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bxparks
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Description

An adjustable, compact, event-driven button library for Arduino that debounces and dispatches events to a user-defined event handler.

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AceButton

AUnit Tests

An adjustable, compact, event-driven button library for Arduino platforms.

This library provides classes which accept inputs from a mechanical button connected to a digital input pin on the Arduino. The library should be able to handle momentary buttons, maintained buttons, and switches, but it was designed primarily for momentary buttons.

The library is named "AceButton" because:

  • many configurations of the button are adjustable, either at compile-time or run-time
  • the library is optimized to create compact objects which take up a minimal amount of static memory
  • the library detects changes in the button state and sends events to a user-defined
    EventHandler
    callback function

Most of the features of the library can be accessed through 2 classes, 1 callback function, and 1 interface:

  • AceButton
    (class)
  • ButtonConfig
    (class)
  • EventHandler
    (typedef)
  • IEventHandler
    (interface)

The

AceButton
class contains the logic for debouncing and determining if a particular event has occurred.

The

ButtonConfig
class holds various timing parameters, the event handler, code for reading the button, and code for getting the internal clock.

The

EventHandler
is a user-defined callback function with a specific signature which is registered with the
ButtonConfig
object. When the library detects interesting events, the callback function is called by the library, allowing the client code to handle the event.

The

IEventHandler
is an interface (pure abstract class) that provides an alternative to the
EventHandler
. Instead of using a callback function, an object of type
IEventHandler
can be used to handle the button events.

The supported events are:

  • AceButton::kEventPressed
  • AceButton::kEventReleased
  • AceButton::kEventClicked
  • AceButton::kEventDoubleClicked
  • AceButton::kEventLongPressed
  • AceButton::kEventRepeatPressed
  • AceButton::kEventLongReleased
    (v1.8)

The basic

ButtonConfig
class assumes that each button is connected to a single digital input pin. In some situations, the number of buttons that we want is greater than the number of input pins available. This library provides 2 subclasses of
ButtonConfig
which may be useful:
  • EncodedButtonConfig
    • Supports binary encoded buttons, to read
      2^N - 1
      buttons using
      N
      pins (e.g. 7 buttons using 3 digital pins).
  • LadderButtonConfig
    • Supports 5-8 buttons (maybe more) on a single analog pin through a resistor ladder. The
      analogRead()
      method is used to read the different voltage levels corresponding to each button.

Both

EncodedButtonConfig
and
LadderButtonConfig
support all 7 events listed above (e.g.
kEventClicked
and
kEventDoubleClicked
).

Version: 1.8.2 (2021-01-22)

Changelog: CHANGELOG.md

Table of Contents

Features

Here are the high-level features of the AceButton library:

  • debounces the mechanical contact
  • supports both pull-up and pull-down wiring
  • event-driven through a user-defined
    EventHandler
    callback function
  • event-driven through an object-based
    IEventHandler
    (>= v1.6)
  • supports 7 event types:
    • kEventPressed
    • kEventReleased
    • kEventClicked
    • kEventDoubleClicked
    • kEventLongPressed
    • kEventRepeatPressed
    • kEventLongReleased
  • adjustable configurations at runtime or compile-time
    • timing parameters
    • digitalRead()
      button read function can be overridden
    • millis()
      clock function can be overridden
  • small memory footprint
    • each
      AceButton
      consumes 14 bytes (8-bit) or 16 bytes (32-bit)
    • each
      ButtonConfig
      consumes 18 bytes (8-bit) or 24 bytes (32-bit)
    • one System
      ButtonConfig
      instance created automatically by the library
    • 970-2180 bytes of flash memory for the simple case of 1 AceButton and 1 ButtonConfig, depending on 8-bit or 32-bit processors
  • supports multiple buttons on shared pins using various circuits
  • only 13-15 microseconds (on 16MHz ATmega328P) per polling call to
    AceButton::check()
  • extensive testing
    • thoroughly unit tested using AUnit
    • tested on Arduino AVR (UNO, Nano, Micro etc), Teensy ARM (LC and 3.2), SAMD21 (Arduino Zero compatible), ESP8266 and ESP32

Compared to other Arduino button libraries, I think the unique or exceptional features of the AceButton library are:

  • many supported event types (e.g. LongPressed and RepeatPressed)
  • able to distinguish between Clicked and DoubleClicked
  • small memory usage
  • thorough unit testing
  • support for multiple buttons using Binary Encoding or a Resistor Ladder

HelloButton

Here is a simple program (see examples/HelloButton) which controls the builtin LED on the Arduino board using a momentary button connected to PIN 2.

#include 
using namespace ace_button;

const int BUTTON_PIN = 2; const int LED_ON = HIGH; const int LED_OFF = LOW;

AceButton button(BUTTON_PIN);

void handleEvent(AceButton*, uint8_t, uint8_t);

void setup() { pinMode(LED_BUILTIN, OUTPUT); pinMode(BUTTON_PIN, INPUT_PULLUP); button.setEventHandler(handleEvent); }

void loop() { button.check(); }

void handleEvent(AceButton* /button/, uint8_t eventType, uint8_t /buttonState/) { switch (eventType) { case AceButton::kEventPressed: digitalWrite(LED_BUILTIN, LED_ON); break; case AceButton::kEventReleased: digitalWrite(LED_BUILTIN, LED_OFF); break; } } </acebutton.h>

(The

button
and
buttonState
parameters are commented out to avoid an
unused
parameter
warning from the compiler. We can't remove the parameters completely because the method signature is defined by the
EventHandler
typedef.)

Installation

The latest stable release is available in the Arduino IDE Library Manager. Search for "AceButton". Click install.

The development version can be installed by cloning the GitHub repository (https://github.com/bxparks/AceButton), checking out the

develop
branch, then manually copying over the contents to the
./libraries
directory used by the Arduino IDE. (The result is a directory named
./libraries/AceButton
.)

The

master
branch contains the tagged stable releases.

External Dependencies

The core of the library is self-contained and has no external dependencies.

