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@manuelbl
Created August 3, 2019 09:12
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ESP32 as Bluetooth Keyboard

ESP32 as Bluetooth Keyboard

With its built-in Bluetooth capabilities, the ESP32 can act as a Bluetooth keyboard. The below code is a minimal example of how to achieve it. It will generate the key strokes for a message whenever a button attached to the ESP32 is pressed.

For the example setup, a momentary button should be connected to pin 2 and to ground. Pin 2 will be configured as an input with pull-up.

In order to receive the message, add the ESP32 as a Bluetooth keyboard of your computer or mobile phone:

  1. Go to your computers/phones settings
  2. Ensure Bluetooth is turned on
  3. Scan for Bluetooth devices
  4. Connect to the device called "ESP32 Keyboard"
  5. Open an empty document in a text editor
  6. Press the button attached to the ESP32

The code has been written for the Arduino framework. I recommend using PlatformIO for development as it is far superior to the Arduino IDE while still taking full advantage of the Arduino ecosystem (libraries, support etc.)

/*
* Sample program for ESP32 acting as a Bluetooth keyboard
*
* Copyright (c) 2019 Manuel Bl
*
* Licensed under MIT License
* https://opensource.org/licenses/MIT
*/
//
// This program lets an ESP32 act as a keyboard connected via Bluetooth.
// When a button attached to the ESP32 is pressed, it will generate the key strokes for a message.
//
// For the setup, a momentary button should be connected to pin 2 and to ground.
// Pin 2 will be configured as an input with pull-up.
//
// In order to receive the message, add the ESP32 as a Bluetooth keyboard of your computer
// or mobile phone:
//
// 1. Go to your computers/phones settings
// 2. Ensure Bluetooth is turned on
// 3. Scan for Bluetooth devices
// 4. Connect to the device called "ESP32 Keyboard"
// 5. Open an empty document in a text editor
// 6. Press the button attached to the ESP32
#define US_KEYBOARD 1
#include <Arduino.h>
#include "BLEDevice.h"
#include "BLEHIDDevice.h"
#include "HIDTypes.h"
#include "HIDKeyboardTypes.h"
// Change the below values if desired
#define BUTTON_PIN 2
#define MESSAGE "Hello from ESP32\n"
#define DEVICE_NAME "ESP32 Keyboard"
// Forward declarations
void bluetoothTask(void*);
void typeText(const char* text);
bool isBleConnected = false;
void setup() {
Serial.begin(115200);
// configure pin for button
pinMode(BUTTON_PIN, INPUT_PULLUP);
// start Bluetooth task
xTaskCreate(bluetoothTask, "bluetooth", 20000, NULL, 5, NULL);
}
void loop() {
if (isBleConnected && digitalRead(BUTTON_PIN) == LOW) {
// button has been pressed: type message
Serial.println(MESSAGE);
typeText(MESSAGE);
}
delay(100);
}
// Message (report) sent when a key is pressed or released
struct InputReport {
uint8_t modifiers; // bitmask: CTRL = 1, SHIFT = 2, ALT = 4
uint8_t reserved; // must be 0
uint8_t pressedKeys[6]; // up to six concurrenlty pressed keys
};
// Message (report) received when an LED's state changed
struct OutputReport {
uint8_t leds; // bitmask: num lock = 1, caps lock = 2, scroll lock = 4, compose = 8, kana = 16
};
// The report map describes the HID device (a keyboard in this case) and
// the messages (reports in HID terms) sent and received.
static const uint8_t REPORT_MAP[] = {
USAGE_PAGE(1), 0x01, // Generic Desktop Controls
USAGE(1), 0x06, // Keyboard
COLLECTION(1), 0x01, // Application
REPORT_ID(1), 0x01, // Report ID (1)
USAGE_PAGE(1), 0x07, // Keyboard/Keypad
USAGE_MINIMUM(1), 0xE0, // Keyboard Left Control
USAGE_MAXIMUM(1), 0xE7, // Keyboard Right Control
LOGICAL_MINIMUM(1), 0x00, // Each bit is either 0 or 1
LOGICAL_MAXIMUM(1), 0x01,
REPORT_COUNT(1), 0x08, // 8 bits for the modifier keys
REPORT_SIZE(1), 0x01,
HIDINPUT(1), 0x02, // Data, Var, Abs
REPORT_COUNT(1), 0x01, // 1 byte (unused)
REPORT_SIZE(1), 0x08,
HIDINPUT(1), 0x01, // Const, Array, Abs
REPORT_COUNT(1), 0x06, // 6 bytes (for up to 6 concurrently pressed keys)
REPORT_SIZE(1), 0x08,
LOGICAL_MINIMUM(1), 0x00,
LOGICAL_MAXIMUM(1), 0x65, // 101 keys
USAGE_MINIMUM(1), 0x00,
USAGE_MAXIMUM(1), 0x65,
HIDINPUT(1), 0x00, // Data, Array, Abs
REPORT_COUNT(1), 0x05, // 5 bits (Num lock, Caps lock, Scroll lock, Compose, Kana)
