Controlling Relay using mqtt

General
1

hello guys,
i want to control my relay by mqtt broker, it's already subcribe the data from Soil Moisture Sensor, but the relay is always off

this is the logic i use

image
image905×201 12.7 KB

this is the callback function

void mqttCallback(char* topic, byte* message, unsigned int length) {
  Serial.print("Message arrived on topic: ");
  Serial.print(topic);
  Serial.print(". Message: ");
  String messageTemp;
  
  for (int i = 0; i < length; i++) {
    Serial.print((char)message[i]);
    messageTemp += (char)message[i];
  }
  Serial.println();


  if (String(topic) == DeviceConfig.MqttSub) { // DeviceConfig.MqttSub = /command
    Serial.print("Changing output to ");
    if(messageTemp == "ON"){
      digitalWrite(AIO_SENSOR_PIN_3, HIGH);
      Serial.println("ON");
    }
    else if(messageTemp == "OFF"){
      digitalWrite(AIO_SENSOR_PIN_3, LOW); //AIO_SENSOR_PIN_3 expands to pin32 esp
      Serial.println("OFF");
    }
  }
}

and the value already sended
image

but the relay state is not affected at all

can you guys help me please?

2

At first glance, the piece of code you have posted looks OK.

I assume digitalWrite(AIO_SENSOR_PIN_3, HIGH); maps to an actual pin?

If I was doing it, I would have used the <ArduinoJson.h> library in your sketch as you could send json from your flow which would give you much more flexibility in decoding a number of different commands.
So, for example, you could send commands like...

msg.payload = {"relay":"main","action":"on"};
or
msg.payload = {"relay":"secondary","action":"off"};

The reason I say this is... you are bound to add extra relays or LEDs to your system. Plan ahead.

PS: It's not normal to start a topic-name with a /
Maybe you can change it to just... command (in your flow and in your sketch).

PPS: If you write a simple test-sketch (like the 'blink' sketch), can you turn the relay On and Off ?

3

What are you running the sketch on ? i.e. arduino uno, mini, ESP8266 etc etc Do you have a Fritzing schematic so we can see how that side looks ?

Craig

4

One of my IoT students was asking about nearly the same question that you posted on the forum.
He was using a Wemos D1 Mini - not sure what you are using. But I'm sure it could be adapted.

I've posted what we did on the forum as I think it might go some way to solving your problem.

5

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