Author Topic: DIY-SMU Project  (Read 14113 times)

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Offline RikV

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Re: DIY-SMU Project update?
« Reply #75 on: July 18, 2021, 09:31:32 pm »
Could someone hint me to where I can find the Nextion .HMI file for this project? According to what Dave says it should be included in his latest update but I don't see it. I would love to proceed on this project.

My fault: just found the Github page: https://github.com/djerickson/diy-smu
Thanks again for the interesting work!
« Last Edit: July 18, 2021, 09:50:03 pm by RikV »
 

Offline RikV

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Re: DIY-SMU Project
« Reply #76 on: July 19, 2021, 03:06:19 pm »
Where can I find those exotic USB-to-panel cables?
 

Offline prasimix

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Re: DIY-SMU Project
« Reply #77 on: July 19, 2021, 03:13:03 pm »
All kind of "impossible" and "exotic" cables could be found on aliexpress

Offline RikV

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Re: DIY-SMU Project
« Reply #78 on: July 19, 2021, 09:29:25 pm »
No doubt about that! All kinds of stuff you can imagine and a lot more! But... You must kno how to ask kindlyk. "Cabinet mounted USB-B to USB-Bmicro cable" doesn't return anything useful. how do you describe such a cable in a way ebay or other search engines understand what you mean? Is there a dictionary somewhere? I have the same problem when seaching componenet in an on-line catalogue. "What is the F** name othis f** thing??". I must be getting too old for this I guess.
 

Offline prasimix

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Re: DIY-SMU Project
« Reply #79 on: July 20, 2021, 05:27:25 am »
 
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Offline poorchava

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Re: DIY-SMU Project
« Reply #80 on: July 20, 2021, 08:31:41 am »
As for GUI I'd say: TouchGFX is the best by a large margin. At least when it comes to performance & capabilities vs cost (which is 0). It used to be horrendously expensive, but ST bought them and provides it for free. Obviously works only with STM32 now. It can provide a modern Android-like experience.

LVGL is nice, but waaaay more rudimentary than TGFX and waaaay lower performance, despite TGFX being written in C++ (and not the reduced kind, full blown with virtual methods and abstract classes). I also found, that LVGL requires much more coding to obtain same basic functionality as compared to TGFX.

But I'm one of those people who can't stand the Arduino crowd (maybe because of number of customers begging their inquiry with 'i've done it with Arduino so 3 weeks is plenty to go into series production for market, right? That's what we told the investors....'). Ohh, and the questions along the lines of 'how to run my AVR at 100Mhz' and 'I CAN HAZ HDMI ON AT MEGA?' </flame>
I love the smell of FR4 in the morning!
 

Offline RikV

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Re: DIY-SMU Project
« Reply #81 on: July 20, 2021, 04:44:29 pm »
@Prasimix: not only creative with chips but also with words.
Thanks for the extra hint. I had already found what I was looking for, only took waaay tooo long. Must be the age.
As lon as I can handsolder a 0603, you won't hear me complain.
 

Offline ducreux92

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Re: DIY-SMU Project
« Reply #82 on: July 26, 2021, 02:24:52 pm »
Hi,
Is this project reproducible ?

How many are working properly in the world ?

Thanks.
 

Offline ducreux92

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Re: DIY-SMU Project
« Reply #83 on: July 28, 2021, 02:20:31 pm »
Hi,

I tested a prototype on breadboard with TL074 with sucess.

I used +-15V powers instead +-170 V and only two powers mosfet ( doesn't works with 4 mosfets at 15V)
At output i have about 3 mVpp noise.

Why not replace the circuits OPA2140  with cheaper circuits like ADA4522-X for example ?
idem for AD5686  ?

 

Online Kleinstein

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Re: DIY-SMU Project
« Reply #84 on: July 28, 2021, 03:46:02 pm »
I had asked about the OPA2140 before - it just was available and cost was not such an issue for just a prototype.
There are different places the chip is used and different places may really want that chip or could use different alternatives (e.g. the ADA4522, MCP6V51, maybe OPA2202 or maybe even TL032 at some places).
 

