Read data from BLE device

Question

I am trying to read data from a bluetooth device (BR-LE4.0-S2). I was able to connect BLE device, but not able to read data from it.I don't have any specification about BLE services and it's characteristics. Here what my issue is - (void)peripheral:didUpdateValueForCharacteristic:error: not getting called. I followed tutorial "https://developer.apple.com/library/ios/documentation/NetworkingInternetWeb/Conceptual/CoreBluetooth_concepts/PerformingCommonCentralRoleTasks/PerformingCommonCentralRoleTasks.html#//apple_ref/doc/uid/TP40013257-CH3-SW2" .Following is my code.

What my requirement is to read data continuously from BLE device. Any help is greatly appreciated.

- (void)viewDidLoad {     self.myCentralManager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];     self.peripheral = [[CBPeripheral alloc] init];     self.peripheral.delegate = self;     [super viewDidLoad]; }  - (void) centralManagerDidUpdateState:(CBCentralManager *)central {      switch (central.state) {         case CBCentralManagerStatePoweredOn:         [self.myCentralManager scanForPeripheralsWithServices:nil options:nil];             break;         default:             NSLog(@"Central Manager did change state");             break;     }  }  - (void)centralManager:(CBCentralManager *)central  didDiscoverPeripheral:(CBPeripheral *)peripheral      advertisementData:(NSDictionary *)advertisementData                   RSSI:(NSNumber *)RSSI {      NSLog(@"Discovered %@", peripheral.name);     [self.myCentralManager stopScan];     NSLog(@"Scanning stopped");      if (self.peripheral != peripheral) {         self.peripheral = peripheral;         NSLog(@"Connecting to peripheral %@", peripheral);         // Connects to the discovered peripheral     [self.myCentralManager connectPeripheral:peripheral options:nil];     } }  - (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral {      NSLog(@"Peripheral connected");      NSLog(@"Peripheral services : %@",peripheral.services );      [self.peripheral setDelegate:self];      [peripheral discoverServices:nil];  } - (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error {      if (error) {         NSLog(@"Error discovering service: %@", [error localizedDescription]);         return;     }      for (CBService *service in peripheral.services) {         [peripheral discoverCharacteristics:nil forService:nil];     } }  - (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service              error:(NSError *)error {      int i = 0;     for (CBCharacteristic *characteristic in service.characteristics) {  [peripheral setNotifyValue:YES forCharacteristic: characteristic];      } }  - (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic              error:(NSError *)error {      NSData *data = characteristic.value;     NSString *value = [[NSString alloc] initWithData:characteristic.value encoding:NSUTF8StringEncoding];      NSLog(@"Value %@",value);     NSString *stringFromData = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];      NSLog(@"Data ====== %@", stringFromData); }   - (void)peripheral:(CBPeripheral *)peripheral didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic              error:(NSError *)error {      if (error) {         NSLog(@"Error changing notification state: %@",               [error localizedDescription]);     }     NSString *value = [[NSString alloc] initWithData:self.interestingCharacteristic.value encoding:NSUTF8StringEncoding];      NSLog(@"Value %@",value);      NSLog(@"description: %@, descriptors: %@, properties: %d, service :%@, value:%@", characteristic.description, characteristic.descriptors, characteristic.properties, characteristic.service, characteristic.value);     NSData *data = characteristic.value;      if (characteristic.isNotifying) {         NSString *stringFromData = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];         [peripheral readValueForCharacteristic:characteristic];          NSLog(@"Data ====== %@", @"ccdc");      } else {         [self.myCentralManager cancelPeripheralConnection:peripheral];      }  }  - (void)centralManager:(CBCentralManager *)central didDisconnectPeripheral:(CBPeripheral *)peripheral error:(NSError *)error {     NSLog(@"Peripheral Disconnected");     self.peripheral = nil;      // We're disconnected, so start scanning again     NSDictionary *scanOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:NO] forKey:CBCentralManagerScanOptionAllowDuplicatesKey];      [self.myCentralManager scanForPeripheralsWithServices:nil options:scanOptions]; } 

Answer 1

To read a value from a BLE peripheral device, follow these steps

1. Scan for avilable devices

   NSDictionary *options = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:CBCentralManagerScanOptionAllowDuplicatesKey]; [self.myCentralManager scanForPeripheralsWithServices:nil options:options];` 

2. On detecting a device, will get a call back to "didDiscoverPeripheral" delegate method. Then establish a connection with detected BLE device

   -(void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI {      //Connect detected device....     if (!peripheral.isConnected) {         peripheral.delegate = self;         [bluetoothManager_ connectPeripheral:peripheral options:nil];      } } 

3. On successful connection, request for all the services available in the BLE device

   - (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral{ NSLog(@"Peripheral Connected");      // Make sure we get the discovery callbacks     peripheral.delegate = self;      // Search only for services that match our UUID     [peripheral discoverServices:nil]; } 

4. Request all the characteristics available in each services

   - (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error {      if (error) {         NSLog(@"Error discovering services: %@", [error localizedDescription]);         return;     }     // Loop through the newly filled peripheral.services array, just in case there's more than one.     for (CBService *service in peripheral.services) {         [peripheral discoverCharacteristics:nil forService:service];     } } 

5. Once we get the required characteristics detail, we need to subscribe to it, which lets the peripheral know we want the data it contains

   - (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error{      // Deal with errors (if any)     if (error) {         NSLog(@"Error discovering characteristics: %@", [error localizedDescription]);         return;     }      // Again, we loop through the array, just in case.     for (CBCharacteristic *characteristic in service.characteristics) {         if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:REQUIRED_CHARA_ID]]) {             // If it is, subscribe to it             [peripheral setNotifyValue:YES forCharacteristic:characteristic];         }     } } 

6. Completing all these steps, BLE device will let you know the notification status change through delegate method

   - (void)peripheral:(CBPeripheral *)peripheral didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error{      if (error) {         NSLog(@"Error changing notification state: %@", error.localizedDescription);     }      // Notification has started     if (characteristic.isNotifying) {         NSLog(@"Notification began on %@", characteristic);     } } 

You will recieve any notification from BLE device in the following method

- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error {     if (error) {         NSLog(@"Error reading characteristics: %@", [error localizedDescription]);         return;     }      if (characteristic.value != nil) {           //value here.             } }