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.raviyp.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 &amp; 0xFF);
  Serial.print(MQTTProtocolName);
  Serial.write(MQTTLVL); // LVL
  Serial.write(MQTTFlags); // Flags
  Serial.write(MQTTKeepAlive >> 8);
  Serial.write(MQTTKeepAlive &amp; 0xFF);
  Serial.write(MQTTClientIDLength >> 8);
  Serial.write(MQTTClientIDLength &amp; 0xFF);
  Serial.print(MQTTClientID);
  Serial.write(MQTTUsernameLength >> 8);
  Serial.write(MQTTUsernameLength &amp; 0xFF);
  Serial.print(MQTTUsername);
  Serial.write(MQTTPasswordLength >> 8);
  Serial.write(MQTTPasswordLength &amp; 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 &amp; 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 &amp; 0xFF);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength &amp; 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.raviyp.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 &amp; 0xFF);
  Serial.print(MQTTProtocolName);
  Serial.write(MQTTLVL); // LVL
  Serial.write(MQTTFlags); // Flags
  Serial.write(MQTTKeepAlive >> 8);
  Serial.write(MQTTKeepAlive &amp; 0xFF);
  Serial.write(MQTTClientIDLength >> 8);
  Serial.write(MQTTClientIDLength &amp; 0xFF);
  Serial.print(MQTTClientID);
  Serial.write(MQTTUsernameLength >> 8);
  Serial.write(MQTTUsernameLength &amp; 0xFF);
  Serial.print(MQTTUsername);
  Serial.write(MQTTPasswordLength >> 8);
  Serial.write(MQTTPasswordLength &amp; 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 &amp; 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 &amp; 0xFF);
  Serial.write(topiclength >> 8);
  Serial.write(topiclength &amp; 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 .

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3 thoughts on “Arduino MQTT Library with Publish and Subscribe example”

Harshal Deshpande
February 6, 2020 at 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

1. Ravi Pujar
  February 9, 2020 at 10:08 PM
  
  Hi Harshal,
  The code remains same for SIM900 and SIM800 series modules. The commands are compatible.
  For technical queries you can post on http://www.embeddedadvice.com
  
2. Ravi Pujar
  February 15, 2020 at 11:04 PM
  
  Hi Harshal,
  Glad you liked the videos.
  The SIM800L uses same AT commands. Shouldnt be a problem. You need to add appropriate delays where necessary and wait for AT command responses. I have just put delays for demonstration. You need to tweak the code and fine tune it. We discuss technical queries on my forum http://www.embeddedadvice.com, post a topic there and we can discuss

3 thoughts on “Arduino MQTT Library with Publish and Subscribe example”

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