So, first of all I just want to point out this code is from: Reading Rotary Encoders and is not mine.

I have a magnetic shaft encoder mounted on a regular DC motor, my problem is that I cannot receive the exact angle of the motor. The encoder outputs +1 each 90 degrees (I then multiply by 90). And is there any relationship between valx, valy, valz and the angle?

#define encoder0PinA 2
#define encoder0PinB 3
int rounds= 0;
volatile unsigned int encoder0Pos = 0;
unsigned int tmp_Pos = 1;
unsigned int valx;
unsigned int valy;
unsigned int valz;

boolean A_set;
boolean B_set;

int enA = 9;
int in1 = 10;
int in2 = 11;

void setup() {

  pinMode(encoder0PinA, INPUT); 
  pinMode(encoder0PinB, INPUT); 
  // encoder pin on interrupt 0 (pin 2)
  attachInterrupt(0, doEncoderA, CHANGE);

  // encoder pin on interrupt 1 (pin 3)
  attachInterrupt(1, doEncoderB, CHANGE);
  Serial.begin( 9600 );

  pinMode(enA, OUTPUT);

  pinMode(in1, OUTPUT);
  pinMode(in2, OUTPUT);
  digitalWrite(in1, HIGH);
  digitalWrite(in2, LOW); 
  analogWrite(enA, 225);
  Serial.begin (9600);

void loop(){ 
//Check each second for change in position

  if (tmp_Pos != encoder0Pos) {
    Serial.print("Index:"); Serial.print(encoder0Pos * 90,DEC);
    tmp_Pos = encoder0Pos;

// Interrupt on A changing state
void doEncoderA(){

  // Low to High transition?
  if (digitalRead(encoder0PinA) == HIGH) { 
    A_set = true;
    if (!B_set) {
      encoder0Pos = encoder0Pos + 1;

  // High-to-low transition?
  if (digitalRead(encoder0PinA) == LOW) {
    A_set = false;

// Interrupt on B changing state
void doEncoderB(){

  // Low-to-high transition?
  if (digitalRead(encoder0PinB) == HIGH) {   
    B_set = true;
    if (!A_set) {
      encoder0Pos = encoder0Pos - 1;

  // High-to-low transition?
  if (digitalRead(encoder0PinB) == LOW) {
    B_set = false;
  • 1
    Provide a link to the rotary encoder used. Commented Feb 20, 2016 at 23:40
  • Wiring? Picture?
    – Dave X
    Commented Mar 9, 2016 at 16:15
  • 1
    If the motor speed is fairly steady with only gradual speed up slowdown, you may be able to model it with a software locked loop running faster and adjusted to match the timing of the four pulses you do get. You can then use that to interpolate the likely position at any point in time to a higher resolution. Commented Aug 6, 2016 at 19:20

1 Answer 1


If the encoder only gives +1 pulse per 90 degrees, you aren't going to get better than 90 degree accuracy out of it.

In the example code at the link, the val{x,y,z} are measured analog variables of some other thing that are sampled at each encoder lcoation:

My project is a data loger where three analogue inputs are sampled each time a rotary encoder pulse steps clockwise. On an Arduino, time is of the essence to get this data sampled and saved somewhere (I have not included the 'saving somewhere' part of this project yet.) In order to save some processor cycles, I have slightly redesigned the interrupt system to maintain a pair of boolean states outside of the interrupt loop.

These are not directly related to the positioning of the encoder, and there is no reason to think they provide angle information.

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