Optical Rotary Encoder

Hey everyone,
I am willing to measure angle of a boom, when it is lifted from it's pivot point. For this purpose, I thought of using optical rotary encoder, as CW and CCW counter, thus giving me required pulses. But i can not make the programme work as it keeps on counting on its own.
here is my code.

int led = 13; // just to check my condition
int cw=2; // Encoder pin A at 2
int ccw=4; // Encoder pin B at 4
int valP=0; // to read A which is positive direction or cw
int counter=0;
int valN=0; // to read B which is in negative direction or ccw

void setup(){
pinMode(led, OUTPUT); // declaring to see change
pinMode(cw, INPUT_PULLUP);

void loop(){
valP = digitalRead(cw); // read input value as direction
valN = digitalRead(ccw);
if (valP=HIGH && valP!=valN)
if (valN=HIGH && valN==valP)
digitalWrite(led, HIGH);
digitalWrite(led, LOW);

Pls explain what wrong am i doing?

I haven't the energy on a lazy Sunday afternoon to examine your code 8) , but you might fine my code here useful.

My encoder model is PRI50R8 LTP 360 Z v3.
i have seen the data sheet, but i really cant find this cyclesPerRev.


i really cant find this cyclesPerRev.

Can't you count them?

The circuit in my thread that I linked, uses LEDs to show the status of each channel.

are these pulse per revolution?
here is the data sheet of my encoder.

How are you powering the encoder, and if separately from the Arduino, have you connected the grounds together?

if (valP=HIGH && valP!=valN)
if (valN=HIGH && valN==valP)

You need == where you have =

well, @ jremington......I have the ground common, but it didn't make any difference. And yes, I have an LED attached with the pins 2 and 3. They keep on blinking but pretty much dim, even if am not rotating the shaft.
This encoder is totempole type encoder, which is actually putting a glitch in my mind.

@ cattledog, I tried that. the counter gives i dont know what language and keeps on going in serial monitor.


Please take a look at the Arduino Playground tutorial on rotary encoders


The error that you are making is that you need to detect when PinA or PinB changes state.

Example 1 is using your approach of testing whether or not the two pins are the same or different after pinA changes from low to high.

int val; 
 int encoder0PinA = 3;
 int encoder0PinB = 4;
 int encoder0Pos = 0;
 int encoder0PinALast = LOW;
 int n = LOW;

 void setup() { 
   pinMode (encoder0PinA,INPUT);
   pinMode (encoder0PinB,INPUT);
   Serial.begin (9600);

 void loop() { 
   n = digitalRead(encoder0PinA);
   if ((encoder0PinALast == LOW) && (n == HIGH)) {
     if (digitalRead(encoder0PinB) == LOW) {
     } else {
     Serial.print (encoder0Pos);
     Serial.print ("/");
   encoder0PinALast = n;

This algorithm counts only 1/4 of the available quadrature counts, which may be sufficient for your encoder and the resolution you require. Once you understand this basic code, you can uses other algorithms which test for rising and falling changes on one or both pins, and read, 1,2, or all 4 of the available quadrature counts.

To control the serial printing, you need to print only after the count changes, or perhaps with your application only the max counts on either side. Please be aware that the serial printing is slow, and may not keep up with your counts, or may cause you to miss some counts.

For now, move the encoder slowly, and work to understand the fundamentals of the quadrature states and the counts.

Thanks all