_FEEDBACK);.
This is often due to timer resource conflicts with the other library. Please see below.

Multiple IR receiver and sender

This library supports only one IR receiver and one IR sender object (IRrecv and IRsend) per CPU.
However since sending is a serial task, you can use setSendPin() to switch the pin to send, thus emulating multiple sender.
The receiver uses a special timer triggered function, which reads the digital IR signal value from one pin every 50 µs.
So multiple IR receivers can only be used by connecting the output pins of several IR receivers together. The IR receiver modules internally use an NPN transistor as output device with just a 30k resistor to VCC. This is basically an "open collector" and allows multiple output pins to be connected to one Arduino input pin.
However, keep in mind that any weak / disturbed signal from one of the receivers will also interfere with a good signal from another receiver.

Increase strength of sent output signal

The best way to increase the IR power for free is to use 2 or 3 IR diodes in series. One diode requires 1.2 volt at 20 mA or 1.5 volt at 100 mA so you can supply up to 3 diodes with a 5 volt output.
To power 2 diodes with 1.2 V and 20 mA and a 5 V supply, set the resistor to: (5 V - 2.4 V) -> 2.6 V / 20 mA = 130 Ω.
For 3 diodes it requires 1.4 V / 20 mA = 70 Ω.
The actual current might be lower since of loss at the AVR pin. E.g. 0.3 V at 20 mA.
If you do not require more current than 20 mA, there is no need to use an external transistor (at least for AVR chips).

On my Arduino Nanos, I always use a 100 Ω series resistor and one IR LED 😀.

Minimal CPU clock frequency

For receiving, the minimal CPU clock frequency is 4 MHz, since the 50 µs timer ISR (Interrupt Service Routine) takes around 12 µs on a 16 MHz ATmega.
The TinyReceiver, which reqires no polling, runs with 1 MHz.
For sending, the default software generated PWM has problems on AVR running with 8 MHz. The PWM frequency is around 30 instead of 38 kHz and RC6 is not reliable. You can switch to timer PWM generation by #define SEND_PWM_BY_TIMER.

Bang & Olufsen protocol

The Bang & Olufsen protocol decoder is not enabled by default, i.e if no protocol is enabled explicitly by #define DECODE_<XYZ>. It must always be enabled explicitly by #define DECODE_BEO. This is because it has an IR transmit frequency of 455 kHz and therefore requires a different receiver hardware (TSOP7000).
And because generating a 455 kHz PWM signal is currently only implemented for SEND_PWM_BY_TIMER, sending only works if SEND_PWM_BY_TIMER or USE_NO_SEND_PWM is defined.
For more info, see ir_BangOlufsen.hpp.

Handling unknown Protocols


This library was designed to fit inside MCUs with relatively low levels of resources and was intended to work as a library together with other applications which also require some resources of the MCU to operate.

For air conditioners see this fork, which supports an impressive set of protocols and a lot of air conditioners.

For long signals see the blog entry: "Recording long Infrared Remote control signals with Arduino".


If you get something like this:

PULSE_DISTANCE: HeaderMarkMicros=8900 HeaderSpaceMicros=4450 MarkMicros=550 OneSpaceMicros=1700 ZeroSpaceMicros=600  NumberOfBits=56 0x43D8613C 0x3BC3BC

then you have a code consisting of 56 bits, which is probably from an air conditioner remote.
You can send it with sendPulseDistanceWidth().

uint32_t tRawData[] = { 0xB02002, 0xA010 };
IrSender.sendPulseDistance(38, 3450, 1700, 450, 1250, 450, 400, &tRawData[0], 48, false, 0, 0);

You can send it with calling sendPulseDistanceWidthData() twice, once for the first 32 bit and next for the remaining 24 bits.
The PULSE_DISTANCE / PULSE_WIDTH decoder just decodes a timing stream to a bitstream stored as hex values. These decoders can not put any semantics like address, command or checksum on this bitstream. But the bitstream is way more readable, than a timing stream. This bitstream is read LSB first by default. If LSB does not suit for further research, you can change it here.

