Arduino readString(); code runs slow

Question

I have the following code which I need to execute quickly, yet its taking a lot of time to change the value, anyway over way of making this task quicker?

I am using indexOf() and substring() to accomplish this task. This is for changing the strip LED colors.

// declare LED Series A Pins R-G-B (PWM Pins)
  int const AledRedPin = 6;
  int const AledGreenPin = 5;
  int const AledBluePin = 3;

// declare LED Series B Pins R-G-B (PWM Pins)
  int const BledRedPin = 10;
  int const BledGreenPin = 11;
  int const BledBluePin = 9;

// serial input variable & string
// initialise LED Series A Pins R-G-B (PWN Value: 0 to 255)
// initial value = 255
  int AledRed = 255;
  int AledGreen = 255;
  int AledBlue = 255;

// initialise LED Series A Pins R-G-B (PWN Value: 0 to 255)
// initial value = 255
  int BledRed = 255;
  int BledGreen = 255;
  int BledBlue = 255;

//serial input
  String Command = "";

//string manipulation
  int cmdindexval = 0;
  String CommandType = "";
  int CommandValue = 0;
  String Series = "";

void setup() {
  // put your setup code here, to run once:
  // start serial
    Serial.begin(9600);
      while (!Serial) {
        ; // wait for serial port to connect. Needed for native USB
      }

  // set LED Series A Pins as Output R-G-B
    pinMode(AledRedPin, OUTPUT);
    pinMode(AledGreenPin, OUTPUT);
    pinMode(AledBluePin, OUTPUT);

  // set LED Series B Pins as Output R-G-B
    pinMode(BledRedPin, OUTPUT);
    pinMode(BledGreenPin, OUTPUT);
    pinMode(BledBluePin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  // read from serial if it's available
    if (Serial.available() > 0) {
      Command = Serial.readString(); //read string from serial monitor
      cmdindexval = Command.indexOf('='); //read characters until '=' then assign the value
      CommandType = Command.substring(0, cmdindexval); //assign the value from 0 to cmdindexval
      //Series = Command.substring(0, 1); //read first character
      CommandValue = Command.substring(cmdindexval + 1).toInt(); //assign the value after '=' and convert string to Int
      Serial.println(CommandType + " ,is equal to " + CommandValue + " ,Series: " + Series);    
      //if (Series == "A") {
        if (CommandType == "ACledRed"){
          AledRed = CommandValue;
        }
       else if (CommandType == "ACledGreen"){
          AledGreen = CommandValue;
        }
        else if (CommandType == "ACledRedBlue") {
          AledBlue = CommandValue;
        }
      //}
      //else if (Series == "B") {
        if (CommandType == "BCledRed") {
          BledRed = CommandValue;
        }
        else if (CommandType == "BCledGreen") {
          BledGreen = CommandValue;
        }
        else if (CommandType == "BCledBlue") {
          BledBlue = CommandValue;
        }
     //}
    } //end serial

    analogWrite(AledRedPin, AledRed);
    analogWrite(AledGreenPin, AledGreen);
    analogWrite(AledBluePin, AledBlue);

    analogWrite(BledRedPin, BledRed);
    analogWrite(BledGreenPin, BledGreen);
    analogWrite(BledBluePin, BledBlue);

}

Answer 1

From the Arduino docs on readString:

Serial.readString() reads characters from the serial buffer into a string. The function terminates if it times out (see setTimeout()).

and the docs on setTimeout:

Serial.setTimeout() sets the maximum milliseconds to wait for serial data when using Serial.readBytesUntil(), Serial.readBytes(), Serial.parseInt() or Serial.parseFloat(). It defaults to 1000 milliseconds.

This means that the readString is always waiting 1 sec to make sure that the sending of the string is finished and has the complete string.
Unfortunately that means it's slow to respond. You could lower the timeout with the setTimeout, but you would still have some delay, or if you set it too low you could potentially get incomplete stings.

The best solution would be to use readStringUntil, so you know you have a complete string when you get a terminator character (like a newline).

Replace

Command = Serial.readString();

with

Command = Serial.readStringUntil('\n');

and make sure you set the Serial monitor so send the newline character.