Automatic pairing of ESP32 using BLE

salmanfaris

@kowshik1729 Ok, then could you please share the central and peripheral code? can't find anything from the error instead of the missing function!

kowshik1729

@salmanfaris
Sure...Here are my the codes that I have used.

kowshik1729

@kowshik1729

//                                Server side code
/*
  A connect hander associated with the server starts a background task that performs notification
  every couple of seconds.
*/
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>


#ifdef __cplusplus
extern "C" {
#endif
uint8_t temprature_sens_read();
#ifdef __cplusplus
}
#endif
uint8_t temprature_sens_read();



BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
float mea = 0;
int LED13 = 5;   //  The on-board Arduion LED

// https://www.uuidgenerator.net/

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"


class MyServerCallbacks: public BLEServerCallbacks {
   void onConnect(BLEServer* pServer) {
     deviceConnected = true;
   };

   void onDisconnect(BLEServer* pServer) {
     deviceConnected = false;
   }
};




void setup() {
 Serial.begin(115200);

 // Create the BLE Device
 BLEDevice::init("ESP32");

 // Create the BLE Server
 pServer = BLEDevice::createServer();
 pServer->setCallbacks(new MyServerCallbacks());

 // Create the BLE Service
 BLEService *pService = pServer->createService(SERVICE_UUID);

 // Create a BLE Characteristic
 pCharacteristic = pService->createCharacteristic(
                     CHARACTERISTIC_UUID,
                     BLECharacteristic::PROPERTY_READ   |
                     BLECharacteristic::PROPERTY_WRITE  |
                     BLECharacteristic::PROPERTY_NOTIFY 
                   );

 // https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml
 // Create a BLE Descriptor
 pCharacteristic->addDescriptor(new BLE2902());

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

 // Start advertising
 BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
 pAdvertising->addServiceUUID(SERVICE_UUID);
 pAdvertising->setScanResponse(false);
 pAdvertising->setMinPreferred(0x0);  // set value to 0x00 to not advertise this parameter
 BLEDevice::startAdvertising();
 pinMode(LED13, OUTPUT);
 Serial.println("Waiting a client connection to notify...");

}

void loop() {
 // notify changed value
  // Read the PulseSensor's value.
 // Assign this value to the "Signal" variable.
 if (deviceConnected) 
 {
   mea = (temprature_sens_read()-32)/1.8;
   String send_Data = String(mea);
   pCharacteristic->setValue(send_Data);
   pCharacteristic->notify();
   
   // bluetooth stack will go into congestion, if too many packets are sent, in 6 hours test i was able to go as low as 3ms
 }
 else 
 {
   digitalWrite(LED13, LOW);               //  Else, the sigal must be below "550", so "turn-off" this LED.
 }

 delay(10);

}

The following code is for the Client side.

//                                             Client Side code

#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    charUUID("beb5483e-36e1-4688-b7f5-ea07361b26a8");

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

static void notifyCallback(
  BLERemoteCharacteristic* pBLERemoteCharacteristic,
  uint8_t* pData,
  size_t length,
  bool isNotify) {
  Serial.print("Notify callback for characteristic ");
  Serial.print(pBLERemoteCharacteristic->getUUID().toString().c_str());
  Serial.print(" of data length ");
  Serial.println(length);
  Serial.print("data: ");
  Serial.println((char*)pData);
}

class MyClientCallback : public BLEClientCallbacks {
  void onConnect(BLEClient* pclient) {
  }

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

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");

    // 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.
    pRemoteCharacteristic = pRemoteService->getCharacteristic(charUUID);
    if (pRemoteCharacteristic == nullptr) {
      Serial.print("Failed to find our characteristic UUID: ");
      Serial.println(charUUID.toString().c_str());
      pClient->disconnect();
      return false;
    }
    Serial.println(" - Found our characteristic");

    // Read the value of the characteristic.
    if(pRemoteCharacteristic->canRead()) {
      std::string value = pRemoteCharacteristic->readValue();
      Serial.print("The characteristic value was: ");
      Serial.println(value.c_str());
    }

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

    connected = true;
}
/**
 * Scan for BLE servers and find the first one that advertises the service we are looking for.
 */
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...");
  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());
  pBLEScan->setInterval(1349);
  pBLEScan->setWindow(449);
  pBLEScan->setActiveScan(true);
  pBLEScan->start(5, false);
} // End of setup.


// This is the Arduino main loop function.
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;
  }

  delay(1000); // Delay a second between loops.
} // End of loop

salmanfaris

@kowshik1729 You are trying to pass a string value (send_Data) to a pointer object(setValue), to solve that you should use std::string class which is an instantiation of the basic_string class template that uses char (i.e., bytes) as its character type.

