Arduino reading from serial gives unwanted input

Question

I am trying to build a small program to control 3 led's. The led's are connected on pins 11 (red), 12 (yellow) and 13 (green).

For some to me unknow reason the following code does not seem to work. If I enter 1 in the serial input, the yellow led will light up. But after about 1 second it's turned off again and the red led is turned on. It looks to me like there is alway's a 0 on the serial input, but that can't be right is it?

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(Serial.available() > 0) {
    changeLed(Serial.parseInt());
  }
}

void changeLed(int color) {
  turnAllLedsOff();
  turnOnLed(color);
}

void turnOnLed(int ledPin) {
  enum ledControl {RED, YELLOW, GREEN};
  if(ledPin == RED) {
    digitalWrite(11, HIGH);
  }
  if(ledPin == YELLOW) {
    digitalWrite(12, HIGH);
  }
  if(ledPin == GREEN) {
    digitalWrite(13, HIGH);
  }
}

void turnAllLedsOff() {
  digitalWrite(11, LOW);
  digitalWrite(12, LOW);
  digitalWrite(13, LOW);
}

Kentaro Okuda Kentaro Okuda · Accepted Answer · 2019-07-05T23:18:12

I believe your Serial Monitor's line ending setting is set to Both NL & CR. One triggers Serial.parseInt() and the other triggers another Serial.parseInt(). So, each serial input, you are calling the function twice. And the second one always returns 0 as newline only (or carriage return only) is not valid digits. That is why your red LED gets turned on. Try other line ending settings.

Arduino reading from serial gives unwanted input

1 Answers