OSHW - 24bit ADC measurement system for voltage references - Page 1
Forum section: electronics / projects

author: branadic
author_rank: Super Contributor
timestamp: April 17, 2014, 08:24:26 pm
content: Hi guys,volt-nutting is fun, that's for sure. But there are several reasons having no 3458A, Keithley 2002 or similar gear in the lab, such as the woman acceptance factor, enough space in the lab or the money to own such a "high end" device.Based on information and schematics of a measurement system given by Andreas for characterizing voltage references I've started to redesign his boards and like to share (with the agree by Andreas) the circuits and layouts with everyone out there (zipped EagleFiles).Attached you find the board for:1. an opto-isolated 24bit ADC based on the LTC2400 and the LT1236LS8 that can be directly connected to USB,2. a resistor divider board with LTC2057 buffer, to calibrate and linearize the ADC.The boards fit into a Hammond 1455C801 case, so they require not much space. Connectors are chosen such that the complete system is biunique.I'm currently building up both boards and will show pictures of them when finished.Next step is to design the third module, a 2:1 divider board based on the LTC1043. The idea of Andreas was to have everthing modular and to combine several modules together and I've copied that concept. Currently it is straight forward in design and connections.References <=5V are connected via D-Sub9 connector directly to the ADC board and references >5V that anyhow need a divider via D-Sub15 connector.At this point I'd like to thank Andreas for sharing all his worthwhile information with me.QuoteRegards, branadic

author: tszaboo
author_rank: Super Contributor
timestamp: April 17, 2014, 09:48:00 pm
content: Include pix or pdf... No one has that software you are using.

author: Lizerd
author_rank: Contributor
timestamp: April 18, 2014, 07:22:30 am
content: second that. pdf would be nice.

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 07:33:22 am
content: They are eagle files, sure you can download that!Edit: You can use the free version of eagleBTW branadic, thanks for sharing!

author: branadic
author_rank: Super Contributor
timestamp: April 18, 2014, 08:04:52 am
content: Interesting, you get something for free and all that comes to your mind is to beef?What is wrong with you?@miguelvpYour welcome...I thought EagleFiles would be best because as mentioned there is EagleLight available and if someone likes Gerber you can CAM the data and if you like pdf you can print them. But you don't want pdf-Files to reproduce the boards, right?

author: BravoV
author_rank: Super Contributor
timestamp: April 18, 2014, 08:26:35 am
content: Quote from: branadic on April 18, 2014, 08:04:52 amHow hard could it be to have a easy viewable format like pdf, or even printscreen or picture version (png/jpg) of the schematic just for people to take a quick "glance" at the circuit without having the hassle to install the eagle even its free ? I guess this must be a really difficult task, right ?If they're really interested to go further, then they can go download the free eagle to reproduce the pcb.Unless this is NOT about the spirit of sharing the circuit, instead its a Eagle softwarespamcampaign ?So much about the jargon words "OSHW" eh ?

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 08:56:51 am
content: Hmmm, so If I have open source software do I need to port it to the chip/compiler anyone might use?Makes no sense.Edit: the image will be to big and will break the thread btw, and eagle doesn't have an easy way I can find to do a pdf file, so he will need to research how to make it more convenient?Maybe he should also provide it as latex, svn, or logoEdit again: more so, he should purchase every available piece of software that draws and provide it in all of them for all the OS's available and even to the ones under development.

author: ovnr
author_rank: Frequent Contributor
timestamp: April 18, 2014, 09:03:01 am
content: No, but not everyone has Eagle installed (I don't!), and I'm not going to install a whole PCB layout package just to view your stuff.At least have the decency to drop a PNG or PDF of it in your post - if you can't be bothered to do that, why should anyone be bothered to give two shits about your design? And if someone wants to edit it or make it or print it orwhatever, they can grab your source files.Edit because of your edit: Really? Take a screenshot of it so we can get some idea of what it is, and downscale it to 1024px wide or so. Job done. As for PDF: Install one of the free tools that let you print to PDF, then use it.

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 09:13:52 am
content: Quote from: ovnr on April 18, 2014, 09:03:01 amhere you goEdit: and it's not my stuff, it's the OP stuff, but really is it that hard to install software, what if I don't want to load pdf because it might have exploits (and it does)To the OP, please give me a visio version pronto!

author: BravoV
author_rank: Super Contributor
timestamp: April 18, 2014, 09:19:58 am
content: Quote from: ovnr on April 18, 2014, 09:03:01 amSave your breath, some are not that bright enough to get that.Quote from: ovnr on April 18, 2014, 09:03:01 amSome never get it, they thought they have to install a program just to view PNG or JPG. And today's modern browsers can handle PDF natively.Quote from: ovnr on April 18, 2014, 09:03:01 amI guess some are still using 800 x 600 monitor, so you have to understand the idea of scrolling is sux in that resolution for them.

author: miguelvp
author_rank: Super Contributor
timestamp: April 18, 2014, 09:24:30 am
content: Well, more and more people use their phones/tablets instead of computers, it's bad norm to break the 800 pixels across in forums nowadays.

author: poorchava
author_rank: Super Contributor
timestamp: April 18, 2014, 12:13:52 pm
content: QuoteI need to write that one down

author: Monkeh
author_rank: Super Contributor
timestamp: April 18, 2014, 02:06:32 pm
content: Quote from: BravoV on April 18, 2014, 09:19:58 amFor varying degrees of 'handle'. But misrenderings and crashing are totally fine..Please do everyone a favour and stop crying that the OP didn't do something to please you.

