acid-drop/lib/AceButton

AceButton

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

Version: 1.3.3 (2019-03-10)

Summary

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 called the ACE Button Library (or AceButton Library) 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 and 1 callback function:

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

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 supported events are:

• AceButton::kEventPressed
• AceButton::kEventReleased
• AceButton::kEventClicked
• AceButton::kEventDoubleClicked
• AceButton::kEventLongPressed
• AceButton::kEventRepeatPressed

(TripleClicked is not supported but can be easily added to the library if requested.)

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 funcition
• supports 6 event types:
  • Pressed
  • Released
  • Clicked
  • DoubleClicked
  • LongPressed
  • RepeatPressed
• can distinguish between Clicked and DoubleClicked
• 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
  • each ButtonConfig consumes 20 bytes
  • one System ButtonConfig instance created automatically by the library
• thoroughly unit tested using AUnit
• properly handles reboots while the button is pressed
• properly handles orphaned clicks, to prevent spurious double-clicks
• only 13-15 microseconds (on 16MHz ATmega328P) per polling call to AceButton::check()
• can be instrumented to extract profiling numbers
• tested on Arduino AVR (UNO, Nano, etc), Teensy ARM (LC and 3.2), ESP8266 and ESP32 platforms

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
• proper handling of orphaned clicks
• proper handling of a reboot while button is pressed

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, the examples/AutoBenchmark program shows that AceButton::check() takes between 13-15 microseconds on a 16MHz ATmega328P chip on average. Hopefully that is fast enough for the vast majority of people.

HelloButton

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

#include <AceButton.h>
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;
  }
}

(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, 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 stable release.

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

Docs

Besides this README.md file, the docs/ directory contains the Doxygen docs published on GitHub Pages. It can help you navigate an unfamiliar code base.

Examples

The following example sketches are provided:

• HelloButton.ino
  • minimal program that reads a switch and control the built-in LED
• SingleButton.ino
  • controls a single button wired with a pull-up resistor
  • prints out a status line for every supported event
• SingleButtonPullDown.ino
  • same as SingleButton.ino but with an external pull-down resistor
• Stopwatch.ino
  • measures the speed of AceButton:check() with a start/stop/reset button
  • uses kFeatureLongPress
• TunerButtons.ino
  • implements 5 radio buttons (tune-up, tune-down, and 3 presets)
  • shows multiple ButtonConfig instances
  • shows multiple EventHandlers
  • shows an example of how to use getId()
  • uses kFeatureLongPress, kFeatureRepeatPress, kFeatureSuppressAfterLongPress, and kFeatureSuppressAfterRepeatPress
• ClickVersusDoubleClickUsingReleased.ino
  • a way to distinguish between a kEventClicked from a kEventDoubleClicked using a kEventReleased instead
• ClickVersusDoubleClickUsingSuppression.ino
  • another way to dstinguish between a kEventClicked from a kEventDoubleClicked using the kFeatureSuppressClickBeforeDoubleClick flag at the cost of increasing the response time of the kEventClicked event
• ClickVersusDoubleClickUsingBoth.ino
  • an example that combines both the "UsingPressed" and "UsingSuppression" techniques
• CapacitiveButton
  • reads a capacitive button using the CapacitiveSensor 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)

Usage

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

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

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 <AceButton.h>
using namespace ace_button;

If you are dependent on just AceButton, the following might be sufficient:

#include <AceButton.h>
using ace_button::AceButton;

Pin Wiring and Initialization

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 pintMode(pin, INPUT_PULLUP) on the given pin. This mode is very convenient because it eliminates the external resistor, making the wiring simpler.

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

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:

AceButton(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);

• 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 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();
  ...
}

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 ButtonConfig can be created and assigned to one or more AceButton instances using dependency injection through the AceButton(ButtonConfig*) constructor. If this constructor is used, then the AceButton::init() method must be used to set the pin number of the button. For example:

const uint8_t PIN1 = 2;
const uint8_t PIN2 = 4;

ButtonConfig buttonConfig;
AceButton button1(&buttonConfig);
AceButton button2(&buttonConfig);

void setup() {
  pinMode(PIN1, INPUT_PULLUP);
  button1.init(PIN1);

  pinMode(PIN2, INPUT_PULLUP);
  button2.init(PIN2);
  ...
}

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 Callback section.

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

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 has the following signature:

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: Comment out the unused parameter(s) in the handleEvent() method to avoid the unused parameter compiler warning:

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:

void handleEvent(AceButton*, uint8_t, uint8_t);

EventHandler Parameters

The EventHandler function receives 3 parameters from the AceButton:

• aceButton
  • 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 aceButton 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 was tempted to make the aceButton a pointer to a const AceButton but this cause too many viral changes to the code which seemed to increase the complexity without too much benefit.)

