NEW Brymen Bluetooth BM787BT Multimeter

[EEVblog]

I think there's too much market micro-segmentation here--there's now 5 different meters (785, 786, 787BT, 788BT, 789) based on one common design and with one feature added or deleted here and there.  Does it really change the cost to add or delete the dBm or 4-20mA loop features?  Perhaps there is a good reason for some of this, namely allowing for an EEVBlog version without violating current agreements with other distributors.

Correct. Brymen are super loyal to distributors. I wanted to sell the BM869 and BM257 back in the day, but they already had an agreement with CABAC here in Australia. Try buying a Brymen meter from CABAC, LOL.
I only got the BM235 because I got wind of it a year before release and CABAC didn't know or didn't care about it.

[EEVblog]

BM787BT got LoZ, this feature is missing on BM786.

Yes. It originally didn't have the LowZ and was going to be called the BM786BT, but I asked for the LowZ to be added, so they changed the number to the BM787BT.

[joeqsmith]

  If Dave stays with the provided software, I expect it will just work.   I'm a ways off from being able to do any sort of testing with it.

...
I'd show you a screen shot, but I just get the message "Pairing rejected by BM78xBT" 

    having never owned a cell phone, do you even need any software to pair it?   I was able to pair to it with the PC (shown in that short video).   The microsoft BLE tools talk to it to some extent.   My custom test program will sniff the meter's advertisements.  That comes back correctly per the manual.   I can pair to it, and download the meter's handles.  The UUIDs all match with the new manual.   From there I can read the meter's ID.   The problem is you can't do anything until you send the password.   I have provided Brymen with details on what I send to the meter (part of the reason for the manual updates).   I believe we now have the CRC sorted.  But the meter always responds with the same error.   The error code is not listed in the spec.   It seems pretty straight forward, but if you are having problems getting their software to work I wonder if something else is going on outside of my software. 

Oh well, I'm sure we can sort it all out in time. 

[EEVblog]

   having never owned a cell phone, do you even need any software to pair it?   

The Android OS does the pairing, just how you pair to any other bluetooth device like headphones etc.
The meter shows up under new devices but it will not pair.

[floobydust]

What batteries does this use? Generally a PITA with Bluetooth is the higher power consumption if it's streaming.
How much (logging) memory does it have? I'm wondering if you could use it to log a few day's data, then use BT to retrieve that log, to save power.

[joeqsmith]

The Android OS does the pairing, just how you pair to any other bluetooth device like headphones etc.
The meter shows up under new devices but it will not pair.

Really odd.  I have been able to pair using that old tablet (latest Windows 10) and my desktop PC (old Win 10) using a Targus and another BLE adapter.   

We just tried to use my wife's iPhone.   It does not list the BM788BT or the two radios in my desktop PC.  Both radios are able to see the iPhone and pair with it.  Her iPhone does see her watch and car just fine.   

[EEVblog]

What batteries does this use?

Three AAA, same as the BM780 series. It is not a "new" meter as such, it's the exact same hardware as the BM780 series, but with the bluetooth module soldered in

[EEVblog]

Teardown photos:
https://www.flickr.com/photos/eevblog/albums/72177720324728017

[mwb1100]

I had asked why they dropped support for dBm with the BM788BT.  Apparently they ran out of code space when adding the BLE option. 

So there's a good chance they planned on a BM789BT but had to punt on that because of the ROM space.  That probably made for some very unhappy people at Brymen.

[EEVblog]

Live teardown for those interested:

[joeqsmith]

The four pin header on the BT module had an unpopulated pin.  Note the new PCB has only 3 holes where the older one was 4. 

In 2019, they did not list the BT option but note how it used 2X4 pin headers.   You mentioned in your video how you voiced your concerns to Brymen about potential problems screwing up their meter when using the Bluetooth:   

https://youtu.be/TkmMitYnHUA?t=2208

I am curious what their response was and if you mentioned to them my comment to you about the undocumented handles?

[Aldo22]

How much (logging) memory does it have? I'm wondering if you could use it to log a few day's data, then use BT to retrieve that log, to save power.

That's a good thing.
My Owon CM2100B does that. They call it: “Offline Recording Function”.
It can record 10000 measurements.
How long this takes depends on the selected interval.
With an interval of 30s, it records approx. 83 hours.
This could be similar with the Brymen.

[Nuts and Proud]

Dave, will this meter work on Linux?  This will be a deal breaker for me and many others.

