Can't pair with Omron Evolv (HEM-7600T) on macOS

[ockham]

I'm trying to pair my Omron Evolv on macOS, using

python3 ./omblepy.py -p -d HEM-7600T

I've verified that the device is in pairing mode (blinking "P"). I've also removed the pairing from my Android phone (via Android's Bluetooth menu's "Forget" option). The Evolv is in the list that omblepy shows, but when I select it, I get the following error:

ValueError: Could not enter key programming mode after 10 attempts. Has the device been started in pairing mode? Last response: bytearray(b'\x82\x0f\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00')

Can you please advise what could be the reason for this issue, and how to possibly fix it?

[userx14]

Hi, I do not have any option to test on mac os, so the help I can provide is limited.
Do you get a system bluetooth pairing dialog when you try to pair the device?

One option might be to write the pairing key once, using another supported platform.
Then you could try to connect without pairing on the mac.

[ockham]

I think I got the system bluetooth pairing dialog when I first tried a couple of days ago, but not since then. (However, the device isn't listed among the known devices in macOS' bluetooth settings 🤔)

I don't have Windows or Linux available to me right now. I'm wondering if I can write the key from my Android phone (or alternatively intercept bluetooth traffic and read the key that was set there)?

[ockham]

I'm wondering if I can write the key from my Android phone (or alternatively intercept bluetooth traffic and read the key that was set there)?

I'll try these instructions found in the UPBM repo wiki.

[userx14]

I think I got the system bluetooth pairing dialog when I first tried a couple of days ago, but not since then. (However, the device isn't listed among the known devices in macOS' bluetooth settings 🤔)

I don't have Windows or Linux available to me right now. I'm wondering if I can write the key from my Android phone (or alternatively intercept bluetooth traffic and read the key that was set there)?

Both is possible, for capturing when you do the initial pairing with the app, you can use instructions you mention from UBPM + wireshark. For sending commands from android I have some instructions here: #16 (comment)
You would need to modify the pairing code in the xml (112211...) to this one.

[ockham]

Thanks! I tried the instructions you shared. However, I'm still getting the same errors when trying to connect on macOS afterwards.

I've noticed that the assertions in the macro are failing, so I guess it isn't quite working?

[ockham]

So the NRF-based approach didn't work for me.

However! I was able to capture bluetooth traffic between my Android phone and the blood pressure monitor, and analyze it in Wireshark, per UBPM instructions. And I managed to locate the key in Wireshark, with a little guidance from Claude:

Since you know exactly what the write payload looks like, just filter for all ATT writes and scan for the prefix byte:

btatt.opcode == 0x12 || btatt.opcode == 0x52
This shows all Write Requests (0x12) and Write Commands (0x52). Then look in the packet bytes for writes that start with 02 followed by 16 zero bytes (enter programming mode) or 00/01 followed by 16 non-zero bytes (the key). There shouldn't be that many write packets total, so you can scroll through them fairly quickly.

That was easy enough to find:

I could then simply copy the value after the 01 and use it to replace the key in omblepy.py. The next time I tried pairing, it worked (I got the macOS device pairing dialog). I had to turn off bluetooth on my phone to make sure it wouldn't interfere, and was finally able to download my BP readings 🎉

[userx14]

Nice, that you were able to get it working. Still find it strange that the pairing does not work with either android or macos. Maybe the HEM-7600T needs some additional read / command for this or something is off timing wise.

Probably the "shared" pairing code is the most convenient, when you want to read records from phone and mac.