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. The helper function AceButton::isReleased(uint8_t buttonState) is provided to make this determination if you need it.

One EventHandler

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.

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:

• AceButton::kEventPressed (always enabled)
• AceButton::kEventReleased (conditionally enabled)
• AceButton::kEventClicked (default: disabled)
• AceButton::kEventDoubleClicked (default: disabled)
• AceButton::kEventLongPressed (default: disabled)
• AceButton::kEventRepeatPressed (default: disabled)

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:

ButtonConfig* config = button.getButtonConfig();

config->setFeature(ButtonConfig::kFeatureLongPress);

config->clearFeature(ButtonConfig::kFeatureLongPress);

if (config->isFeature(ButtonConfig::kFeatureLongPress)) {
  ...
}

The meaning of these flags are described below.

Event Activation

Of the 6 event types, 4 are disabled by default:

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

To receive these events, call ButtonConfig::setFeature() with the following flags respectively:

• ButtonConfig::kFeatureClick
• ButtonConfig::kFeatureDoubleClick
• ButtonConfig::kFeatureLongPress
• ButtonConfig::kFeatureRepeatPress

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 Released 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 Released event and the second Clicked event if a DoubleClicked event is detected
• ButtonConfig::kFeatureSuppressAfterLongPress
  • suppresses the Released event if a LongPressed event is detected
• ButtonConfig::kFeatureSuppressAfterRepeatPress
  • suppresses the Released event after the last RepeatPressed event
• ButtonConfig::kFeatureSuppressAll
  • a convenience parameter that is the equivalent of suppressing all of the previous events
• ButtonConfig::kFeatureSuppressClickBeforeDoubleClick
  • The first Clicked event is postponed by getDoubleClickDelay() millis until the code can determine if a DoubleClick has occurred. If so, then the postponed Clicked message to the EventHandler is suppressed.
  • See the section Distinguishing Between a Clicked and DoubleClicked for more info.

By default, no suppression is performed.

As an example, to suppress the Released event after a LongPressed event (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:

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.

Distinguishing Between a 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:

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 to quickly, it generates a Clicked event, which will cause the program to do nothing.

The ButtonConfig configuration looks like this:

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:

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/.

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.

See the example sketch TunerButtons.ino to see how to use multiple ButtonConfig instances with multiple AceButton instances.

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.

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): 20

(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:

LibrarySizeBenchmark was used to determine the size of the library. For a single button, the library consumed:

• flash memory: 1100-1330 bytes
• static memory: 14-28 bytes

depending on the target board. See the README.md in the above link for more details.

CPU cycles:

The profiling numbers for AceButton::check() can be found in examples/AutoBenchmark.

In summary, the average numbers for various boards are:

• Arduino Nano: 13-15 microsesconds
• Teensy 3.2: 3 microseconds
• ESP8266: 8-9 microseconds
• ESP32: 2-3 microseconds

System Requirements

This library was developed and tested using:

• Arduino IDE 1.8.5 - 1.8.7
• Teensyduino 1.41
• ESP8266 Arduino Core 2.4.1 - 2.4.2
• arduino-esp32

I used MacOS 10.13.3 and Ubuntu Linux 17.10 for most of my development.

The library has been verified to work on the following hardware:

• Arduino Nano clone (16 MHz ATmega328P)
• Arduino UNO R3 clone (16 MHz ATmega328P)
• Arduino Pro Micro clone (16 MHz ATmega32U4)
• Teensy LC (48 MHz ARM Cortex-M0+)
• Teensy 3.2 (72 MHz ARM Cortex-M4)
• NodeMCU 1.0 clone (ESP-12E module, 80MHz ESP8266)
• ESP32 Dev Module (ESP-WROOM-32 module, 240MHz dual core Tensilica LX6)

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.

Changelog

See CHANGELOG.md.

License

• Versions 1.0 to 1.0.6: Apache License 2.0
• Versions 1.1 and above: MIT 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 have any questions, comments, bug reports, or feature requests, please file a GitHub ticket or send me an email. I'd love to hear about how this software and its documentation can be improved. Instead of forking the repository to modify or add a feature for your own projects, let me have a chance to incorporate the change into the main repository so that your external dependencies are simpler and so that others can benefit. I can't promise that I will incorporate everything, but I will give your ideas serious consideration.

Author

Created by Brian T. Park (brian@xparks.net).