IRremote Documentation

Arduino IRremote

A library enabling the sending & receiving of infra-red signals.
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Available as Arduino library "IRremote".
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Supported IR Protocols

NEC / Onkyo / Apple     Denon / Sharp     Panasonic / Kaseikyo

JVC     LG     RC5     RC6     Samsung     Sony

Universal Pulse Distance     Universal Pulse Width     Hash     Pronto

BoseWave     Bang & Olufsen     Lego     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

  • New universal Pulse Distance / Pulse 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 contains complete frame information for more protocols.
  • Callback after receiving a command - call your own code if a message was received.

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

  • You must replace #define DECODE_DISTANCE_WIDTH by #define DECODE_DISTANCE_WIDTH (only if you explicitly enabled this decoder).

New features with version 3.x

  • Any pin can be used for sending -if SEND_PWM_BY_TIMER is not defined- and receiving.
  • 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 3.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(ENABLE_LED_FEEDBACK); or IrSender.begin(DISABLE_LED_FEEDBACK); in setup().
    If IR_SEND_PIN is not defined 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 for NEC and JVC were renamed to sendNECMSB, 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.
    For converting MSB codes to LSB see below.


2.x program:

#include <IRremote.h>
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

3.x program:

#include <IRremote.hpp>
void setup()
IrReceiver.begin(IR_RECEIVE_PIN, ENABLE_LED_FEEDBACK); // Start the receiver
void loop() {
if (IrReceiver.decode()) {
Serial.println(IrReceiver.decodedIRData.decodedRawData, HEX);
IrReceiver.printIRResultShort(&Serial); // optional use new print version
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.

Errors with using the 3.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 3.x is at least trying to be backwards compatible, so your old examples should still work fine.


  • 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.
  • The old functions sendNEC() and sendJVC() are renamed to sendNECMSB() and sendJVCMSB().
    Use them to send your old MSB-first 32 bit IR data codes.
  • No decoding by a (constant) 8/16 bit address and an 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:


Receiving IR codes

Check for received data with:
if (IrReceiver.decode()) {}
This also decodes the received data.

Data format

After successful decoding, the IR data is contained in the IRData structure, available as IrReceiver.decodedIRData.

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; // See IRDATA_FLAGS_* definitions
uint32_t decodedRawData; // Up to 32 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.

To access the RAW data, use:

uint32_t myRawdata= IrReceiver.decodedIRData.decodedRawData;

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

Print all fields:


Print the raw timing data received:

``c++ IrReceiver.printIRResultRawFormatted(&Serial, true);

# Tiny NEC receiver
For applications only requiring NEC protocol, there is a special receiver included,<br/>
which has very **small code size of 500 bytes and does NOT require any timer**.
Check out the [TinyReceiver]( and [IRDispatcherDemo]( examples.
# 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.<br/>
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.
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)`.<br/>
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.
**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.<br/>
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.
The old send*Raw() functions for sending like e.g. `IrSender.sendNECRaw(0xE61957A8,2)` are kept for backward compatibility to **(old)** tutorials and unsupported as well as error prone.
### List of public IR code databases
# FAQ and hints
## 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 &micro;s).<br/>
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 &micro;s.
In turn, this stops the IR interrupt handler from running when it needs to.
One **workaround** is to wait for the IR receiver to be idle before you send the Neopixel data with `if (IrReceiver.isIdle()) {;}`.<br/>
This **prevents at least breaking a running IR transmission** and -depending of the update rate of the Neopixel- may work quite well.<br/>
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);`.<br/>
This is often due to **timer resource conflicts** with the other library. Please see [below](
## Multiple IR receivers
You can use **multiple IR receiver** by just connecting the output pins of several IR receivers together.
The IR receivers use an NPN transistor as output device with just a 30k resistor to VCC.
This is almost "open collector" and allows connecting of several output pins to one Arduino input pin.
## 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.<br/>
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 &ohm;**.<br/>
For **3 diodes** it requires 1.4 V / 20 mA = **70 &ohm;**.<br/>
The actual current might be lower since of **loss at the AVR pin**. E.g. 0.3 V at 20 mA.<br/>
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 &ohm; series resistor and one IR LED :grinning:.
## Minimal CPU frequency
For receiving, the **minimal CPU frequency is 4 MHz**, since the 50 &micro;s timer ISR (Interrupt Service Routine) takes around 12 &micro;s on a 16 MHz ATmega.<br/>
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).<br/>
And because **generating a 455 kHz PWM signal is currently not implemented**, sending only works if `USE_NO_SEND_PWM` is defined!<br/>
For more info, see [ir_BangOlufsen.hpp](
# Handling unknown Protocols
## Disclaimer
**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.<br/>
You can send it with sendPulseDistance().
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 PulseDistance or PulseWidth decoders just decode a timing steam to a bit stream. They can not put any semantics like address, command or checksum on this bitstream, since it is no known protocol. But the bitstream is way more readable, than a timing stream. This bitstream is read LSB first by default. If this does not suit you for further research, you can change it here.