If RAM is not more than 2k, the decoder only accepts mark or space durations up to 2500 microseconds to save RAM space, otherwise it accepts durations up to 10 ms.


If you see something like Protocol=UNKNOWN Hash=0x13BD886C 35 bits received as output of e.g. the ReceiveDemo example, you either have a problem with decoding a protocol, or an unsupported protocol.

  • If you have an odd number of bits received, your receiver circuit probably has problems. Maybe because the IR signal is too weak.
  • If you see timings like + 600,- 600 + 550,- 150 + 200,- 100 + 750,- 550 then one 450 µs space was split into two 150 and 100 µs spaces with a spike / error signal of 200 µs between. Maybe because of a defective receiver or a weak signal in conjunction with another light emitting source nearby.
  • If you see timings like + 500,- 550 + 450,- 550 + 500,- 500 + 500,-1550, then marks are generally shorter than spaces and therefore MARK_EXCESS_MICROS (specified in your ino file) should be negative to compensate for this at decoding.
  • If you see Protocol=UNKNOWN Hash=0x0 1 bits received it may be that the space after the initial mark is longer than RECORD_GAP_MICROS. This was observed for some LG air conditioner protocols. Try again with a line e.g. #define RECORD_GAP_MICROS 12000 before the line #include <IRremote.hpp> in your .ino file.
  • To see more info supporting you to find the reason for your UNKNOWN protocol, you must enable the line //#define DEBUG in IRremoteInt.h.

How to deal with protocols not supported by IRremote

If you do not know which protocol your IR transmitter uses, you have several choices.

  • Use the IRreceiveDump example to dump out the IR timing. You can then reproduce/send this timing with the SendRawDemo example. For long codes with more than 48 bits like from air conditioners, you can change the length of the input buffer in IRremote.h.
  • The IRMP AllProtocol example prints the protocol and data for one of the 40 supported protocols. The same library can be used to send this codes.
  • If you have a bigger Arduino board at hand (> 100 kByte program memory) you can try the IRremoteDecode example of the Arduino library DecodeIR.
  • Use IrScrutinizer. It can automatically generate a send sketch for your protocol by exporting as "Arduino Raw". It supports IRremote, the old IRLib and Infrared4Arduino.

Examples for this library

The examples are available at File > Examples > Examples from Custom Libraries / IRremote.
In order to fit the examples to the 8K flash of ATtiny85 and ATtiny88, the Arduino library ATtinySerialOut is required for this CPU's.
See also DroneBot Workshop SimpleReceiver and SimpleSender.

SimpleReceiver + SimpleSender

The SimpleReceiver and SimpleSender examples are a good starting point. A simple example can be tested online with WOKWI.

TinyReceiver + TinySender

If code size or timer usage matters, look at these examples.
The TinyReceiver example uses the TinyIRReceiver library which can only receive NEC, Extended NEC, ONKYO and FAST protocols, but does not require any timer. They use pin change interrupt for on the fly decoding, which is the reason for the restricted protocol choice.
TinyReceiver can be tested online with WOKWI.

The TinySender example uses the TinyIRSender library which can only send NEC, ONKYO and FAST protocols.
It sends NEC protocol codes in standard format with 8 bit address and 8 bit command as in SimpleSender example. It has options to send using Extended NEC, ONKYO and FAST protocols. Saves 780 bytes program memory and 26 bytes RAM compared to SimpleSender, which does the same, but uses the IRRemote library (and is therefore much more flexible).


If the protocol is not NEC and code size matters, look at this example.

ReceiveDemo + AllProtocolsOnLCD

ReceiveDemo receives all protocols and generates a beep with the Arduino tone() function on each packet received.
Long press of one IR button (receiving of multiple repeats for one command) is detected.
AllProtocolsOnLCD additionally displays the short result on a 1602 LCD. The LCD can be connected parallel or serial (I2C).
By connecting debug pin to ground, you can force printing of the raw values for each frame. The pin number of the debug pin is printed during setup, because it depends on board and LCD connection type.
This example also serves as an example how to use IRremote and tone() together.


