#include <ArduinoBLE.h>
REDIRECT_STDOUT_TO(Serial);
BLEService ledService("19B10000-E8F2-537E-4F6C-D104768A1214"); // Bluetooth® Low Energy LED Service
// Bluetooth® Low Energy LED Switch Characteristic - custom 128-bit UUID, read and writable by central
BLEByteCharacteristic switchCharacteristic("19B10001-E8F2-537E-4F6C-D104768A1214", BLERead | BLEWrite);
bool turnedOn = false;
const int ledPin = LED_BUILTIN; // pin to use for the LED
uint32_t lastChange = 0;
void turnBLEon(){
 // begin initialization
 if (!BLE.begin()) {
 Serial.println("starting Bluetooth® Low Energy module failed!");
 while (1);
 }
 // set advertised local name and service UUID:
 BLE.setLocalName("LED");
 BLE.setAdvertisedService(ledService);
 // add the characteristic to the service
 ledService.addCharacteristic(switchCharacteristic);
 // add service
 BLE.addService(ledService);
 // set the initial value for the characeristic:
 switchCharacteristic.writeValue(0);
 // start advertising
 BLE.advertise();
 Serial.println("BLE LED Peripheral");
 turnedOn = true;
}
void turnBLEoff(){
 BLEDevice central = BLE.central();
 if(central && central.connected()){
 BLE.disconnect();
 }
 BLE.end();
 turnedOn=false;
}
void setup() {
 Serial.begin(9600);
 while (!Serial);
 //BLE.debug(Serial);
 // set LED pin to output mode
 pinMode(ledPin, OUTPUT);
 turnBLEon();
 lastChange = millis();
}
void loop() {
 if(lastChange + 20000 < millis()){
 if(turnedOn){
 Serial.println("change turn off");
 turnBLEoff();
 }else{
 Serial.println("change turn on");
 turnBLEon();
 }
 lastChange = millis();
 }
 if(turnedOn){
 // listen for Bluetooth® Low Energy peripherals to connect:
 BLEDevice central = BLE.central();
 // if a central is connected to peripheral:
 if (central) {
 Serial.print("Connected to central: ");
 // print the central's MAC address:
 Serial.println(central.address());
 // while the central is still connected to peripheral:
 while (central.connected()) {
 // if the remote device wrote to the characteristic,
 // use the value to control the LED:
 if (switchCharacteristic.written()) {
 if (switchCharacteristic.value()) { // any value other than 0
 Serial.println("LED on");
 digitalWrite(ledPin, HIGH); // will turn the LED on
 } else { // a 0 value
 Serial.println(F("LED off"));
 digitalWrite(ledPin, LOW); // will turn the LED off
 }
 }
 }
 // when the central disconnects, print it out:
 Serial.print(F("Disconnected from central: "));
 Serial.println(central.address());
 }
 }
}