Arduino MQTT Library with Publish and Subscribe example

List of my MQTT tutorials you can go through to understand the below code,

Blog posts :

Videos :

Download link to MQTT packet format Excel file used in demo videos :

Click here to for downloading MQTT.xlsx

Note:

The code is just a guideline it needs tuning to work properly. Directly it wont work.

The modified code which Peter had shared works for SIM800L and SIM900 both.

The modified working code is available here. You can register and post on the same forum if you have any questions.

Code used to demonstrate the MQTT connection to CloudMQTT.com using SIM900/SIM800 GSM module

int led = 13;
unsigned int Counter = 0;
unsigned long datalength, CheckSum, RLength;
unsigned short topiclength;
unsigned char topic[30];
char str[250];
unsigned char encodedByte;
int X;
unsigned short MQTTProtocolNameLength;
unsigned short MQTTClientIDLength;
unsigned short MQTTUsernameLength;
unsigned short MQTTPasswordLength;
const char MQTTHost[30] = "m10.cloudmqtt.com";
const char MQTTPort[10] = "17434";
const char MQTTClientID[20] = "ABCDEF";
const char MQTTTopic[30] = "valetron";
const char MQTTProtocolName[10] = "MQIsdp";
const char MQTTLVL = 0x03;
const char MQTTFlags = 0xC2;
const unsigned int MQTTKeepAlive = 60;
const char MQTTUsername[30] = "dxxkgkpp";
const char MQTTPassword[35] = "qAUZBdaSIULx";
const char MQTTQOS = 0x00;
const char MQTTPacketID = 0x0001;
void setup() {
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  Serial.println("Arduino MQTT Tutorial, Valetron Systems @www.valetron.com ");
  delay(3000);
}
void SendConnectPacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  Serial.write(0x10);
  MQTTProtocolNameLength = strlen(MQTTProtocolName);
  MQTTClientIDLength = strlen(MQTTClientID);
  MQTTUsernameLength = strlen(MQTTUsername);
  MQTTPasswordLength = strlen(MQTTPassword);
  datalength = MQTTProtocolNameLength + 2 + 4 + MQTTClientIDLength + 2 + MQTTUsernameLength + 2 + MQTTPasswordLength + 2;
  X = datalength;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(MQTTProtocolNameLength >> 8);
  Serial.write(MQTTProtocolNameLength & 0xFF);
  Serial.print(MQTTProtocolName);
  Serial.write(MQTTLVL); // LVL
  Serial.write(MQTTFlags); // Flags
  Serial.write(MQTTKeepAlive >> 8);
  Serial.write(MQTTKeepAlive & 0xFF);
  Serial.write(MQTTClientIDLength >> 8);
  Serial.write(MQTTClientIDLength & 0xFF);
  Serial.print(MQTTClientID);
  Serial.write(MQTTUsernameLength >> 8);
  Serial.write(MQTTUsernameLength & 0xFF);
  Serial.print(MQTTUsername);
  Serial.write(MQTTPasswordLength >> 8);
  Serial.write(MQTTPasswordLength & 0xFF);
  Serial.print(MQTTPassword);
  Serial.write(0x1A);
}
void SendPublishPacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  memset(str, 0, 250);
  topiclength = sprintf((char * ) topic, MQTTTopic);
  datalength = sprintf((char * ) str, "%s%u", topic, Counter);
  delay(1000);
  Serial.write(0x30);
  X = datalength + 2;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength & 0xFF);
  Serial.print(str);
  Serial.write(0x1A);
}
void SendSubscribePacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  memset(str, 0, 250);
  topiclength = strlen(MQTTTopic);
  datalength = 2 + 2 + topiclength + 1;
  delay(1000);
  Serial.write(0x82);
  X = datalength;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(MQTTPacketID >> 8);
  Serial.write(MQTTPacketID & 0xFF);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength & 0xFF);
  Serial.print(MQTTTopic);
  Serial.write(MQTTQOS);
  Serial.write(0x1A);
}
void loop() {
  Serial.print("AT+CSTT=\"www\",\"\",\"\"\r\n");
  delay(1000);
  Serial.print("AT+CIPMODE=0\r\n");
  delay(1000);
  Serial.print("AT+CIICR\r\n");
  delay(5000);
  Serial.print("AT+CIPSTART=\"TCP\",\"m10.cloudmqtt.com\",\"17434\"\r\n");
  delay(4000);
  SendConnectPacket();
  delay(5000);
  SendSubscribePacket();
  while (1) {
    if (Serial.available() > 0) {
      str[0] = Serial.read();
      Serial.write(str[0]);
      if (str[0] == '1')
        digitalWrite(led, HIGH);
      if (str[0] == '0')
        digitalWrite(led, LOW);
    }
  }
}

