Send big string through BLE

Using Arduino Project Guidance
1

Hello,

I am trying to send image data captured using Arduino nano BLE 33 sense to Raspberry pi using BLE.
I storing image pixels values in a String variable then I want to send this string to Pi.
when I try to write value to characteristic using writeValue() function, it does not work for string variable but if I write a string in quotation marks it does not show errors.
This code:
imgChar.writeValue(img);
shows this error:
Note: img is the string that I use to store image data


CaptureImgSendPiBle:102:28: error: no matching function for call to 
'BLECharacteristic::writeValue(arduino::String&)'
      imgChar.writeValue(img);

This is part of the image data that I am trying to send

0x905B, 0x905B, 0xB05B, 0xB05B, 0xB05B, 0xB05B, 0xB05B, 0xD05B, 0xD05B, 0xD05B, 0xD05B, 0xD05B, 0xD05B, 0xB063, 0xB05B, 0xB05B, 0xD05B, 0xD05B, 0xD05B, 0xD05B, 0xB05B, 0xD063, 0xB063, 0xB15B, 0xD163, 0xD063, 0xD063, 0xD163, 0xD163, 0xD163, 0xF163, 0xF163, 0xD163, 0xD163, 0xD163, 0xD163, 0xD16B, 0xF16B, 0xF16B, 0xF16B, 0xF16B, 0xF16B, 0xF16B, 0xF16B ....

How can I send these data through BLE?

The full code:


#include <ArduinoBLE.h>
#include <Arduino_OV767X.h>

 // BLE Battery Service
BLEService imgService("66CCBD0A-4051-43E9-8298-C1BD33088331");

// BLE Battery Level Characteristic
BLECharacteristic imgChar("3B4ED73A-7853-4CA8-AED2-AEB6F68F39A3",  BLERead, ""); // remote clients will be able to get notifications if this characteristic changes

byte image[176 * 144 * 2]; // QCIF: 176x144 X 2 bytes per pixel (RGB565)
int bytesPerFrame;
bool c = true;
String img = "";

void setup() {
  Serial.begin(9600);    // initialize serial communication
 // while (!Serial);

  pinMode(LED_BUILTIN, OUTPUT); // initialize the built-in LED pin to indicate when a central is connected

  // begin initialization
  if (!BLE.begin()) {
    Serial.println("starting BLE failed!");
    while (1);
  }

  /* Set a local name for the BLE device
     This name will appear in advertising packets
     and can be used by remote devices to identify this BLE device
     The name can be changed but maybe be truncated based on space left in advertisement packet
  */
  BLE.setLocalName("Nano");
  BLE.setAdvertisedService(imgService); // add the service UUID
  
  imgService.addCharacteristic(imgChar); // add the battery level characteristic
  
  BLE.addService(imgService); // Add the battery service
  imgChar.setValue(0); // set initial value for this characteristic

  /* Start advertising BLE.  It will start continuously transmitting BLE
     advertising packets and will be visible to remote BLE central devices
     until it receives a new connection */

  // start advertising
  BLE.advertise();
  Serial.println("Bluetooth device active, waiting for connections...");
  Serial.println(BLE.address());

  //init camera
    if (!Camera.begin(QCIF, RGB565, 1)) {
    Serial.println("Failed to initialize camera!");
    while (1);}
    
    bytesPerFrame = Camera.width() * Camera.height() * Camera.bytesPerPixel();
}

void loop() {
  // wait for a BLE central
  BLEDevice central = BLE.central();
  // if a central is connected to the peripheral:
  if (central) {
    Serial.print("Connected to central: ");
    // print the central's BT address:
    Serial.println(central.address());
    // turn on the LED to indicate the connection:
    digitalWrite(LED_BUILTIN, HIGH);

    // check the battery level every 200ms
    // while the central is connected:
    while (central.connected()) {
      // Take a photo
      if (c){
      Camera.readFrame(image);
      for (int i = 0; i < bytesPerFrame - 1; i += 2) {
        Serial.print("0x");
        Serial.print(image[i+1], HEX);
        Serial.print(image[i], HEX);
        if (i != bytesPerFrame - 2) {
          Serial.print(", ");
        }
         img += "0x" + String(image[i+1], HEX) + String (image[i], HEX) + ", ";
      }
      c = false;
      }
     imgChar.writeValue(img);
    }
    // when the central disconnects, turn off the LED:
    digitalWrite(LED_BUILTIN, LOW);
    Serial.print("Disconnected from central: ");
    Serial.println(central.address());
  }
}

Thank you.

2

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