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How to Read from an Active High Digital Input

An active high digital input reads as true/1/HIGH when the attached digital sensor is active (e.g. button pressed, door open, engine overheated, or motion detected). Read the state of an active high digital input with digitalRead(pin).

#define SENSOR1   2  // Some kind of digital sensor connected to D2

void setup()
{
  pinMode(SENSOR1, INPUT);
}

void loop()
{
  // Persistent logic state variable, value preserved between calls
  // to loop()
  static bool oldstate;

  // Nonpersistent logic state variable, value NOT preserved between
  // calls to loop()
  bool newstate;

  // Read digital input state into a logic state variable
  newstate = digitalRead(SENSOR1);

  // Do something if the sensor input is active
  if (newstate)
  {
    DoSomething();
  }

  // Do something if the sensor input is active (do not save state)
  if (digitalRead(SENSOR1))
  {
    DoSomething();
  }

  // Do something if the sensor input is active (save state)

  if (newstate = digitalRead(Sensor1))
  {
    DoSomething();
  }

  // Do something if the sensor input CHANGES

  if (newstate != oldstate)
  {
    DoSomething();
  }

  // Save logic state for next call to loop()
  oldstate = newstate;
}

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