Amazon Price History

http://camelcamelcamel.com/

Arduino Rotary Encoder

http://www.buxtronix.net/2011/10/rotary-encoders-done-properly.html
Implementation with and without external interrupt. Using two encoders is also possible.

Stepper Motor 28BYJ-48 5V

http://arduino.cc/forum/index.php/topic,71964.0.html
Gear ratio: (22X26X31X32)/(9X9X10X11) = 63.68395.    ( 283712/4455) 

Arduino Interrupt Software Debounce

Ref: http://www.dave-auld.net/index.php?option=com_content&view=article&id=107:arduino-interrupts&catid=53:arduino-input-output-basics&Itemid=107

int pbIn = 0;                  // Interrupt 0 is on DIGITAL PIN 2!

02.int ledOut = 4;                // The output LED pin

03.volatile int state = LOW;      // The input state toggle

04. 

05.void setup()

06.{               

07.// Set up the digital pin 2 to an Interrupt and Pin 4 to an Output

08.pinMode(ledOut, OUTPUT);

09. 

10.//Attach the interrupt to the input pin and monitor for ANY Change

11.attachInterrupt(pbIn, stateChange, CHANGE);

12.}

13. 

14.void loop()                    

15.{

16.//Simulate a long running process or complex task

17.for (int i = 0; i < 100; i++)

18.{

19.// do nothing but waste some time

20.delay(10);

21.}

22.}

23. 

24.void stateChange()

25.{

26.state = !state;

27.digitalWrite(ledOut, state); 

28.}