Swift Core Bluetooth communication with OBD2

Question

I'm trying to observe velocity of my car using an OBD2, to try if the hardware works i had use the app "Auto Doctor" and it works. But i need some more features and so i started to create my own application

To send command to the characteristic i use the following code:

var commandSended = String() {
        didSet {
            if let peripheral = self.peripheralConnected {
                for char in characteristicConnected {
                    peripheral.writeValue(self.commandSended.data(using: .utf8)!, for: char, type: .withoutResponse)
                    peripheral.writeValue(self.commandSended.data(using: .ascii)!, for: char, type: .withoutResponse)
                    peripheral.readValue(for: char)
                }
            } else {
                self.myTerminal.printToTerminalCommand("You are not connected to the peripheral")
            }
        }
    }

characteristicConnected: are all the characteristic found

Independently which command i send to the characteristic i receive every time the same amount of byte and i can't decode it using utf8 or ascii.

I hope I have supply you enough information.

"and i can't decode it using utf8 or ascii." Why should it be a String in UTF8 or ASCII ? Why can't it be an image (well I guess not), a custom struct ? Read the doc of characteristic (either it's public or it's custom). — Larme, Sep 02 '19 at 10:46
@Larme I bought this OBD https://www.amazon.it/gp/product/B07FMFRLN3/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 If you tell me to read the documentation mean that every device has own encoding, right? I will contact the owner to receive a documentation — Marius, Sep 02 '19 at 10:57
Read the characteristic/services UUID. If they are "official", you can check them there: https://www.bluetooth.com/specifications/gatt/characteristics/ If not, it can has its own undocumented specifications. And then it's reverse engeneering. — Larme, Sep 02 '19 at 11:00

DrMickeyLauer · Accepted Answer · 2021-08-18T10:18:02.613

The answers from (almost all) OBD2 adapters are ASCII string responses, so you need to decode the NSData into ASCII. To extract the actual payload for your responses, you need to learn about decoding the various car protocols. A lot of this information is freely available on the web, for some things you might want to buy the official SAE standards.

That said, even though you are using Swift, you might be interested in using an OBD2 library that does all the heavy lifting for you. As a matter of fact, I wrote one, which you can download at https://github.com/mickeyl/LTSupportAutomotive.

Update: And since then I rewrote something similar in Swift, which might be even more interesting for you. Please have a look at https://github.com/Cornucopia-Swift/CornucopiaUDS

Swift Core Bluetooth communication with OBD2

1 Answers1