Author Topic: New EEVblog BM786 Multimeter  (Read 57877 times)

J-R, Microdoser and 5 Guests are viewing this topic.

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #275 on: January 21, 2021, 10:24:46 pm »
The batteries were in the package (3 energizer aaa in a small ziplock bag) but not installed in the meter -- so I guess DHL didn't remove all of them...

No, I shipped a lot more than they sent batteries back for. Maybe it was a sorted batch for one country and some dilligent handler opened one.
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #276 on: January 22, 2021, 02:09:59 am »
I just checked the signals on the internal header (not the one in the battery compartment) on the latest firmware model and still don't get any signals  :(
Was hoping they would have enabled support for the internal bluetooth module.
There is a chance it requires a pull up or something to activate it on bootup, but not likely.
 

Offline dougg

  • Regular Contributor
  • *
  • Posts: 56
Re: New EEVblog BM786 Multimeter
« Reply #277 on: January 22, 2021, 02:24:28 am »
After having a 4 week, 10 phone call experience with DHL Express *** I was worried when the EEVBlog shop told me on Monday that the same courier company had my 768. It arrived today in Toronto, Canada so that I now have 4.5 multimeters. The 0.5 is a Metex M-3650 (from Dick Smiths ?) whose AC ranges are shot; it sits behind the TV and is used to determine the health of AA and AAA batteries. Went looking for that elusive 768 user manual and came up with this url: http://www.brymen.com/images/ProductsList/BM780_List/BM789-5-manual-print1-r7.pdf . It has the same snafu describing a north American outlet on page 18. Dave should fix the dead url at the start of this thread.
The 768 probes feel really good and the screw-on banana plug fittings are really useful. Did some measurements with a REF-101 from www.syscompdesign.com at 250 mV on 3 meters: Fluke 233, 121GW and the BM768: 249.7, 249.79 and 249.82 . Then set a SDG 2042X to the same voltage and got 251.3, 251.45 and 251.43 . A pretty good result IMO. The BM768 looks larger than the 121GW but the latter is higher and weighs about 80 grams more.

*** Jakarta -> Toronto, original package "EMS International". POS Indonesia handed it off to DHL who put it inside their packet and dropped a digit off my street number. DHL say they are innocent, IMO they are culpable, they should have put their label on the other side of the _original_ package.
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #278 on: January 22, 2021, 03:01:49 am »
I just checked the signals on the internal header (not the one in the battery compartment) on the latest firmware model and still don't get any signals  :(
Was hoping they would have enabled support for the internal bluetooth module.
There is a chance it requires a pull up or something to activate it on bootup, but not likely.

Yeah, I had tried that as well with the same results.
https://www.eevblog.com/forum/testgear/new-eevblog-bm786-multimeter/msg3417392/#msg3417392
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #279 on: January 22, 2021, 07:49:33 am »
Just a quick check, the unpopulated 4-pin connector with the two pairs of common pins is on the back side of U20 and ground, used to power the meter during development or provide power to some peripheral. 

The other unpopulated connector is not in parallel with the one you asked about.   It's possible that these two unpopulated connectors were both intended to control an add-on peripheral rather than development.  The LCD is far enough away that there is certainly room to add something but with the lack of mounting holes in this area, my guess is they are both for development.   Probing the two connectors,  I didn't see anything while trying different modes.

Missed this post.
I do believe this is for the optional bluetooth module.
Brymen said way back
Quote
We plan to just put Bluetooth capability on the PCB but leave it off for BM78x first generation models. Once we complete the software development, we will launch out BM78x with Bluetooth version models.
I asked then if it was possibble to at least make the processor output serial data or whatever so that users could retrofit their own module if needed. That would make it cool feature "hack". But it seems they didn't do it.
They memtioned a CYPRESS CYBLE-212006-01 module, but that pinout doesn't match, maybe a daughterboard?
 
The following users thanked this post: joeqsmith

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1857
  • Country: ca
  • Hardcore Geek
Re: New EEVblog BM786 Multimeter
« Reply #280 on: January 22, 2021, 01:31:34 pm »
Speaking of cool feature hacks....

I almost pulled the trigger and ordered one of these when Dave first released them as it looks like it would make a great "daily driver" replacement for my well-worn, aging Amrel (American Reliance) model 37 I've been using for the past 30 years...   ???  The good ol' 37 has served me well over the years (it is basically a functional clone of a Fluke 87, which was way out of my price range back in those days, sold for less than half the price, even has a yellow holster  8) ) but it is getting temperamental as a daily-use meter being carted around, left in vehicles in temperature extremes, etc.  I have to clean the zebra strip for the LCD and the button pads etc. every few months to keep it properly operational.  It's simply just wearing out from 30 years of constant use.