Receives all protocols and dumps the received signal in different flavors including Pronto format. Since the printing takes much time, repeat signals may be skipped or interpreted as UNKNOWN.


Sends all available protocols at least once.


Demonstrates receiving while sending.


Record and play back last received IR signal at button press. IR frames of known protocols are sent by the approriate protocol encoder. UNKNOWN protocol frames are stored as raw data and sent with sendRaw().


Try to decode each IR frame with the universal DistanceWidth decoder, store the data and send it on button press with sendPulseDistanceWidthFromArray().
If RAM is not more than 2k, the decoder only accepts mark or space durations up to 2500 microseconds to save RAM space, otherwise it accepts durations up to 10 ms.
Storing data for distance width protocol requires 17 bytes. The ReceiveAndSend example requires 16 bytes for known protocol data and 37 bytes for raw data of e.g.NEC protocol.


Serves as a IR remote macro expander. Receives Samsung32 protocol and on receiving a specified input frame, it sends multiple Samsung32 frames with appropriate delays in between. This serves as a Netflix-key emulation for my old Samsung H5273 TV.


Framework for calling different functions of your program for different IR codes.


Control a relay (connected to an output pin) with your remote.


Example for a user defined class, which itself uses the IRrecv class from IRremote.


Example for sending LG air conditioner IR codes controlled by Serial input.
By just using the function bool Aircondition_LG::sendCommandAndParameter(char aCommand, int aParameter) you can control the air conditioner by any other command source.
The file acLG.h contains the command documentation of the LG air conditioner IR protocol. Based on reverse engineering of the LG AKB73315611 remote. LG AKB73315611 remote
IReceiverTimingAnalysis can be tested online with WOKWI Click on the receiver while simulation is running to specify individual IR codes.


Example for receiving and sending AEG / Elektrolux Hob2Hood protocol.


This example analyzes the signal delivered by your IR receiver module. Values can be used to determine the stability of the received signal as well as a hint for determining the protocol.
It also computes the MARK_EXCESS_MICROS value, which is the extension of the mark (pulse) duration introduced by the IR receiver module.
It can be tested online with WOKWI. Click on the receiver while simulation is running to specify individual NEC IR codes.


ReceiveDemo + SendDemo in one program. Demonstrates receiving while sending. Here you see the delay of the receiver output (blue) from the IR diode input (yellow). Delay

WOKWI online examples

Issues and discussions

  • Do not open an issue without first testing some of the examples!
  • If you have a problem, please post the MCVE (Minimal Complete Verifiable Example) showing this problem. My experience is, that most of the times you will find the problem while creating this MCVE 😄.
  • Use code blocks; it helps us to help you when we can read your code!

Compile options / macros for this library

To customize the library to different requirements, there are some compile options / macros available.
These macros must be defined in your program before the line #include <IRremote.hpp> to take effect.
Modify them by enabling / disabling them, or change the values if applicable.

