Don't forget the pull-up resistors!

On the Arduino, you can use the internal resistors by defining your inputs with INPUT_PULLUP.

This is my code to use it:

 #define rotaryA 2
 #define rotaryB 3
 #define LED 13

 volatile int stateA = LOW;
 volatile int stateB = LOW;
 volatile int counter = 0;
 volatile int lastCounter = 0;

 void setup() { 
   pinMode (rotaryA, INPUT_PULLUP);
   pinMode (rotaryB, INPUT_PULLUP);
   pinMode (LED, OUTPUT);

   Serial.begin (9600);

   attachInterrupt(digitalPinToInterrupt(rotaryA), changeA, CHANGE);
   attachInterrupt(digitalPinToInterrupt(rotaryB), changeB, CHANGE);

   stateA = digitalRead(rotaryA);
   stateB = digitalRead(rotaryB);
 } 
 void loop() {
   digitalWrite(LED, stateA);

   if (counter != lastCounter) {
    Serial.println(counter);
    lastCounter = counter;
   }
 }

 void changeA() {
   stateA = !stateA;

   if (stateA == HIGH) {
     if (stateB == LOW ) {
       counter++;
       if (counter == 200) {
         counter = 0;
       }
     } else {
         counter--;
         if (counter == -1) {
           counter = 199;
         }
     }
 }

 void changeB() {
   stateB = !stateB;
 }

I´m trying to read the encoder with the Arduino and everything is okay. But when I read an analog signal the arduino only reads the analog input. I connect both GND, but its still not reading. Does anyone know how can I fix this? Thanks

as opposed to the example above, here's some code that will get this working right-away in true quadrature fashion. [model #E6A2-CW3C]

sorry if it is wrong to post this here, but it's free to the world, have spark-fun!

// code start

[put pound sign here!]include "digitalWriteFast.h" // google this and install it

const byte pin_A =  2; // connect white wire here
const byte pin_B =  3; // connect black wire here
int A_set =         0;
int B_set =         0;
long pulses =       0;


void setup()
{
  pinMode(pin_A, INPUT);
  digitalWrite(pin_A, HIGH); // enables pull-up resistor
  pinMode(pin_B, INPUT);
  digitalWrite(pin_B, HIGH); // enables pull-up resistor  

  A_set = digitalRead(pin_A);
  B_set = digitalRead(pin_B);

  attachInterrupt(0, encoderPinChange_A, CHANGE); // pin 2
  attachInterrupt(1, encoderPinChange_B, CHANGE); // pin 3

  Serial.begin(115200);  
}


void loop()
{
  Serial.println(pulses);
}


void encoderPinChange_A()
{
  A_set = digitalReadFast2(pin_A) == HIGH;
  pulses += (A_set != B_set) ? +1 : -1;
}


void encoderPinChange_B()
{
  B_set = digitalReadFast2(pin_B) == HIGH;
  pulses += (A_set == B_set) ? +1 : -1;
}

Great little encoder for the price. Here's my experience:

1. Easy hookup, especially since the wiring is documented on the encoder. Wish other products did this! Ground, +5, Out A and Out B. I wired the outputs to my Arduino interrupts, in the case of my Uno that's D2 and D3.

2. Don't forget the pullups between each output and +5! (I did at first.) The output is open collector and so won't go up to +5 otherwise. I used 10K.

3. I used the Quadrature encoder library QuadratureEncoder.h pretty much right out of Dr. Rainer Hessmer blog here. Thanks Dr. Hessmer!

4. In Arduino 1.0 Wprogram.h has been replaced by Arduino.h

5. In my sketch I copied the example usage from the library and added the following:

   Serial.println ( encoder.getPosition()); delay (10);

6. Don't forget to initialize the serial port in setup()

That's it! worked right away.

I'm having a hard time figuring out how to wire the shield wire. It says "Shield: GND" on the rotary encoder. But it's very confusing because the blue wire is "0V(Common)", which is what I connect the negative terminal of the power source to (I think). And the negative side is usually called "ground" right? So, Why is the shield called ground? And what do I connect that to? I'm planning to use an arduino mega with the encoder.

Hmm... Why is there a photo of 5 wires? This rotary encoder only comes with 4 wires, there is no yellow wire. I'm new to all this stuff, a wiring diagram would be fantastic

I played with an implementation of a quadrature encoder on Arduino and documented some of my understandings / learnings. Might help someone understand the basics...

Index tic would be nice.

Outputs gray code? What I could gather from the datasheet is that the encoder outputs quadrature signals, is that the case really?

how one could mount it on a DC motor?

This would of been very handy for when I converted my L1011 altitude encoder to digital output for flight simulation.. Better yet, a board that could interpret the 400hz ac resolvers that were originally inside the instrument would of been best!