Control Surface main
MIDI Control Surface library for Arduino
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:

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 "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;
}
}
}
Dummy header file for Arduino builder.
Print & endl(Print &printer)
Definition: PrintStream.cpp:27