After watching Joe's video series, it looks pretty much perfect for me except for one aspect of one feature that I do use on a fairly regular basis, and that is being able to measure audio-frequency AC voltages to within a few percent, right up to at least 20 kHz.  Joe's testing indicates that the -3 dB point is way down at 7-8 kHz, which would be really annoying to have to attempt correct for or carry another meter all the time for making AF measurements.

Joe, since you've at least taken a cursory glance at the circuitry, is it likely that I could modify one to extend the frequency range slightly?  Do you suppose that the limit is coming from something in hardware, like where I could possibly just change a couple capacitors in a filter or something and get it up to at least 20-25 kHz for the -3 dB point, (ideally it would be nicer to have the -3 dB point up at 40-50 kHz but I could live with 20,) or is it something integrated into the chipset that is causing the limitation?  Like, how is it doing the RMS, is it being calclated in the main chip?  Not being able to field-update the firmware makes that a show-stopper if it's in the chip I suppose.

I have a tube of decent quality RMS converters somewhere (Analog Devices, I think) that I could make an adapter box or something with better response, but then guaranteed I won't have it with me when I need it, and it is not really practical to try to replace the whole AC front end unless it is already using a separate converter chip and that's where the limitation lies, which I highly doubt....

Anyway, any thoughts on whether I might be able to extend the AC frequency response about an octave and a half?

... that would turn it into pretty much the ideal meter for me!
 

Online HKJ

  • Super Contributor
  • ***
  • Posts: 1957
  • Country: dk
    • Tests
Re: New EEVblog BM786 Multimeter
« Reply #281 on: January 22, 2021, 01:47:15 pm »
Anyway, any thoughts on whether I might be able to extend the AC frequency response about an octave and a half?

You could move to the next model in the line: BM789
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #282 on: January 22, 2021, 02:04:14 pm »
After watching Joe's video series, it looks pretty much perfect for me except for one aspect of one feature that I do use on a fairly regular basis, and that is being able to measure audio-frequency AC voltages to within a few percent, right up to at least 20 kHz.  Joe's testing indicates that the -3 dB point is way down at 7-8 kHz, which would be really annoying to have to attempt correct for or carry another meter all the time for making AF measurements.

The BM789 does that.
I don't have a BM789 to compare, but it's the same PCB.
 

Offline Fungus

  • Super Contributor
  • ***
  • Posts: 12371
  • Country: 00
Re: New EEVblog BM786 Multimeter
« Reply #283 on: January 22, 2021, 02:05:35 pm »
After watching Joe's video series, it looks pretty much perfect for me except for one aspect of one feature that I do use on a fairly regular basis, and that is being able to measure audio-frequency AC voltages to within a few percent, right up to at least 20 kHz.  Joe's testing indicates that the -3 dB point is way down at 7-8 kHz, which would be really annoying to have to attempt correct for or carry another meter all the time for making AF measurements.

Anyway, any thoughts on whether I might be able to extend the AC frequency response about an octave and a half?

... that would turn it into pretty much the ideal meter for me!

Brymen makes plenty of meters simliar to this one. A lot of them go up to 100kHz.

 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1857
  • Country: ca
  • Hardcore Geek
Re: New EEVblog BM786 Multimeter
« Reply #284 on: January 22, 2021, 02:12:35 pm »
Anyway, any thoughts on whether I might be able to extend the AC frequency response about an octave and a half?

You could move to the next model in the line: BM789

Well, obviously...  but then I wouldn't be buying the EEVblog version from Dave.  :)

The BM789 also doesn't appear to be very widely available yet and most places also appear to want way more money than Dave is charging for his BM786.
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1857
  • Country: ca
  • Hardcore Geek
Re: New EEVblog BM786 Multimeter
« Reply #285 on: January 22, 2021, 02:15:03 pm »
After watching Joe's video series, it looks pretty much perfect for me except for one aspect of one feature that I do use on a fairly regular basis, and that is being able to measure audio-frequency AC voltages to within a few percent, right up to at least 20 kHz.  Joe's testing indicates that the -3 dB point is way down at 7-8 kHz, which would be really annoying to have to attempt correct for or carry another meter all the time for making AF measurements.

The BM789 does that.
I don't have a BM789 to compare, but it's the same PCB.

Yeah, I know...  That's why I was wondering if it is a component-stuffing difference or a firmware difference.

I don't really need any of the "other" features on the 789, hence my question.  :)
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #286 on: January 22, 2021, 02:16:33 pm »
That's why I was wondering if it is a component-stuffing difference or a firmware difference.

