button-events

Button Events

Button event module used to debounce a digital input signal and produce button action events.

The module provides a method that accepts a binary input state that is called each time an input changes. The module then uses timing and the last received input state to generate events to denote the user's intention.

Debounce logic is used to clean up noisy button signals and the module generates a variety of high level button event types, i.e. 'clicked', 'double_clicked', 'pressed', 'released', 'clicked_pressed'.

Usage

Create an instance of button-events for each button that requires events, add listeners for the desired button events, and call the gpioChange(value) method each time the button input state changes.

The gpioChange() method will return a status string to indicate how the value was handled.

• "disabled", The button event handler is disabled and will not process gpioChange() values.
• "debounced", The debounce timer is running and the input value has been updated with the last gpioChange() value.
• "accepted", The gpioChange() value has been accepted as the starting value and the debounce timer started.
• "final", The debounce timer is disabled and the gpioChange() value is accepted as the final value.

Example

const ButtonEvents = require('button-events');

// create event processor for up button
let upEvents = new ButtonEvents();
// watch for 'clicked' events on the up button
upEvents.on('clicked', () => {
  console.log('User clicked up.');
});

// each time gpio input for up button changes call the upEvents gpioChange() method
gpio.on('change', (value) => upEvents.gpioChange(value));

NOTE The example assumes the gpio object has been instantiated from some gpio library.

A cleanup() method is provided to disable a button events instance, remove all listeners and clear any active timers when the button events instance is no longer required.

Example

const ButtonEvents = require('button-events');

// create event processor for up button
let bevents = new ButtonEvents();
// watch for 'clicked' events on the up button
bevents.on('button_event', (type) => {
  console.log(`Button event type ${type}`);
});

// run for 30 seconds then cleanup
setTimeout(() => {
  bevents.cleanup();
}, 30000);

Debounce

When a hardware button is pressed or released it will initially produce an oscillating electrical signal before stabilizing at a set level. The oscillation of the signal will result in a bouncing value in the software that is monitoring the button signal.

A debounce algorithm in the software is used to eliminate the bounce by waiting for input stabilization after a specified amount of time. The first call to gpioChange(value) will record the value and start a timer for debounce stabilization. Each followup call to gpioChange(value) will update the recorded input value. When the timer completes the final recorded value is processed as the stabilized input value.

Use the debounce timing value to adjust the debounce timer as needed for the hardware used.

Configuration

The constructor for the button-events instance accepts a configuration object to adjust the operation of the event processor.

Example:

let bevents = new ButtonEvents({
  usePullUp: true,
  timing: {
    debounce: 30, // milliseconds to debounce input
    pressed: 200, // milliseconds to wait until we assume the user intended a button press event
    clicked: 200  // milliseconds to wait until we assume the user intended a button clicked event
  }
});

usePullUp

Boolean used to specify if the button gpio input is configured with a pull up resistor. The default value is true which assumes the idle value for the input is 1 and when the button on the input is pressed the value is 0.

timing

The timing object in the configuration holds timing settings for the debounce logic and the delays used for button transitions to different states for clicked, double clicked, etc.

timing.debounce

The debounce timing value is the number of milliseconds to wait before assuming the input state has stabilized.

NOTE To disable debounce set the timing.debounce value to 0.

timing.pressed

Milliseconds to wait after a button is pressed before settling on a pressed type event.

timing.clicked

Milliseconds to wait after a button is released before settling on a clicked type event.

Events

The package provides a variety of high level button events to which an application can bind.

Possible events include the following...

Events that indicate user intent

• pressed
• clicked
• clicked_pressed
• double_clicked
• released

Unified event for user intent, passes the user event state

• button_event

Low level events

• button_changed
• button_press
• button_release

pressed

The pressed event is emitted when a button is pressed and held down. This will eventually be followed with a released event when the button is released.

buttons.on('pressed', function (pin) {
  console.log('User pressed button on pin ', pin);
});

clicked

When a button is pressed and released rapidly this is interpreted as a click and results in the emit of the clicked event.

buttons.on('clicked', function (pin) {
  console.log('User clicked button on pin ', pin);
});

clicked_pressed

If a clicked event is detected and quickly followed by pressing and holding the button then a clicked_pressed event will be emitted. Eventually when the button is released then a released event will be emitted.

buttons.on('clicked_pressed', function (pin) {
  console.log('User clicked then pressed button on pin ', pin);
});

double_clicked

If a clicked event is immediately followed with another clicked detection then it is interpreted as a double click and a double_clicked event is emitted.

buttons.on('double_clicked', function (pin) {
  console.log('User double clicked button on pin ', pin);
});

released

When one of the pressed type events is generated the button is placed in a state where it will wait for the user to release the pressed button. When this happens the released event is emitted.

buttons.on('released', function (pin) {
  console.log('User released button on pin ', pin);
});

button_event

The button_event event is a unified event triggered in combination with the user intent events and will pass the value of the user intent as an argument.

button.on('button_event', (type) => {
  switch (type) {
    case 'clicked':
    console.log('User clicked.');
    break;

    case 'double_clicked':
    console.log('User double clicked.');
    break;
  }
});

button_changed

This is a low level event and is only used in special circumstances. The button_changed event occurs anytime there is a button press or release. This event may be accompanied by the higher level events that detect user intention, i.e. clicked, double_clicked, etc.

button_press

This is a low level event and is only used in special circumstances. When the user presses a button the button_press event will occur. This may be accompanied by other high level events that detect user intent.

button_release

This is a low level event and is only used in special circumstances. A button_release event occurs whenever the user releases a button. This may be accompanied by other high level events that detect user intent.