Name Default value Description
RAW_BUFFER_LENGTH 100 Buffer size of raw input buffer. Must be even! If it is too small, overflow flag will be set. 100 is sufficient for regular protocols of up to 48 bits, but for most air conditioner protocols a value of up to 750 is required. Use the ReceiveDump example to find smallest value for your requirements.
EXCLUDE_UNIVERSAL_PROTOCOLS disabled Excludes the universal decoder for pulse distance width protocols and decodeHash (special decoder for all protocols) from decode(). Saves up to 1000 bytes program memory.
DECODE_<Protocol name> all Selection of individual protocol(s) to be decoded. You can specify multiple protocols. See here
DECODE_STRICT_CHECKS disabled Check for additional required characteristics of protocol timing like length of mark for a constant mark protocol, where space length determines the bit value. Requires up to 194 additional bytes of program memory.
IR_REMOTE_DISABLE_RECEIVE_COMPLETE_CALLBACK disabled Saves up to 60 bytes of program memory and 2 bytes RAM.
MARK_EXCESS_MICROS 20 MARK_EXCESS_MICROS is subtracted from all marks and added to all spaces before decoding, to compensate for the signal forming of different IR receiver modules.
RECORD_GAP_MICROS 5000 Minimum gap between IR transmissions, to detect the end of a protocol.
Must be greater than any space of a protocol e.g. the NEC header space of 4500 µs.
Must be smaller than any gap between a command and a repeat; e.g. the retransmission gap for Sony is around 24 ms.
Keep in mind, that this is the delay between the end of the received command and the start of decoding.
DISTANCE_WIDTH_DECODER_DURATION_ARRAY_SIZE 50 if RAM <= 2k, else 200 A value of 200 allows to decode mark or space durations up to 10 ms.
IR_INPUT_IS_ACTIVE_HIGH disabled Enable it if you use a RF receiver, which has an active HIGH output signal.
IR_SEND_PIN disabled If specified, it reduces program size and improves send timing for AVR. If you want to use a variable to specify send pin e.g. with setSendPin(uint8_t aSendPinNumber), you must not use / disable this macro in your source.
SEND_PWM_BY_TIMER disabled Disables carrier PWM generation in software and use hardware PWM (by timer). Has the advantage of more exact PWM generation, especially the duty cycle (which is not very relevant for most IR receiver circuits), and the disadvantage of using a hardware timer, which in turn is not available for other libraries and to fix the send pin (but not the receive pin) at the dedicated timer output pin(s). Is enabled for ESP32 and RP2040 in all examples, since they support PWM gereration for each pin without using a shared resource (timer).
IR_SEND_DUTY_CYCLE_PERCENT 30 Duty cycle of IR send signal.
USE_NO_SEND_PWM disabled Uses no carrier PWM, just simulate an active low receiver signal. Used for transferring signal by cable instead of IR. Overrides SEND_PWM_BY_TIMER definition.
USE_OPEN_DRAIN_OUTPUT_FOR_SEND_PIN disabled Uses or simulates open drain output mode at send pin. Attention, active state of open drain is LOW, so connect the send LED between positive supply and send pin!
USE_ACTIVE_HIGH_OUTPUT_FOR_SEND_PIN disabled Only if USE_NO_SEND_PWM is enabled. Simulate an active high receiver signal instead of an active low signal.
DISABLE_CODE_FOR_RECEIVER disabled Disables static receiver code like receive timer ISR handler and static IRReceiver and irparams data. Saves 450 bytes program memory and 269 bytes RAM if receiving functions are not required.
EXCLUDE_EXOTIC_PROTOCOLS disabled Excludes BANG_OLUFSEN, BOSEWAVE, WHYNTER, FAST and LEGO_PF from decode() and from sending with IrSender.write(). Saves up to 650 bytes program memory.
FEEDBACK_LED_IS_ACTIVE_LOW disabled Required on some boards (like my BluePill and my ESP8266 board), where the feedback LED is active low.
NO_LED_FEEDBACK_CODE disabled Disables the LED feedback code for send and receive. Saves around 100 bytes program memory for receiving, around 500 bytes for sending and halving the receiver ISR (Interrupt Service Routine) processing time.
MICROS_PER_TICK 50 Resolution of the raw input buffer data. Corresponds to 2 pulses of each 26.3 µs at 38 kHz.
TOLERANCE_FOR_DECODERS_MARK_OR_SPACE_MATCHING_PERCENT 25 Relative tolerance for matchTicks(), matchMark() and matchSpace() functions used for protocol decoding.
DEBUG disabled Enables lots of lovely debug output.
IR_USE_AVR_TIMER* Selection of timer to be used for generating IR receiving sample interval.

These next macros for TinyIRReceiver must be defined in your program before the line #include <TinyIRReceiver.hpp> to take effect.