author: kruszi
author_rank: Newbie
timestamp: April 18, 2014, 03:19:36 pm
content: Why have these cut-outs of the PCB around the IC on the bottom side ?

author: con-f-use
author_rank: Unknown
timestamp: April 18, 2014, 05:24:33 pm
content: A bit of context would be nice for people like me who just stumbled upon this. Why should I care?NowI found outthat many DIY 5.5/6.5 digit DVMs use these. But that info should be included in the top post. Other than that: yay! Thank you, I might come back to this if I ever need it...And btw. jeez, you ungrateful bunch.

author: Lizerd
author_rank: Contributor
timestamp: April 18, 2014, 06:48:59 pm
content: I did a similar board for my modular test board system, ADS1256 8ch 24bit ADC with 2.5v precision ref LTC6655.I have other boards for the MCU and opto isolation and PC communications.

author: Andreas
author_rank: Super Contributor
timestamp: April 18, 2014, 07:20:06 pm
content: Quote from: Lizerd on April 18, 2014, 06:48:59 pmVery interesting, as the ADS1256 has lower noise than the LTC2400.Did you make tests with linearity of the ADC and the temperature + ageing drift of the system?In this regard the LTC2400 seems to be better from datasheet because every conversion a self adjustment of offset and full scale is done automatically.With a similar system of LTC2400 + LT1236AILS8-5 after 5kHrs pre-ageing I have a standard deviation < 0.4 ppm/kHr against two LTZ1000A references.With best regardsAndreas

author: Lizerd
author_rank: Contributor
timestamp: April 18, 2014, 07:47:06 pm
content: No, I have been a bit preoccupied so I haven't had any time testing this board.But it's on the to do listat first I was aiming for the LTC2400 , but I wanted more then one channel so i could use this board for my power supply that I am working on.So I could sens much more signals without using a external multiplexer, with this I get better spec with fewer components.And the ADS1256 has 8ch with PGA and i can get 23 Bits Noise-Free if the signal in is good, so I went with this one instead.

author: tszaboo
author_rank: Super Contributor
timestamp: April 18, 2014, 09:33:04 pm
content: Quote from: miguelvp on April 18, 2014, 09:13:52 amAre you finished? It is a perfectly valid request to post the SCH in an open format, like PDF or PNG or XPS or whatever. You know why? Because I'm not going to install eagle. That would be the last thing I'm going to do, even if it is free, even if it is only 8 MB even if it wouldn't pollute my registry, wouldn't overwrite my default programs for SCH and PCB extensions.Making PDF is so horribly complicated, I doubt that someone doesn't have a virtual PDF printer. Besides, how do you think, you can make something, which you can open in 20 years? Some proprietary application or an open source widely used format.

author: dannyf
author_rank: Super Contributor
timestamp: April 18, 2014, 09:45:40 pm
content: QuoteThe entire ads123x family is quite interesting too. I have used ads1232/34 and really liked them for their simplicity, high input impedance and low noise.

author: branadic
author_rank: Super Contributor
timestamp: April 27, 2014, 07:40:11 pm
content: My inital post wasn't meant to be for entertainment but for people who perfer using their soldering ironinstead of using tablets, pads or smartphonesand those people won't use pdf or similar to duplicate the board.After all this wasted discussion about file format and nagging that I posted original source filesinstead of pictures we can maybe get back on topic?

author: gxti
author_rank: Frequent Contributor
timestamp: April 27, 2014, 08:22:23 pm
content: You didn't post any questions, nor any indication of where you wanted the discussion to go. What were you expecting? If you want people to be interested in something it's your job to plant the seed. Maybe talk about what you've done with it so far? Results? Expectations? Anything?

author: MacAttak
author_rank: Unknown
timestamp: April 28, 2014, 12:08:48 am
content: Quote from: kruszi on April 18, 2014, 03:19:36 pmI wondered the same thing, but it appears your question got buried in under the file format griping.Can anyone explain why this is done? There obviously must be a reason because it also shows up in Lizerd's board design.

author: kt315
author_rank: Regular Contributor
timestamp: April 28, 2014, 12:47:06 am
content: I believe the slots are to relieve the mechanical stress from the pcb around the voltage reference. There are a couple long threads on the forum regarding voltage references that has a lot of info on it.Branadic, thanks for sharing the board. Did you have a chance to build it yet?

author: TiN
author_rank: Super Contributor
timestamp: April 28, 2014, 12:53:06 am
content: Quote from: branadic on April 27, 2014, 07:40:11 pmI'd like to check out your design (as working on design with LTC2442 at moment too), but as some already stated, not everyone have Eagle, or going to install it just to view ur board, sorry.And Eagle source files are no good for duplicating boards anyway, that's what is Gerber is designed forAs for ontopic note - i'd rather make board "compatible" with original LT devkit, so could use their software to avoid initial work of doing software to read/debug ADC operation.P.S. I do use 2 smartphones and bunch of computers, but it does not mean that like to install everything from web to see every format out therePDF would do great for all, as everyone have it to read datasheets.

author: liquibyte
author_rank: Frequent Contributor
timestamp: April 28, 2014, 01:20:13 am
content: Damn what a clusterf***. Here. The next person that posts Eagle schematics without realizing there's a image export under File, I'm going to spam them with PM's until they beg the mods for me to stop.

