Encoder values only moving in one direction on one motor, totally fine on the other

[garberchov]

Hi, I have two motors plugged into an arduino mega as shown in the diagram below however when I rotate motor b it works totally fine and the encoder shows the increase or decrease in values, however, for it just decreases without stop. does anybody know why this might happen and how to fix it? Code and pinout below.

Code:

#include <Arduino.h>

#define ENC1A 3
#define ENC1B 2

#define ENC2A 20
#define ENC2B 21


int apos = 0;
int bpos = 0;

void readEncoderA()
{
	int a = digitalRead(ENC2A);
	if(a>0){
		apos++;
	}
	else {
		apos--;
	}
}

void readEncoderB()
{
	int b = digitalRead(ENC2B);
	if(b>0){
		bpos++;
	}
	else {
		bpos--;
	}
}

void setup() 
{
	Serial.begin(9600);
	pinMode(ENC2A, INPUT);
	pinMode(ENC2B, INPUT);
	pinMode(ENC1A, INPUT);
	pinMode(ENC1B, INPUT);
	attachInterrupt(digitalPinToInterrupt(ENC1A), readEncoderA, RISING);
	attachInterrupt(digitalPinToInterrupt(ENC2A), readEncoderB, RISING);
}

void loop()
{
	Serial.println("A Pos = " + String(apos) + " B pos = " + String(bpos));
}

[groundFungus]

Check the connections of the A and B pins from the encoder. If the processor gets only the A or only the B it can still count, but has not way to know direction.

[groundFungus]

I don't know about your method for reading the encoder. It does not look right.

Do you have a data sheet on the motor that shows the encoder output type?

[garberchov]

Attached is data sheet. It works fine for me, but maybe I am doing something wrong I don't even know about. How would I check the A+B pins, I have tried changing the jumper wires and using different pins on the board with no luck.

[jremington]

@garberchov

How would I check the A+B pins

Use your multimeter to read out the logic levels on each of the encoder outputs, as you very slowly rotate the motor shaft by hand. Are they what you expect?

[garberchov]

The voltage does go up and down, but I don't know what that is supposed to prove?

[jremington]

It is pretty hard to debug a problem like this if you don't know what to expect. Study this tutorial to learn how quadrature encoders work.

In summary, a quadrature encoder has two pins, and two voltages. The voltages should go "up and down" as the shaft rotates, according to this diagram:

If they don't, there is a wiring problem, or a defective encoder.

Finally, have you checked whether ENC1A and ENC2A pins actually support rising edge interrupts?

Edit: I just noticed that you violated two important rules. Variables shared with interrupt routines MUST be declared volatile, and protected from corruption by the interrupt, when accessed by the main routine.

volatile int apos = 0;
volatile int bpos = 0;

...
noInterrupts();
int apos_copy=apos;
int bpos_copy=bpos;
interrupts();

Serial.print("A Pos = ");
Serial.print(apos_copy);  //avoid using Strings!
Serial.print(" B pos = ");
Serial.println(bpos_copy);

[Juraj]

ENC1A -> ENC2A and ENC2A -> ENC2B ? where should be the ENC1B? the encoders have A and B pin and you named the encoders A and B?

maybe use the Encoder library

[garberchov]

This was the problem, not sure how I didn't spot it but thanks for the help