#include <ArduinoBLE.h>
void setup() {
 Serial.begin(9600);
 while (!Serial);
 // initialize the Bluetooth® Low Energy hardware
 BLE.begin();
 BLE.scanForUuid("19B10000-E8F2-537E-4F6C-D104768A1214");
}
void loop() {
 // put your main code here, to run repeatedly:
BLEDevice peripheral = BLE.available();
 if (peripheral) {
 // discovered a peripheral, print out address, local name, and advertised service
 Serial.print("Found ");
 Serial.print(peripheral.address());
 Serial.print(" '");
 Serial.print(peripheral.localName());
 Serial.print("' ");
 Serial.print(peripheral.advertisedServiceUuid());
 Serial.println();
 // stop scanning
 BLE.stopScan();
 controlLed(peripheral);
 delay(10000);
 // peripheral disconnected, start scanning again
 BLE.scanForUuid("19b10000-e8f2-537e-4f6c-d104768a1214");
 }
}
void controlLed(BLEDevice peripheral) {
 // connect to the peripheral
 Serial.println("Connecting ...");
 if (peripheral.connect()) {
 Serial.println("Connected");
 } else {
 Serial.println("Failed to connect!");
 return;
 }
 // discover peripheral attributes
 Serial.println("Discovering attributes ...");
 if (peripheral.discoverAttributes()) {
 Serial.println("Attributes discovered");
 } else {
 Serial.println("Attribute discovery failed!");
 peripheral.disconnect();
 return;
 }
 BLECharacteristic byteCharacteristic = peripheral.characteristic("19B10001-E8F2-537E-4F6C-D104768A1214");
 if (!byteCharacteristic) {
 Serial.println("Peripheral does not have LED characteristic!");
 peripheral.disconnect();
 return;
 } else if (!byteCharacteristic.canSubscribe()) {
 Serial.println("Peripheral does not have a writable LED characteristic!");
 peripheral.disconnect();
 return;
 } else if (!byteCharacteristic.subscribe()) {
 Serial.println("subscription failed!");
 peripheral.disconnect();
 return;
 } else {
 Serial.println("Subscribed");
 }
 while (peripheral.connected()) {
 // while the peripheral is connected
 // check if the value of the simple key characteristic has been updated
 if (byteCharacteristic.valueUpdated()) {
 // yes, get the value, characteristic is 1 byte so use byte value
 byte value = 0;
 
 byteCharacteristic.readValue(value);
 Serial.print("received: ");
 Serial.println(value, HEX);
 
 }
 }
 Serial.println("Disconnected");
 
}

#include <ArduinoBLE.h>
BLEService testService("19B10000-E8F2-537E-4F6C-D104768A1214");
BLEByteCharacteristic byteCharacteristic("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead | BLEIndicate | BLEWrite);
volatile bool disconnect = false;
void byteRead(BLEDevice central, BLECharacteristic characteristic){
 Serial.println("Characteristic subscribed, sending data");
 byte c = 0x01; 
 int written = byteCharacteristic.writeValue(c);
 disconnect=true;
}
void setup() {
 Serial.begin(9600);
 while (!Serial);
 // put your setup code here, to run once:
 if (!BLE.begin()) {
 Serial.println("starting Bluetooth® Low Energy module failed!");
 while (1);
 }
 // set advertised local name and service UUID:
 if(!BLE.setLocalName("TEST-LOCAL-NAME")){
 Serial.println("error setting the local name");
 }
 byteCharacteristic.setEventHandler(BLESubscribed, byteRead);
 BLE.setAdvertisedService(testService);
 // add the characteristic to the service
 testService.addCharacteristic(byteCharacteristic);
 // add service
 BLE.addService(testService);
 // start advertising
 BLE.advertise();
 Serial.println("BLE Peripheral");
}
void loop() {
 // put your main code here, to run repeatedly:
 if(disconnect){
 BLE.disconnect();
 disconnect = false;
 Serial.println("disconnected");
 }
 BLE.poll();
 
}

11:18:48.793 -> Found 34:94:54:27:05:66 'TEST-LOCAL-NAME' 19b10000-e8f2-537e-4f6c-d104768a1214
11:18:48.829 -> Connecting ...
11:18:48.897 -> Connected
11:18:48.897 -> Discovering attributes ...
11:18:49.291 -> Attributes discovered
11:18:49.330 -> Subscribed
11:18:49.330 -> received: 1
11:18:49.330 -> Disconnected
//End of the first run
11:18:59.416 -> Found 34:94:54:27:05:66 'TEST-LOCAL-NAME' 19b10000-e8f2-537e-4f6c-d104768a1214
11:18:59.448 -> Connecting ...
11:18:59.527 -> Connected
11:18:59.527 -> Discovering attributes ...
11:18:59.948 -> Attributes discovered
11:18:59.948 -> Subscribed
//Has never received new data since the peripheral never sends it

11:18:27.926 -> BLE Peripheral
11:18:49.291 -> Characteristic subscribed, sending data
11:18:49.330 -> disconnected
// Note that the subscribed event at 11:18:59.948 has never been notified to the sketch