Author Topic: DIY 6.5 Digit Multimeter (Read 13761 times)

0.01C · « **on:** March 11, 2018, 03:34:19 am »

Bought from bbs.38hot.net diyer

https://youtu.be/FGSK1lUwNes

technogeeky · « **Reply #1 on:** March 11, 2018, 06:21:47 am »

Quote from: 0.01C on March 11, 2018, 03:34:19 am

Bought from bbs.38hot.net diyer

https://youtu.be/FGSK1lUwNes

On the one hand, that's pretty impressive. On the other hand, that's at 50 PLC.

On the other other hand, a 1 minute long video and you didn't even try to demonstrate linearity?

I have no more hands, but I think overall it's pretty impressive. And it looks nice. The 100V range is kind of limiting for a multimeter. Yeah, impressive. More details or a teardown would be appreciated.

Kleinstein · « **Reply #2 on:** March 11, 2018, 09:04:10 am »

This is odd - the label says 6.5 digits, but the display shown 7.5 digits with reasonable stability.

Getting the noise down to the 7th digit is OK for a 6.5 digit meter, especially if this is with an external voltage near the full scale so that there is not only the ADC noise but also the noise of the internal and external reference.

The limitation to a 100 V range is likely a question of input protection and the input divider. Precise dividers for a 500 or 1000 V range are expensive and protection gets increasingly difficult (e.g. not much choice of relays specified to 1000 V). For more normal Bench work 100 V is usually enough.

nidlaX · « **Reply #3 on:** March 11, 2018, 11:06:13 am »

So when's the group buy?

chickenHeadKnob · « **Reply #4 on:** March 11, 2018, 11:55:45 pm »

@0.01C
Do you know what the +00.27 PPM refers to?. That is I want to know what is being measured there and over what range. It never goes negative during the video even though the noise is bouncing around.

Marco · « **Reply #5 on:** March 12, 2018, 12:24:28 am »

Quote from: Kleinstein on March 11, 2018, 09:04:10 am

not much choice of relays specified to 1000 V

It's not a safety feature and it's only going to be conducting a couple mA ... just try a mains relay, it will probably work. Let the user decide whether he finds the non-linearity at higher voltages with a cheap divider an issue.

tooki · « **Reply #6 on:** March 13, 2018, 10:22:08 am »

:following:

BravoV · « **Reply #7 on:** March 13, 2018, 10:23:28 am »

Quote from: 0.01C on March 11, 2018, 03:34:19 am

Bought from bbs.38hot.net diyer

Where is the exact link ?

Jon.C · « **Reply #8 on:** March 13, 2018, 01:31:58 pm »

Quote from: BravoV on March 13, 2018, 10:23:28 am

Quote from: 0.01C on March 11, 2018, 03:34:19 am
Bought from bbs.38hot.net diyer

Where is the exact link ?

and price , please @0.01C

0.01C · « **Reply #9 on:** March 13, 2018, 02:03:42 pm »

Quote from: BravoV on March 13, 2018, 10:23:28 am

Quote from: 0.01C on March 11, 2018, 03:34:19 am
Bought from bbs.38hot.net diyer

Where is the exact link ?

http://bbs.38hot.net/forum.php?mod=viewthread&tid=250989&extra=page%3D1

technogeeky · « **Reply #10 on:** March 13, 2018, 07:13:17 pm »

The voltage reference is the LTC6655, evidently.

Iwanushka · « **Reply #11 on:** March 17, 2018, 02:37:40 am »

Looks, interesting main question how much total cost would be to get this thing in EU...

Vgkid · « **Reply #12 on:** March 17, 2018, 03:17:22 am »

Following this thread. I see thdy are using a ltc2440 .

Kleinstein · « **Reply #13 on:** March 17, 2018, 10:36:11 am »

From what I could see from the BBS38.hot pictures, there have been similar versions (mainly in a different case before). The only thing new is what looks like a RF (Blue tooth ?) module.

There seem to have been even a "commercial" Version of this under the Victor 70A name.

The input protection is rather minimal, with rather tiny fuse and just a bunch of SMT resistors - thus the 100 V rating.
It looks like the main range is 1 V and 10 V and 100 V would already go through the input divider with a 10 M Impedance.

In one of the links there where INL plots and they show about what one can expect from the LTC2440 ADC and relatively cheap resistors.
It might still be a useful meter in same cases.

The design with AZ input amplifier and SD ADC is more what you expect from 5.5 digit meters today, though the noise performance in the 1 V range can be quite good with the LTC2440.

coromonadalix · « **Reply #14 on:** March 25, 2018, 12:12:04 pm »

trying to replicate an Gossen Metratop 51 lolll boy i would like to have one

Chris56000 · « **Reply #15 on:** April 04, 2018, 09:12:59 pm »

Hi!

Is this an open-source or documented design that can be looked up or have the Chinese kept it to themselves like they're so fond of doing?

Chris Williams

2N3055 · « **Reply #16 on:** April 04, 2018, 09:37:18 pm »

Quote from: chickenHeadKnob on March 11, 2018, 11:55:45 pm

@0.01C
Do you know what the +00.27 PPM refers to?. That is I want to know what is being measured there and over what range. It never goes negative during the video even though the noise is bouncing around.

It is standard deviation of the measured value..

Arek_R · « **Reply #17 on:** April 04, 2018, 10:47:28 pm »

Whoa how to make front panel like this one?

