Hello Raspberry Pi: ESP32 BLE Client remote control Raspberry Pi Pico/HC-08 via Bluetooth

Friday, February 5, 2021

ESP32 BLE Client remote control Raspberry Pi Pico/HC-08 via Bluetooth

Previous exercise show how Raspberry Pi/Python remote control LED on Raspberry Pi Pico/MicroPython with HC-08. It's a ESP32 (Arduino framework) implementation on the client side, connect and send command to Pico/HC-08 BLE server to turn on/off the LED.

The code modified from Arduino IDE's Examples > ESP32 BLE Arduino > BLE_client. To make it simple, just apply minimum change to search target UUIDs, connect to BLE server and send commands ("#LEDON\r\n"/"#LEDOFF\r\n") to toggle LED repeatedly.

The main point is BLE_client example assume the BLE server have one UUID for both advertise and service, both on HC-08 have two separated UUIDs for search (LUUID) and service(SUUID). So I have to define LUUID and SUUID separately. I fix it by guessing and trying, not sure is it a correct practice or not.

Tested on ESP32-DevKitC V4, with Raspberry Pi Pico/HC-08 BLE server.

Arduino code run on ESP32, ESP32_BLE_client_HC08.ino

/**
 * 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"

//Following UUIDs have to match with
// HC-08 LUUID/SUUID/TUUID
// The remote service we wish to connect to.
static BLEUUID  LUUID("FFF0");
static BLEUUID  SUUID("FFE0");
// The characteristic of the remote service we are interested in.
static BLEUUID  charUUID("FFE1");

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

boolean onLED = true;

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(SUUID);
    if (pRemoteService == nullptr) {
      Serial.print("Failed to find our search UUID: ");
      Serial.println(SUUID.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;
    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());

    //for information
    Serial.println("advertisedDevice.haveServiceUUID(): " + 
                      String(advertisedDevice.haveServiceUUID()));
    Serial.println("advertisedDevice.isAdvertisingService(LUUID): " + 
                      String(advertisedDevice.isAdvertisingService(LUUID)));

    // We have found a device, let us now see if it contains the service we are looking for.
    if (advertisedDevice.haveServiceUUID() && advertisedDevice.isAdvertisingService(LUUID)) {

      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
  // to toggle LED.
  if (connected) {
    String newValue;

    if(onLED){
      onLED = false;
      newValue = "#LEDON\r\n";
    }else{
      onLED = true;
      newValue = "#LEDOFF\r\n";
    }
    
    Serial.println("Setting new characteristic value to \"" + newValue + "\"");
    
    // Set the characteristic's value to be the array of bytes that is actually a string.
    pRemoteCharacteristic->writeValue(newValue.c_str(), newValue.length());
  }else if(doScan){
    BLEDevice::getScan()->start(0);  
    // this is just eample to start scan after disconnect, 
    // most likely there is better way to do it in arduino
  }
  
  delay(1000); // Delay a second between loops.
} // End of loop