Sending Hex String using WriteValue in Swift

Question

I've been creating an app using XCode and Swift to connect to a bluetooth device (that has a LED colour strip connected to it) and I have written a piece of code that will make it change colour.

Using a bluetooth sniffer, I know that I need to send the value of '52130056FF000000AA' which would make it change to red, in this example. Here's a snippet of the code I have already. Characteristicx is defined before this code.

let data: NSData = "52130056FF000000AA".dataUsingEncoding(NSUTF8StringEncoding)!
peripheral.writeValue(data, forCharacteristic: characteristicx, type: CBCharacteristicWriteType.WithoutResponse)

This code converts the hex string given to this, which I do not want to send. '<35323133 30303536 46463030 30303030 4141>'

So, the question is, How do I get Swift to send just the 52130056FF000000AA to the BLE device and not the converted string? The issue here is that the writeValue command requires NSData (as far as I can see) and I'm not sure how to use a plain hex string as the data to send in NSData form.

Hope someone can help with this! Any help or even suggestions would be greatly appreciated.

Answer 1

If you don't insist on using a hex string then the easiest solution would be to create the data from an array with hex integer values:

let bytes : [UInt8] = [ 0x52, 0x13, 0x00, 0x56, 0xFF, 0x00, 0x00, 0x00, 0xAA ]
let data = NSData(bytes: bytes, length: bytes.count)

And even easier in Swift 3:

let bytes : [UInt8] = [ 0x52, 0x13, 0x00, 0x56, 0xFF, 0x00, 0x00, 0x00, 0xAA ]
let data = Data(bytes:bytes)