author: branadic
author_rank: Super Contributor
timestamp: April 28, 2014, 07:50:31 am
content: QuoteI followed the suggestion given in this video for the reference packagehttp://www.linear.com/solutions/1129QuoteNot yet finished, cause I'm currently on vacation.

author: CaptnYellowShirt
author_rank: Frequent Contributor
timestamp: April 28, 2014, 05:30:25 pm
content: Subscribed!

author: bingo600
author_rank: Super Contributor
timestamp: April 30, 2014, 06:51:14 pm
content: Thanx BranadicLooks interesting.I do hope you are going to continue this thread , despite the IMHO quite unreasonable people attacking.The first post about a .pdf request was ok , but the others .....Keep on the good work , and you did get me interested immediately. Wo.any further seed./Bingo

author: EEVblog
author_rank: Unknown
timestamp: May 01, 2014, 07:59:46 am
content: Quote from: bingo600 on April 30, 2014, 06:51:14 pmI agree. A first polite request to post in a common format like PNG or PDF is fine (and fully expected, Eagle isn't the way you'd normally show of your project in a forum).But yes, the rest was definitely not coolPlay nice.

author: branadic
author_rank: Super Contributor
timestamp: May 30, 2014, 06:14:36 pm
content: I've finished (soldered the missing parts and cleaned them with ultrasonic and IPA) the boards today. Next step is to flash the microcontroller, to do some test and write a pc software (I guess that will be done in Matlab/Octave). Not to forget to mention that the boards will be packaged, I've choosen Hammond 1455C801.I made some minor changes in the board files and will update them (first post).After that the next board will be layouted, the LTC1043 divider.Feel free to duplicate...

author: Neganur
author_rank: Unknown
timestamp: May 30, 2014, 08:30:30 pm
content: sehr geil, danke!

author: branadic
author_rank: Super Contributor
timestamp: June 15, 2014, 02:05:44 pm
content: Updated the files in the first post, because the value of C5 in 24 Bit ADC.sch was changed. I also modified the dimension layers in both files somewhat, so that the board better fits into the Hammond cases.Current status:I calibrated the NTC of my both ADC boards using a SHT75 reference sensor, but will verify my calibration soon with an environmental chamber again.After a first 300h preaging periode with extended load on the LT1236LS8 I will measure the current reference voltage and the TC on a Keithley 2002 with an oven. Andreas suggested to use a cross-adapter and to measure the TC with one board heated while the other stays at room temperature. Thats for sure a good possibility if you don't have access to calibrated gear.I'll than check linearity using the resistor divider board and the voltage reference of both ADC boards, because of the lag for the 2:1 LTC1043 board to do that with my LM399 reference, that is now running for more than one year.I also started to write a Matlab program, that requests the data via serial interface and display them in a diagram. That works fine up to now. Next step is to build a gui around that code and make it a standalone application.

author: branadic
author_rank: Super Contributor
timestamp: June 19, 2014, 01:44:17 pm
content: While the voltage reference is still preaged with extended load for another few days until 300h have passed and in most places of germany christian people celebrate "happy cadaver" and the none christian people have a free day too, I decided to do something 'bit off topic to this theme. I started to build myself a small temperature chamber, because our climate chambers at work are in use for the next weeks. Well, no problem at all.I found all the required parts for that in my home lab, a Styropor box with inner dimensions of 270x165x160mm³ and 30mm wall thickness, a heatsink with a size of 150x150mm², a CPU cooler with fan, a Peltier element with size 40x40mm² 12V/30W, a heater foil and a fitting sheet aluminium, two laser cut D-Sub panels and several D-Sub connectors.All that is still missing are a few mechanical components, that will be finished by the end of the week.A solution to read out two SHT25, less then half the price of a SHT75 and somewhat more accurate, via VCOM with additional 3x16 LCD display is currently in progress and will complete the setup.One SHT25 is to track the chambers temperature, the second one is for the device under test, e.g. the NTC of the ADC board inside its case to calibrate it.It would have been deluxe if the temperature is controlled via a µC or something similar, but as such controllers are very expensive I will start using one of my lab power supply and set the temperature by manuelly adjust the current on the PSU.I've also drawn the panels for the Hammond cases and will post them here soon in DXF format. I used the free front panel designer by Schaeffer AG for that purpose. Pictures will follow when finished.

author: branadic
author_rank: Super Contributor
timestamp: June 22, 2014, 10:10:49 am
content: It's not yet finished, but here is a picture of my temperature box with heater foil and TEC. A few D-Sub9 connectors as feedthrough the wall.I will order some pcbs next week and put a small ADC extension board to the batch with PT1000 + AE / Vishay 10K 0.01% 5ppmeBay auction: #380191504233Couldn't find PWW available from stock at lower cost.

author: branadic
author_rank: Super Contributor
timestamp: July 05, 2014, 10:39:23 pm
content: Found an intersting link today and I can't remember that it was linked somewhere on eevblog before:Long term characterization of voltage references

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2014, 03:34:26 am
content: Just a thought, and feel free to point me to another thread if this has already been discussed, but the cut-outs around the voltage reference seem a bit sub-optimal? There are little PCB bridges on all four sides of the voltage reference "island", which means that that islandcan'tfreely thermally expand or contract. I don't see that thermal stresses will be reduced much at all. The suggestions in the relevant datasheet, to have a cut-out running continuously around all three sides of the reference so that it's freely cantilevered in space seem more effective and more space-efficient.