Name Default value Description
IR_RECEIVE_PIN 2 The pin number for TinyIRReceiver IR input, which gets compiled in.
IR_FEEDBACK_LED_PIN LED_BUILTIN The pin number for TinyIRReceiver feedback LED, which gets compiled in.
NO_LED_FEEDBACK_CODE disabled Disables the feedback LED function. Saves 14 bytes program memory.
DISABLE_PARITY_CHECKS disabled Disables the addres and command parity checks. Saves 48 bytes program memory.
USE_EXTENDED_NEC_PROTOCOL disabled Like NEC, but take the 16 bit address as one 16 bit value and not as 8 bit normal and 8 bit inverted value.
USE_ONKYO_PROTOCOL disabled Like NEC, but take the 16 bit address and command each as one 16 bit value and not as 8 bit normal and 8 bit inverted value.
USE_FAST_PROTOCOL disabled Use FAST protocol (no address and 16 bit data, interpreted as 8 bit command and 8 bit inverted command) instead of NEC.
ENABLE_NEC2_REPEATS disabled Instead of sending / receiving the NEC special repeat code, send / receive the original frame for repeat.
USE_CALLBACK_FOR_TINY_RECEIVER disabled Call the fixed function void handleReceivedTinyIRData() each time a frame or repeat is received.

The next macro for IRCommandDispatcher must be defined in your program before the line #include <IRCommandDispatcher.hpp> to take effect. | USE_TINY_IR_RECEIVER | disabled | Use TinyReceiver for receiving IR codes. | | IR_COMMAND_HAS_MORE_THAN_8_BIT | disabled | Enables mapping and dispatching of IR commands consisting of more than 8 bits. Saves up to 160 bytes program memory and 4 bytes RAM + 1 byte RAM per mapping entry. | | BUZZER_PIN | | If USE_TINY_IR_RECEIVER is enabled, the pin to be used for the optional 50 ms buzzer feedback before executing a command. Other IR libraries than Tiny are not compatible with tone() command. |

Changing include (*.h) files with Arduino IDE

First, use Sketch > Show Sketch Folder (Ctrl+K).
If you have not yet saved the example as your own sketch, then you are instantly in the right library folder.
Otherwise you have to navigate to the parallel libraries folder and select the library you want to access.
In both cases the library source and include files are located in the libraries src directory.
The modification must be renewed for each new library version!

Modifying compile options / macros with PlatformIO

If you are using PlatformIO, you can define the macros in the platformio.ini file with build_flags = -D MACRO_NAME or build_flags = -D MACRO_NAME=macroValue.

Modifying compile options / macros with Sloeber IDE

If you are using Sloeber as your IDE, you can easily define global symbols with Properties > Arduino > CompileOptions.
Sloeber settings

Supported Boards

Issues and discussions with the content "Is it possible to use this library with the ATTinyXYZ? / board XYZ" without any reasonable explanations will be immediately closed without further notice.
For ESP8266/ESP32, this library supports an impressive set of protocols and a lot of air conditioners

Digispark boards are only tested with ATTinyCore using New Style pin mapping for the Digispark Pro board.
ATtiny boards are only tested with ATTinyCore or megaTinyCore.

  • Arduino Uno / Mega / Leonardo / Duemilanove / Diecimila / LilyPad / Mini / Fio / Nano etc.
  • Arduino Uno R4, but not yet tested, because of lack of a R4 board. Sending does not work on the arduino:renesas_uno:unor4wifi.
  • Teensy 1.0 / 1.0++ / 2.0 / 2++ / 3.0 / 3.1 / 3.2 / Teensy-LC - but limited support; Credits: PaulStoffregen (Teensy Team)
  • Sanguino
  • ATmega8, 48, 88, 168, 328
  • ATmega8535, 16, 32, 164, 324, 644, 1284,
  • ATmega64, 128
  • ATmega4809 (Nano every)
  • ATtiny3217 (Tiny Core 32 Dev Board)
  • ATtiny84, 85, 167 (Digispark + Digispark Pro)
  • SAMD21 (Zero, MKR*, but not SAMD51 and not DUE, the latter is SAM architecture)
  • ESP8266
  • ESP32 (ESP32-C3 since board package 2.0.2 from Espressif) not for ESP32 core version > 3.0.0
  • Sparkfun Pro Micro
  • Nano Every, Uno WiFi Rev2, nRF5 BBC MicroBit, Nano33_BLE
  • BluePill with STM32
  • RP2040 based boards (Raspberry Pi Pico, Nano RP2040 Connect etc.)

