Linux Bluetooth Client for Owon B35 Multimeter

[DeanCording]

Late last year I purchased an Owon B35T+ to replace my very old Metex 3650CR.  The remote Bluetooth logging was the main attracting feature, particularly as there were a couple of Linux clients available.  Unfortunately those clients would not work with my meter.

After a bit of disassembly of both code and hardware, it turns out that Owon has changed the chip on this meter from the Fortune Semiconductor FS9922 to the Semic CS7729CN-001.  Where as the FS9922 just output encapsulated serial data, the CS7729CN puts out data encoded using the Bluetooth Low Energy Generic Attributes (BLE GATT).

I haven't been able to find any documentation for the CS77729CN so it took a bit of packet sniffing to decode the data protocol.  Turns out to be reasonablly simple with the measurements and functions being encoded in just six bytes.

I've written a new Linux client for this meter.  It has been designed in the Unix philosophy of tools doing one thing well and working well with other programs.  The client will connect to a meter and output the measurement readings in a variety of formats that are suitable for saving to file or feeding into other programs like gnuplot, KST, or even MQTT.  Using feedgnuplot allows you to have nice graphs that update in real time, such as the one below which show the discharge voltage profile of a battery pack I'm working on.

I'm still investigating the offline logging feature but that protocol is looking a bit obscure at the moment.


The client and more details are available from https://github.com/DeanCording/owonb35


Enjoy,

Dean

[DeanCording]

For those following along at home, a new version of the client has been released that supports offline measurement recording and interactive remote control.

[DeanCording]

Another new version, this time it adds a connection watchdog and automatic reconnection to deal with the flaky Bluetooth connection.

[Bob Sava]

I've been considering getting one of those multimeters, though I am leaning towards B41 version (when it comes down in price a bit).  Do you know if B41 and B35 are compatible?

[DeanCording]

I've no idea if they are compatible but it all depends on the chipset manufacturer as to what protocol it uses.  There is a chance that it may be but in any case it isn't too difficult to reverse engineer.

[bkw]

This is great. Thank you!

[linux-works]

fyi, I added to this code base (and/or another like it) and have a working version for the owon cm2100b clamp meter.

will start a new topic for that linux code.  but at least there's another owon with BLE that was not hard to decode and get working.

[linux-works]

git clone url:

https://github.com/sercona/owon-cm2100b-clamp-meter

enjoy