The some programs in

examples/
may depend on: * AceCommon (https://github.com/bxparks/AceCommon)

The unit tests under

tests
depend on: * AUnit (https://github.com/bxparks/AUnit)

Source Code

The source files are organized as follows: *

src/AceButton.h
- main header file *
src/ace_button/
- all implementation files *
src/ace_button/testing/
- internal testing files *
tests/
- unit tests which require AUnit *
examples/
- example sketches

Documentation

Examples

The following example sketches are provided:

  • HelloButton.ino
    • minimal program that reads a switch and control the built-in LED
  • SingleButton.ino
    • single button wired with an internal pull-up resistor
  • SingleButtonPullDown.ino
    • same as SingleButton.ino but with an external pull-down resistor
  • SingleButtonUsingIEventHandler.ino
    • same as SingleButton.ino using an object-based
      IEventHandler
  • Stopwatch.ino
    • measures the speed of
      AceButton:check()
      with a start/stop/reset button
    • uses
      kFeatureLongPress
  • Multiple Buttons
    • TwoButtonsUsingOneButtonConfig.ino
      • two buttons using one ButtonConfig
    • TwoButtonsUsingTwoButtonConfigs.ino
      • two buttons using two ButtonConfigs
    • TunerButtons.ino
      • implements 5 radio buttons (tune-up, tune-down, and 3 presets)
      • shows multiple
        ButtonConfig
        and
        EventHandler
        instances
      • shows an example of how to use
        getId()
      • uses
        kFeatureLongPress
        ,
        kFeatureRepeatPress
        ,
        kFeatureSuppressAfterLongPress
        , and
        kFeatureSuppressAfterRepeatPress
    • ArrayButtons
      • shows how to define an array of
        AceButton
        and initialize them using the
        init()
        method in a loop
  • distinguishing Click versus Double-Click
  • distinguishing Pressed and LongPressed
  • CapacitiveButton
  • Binary Encoded Buttons
    • Encoded8To3Buttons
      • demo of
        Encoded4To2ButtonConfig
        and
        Encoded8To3Buttonconfig
        classes to decode
        M=3
        buttons with
        N=2
        pins, or
        M=7
        buttons with
        N=3
        pins
    • Encoded16To4Buttons
      • demo of general M-to-N
        EncodedButtonConfig
        class to handle
        M=15
        buttons with
        N=4
        pins
  • Resistor Ladder Buttons
    • LadderButtons
      • demo of 4 buttons on a single analog pin using
        analogRead()
  • Benchmarks
    • These are internal benchmark programs. They were not written as examples of how to use the library.
    • AutoBenchmark.ino
      • generates the timing stats (min/average/max) for the
        AceButton::check()
        method for various types of events (idle, press/release, click, double-click, and long-press)
    • MemoryBenchmark.ino
      • determines the amount of flash memory consumes by various objects and features of the library

Usage

There are 2 classes and one typedef that a user will normally interact with:

  • AceButton
    (class)
  • ButtonConfig
    (class)
  • EventHandler
    (typedef)

Advanced usage is supported by:

  • EncodedButtonConfig
    - binary encoded buttons supporting
    2^N-1
    buttons on
    N
    digital pins
  • LadderButtonConfig
    - resistor ladder buttons using analog pins

We explain how to use these below.

Include Header and Use Namespace

Only a single header file

AceButton.h
is required to use this library. To prevent name clashes with other libraries that the calling code may use, all classes are defined in the
ace_button
namespace. To use the code without prepending the
ace_button::
prefix, use the
using
directive:
#include 
using namespace ace_button;

If you are dependent on just

AceButton
, the following might be sufficient:
#include 
using ace_button::AceButton;

Pin Wiring and Initialization

The

ButtonConfig
class supports the simplest wiring. Each button is connected to a single digital input pin, as shown below. In the example below, 3 buttons labeled
S0
,
S1
and
S2
are connected to digital input pins
D2
,
D3
, and
D4
:

Direct Digital

An Arduino microcontroller pin can be in an

OUTPUT
mode, an
INPUT
mode, or an
INPUT_PULLUP
mode. This mode is controlled by the
pinMode()
method.

By default upon boot, the pin is set to the

INPUT
mode. However, this
INPUT
mode puts the pin into a high impedance state, which means that if there is no wire connected to the pin, the voltage on the pin is indeterminant. When the input pin is read (using
digitalRead()
), the boolean value will be a random value. If you are using the pin in
INPUT
mode, you must connect an external pull-up resistor (connected to Vcc) or pull-down resistor (connected to ground) so that the voltage level of the pin is defined when there is nothing connected to the pin (i.e. when the button is not pressed).

The

INPUT_PULLUP
mode is a special
INPUT
mode which tells the microcontroller to connect an internal pull-up resistor to the pin. It is activated by calling
pinMode(pin, INPUT_PULLUP)
on the given
pin
. This mode is very convenient because it eliminates the external resistor, making the wiring simpler.

The 3 resistors

Rc1
,
Rc2
andc
Rc3
are optional current limiting resistors. They help protect the microcontroller in the case of misconfiguration. If the pins are accidentally set to
OUTPUT
mode, then pressing one of the buttons would connect the output pin directly to ground, causing a large amount of current to flow that could permenantly damage the microcontroller. The resistance value of 220 ohms (or maybe 330 ohms) is high enough to keep the current within safety limits, but low enough compared to the internal pullup resistor that it is able to pull the digital pin to a logical 0 level. These current limiting resistors are good safety measures, but I admit that I often get lazy and don't use them when doing quick experiments.

The AceButton library itself does not call the

pinMode()
function. The calling application is responsible for calling
pinMode()
. Normally, this happens in the global
setup()
method but the call can happen somewhere else if the application requires it. The reason for decoupling the hardware configuration from the AceButton library is mostly because the library does not actually care about the specific hardware wiring of the button. It does not care whether an external resistor is used, or the internal resistor is used. It only cares about whether the resistor is a pull-up or a pull-down.

See https://www.arduino.cc/en/Tutorial/DigitalPins for additional information about the I/O pins on an Arduino.

AceButton Class

The

AceButton
class looks like this (not all public methods are shown): ```C++ namespace ace_button {

class AceButton { public: static const uint8t kEventPressed = 0; static const uint8t kEventReleased = 1; static const uint8t kEventClicked = 2; static const uint8t kEventDoubleClicked = 3; static const uint8t kEventLongPressed = 4; static const uint8t kEventRepeatPressed = 5; static const uint8t kEventLongReleased = 6; static const uint8t kButtonStateUnknown = 127;

explicit AceButton(uint8_t pin = 0, uint8_t defaultReleasedState = HIGH,
    uint8_t id = 0);
explicit AceButton(ButtonConfig* buttonConfig, uint8_t pin = 0,
    uint8_t defaultReleasedState = HIGH, uint8_t id = 0);
void init(uint8_t pin = 0, uint8_t defaultReleasedState = HIGH,
    uint8_t id = 0);
void init(ButtonConfig* buttonConfig, uint8_t pin = 0,
    uint8_t defaultReleasedState = HIGH, uint8_t id = 0);

ButtonConfig* getButtonConfig(); void setButtonConfig(ButtonConfig* buttonConfig); void setEventHandler(ButtonConfig::EventHandler eventHandler);

uint8_t getPin(); uint8_t getDefaultReleasedState(); uint8_t getId();

void check();

};

} ```

Each physical button will be handled by an instance of

AceButton
. At a minimum, the instance needs to be told the pin number of the button. This can be done through the constructor:
const uint8_t BUTTON_PIN = 2;

AceButton button(BUTTON_PIN);

void setup() { pinMode(BUTTON_PIN, INPUT_PULLUP); ... }

Or we can use the

init()
method in the
setup()
:
AceButton button;

void setup() { pinMode(BUTTON_PIN, INPUT_PULLUP); button.init(BUTTON_PIN); ... }

Both the constructor and the

init()
function take 3 optional parameters as shown above:
  • pin
    : the I/O pin number assigned to the button
  • defaultReleasedState
    : the logical value of the button when it is in its default "released" state (
    HIGH
    using a pull-up resistor,
    LOW
    for a pull-down resistor)
  • id
    : an optional, user-defined identifier for the the button, for example, an index into an array with additional information

The

pin
must be defined either through the constructor or the
init()
method. But the other two parameters may be optional in many cases.

