Added new button state change detection example

build/shared/dist/examples/Digital/StateChangeDetection/StateChangeDetection.pde

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+/*
+  State change detection (edge detection)
+ 	
+ Often, you don't need to know the state of a digital input all the time,
+ but you just need to know when the input changes from one state to another.
+ For example, you want to know when a button goes from OFF to ON.  This is called
+ state change detection, or edge detection.
+ 
+ This example shows how to detect when a button or button changes from off to on
+ and on to off.
+ 	
+ The circuit:
+ * pushbutton attached to pin 2 from +5V
+ * 10K resistor attached to pin 2 from ground
+ * LED attached from pin 13 to ground (or use the built-in resistor on
+   (most Arduino boards)
+ 
+ created  27 Sep 2005
+ modified 17 Jun 2009
+ by Tom Igoe
+ 	
+ http://arduino.cc/en/Tutorial/ButtonStateChange
+ 
+ */
+
+// this constant won't change:
+const int  buttonPin = 2;    // the pin that the pushbutton is attached to
+const int ledPin = 13;       // the pin that the LED is attached to
+
+// Variables will change:
+int buttonPushCounter = 0;   // counter for the number of button presses
+int buttonState = 0;         // current state of the button
+int lastButtonState = 0;     // previous state of the button
+
+void setup() {
+  // initialize the button pin as a input:
+  pinMode(buttonPin, INPUT);
+  // initialize serial communication:
+  Serial.begin(9600);
+}
+
+
+void loop() {
+  // read the pushbutton input pin:
+  buttonState = digitalRead(buttonPin);
+
+  // compare the buttonState to its previous state
+  if (buttonState != lastButtonState) {
+    // if the state has changed, increment the counter
+    if (buttonState == HIGH) {
+      // if the current state is HIGH then the button
+      // wend from off to on:
+      buttonPushCounter++;
+      Serial.println("on");
+      Serial.print("number of button pushes:  ");
+      Serial.println(buttonPushCounter, DEC);
+    } 
+    else {
+      // if the current state is LOW then the button
+      // wend from on to off:
+      Serial.println("off"); 
+    }
+
+    // save the current state as the last state, 
+    //for next time through the loop
+    lastButtonState = buttonState;
+  }
+  
+  // turns on the LED every four button pushes by 
+  // checking the modulo of the button push counter.
+  // the modulo function gives you the remainder of 
+  // the division of two numbers:
+  if (buttonPushCounter % 4 == 0) {
+    digitalWrite(ledPin, HIGH);
+  } else {
+   digitalWrite(ledPin, LOW);
+  }
+  
+}
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