author: branadic
author_rank: Super Contributor
timestamp: July 06, 2014, 06:34:36 am
content: Please refer to the video available by Linear Technology (Brendan Whelan) that suggest this 4-sided cutout geometry to give similar or better performance compared to the 3-sided pcb tab cutout:http://www.engineeringtv.com/video/Linear-Technology-LS8-Package-I(watch minute 6:34)Furthermore you have the advantage of running the traces over the corners instead of having all traces at one side. So, I preferd using the 4-sided cutouts and while the device runs within +10°C ... +40°C I'm not affraid of any form of cutouts.

author: rs20
author_rank: Super Contributor
timestamp: July 06, 2014, 07:08:30 am
content: Point taken, although I can't reconcile this with my intuition. Interesting that the context was FR4 swelling due to humidity. I'd be curious if anyone's come across some actual studies on this -- all the video tautologically says is "Acangive similar or better performance than B", which doesn't rule out A being better than B at all.</ot>

author: Andreas
author_rank: Super Contributor
timestamp: July 06, 2014, 08:06:29 am
content: Quote from: rs20 on July 06, 2014, 07:08:30 amYou are invited to do some studies on this.I for my part prefer the "dead bug in hole mounting" method for LS8-devices. (do not try this in production).https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg278825/?topicseen#msg278825A other method would be mounting the reference on a ceramic substrate with the same CTE than the housing of the reference.Or using a flexible part of a PCB (kapton foil) for the mounting of the reference.With best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: July 06, 2014, 08:23:23 am
content: My board is designed with the opportunity to cut the reference part of the pcb and replace it with a flexible substrate, such as 100µm FR4. I had that in mind when I designed the board, but my pcb manufactor doesn't offer 100µm substrates and I don't have such a thin substrate for home-processing. I wouldn't use capton, it's expensive and there is no need for it.The method of Andreas using "dead bug" is a way, but I wanted to avoid such solutions.A complete board made of ceramic would be very expensive I guess and you'll never now what ceramic the package is made of to match the CTEs as close as possible.Edit: In addition to the linked publication, I wonder why they used AD587 (10V) instead off AD586 (5V) and why they have used LTC6655BHM (MSOP8) instead of LTC6655BHLS8. I would expect somewhat better performance of that devices.

author: Andreas
author_rank: Super Contributor
timestamp: July 06, 2014, 08:34:26 am
content: Quote from: branadic on July 06, 2014, 08:23:23 amI can understand this: this mounting method needs much time in assembling.I did not think about a complete board: but what about a small ceramic with 4-5 pins (mechanical decoupled from PCB) on one side (upright mounting) together with a small temperature controller for the reference on the back side.Note that I have also a influence of the PCB on the reference on ceramic references like VRE3050AS when I solder all PINs around the ceramic case to the PCB.Quote from: branadic on July 06, 2014, 08:23:23 amEdit:AD587 and AD586 should not differ much. (in LQ or UQ option).For the LTC6655BHM I think that they simply started the study before the LS8-Option was available.On the other side I have large hysteresis with the BHM package. I do not think that the same chip with similar die attach will behave much better in LS8 housing. (would be a interesting test).With best regards.Andreas

author: SeanB
author_rank: Super Contributor
timestamp: July 06, 2014, 09:16:44 am
content: You can get flexible boards made cheaply now, so probably you can get a sheet made with multiple small adaptors, screen the solder paste on them and mount multiple devices then reflow them, then afterwards simply cut them out of the sheet when needed for use. Easy to have the connections on one side with the space for a thermistor and decoupling caps as well, then simply have some larger pads with a large solder ring on them ( probably on a 0.2in pitch so you can either solder the board to the board direct or use a pin header) so you can mount them. You can even include a guard trace around the unit and a copper trace for a cutting guide. Assemble with ordinary kitchen scissors.

author: branadic
author_rank: Super Contributor
timestamp: July 06, 2014, 09:27:38 am
content: QuoteCould be the reason, yes.QuoteI would expect better results even in the lower 0.1Hz region as the die is glued with only the bottom side to the package, while in the BHM package the die is surrounded by the thermoset and glued to the lead frame. But this is all speculation.QuoteThis is true only for manufactors outside of germanyWhile complete devboards are offered by Asian you wouldn't even get the board fabricated nor the parts from a distributor for a comparable price here. And 100µm substrate is called to be "special" not standard and you have to pay for something "special".

author: branadic
author_rank: Super Contributor
timestamp: September 16, 2015, 07:33:10 pm
content: Added the files for the 2:1 Resistor Divider with LT5400-1 in the first post. Finished the assembly for this board today. Still to do: layout the 2:1 divider with LTC1043 for the Hammond case.

author: branadic
author_rank: Super Contributor
timestamp: June 24, 2016, 07:30:56 pm
content: Since LT1027DxLS8 is available and seems to be a good choice as a reference for this system here's a version of the ADC board with this reference replacing the former LT1236LS8. Hope you like it.I will build up this version as well, as it is interesting to see what it's about.

author: branadic
author_rank: Super Contributor
timestamp: June 28, 2016, 07:28:34 pm
content: I plan to order pcb's. If someone is interested in pcb's, version with LT1236LS or version with LT1027LS8 and/or the resistive divider board, please write me an obliging email and let me know how much boards of which version. The more we get together, the cheaper the boards.Boards are made for Hammond 1455 cases.Deadline is the 10.07.2016.