Code used to demonstrate the MQTT connection to Adafruit.io broker using SIM900/SIM800 GSM module :

int led = 13;
unsigned int Counter = 0;
unsigned long datalength, CheckSum, RLength;
unsigned short topiclength;
unsigned char topic[30];
char str[250];
unsigned char encodedByte;
int X;
unsigned short MQTTProtocolNameLength;
unsigned short MQTTClientIDLength;
unsigned short MQTTUsernameLength;
unsigned short MQTTPasswordLength;
const char MQTTHost[30] = "io.adafruit.com";
const char MQTTPort[10] = "1883";
const char MQTTClientID[20] = "ABCDEF";
const char MQTTTopic[30] = "raviypujar/feeds/switchfeed";
const char MQTTProtocolName[10] = "MQTT";
const char MQTTLVL = 0x03;
const char MQTTFlags = 0xC2;
const unsigned int MQTTKeepAlive = 60;
const char MQTTUsername[30] = "raviypujar";
const char MQTTPassword[35] = "993df7b916494d19b430d53cfcbe677d";
const char MQTTQOS = 0x00;
const char MQTTPacketID = 0x0001;
void setup() {
  pinMode(led, OUTPUT);
  Serial.begin(9600);
  Serial.println("Arduino MQTT Tutorial, Valetron Systems @www.valetron.com ");
  delay(3000);
}
void SendConnectPacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  Serial.write(0x10);
  MQTTProtocolNameLength = strlen(MQTTProtocolName);
  MQTTClientIDLength = strlen(MQTTClientID);
  MQTTUsernameLength = strlen(MQTTUsername);
  MQTTPasswordLength = strlen(MQTTPassword);
  datalength = MQTTProtocolNameLength + 2 + 4 + MQTTClientIDLength + 2 + MQTTUsernameLength + 2 + MQTTPasswordLength + 2;
  X = datalength;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(MQTTProtocolNameLength >> 8);
  Serial.write(MQTTProtocolNameLength & 0xFF);
  Serial.print(MQTTProtocolName);
  Serial.write(MQTTLVL); // LVL
  Serial.write(MQTTFlags); // Flags
  Serial.write(MQTTKeepAlive >> 8);
  Serial.write(MQTTKeepAlive & 0xFF);
  Serial.write(MQTTClientIDLength >> 8);
  Serial.write(MQTTClientIDLength & 0xFF);
  Serial.print(MQTTClientID);
  Serial.write(MQTTUsernameLength >> 8);
  Serial.write(MQTTUsernameLength & 0xFF);
  Serial.print(MQTTUsername);
  Serial.write(MQTTPasswordLength >> 8);
  Serial.write(MQTTPasswordLength & 0xFF);
  Serial.print(MQTTPassword);
  Serial.write(0x1A);
}
void SendPublishPacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  memset(str, 0, 250);
  topiclength = sprintf((char * ) topic, MQTTTopic);
  datalength = sprintf((char * ) str, "%s%u", topic, Counter);
  delay(1000);
  Serial.write(0x30);
  X = datalength + 2;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength & 0xFF);
  Serial.print(str);
  Serial.write(0x1A);
}
void SendSubscribePacket(void) {
  Serial.print("\r\nAT+CIPSEND\r\n");
  delay(3000);
  memset(str, 0, 250);
  topiclength = strlen(MQTTTopic);
  datalength = 2 + 2 + topiclength + 1;
  delay(1000);
  Serial.write(0x82);
  X = datalength;
  do {
    encodedByte = X % 128;
    X = X / 128;
    if (X > 0) {
      encodedByte |= 128;
    }
    Serial.write(encodedByte);
  }
  while (X > 0);
  Serial.write(MQTTPacketID >> 8);
  Serial.write(MQTTPacketID & 0xFF);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength & 0xFF);
  Serial.print(MQTTTopic);
  Serial.write(MQTTQOS);
  Serial.write(0x1A);
}
void loop() {
  Serial.print("AT+CIPSHUT\r\n");
  delay(2000);
  Serial.print("AT+CSTT=\"www\",\"\",\"\"\r\n");
  delay(1000);
  Serial.print("AT+CIPMODE=0\r\n");
  delay(1000);
  Serial.print("AT+CIICR\r\n");
  delay(9000);
  Serial.print("AT+CIPSTART=\"TCP\",\"io.adafruit.com\",\"1883\"\r\n");
  delay(6000);
  SendConnectPacket();
  delay(5000);
  SendSubscribePacket();
  delay(5000);
  while (1) {
    if (Serial.available() > 0) {
      str[0] = Serial.read();
      Serial.write(str[0]);
      if (str[0] == 'N')
        digitalWrite(led, HIGH);
      if (str[0] == 'F')
        digitalWrite(led, LOW);
    }
  }
}

Have any questions ?
Please register and post to www.EmbeddedAdvice.com. I will answer them .

Hope it helps someone. Don’t forget to share and Subscribe 🙂

One comment

Harshal Deshpande
February 6, 2020 - 4:36 pm
Dear Ravi,
Thanks for putting very interesting and useful videos. I really appreciate your work and knowledge. I’m trying to get the MQTT working on my arduino uno using SIM800 L. Can you please confirm if your code should work SIM800 L. Somehow there are no errors but I am not able to see the messages on Cloud MQTT portal – websocket UI that are being published from my code. Can you please help.

Thanks a ton,
Harshal Deshpande

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Arduino MQTT Library with Publish and Subscribe example

Arduino MQTT Library with Publish and Subscribe example

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Harshal Deshpande

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