Elektor Voltage Current Calibrator Project

[Martin72]

Argh, excel again...
So you also found out that D4 does not exist?
I looked at the MAX6350 datasheet again, 1µF for the NR input is recommended, but if it's more it won't have any effect, so the 2µ2 can stay that way.

[KungFuJosh]

I exported a BOM from Kicad and verified that way. Much easier than the original goofy BOM that had some bad info in it.

[Martin72]

The right display arrived...
But it seems not so easy just to take a common usb-serial adaptor and then everything´s fine.
I got a notebook with a native com port, tried this first...nothing.
Then took the adaptor, tried again...nothing.
The display won´t start when the RX/TX pins are connected to the com port or to the adaptor.
Maybe the RESET pin plays a role too, must examine it further.
Or buy the original adaptor.
(adaptor pic made before changing the connection)

[KungFuJosh]

Your pictures don't make the wiring clear. Do this:

If you're powering from an external PSU, connect power and ground to the screen, and make sure ground also goes to the serial port adapter.

Connect Rx/Tx backwards at the serial port adapter and see if that works.

[Martin72]

Thank you josh, but this was already made.
Will continue testing.

[KungFuJosh]

Thank you josh, but this was already made.
Will continue testing.

Do you mean you got it working?

[Martin72]

Sorry, the connections were meant...

[Martin72]

I have now rather stopped experimenting, not that I still break the 120 euro display.
USB to serial TTL converters are available like sand on the beach and super cheap.
And many look almost exactly like the "original" from 4D.
I ordered one from Amazon and it will arrive on Monday.
It's so cheap that it doesn't hurt if it doesn't work.
Because the adapter from 4D has something that all the others don't have, the reset output.
And it is also triggered, for a hundred milliseconds.
If it turns out on Monday that the ordered adapter does not work with it, well then I have to buy the original.

I have made again parts list control, what do I have here, what am I still missing....
I soldered nothing yet, I will take the board with me to work and let the coils L1/L2 and the USB port soldering there because no way to do it here.
Oh, and the Heater board is now also ordered.

[KungFuJosh]

I usually use the FT232 USB chip stuff, I'm guessing that will work when I eventually get this. I'm also curious if my PicKits would work or not.

If you know which pin to connect the RES to, then it may work with what you have. I think RTS (pin 7) is the correct pin.

[Martin72]

If I remember it right it is DTS, will confirm this yes/no later.
What I haven't quite figured out yet is why the display turns off/not even starts up once the RX/TX lines are/will be connected.
And I know about potentials, believe me....

[Andreas]

I looked at the MAX6350 datasheet again, 1µF for the NR input is recommended, but if it's more it won't have any effect, so the 2µ2 can stay that way.

The NR pin is rather high-ohmic and has direct influence on the output voltage stability.
I would never use a tantalum (with high leakage current) here.
I would use a film capacitor. (or leave it unpopulated since it only helps with wideband noise).

with best regards

Andreas

[Kleinstein]

Most of the cheap USB to uart adapter are just that: UART output (3.3 or 5 V level), similar to what a µC provides or wants. So there are no drivers to get the +-10 V levels for RS232 like a generic PC serial part.
+1 with using a film capacitor for the NR pin of the reference. A tantalum or Al electrolytic is more a no go.  A ceramic  X7R or similar may work, but is not ideal. Even if only for the higher frequency noise, it helps to have at least some filtering. 1 µF film caps (MKS) are still afordable and not excessively large.

[djsb]

Where are the UPDATED Kicad files for this project? And where is the link to the ORIGINAL Elektor article? Thanks.

David.

[KungFuJosh]

MKS caps are only radial, it needs to be SMD for this project. 25MU105MA23216 25V 1µF 1206 SMD 20% would probably be a good 1µF film substitute to fit the same footprint. Not cheap, but certainly not that expensive compared to other parts in this project.

Why wouldn't an X7R cap be good for that? C1206C105J3RACAUTO 25V 1uF X7R 1206 5% is only 40 cents instead of $4.00.

[Martin72]

Hi Josh,

MKS02 wouldn´t be a problem, I just test it out...

[Martin72]

Where are the UPDATED Kicad files for this project? And where is the link to the ORIGINAL Elektor article? Thanks.

David.

Link see first post.
Updated Kicad files ask Josh...

[KungFuJosh]

Hi Josh,

MKS02 wouldn´t be a problem, I just test it out...

There's a plastic enclosure that covers that area for the heater block. MKS won't likely be a good idea/fit there. You can try when you get the 3D printed stuff in and see how tight it is.


Sorry, I'm not sharing my kicad files. I blew a lot of time on them, and I refuse liability for any errors anyway. 😉

[Martin72]

You can try when you get the 3D printed stuff in and see how tight it is.

Or make it a litle bit deeper.

Sorry, I'm not sharing my kicad files.

Eehhh...

[Martin72]

Pic showed wrong place (C30), now on the right place.

[KungFuJosh]

So now it's going to be compressed between U9, and the 3D part that won't fit if you don't change it. Not worth it. If you're going to spend $500 on parts to make a VA reference, spend the $4 or 40 cents to get the appropriate part. The entire design is only as strong as the weakest point you introduce.

[Martin72]

Well,
As long as not all ICs are avaible yet, we´ll have all the time to think about it.
BTW, the AD8676ARZ we need is avaible in Ebay, from a chinese vendor....

Fake or not..

[KungFuJosh]

I'd be patient, same statement as above regarding introducing weaknesses into your expensive project.

I also found somebody who would sell the expensive chip for $70, but I don't trust them. 🤷

[Martin72]

Yes, I also think I will first equip everything I already have and then we'll see.
As mentioned, tomorrow the USB port and the chokes soldered, then the thing with the display and if that has all worked, you can continue with the housing and eventually the missing ICs are available again.

[Kleinstein]

Well,
As long as not all ICs are avaible yet, we´ll have all the time to think about it.
BTW, the AD8676ARZ we need is avaible in Ebay, from a chinese vendor....

Fake or not..

The AD8676 is not that unique. There is a very good chance that one could substiture with a similar part that is better awailable, like AD8672 or ISL28227 or depening maybe also slower chips.

[Martin72]

USB port and the coils, soldered at work...
Looks good ( bad light for the pics) and I could start soldering the avaible components.
Maybe next weekend, until then a part of the Digikey order should have arrived, with the sinfully expensive 0.01% 0.2PPM resistor in 1206 format, which alone costs almost 15€, I ordered then also only one...
Heater pcbs are shipped.