digitalwrite with function parameter as parameter

Question

Firstly, excuse my poor English, this is not my native langage.

I'm trying to use an Arduino Uno to drive an 8 relay board from an MQTT Subscription. I ask for help because i'm some kind of beginner in arduino, i'm just a Linux addict.

The idea is to get a payload from PubSubclient and use it to manage relays. For example, the payload '71' ask the relay 7 to turn on and '42' make the relay 4 to turn off.

All works fine until I wanted to write a function with two parameters : 'relay_number' and 'Action'

All parameters are received but the relay never goes up or down.

My code :

void callback(char* topic, byte* payload, unsigned int length) {
  
  Relay_Nb = (char)payload[0];
  Action = char(payload[1]);

  Serial.println(Relay_Nb);
  Serial.println(Action);
  
  RelayControl(Relay_Nb, Action);
}

void RelayControl(char Relay_Nb, char Action) {
  Serial.println(Relay_Nb);   // for debugging purpose
  Serial.println(Action);
   
  if ( Action == '0') {
    Serial.print("Bringing down Relay ");
    Serial.println(Relay_Nb);
    digitalWrite(Relay_Nb, LOW); 
  } else if (Action == '1') {
    Serial.print("Bringing up Relay ");
    Serial.println(Relay_Nb);
    digitalWrite(Relay_Nb, HIGH);
  } else if (Action == '2') {
    // Relay temporisé (ouverture portail par ex)
    Serial.println("Bringing up, and down Relay ");
    digitalWrite(Relay_Nb, HIGH);
    delay(750);
    digitalWrite(Relay_Nb, LOW);
  } 
}

I'm sure an old maker have the solution i'm searching for hours now.

Please help and don't hesitate to show me others ways. Thanks.

Answer 1

You are sending the parameter Relay_Nb as a character, and then using it as an integer.

You need to turn the character into an integer - and the simplest way is to subtract the ASCII value of 0 from it:

Relay_Nb = payload[0] - '0';

But with that said, a note on how you have written your callback:

• You aren't checking the data is valid.

You should really be doing, at the very least, the following:

1. Check that the length parameter is at least 2,
2. Check that the two data values are within the correct range for your function