Brymen provided me with a 789 as well which I plan to run soon.   It has the latest firmware installed but may no longer be in calibration.  The firmware is different for the 786 and 789.   

I'll ask them about the BT interface.  It would be nice to connect one of these up with LabView. 
« Last Edit: January 22, 2021, 03:04:44 pm by joeqsmith »
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Offline drussell

  • Super Contributor
  • ***
  • Posts: 1857
  • Country: ca
  • Hardcore Geek
Re: New EEVblog BM786 Multimeter
« Reply #287 on: January 22, 2021, 02:26:35 pm »
Brymen provided me with a 789 as well which I plan to run soon.   It has the latest firmware installed but may no longer be in calibration.  The firmware is different for the 786 and 789.   

Ah, you have a 789 also...  Sweet!

Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.

I would just like to know if you happen to notice any differences in the actual circuitry, thanks!   :)
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #288 on: January 22, 2021, 03:15:09 pm »
Brymen provided me with a 789 as well which I plan to run soon.   It has the latest firmware installed but may no longer be in calibration.  The firmware is different for the 786 and 789.   

Ah, you have a 789 also...  Sweet!

Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.

I would just like to know if you happen to notice any differences in the actual circuitry, thanks!   :)

I have no idea what the hardware/firmware differences are.  If you need a feature not available on the 786, I suggest just buying one that meets your needs rather than attempting to modify it.   I use that 2 X K-type feature on the BM869s a fair amount.   It's one of the reasons I bought it.  The UNI-T UT181A also supports it. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #289 on: January 22, 2021, 09:58:21 pm »
Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.

If they are smart then the firmware will be indentical, and only a single fuse bit determines what features it has.
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #290 on: January 23, 2021, 02:58:54 am »
Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.

If they are smart then the firmware will be indentical, and only a single fuse bit determines what features it has.

What do you feel makes this the smart thing to do?  Makes it easier to maintain the code base?   Like the idea of promoting upgrades for beginners with a soldering iron?   Sell more meters?   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Online Monkeh

  • Super Contributor
  • ***
  • Posts: 7147
  • Country: gb
Re: New EEVblog BM786 Multimeter
« Reply #291 on: January 23, 2021, 03:04:51 am »
Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.

If they are smart then the firmware will be indentical, and only a single fuse bit determines what features it has.

What do you feel makes this the smart thing to do?  Makes it easier to maintain the code base?   Like the idea of promoting upgrades for beginners with a soldering iron?   Sell more meters?

Fuse bit would be internal to the chip, not something you can solder. Potentially means you can flash the firmware image on a device, not set the fuse bits, perform a full test and calibration, and then later down the chain determine which model it is - less stock to keep of the boards, easier for replacements under warranty, and so forth. Less chance of strange and obscure bugs from different firmware builds, no 'oops we can't fit the image for this model in but all the others are fine', no need to build and ship multiple firmware images when you update it, which removes a potential human error leaving an old build in place..

Sorry, sort of a wall-o-thoughts there, but in general one image to rule them all removes a lot of problems.
« Last Edit: January 23, 2021, 03:06:49 am by Monkeh »
 
The following users thanked this post: Jacon

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #292 on: January 23, 2021, 03:41:38 am »
Quote
less stock to keep of the boards,
Could you please explain this?
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Online Monkeh

  • Super Contributor
  • ***
  • Posts: 7147
  • Country: gb
Re: New EEVblog BM786 Multimeter
« Reply #293 on: January 23, 2021, 03:59:38 am »
Quote
less stock to keep of the boards,
Could you please explain this?

If you only have one board design with one set of components and one firmware image, you may not need to keep as many assembled and tested on hand for warranty replacement, for example. Yes, it sort of mushes in with a second point from my post. I don't know that the boards are identical between versions of this meter (quite possibly not, honestly), but ticking both boxes potentially leaves you with more flexible stock. Same idea as using one case moulding with just different print on it, in some products that would be just a label stuck on covering unused button holes and so forth.
« Last Edit: January 23, 2021, 04:04:44 am by Monkeh »
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #294 on: January 23, 2021, 04:19:58 am »
Bare boards are the same but once populated they are different sub assemblies.  The hardware and firmware are unique.  Even at final assembly, we have a case using custom colors.  I doubt there's much concern about it.
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 33171
  • Country: au
    • EEVblog
Re: New EEVblog BM786 Multimeter
« Reply #295 on: January 23, 2021, 05:26:13 am »
Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.
If they are smart then the firmware will be indentical, and only a single fuse bit determines what features it has.
What do you feel makes this the smart thing to do?  Makes it easier to maintain the code base?   Like the idea of promoting upgrades for beginners with a soldering iron?   Sell more meters?