REPORT_SIZE(1), 0x01,
USAGE_PAGE(1), 0x08, // LEDs
USAGE_MINIMUM(1), 0x01, // Num Lock
USAGE_MAXIMUM(1), 0x05, // Kana
LOGICAL_MINIMUM(1), 0x00,
LOGICAL_MAXIMUM(1), 0x01,
HIDOUTPUT(1), 0x02, // Data, Var, Abs
REPORT_COUNT(1), 0x01, // 3 bits (Padding)
REPORT_SIZE(1), 0x03,
HIDOUTPUT(1), 0x01, // Const, Array, Abs
END_COLLECTION(0) // End application collection
};
BLEHIDDevice* hid;
BLECharacteristic* input;
BLECharacteristic* output;
const InputReport NO_KEY_PRESSED = { };
/*
* Callbacks related to BLE connection
*/
class BleKeyboardCallbacks : public BLEServerCallbacks {
void onConnect(BLEServer* server) {
isBleConnected = true;
// Allow notifications for characteristics
BLE2902* cccDesc = (BLE2902*)input->getDescriptorByUUID(BLEUUID((uint16_t)0x2902));
cccDesc->setNotifications(true);
Serial.println("Client has connected");
}
void onDisconnect(BLEServer* server) {
isBleConnected = false;
// Disallow notifications for characteristics
BLE2902* cccDesc = (BLE2902*)input->getDescriptorByUUID(BLEUUID((uint16_t)0x2902));
cccDesc->setNotifications(false);
Serial.println("Client has disconnected");
}
};
/*
* Called when the client (computer, smart phone) wants to turn on or off
* the LEDs in the keyboard.
*
* bit 0 - NUM LOCK
* bit 1 - CAPS LOCK
* bit 2 - SCROLL LOCK
*/
class OutputCallbacks : public BLECharacteristicCallbacks {
void onWrite(BLECharacteristic* characteristic) {
OutputReport* report = (OutputReport*) characteristic->getData();
Serial.print("LED state: ");
Serial.print((int) report->leds);
Serial.println();
}
};
void bluetoothTask(void*) {
// initialize the device
BLEDevice::init(DEVICE_NAME);
BLEServer* server = BLEDevice::createServer();
server->setCallbacks(new BleKeyboardCallbacks());
// create an HID device
hid = new BLEHIDDevice(server);
input = hid->inputReport(1); // report ID
output = hid->outputReport(1); // report ID
output->setCallbacks(new OutputCallbacks());
// set manufacturer name
hid->manufacturer()->setValue("Maker Community");
// set USB vendor and product ID
hid->pnp(0x02, 0xe502, 0xa111, 0x0210);
// information about HID device: device is not localized, device can be connected
hid->hidInfo(0x00, 0x02);
// Security: device requires bonding
BLESecurity* security = new BLESecurity();
security->setAuthenticationMode(ESP_LE_AUTH_BOND);
// set report map
hid->reportMap((uint8_t*)REPORT_MAP, sizeof(REPORT_MAP));
hid->startServices();
// set battery level to 100%
hid->setBatteryLevel(100);
// advertise the services
BLEAdvertising* advertising = server->getAdvertising();
advertising->setAppearance(HID_KEYBOARD);
advertising->addServiceUUID(hid->hidService()->getUUID());
advertising->addServiceUUID(hid->deviceInfo()->getUUID());
advertising->addServiceUUID(hid->batteryService()->getUUID());
advertising->start();
Serial.println("BLE ready");
delay(portMAX_DELAY);
};
void typeText(const char* text) {
int len = strlen(text);
for (int i = 0; i < len; i++) {
// translate character to key combination
uint8_t val = (uint8_t)text[i];
if (val > KEYMAP_SIZE)
continue; // character not available on keyboard - skip
KEYMAP map = keymap[val];
// create input report
InputReport report = {
.modifiers = map.modifier,
.reserved = 0,
.pressedKeys = {
map.usage,
0, 0, 0, 0, 0
}
};
// send the input report
input->setValue((uint8_t*)&report, sizeof(report));
input->notify();
delay(5);
// release all keys between two characters; otherwise two identical
// consecutive characters are treated as just one key press
input->setValue((uint8_t*)&NO_KEY_PRESSED, sizeof(NO_KEY_PRESSED));
input->notify();
delay(5);
}
}
@solilu7
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solilu7 commented Aug 5, 2024

Hi,
i've a problem with some android devices with some Andorid devices (10 12 and 13 version, all chinese brand, oukitel, ulefone, hugerock)
EP32-C3 boards, i have this behavior:

I connect Esp32 board to smatphone searching a new device, it connects.
Then i switch-off and then switch-on (or simply reboot) Esp32 board, on the smatphone ESP-32 appears on "device cennected" section just for an instant, then disappears (obviusly it is not connected).
if i want reconnect i have to repeat all procedure (searching ecc).

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