Execution time with a rotary encoder

Projects General Guidance
1

Hi all! Having a problem with using rotary encoder. I'm updating a counter with a rotary encoder and displaying the value on a display. I'm having trouble figuring out how to read the encoder's value without being influenced by the execution time of the display (at least I believe this is what's happening).

When I turn the encoder slowly, it works great but when I go too fast, it skips some steps, like if the contact time was during the display update execution and the Arduino doesn't get it. I'm still a bit new to this so I might be in the wrong direction here :stuck_out_tongue:

Here's the sketch :

#include <U8g2lib.h>;

U8G2_SH1107_PIMORONI_128X128_F_HW_I2C u8g2(U8G2_R0, 21, 20);

bool a_value;
bool b_value;
bool a_last_value;
volatile long counter_value = 0;

void update_rotary_encoder() {
  a_value = digitalRead(2);
  b_value = digitalRead(3);

  // if the A value has changed and == 1
  if (a_value != a_last_value && a_value) {
    // check if going forward or backwards
    if (a_value != b_value) {
      counter_value++;
    } else {
      counter_value--;
    }
  }
  a_last_value = a_value;
}

void setup() {
  Serial.begin(9600);

  pinMode(2, INPUT);
  pinMode(3, INPUT);

  // setup the display
  u8g2.begin();
  u8g2.setFont(u8g2_font_6x10_mf);

  // display the initial counter value
  u8g2.clearBuffer();
  u8g2.setCursor(4, 124);
  u8g2.print(counter_value);
  u8g2.sendBuffer();

  // set the initial A value
  a_last_value = digitalRead(2);

  // set interrupts for the 2 encoder values
  attachInterrupt(digitalPinToInterrupt(2), update_rotary_encoder, CHANGE);
  attachInterrupt(digitalPinToInterrupt(3), update_rotary_encoder, CHANGE);
}

void loop() {

  // display the counter value
  u8g2.clearBuffer();
  u8g2.setCursor(4, 124);
  u8g2.print(counter_value);
  u8g2.updateDisplayArea(0, 14, 4, 2);
}

I've tried not using the interrupts and manually checking every loop for a value change but it doesn't get better.

EDIT :
I removed the second condition in the IF statement to have only

if (a_value != a_last_value) { ... }

and now it works perfectly except that it counts in doubles. I figure this is because it's now counting the start of stepping AND the end of stepping, so basically anytime the A value changes.

Any clue why the storing and comparing of the last A value would change something in the execution time enough to skip some values..?

2

Plot the four quadrant pulsetrain. Decide the points for upcount resp downcount.
I did that 35 years ago but the details lay too deep down in the memory.
Especially handling the logic when the direction is changed is sometimes important, sometimes not.

3

Well you are doing twice the amount of work for a start.

Plus this is a very poor way of reading a rotary encoder. Basically mechanical rotary bounce, but the protocol allows for an auto debounce protocol using a state machine You need a good library and I have found this one very good at doing things.

http://www.pjrc.com/teensy/td_libs_Encoder.html

4

Rotary encoder mechanical or optical??

5

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