BLE Swift write characterisitc - ios

Question

I am trying hard to get my TI sensortag temperature sensor to notify. According to http://processors.wiki.ti.com/images/a/a8/BLE_SensorTag_GATT_Server.pdf I need to set the value of the characteristic with UUID F000AA02-0451-4000-B000-000000000000 to "01:00". Here is what I do:
import UIKit
import CoreBluetooth
class ViewController: UIViewController, CBCentralManagerDelegate, CBPeripheralDelegate{
var centralManager:CBCentralManager!
var blueToothReady = false
var connectingPeripheral: CBPeripheral!
#IBOutlet weak var textField: UITextView!
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
override func viewDidLoad() {
super.viewDidLoad()
startUpCentralManager()
}
func startUpCentralManager() {
centralManager = CBCentralManager(delegate: self, queue: nil)
}
func discoverDevices() {
centralManager.scanForPeripheralsWithServices(nil, options: nil)
}
func centralManager(central: CBCentralManager!, didDiscoverPeripheral peripheral: CBPeripheral!, advertisementData: (NSDictionary), RSSI: NSNumber!) {
output("Discovered", data: peripheral.name)
self.connectingPeripheral = peripheral
centralManager.stopScan()
self.centralManager.connectPeripheral(peripheral, options: nil)
}
func centralManagerDidUpdateState(central: CBCentralManager!) { //BLE status
var msg = ""
switch (central.state) {
case .PoweredOff:
msg = "CoreBluetooth BLE hardware is powered off"
println("\(msg)")
case .PoweredOn:
msg = "CoreBluetooth BLE hardware is powered on and ready"
blueToothReady = true;
case .Resetting:
var msg = "CoreBluetooth BLE hardware is resetting"
case .Unauthorized:
var msg = "CoreBluetooth BLE state is unauthorized"
case .Unknown:
var msg = "CoreBluetooth BLE state is unknown"
case .Unsupported:
var msg = "CoreBluetooth BLE hardware is unsupported on this platform"
}
output("State", data: msg)
if blueToothReady {
discoverDevices()
}
}
func centralManager(central: CBCentralManager!,didConnectPeripheral peripheral: CBPeripheral!)
{
peripheral.delegate = self
peripheral.discoverServices([CBUUID.UUIDWithString("F000AA00-0451-4000-B000-000000000000")])
output("Connected", data: peripheral.name)
}
func peripheral(peripheral: CBPeripheral!, didDiscoverServices error: NSError!)
{
if let servicePeripherals = peripheral.services as? [CBService]
{
for servicePeripheral in servicePeripherals
{
output("Service", data: servicePeripheral.UUID)
peripheral.discoverCharacteristics(nil, forService: servicePeripheral)
}
}
}
#IBAction func refreshBLE(sender: UIButton) {
centralManager.scanForPeripheralsWithServices(nil, options: nil)
}
func peripheral(peripheral: CBPeripheral!, didDiscoverCharacteristicsForService service: CBService!, error: NSError!) {
if let charactericsArr = service.characteristics as? [CBCharacteristic]
{
for charactericsx in charactericsArr
{
peripheral.setNotifyValue(true, forCharacteristic: charactericsx)
// *************************
if charactericsx.UUID.UUIDString == "F000AA02-0451-4000-B000-000000000000"{
output("Characteristic", data: charactericsx)
let data: NSData = "01:00".dataUsingEncoding(NSUTF8StringEncoding)!
peripheral.writeValue(data, forCharacteristic: charactericsx, type: CBCharacteristicWriteType.WithResponse)
output("Characteristic", data: charactericsx)
}
// *************************
peripheral.readValueForCharacteristic(charactericsx)
}
}
}
func peripheral(peripheral: CBPeripheral!, didUpdateValueForCharacteristic characteristic: CBCharacteristic!, error: NSError!) {
if var data :NSData = characteristic.value {
output("Data", data: characteristic.value)
}
}
func output(description: String, data: AnyObject){
println("\(description): \(data)")
textField.text = textField.text + "\(description): \(data)\n"
}
}
Problem is that peripheral.writeValue... doesn't seem to change anything. I looked at the objective c example found here http://www.ti.com/tool/sensortag-sw and think the corresponding lines to
let data: NSData = "01:00".dataUsingEncoding(NSUTF8StringEncoding)!
peripheral.writeValue(data, forCharacteristic: characteric, type: CBCharacteristicWriteType.WithResponse)
are these:
uint8_t data = 0x01;
[BLEUtility writeCharacteristic:self.d.p sCBUUID:sUUID cCBUUID:cUUID data:[NSData dataWithBytes:&data length:1]];
What am I missing?

Answer 1

The Swift code written by you is not equivalent to the Objective-C example. The data parameter should be initialized with binary "1" instead of a string "01:00":
var parameter = NSInteger(1)
let data = NSData(bytes: &parameter, length: 1)
peripheral.writeValue(data, for: characteristic, type: .withResponse)
I think that whenever TI docs specify a value in quotes like "01:00" they really mean a hexadecimal value like 0x0100, which is a bit confusing.