Help needed: UM25C connection fails with "Bluetooth service not found, try to initiate Setup again"

[AlexHuebi]

Hi there.

I tried to use the rd-usb to better utilize my um25c usb meter. I bought the meter from here, which as far as I could tell, should be the "official" Storefront.

I am also using the UM Meter App on my phone which works, but just barely. (plagued by bad UI) That also brings be back to this repo.

I tried to use rd-usb on multiple Windows (one has the manufacturing date at 2024 and one 2017) Laptops, on my Linux Machine and on an Raspberry Pi 4. While rd-usb finds the meter just fine, it always throws the error "interfaces.interface.FatalErrorException: Bluetooth service not found, try to initiate Setup again". Which I traced back to the "um.py" File on line 100 where bluetooth.find_service is called, but returns an empty list. The address is set correctly but I lack the knowledge to further debug anything that has to do with Bluetooth so any help, that would get this back up and running would be very appreciated.

Full Stacktrace:

Traceback (most recent call last):
  File "/root/rd-usb/webapp/backend.py", line 252, in run
    self.retry(self.interface.connect)
  File "/root/rd-usb/webapp/backend.py", line 363, in retry
    return callback()
           ^^^^^^^^^^
  File "/root/rd-usb/interfaces/wrapper.py", line 34, in connect
    self.get_result(60)
  File "/root/rd-usb/interfaces/wrapper.py", line 65, in get_result
    raise FatalErrorException(result)
interfaces.interface.FatalErrorException: Traceback (most recent call last):
  File "/root/rd-usb/interfaces/wrapper.py", line 112, in call
    result = callback()
             ^^^^^^^^^^
  File "/root/rd-usb/interfaces/um.py", line 108, in connect
    raise FatalErrorException("Bluetooth service not found, try to initiate Setup again")
interfaces.interface.FatalErrorException: Bluetooth service not found, try to initiate Setup again

One thing that I have noticed that may help: I am unable to connect via the normal bluetoothctl to the USB Meter:

[bluetooth]# connect 00:15:A3:00:5B:49
Attempting to connect to 00:15:A3:00:5B:49
[bluetooth]# hci0 00:15:A3:00:5B:49 type BR/EDR connected eir_len 12
[CHG] Device 00:15:A3:00:5B:49 Connected: yes
[UM25C]# [CHG] Device 00:15:A3:00:5B:49 ServicesResolved: yes
[UM25C]# Failed to connect: org.bluez.Error.NotAvailable br-connection-profile-unavailable
[UM25C]# hci0 00:15:A3:00:5B:49 type BR/EDR disconnected with reason 2
[UM25C]# [CHG] Device 00:15:A3:00:5B:49 ServicesResolved: no
[CHG] Device 00:15:A3:00:5B:49 Connected: no

[kolinger]

Hi, this is not easy to debug since the error message is generic. The underlying bluetooth layer just gives up for whatever reason and doesn't tell why.

You are saying that official app on phone barely works and that's not something I would expect if multiple computers with different operating systems don't. What barely means? Do you see data from the meter like voltage? Is the reporting continuous and reliable?

Bluetooth has funny bahaviour where the communication is plain broken yet discovery works so it seem to "connect" and then fails so until you see actual data it doesn't mean anything.

If indeed Android app reports data reliably and rd-usb doesn't work at all anywhere then this may be case where they change firmware or something about the meter making it incompatible with older version of the UM25C. This happened once in past but with the TC66C.

If meter didn't report data anywhere I would start to think there is problem with the meter. But that doesn't make sense if Android app sees data.

Anyway in past there were multiple instances where people had issue with construction of the UMxxC meters. The meter is sandwich of two boards where one is the main doing everything and the other is handling bluetooth and they communicate via spring contacts and this spring contact connection is sometimes unreliable. Disassembling and reassembling the meter and/or cleaning the spring contacts and/or landing pads did help people to solve this issue.

[AlexHuebi]

Hi, I have to correct myself: the "barely works" was kinda wrong.

The Connection between the phone and USB meter works and I am getting data points that correlate with the ones I am seeing on the display. But I have been unable to export the recorded data and the UI is not really great to analyze it when I charged something big like a power bank.

But sometimes, when the session is longer, the data points seem to stop but that may be a different problem from the app which also was one of the reasons why I want to get away from it.

As far as I could tell, the built in BT-UART Transceiver is the dx-bt18 which I'd guess, didn't change over the different revisions. Sadly though, I was unable to find any firmware versions that'd explain any difference in behavior.

[kolinger]

Well unless they changed the protocol completely (like switching from Bluetooth to Bluetooth LE) then I don't see why the meter doesn't return any Bluetooth services. This step is universal and even if those services changed there should be something not nothing.

What methods of connection did you try? Did you try to pair first to create serial/COM ports?

If you didn't try to use UM25C Serial then give it a try. Try to pair with the meter - can be done normally via Settings on Windows or via rfcomm bind 0 aa:bb:cc:dd:ee:ff on Linux. This should generate couple of COMx on Windows or /dev/rfcomm0 on Linux and give this to RD-USB via the UM25C Serial profile and see if something happens. More info in readme.

[AlexHuebi]

I tried the UM25C Serial just now and it worked without any issues.

So it seems like the issue isn't the bluetooth connection itself but maybe the way how the python script tries to connect?

[kolinger]

Python side is very plain there is not much to do, all is handled by the library and (mostly) underlying bluetooth stack of your OS. If find_services returns empty list then python can't do much about it.

Did you pair the meter with your OS before trying RD-USB for the first time (with the regular UM25C direct connection)? There could be some funny business where bluetooth stack of your OS hides the device if it's used in any other way.

Does all the platforms you tested (Windows, Linux) behave exactly the same (Bluetooth service not found)?

[AlexHuebi]

The error in RD-USB was both in Windows and Linux the same.

I also tried both first pairing it and not pairing the device and both still had the same error message.

[kolinger]

From you message it's not clear if you tested before pairing for the first time or try to unpair and then test. Did you make test where your OS isn't paired and doesn't have previous paired profile saved?

This is very strange. I have no explanation for such situation where everything seems to be correct yet no services are found, such situation shouldn't be possible.

Did you try other PC software? For example sigrok supports UM series over Bluetooth and there are other projects and scripts (rdumtool) that can sample UM25C over Bluetooth, this way you cold confirm if indeed everything else is working and just RD-USB isn't.

[AlexHuebi]

Hi, sorry for the grammatical mess that I wrote. Yes, I initially tried to use it without pairing the device to the PC. Because I got the strange error, I then tried to pair it with my device where it connected for a few seconds, then disconnected again. (debug log from that is in the initial message) I then deleted the device, and tried once more then on all the mentioned other devices with the same steps. Unpaired (not working) -> paired (not working and disconnected after a few seconds) -> deleted and tried one last time (not working)

As for the other software: I will try sigrok and rdumtool and get back to you with an update.