Comment line no.96 which doing convertion from Float value into String using the String constructor

// String send_Data = String(mea);

and add the following line to use the std:string this will help represent the sequence of characters as an object of the class .

std::string send_Data((char*)&mea, 2);

edited code

//                                Server side code
/*
  A connect hander associated with the server starts a background task that performs notification
  every couple of seconds.
*/
#include <BLEDevice.h>
#include <BLEServer.h>
#include <BLEUtils.h>
#include <BLE2902.h>
#include <BLECharacteristic.h>


#ifdef __cplusplus
extern "C" {
#endif
uint8_t temprature_sens_read();
#ifdef __cplusplus
}
#endif
uint8_t temprature_sens_read();



BLEServer* pServer = NULL;
BLECharacteristic* pCharacteristic = NULL;
bool deviceConnected = false;
bool oldDeviceConnected = false;
float mea = 0;
int LED13 = 5;   //  The on-board Arduion LED

// https://www.uuidgenerator.net/

#define SERVICE_UUID        "4fafc201-1fb5-459e-8fcc-c5c9c331914b"
#define CHARACTERISTIC_UUID "beb5483e-36e1-4688-b7f5-ea07361b26a8"


class MyServerCallbacks: public BLEServerCallbacks {
   void onConnect(BLEServer* pServer) {
     deviceConnected = true;
   };

   void onDisconnect(BLEServer* pServer) {
     deviceConnected = false;
   }
};




void setup() {
 Serial.begin(115200);

 // Create the BLE Device
 BLEDevice::init("ESP32");

 // Create the BLE Server
 pServer = BLEDevice::createServer();
 pServer->setCallbacks(new MyServerCallbacks());

 // Create the BLE Service
 BLEService *pService = pServer->createService(SERVICE_UUID);

 // Create a BLE Characteristic
 pCharacteristic = pService->createCharacteristic(
                     CHARACTERISTIC_UUID,
                     BLECharacteristic::PROPERTY_READ   |
                     BLECharacteristic::PROPERTY_WRITE  |
                     BLECharacteristic::PROPERTY_NOTIFY 
                   );

 // https://www.bluetooth.com/specifications/gatt/viewer?attributeXmlFile=org.bluetooth.descriptor.gatt.client_characteristic_configuration.xml
 // Create a BLE Descriptor
 pCharacteristic->addDescriptor(new BLE2902());

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

 // Start advertising
 BLEAdvertising *pAdvertising = BLEDevice::getAdvertising();
 pAdvertising->addServiceUUID(SERVICE_UUID);
 pAdvertising->setScanResponse(false);
 pAdvertising->setMinPreferred(0x0);  // set value to 0x00 to not advertise this parameter
 BLEDevice::startAdvertising();
 pinMode(LED13, OUTPUT);
 Serial.println("Waiting a client connection to notify...");

}

void loop() {
 // notify changed value
  // Read the PulseSensor's value.
 // Assign this value to the "Signal" variable.
 if (deviceConnected) 
 {
   mea = (temprature_sens_read()-32)/1.8;
  // String send_Data = String(mea);
   std::string send_Data((char*)&mea, 2);
   pCharacteristic->setValue(send_Data);
   pCharacteristic->notify();
   
   // bluetooth stack will go into congestion, if too many packets are sent, in 6 hours test i was able to go as low as 3ms
 }
 else 
 {
   digitalWrite(LED13, LOW);               //  Else, the sigal must be below "550", so "turn-off" this LED.
 }

 delay(10);

}

Try it out.

kowshik1729

@salmanfaris Thanks for correcting me back. I implemented this on my ESP's and the data that I acquired on the client end is very weird as shown in the below image and whereas my client-side code remained the same as shown in the previous post.

salmanfaris

@kowshik1729 The value you are getting is hex, you should convert the receved hex into to string, int or float in order to see the data.

you can also debug BLE applications using the nRF Connect by Nordic Semiconductor.

kowshik1729

@salmanfaris Thanks for the reply. I have two concerns with the reply.

I am making an application where the information from the server ESP32 must be sent only to another ESP which means I am not going to read it over phone or anything like that. So, I can't use nRF connect app for my project.
But, anyways I used the app for debugging my project and the information received by me on the phone is something as shown in the below snapshot.

Please help me out with this sir..!!

salmanfaris

@kowshik1729 The nRF app is very helpful for debugging the BLE application like I said the previous replay " The value you are getting as hex,so you should convert the received hex into to string, int or float in order to see the data. " .

kowshik1729

static void notifyCallback (BLERemoteCharacteristic * pBLERemoteCharacteristic,
uint8_t * pData, size_t length, bool isNotify)
{
  Serial.print ("Notify callback for characteristic ");
  Serial.print (pBLERemoteCharacteristic->getUUID ().toString ().c_str ());
  Serial.print (" of data length ");
  Serial.println (length);
  Serial.print ("data: ");
  Serial.println ((char *) pData); 
}

@salmanfaris With a little research I got to know I need to work out on this notifyCallBack function. I have a doubt, just by type casting the last line of code to my required data type will solve the problem?

Serial.println(int((char* )pData));

Will this solve my problem?

salmanfaris

@kowshik1729 You may try it out , that's the best way to check it's working or not .

Automatic pairing of ESP32 using BLE

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