author: kutte
author_rank: Contributor
timestamp: June 29, 2016, 08:51:58 am
content: Quote from: branadic on June 24, 2016, 07:30:56 pmthank you, but once again: is it really that difficult to include a pdf-version of the schematics?Kutte

author: branadic
author_rank: Super Contributor
timestamp: June 29, 2016, 07:40:09 pm
content: QuoteGive me a good reason what you want to do with a pdf? I don't see any advantage. The only argument I can agree are Gerber production files.

author: kutte
author_rank: Contributor
timestamp: June 30, 2016, 10:08:58 am
content: Quote from: branadic on June 29, 2016, 07:40:09 pmhow can I have a look at the schematic ( filename.sch ) without installing Eagle ?Kutte

author: branadic
author_rank: Super Contributor
timestamp: June 30, 2016, 12:25:24 pm
content: Almost every CAD for printed circuit boards is able to import Eagle Files.What can you do with the schematics in PDF format? Almost nothing, just viewing it. Please don't repeat this discussion we already had before. If you don't have Eagle or similar CAD software with import function it's not my problem.

author: rs20
author_rank: Super Contributor
timestamp: June 30, 2016, 12:37:53 pm
content: Sorry, but think: phone, tablet, my locked down work computer, internet cafe, borrowed devices. Every one of my devices except my home PC, the only one which I have complete dominion over. All places which have no CAD software, and all support PDFs near-natively. And viewing a schematic is all that 90% of people well ever want to do. You're free to keep your design behind a proprietary wall, just don't pretend that it's sensible or in the spirit of a forum.To be clear, if you had just said "no", I'd have not said anything. But you said "no,it's easy for you to use what I've provided". And I have to point out that this is massively, massively untrue for many people.

author: branadic
author_rank: Super Contributor
timestamp: June 30, 2016, 08:23:53 pm
content: QuoteAnd I'm not adressing exactly those 90% of peopleSome design parameters of the pcb to be ordered:- size: 83 x 50 mm²- thickness: 1.55mm- smallest width: 0.2mm (due to guard at reference noise reduction pin)- smallest via: 0.4mm- finish: Ni/Au- no silk screen- stop mask: green on both sides

author: timb
author_rank: Super Contributor
timestamp: June 30, 2016, 10:17:00 pm
content: As an FYI, I would be in the target audience for this device, however I browse the forum (and do research, etc.) almost exclusively on my tablet. Further, I don't use Eagle for design work. If you can't be bothered to provide a PDF, or at the *very least* a PNG of the schematic, then I'm not going to bother with your device.PDF is the de facto standard for distributing documents on the Internet. If I have to install Eagle on my main computer, just to view your schematic, then I'm not going to even consider your device. Period. What it tells me is you're either lazy or don't have any attention for detail. All you have to do is download Ghostscript... (Or one of the other numerous PDF printers freely available, assuming you're on Windows; if you're on OS X you can natively print to a PDF, so there's no excuse there.)Sorry for being blunt, but that's just the way things are. (This would be like TI distributing datasheets exclusively in Word or PowerPoint formats. Can you imagine?)

author: branadic
author_rank: Super Contributor
timestamp: July 01, 2016, 10:57:11 am
content: The former version with LT1236LS8 has already been shown. Is it really that complicate for you to imagine that LT1236LS8 was replaced by LT1027LS8 and therefore minor changes on the layout had to be performed? The complete rest is identical to the former version.If your answer is yes, than you really don't need the pcb, trust me and you are one of the 90% of people out there that don't need a 24bit ADC measurement system for voltage references either.

author: timb
author_rank: Super Contributor
timestamp: July 01, 2016, 01:53:50 pm
content: I actually would be in the market for something like this, but since you can't be bothered to keep your documents current, I won't bother either.

author: TiN
author_rank: Super Contributor
timestamp: July 01, 2016, 02:23:35 pm
content: It takes 5 seconds to export PDF and attach to files, and saves all that time wasted with valid and invalid complains. If every engineer will post their hobby stuff only in software they used, discussion would be less open and wide. Viewing schematics is all that most of interested folks need, as those who will bother building something likely to use their own chassis, own PCB layout, own components set they want anyway, and PDF-schematics is more than enough to test your idea.Quote3000 EUR OrCAD can do nothing with Eagle files. Yes, it's not your problem.I was remotely interested as just got few LTC6655's and ADCs not long time ago and going to bodge little PCB for few tests into my order, so hence came to this thread to check out on similar design ideas.. Baa, can't see files.

author: AlfBaz
author_rank: Super Contributor
timestamp: June 22, 2019, 07:35:35 am
content: Hi Branadic, first let me thank you for posting this and Andreas for allowing it.I'm in the process of duplicating the circuit using altium, roughly copying your PCB layout and routing.I'm sure this circuit has been tweaked for minimum noise and as I work through the design I see some of the choices you've made but I still have a few questionsThe relatively high series resistance to the optos seems to be to round off the edges on the pulses and the even higher resistances (22k and 47k) to allow the pic to be programmedThe one part I'm stuck on is why the parallel 2.2nF cap across the 3k3 resistor from the PIC to the opto. This seems to consume a large spike of current from VDD on transitions given the typical 10ns rise and fall times, am I missing something here?B1 and B2, are they ferrite beads? If so i'm curious which frequency you chose 70, 100MHz or something elseThe choice of micro, was it based on its low current consumption and adc for the thermistor? Did you create a software UART and SPI for the interface to the ftdi usb and LTC2400 or is it just some rudimentary bit banging? I ask this because the PIC you have chosen is quite low current and don't know if I'll find anything lowerWhen you run this in conjunction with the 2-1 divider where do you power the whole lot from, DB9 plug or from the JP1 header on the LTC2400 board?And finally after you tested did you end up cutting out the LTC2400's mounting square and go dead bug like Andreas did. In other words, did you end up noticing the effects of humidity