Kleinstein · « **Reply #18 on:** April 05, 2018, 06:12:48 pm »

The front panel seems to be a kind of transparent acrylic with a printed sheet behind it. So the main difficulty would be getting the CNC milled acrylic made or file it yourself.

There seem to be a little more information on the older versions. I have seen schematics, but don't know about the software side.

2N3055 · « **Reply #19 on:** April 05, 2018, 07:59:17 pm »

I'm guessing laser cut acrylic....

Arek_R · « **Reply #20 on:** April 06, 2018, 09:01:23 pm »

Yeah my bet is on laser.
Is it possible to just paint back of the panel and then use laser to burn it out, then apply different color(layer), then burn again and again?
Also what's the downside compared to proper $2000 6 1/2 bench multimeter(apart from max 100V)?

floobydust · « **Reply #21 on:** April 06, 2018, 09:28:08 pm »

It looks like the original author mengxin is developing a commercial product, for about 7 years.
Posts say it's open source but I don't see files. Parts cost said around $100 (in china) but I would say $150? LTC2440 is about USD $12, LTC6655 SOIC is about $8, $13 for ceramic.

I see lots of digits but the precision foundation doesn't seem there.
The resistors are 25ppm and they wanted to characterize their temperature drift to save money using cheap resistors through software correction.

The 7.5 digit bench meter uses ADS1256
http://bbs.38hot.net/forum.php?mod=viewthread&tid=85405&extra=page%3D5

Someday we rollin a DIY multi-slope A/D or should we give up and use LTC2400 parts and get some real digits

Kleinstein · « **Reply #22 on:** April 07, 2018, 10:34:10 am »

Quote from: Arek_R on April 06, 2018, 09:01:23 pm

Yeah my bet is on laser.
Is it possible to just paint back of the panel and then use laser to burn it out, then apply different color(layer), then burn again and again?
Also what's the downside compared to proper $2000 6 1/2 bench multimeter(apart from max 100V)?

There are a few extra limitation compared to proper meters.
The INL if those SD ADCs is not that great. Besides the ADC the cheap resistors can add to this.
Only small ranges (if at all) have high impedance. So not > 10 GOhms for a 10 V range.
Due to the cheap resistors used the drift / accuracy are likely more like at the low end 5 digit level.
The possibilities for a proper calibration may be limited.
It looks like there is no Isolation from the inputs to the display and maybe even interface (if there is one). Having a PC interface (like GPIB) can be an important factor.

However there are also a few up's: the SD ADC can read rather fast and has low noise. There is also internal anti aliasing filtering. So used as a digitizer at something like 1 kSPS this can be rather good.

Marco · « **Reply #23 on:** April 07, 2018, 10:59:20 am »

Quote from: Kleinstein on April 07, 2018, 10:34:10 am

Only small ranges (if at all) have high impedance. So not > 10 GOhms for a 10 V range.

That's just a question of design, you don't need to put all the attenuators in front of the buffer.

rhb · « **Reply #24 on:** April 07, 2018, 06:22:50 pm »

Does anyone know a price and source for the kits? The 2nd one looked to be interesting, but I can't read Chinese. Not difficult to use better resistors than those supplied.

TheAmmoniacal · « **Reply #25 on:** April 07, 2018, 07:07:04 pm »

Looks like someone did their best to reverse-engineer the METRAHit 30M? http://bbs.38hot.net/thread-181-1-5.html

floobydust · « **Reply #26 on:** April 07, 2018, 11:59:41 pm »

They figure the mystery A/D (shrink DIP-28) is ADS1211 datasheet pdf USD $32 at Digikey. OUCH

coromonadalix · « **Reply #27 on:** April 14, 2018, 03:51:00 am »

32$ outch for the chip loll

But the Gossen 30m meter is way more than that

used 300$ to 600$ usd range, lost an ebay bid by 1$ loll

floobydust · « **Reply #28 on:** April 14, 2018, 06:52:18 pm »

I've never used a Gossen Metrawatt DMM.
6-1/2 digit display in a handheld, looks nice for precision work away from the bench.

The Metrahit 30M discontinued, replaced by Metrahit Ultra.
Bluetooth option and 310,000 count... $1,000 on Amazon for M249A.

coromonadalix · « **Reply #29 on:** April 18, 2018, 12:03:29 am »

well i have 28s and 29s they are better than the new versions series, even the ultra bt has crippled specs compared to the oldies loll
its a shame they did not improve the reading speeds, they are wonderful meters, almost 99% perfect

coromonadalix · « **Reply #30 on:** April 19, 2018, 10:40:47 am »

@flooby
saw an metrahit 30m nib for 670$ usd loll

http://globalsurveyingtools.com/gossen-metrawatt-metrahit-30m-sale they say they have them in stock

ass20 · « **Reply #31 on:** February 28, 2021, 03:31:54 pm »

hi
i found new docs for this DMM
schematic and firmware are avaliable
and little article
https://www.mydigit.cn/forum.php?mod=viewthread&tid=205607&extra=&page=1

shematic and firmware you can download from baidu cloud

https://pan.baidu.com/s/1zIs8DLQz1qlZEQ9z9XYcpA
psw ftj9
https://pan.baidu.com/s/1Nz-hRHCY4vjXKJLmmZOdnQ
psw tcmg

autor of this device selena2211

china qq group 3 8 4 4 5 6 0 7 0

I make digital board and test it. it is work fine
but my analog board has bugs in ohm meter part ....
current sinc do not make 1 ma current? it is make 1.5 ma current Why? i dont no ...


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Author Topic: DIY 6.5 Digit Multimeter (Read 13761 times)

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