if central.state == CBManagerState.poweredOn {
        debugPrint("poweredOn")

        let serviceUUIDs:[AnyObject] = [serviceCBUUID_READ]
        let lastPeripherals = centralManager.retrieveConnectedPeripherals(withServices: serviceUUIDs as! [CBUUID])

        if lastPeripherals.count > 0{
            let device = lastPeripherals.last! as CBPeripheral;
            deviceX = device;
            centralManager.connect(deviceX, options: nil)
            if(device.state == .disconnected){
                self.alertShowing(msg: "Device is disconnected restart the device and connect again.")
            }
        }
        else {
            centralManager.scanForPeripherals(withServices: nil, options: nil)
        }

        debugPrint(lastPeripherals)
    } else if(central.state == CBManagerState.poweredOff) {
        self.alertShowing(msg: "Make sure that your bluetooth is turned on.")
    }
    else if(central.state == CBManagerState.unsupported) {
        self.alertShowing(msg: "This device is unsupported.")
    }else{
        self.alertShowing(msg: "Try again after restarting the device.")
    }
}

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    if(peripheral.name == "Peripheral Observer") || (peripheral.name == "BLE Device"){
        if let services = peripheral.services{
            for service in services{
                debugPrint(service)
            }
        }
        debugPrint("advertisementData :(advertisementData)")
        deviceX = peripheral
        peripheral.delegate = self
        centralManager.stopScan()
        centralManager.connect(peripheral)
    }
}

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    debugPrint("Connected")
    var i = 0
    timerForService = Timer.scheduledTimer(withTimeInterval: 1, repeats: true, block: { (timer) in
        if(self.service_Read == nil) && (self.service_Write == nil){
            i += 1

            if(i%2 == 1){
                debugPrint("loop1")
                peripheral.discoverServices(nil)
                self.deviceX!.discoverServices(nil)
            }else if( i&2 == 0){
                debugPrint("loop0")
                self.deviceX!.discoverServices([self.serviceCBUUID_READ, self.serviceCBUUID_Write])
            }

        }else{
            self.timerForService.invalidate()
        }
    })
}

@interface CentralManager()
property (nonatomic, strong) CBPeripheral *golablePeripheral;
@end

- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary<NSString *,id> *)advertisementData RSSI:(NSNumber *)RSSI {
    self.golablePeripheral = peripheral;
    self.golablePeripheral.delegate = self;
}

- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral {
    [self.golablePeripheral discoverServices: _serviceUUID];
}

- (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error {
    for (CBService *service in peripheral.services) {
        if ([_serviceUUID containsObject: service.UUID]) {
            [self.golablePeripheral discoverCharacteristics:_serviceCharacteristics forService:service];
            [self.golablePeripheral discoverCharacteristics:_serviceNotifyCharacteristics forService:service];
        }
    }
}