add rotary encoder sample code from arduino playground

src/rotary.cpp.txt

@@ -0,0 +1,90 @@
+ /* interrupt routine for Rotary Encoders
+   tested with Noble RE0124PVB 17.7FINB-24 http://www.nobleusa.com/pdf/xre.pdf - available at pollin.de
+   and a few others, seems pretty universal
+
+   The average rotary encoder has three pins, seen from front: A C B
+   Clockwise rotation A(on)->B(on)->A(off)->B(off)
+   CounterCW rotation B(on)->A(on)->B(off)->A(off)
+
+   and may be a push switch with another two pins, pulled low at pin 8 in this case
+   raf@synapps.de 20120107
+
+*/
+
+// usually the rotary encoders three pins have the ground pin in the middle
+enum PinAssignments {
+  encoderPinA = 2,   // right
+  encoderPinB = 3,   // left
+  clearButton = 8    // another two pins
+};
+
+volatile unsigned int encoderPos = 0;  // a counter for the dial
+unsigned int lastReportedPos = 1;   // change management
+static boolean rotating = false;    // debounce management
+
+// interrupt service routine vars
+boolean A_set = false;
+boolean B_set = false;
+
+
+void setup() {
+  pinMode(encoderPinA, INPUT);
+  pinMode(encoderPinB, INPUT);
+  pinMode(clearButton, INPUT);
+  // turn on pullup resistors
+  digitalWrite(encoderPinA, HIGH);
+  digitalWrite(encoderPinB, HIGH);
+  digitalWrite(clearButton, HIGH);
+
+  // encoder pin on interrupt 0 (pin 2)
+  attachInterrupt(0, doEncoderA, CHANGE);
+  // encoder pin on interrupt 1 (pin 3)
+  attachInterrupt(1, doEncoderB, CHANGE);
+
+  Serial.begin(9600);  // output
+}
+
+// main loop, work is done by interrupt service routines, this one only prints stuff
+void loop() {
+  rotating = true;  // reset the debouncer
+
+  if (lastReportedPos != encoderPos) {
+    Serial.print("Index:");
+    Serial.println(encoderPos, DEC);
+    lastReportedPos = encoderPos;
+  }
+  if (digitalRead(clearButton) == LOW )  {
+    encoderPos = 0;
+  }
+}
+
+// Interrupt on A changing state
+void doEncoderA() {
+  // debounce
+  if ( rotating ) delay (1);  // wait a little until the bouncing is done
+
+  // Test transition, did things really change?
+  if ( digitalRead(encoderPinA) != A_set ) { // debounce once more
+    A_set = !A_set;
+
+    // adjust counter + if A leads B
+    if ( A_set && !B_set )
+      encoderPos += 1;
+
+    rotating = false;  // no more debouncing until loop() hits again
+  }
+}
+
+// Interrupt on B changing state, same as A above
+void doEncoderB() {
+  if ( rotating ) delay (1);
+  if ( digitalRead(encoderPinB) != B_set ) {
+    B_set = !B_set;
+    //  adjust counter - 1 if B leads A
+    if ( B_set && !A_set )
+      encoderPos -= 1;
+
+    rotating = false;
+  }
+}
+