ESP32 BLE Keyboard library

This library allows you to make the ESP32 act as a Bluetooth Keyboard and control what it does.
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Features

[x] Send key strokes
[x] Send text
[x] Press/release individual keys
[x] Media keys are supported
[ ] Read Numlock/Capslock/Scrolllock state
[x] Set battery level (basically works, but doesn’t show up in Android’s status bar)
[x] Compatible with Android
[x] Compatible with Windows
[x] Compatible with Linux
[x] Compatible with MacOS X (not stable, some people have issues, doesn’t work with old devices)
[x] Compatible with iOS (not stable, some people have issues, doesn’t work with old devices)

Installation

(Make sure you can use the ESP32 with the Arduino IDE. Instructions can be found here.)
Download the latest release of this library from the release page.
In the Arduino IDE go to “Sketch” -> “Include Library” -> “Add .ZIP Library…” and select the file you just downloaded.
You can now go to “File” -> “Examples” -> “ESP32 BLE Keyboard” and select any of the examples to get started.

Example

/**
 * This example turns the ESP32 into a Bluetooth LE keyboard that writes the words, presses Enter, presses a media key and then Ctrl+Alt+Delete
 */
#include <BleKeyboard.h>

BleKeyboard bleKeyboard;

void setup() {
  Serial.begin(115200);
  Serial.println("Starting BLE work!");
  bleKeyboard.begin();
}

void loop() {
  if(bleKeyboard.isConnected()) {
    Serial.println("Sending 'Hello world'...");
    bleKeyboard.print("Hello world");

    delay(1000);

    Serial.println("Sending Enter key...");
    bleKeyboard.write(KEY_RETURN);

    delay(1000);

    Serial.println("Sending Play/Pause media key...");
    bleKeyboard.write(KEY_MEDIA_PLAY_PAUSE);

    delay(1000);

   //
   // Below is an example of pressing multiple keyboard modifiers
   // which by default is commented out.
   //
   /* Serial.println("Sending Ctrl+Alt+Delete...");
    bleKeyboard.press(KEY_LEFT_CTRL);
    bleKeyboard.press(KEY_LEFT_ALT);
    bleKeyboard.press(KEY_DELETE);
    delay(100);
    bleKeyboard.releaseAll();
    */

  }
  Serial.println("Waiting 5 seconds...");
  delay(5000);
}

API docs

The BleKeyboard interface is almost identical to the Keyboard Interface, so you can use documentation right here: https://www.arduino.cc/reference/en/language/functions/usb/keyboard/

Just remember that you have to use bleKeyboard instead of just Keyboard and you need these two lines at the top of your script:

#include <BleKeyboard.h>
BleKeyboard bleKeyboard;

In addition to that you can send media keys (which is not possible with the USB keyboard library). Supported are the following:

KEY_MEDIA_NEXT_TRACK
KEY_MEDIA_PREVIOUS_TRACK
KEY_MEDIA_STOP
KEY_MEDIA_PLAY_PAUSE
KEY_MEDIA_MUTE
KEY_MEDIA_VOLUME_UP
KEY_MEDIA_VOLUME_DOWN
KEY_MEDIA_WWW_HOME
KEY_MEDIA_LOCAL_MACHINE_BROWSER // Opens “My Computer” on Windows
KEY_MEDIA_CALCULATOR
KEY_MEDIA_WWW_BOOKMARKS
KEY_MEDIA_WWW_SEARCH
KEY_MEDIA_WWW_STOP
KEY_MEDIA_WWW_BACK
KEY_MEDIA_CONSUMER_CONTROL_CONFIGURATION // Media Selection
KEY_MEDIA_EMAIL_READER

There is also Bluetooth specific information that you can set (optional): Instead of BleKeyboard bleKeyboard; you can do BleKeyboard bleKeyboard("Bluetooth Device Name", "Bluetooth Device Manufacturer", 100);. (Max lenght is 15 characters, anything beyond that will be truncated.)
The third parameter is the initial battery level of your device. To adjust the battery level later on you can simply call e.g. bleKeyboard.setBatteryLevel(50) (set battery level to 50%).
By default the battery level will be set to 100%, the device name will be ESP32 Bluetooth Keyboard and the manufacturer will be Espressif.
There is also a setDelay method to set a delay between each key event. E.g. bleKeyboard.setDelay(10) (10 milliseconds). The default is 8.
This feature is meant to compensate for some applications and devices that can’t handle fast input and will skip letters if too many keys are sent in a small time frame.

NimBLE-Mode

The NimBLE mode enables a significant saving of RAM and FLASH memory.

Comparison (SendKeyStrokes.ino at compile-time)

Standard

RAM:   [=         ]   9.3% (used 30548 bytes from 327680 bytes)
Flash: [========  ]  75.8% (used 994120 bytes from 1310720 bytes)

NimBLE mode

RAM:   [=         ]   8.3% (used 27180 bytes from 327680 bytes)
Flash: [====      ]  44.2% (used 579158 bytes from 1310720 bytes)

Comparison (SendKeyStrokes.ino at run-time)

	Standard	NimBLE mode	difference
`ESP.getHeapSize()`	296.804	321.252	+ 24.448
`ESP.getFreeHeap()`	143.572	260.764	+ 117.192
`ESP.getSketchSize()`	994.224	579.264	- 414.960

How to activate NimBLE mode?

ArduinoIDE:

Uncomment the first line in BleKeyboard.h

#define USE_NIMBLE

PlatformIO:

Change your platformio.ini to the following settings

lib_deps =
  NimBLE-Arduino

build_flags =
  -D USE_NIMBLE

Credits

Credits to chegewara and the authors of the USB keyboard library as this project is heavily based on their work!
Also, credits to duke2421 who helped a lot with testing, debugging and fixing the device descriptor! And credits to sivar2311 for adding NimBLE support, greatly reducing the memory footprint, fixing advertising issues and for adding the setDelay method.