timing within a loop

Projects General Guidance
14

Joes:
ok
do we have an example of this?

What you're looking for is called edge detection. Here is an example of such using a button:

/*

  • Example for "Edge Detection"
  • Edge detection refers to determining the point at which a digital signal moves
  • from low to high or high to low. Low to high is refered to as the 'positive' or
  • rising edge. High to low is the 'negative or falling' edge. This example uses a
  • button to run a commands at each edge, identifying the edge. Edges occur on a
  • a button when it is either pushed or released. If the input pin is pulled high,
  • pushing the button down wil be the falling edge, while releasing it will be th
  • rising edge. If the input pin is pulled high, the opposite will be true.
  • NOTE: This example does not utilize a debounce, so it's entirely possible that
  • you'll see multiple prints if using a device, such as a button, that bounces
  • during signal change.
    */

// Pin used for our digital signal
const short inputPin = 5;

void setup() {
Serial.begin(57600);
Serial.println("[EdgeDetection]");

pinMode(inputPin, INPUT); // Set the pin as input
digitalWrite(inputPin, HIGH); // enable pull-up resistor. (Pulled high)

}

void loop() {
/* Keep track of the last state of the button. A static variable will

  • only be initialized the first time and will hold it's value through
  • each loop. */
    static short lastState = HIGH;
    // Get the current state of the pin
    short currentState = digitalRead(inputPin);

// Check for the falling edge
if ( (currentState==HIGH) && (lastState==LOW) ) {
fallingEdge();
}
// Check for rising edge
if ( (currentState==LOW) && (lastState==HIGH) ) {
risingEdge();
}

lastState = currentState;
}

void fallingEdge() {
Serial.println("Falling edge");
}

void risingEdge() {
Serial.println("Rising edge");
}