OneButton Library

For processors with very limited memory and low CPU frequencies (like the ATtiny84), use the OneButtonTiny class. It provides a subset of features to save up to 1k of binary program space.

Supported events in OneButtonTiny:

• Click event
• DoubleClick event
• LongPressStart event
• Callbacks without parameters

For the library to detect events, you must call tick() on every OneButton instance inside your main loop() function.

void loop() {
  btn.tick();
  // Do other things...
}

Standard C++ function pointers do not support lambdas with captured variables. To use a lambda that captures context (like this), use the parameterized callback pattern. Pass the context pointer to the library, which will then pass it back to your lambda.

// Using 'this' as context
okBtn.attachClick([](void *ctx){ 
  Serial.println(*((BtnHandler*)ctx)->state); 
}, this);

You can install the OneButton library by cloning the repository into your Arduino/Libraries folder or by using the built-in Arduino IDE Library Manager.

#include <Arduino.h>
#include <OneButton.h>

The library relies on a Finite State Machine (FSM) that must be updated regularly. You must call the tick() method in your loop() function to process button states and trigger events. To ensure responsive detection, avoid using delay() in the main loop, as it prevents tick() from running frequently enough.

void loop() {
  btn.tick();  // Must be called regularly
  // Other non-blocking code...
}

To ensure proper hardware initialization and maximum compatibility, avoid initializing the button during instance creation. Instead, declare the OneButton object globally and call .setup() within the Arduino setup() function.

Parameters for setup(pin, mode, activeLow):

• pin: The digital input pin number.
• mode: The pin mode (e.g., INPUT_PULLUP).
• activeLow: A boolean indicating if the button is active low (true) or active high (false).

// Declaration
OneButton btn;

// In setup()
btn.setup(BUTTON_PIN, INPUT_PULLUP, true);  // pin, mode, activeLow

To manage multiple buttons efficiently, you can use an array of OneButton instances and pass a unique identifier (like the index) to a parameterized callback using (void*)index.

#define NUM_BUTTONS 3
OneButton buttons[NUM_BUTTONS];
int btn_pins[NUM_BUTTONS] = {2, 3, 4};

void setup() {
  for (int i = 0; i < NUM_BUTTONS; i++) {
    buttons[i].setup(btn_pins[i], INPUT_PULLUP, true);
    buttons[i].attachClick(handleButtonClick, (void*)i);
  }
}

void loop() {
  for (int i = 0; i < NUM_BUTTONS; i++) {
    buttons[i].tick();
  }
}

void handleButtonClick(void *param) {
  int buttonId = (int)param;
  // Handle click for specific buttonId
}

You can handle button events by attaching static functions or lambdas (without captured variables) to the button instance.

For attachMultiClick, you can pass a pointer to the OneButton instance itself as a parameter to the handler function to access button metadata like the pin number or debounced value.

// Static function handler
static void handleClick() {
  Serial.println("Clicked!");
}

// Attach static function
btn.attachClick(handleClick);

// Attach lambda (no capture)
btn.attachDoubleClick([]() {
  Serial.println("Double Pressed!");
});

// MultiClick with self-pointer
static void handleMultiClick(OneButton *oneButton) {
  Serial.println(oneButton->pin());
}
btn.attachMultiClick(handleMultiClick, &btn);