Example Code for Arduino-Two ESP32C3 Bluetooth Communication

Hardware Preparation

• DFR0868 Beetle ESP32-C3 x 2

Software Preparation

• Download Arduino IDE: Click to download Arduino IDE
• Add ESP32 board to Arduino IDE

Sample Code

Host code

/**
 * A BLE client example that is rich in capabilities.
 * There is a lot new capabilities implemented.
 * author unknown
 * updated by chegewara
 */

#include "BLEDevice.h"
//#include "BLEScan.h"

// The remote service we wish to connect to.
static BLEUUID serviceUUID("4fafc201-1fb5-459e-8fcc-c5c9c331914b");
// The characteristic of the remote service we are interested in.
static BLEUUID    charTXUUID("beb5483e-36e1-4688-b7f5-ea07361b26a8");

static BLEUUID    charRXUUID("beb5483f-36e1-4688-b7f5-ea07361b26a8");

static boolean doConnect = false;
static boolean connected = false;
static boolean doScan = false;
static BLERemoteCharacteristic* pTXRemoteCharacteristic;
static BLERemoteCharacteristic* pRXRemoteCharacteristic;
static BLEAdvertisedDevice* myDevice;


/****************Data receiving section*************/
/****************************************/
//Bluetooth receive data processing, automatically trigger when data is received
static void notifyCallback(BLERemoteCharacteristic* pBLERemoteCharacteristic, uint8_t* pData, size_t length, bool isNotify) {  //Transfer in uint8_t* pData to store data
    String BLEData = "";
    for(int i = 0; i < length; i++)  //
      BLEData += (char)pData[i];
    Serial.println("*********");
    Serial.print("Received Value: ");
    Serial.println(BLEData);
    Serial.println("*********");

    //if(BLEData == "ON"){Serial.println("Turn on the light");}  //Determine whether the received character is "ON"

    //Serial.print("Notify callback for characteristic ");
    //Serial.print(pBLERemoteCharacteristic->getUUID().toString().c_str());
    //Serial.print(" of data length ");
    //Serial.println(length);
}
/****************************************/
/****************************************/

//Bluetooth connect/disconnect handling. Triggered automatically when a connect/disconnect event occurs
class MyClientCallback : public BLEClientCallbacks {
  void onConnect(BLEClient* pclient) {
  }

  void onDisconnect(BLEClient* pclient) {
    connected = false;
    Serial.println("onDisconnect");
  }
};


/**
 * Scan for BLE servers and find the first one that advertises the service we are looking for.
 */
 //Bluetooth scan processing event. Triggered automatically when scanning is turned on
class MyAdvertisedDeviceCallbacks: public BLEAdvertisedDeviceCallbacks {
 /**
   * Called for each advertising BLE server.
   */
  void onResult(BLEAdvertisedDevice advertisedDevice) {
    //Serial.print("BLE Advertised Device found: ");
    //Serial.println(advertisedDevice.toString().c_str());

    // We have found a device, let us now see if it contains the service we are looking for.
    if (advertisedDevice.haveServiceUUID() && advertisedDevice.isAdvertisingService(serviceUUID)) {
      BLEDevice::getScan()->stop();
      myDevice = new BLEAdvertisedDevice(advertisedDevice);
      doConnect = true;
      doScan = true;

    } // Found our server
  } // onResult
}; // MyAdvertisedDeviceCallbacks



void setup() {
  Serial.begin(115200);
  Serial.println("Starting Arduino BLE Client application...");
  bleBegin();

}

void loop() {
  // If the flag "doConnect" is true then we have scanned for and found the desired
  // BLE Server with which we wish to connect.  Now we connect to it.  Once we are 
  // connected we set the connected flag to be true.
  if (doConnect == true) {
    if (connectToServer()) {
      Serial.println("We are now connected to the BLE Server.");
    } else {
      Serial.println("We have failed to connect to the server; there is nothin more we will do.");
    }
    doConnect = false;
  }
/****************Data transmitting section*************/
/****************************************/
  if (connected) {  //Send data when connected to bluetooth slave
    pTXRemoteCharacteristic->writeValue("I am the host");
    pTXRemoteCharacteristic->writeValue("Hello client");
  }
  if(!connected){  //Rescan when not connected to bluetooth slave
    BLEDevice::getScan()->start(5,false);  // this is just example to start scan after disconnect, most likely there is better way to do it in arduino
  }
/****************************************/
/****************************************/
  delay(1000); 
}


void bleBegin()
{
  BLEDevice::init("");

  // Retrieve a Scanner and set the callback we want to use to be informed when we
  // have detected a new device.  Specify that we want active scanning and start the
  // scan to run for 5 seconds.
  BLEScan* pBLEScan = BLEDevice::getScan();
  pBLEScan->setAdvertisedDeviceCallbacks(new MyAdvertisedDeviceCallbacks());//Scan processing function
  pBLEScan->setInterval(1349);//Set the scan interval time
  pBLEScan->setWindow(449);//Active scan time
  pBLEScan->setActiveScan(true);
  pBLEScan->start(5, false);//Scan time, in seconds
  }


//Bluetooth connection processing
bool connectToServer() {
    Serial.print("Forming a connection to ");
    Serial.println(myDevice->getAddress().toString().c_str());

