Calculation error with Optical Encoder

Question

I have corrected my code for reading the optical encoder index but I am now getting a different calculation error. At the index the encoder reset's to zero but now my readouts are as follows: Index point - resets to zero. - At the 90 degree rotation mark I have a readout of 180 degrees. - At the 180 degree rotation mark I have a readout of 0 because the code has it reset to zero after 359 degrees. - At the 270 degree rotation mark I have a readout of 180 degrees. - At the 0 degree mark it is zero again and that's what I would expect from the index. If I restart the Arduino Mega at the 270 degree mark, the index resets itself to zero like it should. Being new to this, before I had the index working it was working correctly minus the index function, now it seems to be double counting. Any ideas?

// Wiring connections for my encoder:
// Brown : VCC = 5V
// Blue + Shield : 0V = GND
// Black : ENCODER0PINA, Pin 20
// White : ENCODER0PINB, Pin 17
// Orange : ENCODER0PINI, Pin 19
#define ENCODER0PINA 20 // this pin needs to support interrupts
#define ENCODER0PINB 17 // no interrupt required
#define ENCODER0PINI 19 // this pin needs to support interrupts
// variables modified by interrupt handler must be declared as volatile
volatile long encoder0Position = 0;
volatile long interruptsReceived = 0;
volatile byte INTFLAG1 = 0;
// track last position so we know whether it's worth printing new output
long previousPosition = 0;
void setup()
{
 // inputs
 pinMode(ENCODER0PINA, INPUT);
 digitalWrite(ENCODER0PINA, HIGH); // turn on pullup resistor
 pinMode(ENCODER0PINB, INPUT);
 digitalWrite(ENCODER0PINB, HIGH); // turn on pullup resistor
 pinMode(ENCODER0PINI, INPUT);
 digitalWrite(ENCODER0PINI, HIGH); // turn on pullup resistor
 // interrupts
 attachInterrupt(3, onInterrupt, CHANGE); // encoder track A on interrupt 3 - pin 20
 attachInterrupt(4, onReset, CHANGE); // encoder Index track on interrupt 4 - pin 19
 // enable diagnostic output
 Serial.begin (115200);
 Serial.println("Ready.");
}
void loop()
{
 // only display position info if has changed
 if (encoder0Position != previousPosition )
 {
 Serial.println(encoder0Position, DEC);
 previousPosition = encoder0Position;
 }
}
// interrupt function needs to do as little as possible
void onReset()
{
 // read Index input
 int i = digitalRead(ENCODER0PINI);
 if (i == 1)
 {
 encoder0Position = INTFLAG1;
 }
}
void onInterrupt()
{
 // read both directional inputs
 int a = digitalRead(ENCODER0PINA);
 int b = digitalRead(ENCODER0PINB);
 if (a == b)
 {
 // b is leading a (counter-clockwise)
 encoder0Position--;
 if (encoder0Position < 0)
 {
 encoder0Position = (encoder0Position + 360);
 }
 }
 else
 {
 // a is leading b (clockwise)
 encoder0Position++;
 if (encoder0Position >= 360)
 {
 encoder0Position = (encoder0Position - 360);
 }
 }
}

• jsotola: please format your code as "code" .... highlight all the code text and click the {} button
• Delta_G: I did it for him/her.
• Bkukuk62: Thank you, I was wondering how to get the code to format as "code". (him).
• evolutionizer: What is the encoder that you are using? Does it have a 0.5 degree increment?
• Bkukuk62: It is a Omron E6B2-CWZ6C Incremental Rotary Encoder w/Index (360P/R).

Answer 1

I have figured out my issue, at least I am getting good results. With this code I had to change interrupts from CHANGE to RISING. I want to thank everyone that has made comments on this question. –