Ich hätts so versucht (ungetestet):
Code:
#include <Bounce2.h>
#include <Wire.h>

boolean start = false;
Bounce  pin5  = Bounce();

void setup() {
  pinMode(5, INPUT_PULLUP);
  Serial.begin(115200);
  pin5.attach(5);
  pin5.interval(5);
}

void loop() {
  if(pin5.update()) {
    if(pin5.fell()) { 
      start = !start; // toggle start each time button is pressed
    }
  }

  if(start) {
    Serial.println("started!");
  }
}