DIY 6.5 Digit Multimeter - Page 1
Forum section: electronics / general

author: 0.01C
author_rank: Regular Contributor
timestamp: March 11, 2018, 03:34:19 am
content: Bought from bbs.38hot.net diyerhttps://youtu.be/FGSK1lUwNes

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 11, 2018, 06:21:47 am
content: Quote from: 0.01C on March 11, 2018, 03:34:19 amOn 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 11, 2018, 09:04:10 am
content: 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.

author: nidlaX
author_rank: Frequent Contributor
timestamp: March 11, 2018, 11:06:13 am
content: So when's the group buy?

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: March 11, 2018, 11:55:45 pm
content: @0.01CDo 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.

author: Marco
author_rank: Super Contributor
timestamp: March 12, 2018, 12:24:28 am
content: Quote from: Kleinstein on March 11, 2018, 09:04:10 amIt'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.

author: tooki
author_rank: Super Contributor
timestamp: March 13, 2018, 10:22:08 am
content: :following:

author: BravoV
author_rank: Super Contributor
timestamp: March 13, 2018, 10:23:28 am
content: Quote from: 0.01C on March 11, 2018, 03:34:19 amWhere is the exact link ?

author: Jon.C
author_rank: Unknown
timestamp: March 13, 2018, 01:31:58 pm
content: Quote from: BravoV on March 13, 2018, 10:23:28 amand price , please @0.01C

author: 0.01C
author_rank: Regular Contributor
timestamp: March 13, 2018, 02:03:42 pm
content: Quote from: BravoV on March 13, 2018, 10:23:28 amhttp://bbs.38hot.net/forum.php?mod=viewthread&tid=250989&extra=page%3D1

author: technogeeky
author_rank: Frequent Contributor
timestamp: March 13, 2018, 07:13:17 pm
content: The voltage reference is theLTC6655, evidently.

author: Iwanushka
author_rank: Frequent Contributor
timestamp: March 17, 2018, 02:37:40 am
content: Looks, interesting main question how much total cost would be to get this thing in EU...

author: Vgkid
author_rank: Super Contributor
timestamp: March 17, 2018, 03:17:22 am
content: Following this thread. I see thdy are using a ltc2440 .

author: Kleinstein
author_rank: Super Contributor
timestamp: March 17, 2018, 10:36:11 am
content: 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 25, 2018, 12:12:04 pm
content: trying to replicate an Gossen Metratop 51 lolll boy i would like to have one

author: Chris56000
author_rank: Frequent Contributor
timestamp: April 04, 2018, 09:12:59 pm
content: 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

author: 2N3055
author_rank: Super Contributor
timestamp: April 04, 2018, 09:37:18 pm
content: Quote from: chickenHeadKnob on March 11, 2018, 11:55:45 pmIt is standard deviation of the measured value..

author: Arek_R
author_rank: Regular Contributor
timestamp: April 04, 2018, 10:47:28 pm
content: Whoa how to make front panel like this one?

author: Kleinstein
author_rank: Super Contributor
timestamp: April 05, 2018, 06:12:48 pm
content: 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.

author: 2N3055
author_rank: Super Contributor
timestamp: April 05, 2018, 07:59:17 pm
content: I'm guessing laser cut acrylic....

author: Arek_R
author_rank: Regular Contributor
timestamp: April 06, 2018, 09:01:23 pm
content: 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)?

author: floobydust
author_rank: Super Contributor
timestamp: April 06, 2018, 09:28:08 pm
content: 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?LTC2440is about USD $12,LTC6655SOIC 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 usesADS1256http://bbs.38hot.net/forum.php?mod=viewthread&tid=85405&extra=page%3D5Someday we rollin a DIY multi-slope A/D or should we give up and use LTC2400 parts and get some real digits

author: Kleinstein
author_rank: Super Contributor
timestamp: April 07, 2018, 10:34:10 am
content: Quote from: Arek_R on April 06, 2018, 09:01:23 pmThere 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.

author: Marco
author_rank: Super Contributor
timestamp: April 07, 2018, 10:59:20 am
content: Quote from: Kleinstein on April 07, 2018, 10:34:10 amThat's just a question of design, you don't need to put all the attenuators in front of the buffer.

author: rhb
author_rank: Super Contributor
timestamp: April 07, 2018, 06:22:50 pm
content: 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.

author: TheAmmoniacal
author_rank: Unknown
timestamp: April 07, 2018, 07:07:04 pm
content: Looks like someone did their best to reverse-engineer the METRAHit 30M?http://bbs.38hot.net/thread-181-1-5.html

author: floobydust
author_rank: Super Contributor
timestamp: April 07, 2018, 11:59:41 pm
content: They figure the mystery A/D (shrink DIP-28) isADS1211 datasheet pdfUSD $32 at Digikey. OUCH

author: coromonadalix
author_rank: Super Contributor
timestamp: April 14, 2018, 03:51:00 am
content: 32$ outch for the chip lollBut the Gossen 30m meter is way more than thatused 300$ to 600$ usd range, lost an ebay bid by 1$ loll

author: floobydust
author_rank: Super Contributor
timestamp: April 14, 2018, 06:52:18 pm
content: 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.TheMetrahit 30Mdiscontinued, replaced by Metrahit Ultra.Bluetooth option and 310,000 count... $1,000 on Amazon for M249A.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 18, 2018, 12:03:29 am
content: 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 lollits a shame they did not improve the reading speeds, they are wonderful meters, almost 99% perfect

author: coromonadalix
author_rank: Super Contributor
timestamp: April 19, 2018, 10:40:47 am
content: @floobysaw an metrahit 30m nib for 670$ usd lollhttp://globalsurveyingtools.com/gossen-metrawatt-metrahit-30m-salethey say they have them in stock

author: ass20
author_rank: Regular Contributor
timestamp: February 28, 2021, 03:31:54 pm
content: hii found new docs for this DMMschematic and firmware are avaliableand little articlehttps://www.mydigit.cn/forum.php?mod=viewthread&tid=205607&extra=&page=1shematic and firmware you can download from baidu cloudhttps://pan.baidu.com/s/1zIs8DLQz1qlZEQ9z9XYcpApsw ftj9https://pan.baidu.com/s/1Nz-hRHCY4vjXKJLmmZOdnQpsw tcmgautor of this device selena2211china qq group 3 8 4 4 5 6 0 7 0I make digital board and test it. it is work finebut 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 ...

author: sethuraghul
author_rank: Newbie
timestamp: December 03, 2024, 04:16:58 pm
content: @ass20Can't able to download from baidu cloud could you have any other source to download?