Timer-Interrupt-Encoders.ino

Timer-Interrupt-Encoders

This example reads multiple encoders using a timer interrupt, on an Arduino Uno or Nano.

Boards: 🛈

AVR

The ATmega328P microcontroller only has two interrupt pins (2 and 3), so if you want to use more than two interrupt-driven encoders, you'll either have to use a timer interrupt to continuously poll the encoders, or use the chip's pin change interrupts. This example demonstrates the former.

See also

Pin-Change-Interrupt-Encoders.ino

Familiarity with direct port manipulation is assumed.

Connections

Connect three encoders to the pins of port C as follows:

• A0: pin A of encoder #0
• A1: pin B of encoder #0
• A2: pin A of encoder #1
• A3: pin B of encoder #1
• A4: pin A of encoder #2
• A5: pin B of encoder #2

Connect the common pins to ground, the internal pull-up resistors will be enabled.

Behavior

When the position of one of the encoders changes, it is printed to the Serial monitor.

Written by PieterP, 2021-08-11
https://github.com/tttapa/Arduino-Helpers

 
#include <Arduino_Helpers.h>
#include <AH/Hardware/RegisterEncoders.hpp>
#include "TimerHelpers.hpp"
 
// The number of encoders to read:
constexpr uint8_t num_enc = 3;
// Mask the bottom 6 bits of the GPIO registers (2 pins × 3 encoders).
// This determines which pins are used:
const uint8_t pin_mask = 0x3F;
// The actual encoder object that keeps track of the encoder state:
RegisterEncoders<uint8_t, num_enc, int32_t, true> encoders;
// AVR uses 8-bit GPIO registers, so the register type is uint8_t.
// Then we specify the number of encoders, the position type,
// and whether the encoders should be interrupt-safe: since we'll
// be calling `encoders.update()` in an interrupt handler, it is 
// important that this is set to true.
 
// Timer interrupt handler that reads the pins and updates the state:
ISR (TIMER2_COMPA_vect) { encoders.update(PINC & pin_mask); } // read port C
 
void setup() {
  DDRC &= ~pin_mask; // input mode for port C
  PORTC |= pin_mask; // enable pull-up resistors for port C
  setTimer2Prescaler(Timer2Prescaler::S8);
  setTimer2WGMode(Timer2WGMode::CTC);
  OCR2A = 250 - 1; // 8 kHz poll rate (if FCPU = 16'000'000)
  bitSet(TIMSK2, OCIE2A); // Timer2 Compare A Match Interrupt Enable
  Serial.begin(115200);
}
 
void loop() {
  // The previous position of each encoder, to detect changes:
  static int32_t prevPos[num_enc] {};
 
  // Read the encoder positions and print if they changed:
  for (uint8_t i = 0; i < num_enc; ++i) {
    int32_t newPos = encoders[i].read();
    if (newPos != prevPos[i]) {
      Serial << '[' << i << "] " << newPos << endl;
      prevPos[i] = newPos;
    }
  }
}