We are open to suggestions for adding support to new boards, however we highly recommend you contact your supplier first and ask them to provide support from their side.
If you can provide examples of using a periodic timer for interrupts for the new board, and the board name for selection in the Arduino IDE, then you have way better chances to get your board supported by IRremote.

Timer and pin usage

The receiver sample interval of 50 µs is generated by a timer. On many boards this must be a hardware timer. On some boards where a software timer is available, the software timer is used.
On ESP8266 timer1 is used for receive interrupts, which makes it incompatible to the Servo and other libraries.
On ESP32 hw_timer_t is used for receive interrupts and ledc channel 0 is used for generating the IR PWM.

Every pin can be used for receiving.
If software PWM is selected, which is default, every pin can also be used for sending. Sending with software PWM does not require a timer!

The TinyReceiver example uses the TinyReceiver library, which can only receive NEC codes, but does not require any timer and runs even on a 1 MHz ATtiny85.

The code for the timer and the timer selection is located in private/IRTimer.hpp. The selected timer can be adjusted here.

Be aware that the hardware timer used for receiving should not be used for analogWrite()!.

Board/CPU Receive
& send PWM Timer
Default timer is bold
Hardware-Send-PWM Pin analogWrite()
pins occupied by timer
ATtiny84 1 6
ATtiny85 > 4 MHz 0, 1 0, 4 0, 1 & 4
ATtiny88 > 4 MHz 1 PB1 / 8 PB1 / 8 & PB2 / 9
ATtiny167 > 4 MHz 1 9, 8 - 15 8 - 15
ATtiny1604 TCB0 PA05
ATtiny1614, ATtiny816 TCA0 PA3
ATtiny3217 TCA0, TCD %
ATmega8 1 9
ATmega1284 1, 2, 3 13, 14, 6
ATmega164, ATmega324, ATmega644 1, 2 13, 14
ATmega8535 ATmega16, ATmega32 1 13
ATmega64, ATmega128, ATmega1281, ATmega2561 1 13
ATmega8515, ATmega162 1 13
ATmega168, ATmega328 1, 2 9, 3 9 & 10, 3 & 11
ATmega1280, ATmega2560 1, 2, 3, 4, 5 5, 6, 9, 11, 46 5, 6, 9, 11, 46
ATmega4809 TCB0 A4
Leonardo (Atmega32u4) 1, 3, 4_HS 5, 9, 13 5, 9, 13
Zero (SAMD) TC3 *, 9
ESP8266 timer1 %
ESP32 hw_timer_t
Ledc channel 0
All pins
Sparkfun Pro Micro 1, 3 5, 9
Teensy 1.0 1 17 15, 18
Teensy 2.0 1, 3, 4_HS 9, 10, 14 12
Teensy++ 1.0 / 2.0 1, 2, 3 1, 16, 25 0
Teensy-LC TPM1 16 17
Teensy 3.0 - 3.6 CMT 5
Teensy 4.0 - 4.1 FlexPWM1.3 8 7, 25
BluePill / STM32F103C8T6 3 % PA6 & PA7 & PB0 & PB1
BluePill / STM32F103C8T6 TIM4 % PB6 & PB7 & PB8 & PB9
RP2040 / Pi Pico default alarm pool All pins No pin
RP2040 / Mbed based Mbed Ticker All pins No pin

No timer required for sending

The send PWM signal is by default generated by software. Therefore every pin can be used for sending. The PWM pulse length is guaranteed to be constant by using delayMicroseconds(). Take care not to generate interrupts during sending with software generated PWM, otherwise you will get jitter in the generated PWM. E.g. wait for a former Serial.print() statement to be finished by Serial.flush(). Since the Arduino micros() function has a resolution of 4 µs at 16 MHz, we always see a small jitter in the signal, which seems to be OK for the receivers.