Obviously from a code point of view it's highly preferable to have a single code base for all 3 meters in the series. So when you fix a bug or change/add a feature in one it gets fixed in all the others.
The code just reads a single flag like "if 786 or 789 then do this" etc.
You'd have to be crazy to want to maintain and compile three entirely different code bases for effectively the same meter. The model bit just gets set in the programmer software in a non-volatile register somewhere and the code reads that as required and either ignores or does that function that models has.
« Last Edit: January 23, 2021, 05:28:50 am by EEVblog »
 

Online Kleinstein

  • Super Contributor
  • ***
  • Posts: 9242
  • Country: de
Re: New EEVblog BM786 Multimeter
« Reply #296 on: January 23, 2021, 12:49:10 pm »
One can have a common code base with a check in the actual meter, or one can do the different versions at compile time, e.g. with a constant to change between versions - this would need less momory in the meter (or at least be lowest range one).

I would not expect the AC frequency limit to be a software point. AFAIK they use hardware RMS chips, so there is not much to adjust in software. The difference would be more a thing of the used amplifer and RMS converter grade, maybe filter caps. Even for the numerical RMS way that some chip sets more support, there is usually no provision for extra filtering, other than maybe choose the sampling rate. It could be a nice feature to have a choosable BW for RMS. Higher BW also means more noise / background.  After all his is a DMM and not a spectrum analyser - so don't expect too much.
 

Online HKJ

  • Super Contributor
  • ***
  • Posts: 1957
  • Country: dk
    • Tests
Re: New EEVblog BM786 Multimeter
« Reply #297 on: January 23, 2021, 01:58:13 pm »
If the controller is programmed in-circuit, there is no problem with separate firmware builds for the different models, but they could still use the same code base.
If the controller is programmed before mounting it on the PCB, it would be easier to use a common code for all models and then use a bit in the calibration memory or a link on the circuit board to select the actual model.

The 100kHz bandwidth requires compensation capacitors for the input stage, the 7kHz probably not.
 

Online 2N3055

  • Super Contributor
  • ***
  • Posts: 3670
  • Country: hr
Re: New EEVblog BM786 Multimeter
« Reply #298 on: January 23, 2021, 03:14:33 pm »
Next to the LCD controller, there is an empty footprint for an IC and its components..
By the looks of it, it might be AD8436 True RMS converter chip. Some of the multimeter chips have built in low bandwidth RMS converters, for low cost options, with option to add external higher performance RMS converter for better specced meters.
Here we might have the same situation..
 

Offline joeqsmith

  • Super Contributor
  • ***
  • Posts: 7889
  • Country: us
Re: New EEVblog BM786 Multimeter
« Reply #299 on: January 23, 2021, 04:49:38 pm »
Obviously the 786 and 789 will have different firmware since the 789 supports the LowZ AutoV, dBm, has T2, etc. I'm just curious if the one spec difference of the ACV frequency is an intentional firmware limitation or if it is related to actual filter components on the PCB, thats all.  My suspicion is that it is most likely a software limitation.
If they are smart then the firmware will be indentical, and only a single fuse bit determines what features it has.
What do you feel makes this the smart thing to do?  Makes it easier to maintain the code base?   Like the idea of promoting upgrades for beginners with a soldering iron?   Sell more meters?

Obviously from a code point of view it's highly preferable to have a single code base for all 3 meters in the series. So when you fix a bug or change/add a feature in one it gets fixed in all the others.
The code just reads a single flag like "if 786 or 789 then do this" etc.
You'd have to be crazy to want to maintain and compile three entirely different code bases for effectively the same meter. The model bit just gets set in the programmer software in a non-volatile register somewhere and the code reads that as required and either ignores or does that function that models has.
I agree about using a common code base and conditional builds.  Of course, if it's the identical firmware there's no need for that. 

I never asked them why they spun up different firmware.  To me, it doesn't matter as long as they are able to maintain it.  Based on how well they kept up with me, I don't see that as a problem.   UEI had one meter to maintain and couldn't pull it off.   I think there's a difference in the skill level of the developers which may be a much bigger factor. 

Next to the LCD controller, there is an empty footprint for an IC and its components..
By the looks of it, it might be AD8436 True RMS converter chip. Some of the multimeter chips have built in low bandwidth RMS converters, for low cost options, with option to add external higher performance RMS converter for better specced meters.
Here we might have the same situation..

I didn't spend any time trying to sort out the differences beyond changing the IC.   While apart, I noticed the additional shield and trimmers.
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
Software, documentation and test reports for the low cost NanoVNA & V2 Plus 4 may be found here:
https://github.com/joeqsmith
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf