I was recently working on an ESP32-based project and wanted to integrate a simple, cheap IR remote control into it. Initially, I assumed this would be straightforward—after all, there are plenty of IR remote libraries available for Arduino.

However, after testing multiple popular libraries, I ran into reliability issues on ESP32 and ESP8266 devices. Some libraries had timing inconsistencies, while others didn’t handle interrupts well on these architectures. Others simply weren’t designed with ESP-specific constraints in mind.

Why HX1838Decoder? Rather than hacking existing libraries, I decided to build my own lightweight NEC-compatible IR decoder, focusing on:

• ESP32 & ESP8266 Compatibility – Designed with their architecture in mind.
• Interrupt-Based Decoding – Ensures accurate and efficient signal capture.
• Minimal Overhead – No unnecessary dependencies or features.
• Support for Repeat Signals – Properly detects when a key is held down.

To integrate HX1838Decoder into your project:

• Install the library via the Arduino Library Manager or GitHub.
• Connect an IR receiver module (HX1838 or similar) to an interrupt-capable pin.
• Use the API to capture and decode IR signals.

This library provides an Arduino-compatible NEC IR remote decoder for HX1838 and similar IR receivers. It captures and processes infrared signals, extracts 32-bit NEC codes, and provides a simple interface for retrieval.

The NEC IR transmission protocol uses pulse distance encoding of the message bits. Each pulse burst (mark – RC transmitter ON) is 562.5µs in length, at a carrier frequency of 38kHz (26.3µs). Logical bits are transmitted as follows:

• Logical '0' – a 562.5µs pulse burst followed by a 562.5µs space, with a total transmit time of 1.125ms
• Logical '1' – a 562.5µs pulse burst followed by a 1.6875ms space, with a total transmit time of 2.25ms

When transmitting or receiving remote control codes using the NEC IR transmission protocol, the WB_IRRC performs optimally when the carrier frequency (used for modulation/demodulation) is set to 38.222kHz.

Logical 0 and Logical 1 Sequence Captured on an Oscilloscope

When a key is pressed on the remote controller, the message transmitted consists of the following, in order:

• a 9ms leading pulse burst (16 times the pulse burst length used for a logical data bit)
• a 4.5ms space
• the 8-bit address for the receiving device
• the 8-bit logical inverse of the address
• the 8-bit command
• the 8-bit logical inverse of the command
• a final 562.5µs pulse burst to signify the end of message transmission.

The four bytes of data bits are each sent least significant bit first.

Key Press Captured on an Oscilloscope

If the key on the remote controller is kept depressed, a repeat code will be issued, typically around 40ms after the pulse burst that signified the end of the message. A repeat code will continue to be sent out at 108ms intervals, until the key is finally released. The repeat code consists of the following, in order:

• a 9ms leading pulse burst
• a 2.25ms space
• a 562.5µs pulse burst to mark the end of the space (and hence end of the transmitted repeat code).

Key Repeat Sequence on an Oscilloscope

An interrupt is attached to the specified IR receiver pin. Each pulse transition (HIGH/LOW) is recorded in pulseTimes[] along with its duration (in microseconds).

After receiving a signal, we pause briefly (100ms) to ensure full capture. If the signal is too short (<4 transitions), it is discarded as noise. NEC repeat signals (9ms LOW + 2.25ms HIGH) are detected and ignored. Valid NEC signals (9ms LOW + 4.5ms HIGH) proceed to decoding.

The length of each pulse determines whether it is a 1 or 0. The 32-bit NEC code is reconstructed from the captured pulse train. Since the NEC protocol transmits LSB (Least Significant Bit) first, we reverse the bit order for correct decoding.

Use available() to check if a valid signal was received. Use getDecodedData() to retrieve the decoded 32-bit NEC command in hexadecimal format.

#include "HX1838Decoder.h"

IRDecoder irDecoder(4);  // IR Receiver on pin 4

void setup() {
    Serial.begin(115200);
    irDecoder.begin();
}

void loop() {
    if (irDecoder.available()) {
        Serial.print("Decoded NEC Data: 0x");
        Serial.print(irDecoder.getDecodedData(), HEX);
        
        if (irDecoder.isRepeatSignal()) {
            Serial.println(" (REPEATED)");
        } else {
            Serial.println(" (NEW PRESS)");
        }
    }
}

• Interrupt-based decoding (efficient and accurate).
• Filters out noise and identifies NEC repeat signals.
• Reconstructs 32-bit NEC codes with correct bit order.
• Simple API for integration into Arduino projects.

Important: The IR receiver must be connected to an interrupt-capable pin. Check your microcontroller’s documentation for interrupt-capable pins.

• Arduino Uno/Nano: Pins 2, 3

• ESP8266: Pins 0, 2, 4, 5, 12, 13, 14, 15

• ESP32: Almost all GPIO pins (except 6-11)

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