author: Andreas
author_rank: Super Contributor
timestamp: June 22, 2019, 09:56:27 am
content: Quote from: AlfBaz on June 22, 2019, 07:35:35 amHello,intention of the 2.2nF is to speed up the rise time at relatively low power (~1mA).Otherwise 9600 Baud are marginal with PC817 and 1 mA.The LTC2400 does not need decoupling from the PCB. (Self adjustment during each measurement).Only the voltage reference shows a dependancy from PCB stress and should be decoupled.with best regardsAndreas

author: branadic
author_rank: Super Contributor
timestamp: June 22, 2019, 10:16:16 am
content: Hi,B1 and B2 were choosen to be 600ohms at 100MHz, if I remember correct. Micro was choosen by Andreas because of battery operation and thus low power consumption required.Power is always supplied via JP1, DB9 powers additional modules connected to it.I didn't test the ADC to excess as Andreas did, however I have the reference still mounted directly onto pcb but NTC was changed to 0402 type and this way is much closer to the reference compared to through hole NTCs.What I wanted to try is to place reference on a flexboard, which is then soldered to the board giving some strain-relief. Since real semi rigid pcb's are barely expensive and dead bug style is not a good production process I thought this tradeoff should give best results to keep board stress due to humidity away from the reference. But haven't tried that yet as some other projects came into focus.-branadic-

author: AlfBaz
author_rank: Super Contributor
timestamp: June 24, 2019, 05:25:22 am
content: Quote from: Andreas on June 22, 2019, 09:56:27 amMy mistake, LTC2400 on the brain, meant LT1236Thank you gentlemen, about to order parts and PCB, will post pics when complete. Lots of measurement fun aheadJust one more thing, is there any reason to go without solder mask? I seem to recall seeing you guys post pictures of your various pcb's without it and always assumed it was an artifact of an in house manufacturing process. I see Dr Frank's LTZ1000 boards I got from you Branadic have it thoughRegards, Alf

author: branadic
author_rank: Super Contributor
timestamp: June 24, 2019, 07:07:48 am
content: Andreas made is first boards at home and I once had a cheap and fast german pcb manufaturer with the only drawback of having no solder stop mask nor silk screen. Unfortunately he's no longer in business.-branadic-

author: AlfBaz
author_rank: Super Contributor
timestamp: June 24, 2019, 07:58:28 am
content: Ok thanks

author: Andreas
author_rank: Super Contributor
timestamp: January 31, 2020, 10:26:52 pm
content: Hello,Thanks for the summary.But noise is not all.For a absolute measurement the offset and gain drift and INL is also important.That is why I love the LTC2400:Offset + Gain drift is self adjusted.INL can be easily modeled and canceled out to below 1 ppm.with best regardsAndreas

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: February 02, 2020, 02:27:30 am
content: Quote from: 3roomlab on January 31, 2020, 12:00:21 pmThank you for the work you put into this, My first impression is that you have been overly optimistic in two dimensions. Both in using the data-sheet specmanship Enob of the ADC's as well as relying on getting more than 2 extra bits from averaging. Two extra bits with simple averaging in the presence of gaussian noise, easy. The next bits progressively more difficult, then you will hit some system noise floor that becomes an insurmountable limit.The ADS8699/8689 is indeed interesting, I have been planning a design for a year now and I need to get off my ass. One complicating factor is the bandwidth of the analogue front end. From the data sheet (page 25):In order to mitigate the noise of the front-end amplifier and gain resistors of the PGA,the AFE circuit of the device features a second-order,anti-aliasing LPF at the output of the PGA.The magnitude and phase response of the analog anti-aliasing filter are shown in Figure51 and Figure52, respectively.For maximum performance,the –3-dBcutoff frequency for the anti-aliasing filter is typically set to 15 kHz.The performance of the filter is consistent across all input ranges supported by the ADC.I read this as you won't get near nyquist performance suggested by the sample rate if you are simply brute force adding these puppies in parallel.

author: jeffheath
author_rank: Regular Contributor
timestamp: February 02, 2020, 03:44:36 am
content: I found this thread, files were eagle cad... so I installed eagle cad.... now I can open eagle cad files! It's not that hard...

author: CarlO
author_rank: Newbie
timestamp: September 09, 2025, 02:54:32 pm
content: Hi All. I came across this old thread and am very interested in building some of these devices. I was able to open the PCB files in Eagle and produce Gerber files for PCB production. I have searched the forum and I have not been able to find any firmware or other software to complete this project. Can someone please point me to a thread with firmware files for this project? Or perhaps someone could PM me the files? Note that I seem to be unable to send a PM on this forum, perhaps because I am a Newbie? Thanks in advance for any assistance you can provide.-Carl

