Bluetooth Connection with Smart BP Monitor 808A0 aka Transtek-LS808-B

[doenerminister]

Hi,
I recently got a BP Monitor from Transtek model LS808-B. I can't get IT connected with the app. The original App isn't available ans more. The only App I can Connect is "Blutdruck" by MedM. Is there any way of logging what's going wrong in blood-pressure-monitor?

Greetings

Wolfgang

[derdilla]

Hi Wolfgang,
To get logs you would have to install flutter and run the app in debug mode. If you could investigate it and provide patches that would of course be highly appreciated and I'd happy to help wherever I could.

If that's too much trouble, you could manually check whether your device implements the BLE GATT spec correctly using the great nRF Connect App.

Another thing to check for is whether 1.8.3 1.8.2 works. There is a bug report for the current version that might be related.

[doenerminister]

Hi derdilla,

Thank you for the realy very quick reply.
That's a lot of information :)
I think I will First Check an older Version.
If that's Not working, I will Install nrf to Check the protocol.
I Work as Systems Support engineer since nearly 30 years now, but coding skills are Not too great ;) but I would try to.
Building and Debugging is done on the device or do I need an Environment e.g on Linux? Could you provide some links for a dummie Like me?

Greetings Wolfgang

[doenerminister]

Version 1.8.2 No success

Installed nrf tried to Connect the device -> success
Bonding -> No success

Log (debug) attached
Log 2025-02-17 19_08_28.txt

[derdilla]

What this log tells me is that your device uses a proprietary protocol this app can't support. Specifically we rely on these characteristics:

blood-pressure-monitor-fl/app/lib/features/old_bluetooth/bluetooth_input.dart

Lines 97 to 98 in 4d04b59

	final Guid serviceUUID = Guid('1810');
	final Guid characteristicUUID = Guid('2A35');

If you or someone wants to port it I would of course be happy to accept it.

[doenerminister]

Is there any Chance to Log the Traffic between the device and MedM, the App that is able to speak with the Monitor, with nrf?

[derdilla]

Sorry, I wanted to do some more research and forgot about this.

I couldn't find public discussions about your devices protocol at all. Other Transtek devices seem to use the lifesense protocol. I found this java implementation you could use to match available services, ect.: https://gist.github.com/NecoHorne/2dd9713fbaf94d1d74259f554351975f If that's the case: test some manual value reading from the nrf app. You could then try to port the java code to dart. Maybe try to reach the author for details / permission (its not open source).

Reverse engineering

Reverse engineering a protocol is hard. The first step, as you correctly guessed, would be to log the traffic. The nrf app isn't really capable of this as far as I know. It's much easier to sniff packages externally: either through dedicated devices/hardware (I heard flipper zero is user friendly and can be used for quick testing) or any other device with a Bluetooth chip over which you have sufficient control. You should google for that (this came up for me and looks ok).

From my experience blood pressure BLE services either send single measurements, stream a measurement, or send a batch with all measurements ever taken. A proprietary protocol is, of course, not guaranteed to be readable: every message could be encrypted and only decryptable through their app / some Transtek cloud service (although that would seem paranoid and evil to me).

All of these steps don't need code and are basically just research. In case you find something workable I would be happy to help with the code. It should be easy to add an alternative code path for devices that have Transtek's services.

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Don't feel discouraged from toying around with this, but expect this to be a medium to long term passion project.