    BLEClient*  pClient  = BLEDevice::createClient();
    Serial.println(" - Created client");

    pClient->setClientCallbacks(new MyClientCallback());

    // Connect to the remove BLE Server.
    pClient->connect(myDevice);  // if you pass BLEAdvertisedDevice instead of address, it will be recognized type of peer device address (public or private)
    Serial.println(" - Connected to server");
    pClient->setMTU(517); //set client to request maximum MTU from server (default is 23 otherwise)

    // Obtain a reference to the service we are after in the remote BLE server.
    BLERemoteService* pRemoteService = pClient->getService(serviceUUID);
    if (pRemoteService == nullptr) {
      Serial.print("Failed to find our service UUID: ");
      Serial.println(serviceUUID.toString().c_str());
      pClient->disconnect();
      return false;
    }
    Serial.println(" - Found our service");


    // Obtain a reference to the characteristic in the service of the remote BLE server.
    pTXRemoteCharacteristic = pRemoteService->getCharacteristic(charTXUUID);
    if (pTXRemoteCharacteristic == nullptr) {
      Serial.print("Failed to find our characteristic UUID: ");
      Serial.println(charTXUUID.toString().c_str());
      pClient->disconnect();
      return false;
    }
    pRXRemoteCharacteristic = pRemoteService->getCharacteristic(charRXUUID);
    if (pRXRemoteCharacteristic == nullptr) {
      Serial.print("Failed to find our characteristic UUID: ");
      Serial.println(charRXUUID.toString().c_str());
      pClient->disconnect();
      return false;
    }
    Serial.println(" - Found our characteristic");

    if(pRXRemoteCharacteristic->canNotify())
      pRXRemoteCharacteristic->registerForNotify(notifyCallback);

    connected = true;
    return true;
}

Slave code

/*
    Based on Neil Kolban example for IDF: https://github.com/nkolban/esp32-snippets/blob/master/cpp_utils/tests/BLE%20Tests/SampleServer.cpp
    Ported to Arduino ESP32 by Evandro Copercini
    updates by chegewara
*/

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

// See the following for generating UUIDs:
// https://www.uuidgenerator.net/

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID_RX "beb5483e-36e1-4688-b7f5-ea07361b26a8"
#define CHARACTERISTIC_UUID_TX "beb5483f-36e1-4688-b7f5-ea07361b26a8"
uint8_t txValue = 0;
bool deviceConnected = false;
BLECharacteristic *pTxCharacteristic;


//Bluetooth connect/disconnect processing. Triggered automatically when a connect/disconnect event occurs
class MyServerCallbacks: public BLEServerCallbacks {
    void onConnect(BLEServer* pServer) {   //This function will be executed when Bluetooth is connected
      Serial.println("Bluetooth connected");
      deviceConnected = true;
    };

    void onDisconnect(BLEServer* pServer) {  //This function will be executed when Bluetooth is disconnected
        Serial.println("Bluetooth disconnected");
        deviceConnected = false;
        delay(500); // give the bluetooth stack the chance to get things ready
        BLEDevice::startAdvertising(); // restart advertising
    }
};
/****************Data receiving section*************/
/****************************************/
//Bluetooth receive data processing. Triggered automatically when data is received
class MyCallbacks: public BLECharacteristicCallbacks {
    void onWrite(BLECharacteristic *pCharacteristic) {
      String rxValue = pCharacteristic->getValue();  //Use rxValue to receive data

      //if(rxValue == "ON"){Serial.println("Turn on the light");}   //Determine whether the received character is "ON"

      if (rxValue.length() > 0) {
        Serial.println("*********");
        Serial.print("Received Value: ");
        for (int i = 0; i < rxValue.length(); i++)
              Serial.print(rxValue[i]);    //Print the received data

        Serial.println();
        Serial.println("*********");
      }
    }
};
/****************************************/
/****************************************/

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

/****************Data sending section*************/
/****************************************/
void loop() {
  if(deviceConnected){  //Send data when a device is connected
    pTxCharacteristic->setValue("I am a slave");
    pTxCharacteristic->notify();

    pTxCharacteristic->setValue("Hello Sever");
    pTxCharacteristic->notify();
  }
  /****************************************/
  /****************************************/
  delay(1000);
}


void bleBegin()
{
  BLEDevice::init(/*BLE name*/"Long name works now");
  BLEServer *pServer = BLEDevice::createServer();
  pServer->setCallbacks(new MyServerCallbacks());
  BLEService *pService = pServer->createService(SERVICE_UUID);
  BLECharacteristic *pRxCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID_RX,
                                         BLECharacteristic::PROPERTY_WRITE 
                                       );
  pRxCharacteristic->setCallbacks(new MyCallbacks()); 

 pTxCharacteristic = pService->createCharacteristic(
                                         CHARACTERISTIC_UUID_TX,
                                         BLECharacteristic::PROPERTY_NOTIFY
                                       );
 pTxCharacteristic->addDescriptor(new BLE2902());

  pService->start();
  // BLEAdvertising *pAdvertising = pServer->getAdvertising();  // this still is working for backward compatibility
  BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
  pAdvertising->addServiceUUID(SERVICE_UUID);
  pAdvertising->setScanResponse(true);
  pAdvertising->setMinPreferred(0x06);  // functions that help with iPhone connections issue
  pAdvertising->setMinPreferred(0x12);
  BLEDevice::startAdvertising();

  }