Finally, the

AceButton::check()
method should be called from the
loop()
method periodically. Roughly speaking, this should be about 4 times faster than the value of
getDebounceDelay()
so that the various event detection logic can work properly. (If the debounce delay is 20 ms,
AceButton::check()
should be called every 5 ms or faster.)
void loop() {
  ...
  button.check();
  ...
}

Warning:

If you attempt to use Pin 0 in the

AceButton()
constructor:
C++
AceButton button(0);
you may encounter a compile-time error such as this:
error: call of overloaded 'AceButton(int)' is ambiguous

The solution is to explicitly cast the

0
to a
uint8_t
type, or to assign it explicitly to a
uint8_t
const, like this: ```C++ // Explicit cast AceButton button((uint8_t) 0);

// Or assign to a const first. static const uint8_t PIN = 0; AceButton button(PIN);

See [Issue #40](https://github.com/bxparks/AceButton/issues/40) for details.


ButtonConfig Class

The core concept of the AceButton library is the separation of the button (AceButton) from its configuration (ButtonConfig).

  • The AceButton class has the logic for debouncing and detecting the various events (Pressed, Released, etc), and the various bookkeeping variables needed to implement the logic. These variables are associated with the specific instance of that AceButton.
  • The ButtonConfig class has the various timing parameters which control how much time is needed to detect certain events. This class also has the ability to override the default methods for reading the pin (readButton()) and the clock (getClock()). This ability allows unit tests to be written.

