Fix Debounce example to work as described

This alters the debounce example code to toggle the LED rather than just use
the button state to set the LED state.

Fixes arduino#293

Author: miek

build/shared/examples/02.Digital/Debounce/Debounce.ino

@@ -19,6 +19,8 @@
  by David A. Mellis
  modified 30 Aug 2011
  by Limor Fried
+ modified 28 Dec 2012
+ by Mike Walters
  
 This example code is in the public domain.
  
@@ -43,6 +45,9 @@ long debounceDelay = 50;    // the debounce time; increase if the output flicker
 void setup() {
   pinMode(buttonPin, INPUT);
   pinMode(ledPin, OUTPUT);
+
+  // set initial LED state
+  digitalWrite(ledPin, ledState);
 }
 
 void loop() {
@@ -62,12 +67,21 @@ void loop() {
   if ((millis() - lastDebounceTime) > debounceDelay) {
     // whatever the reading is at, it's been there for longer
     // than the debounce delay, so take it as the actual current state:
-    buttonState = reading;
+
+    // if the button state has changed:
+    if (reading != buttonState) {
+      buttonState = reading;
+
+      // only toggle the LED if the new button state is HIGH
+      if (buttonState == HIGH) {
+        ledState = !ledState;
+
+        // set the LED:
+        digitalWrite(ledPin, ledState);
+      }
+    }
   }
 
-  // set the LED using the state of the button:
-  digitalWrite(ledPin, buttonState);
-
   // save the reading.  Next time through the loop,
   // it'll be the lastButtonState:
   lastButtonState = reading;