Word Commands

Part of the Inputs section of Coddy's Arduino journey. Lesson 16 of 22.

One character per command runs out fast. Words are clearer: on, off. A word is several characters, so read the whole line at once. A piece of text is a String, and Serial.readStringUntil() reads characters until it meets the one you give it, the newline, which it throws away:

if (Serial.available() > 0) {
  String command = Serial.readStringUntil('\n');
  if (command == "on") {
    // ...
  }
}

Text goes in double quotes, "on"; a single character in single quotes, 'o'.

To pick one of several commands, chain the tests with else if. The board tries them in order and runs only the first that is true; the last else catches everything else:

if (command == "on") {
  // ...
} else if (command == "off") {
  // ...
} else {
  Serial.println("Unknown command");
}

Challenge

Easy

The LED is on pin 13. Control it with words typed into the Serial monitor:

read a whole line into a String
on turns the LED on, off turns it off
any other word prints Unknown command

Press Run, send on, off or a word of your own from the Serial monitor, then Check.

Try it yourself

const int ledPin = 13;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  if (Serial.available() > 0) {
    // read the line, then act on "on", "off" or anything else
  }
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Inputs

Practice on your own: Arduino playground