The class looks like this (not all public methods are shown):

```C++ namespace ace_button {

class ButtonConfig { public: static const uint16_t kDebounceDelay = 20; static const uint16_t kClickDelay = 200; static const uint16_t kDoubleClickDelay = 400; static const uint16_t kLongPressDelay = 1000; static const uint16_t kRepeatPressDelay = 1000; static const uint16_t kRepeatPressInterval = 200;

typedef uint16_t FeatureFlagType;
static const FeatureFlagType kFeatureClick = 0x01;
static const FeatureFlagType kFeatureDoubleClick = 0x02;
static const FeatureFlagType kFeatureLongPress = 0x04;
static const FeatureFlagType kFeatureRepeatPress = 0x08;
static const FeatureFlagType kFeatureSuppressAfterClick = 0x10;
static const FeatureFlagType kFeatureSuppressAfterDoubleClick = 0x20;
static const FeatureFlagType kFeatureSuppressAfterLongPress = 0x40;
static const FeatureFlagType kFeatureSuppressAfterRepeatPress = 0x80;
static const FeatureFlagType kFeatureSuppressClickBeforeDoubleClick = 0x100;
static const FeatureFlagType kFeatureSuppressAll =
    (kFeatureSuppressAfterClick |
    kFeatureSuppressAfterDoubleClick |
    kFeatureSuppressAfterLongPress |
    kFeatureSuppressAfterRepeatPress |
    kFeatureSuppressClickBeforeDoubleClick);

typedef void (*EventHandler)(AceButton* button, uint8_t eventType,
    uint8_t buttonState);

ButtonConfig() = default;

uint16_t getDebounceDelay();
uint16_t getClickDelay();
uint16_t getDoubleClickDelay();
uint16_t getLongPressDelay();
uint16_t getRepeatPressDelay();
uint16_t getRepeatPressInterval();

void setDebounceDelay(uint16_t debounceDelay);
void setClickDelay(uint16_t clickDelay) {
void setDoubleClickDelay(uint16_t doubleClickDelay);
void setLongPressDelay(uint16_t longPressDelay);
void setRepeatPressDelay(uint16_t repeatPressDelay);
void setRepeatPressInterval(uint16_t repeatPressInterval);

virtual unsigned long getClock();
virtual int readButton(uint8_t pin);

bool isFeature(FeatureFlagType features);
void setFeature(FeatureFlagType features);
void clearFeature(FeatureFlagType features);
void resetFeatures();

void setEventHandler(EventHandler eventHandler);

static ButtonConfig* getSystemButtonConfig();

};

}

The

ButtonConfig
(or a customized subclass) can be created and assigned to one or more
AceButton
instances using dependency injection through the
AceButton(ButtonConfig*)
constructor. This constructor also accepts the same
(pin, defaultReleasedState, id)
parameters as
init(pin, defaultReleasedState,
id)
method. Sometimes it's easier to set all the parameters in one place using the constructor. Other times, the parameters are not known until the
AceButton::init()
method can be called from the global
setup()
method.
const uint8_t PIN1 = 2;
const uint8_t PIN2 = 4;

ButtonConfig buttonConfig; AceButton button1(&buttonConfig, PIN1); AceButton button2(&buttonConfig, PIN2);

void setup() { pinMode(PIN1, INPUT_PULLUP); pinMode(PIN2, INPUT_PULLUP); ... }

Another way to inject the

ButtonConfig
dependency is to use the
AceButton::setButtonConfig()
method but it is recommended that you use the constructor instead because the dependency is easier to follow.

System ButtonConfig

A single instance of

ButtonConfig
called the "System ButtonConfig" is automatically created by the library at startup. By default, all instances of
AceButton
are automatically assigned to this singleton instance. We explain in the Single Button Simplifications section below how this simplifies the code needed to handle a single button.

Configuring the EventHandler

The

ButtonConfig
class provides a number of methods which are mostly used internally by the
AceButton
class. The one method which is expected to be used by the calling client code is
setEventHandler()
which assigns the user-defined
EventHandler
callback function to the
ButtonConfig
instance. This is explained in more detail below in the EventHandler section below.

Timing Parameters

Here are the methods to retrieve the timing parameters:

  • uint16_t getDebounceDelay();
    (default: 20 ms)
  • uint16_t getClickDelay();
    (default: 200 ms)
  • uint16_t getDoubleClickDelay();
    (default: 400 ms)
  • uint16_t getLongPressDelay();
    (default: 1000 ms)
  • uint16_t getRepeatPressDelay();
    (default: 1000 ms)
  • uint16_t getRepeatPressInterval();
    (default: 200 ms)

The default values of each timing parameter can be changed at run-time using the following methods:

  • void setDebounceDelay(uint16_t debounceDelay);
  • void setClickDelay(uint16_t clickDelay);
  • void setDoubleClickDelay(uint16_t doubleClickDelay);
  • void setLongPressDelay(uint16_t longPressDelay);
  • void setRepeatPressDelay(uint16_t repeatPressDelay);
  • void setRepeatPressInterval(uint16_t repeatPressInterval);

Hardware Dependencies

The

ButtonConfig
class has 2 methods which provide hooks to its external hardware dependencies:
  • virtual unsigned long getClock();
  • virtual int readButton(uint8_t pin);

By default these are mapped to the underlying Arduino system functions respectively:

  • millis()
  • digitalRead()

Unit tests are possible because these methods are

virtual
and the hardware dependencies can be swapped out with fake ones.

Multiple ButtonConfig Instances

We have assumed that there is a 1-to-many relationship between a

ButtonConfig
and the
AceButton
. In other words, multiple buttons will normally be associated with a single configuration. Each
AceButton
has a pointer to an instance of
ButtonConfig
. So the cost of separating the
ButtonConfig
from
AceButton
is 2 bytes in each instance of
AceButton
. Note that this is equivalent to adding virtual methods to
AceButton
(which would add 2 bytes), so in terms of static RAM size, this is a wash.

The library is designed to handle multiple buttons, and it assumes that the buttons are normally grouped together into a handful of types. For example, consider the buttons of a car radio. It has several types of buttons:

  • the tuner buttons (2, up and down)
  • the preset buttons (6)
  • the AM/FM band button (1)

In this example, there are 9 buttons, but only 3 instances of

ButtonConfig
would be needed.

EventHandler Typedef

The event handler is a callback function that gets called when the

AceButton
class determines that an interesting event happened on the button. The advantage of this mechanism is that all the complicated logic of determining the various events happens inside the
AceButton
class, and the user will normally not need to worry about the details.

EventHandler Signature

The event handler is defined in the

ButtonConfig
class and has the following signature:
class ButtonConfig {
  public:
    typedef void (*EventHandler)(AceButton* button, uint8_t eventType,
        uint8_t buttonState);
    ...
};

The event handler is registered with the

ButtonConfig
object, not with the
AceButton
object, although the convenience method
AceButton::setEventHandler()
is provided as a pass-through to the underlying
ButtonConfig
(see the Single Button Simplifications section below):
ButtonConfig buttonConfig;

void handleEvent(AceButton* button, uint8_t eventType, uint8_t buttonState) { ... }

void setup() { ... buttonConfig.setEventHandler(handleEvent); ... }

The motivation for this design is to save static memory. If multiple buttons are associated with a single

ButtonConfig
, then it is not necessary for every button of that type to hold the same pointer to the
EventHandler
function. It is only necessary to save that information once, in the
ButtonConfig
object.

Pro Tip 1: Comment out the unused parameter(s) in the

handleEvent()
method to avoid the
unused parameter
compiler warning:
C++
void handleEvent(AceButton* /*button*/, uint8_t eventType,
    uint8_t /*buttonState*/) {
  ...
}
The Arduino sketch compiler can get confused with the parameters commented out, so you may need to add a forward declaration for the
handleEvent()
method before the
setup()
method:
C++
void handleEvent(AceButton*, uint8_t, uint8_t);

Pro Tips 2: The event handler can be an object instead of just a function pointer. An object-based event handler can be useful in more complex applications with numerous buttons. See the section on Object-based Event Handler in the Advanced Topics below.

EventHandler Parameters

The

EventHandler
function receives 3 parameters from the
