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

@@ -1,52 +1,73 @@
-/* Debounce
- * 
- * Each time the input pin goes from LOW to HIGH (e.g. because of a push-button
- * press), the output pin is toggled from LOW to HIGH or HIGH to LOW.  There's
- * a minimum delay between toggles to debounce the circuit (i.e. to ignore
- * noise).  
- *
- * David A. Mellis
- * 21 November 2006
- *
- * http://www.arduino.cc/en/Tutorial/Debounce
+/* 
+ Debounce
+ 
+ Each time the input pin goes from LOW to HIGH (e.g. because of a push-button
+ press), the output pin is toggled from LOW to HIGH or HIGH to LOW.  There's
+ a minimum delay between toggles to debounce the circuit (i.e. to ignore
+ noise).  
+ 
+ The circuit:
+ * LED attached from pin 13 to ground
+ * pushbutton attached from pin 7 to +5V
+ * 10K resistor attached from pin 7 to ground
+ 
+ * Note: On most Arduino boards, there is already an LED on the board
+ connected to pin 13, so you don't need any extra components for this example.
+ 
+ 
+ created 21 November 2006
+ by David A. Mellis
+ modified 17 Jun 2009
+ by Tom Igoe
+ 
+ 
+ http://www.arduino.cc/en/Tutorial/Debounce
  */
 
-int inPin = 7;         // the number of the input pin
-int outPin = 13;       // the number of the output pin
+// constants won't change. They're used here to 
+// set pin numbers:
+const int buttonPin = 7;     // the number of the pushbutton pin
+const int ledPin =  13;      // the number of the LED pin
 
-int state = HIGH;      // the current state of the output pin
-int reading;           // the current reading from the input pin
-int previous = LOW;    // the previous reading from the input pin
+// Variables will change:
+int ledState = HIGH;         // the current state of the output pin
+int buttonState;             // the current reading from the input pin
+int lastButtonState = LOW;   // the previous reading from the input pin
 
 // the follow variables are long's because the time, measured in miliseconds,
 // will quickly become a bigger number than can be stored in an int.
-long time = 0;         // the last time the output pin was toggled
-long debounce = 200;   // the debounce time, increase if the output flickers
+long lastDebounceTime = 0;  // the last time the output pin was toggled
+long debounceDelay = 200;   // the debounce time, increase if the output flickers
 
-void setup()
-{
-  pinMode(inPin, INPUT);
-  pinMode(outPin, OUTPUT);
+void setup() {
+  pinMode(buttonPin, INPUT);
+  pinMode(ledPin, OUTPUT);
 }
 
-void loop()
-{
-  reading = digitalRead(inPin);
+void loop() {
+  buttonState = digitalRead(buttonPin);
 
-  // if we just pressed the button (i.e. the input went from LOW to HIGH),
-  // and we've waited long enough since the last press to ignore any noise...  
-  if (reading == HIGH && previous == LOW && millis() - time > debounce) {
-    // ... invert the output
-    if (state == HIGH)
-      state = LOW;
-    else
-      state = HIGH;
-
-    // ... and remember when the last button press was
-    time = millis();    
+  // check to see if you just pressed the button 
+  // (i.e. the input went from LOW to HIGH),  and you've waited 
+  // long enough since the last press to ignore any noise:  
+  if ((buttonState == HIGH) && 
+    (lastButtonState == LOW) && 
+    (millis() - lastDebounceTime) > debounceDelay) {
+    // toggle the output
+    if (ledState == HIGH) {
+      ledState = LOW;
+    } else {
+      ledState = HIGH;
+    }
+    // ... and store the time of the last button press
+    // in a variable:
+    lastDebounceTime = millis();    
   }
 
-  digitalWrite(outPin, state);
+  // set the LED using the ledState variable:
+  digitalWrite(ledPin, ledState);
 
-  previous = reading;
+  // save the buttonState.  Next time through the loop,
+  // it'll be the lastButtonState:
+  lastButtonState = buttonState;
 }