Software generated PWM showing small jitter because of the limited resolution of 4 µs of the Arduino core micros() function for an ATmega328 Detail (ATmega328 generated) showing 30% duty cycle
Software PWM Software PWM detail

Incompatibilities to other libraries and Arduino commands like tone() and analogWrite()

If you use a library which requires the same timer as IRremote, you have a problem, since the timer resource cannot be shared simultaneously by both libraries.

Change timer

The best approach is to change the timer used for IRremote, which can be accomplished by specifying the timer before #include <IRremote.hpp>.
The timer specifications available for your board can be found in private/IRTimer.hpp.

// Arduino Mega
#elif defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
#  if !defined(IR_USE_AVR_TIMER1) && !defined(IR_USE_AVR_TIMER2) && !defined(IR_USE_AVR_TIMER3) && !defined(IR_USE_AVR_TIMER4) && !defined(IR_USE_AVR_TIMER5)
//#define IR_USE_AVR_TIMER1   // send pin = pin 11
#define IR_USE_AVR_TIMER2     // send pin = pin 9
//#define IR_USE_AVR_TIMER3   // send pin = pin 5
//#define IR_USE_AVR_TIMER4   // send pin = pin 6
//#define IR_USE_AVR_TIMER5   // send pin = pin 46
#  endif

Here you see the Arduino Mega board and the available specifications are IR_USE_AVR_TIMER[1,2,3,4,5].
You just have to include a line e.g. #define IR_USE_AVR_TIMER3 before #include <IRremote.hpp> to enable timer 3.

But be aware that the new timer in turn might be incompatible with other libraries or commands.
For other boards/platforms you must look for the appropriate section guarded by e.g. #elif defined(ESP32).

Stop and start timer

Another approach can be to share the timer sequentially if their functionality is used only for a short period of time like for the Arduino tone() command. An example can be seen here, where the timer settings for IR receive are restored after the tone has stopped. For this we must call IrReceiver.restartTimer() or better IrReceiver.restartTimer(microsecondsOfToneDuration).
This only works since each call to tone() completely initializes the timer 2 used by the tone() command.

Hardware-PWM signal generation for sending

If you define SEND_PWM_BY_TIMER, the send PWM signal is forced to be generated by a hardware timer on most platforms.
By default, the same timer as for the receiver is used.
Since each hardware timer has its dedicated output pin(s), you must change timer or timer sub-specifications to change PWM output pin. See private/IRTimer.hpp
Exeptions are currently ESP32, ARDUINO_ARCH_RP2040, PARTICLE and ARDUINO_ARCH_MBED, where PWM generation does not require a timer.

Why do we use 30% duty cycle for sending

We do it according to the statement in the Vishay datasheet:

  • Carrier duty cycle 50 %, peak current of emitter IF = 200 mA, the resulting transmission distance is 25 m.
  • Carrier duty cycle 10 %, peak current of emitter IF = 800 mA, the resulting transmission distance is 29 m. - Factor 1.16 The reason is, that it is not the pure energy of the fundamental which is responsible for the receiver to detect a signal. Due to automatic gain control and other bias effects, high intensity of the 38 kHz pulse counts more than medium intensity (e.g. 50% duty cycle) at the same total energy.

