Elektor Voltage Current Calibrator Project

[Martin72]

Hi,

Start the thread anyway.

Here we go...
To keep the other thread cleaner.

Stumbled over this a few days ago:

https://www.elektormagazine.de/labs/voltage-current-calibrator-0-to-10v-and-0-to-40ma-0001



Looks really neat..
Already ordered the PCB, then look into the BOMs....Boy...not a cheapo. 
JLCPCB also offer 3d printing even in metal (interesting for the frontpanel and the heater housing)and so damn cheap, that the one, two expensive components (one chip, then the display) won´t hurt so much.
10ppm accuracy sounds not too bad, for the calibration of the calibrator a voltmeter with at least 6.5 digits is recommended.
When I decide to build this I would let it calibrate, not by myself.

[Martin72]

Here a (temporary, will delete it in 24h) link to the docs:

[KungFuJosh]

Ooh, I'm happy to see the KiCad files. That means I can run DRC and mess around a little before ordering.

[Martin72]

Nice...
Maybe I change to KiCad too, my premium license for Eagle is void.

[KungFuJosh]

I love KiCad. It works great, and it's free. 😉

I've also used FreeCAD to make 3D objects for my PCB projects. Like the largest inductor on my PCB in the other thread.

[KungFuJosh]

I'm cleaning up the silkscreens. C12 and C14 are labeled backwards. This is somewhat obvious if you pay attention to the fact that C14 is polarized, and the silkscreen next to C12 is polarized. They're parallel to each other, so it doesn't really matter, but it's pretty sloppy on their part.

[KungFuJosh]

Much better. Now it's accurate and easier to read. 👍

[Martin72]

For whatever reason JLPCB has problems with the correct display of the placement imprint anyway.
So the designations like to "disappear" into the component print, when I think of it, I always position the designations with some distance to it.
This time I have not thought about it, because not my board..

[KungFuJosh]

I've been using JLC for years, and I haven't really had any trouble with that. This design had the silkscreens literally on top of pads and other stuff that would make it useless anyway. The heater board was worse, but I fixed that too.

Right now, I'm cleaning of the tracks. It's a real mess. It had pretty close to 100 errors in DRC. Nothing terrible yet, mostly just really sloppy traces going nowhere for no reason in random spots.

Edit: What thickness did you order for these PCBs?

[Martin72]

Always the standard, 1.6mm .
It´s more than enough as you don´t have any heavy weight parts on it.
For a e.g. transformer board we use 2.4mm, anything less than this let it all hang down.

[Martin72]

Interesting, the 3d printing parts were rejected from JLCPCB, reason:
Too thin, they recommend at least 1.5mm thickness.
No problem, I must calculate the whole thing, because:

https://www.ianjohnston.com/index.php/onlineshop/handheld-precision-digital-voltage-source-2-mini-detail

Con: No current source, Pros: More precise, (inhouse-) calibrated on a 8.5 digit meter...
And it´s complete assembled, tested, for 325 pounds.

[KungFuJosh]

Con: No current source, Pros: More precise, (inhouse-) calibrated on a 8.5 digit meter...
And it´s complete assembled, tested, for 325 pounds.

Knowing you, it's going out for calibration either way. 😉

The DIY version looks like a fun project. If I make it, I'll use my laser to cut a clear panel for it. I can also mark the outside of the enclosure for the cuts. I eventually want a fiber laser, so if I get that first, that can make the enclosure cuts too.

Edit: It's a touch screen. I'll probably just put a screen protector on it.

I wouldn't be surprised if you went for both projects anyway. Look at it this way, you can get the PDVS2mini now, and then wait until next year when the parts are cheaper to build the project reference. That practically pays for the PDVS2.

...and then buy another reference you find somewhere else. 🤣

[Martin72]

At work, I am the testfield manager.
At home, I cultivate my hobby, which also happens to have something to do with electronics.
Then there's the fact that I'm curious and open to everything that goes in that direction.
And I like to pay apprenticeship money, because as ALF once said:
There is nothing good, unless you do it.

[KungFuJosh]

ALF also said: “Where do you keep your casserole dishes? The cat wont fit in the toaster.”

[KungFuJosh]

I made a project on Mouser with all the main board parts. It's $366 USD including the $85 version of that out of stock chip.

I attached a Mouser BOM, but the parts need to be verified. The original supplied BOM has accuracy issues with the reference numbers.

[KungFuJosh]

Here's the heater's BOM. Also needs verification. The original had quantity issues.

[Martin72]

Hi,

Sure that these are the complete BOMs ?

[KungFuJosh]

Pretty sure. 😉

As I said, they need verification. I did substitute some parts that were no longer available.

[Martin72]

Then I´ve done something wrong..I count 13 lines on the first excel list(I don´t have Excel on my notebook, so I went to my PC and printed it out as a pdf, maybe a failure occured then)

[KungFuJosh]

I don't think it was you. This forum (SMF) is buggy sometimes, and it screwed up the files. The main BOM has 44 lines, and I downloaded it, and it showed the heater BOM instead.

Here's both again. Hopefully it works this time. They both need verification for quantity and part accuracy. As mentioned previously, reference numbers were not all correct in the original BOMs.

[tautech]

This forum (SMF) is buggy sometimes, and it screwed up the files.

Yup.
Never use the first Choose File option, never !

Instead select more attachments and link yours in there however then you are restricted to 9/post but it sidesteps the forum problems.

[KungFuJosh]

This forum (SMF) is buggy sometimes, and it screwed up the files.

Yup.
Never use the first Choose File option, never !

Instead select more attachments and link yours in there however then you are restricted to 9/post but it sidesteps the forum problems.

I usually drag and drop, and it usually works. AFAIK, this was the first time it actually confused the files like that.

[Martin72]

I had/have the same with pics...

When I´ll upload more than one and then in an order, I always ignore the first upload and start with the second.
The DAC in this project..
There´s a "combo" with it and the LTZ1000 reference, together you "gain" a reference with 1ppm accuracy..Nice.

[KungFuJosh]

Do you think this project is worth the $400+ USD price tag?

[Martin72]

Honestly?
When you stretch it for month so it doesn´t hurt you directly in case of the costs, why not.
But if you take the money instantly in your hands I would go for the complete assembled, tested and burned-in reference I´ve linked a few posts before.
It do not have the current source, but it is "calibrated" with a 8.5 digit meter.
Me I would go the way of "stretching" this project.
Like I said before, theoretically it could be "tuned" to a 1ppm reference..awesome.
But most of what I expect from it is to learn how things work in detail and then possibly improve them.
That's actually how I've always done it in the past.