ESP32/Arduino BLE UART Client connect to Raspberry Pi Pico/CircuitPython + ESP32/nina-fw

It's a BLE UART Client exercise run on ESP2-DevKitC using arduino-esp32 framework. Connect to cpyPico_ESP32_BLE.py in Raspberry Pi Pico/CircuitPython + ESP32/adafruit nina-fw (act as WiFi/BLE Co-Processor).

It search BLE device with specified service UUID, and characteristics for TX and RX. Then sending something every 5 seconds. In the Pico/CircuitPython +ESP32/nina-fw server side, receive and echo back every bytes. This client then print the received byte on Terminal.

ESP32_BLE_client.ino

/*
Modify from Arduino Examples for ESP32 Dev Module:
>  ESP32 BLE Arduino > BLE_client
 */

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

#define SERVICE_UUID           "6E400001-B5A3-F393-E0A9-E50E24DCCA9E" // UART service UUID
#define CHARACTERISTIC_UUID_RX "6E400002-B5A3-F393-E0A9-E50E24DCCA9E" // RX Characteristic
#define CHARACTERISTIC_UUID_TX "6E400003-B5A3-F393-E0A9-E50E24DCCA9E" // TX Characteristic
static BLEUUID serviceUUID(SERVICE_UUID);
static BLEUUID charUUID_RX(CHARACTERISTIC_UUID_RX);   
static BLEUUID charUUID_TX(CHARACTERISTIC_UUID_TX);  

static boolean doConnect = false;
static boolean connected = false;
static boolean doScan = false;
static BLERemoteCharacteristic* pTXCharacteristic;
static BLERemoteCharacteristic* pRXCharacteristic;
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);
    */
    Serial.print((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.
    // charUUID_TX
    pTXCharacteristic = pRemoteService->getCharacteristic(charUUID_TX);
    if (pTXCharacteristic == nullptr) {
      Serial.print("Failed to find our characteristic UUID: ");
      Serial.println(charUUID_TX.toString().c_str());
      pClient->disconnect();
      return false;
    }
    Serial.println(" - Found charUUID_TX characteristic");

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

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

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

    String helloValue = "Hello Remote Server";
    pRXCharacteristic->writeValue(helloValue.c_str(), helloValue.length());

    

    // =================================================================================
    connected = true;
    return 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;
  }

  // If we are connected to a peer BLE Server, 
  // update the characteristic each time we are reached
  // with the current time since boot.
  if (connected) {
    //String newValue = "Time since boot: " + String(millis()/1000 + "\n");
    //Serial.println("Setting new characteristic value to \"" + newValue + "\"");

    String newValue = " " + String(millis()/1000);
    // Set the characteristic's value to be the array of bytes that is actually a string.
    pRXCharacteristic->writeValue(newValue.c_str(), newValue.length());
  }else if(doScan){
    BLEDevice::getScan()->start(0);  
    // this is just example to start scan after disconnect, 
    // most likely there is better way to do it in arduino
  }
  
  delay(5000); // Delay a second between loops.
} // End of loop