How we decode signals

The IR signal is sampled at a 50 µs interval. For a constant 525 µs pulse or pause we therefore get 10 or 11 samples, each with 50% probability.
And believe me, if you send a 525 µs signal, your receiver will output something between around 400 and 700 µs!
Therefore we decode by default with a +/- 25% margin using the formulas here.
E.g. for the NEC protocol with its 560 µs unit length, we have TICKS_LOW = 8.358 and TICKS_HIGH = 15.0. This means, we accept any value between 8 ticks / 400 µs and 15 ticks / 750 µs (inclusive) as a mark or as a zero space. For a one space we have TICKS_LOW = 25.07 and TICKS_HIGH = 45.0.
And since the receivers generated marks are longer or shorter than the spaces, we have introduced the MARK_EXCESS_MICROS macro to compensate for this receiver (and signal strength as well as ambient light dependent 😞 ) specific deviation.
Welcome to the world of real world signal processing.

NEC encoding diagrams

Created with sigrok PulseView with IR_NEC decoder by DjordjeMandic.
8 bit address NEC code 8 bit address NEC code 16 bit address NEC code 16 bit address NEC code

Quick comparison of 5 Arduino IR receiving libraries

This is a short comparison and may not be complete or correct.

I created this comparison matrix for myself in order to choose a small IR lib for my project and to have a quick overview, when to choose which library.
It is dated from 24.06.2022 and updated 10/2023. If you have complains about the data or request for extensions, please send a PM or open a discussion.

Here you find an ESP8266/ESP32 version of IRremote with an impressive list of supported protocols.

Subject IRMP IRLremote IRLib2
mostly unmaintained
IRremote TinyIR IRsmallDecoder
Number of protocols 50 Nec + Panasonic + Hash * 12 + Hash * 17 + PulseDistance + Hash * NEC + FAST NEC + RC5 + Sony + Samsung
Timing method receive Timer2 or interrupt for pin 2 or 3 Interrupt Timer2 or interrupt for pin 2 or 3 Timer2 Interrupt Interrupt
Timing method send PWM and timing with Timer2 interrupts Timer2 interrupts Timer2 and blocking wait PWM with Timer2 and/or blocking wait with delay
blocking wait with delay
Send pins All All All ? Timer dependent All %
Decode method OnTheFly OnTheFly RAM RAM OnTheFly OnTheFly
Encode method OnTheFly OnTheFly OnTheFly OnTheFly or RAM OnTheFly %
Callback support x % % x x %
Repeat handling Receive + Send (partially) % ? Receive + Send Receive + Send Receive
LED feedback x % x x Receive %
FLASH usage (simple NEC example with 5 prints) 1820
(4300 for 15 main / 8000 for all 40 protocols)
(+200 for callback)
(+80 for interrupt at pin 2+3)
(1400 for pin 2+3)
4830 1770 900 ?1100?
RAM usage 52
(73 / 100 for 15 (main) / 40 protocols)
62 334 227 19 29
Supported platforms avr, megaavr, attiny, Digispark (Pro), esp8266, ESP32, STM32, SAMD 21, Apollo3
(plus arm and pic for non Arduino IDE)
avr, esp8266 avr, SAMD 21, SAMD 51 avr, attiny, esp8266, esp32, SAM, SAMD All platforms with attach
All platforms with attach
Last library update 5/2023 4/2018 11/2022 9/2023 5/2023 2/2022
Remarks Decodes 40 protocols concurrently.
39 Protocols to send.
Work in progress.
Only one protocol at a time. Consists of 5 libraries. *Project containing bugs - 63 issues, 10 pull requests. Universal decoder and encoder.
Supports Pronto codes and sending of raw timing values.
Requires no timer. Requires no timer.

* The Hash protocol gives you a hash as code, which may be sufficient to distinguish your keys on the remote, but may not work with some protocols like Mitsubishi

Useful links


Up to the version 2.7.0, the License is GPLv2. From the version 2.8.0, the license is the MIT license.


Initially coded 2009 Ken Shirriff
Copyright (c) 2016-2017 Rafi Khan
Copyright (c) 2020-2024 Armin Joachimsmeyer