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

In order to fit the examples to the 8K flash of ATtiny85 and ATtiny88, the Arduino library ATtinySerialOut is required for this CPU's.

SimpleReceiver + SimpleSender

This examples are a good starting point. A simple example can be tested online with WOKWI.

TinyReceiver + TinySender

If code size matters, look at these examples.
The TinyReceiver example uses the TinyIRReceiver library which can only receive NEC and FAST codes, but does not require any timer.
TinyReceiver can be tested online with WOKWI. Click on the receiver while simulation is running to specify individual IR codes.

The TinySender example uses the TinyIRSender library which can only send NEC and FAST codes.
Sending NEC protocol codes in standard format with 8 bit address and 8 bit command as in SimpleSender example. 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.
AllProtocolsOnLCD additionally displays the short result on a 1602 LCD. The LCD can be connected parallel or serial (I2C).
By connecting pin debug pin to ground, you can see the raw values for each packet. 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. Since the printing takes so 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.


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.


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.

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 :smile:.
  • Use code blocks; it helps us 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! 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 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 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.
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 (as constant), reduces program size and improves send timing for AVR. If you want to use a runtime variable send pin e.g. with setSendPin(uint8_t aSendPinNumber) , you must disable this macro.
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).
USE_NO_SEND_PWM disabled Uses no carrier PWM, just simulate an active low receiver signal. Overrides SEND_PWM_BY_TIMER definition.
IR_SEND_DUTY_CYCLE_PERCENT 30 Duty cycle of IR send signal.
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!
DISABLE_CODE_FOR_RECEIVER disabled Saves up to 450 bytes program memory and 269 bytes RAM if receiving functionality is not required.
EXCLUDE_EXOTIC_PROTOCOLS disabled Excludes BANG_OLUFSEN, BOSEWAVE, WHYNTER 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 25 Relative tolerance (in percent) 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_INPUT_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_FAST_8_BIT_AND_PARITY_TIMING disabled Receives a special fast protocol instead of NEC.

The next macro for IRCommandDispatcher must be defined in your program before the line #include <IRCommandDispatcher.hpp> to take effect. | 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. |

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.

ATtiny and Digispark boards are only tested with the recommended ATTinyCore using New Style pin mapping for the pro board.

  • Arduino Uno / Mega / Leonardo / Duemilanove / Diecimila / LilyPad / Mini / Fio / Nano etc.
  • Teensy 1.0 / 1.0++ / 2.0 / 2++ / 3.0 / 3.1 / 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)
  • 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.)

For ESP8266/ESP32, this library supports an impressive set of protocols and a lot of air conditioners

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.
Every pin can be used for receiving.

The TinyReceiver example uses the TinyReceiver library, which can only receive NEC codes, but does not require any timer.

The code for the timer and the timer selection is located in private/IRTimer.hpp. It can be adjusted here.
Be aware that the hardware timer used for receiving should not be used for analogWrite()!.

| Board/CPU | Receive
& PWM Timers| Hardware-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 | | ATmega168, ATmega328 | 1, 2 | 9, 3 | 9 & 10, 3 & 11 | | 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 | | ATmega1280, ATmega2560 | 1, 2, 3, 4, 5 | 5, 6, 9, 11, 46 | | ATmega4809 | TCB0 | A4 | | Leonardo (Atmega32u4) | 1, 3, 4_HS | 5, 9, 13 | | Zero (SAMD) | TC3 | *, 9 | | ESP32 | Ledc chan. 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 |

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.start() or better IrReceiver.start(microsecondsOfToneDuration).
This only works since each call totone() 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 value]/ to compensate for this receiver (and signal strength as well as ambient light dependent :disappointed: ) 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

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

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. If you have complains about the data or request for extensions, please send a PM or open a discussion.

Subject IRMP IRLremote IRLib2
**mostly unmaintained**
IRremote Minimal NEC IRsmallDecoder
Number of protocols 50 Nec + Panasonic + Hash * 12 + Hash * 17 + PulseDistance + Hash * NEC 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 6/2022 4/2018 3/2022 6/2022 6/2022 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 - 45 issues, no reaction for at least one year. 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) 2020-2022 Armin Joachimsmeyer