OSHW - 24bit ADC measurement system for voltage references

[branadic]

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. 

...if you want to discuss it, jump on over to the EEVblog forum...

   

Regards, branadic

[tszaboo]

Include pix or pdf... No one has that software you are using.

[Lizerd]

second that. pdf would be nice.

[miguelvp]

They are eagle files, sure you can download that!

Edit: You can use the free version of eagle
BTW branadic, thanks for sharing!

[branadic]

Interesting, you get something for free and all that comes to your mind is to beef?  What is wrong with you?

@miguelvp
Your 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?

[BravoV]

Interesting, you get something for free and all that comes to your mind is to beef?  What is wrong with you?

@miguelvp
Your 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?

How 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 software spam campaign ? 

So much about the jargon words "OSHW" eh ? 

[miguelvp]

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 logo

Edit 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.

[ovnr]

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 or whatever, 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.

[miguelvp]

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.

here you go

Edit: 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!

[BravoV]

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.

Save your breath, some are not that bright enough to get that. 

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 or whatever, they can grab your source files.

Some 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. 

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.

I 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.

[miguelvp]

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.

[poorchava]

woman acceptance factor

I need to write that one down

[Monkeh]

And today's modern browsers can handle PDF natively. 

For 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.

[kruszi]

Why have these cut-outs of the PCB around the IC on the bottom side ?

[con-f-use]

A bit of context would be nice for people like me who just stumbled upon this. Why should I care?

Now I found out that 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.

[Lizerd]

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.

[Andreas]

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.

Very 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 regards

Andreas

[Lizerd]

No, I have been a bit preoccupied so I haven't had any time testing this board.
But it's on the to do list
   
at 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.

[tszaboo]

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.

here you go

Edit: 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!

Are 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.

[dannyf]

as the ADS1256 has lower noise than the LTC2400.

The 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.

[branadic]

My inital post wasn't meant to be for entertainment but for people who perfer using their soldering iron  instead of using tablets, pads or smartphones  and 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 files  instead of pictures we can maybe get back on topic?

[gxti]

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?

[MacAttak]

Why have these cut-outs of the PCB around the IC on the bottom side ?

I 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.

[kt315]

 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?

[TiN]

After all this wasted discussion about file format and nagging that I posted original source files  instead of pictures we can maybe get back on topic?

I'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 for 

As 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 there PDF would do great for all, as everyone have it to read datasheets.