AceButton
:
  • button
    • pointer to the
      AceButton
      instance that generated this event
    • can be used to retrieve the
      getPin()
      or the
      getId()
  • eventType
    • the type of this event given by the various
      AceButton::kEventXxx
      constants
  • buttonState
    • the
      HIGH
      or
      LOW
      button state that generated this event

The

button
pointer should be used only to extract information about the button that triggered the event. It should not be used to modify the button's internal variables in any way within the eventHandler. The logic in
AceButton::check()
assumes that those internal variable are held constant, and if they are changed by the eventHandler, unpredictable results may occur. (I should have made the
button
be a
const AceButton*
but by the time I realized this, there were too many users of the library already, and I did not want to make a breaking change to the API.)

If you are using only a single button, then you should need to check only the

eventType
.

It is not expected that

buttonState
will be needed very often. It should be sufficient to examine just the
eventType
to determine the action that needs to be performed. Part of the difficulty with this parameter is that it has the value of
LOW
or
HIGH
, but the physical interpretation of those values depends on whether the button was wired with a pull-up or pull-down resistor. Use the helper function
button->isReleased(buttonState)
to translate the raw
buttonState
into a more meaningful determination if you need it.

One EventHandler Per ButtonConfig

Only a single

EventHandler
per
ButtonConfig
is supported. An alternative would have been to register a separate event handler for each of the 6
kEventXxx
events. But each callback function requires 2 bytes of memory, and it was assumed that in most cases, the calling client code would be interested in only a few of these event types, so it seemed wasteful to allocate 12 bytes when most of these would be unused. If the client code really wanted separate event handlers, it can be easily emulated by invoking them through the main event handler:
void handleEvent(AceButton* button, uint8_t eventType, uint8_t buttonState) {
  switch (eventType) {
    case AceButton::kEventPressed:
      handleEventPressed(button, eventType, buttonState);
      break;
    case AceButton::kEventReleased:
      handleEventReleased(button, eventType, buttonState);
      break;
    ...
  }
}

EventHandler Tips

The Arduino runtime environment is single-threaded, so the

EventHandler
is called in the middle of the
AceButton::check()
method, in the same thread as the
check()
method. It is therefore important to write the
EventHandler
code to run somewhat quickly, so that the delay doesn't negatively impact the logic of the
AceButton::check()
algorithm. Since
AceButton::check()
should run approximately every 5 ms, the user-provided
EventHandler
should run somewhat faster than 5 ms. Given a choice, it is probably better to use the
EventHandler
to set some flags or variables and return quickly, then do additional processing from the
loop()
method.

Sometimes it is too convenient or unavoidable to perform a long-running operation inside the event handler (e.g. making an HTTP). This is fine, I have done this occasionally. Just be aware that the button scanning operation will not work during that long-running operation.

Speaking of threads, the API of the AceButton Library was designed to work in a multi-threaded environment, if that situation were to occur in the Arduino world.

Event Types

The supported events are defined by a list of constants in

AceButton.h
:
  • AceButton::kEventPressed
    (always enabled, cannot be suppressed)
  • AceButton::kEventReleased
    (default: enabled)
  • AceButton::kEventClicked
    (default: disabled)
  • AceButton::kEventDoubleClicked
    (default: disabled)
  • AceButton::kEventLongPressed
    (default: disabled)
  • AceButton::kEventRepeatPressed
    (default: disabled)
  • AceButton::kEventLongReleased
    (default: disabled, autoenabled by
    kFeatureSuppressAfterLongPress
    , new for v1.8)

These values are sent to the

EventHandler
in the
eventType
parameter.

Two of the events are enabled by default, four are disabled by default but can be enabled by using a Feature flag described below.

ButtonConfig Feature Flags

There are 9 flags defined in

ButtonConfig
which can control the behavior of
AceButton
event handling:
  • ButtonConfig::kFeatureClick
  • ButtonConfig::kFeatureDoubleClick
  • ButtonConfig::kFeatureLongPress
  • ButtonConfig::kFeatureRepeatPress
  • ButtonConfig::kFeatureSuppressAfterClick
  • ButtonConfig::kFeatureSuppressAfterDoubleClick
  • ButtonConfig::kFeatureSuppressAfterLongPress
  • ButtonConfig::kFeatureSuppressAfterRepeatPress
  • ButtonConfig::kFeatureSuppressClickBeforeDoubleClick
  • ButtonConfig::kFeatureSuppressAll

These constants are used to set or clear the given flag:

// Get the current config.
ButtonConfig* config = button.getButtonConfig();

// Set a specific feature config->setFeature(ButtonConfig::kFeatureLongPress);

// Clear a specific feature config->clearFeature(ButtonConfig::kFeatureLongPress);

// Test for a specific feature if (config->isFeature(ButtonConfig::kFeatureLongPress)) { ... }

// Clear all features config->resetFeatures()

The meaning of these flags are described below.

Event Activation

Of the 7 event types, 5 are disabled by default:

  • AceButton::kEventClicked
  • AceButton::kEventDoubleClicked
  • AceButton::kEventLongPressed
  • AceButton::kEventRepeatPressed
  • AceButton::kEventLongReleased

To receive these events, call

ButtonConfig::setFeature()
with the following corresponding flags:
  • ButtonConfig::kFeatureClick
  • ButtonConfig::kFeatureDoubleClick
  • ButtonConfig::kFeatureLongPress
  • ButtonConfig::kFeatureRepeatPress
  • ButtonConfig::kFeatureSuppressAfterLongPress
    (suppresses
    kEventReleased
    after a LongPress, but turns on
    kEventLongReleased
    as a side effect)

To disable these events, call

ButtonConfig::clearFeature()
with one of these flags.

Enabling

kFeatureDoubleClick
automatically enables
kFeatureClick
, because we need to have a Clicked event before a DoubleClicked event can be detected.

It seems unlikely that both

LongPress
and
RepeatPress
events would be useful at the same time, but both event types can be activated if you need it.

Event Suppression

Event types can be considered to be built up in layers, starting with the lowest level primitive events: Pressed and Released. Higher level events are built on top of the lower level events through various timing delays. When a higher level event is detected, it is sometimes useful to suppress the lower level event that was used to detect the higher level event.

For example, a Clicked event requires a Pressed event followed by a Released event within a

ButtonConfig::getClickDelay()
milliseconds (200 ms by default). The Pressed event is always generated. If a Clicked event is detected, we could choose to generate both a Released event and a Clicked event, and this is the default behavior.

However, many times, it is useful to suppress the Released event if the Clicked event is detected. The

ButtonConfig
can be configured to suppress these lower level events. Call the
setFeature(feature)
method passing the various
kFeatureSuppressXxx
constants:
  • ButtonConfig::kFeatureSuppressAfterClick
    • suppresses the
      kEventReleased
      event after a Clicked event is detected
    • also suppresses the Released event from the first Clicked of a DoubleClicked, since
      kFeatureDoubleClick
      automatically enables
      kFeatureClick
  • ButtonConfig::kFeatureSuppressAfterDoubleClick
    • suppresses the
      kEventReleased
      event and the second Clicked event if a DoubleClicked event is detected
  • ButtonConfig::kFeatureSuppressAfterLongPress
    • suppresses the
      kEventReleased
      event if a LongPressed event is detected
    • (v1.8) automatically enables
      kEventLongReleased
      event as a substitute for the suppressed
      kEventReleased
      , see Distinguishing Pressed and Long Pressed subsection below for more details.
  • ButtonConfig::kFeatureSuppressAfterRepeatPress
    • suppresses the
