Isuru Isuru - 5 months ago 61
iOS Question

Receive string data via Bluetooth

I'm creating a simple BLE app that communicates with a single peripheral. The phone acts as the central. I have an iPad which I'm using as the peripheral for testing. It has the app LightBlue installed to simulate a peripheral. The peripheral is supposed to send a string of data in this format.

TEM:25.11 | HUM:70 | PM10:43 | PM25:32

So I created a blank virtual peripheral in LightBlue with one service.

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enter image description here

Below is my code for Bluetooth connectivity handling.

import UIKit
import CoreBluetooth

class ViewController: UIViewController {

fileprivate let serviceUUID = CBUUID(string: "19B10010-E8F2-537E-4F6C-D104768A1214")
fileprivate let characteristicUUID = CBUUID(string: "19B10011-E8F2-537E-4F6C-D104768A1214")

fileprivate var manager: CBCentralManager!
fileprivate var peripheral: CBPeripheral!
fileprivate var characteristic: CBCharacteristic!

override func viewDidLoad() {
manager = CBCentralManager(delegate: self, queue: nil)

override func viewWillDisappear(_ animated: Bool) {

fileprivate func startScan() {
manager.scanForPeripherals(withServices: [serviceUUID], options: nil)

fileprivate func stopScan() {

fileprivate func disconnectFromDevice() {
guard let peripheral = peripheral else { return }

fileprivate func restoreCentralManager() {
manager.delegate = self


// MARK: - CBCentralManagerDelegate
extension ViewController: CBCentralManagerDelegate {
func centralManagerDidUpdateState(_ central: CBCentralManager) {
switch central.state {
case .unsupported:
case .unauthorized:
case .poweredOn:
print("Powered On")
case .resetting:
case .poweredOff:
print("Powered Off")
case .unknown:

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
print("Discovered \(String(describing: at \(RSSI)")

if == nil || == "" {

if self.peripheral == nil || self.peripheral.state == .disconnected {

self.peripheral = peripheral
central.connect(peripheral, options: nil)

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
peripheral.delegate = self

func centralManager(_ central: CBCentralManager, didDisconnectPeripheral peripheral: CBPeripheral, error: Error?) {

self.peripheral = nil
central.scanForPeripherals(withServices: nil, options: nil)

func centralManager(_ central: CBCentralManager, didFailToConnect peripheral: CBPeripheral, error: Error?) {
self.peripheral = nil

func centralManager(_ central: CBCentralManager, willRestoreState dict: [String : Any]) {

// MARK: - CBPeripheralDelegate
extension ViewController: CBPeripheralDelegate {
func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
guard let services = else { return }
print("No. of services: \(services.count)")

for service in services {
if service.uuid == serviceUUID {
peripheral.discoverCharacteristics(nil, for: service)

func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
guard let characteristics = service.characteristics else { return }

for characteristic in characteristics {
print("characteristic: \(characteristic.uuid)")
if characteristic.uuid == characteristicUUID {
self.characteristic = characteristic
peripheral.setNotifyValue(true, for: characteristic)
peripheral.readValue(for: characteristic)

func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) {
if characteristic.uuid == characteristicUUID {
print("Got reply from: \(characteristic.uuid)")
if let data = characteristic.value, let string = String(data: data, encoding: String.Encoding.utf8) {
} else {
print("No response!")


The discovering and connecting part works just fine. The problem is I don't receive that data string from the peripheral.

The method
does get fired. I get the Got reply from: 19B10011-E8F2-537E-4F6C-D104768A1214 output in the console. However when I tried to see if there's any data by printing out the
, it returns

Not sure if it's something wrong with my code. Or I've configured the peripheral on LightBlue wrong. Does LightBlue send out data automatically? I don't see any Send button or anything anywhere either.

I uploaded a demo project here as well.

Answer Source

Your LightBlue configuration showing that you can only write value on that particular characteristic You have to make this read also

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