#6 Arduino Nano 33 BLE - Transmit and Receive data from/to mobile over Bluetooth

Here is a code which enables transmission and reception of data from Arduino Nano 33 BLE board over Bluetooth. nRF Connect App is used to connect to the Arduino Nano 33 BLE board.

We can see the TX Characteristic and RX Characteristic under the Nordic UART service.

Below is the code for the same.

#include <ArduinoBLE.h>

// Nordic UART Service (NUS)

BLEService uartService("6E400001-B5A3-F393-E0A9-E50E24DCCA9E");

BLECharacteristic txChar( // Notify characteristic (Arduino → Phone)

  "6E400003-B5A3-F393-E0A9-E50E24DCCA9E",

  BLENotify,

  512

);

BLECharacteristic rxChar( // Write characteristic (Phone → Arduino)

  "6E400002-B5A3-F393-E0A9-E50E24DCCA9E",

  BLEWrite | BLEWriteWithoutResponse,

  512

);

void setup() {

  Serial.begin(115200);

  while (!Serial);

  // Start BLE

  if (!BLE.begin()) {

    Serial.println("BLE start failed!");

    while (1);

  }

  BLE.setLocalName("Nano33BLE-UART");

  BLE.setAdvertisedService(uartService);

  uartService.addCharacteristic(txChar);

  uartService.addCharacteristic(rxChar);

  BLE.addService(uartService);

  txChar.writeValue((byte)0x00);

  BLE.advertise();

  Serial.println("BLE UART Started. Waiting for central...");

}

void loop() {

  BLEDevice central = BLE.central();

  if (central) {

    Serial.print("Connected to: ");

    Serial.println(central.address());

    while (central.connected()) {

      // ➤ 1. Read USB Serial and send over BLE

      if (Serial.available()) {

        String incoming = Serial.readStringUntil('\n');

        txChar.writeValue(incoming.c_str());

        Serial.print("Sent over BLE: ");

        Serial.println(incoming);

      }

      // ➤ 2. Read BLE (phone → Arduino)

      if (rxChar.written()) {

        int len = rxChar.valueLength();

        const uint8_t* data = rxChar.value();

        String fromBLE = "";

        for (int i = 0; i < len; i++) {

          fromBLE += (char)data[i];

        }

        Serial.print("Received from BLE: ");

        Serial.println(fromBLE);

      }

    }

    Serial.println("Central disconnected!");

  }

}