Sending infrared over mqtt error

Hi hello!

I am trying to combine 2 examples of arduino ( ir receive and mqtt send ) into 1 sketch.
It allmost works...
Only problem is sending the ir code itself
I get the error

incompatible types in assignment of 'uint32_t' {aka 'unsigned int'} to 'char [50]'

I think the problem is
msg = (uint32_t) (results.value >> 32), HEX;
client.publish("outTopic", msg);

when i replace msg with "test" it sends the text.

My code is

 Basic ESP8266 MQTT example

 This sketch demonstrates the capabilities of the pubsub library in combination
 with the ESP8266 board/library.

 It connects to an MQTT server then:
  - publishes "hello world" to the topic "outTopic" every two seconds
  - subscribes to the topic "inTopic", printing out any messages
    it receives. NB - it assumes the received payloads are strings not binary
  - If the first character of the topic "inTopic" is an 1, switch ON the ESP Led,
    else switch it off

 It will reconnect to the server if the connection is lost using a blocking
 reconnect function. See the 'mqtt_reconnect_nonblocking' example for how to
 achieve the same result without blocking the main loop.

 To install the ESP8266 board, (using Arduino 1.6.4+):
  - Add the following 3rd party board manager under "File -> Preferences -> Additional Boards Manager URLs":
  - Open the "Tools -> Board -> Board Manager" and click install for the ESP8266"
  - Select your ESP8266 in "Tools -> Board"


#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include "IRrecv.h"

// Update these with values suitable for your network.

const char* ssid = "xxx";
const char* password = "xxx";
const char* mqtt_server = "xxx";

uint16_t RECV_PIN = 14; // for ESP8266 micrcontroller
IRrecv irrecv(RECV_PIN);
decode_results results;

WiFiClient espClient;
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;

void setup_wifi() {

  // We start by connecting to a WiFi network
  Serial.print("Connecting to ");

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {


  Serial.println("WiFi connected");
  Serial.println("IP address: ");

void callback(char* topic, byte* payload, unsigned int length) {
  Serial.print("Message arrived [");
  Serial.print("] ");
  for (int i = 0; i < length; i++) {

  // Switch on the LED if an 1 was received as first character
  if ((char)payload[0] == '1') {
    digitalWrite(BUILTIN_LED, LOW);   // Turn the LED on (Note that LOW is the voltage level
    // but actually the LED is on; this is because
    // it is active low on the ESP-01)
  } else {
    digitalWrite(BUILTIN_LED, HIGH);  // Turn the LED off by making the voltage HIGH


void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    if (client.connect(clientId.c_str())) {
      // Once connected, publish an announcement...
      client.publish("outTopic", "hello world");
      // ... and resubscribe
    } else {
      Serial.print("failed, rc=");
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying

void setup() {
  pinMode(BUILTIN_LED, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
  client.setServer(mqtt_server, 1883);

void loop() {

  if (!client.connected()) {

//  long now = millis();
//  if (now - lastMsg > 2000) {
//    lastMsg = now;
//    ++value;
//    snprintf (msg, 50, "hello world #%ld", value);
//    Serial.print("Publish message: ");
//    Serial.println(msg);
//    client.publish("outTopic", msg);
//  }

  if (irrecv.decode(&results)) {
    if (results.value >> 32)  // print() & println() can't handle printing long longs. (uint64_t)
    Serial.print((uint32_t) (results.value >> 32), HEX);  // print the first part of the message
    Serial.println((uint32_t) (results.value & 0xFFFFFFFF), HEX); // print the second part of the message
    msg = (uint32_t) (results.value >> 32), HEX;
    client.publish("outTopic", msg);
    irrecv.resume();  // Receive the next value

Why are you casting msg as an unsigned integer?
If you look at the library .h file, the prorotype for the publish function is:
boolean publish(const char* topic, const char* payload);

So, the error message is perfectly reasonable- msg has to be a char array.

Thanks @SteveMann
But to be honest i have no idea how to do that...

Use sprintf(). You don't need to format the number to anything else because to the Arduino a number is just a number. Hex, octal or binary are just human readable representations.

Like this?

 sprintf(msg, ((uint32_t) (results.value >> 32), HEX));

That still gives the error message

and my prefer should be to get hex as output

Google is a wonderful thing. It will reveal the correct syntax for using sprintf() which your code does does not do :frowning:

Thanks @blh64
This is above my level.
My coding skills are more copy pasting and trial and error.
I really dont understand how to solve this challenge with the page you linked to.

If you can not read the documentation for a standard C/C++ function, programming may not be for you. Cut & Pasting without knowing what is going on or trail & error are not good programming techniques. If you do want to learn, there are many, many examples that come with the IDE. Start small, learn, grow.

I know but this is not my daily job and more hobby. Was hoping to find some help here to reach my goal. Thanks anyway

I still haven't figured out what you are trying to send over MQTT. Or why.

I've never used this library, but you might try:
(untested code).

if (irrecv.decode(&results)) {
    sprintf(msg, "%#x", results.value);
    Serial.println(msg);                //Just to see what you are publishing
    client.publish("outTopic", msg);
1 Like

Wow this is the solution! Thank you so much!

What i am trying to do is receiving infrared from a laser gun and send this over mqtt to trigger an effect. It is not the best and cleanest way to do it. but it does the job for me.
For example in this way of using there is no check if full string is received and that stuff but i am not going to burn my hands on that. Thanks again!

Test the value on the receiving end.

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