Read Value

The following example creates a BLE server with a single service and characteristic. The characteristic can be read by a connected BLE client.

Steps:

1. Set up the ESP32 as a BLE server.
2. Advertise the server so that it can be discovered by BLE clients.
3. Define a BLE service and a read-only characteristic.
4. Allow the client to read the characteristic value.

Code:

#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>

// Define the BLE service and characteristic UUIDs
#define SERVICE_UUID           "12345678-1234-1234-1234-123456789abc"
#define CHARACTERISTIC_UUID    "87654321-4321-4321-4321-abcdef123456"

// The characteristic value
const char* value = "Hello from Lonely Binary's ESP32!";

// Set up BLE server and characteristic
BLECharacteristic *pCharacteristic;
BLEServer *pServer;

void setup() {
  // Start Serial Monitor for debugging
  Serial.begin(115200);
  Serial.println("Starting BLE Server...");

  // Initialize BLE device
  BLEDevice::init("Lonely_Binary_ESP32_BLE_Server");

  // Create BLE server
  pServer = BLEDevice::createServer();

  // Create a service
  BLEService *pService = pServer->createService(SERVICE_UUID);

  // Create a characteristic
  pCharacteristic = pService->createCharacteristic(
                        CHARACTERISTIC_UUID,
                        BLECharacteristic::PROPERTY_READ
                      );

  // Set the initial value of the characteristic
  pCharacteristic->setValue(value);

  // Add a descriptor for the characteristic (optional)
  pCharacteristic->addDescriptor(new BLE2902());

  // Start the service
  pService->start();

  // Start advertising the BLE server
  BLEAdvertising *pAdvertising = pServer->getAdvertising();
  pAdvertising->start();

  Serial.println("Waiting for client to connect...");
}

void loop() {
  // Nothing to do in the loop, as BLE is handled in background
  delay(1000);
}

Explanation:

• BLEDevice::init(“Lonely_Binary_ESP32_BLE_Server”) initializes the BLE stack and gives the device a name (ESP32_BLE_Server).
• createServer() creates a BLE server.
• createService(SERVICE_UUID) creates a BLE service using a unique UUID (12345678-1234-1234-1234-123456789abc).
• createCharacteristic(CHARACTERISTIC_UUID, BLECharacteristic::PROPERTY_READ) creates a read-only characteristic with a unique UUID (87654321-4321-4321-4321-abcdef123456).
• setValue(value) sets the initial value of the characteristic to “Hello from Lonely Binary’s ESP32!.
• getAdvertising()->start() starts advertising the BLE server, so it can be discovered by BLE clients.

How to Test:

1. Upload the code to your ESP32.
2. Use a BLE client app nRF Connect for mobile on your phone.
3. Search for ESP32_BLE_Server in the BLE client app and connect to it.
4. Once connected, you should be able to read the characteristic value (“Hello from Lonely Binary’s ESP32!”).