iOS Bluetooth Low Energy (BLE) not discovering TX characteristic - ios

Question

I am using an an arduino feather BLE board and trying to create an iOS app that can send data to the board over BLE. I can connect but I can't get access to the txCharacteristic
func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
guard let characteristics = service.characteristics else {
return
}
for characteristic in characteristics {
if characteristic.properties.contains(.write) || characteristic.properties.contains(.writeWithoutResponse) {
writableCharacteristic = characteristic
}
// if(characteristic.uuid == CBUUID(string: "6e400002-b5a3-f393-e0a9-e50e24dcca9e"))
// {
// txCharacteristic = characteristic
// }
var txUUID = CBUUID(string: "6e400002-b5a3-f393-e0a9-e50e24dcca9e")
let temp = characteristic.uuid.uuidString;
switch characteristic.uuid {
case txUUID:
txCharacteristic = characteristic;
break;
default:
break;
}
peripheral.setNotifyValue(true, for: characteristic)
}
}
This code works, but only discovers the following UUIDs:
temp String "00001532-1212-EFDE-1523-785FEABCD123"
temp String "00001531-1212-EFDE-1523-785FEABCD123"
temp String "00001534-1212-EFDE-1523-785FEABCD123"
I have figured out that these UUID's are DFU UUIDs. How can I discover the txCharacteristic instead?
Added for more information how I am calling discoverCharacteristics():
extension SimpleBluetoothIO: CBPeripheralDelegate {
func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
guard let services = peripheral.services else {
return
}
targetService = services.first
if let service = services.first {
targetService = service
peripheral.discoverCharacteristics(nil, for: service)
}
}

Answer 1

I was able to figure this out, by reading info at this website:
https://learn.adafruit.com/getting-started-with-the-nrf8001-bluefruit-le-breakout/adding-app-support
Particularly this part (notice that UART is the service and TX and RX are characteristics of the service):
UART Service UUID: 6E400001-B5A3-F393-E0A9-E50E24DCCA9E
TX Characteristic UUID: 6E400002-B5A3-F393-E0A9-E50E24DCCA9E
RX Characteristic UUID: 6E400003-B5A3-F393-E0A9-E50E24DCCA9E
So I needed to call peripheral.discoverServices() with the UART Service ID. In my example below self.serviceUUID = "6e400001-b5a3-f393-e0a9-e50e24dcca9e"
func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
//peripheral.discoverServices(nil)
//peripheral.discoverServices([CBUUID(string: "6e400001-b5a3-f393-e0a9-e50e24dcca9e")])
// Disover peripheral with service UUID that was given to us during initialization (self.serviceUUID)
peripheral.discoverServices([CBUUID(string: self.serviceUUID)])
}
Then in didDiscoverCharacteristicsFor service I needed to look for the TX Characteristic ID:
// Did Discover Characteristics
func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
guard let characteristics = service.characteristics else {
return
}
for characteristic in characteristics {
if characteristic.properties.contains(.write) || characteristic.properties.contains(.writeWithoutResponse) {
writableCharacteristic = characteristic
}
// TX Characteristic UUID: 6E400002-B5A3-F393-E0A9-E50E24DCCA9E
// https://learn.adafruit.com/getting-started-with-the-nrf8001-bluefruit-le-breakout/adding-app-support
let txUUID = CBUUID(string: "6e400002-b5a3-f393-e0a9-e50e24dcca9e")
switch characteristic.uuid {
case txUUID:
txCharacteristic = characteristic;
break;
default:
break;
}
peripheral.setNotifyValue(true, for: characteristic)
}
}