      kEventReleased
      event after the last RepeatPressed event
  • ButtonConfig::kFeatureSuppressClickBeforeDoubleClick
    • The first
      kEventClicked
      event is postponed by
      getDoubleClickDelay()
      millis until the code can determine if a DoubleClick has occurred. If so, then the postponed
      kEventClicked
      message to the
      EventHandler
      is suppressed.
    • See Distinguishing Clicked and DoubleClicked subsection below for more info.
  • ButtonConfig::kFeatureSuppressAll
    • a convenience parameter that is the equivalent of suppressing all of the previous events

By default, no suppression is performed.

As an example, to suppress the

kEventReleased
after a
kEventLongPressed
(this is actually often the case), you would do this:
ButtonConfig* config = button.getButtonConfig();
config->setFeature(ButtonConfig::kFeatureSuppressAfterLongPress);

The special convenient constant

kFeatureSuppressAll
is equivalent of using all suppression constants:
ButtonConfig* config = button.getButtonConfig();
config->setFeature(ButtonConfig::kFeatureSuppressAll);

All suppressions can be cleared by using:

C++
ButtonConfig* config = button.getButtonConfig();
config->clearFeature(ButtonConfig::kFeatureSuppressAll);

Note, however, that the

isFeature(ButtonConfig::kFeatureSuppressAll)
currently means "isAnyFeature() implemented?" not "areAllFeatures() implemented?" We don't expect
isFeature()
to be used often (or at all) for
kFeatureSuppressAll
.

You can clear all feature at once using:

C++
ButtonConfig* config = button.getButtonConfig();
config->resetFeatures();
This is useful if you want to reuse a
ButtonConfig
instance and you want to reset its feature flags to its initial state.

Single Button Simplifications

Although the AceButton library is designed to shine for multiple buttons, you may want to use it to handle just one button. The library provides some features to make this simple case easy.

  1. The library automatically creates one instance of
    ButtonConfig
    called a "System ButtonConfig". This System ButtonConfig can be retrieved using the class static method
    ButtonConfig::getSystemButtonConfig()
    .
  2. Every instance of
    AceButton
    is assigned an instance of the System ButtonConfig by default (which can be overridden manually).
  3. A convenience method allows the
    EventHandler
    for the System ButtonConfig to be set easily through
    AceButton
    itself, instead of having to get the System ButtonConfig first, then set the event handler. In other words,
    button.setEventHandler(handleEvent)
    is a synonym for
    button.getButtonConfig()->setEventHandler(handleEvent)
    .

These simplifying features allow a single button to be configured and used like this:

AceButton button(BUTTON_PIN);

void setup() { pinMode(BUTTON_PIN, INPUT_PULLUP); button.setEventHandler(handleEvent); ... }

void loop() { button.check(); }

void handleEvent(AceButton* button, uint8_t eventType, uint8_t buttonState) { ... }

To configure the System ButtonConfig, you may need to add something like this to the

setup()
section:
  button.getButtonConfig()->setFeature(ButtonConfig::kFeatureLongPress);

Multiple Buttons

When transitioning from a single button to multiple buttons, it's important to remember what's happening underneath the convenience methods. The single

AceButton
button is assigned to the System ButtonConfig that was created automatically. When an
EventHandler
is assigned to the button, it is actually assigned to the System ButtonConfig. All subsequent instances of
AceButton
will also be associated with this event handler, unless another
ButtonConfig
is explicitly assigned.

There are at least 2 ways you can configure multiple buttons.

Option 1: Multiple ButtonConfigs

#include 
using namespace ace_button;

ButtonConfig config1; AceButton button1(&config1); ButtonConfig config2; AceButton button2(&config2);

void button1Handler(AceButton* button, uint8_t eventType, uint8_t buttonState) { Serial.println("button1"); }

void button2Handler(AceButton* button, uint8_t eventType, uint8_t buttonState) { Serial.println("button2"); }

void setup() { Serial.begin(115200); pinMode(6, INPUT_PULLUP); pinMode(7, INPUT_PULLUP); config1.setEventHandler(button1Handler); config2.setEventHandler(button2Handler); button1.init(6); button2.init(7); }

void loop() { button1.check(); button2.check(); } </acebutton.h>

See the example sketch TwoButtonsUsingTwoButtonConfigs.ino which uses 2

ButtonConfig
instances to configure 2
AceButton
instances.

Option 2: Multiple Button Discriminators

Another technique keeps the single system

ButtonConfig
and the single
EventHandler
, but use the
AceButton::getPin()
to discriminate between the multiple buttons:
#include 
using namespace ace_button;

AceButton button1(6); AceButton button2(7);

void button1Handler(AceButton* button, uint8_t eventType, uint8_t buttonState) { Serial.println("button1"); }

void button2Handler(AceButton* button, uint8_t eventType, uint8_t buttonState) { Serial.println("button2"); }

void buttonHandler(AceButton* button, uint8_t eventType, uint8_t buttonState) { switch (button->getPin()) { case 6: button1Handler(button, eventType, buttonState); break; case 7: button2Handler(button, eventType, buttonState); break; } }

void setup() { Serial.begin(115200); pinMode(6, INPUT_PULLUP); pinMode(7, INPUT_PULLUP); ButtonConfig* config = ButtonConfig::getSystemButtonConfig(); config->setEventHandler(buttonHandler); }

void loop() { button1.check(); button2.check(); } </acebutton.h>

See the example code TwoButtonsUsingOneButtonConfig. which uses a single

ButtonConfig
instance to handle 2
AceButton
instances.

Sometimes, it is more convenient to use the

AceButton::getId()
method to identify the button instead of the
AceButton::getPin()
. See ArrayButtons.ino for an example.

Advanced Topics

Object-based Event Handler

The

EventHandler
is a typedef that is defined to be a function pointer. This is a simple, low-overhead design that produces the smallest memory footprint, and allows the event handler to be written with the smallest amount of boilerplate code. The user does not have to override a class.

In more complex applications involving larger number of

AceButton
and
ButtonConfig
objects, it is often useful for the
EventHandler
to be an object instead of a simple function pointer. This is especially true if the application uses Object Oriented Programming (OOP) techniques for modularity and encapsulation. Using an object as the event handler allows additional context information to be injected into the event handler.

To support OOP techniques, AceButton v1.6 adds:

  • IEventHandler
    interface class
    • contains a single pure virtual function
      handleEvent()
  • ButtonConfig::setIEventHandler()
    method
    • accepts a pointer to an instance of the
      IEventHandler
      interface.

The

IEventHandler
interface is simply this:
C++
class IEventHandler {
  public:
    virtual void handleEvent(AceButton* button, uint8_t eventType,
        uint8_t buttonState) = 0;
};

At least one of

ButtonConfig::setEventHandler()
or
ButtonConfig::setIEventHandler()
must be called before events are actually dispatched. If both are called, the last one takes precedence.

See examples/SingleButtonUsingIEventHandler for an example.

Distinguishing Clicked and DoubleClicked

On a project using only a small number of buttons (due to physical limits or the limited availability of pins), it may be desirable to distinguish between a single Clicked event and a DoubleClicked event from a single button. This is a challenging problem to solve because fundamentally, a DoubleClicked event must always generate a Clicked event, because a Clicked event must happen before it can become a DoubleClicked event.

Notice that on a desktop computer (running Windows, MacOS or Linux), a double-click on a mouse always generates both a Clicked and a DoubleClicked. The first Click selects the given desktop object (e.g. an icon or a window), and the DoubleClick performs some action on the selected object (e.g. open the icon, or resize the window).

The AceButton Library provides 3 solutions which may work for some projects:

Method 1: The

kFeatureSuppressClickBeforeDoubleClick