[joeqsmith]

...

write my own Windows application

Is it availble for public download? Could you provide link to your software? Perhaps source code?

Here you will find others posted an interface document and someone was creating an open sourced program for it.  I have not released mine. 

https://www.eevblog.com/forum/projects/uni-t-ut-d07a-bluetooth/

[joeqsmith]

Brymen did ask me about running a few more tests.  Sadly, none of that worked out.  I have asked them about the cell phone requirements to run their application.   If I had a working setup, I still have the Adafruit BLE sniffer that works with Wireshark.   Because Dave's Rev 15 Android doesn't pair,  I think I'll hold off.   Going from 0 cell phones to having 10 different ones laying around for testing.....  this is how I end up with so many scopes, meters, VNAs.....

[floobydust]

I see the Infineon (Cypress) CYBLE-212006-01 Bluetooth 4.2 module.
2-3.6V and 90mA TX full power, 17mA TX quiescent, 8mA RX quiescent, 256KB FLASH 32KB SRAM. MCU 48MHz. Thing is expensive $10 but includes the BT stack, it's been around since 2017.
They are likely using the platform stock firmware in the module.
I would look at serial debug info on the comm header to troubleshoot. I don't think the DMM LCD has much to offer for that as far as displaying connection error messages.

The 3-pin header J10U is just battery power to the BT board LDO. Two pins +, and one or two pins for GND.

[joeqsmith]

That is what I ended up doing with Dave's 121GW to sort things out.  Hoping we don't have to go to this level with the Brymen.

[bdunham7]

Going from 0 cell phones to having 10 different ones laying around for testing.....  this is how I end up with so many scopes, meters, VNAs.....

Post your address so we can all mail our old phones to you....

[bdunham7]

I see the Infineon (Cypress) CYBLE-212006-01 Bluetooth 4.2 module.
2-3.6V and 90mA TX full power, 17mA TX quiescent, 8mA RX quiescent, 256KB FLASH 32KB SRAM. MCU 48MHz. Thing is expensive $10 but includes the BT stack, it's been around since 2017.

That's the sort of thing I was concerned about--turning it into a battery-eating monster and then having AAA batteries to boot.  My Fluke IR-BT interface does this, using 2x AAA when there would be plenty of room for AA or even 2x 18650.  Battery life is terrible (like 5-6 hours!)  and I don't think it is because of the IR part. 

[EEVblog]

Dave, will this meter work on Linux?  This will be a deal breaker for me and many others.

They have not mentioned linux. But if the drivers are open source then someone will do it, probaby under Sigrok.
Even if they don't release it, someone will reverse engineer it.

[joeqsmith]

Going from 0 cell phones to having 10 different ones laying around for testing.....  this is how I end up with so many scopes, meters, VNAs.....

Post your address so we can all mail our old phones to you....

Sound like Dave would make better use of them.   

I did try sending incremental data to the meter in an attempt to find out what is causing the error.  I noticed if I don't throttle the communications, the meter will stop sending data.   The BT indicator remains active.   If I close the connection and sniff, the meter is will no longer advertise.  I have to toggle the BT button to get it to clear.   Still, no luck getting beyond the password.   

[joeqsmith]

Brymen reminded me today about their use of the large MTU size.  Of course, that is clearly stated in the spec.     I had not thought about it since Gossen, UNI-T and Kean all stayed within the 20 Byte limit.   Time to order up a new radio.

[EEVblog]

Just put the BM787BT back together (twice), and, umm, it doesn't switch on... 

[EEVblog]

Got the app app working, it DOESN'T need to be paired first! 

[mwb1100]

I think your comments about the shortcomings are on point.  The real time logger should have a button on that main widget on the bottom of the screen.  You can tell that Brymen doesn't do software! 

Their software for logging on their meters that support a serial/USB connection is really clunky - particularly the setup.  There are also at least a few small bugs (for example, I have to hand edit the CSV files to get Excel to read them in). One of the worst things is that each multimeter model (or "family") needs its own completely separate software install.  You'd think they'd have one software module that handles the UI and capture of the data and several driver modules that handle the particulars of the communication.  Kind of like sigrok or HKJ's Test Controller

Brymen's software has the feel that the project was given to a Summer intern and once they got something that mostly works, that was it.

That is one of the reasons they should publish the spec - it'll get better software for the meters out there sooner.  And that'll surely sell more meters.