Problem with encoder readings

Dc1991 · September 16, 2015, 6:19pm

Hi everyone!!

I am using this motor with encoder which gives 8400 counts per revolution of the output shaft of the motor.

I have written simple program to stop the motor after one revolution of the shaft. Below is the code:

#define encoder0PinA 2
#define encoder0PinB 3
int EnablePin = 8;
int PWMPin1 = 11;
int PWMPin2 = 10;
volatile signed int encoder0Pos = 0;


void setup()
{
  pinMode(encoder0PinA, INPUT);
  pinMode(encoder0PinB, INPUT);
  pinMode(EnablePin, OUTPUT);
  pinMode(PWMPin1, OUTPUT);
  pinMode(PWMPin2, OUTPUT);
  attachInterrupt(0, doEncoderA, CHANGE);
  attachInterrupt(1, doEncoderB, CHANGE);
  
  Serial.begin(115200);
}

void rotateCCW()
{
  digitalWrite(EnablePin, HIGH);
  analogWrite(PWMPin2,0);
  analogWrite(PWMPin1,50);
  delay(20);
}
void rotateCW()
{
  digitalWrite(EnablePin, HIGH);
  analogWrite(PWMPin2,10);
  analogWrite(PWMPin1,0);
  delay(20);
}
void motorSTOP()
{
  digitalWrite(EnablePin, LOW);
  delay(20);
}

void doEncoderA(){

  // look for a low-to-high on channel A
  if (digitalRead(encoder0PinA) == HIGH) { 

    // check channel B to see which way encoder is turning
    if (digitalRead(encoder0PinB) == LOW) {  
      encoder0Pos++;         // CW
    } 
    else {
      encoder0Pos--;         // CCW
    }
  }

  else   // must be a high-to-low edge on channel A                                       
  { 
    // check channel B to see which way encoder is turning  
    if (digitalRead(encoder0PinB) == HIGH) {   
      encoder0Pos++;          // CW
    } 
    else {
      encoder0Pos--;          // CCW
    }
  }

}

void doEncoderB()
{
  // look for a low-to-high on channel B
  
  if (digitalRead(encoder0PinB) == HIGH) {   
    // check channel A to see which way encoder is turning
    if (digitalRead(encoder0PinA) == HIGH) {  
      encoder0Pos++;         // CW
    } 
    else {
      encoder0Pos--;;         // CCW
    }
  }

  // Look for a high-to-low on channel B

  else { 
    // check channel B to see which way encoder is turning
    
    if (digitalRead(encoder0PinA) == LOW) {   
      encoder0Pos++;          // CW
    } 
    else {
      encoder0Pos--;          // CCW
    }
  }

} 


void loop()
{

 if(encoder0Pos<=8400)
 {
    rotateCCW();
    doEncoderA();
    doEncoderB();
    Serial.println(encoder0Pos);
   
 }
 
 else
 {
   motorSTOP();
 }

}

After running the code motor does stop after one revolution. The problem is with the encoder reading. Below is the reading I received:

As you can see readings jumps a lot.I am not getting continuous readings. I can't figure out the problem here. I know I am going somewhere wrong in coding (I just started to learn ).

Any suggestions?

dsauriol · September 16, 2015, 9:30pm

Hi Dc1991,

I have taken the encoder values and pasted them into an excel file
The number of steps between each reading seems to be pretty constant (always between 41-42).
We can see a ramp up in speed when the motor initially starts, but after that, everything stabilises.

You are indeed getting 8400 ticks for one turn of the shaft motor, so I would believe that there are no issues.
I think you were expecting the encoder readings to follow the previous one (323, 324, 325, etc), but I think the encoder receives several "ticks" between each time you "poll"/"read" the encoder value.

If you'd poll/read more (or less) frequently, the value between each reading would obviously be different ...

I know next to nothing about encoder, so I could definitely be in left field !

I hope it helps !!!

NOTE : The forum software gave me a message indicating that xls files are not accepted.
However, you can easily do what I did, i.e. paste all of the values in one single column and have the second column indicate the difference between the previous reading..... Sorry about that !!!
Finally, I pasted the excel file in a TXT file, so at least you can analyze the difference between each readings, and see that they are quite consistent, which means that the motor rotates at a steady speed during that single turn...

dan

encoder values.txt (1.99 KB)

cattledog · September 16, 2015, 10:14pm

I know I am going somewhere wrong in coding (I just started to learn ).

Any suggestions?

You are not understanding, or using the interrupts and the interrupt service routines (isr) properly. Take a look at Nick Gammon's excellent tutorial on interrupts Gammon Forum : Electronics : Microprocessors : Interrupts

The interrupts call the interrupt service routines(do EncoderA(), doEncoderB()) every time pin 2 or 3 changes state. The value of encoder0pos will increase or decrease.

You do not call the isr functions in the loop like you are doing. They are called in the background by the interrupts.

You do need to get the value of encoder0pos to use in your program. When you read the value, interrupts should be disabled to prevent the possibility of the value changing while being read.

The counts will not increase by one because you have delays built into the motor driver routines and Serialprint() also takes time, but the motor is still turning and the counts are increasing or decreasing.

Your loop should look like this

void loop()
{
noInterrupts();
signed int copyEncoder0Pos = encoder0Pos;
Interrupts();

 if(copyEncoder0Pos<=8400)
 {
    rotateCCW();
    //doEncoderA();
   // doEncoderB();
    Serial.println(copyEncoder0Pos);
   
 }
 
 else
 {
   motorSTOP();
 }

}

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Problem with encoder readings

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