flag causes the first Clicked event to be detected, but the posting of the event message (i.e. the call to the
EventHandler
) is postponed until the state of the DoubleClicked can be determined. If the DoubleClicked happens, then the first Clicked event message is suppressed. If DoubleClicked does not occur, the long delayed Clicked message is sent via the
EventHandler
.

There are two noticeable disadvantages of this method. First, the response time of all Clicked events is delayed by about 600 ms (

kClickDelay +
kDoubleClickDelay
) whether or not the DoubleClicked event happens. Second, the user may not be able to accurately produce a Clicked event (due to the physical characteristics of the button, or the user's dexterity).

It may also be worth noting that only the Clicked event is postponed. The accompanying Released event of the Clicked event is not postponed. So a single click action (without a DoubleClick) produces the following sequence of events to the EventHandler:

  1. kEventPressed
    - at time 0ms
  2. kEventReleased
    - at time 200ms
  3. kEventClicked
    - at time 600ms (200ms + 400ms)

The

ButtonConfig
configuration looks like this:
C++
ButtonConfig* buttonConfig = button.getButtonConfig();
buttonConfig->setFeature(ButtonConfig::kFeatureDoubleClick);
buttonConfig->setFeature(
    ButtonConfig::kFeatureSuppressClickBeforeDoubleClick);

See the example code at

examples/ClickVersusDoubleClickUsingSuppression/
.

Method 2: A viable alternative is to use the Released event instead of the Clicked event to distinguish it from the DoubleClicked. For this method to work, we need to suppress the Released event after both Clicked and DoubleClicked.

The advantage of using this method is that there is no response time lag in the handling of the Released event. To the user, there is almost no difference between triggering on the Released event, versus triggering on the Clicked event.

The disadvantage of this method is that the Clicked event must be be ignored (because of the spurious Clicked event generated by the DoubleClicked). If the user accidentally presses and releases the button too quickly, it generates a Clicked event, which will cause the program to do nothing.

The

ButtonConfig
configuration looks like this:
C++
ButtonConfig* buttonConfig = button.getButtonConfig();
buttonConfig->setEventHandler(handleEvent);
buttonConfig->setFeature(ButtonConfig::kFeatureDoubleClick);
buttonConfig->setFeature(ButtonConfig::kFeatureSuppressAfterClick);
buttonConfig->setFeature(ButtonConfig::kFeatureSuppressAfterDoubleClick);

See the example code at

examples/ClickVersusDoubleClickUsingReleased/
.

Method 3: We could actually combine both Methods 1 and 2 so that either Released or a delayed Click is considered to be a "Click". This may be the best of both worlds.

The

ButtonConfig
configuration looks like this:
C++
ButtonConfig* buttonConfig = button.getButtonConfig();
buttonConfig->setEventHandler(handleEvent);
buttonConfig->setFeature(ButtonConfig::kFeatureDoubleClick);
buttonConfig->setFeature(
    ButtonConfig::kFeatureSuppressClickBeforeDoubleClick);
buttonConfig->setFeature(ButtonConfig::kFeatureSuppressAfterClick);
buttonConfig->setFeature(ButtonConfig::kFeatureSuppressAfterDoubleClick);

See the example code at

examples/ClickVersusDoubleClickUsingBoth/
.

Distinguishing Pressed and LongPressed

Sometimes it is useful to capture both a Pressed event and a LongPressed event from a single button. Since every button press always triggers a

kEventPressed
event, the only reasonable way to distinguish between Pressed and LongPressed is to use the
kEventReleased
as a substitute for the simple Pressed event. When we active
kFeatureLongPress
, we then must activate the
kFeatureSuppressAfterLongPress
feature to suppress the
kEventReleased
event after the
kEventLongPressed
to avoid yet another overlap of events.
ButtonConfig* config = button.getButtonConfig();
config->setFeature(ButtonConfig::kFeatureLongPress);
config->setFeature(ButtonConfig::kFeatureSuppressAfterLongPress);

This works most of the time, but I encountered an edge case. Occasionally we want to capture the Released event after the LongPressed event, even if

kEventReleased
must be suppressed as described above. To solve this edge case, in v1.8, I added a new event type
kEventLongReleased
which is triggered as a substitute for
kEventReleased
, only if
kFeatureSuppressAfterLongPress
is used to suppress
kEventReleased
.

See the example code at examples/PressVersusLongPress to see how all these come together.

Events After Reboot

A number of edge cases occur when the microcontroller is rebooted:

  • if the button is held down, should the Pressed event be triggered?
  • if the button is in its natural Released state, should the Released event happen?
  • if the button is Pressed down, and
    ButtonConfig
    is configured to support RepeatPress events, should the
    kEventRepeatPressed
    events be triggered initially?

I think most users would expect that in all these cases, the answer is no, the microcontroller should not trigger an event until the button undergoes a human-initiated change in state. The AceButton library implements this logic. (It might be useful to make this configurable using a

ButtonConfig
feature flag but that is not implemented.)

On the other hand, it is sometimes useful to perform some special action if a button is pressed while the device is rebooted. To support this use-case, call the

AceButton::isPressedRaw()
in the global
setup()
method (after the button is configured). It will directly call the
digitalRead()
method associated with the button pin and return
true
if the button is in the Pressed state.

Orphaned Clicks

When a Clicked event is generated, the

AceButton
class looks for a second Clicked event within a certain time delay (default 400 ms) to determine if the second Clicked event is actually a DoubleClicked event.

All internal timestamps in

AceButton
are stored as
uint16_t
(i.e. an unsigned integer of 16 bits) in millisecond units. A 16-bit unsigned counter rolls over after 65536 iterations. Therefore, if the second Clicked event happens between (65.636 seconds, 66.036 seconds) after the first Clicked event, a naive-logic would erroneously consider the (long-delayed) second click as a double-click.

The

AceButton
contains code that prevents this from happening.

Note that even if the

AceButton
class uses an
unsigned long
type (a 32-bit integer on the Arduino), the overflow problem would still occur after
2^32
milliseconds (i.e. 49.7 days). To be strictly correct, the
AceButton
class would still need logic to take care of orphaned Clicked events.

Binary Encoded Buttons

Instead of allocating one pin for each button, we can use Binary Encoding to support large number of buttons with only a few pins. The circuit can be implemented using a 74LS148 chip, or simple diodes like this:

8 To 3 Encoding

Three subclasses of

ButtonConfig
are provided to handle binary encoded buttons:
  • Encoded4To2ButtonConfig
    : 3 buttons with 2 pins
  • Encoded8To3ButtonConfig
    : 7 buttons with 3 pins
  • EncodedButtonConfig
    :
    M=2^N-1
    buttons with
    N
    pins

See docs/binary_encoding/README.md for information on how to use these classes.

Resistor Ladder Buttons

It is possible to attach 5-8 (maybe more) buttons on a single analog pin through a resistor ladder, and use the

analogRead()
to read the different voltages generated by each button. An example circuit looks like this:

Parallel Registor Ladder

The

LadderButtonConfig
class handles this configuration.

See docs/resistor_ladder/README.md for information on how to use this class.

Dynamic Allocation on the Heap

All classes in this library were originally designed to be created statically at startup time and never deleted during the lifetime of the application. Since they were never meant to be deleted through the pointer, I did not include the virtual destructor for polymorphic classes (i.e.

ButtonConfig
and its subclasses). The
AceButton
class is not polymorphic and does not need a virtual destructor.

Most 8-bit processors have limited flash and static memory (for example, 32 kB flash and 2 KB static for the Nano or UNO). Adding a virtual destructor causes 600 additional bytes of flash memory to be consumed. I suspect this is due to the virtual destructor pulling the

