3Pi running Arduino - can't read pushbuttons without LCD

Support Robots
1

I am running the 3Pi using Arduino and have run into an issue when reading the pushbuttons [using low level reads]. It works with the LCD module in place, but when the LCD is removed, it doesn’t work.

Best to first look at the code:

void setup() {
  pinMode(1, OUTPUT);    // red LED
  pinMode(7, OUTPUT);    // green LED
  pinMode(9, INPUT);     // pushbutton A
}

void loop() { 

  if(digitalRead(9) == HIGH) {
    digitalWrite(1, HIGH);    // red ON
    digitalWrite(7, LOW);     // green OFF
  }

  else {
    digitalWrite(1, LOW);       // red OFF
    digitalWrite(7, HIGH);      // green ON
  }
}

The program is designed to read the state of digital pin 9 (button A on the 3Pi). When it’s HIGH, it turns on the red LED; LOW turns on the green LED. According to the pin assignment table (page 17 of the manual - 0J17) digital pin 9 is user pushbutton A, and pressing it pulls it LOW.

This is a bit irksome, as I was planning to create a “shield” that utilized pins 2, 4, 8 when the LCD module was removed.

I get the feeling that pin 9 is floating and is relying on the LCD module to pull it HIGH.

Any thoughts as to 1) if I’m doing something wrong, or 2) how to fix it.

2

Hello.

The 3pi pushbuttons rely on internal pull-ups to give them a default open state. It should work for you as expected if you add the following line to the end of your setup() function:

digitalWrite(9, HIGH); // enable internal pull-up on input pin 9 (PB1)

You will need to do the same thing for the B and C buttons as well. Please let me know if this doesn’t fix your problem.

- Ben

3

Thanks, this worked!