How can i extract RGB numbers from a recieved message

Using Arduino Programming Questions
#1

Hello,
I have a esp32 (lolin D32) recieveing an RGB message from node-red on a raspbery pi.
this RGB message will be used to set a string of leds to this colour using fast.led

Im not sure how to get the numbers from this message and hold them as a byte value to then send to the LED string

the message i recieve from the serial monitor is:

Message arrived on topic: Garage/Colour. Message: rgb(128, 128, 128)

the only variables in the actual message, "rgb(xxx, xxx, xxx)" will be the numbers

I would then store the numbers as a byte and send them to the leds
Here is what i have so far....
serial.print output for debugging purposes. i know the topic and messageTemp part is correct im just struggling to interpret the message.

  if(switch6toggle == HIGH){
   if(topic=="Garage/Colour"){
    //grab the rgb data from node red then set the output colour
    if(messageTemp == ("rgb, (RED, GREEN, BLUE)")){
        Serial.print("SET LEDS TO....");
        Serial.print(RED);
        Serial.print(GREEN);
        Serial.print(BLUE);
        setAll(RED, GREEN, BLUE);
    }
   }

Thank you
James.

#2

Here is something to experiment with

char message[] = {"rgb(126, 127, 128)"};
char * ptr;

void setup()
{
  Serial.begin(115200);
  ptr = strtok(message, "("); //move past (
  ptr = strtok(NULL, ",");  //next comma is red
  byte red = atoi(ptr);
  Serial.println(red);
  
  byte green = atoi(strtok(NULL, ",")); //this works too but may not be so easy to understand
  Serial.println(green);
  
  ptr = strtok(NULL, ",");  //next comma is blue
  byte blue = atoi(ptr);
  Serial.println(blue);
}

void loop()
{
}
#3

Thank you for the reply,
i have been doing a lot of playing around but im still stuck.

this part works great:

        char message[] = {"rgb(126, 127, 128)"};
        char * ptr;
        ptr = strtok(message, "("); //move past (
        ptr = strtok(NULL, ",");  //next comma is red
        byte RED = atoi(ptr);
        Serial.print("SET LEDS TO....");
        Serial.println(RED);
        ptr = strtok(NULL, ",");  //next comma is green
        byte GREEN = atoi(ptr);
        Serial.println(GREEN);
        ptr = strtok(NULL, ",");  //next comma is blue
        byte BLUE = atoi(ptr);
        Serial.println(BLUE);

as expected it outputs 126 127 and 128

I cant figure out how to use the incoming String of data.
i think i have converted it to a charArray so it can be used, but using that converted data to use causes either invalid conversions during a compile or crashes when the data is converted/used.
messageTemp is the incoming data from MQTT.

        messageTemp.toCharArray(charbuf, 20);
        char message[] = {"charbuf"};
        char * ptr;
        ptr = strtok(message, "("); //move past (
        ptr = strtok(NULL, ",");  //next comma is red
        byte RED = atoi(ptr);
        Serial.print("SET LEDS TO....");
        Serial.println(RED);
        ptr = strtok(NULL, ",");  //next comma is green
        byte GREEN = atoi(ptr);
        Serial.println(GREEN);
        ptr = strtok(NULL, ",");  //next comma is blue
        byte BLUE = atoi(ptr);
        Serial.println(BLUE);

I think im heading in the right direction??
Thanks.

#4

"I cant figure out how to use the incoming String of data."

If you capture the data as a string, then just use the String functions to parse out the data. Otherwise you might use something like below to convert the String variable into a character array.

      char carray[6];
      readString.toCharArray(carray, sizeof(carray));
#5

If you capture the data as a string, then just use the String functions to parse out the data.

This is exactly the sort of sloppy use of language that causes confusion

A string in C++ is not the same as a String

If the message is in a string (a zero terminated array of chars) then use strtok() to split it
If the message is in a String (an object of the String library) then use the String functions to split it

#6

"This is exactly the sort of sloppy use of language that causes confusion"

Kind of like when people use string instead of c-string? Maybe it was a kite string.

#7

Thanks for the help, I have managed to do what i needed to using the String functions.
its not the best way but it works and im happy with that.

  if(switch6toggle == HIGH){
   if(topic=="Garage/Colour"){
        int posred = messageTemp.indexOf('(');                        //index the first position
        String red = messageTemp.substring(posred +1, posred +4);     //substring of red using refrence position
        int posgrn = messageTemp.indexOf(',');                        //index the next position
        String green = messageTemp.substring(posgrn +1, posgrn +5);   //substring of green using refrence position
        int posblu = messageTemp.indexOf(')');                        //index the last position
        String blue = messageTemp.substring(posblu -3, posblu);       //substring of blue using refrence positions
        RED = red.toInt();                                            //convert the substrings to an Int so it can be used
        GREEN = green.toInt();
        BLUE = blue.toInt();
        Serial.print("Red: ");
        Serial.println(RED);
        Serial.print("Green: ");
        Serial.println(GREEN);
        Serial.print("Blue: ");
        Serial.println(BLUE);
#8

As long as it works for you then OK, but be aware that Strings (uppercase S) have a reputation for fragmenting memory which is undesirable in the small memory footprint in most microcontrollers

#9