malloc()
and
free()
functions which are needed to implement the
new
and
delete
operators. For a library that consumes only about 1200 bytes on an 8-bit processor, this increase in flash memory size did not seem acceptable.

For 32-bit processors (e.g. ESP8266, ESP32) which have far more flash memory (e.g. 1 MB) and static memory (e.g. 80 kB), it seems reasonable to allow

AceButton
and
ButtonConfig
to be created and deleted from the heap. (See Issue #46 for the motivation.) Testing shows that the virtual destructor adds only about 60-120 bytes of flash memory for these microcontrollers, probably because the
malloc()
and
free()
functions are already pulled in by something else. The 60-120 bytes of additional consumption seems trivial compared to the range of ~256 kB to ~4 MB flash memory available on these 32-bit processors.

Therefore, I added a virtual destructor for the

ButtonConfig
class (v1.5) and enabled it for all architectures other than
ARDUINO_ARCH_AVR
(v1.6.1). This prevents 8-bit processors with limited memory from suffering the overhead of an extra 600 bytes of flash memory usage.

Even for 32-bit processors, I still recommend avoiding the creation and deletion of objects from the heap, to avoid the risk of heap fragmentation. If a variable number of buttons is needed, it might be possible to design the application so that all buttons which will ever be needed are predefined in a global pool. Even if some of the

AceButton
and
ButtonConfig
instances are unused, the overhead is probably smaller than the overhead of wasted space due to heap fragmentation.

Resource Consumption

Here are the sizes of the various classes on the 8-bit AVR microcontrollers (Arduino Uno, Nano, etc):

  • sizeof(AceButton): 14
  • sizeof(ButtonConfig): 18
  • sizeof(Encoded4To2ButtonConfig): 21
  • sizeof(Encoded8To3ButtonConfig): 22
  • sizeof(EncodedButtonConfig): 25
  • sizeof(LadderButtonConfig): 26

and 32-bit microcontrollers:

  • sizeof(AceButton): 16
  • sizeof(ButtonConfig): 24
  • sizeof(Encoded4To2ButtonConfig): 28
  • sizeof(Encoded8To3ButtonConfig): 28
  • sizeof(EncodedButtonConfig): 36
  • sizeof(LadderButtonConfig): 36

(An early version of

AceButton
, with only half of the functionality, consumed 40 bytes. It got down to 11 bytes before additional functionality increased it to 14.)

Program size:

MemoryBenchmark was used to determine the size of the library for various microcontrollers (Arduino Nano to ESP32). Here are some ranges of number to give a rough estimate of how much flash and static memory are consumed for various button configurations:

  • one button using the default system
    ButtonConfig
    • flash memory: 1300-5000 bytes
    • static memory: 40-1150 bytes
  • 3 buttons using one
    Encoded4To2ButtonConfig
    • flash memory: 1600-5200 bytes
    • static memory: 70-1200 bytes
  • 7 buttons using one
    Encoded8To3ButtonConfig
    • flash memory: 1800-5400 bytes
    • static memory: 130-1200 bytes
  • 7 buttons using one
    EncodedButtonConfig
    • flash memory: 1900-5400 bytes
    • static memory: 180-1300 bytes
  • 7 buttons using one
    LadderButtonConfig
    • flash memory: 1900-6000 bytes
    • static memory: 190-1300 bytes

CPU cycles:

The profiling numbers for

AceButton::check()
using a simple
ButtonConfig
can be found in examples/AutoBenchmark.

In summary, the average numbers for various boards are:

  • Arduino Nano: 15-16 microsesconds
  • SparkFun Pro Micro: 15-16 microsesconds
  • SAMD21: 8-9 microseconds
  • STM32: 5 microseconds
  • ESP8266: 8 microseconds
  • ESP32: 3 microseconds
  • Teensy 3.2: 3 microseconds

If you use the more advanced

EncodedButtonConfig
or
LadderButtonConfig
to check more buttons, each iteration through all the buttons takes longer. As a rough summary, to check 7 buttons:
  • Arduino Nano: 100-200 microseconds
  • SparkFun Pro Micro: 100-200 microseconds
  • SAMD21: 53 microseconds (EncodedButtonConfig), 470 microseconds (LadderButtonConfig).
    • Seems like the
      analogRead()
      function on a SAMD21 is significantly slower than other microcontrollers. I recommend double-checking these numbers.
  • STM32: 34-96 microseconds
  • ESP8266: 54-150 microseconds
  • ESP32: 16-24 microseconds
  • Teensy 3.2: 20-25 microseconds

System Requirements

Hardware

The library has been extensively tested on the following boards:

  • Arduino Nano clone (16 MHz ATmega328P)
  • SparkFun Pro Micro clone (16 MHz ATmega32U4)
  • SAMD21 M0 Mini (48 MHz ARM Cortex-M0+)
  • STM32 Blue Pill (STM32F103C8, 72 MHz ARM Cortex-M3)
  • NodeMCU 1.0 (ESP-12E module, 80MHz ESP8266)
  • WeMos D1 Mini (ESP-12E module, 80 MHz ESP8266)
  • ESP32 Dev Module (ESP-WROOM-32 module, 240MHz dual core Tensilica LX6)
  • Teensy 3.2 (96 MHz ARM Cortex-M4)

I will occasionally test on the following boards as a sanity check:

  • Arduino Pro Mini clone (16 MHz ATmega328P)
  • Teensy LC (48 MHz ARM Cortex-M0+)
  • Mini Mega 2560 (Arduino Mega 2560 compatible, 16 MHz ATmega2560)

Tool Chain

This library was developed and tested using:

It should work with PlatformIO but I have not tested it.

The library works on Linux or MacOS (using both g++ and clang++ compilers) using the EpoxyDuino emulation layer.

Operating System

I use Ubuntu Linux 18.04 and 20.04 for most of my development.

Background Motivation

There are numerous "button" libraries out there for the Arduino. Why write another one? I wanted to add a button to an addressable strip LED controller, which was being refreshed at 120 Hz. I had a number of requirements:

  • the button needed to support a LongPress event, in addition to the simple Press and Release events
  • the button code must not interfere with the LED refresh code which was updating the LEDs at 120 Hz
  • well-tested, I didn't want to be hunting down random and obscure bugs

Since the LED refresh code needed to run while the button code was waiting for a "LongPress" delay, it seemed that the cleanest API for a button library would use an event handler callback mechanism. This reduced the number of candidate libraries to a handful. Of these, only a few of them supported a LongPress event. I did not find the remaining ones flexible enough for my button needs in the future. Finally, I knew that it was tricky to write correct code for debouncing and detecting various events (e.g. DoubleClick, LongPress, RepeatPress). I looked for a library that contained unit tests, and I found none.

I decided to write my own and use the opportunity to learn how to create and publish an Arduino library.

Non-goals

An Arduino UNO or Nano has 16 times more flash memory (32KB) than static memory (2KB), so the library is optimized to minimize the static memory usage. The AceButton library is not optimized to create a small program size (i.e. flash memory), or for small CPU cycles (i.e. high execution speed). I assumed that if you are seriously optimizing for program size or CPU cycles, you will probably want to write everything yourself from scratch.

That said, examples/MemoryBenchmark shows that the library consumes between 970-2180 bytes of flash memory, and AutoBenchmark shows that

AceButton::check()
takes between 13-15 microseconds on a 16MHz ATmega328P chip and 2-3 microseconds on an ESP32. Hopefully that is small enough and fast enough for the vast majority of people.

License

I changed to the MIT License starting with version 1.1 because the MIT License is so simple to understand. I could not be sure that I understood what the Apache License 2.0 meant.

Feedback and Support

If you find this library useful, consider starring this project on GitHub. The stars will let me prioritize the more popular libraries over the less popular ones.

If you have any questions, comments, bug reports, or feature requests, please file a GitHub ticket instead of emailing me unless the content is sensitive. (The problem with email is that I cannot reference the email conversation when other people ask similar questions later.) I'd love to hear about how this software and its documentation can be improved. I can't promise that I will incorporate everything, but I will give your ideas serious consideration.

Author

Created by Brian T. Park ([email protected]).

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