author: Andreas
author_rank: Super Contributor
timestamp: September 11, 2025, 08:43:15 am
content: Hello,find the firmware attached.you can use the 9 pin DSUB to program the PIC on the board using a cable with corresponding PINs connected between PICKIT3/PICKIT5 and DSUB.Note that PICKIT5 needs a 5V signal to program the chip. Since the digital 5V are not available on DSUB I use the 5V analog VREF as connection between VCC pin and board.The "thick wires" in the cable are 470 R protection resistors in case of short cirquits.with best regardsAndreasedit:measurements on a similar board from Branadic (the LT1027 variant) are in this thread:https://www.eevblog.com/forum/metrology/t-c-hysteresis-measurements-on-brand-new-lt1027dcls8-5-voltage-reference/msg1003827/#msg1003827

author: CarlO
author_rank: Newbie
timestamp: September 12, 2025, 08:27:32 pm
content: Quote from: AndreasThanks Andreas,For the firmware and the in-circuit programming cable details and the additional link.I have the PIC12F675 programmed and connected to the LTC2400. I am using a AD586LQ as the voltage reference.I was able to determine that the PIC firmware responds to the ascii character "1" with about 9 bytes of data at 9600 baud. I am assuming that this represents the raw bits from the LTC2400 and the temp data from the PIC ADC?I also noticed there seems to be some configuration data in the eeprom memory?This leads to a couple of questions:Are there any additional ascii commands that the firmware recognizes?What is the format for the data the firmware sends to the host?Thank You for all your help,-Carl

author: dobsonr741
author_rank: Frequent Contributor
timestamp: September 12, 2025, 10:34:03 pm
content: For the fans of LTC24xx, I did a design, including PCB, and threw in an ADA4255. Sharing the schematics here.

author: Andreas
author_rank: Super Contributor
timestamp: September 13, 2025, 05:13:18 am
content: Quote from: CarlO on September 12, 2025, 08:27:32 pmHello,so you are gone already very far.Pictures from the board please.Note that serial parameters are 96,8,E,1 (even parity). so actually you have a 8 byte answer.the $31 "1" character is used to determine the baud rate (4800-9600 are possible) after power on and sends the EEPROM data.For reading the temperature sensor raw value together with the LTC raw value you need to send $28 in normal operation.Description is on page 13 of the attached document. Sorry I have it only in german.with best regardsAndreas

author: CarlO
author_rank: Newbie
timestamp: September 15, 2025, 10:31:01 pm
content: Quote from: AndreasThank You for the Specification document. I have not had any time to work on the project. I will share some results and photos soon.Attached is an English translation (Google AI) of your Specification document, in case someone will find it useful.Note to readers: If you open either version of the document with Adobe Acrobat, the first 12 pages form a kind of slide-show. It's really quite cool!

author: CarlO
author_rank: Newbie
timestamp: September 19, 2025, 07:16:03 pm
content: Ok, I finally have some time to work on the project and share some initial results.Quote from: AndreasWell... Maybe not so fast...I ordered the PCBs as can be seen in the first photo. Then after reading through these threads I realized that the AD586LQ may still be the best option, and I have a few in old stock.So I decided to build the circuit on a solderless breadboard to see what else I could learn.From left to right in the photo:7815 voltage regulatorAD586 with NTC thermistorLTC2400PIC12F675 with 7805 regulatorPC817 Opto-IsolatorsFT232 on breakout boardNote: The circuit on the solderless breadboard is totally unsuitable for precision measurement. It's much too fragile and there are unknown thermal EMF from the contacts/plating etc.But at least I can see zero and full-scale and start with some software development.I had a bit of trouble with the opto-isolators. I had to increase the pull-up resistors on the transistor side to 4.7K to get enough voltage swing for reliable communications YMMV.These opto-isolators are really running on low current for the diode side? Might be worth decreasing the series resistance slightly? A small increase in current for the diodes seems to make a large difference.The characteristics of the opto-isolators may vary slightly from batch to batch.The third photo shows the FT232 replaced by a micro-controller. More on this in the next post.I have identified the following changes I will make to the circuit and PCB.1. Change footprint for the reference to 8pin DIL for AD586 using Andreas' "Stressless" method (only 1 pin soldered and oversize holes with fine wire for the other pins)2. Increase input supply voltage to ~18V. This might be too high for some accessory boards with OP-Amps? Possibly add 12V linear regulator for compatibility?3. Modify voltage regulator feedback for 15V for the AD586. Is there any opinion or data here on running the AD586 at 12V vs 15V??? The data sheet specifications are for 15V. Would lower supply voltage cause a shift in the TC?4. Add a 0.1" (2.5mm) pin header on the host side of the opto-isolators for TTL connections to the micro-controller. This would be an option to populate the TTL pin header OR the FT232.5. Increase the pull-up resistors on the opto-isolators to 4.7K or possibly increase the diode current slightly with lower value series resistors.6. Add a solder link to select +5V or GND on the fo pin of the LTC2400. 60Hz here in the USA.Time to cook some new PCB's. Any thoughts or opinions would be appreciated,-Carl

