The following code does what I need it to do (when a start switch is on and door switch is off - a warning light flashes. When the start switch and door switch are both on - a valve opens to allow water in for 2 seconds). I need the light to flash until the door is HIGH too at which point the valve program runs once. The only way I have to get out of this is to use exit(0). Is there a better way to do this? Ideally, I would like to stay away from anything too Boolean! Thank you.

int start = 2;
int door = 3;
int light = 8;
int valve = 9;
int counter = 0;

void setup() {

void loop() {
  if(digitalRead(start)==HIGH && digitalRead(door)==HIGH) {
    digitalWrite(valve, HIGH);
    //breaks out of loop. Arduino then needs reset.

  if (digitalRead(start)==HIGH && digitalRead(door)==LOW) {
  • I don't really see what the exit(0) does here. If the door and start buttons remain pressed, the valve will go open for 2 seconds, then close for a while, but then open again for 2 seconds, etc. The only thing exit(0) does is create a bit of a delay. So replacing exit(0), with delay(3000) will do about the same thing. I think want you want is to remember that the valve has already been opened, on not open it again while both button are being pressed. – Gerben Nov 27 '15 at 21:17
  • A better way to stop execution? Some trap the operation in an endless loop with a while(1){} – Dave X Nov 28 '15 at 5:17
  • I think the infinite loop is the best way. I have to teach this to High School kids who will only do a small part of programming as part of a course. I am trying to find Arduino solutions for questions that were originally designed for PBASIC (picaxe). There are a lot of questions which need the code to run once - and I need to restrict the commands to for, while, if....else commands ideally (in BASIC they would have used if/then, for/next and subroutines and that would be enough). – debkeys Nov 28 '15 at 14:56
  • What you made a mistake is instead of using "if"(first one) you had to use "while". And use the "if" to break out of the "while" using a "break" , what you have done is really a bad practice. – 25mhz Jan 9 '18 at 16:29

What you need to do is learn what a finite state machine (FSM) is.

An FSM is a way of having the Arduino in one of a finite number of states, such as "light flashing", or "letting water in", etc.

I have written a reasonable (IMHO) tutorial here: https://hackingmajenkoblog.wordpress.com/2016/02/01/the-finite-state-machine/

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