Adding an ON/OFF Toggle Switch

Projects Programming
3 
// Connect switch between pin 3 and GND
const int TOGGLE_PIN = 3;

void setup()
{
  pinMode(TOGGLE_PIN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(TOGGLE_PIN), startStop, FALLING);
  ... rest of your stuff
}


void startStop()
{
  while (digitalRead(TOGGLE_PIN) == LOW);
}

Untested, but that should do it.