author: CarlO
author_rank: Newbie
timestamp: September 19, 2025, 07:35:12 pm
content: I have been using a micro-controller to collect data from my 34401A multi-meters. I wrote some software to do some averaging, compute P-P and Standard deviation etc. and log the data in CSV format to flash memory or SD card.Since I already have some software for that application, I decided it should be "Easy" to modify it to collect data from the LTC2400 project.You can see the micro-controller in my previous post. Soon it will have an LCD display and a few buttons like my others.The micro-controller is running "PicoMite BASIC" firmware. It's a lot like the old "Boot to BASIC" computers of the 1980's but much faster and with many enhancements to the BASIC language.https://geoffg.net/picomite.htmlEdit: I forgot to mention that the micro-controller is 3.3V logic levels. I had to reduce the series resistor on the TX side to 1.8K to have about the same diode current as the 5V with 3.3K series resistor.I already wrote a small test program to decode the ADC output from the PIC12F675. Now I "Just" need to merge the decoding routines into my other data collecting program.Here are some initial results:> runPress a key for the command1Byte Hex Binary1 0x31 001100012 0x01 000000013 0x08 000010004 0x41 010000015 0x44 010001006 0x67 011001117 0x00 000000008 0x00 000000009 0x00 0000000010 0x00 0000000011 0x00 0000000012 0x00 0000000013 0x01 0000000114 0x10 0001000015 0x08 0000100016 0x20 0010000017 0x10 0001000018 0x01 0000000119 0x20 0010000020 0x02 0000001021 0x30 0011000022 0x03 0000001123 0x40 0100000024 0x04 0000010025 0x00 0000000026 0x00 0000000027 0x00 0000000028 0x00 0000000029 0x00 0000000030 0x00 0000000031 0x00 0000000032 0x00 000000001Byte Hex Binary1 0x31 001100012 0x01 000000013 0x08 000010004 0x41 010000015 0xF3 111100116 0xF4 111101007 0xFF 111111118 0x1F 00011111$Byte Hex Binary1 0x24 001001002 0x01 000000013 0x08 000010004 0x41 010000015 0x44 010001006 0x67 011001117 0x80 100000008 0x8B 10001011(Byte Hex Binary1 0x28 001010002 0x40 010000003 0x8B 100010114 0x41 010000015 0xFF 111111116 0xF4 111101007 0xFF 111111118 0x1F 00011111Raw VoltsPIC ADC = 557 2.720LTC2400 = -2817 -0.00005247V(Byte Hex Binary1 0x28 001010002 0x00 000000003 0x8A 100010104 0x41 010000015 0xD9 110110016 0xFB 111110117 0x9F 100111118 0x28 00101000Raw VoltsPIC ADC = 552 2.695LTC2400 = 144702425 2.69529270V(Byte Hex Binary1 0x28 001010002 0x40 010000003 0x8A 100010104 0x41 010000015 0x06 000001106 0x21 001000017 0x00 000000008 0x30 00110000Raw VoltsPIC ADC = 553 2.700LTC2400 = 268443910 5.00015747V-Carl

author: Andreas
author_rank: Super Contributor
timestamp: September 20, 2025, 08:54:16 pm
content: Quote from: CarlO on September 19, 2025, 07:16:03 pmHello,nowadays there is not only the LTC1050 available (that is why I chosed initially 14V and -1.2V), but also "high voltage" choppers as ADA4522-1.But if you want to add a LTC1043 2:1 capacitive precision voltage divider you have to stay below 16V.Self heating will differ somewhat depending on supply voltage. (so T.C. may be influenced slightly.)Photocoupler current is minimized for battery operation on the isolated side. (Also to minimize noise on the analog side).So if you change supply voltage or have marginal couplers you might have to adapt the resistors (or reduce the baud rate to 4800 Baud).with best regardsAndreas

author: CarlO
author_rank: Newbie
timestamp: September 22, 2025, 07:01:35 pm
content: Here is my first attempt at measuring the linearity of the LTC2400.Notes:1. Each data point represents the average of 414 readings (~1minute with Fo pin grounded for 60Hz rejection)2. I am still using the "Frankenstein " version of the circuit.3. Still refining my measurement technique4. Measured against my PDVS2 mini (10uV resolution, but I did use the actual measured values when it was calibrated against 3458)5. The uncorrected INL error seems quite high compared to the datasheet specifications?6. The math seems to work! If nothing else I have matched the linearity of my PDVS2 mini. LOL7. The chart shows the error in ppm of full scale. The "Linear" line is the uncorrected error from a linear fit. The other two lines show the error after Quadratic and Cubic correction of the data.-Carl

author: Andreas
author_rank: Super Contributor
timestamp: September 25, 2025, 03:11:39 pm
content: Quote from: CarlO on September 22, 2025, 07:01:35 pmDatasheet specification is +/-15 ppm max. ("best fit" which gives halve the values against calibration at zero and VREF)The INL error also depends on input impedance (resistive + capacitive) and somewhat on impedance on VREF input.(keep GND + VREF wires short between reference and LTC2400).with best regardsAndreas

author: CarlO
author_rank: Newbie
timestamp: September 25, 2025, 04:29:28 pm
content: I was attempting to measure the noise of the LTC2400 and Temperature ADC overnight with VIn tied to VRef. When I looked at the data, I realized I had some preliminary TC data from the overnight temperature drop.As before each data point represents the average of 414 readings. (~1 minute)The noise of the averaged readings appears to be about 1uV P-P. I will need to repeat the measurement under more stable temperature conditions.The TC looks Like about -1.3uV/K or -0.26ppm of full scale (VRef) over a limited temperature range. This would be mostly for the LTC2400 as the input and Vref are both fed from the same AD586? I may have quite some thermal EMF from the circuit construction.I am learning much from just a few simple experiments! Time to transfer the circuit to a proper PCB.-Carl

author: Andreas
author_rank: Super Contributor
timestamp: September 26, 2025, 05:17:37 am
content: The LTC2400 has much lower T.C. -> it is mostly thermal EMFwith best regardsAndreas