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/*
  Arduino Starter Kit example
  Project 15 - Hacking Buttons

  This sketch is written to accompany Project 15 in the Arduino Starter Kit

  Parts required:
  - battery powered component
  - 220 ohm resistor
  - 4N35 optocoupler

  created 18 Sep 2012
  by Scott Fitzgerald

  https://store.arduino.cc/genuino-starter-kit

  This example code is part of the public domain.
*/

const int optoPin = 2; // the pin the optocoupler is connected to
 

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void setup() {
  // make the pin with the optocoupler an output
  pinMode(optoPin, OUTPUT);
}
 

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void loop() {
  digitalWrite(optoPin, HIGH);  // pull pin 2 HIGH, activating the optocoupler

  delay(15); // give the optocoupler a moment to activate

  digitalWrite(optoPin, LOW);  // pull pin 2 low until you're ready to activate again
  delay(21000);                // wait for 21 seconds
}