Offline ducreux92

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Re: DIY-SMU Project
« Reply #85 on: August 09, 2021, 08:47:23 am »
Hi,
I find opa2197 (opa197) which is much cheaper that opa2140 with similar caracteristics, but
architecture is CMOS not JFET amplifier - Is this amp suitable for the project ?
 

Online Kleinstein

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Re: DIY-SMU Project
« Reply #86 on: August 09, 2021, 09:19:29 am »
The OPA2197 has more low frequency noise, but is still  a good OP.  I like the low power consupltion for the speed.
Another cheaper replacement relatively close to the OPA2140 is the OPA1642  (mainly higher offset). It really depends on the positions - the OPA2140 may not even be a good choice in some places.

With hobby projects it is not so uncommon to use the parts you have at hand and know and this may than look odd.
Currently some parts may also not be avialable (or not from the favorite source) - this can also cause strange looking choices.
 

Offline djerickson

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Re: DIY-SMU Project
« Reply #87 on: August 26, 2021, 11:24:25 am »
Thanks for the op amp substitute ideas for the OPA140/2140. I think JFET is the right choice, particularly for low bias current stages. Bipolar is generally higher input current, and CMOS is challenging for +/-15V, generally higher drift and noise. I don't trust the linearity (CMRR) of CMOS: they need circuit tricks to get wide input voltage range that sometimes compromise linearity.

I settled on OPA145/2145 as my go-to precision amp. Similar DC and noise specs to the OPA140/2140, slower (5.5MHz vs 11MHZ), better availability, and ~1/2 the cost.

I have built 2 complete DIY-SMUs so far. I'm getting ready to build the 'final' Rev2 Main boards and Rev3 Amp boards.

Jaromir has designed a very nice take on this project and has built a couple of units. His design uses an off-the shelf enclosure, and a custom AC transformer. And a simpler LED / buttons front panel similar to the original K236 instead of a touch screen.

If there is interest, I can get the new boards machine-assembled and can sell a few. At least the main board with its 175 parts. The Amp board (75 parts) is not bad to hand-build.

There are firmware additions and fixes that I plan:
   EEPROM based calibration. Currently requires recompile. A Python app does the hard part.
   Control of remote sense. Currently SCPI only
   Better Clamp control. Basically works, not accurate.
   Basic plotting page

Thanks,
Dave Erickson

DIY-SMU: www.djerickson.com/diy-smu
Jaromir's DIY-SMU: https://www.eevblog.com/forum/projects/how-i-made-my-smu/new/#new
 
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Offline ducreux92

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Re: DIY-SMU Project
« Reply #88 on: August 28, 2021, 10:37:50 am »
Hi,
Today impossible to find AD5686XX in tssop format.

Do you know an equivalent ?

 

Offline djerickson

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Re: DIY-SMU Project
« Reply #89 on: August 28, 2021, 01:38:07 pm »
Thanks for the heads-up on the AD5686. Last I checked 2 months ago some were available in TSSOP. Just not the most accurate grade.
I guess some options are to change to the harder-to-solder QFN, or add a footprint for the similar 8 channel AD5676.

Dave
 

Offline stephanm

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Re: DIY-SMU Project
« Reply #90 on: September 12, 2021, 10:11:05 am »
Hi,

first of all: awesome project! Using LTspice and looking a bit into Dave's curcuit, I saw that the output voltage can overshoot when the instrument comes out of compliance, depending on the set voltage and compliance. Here's an example: Force voltage is set to 1V, and the current clamp is set to 10mA. The load is just a 1Meg resistor. At 5ms within the simulation I am shorting the 1Meg RLoad resistor with a 1 Milliohms resistor, and keep it shorted until 7.5ms. During the short, the circuit goes into compliance as expected, limiting the output current to the programmed 10mA.

However, there are two transients on the output when applying and, respectively, removing the short:
  • When applying the short, there is a short and large current spike (above 100mA), which is ok because I am basically shorting the 135pF output capacitor of the SMU. There is also some oscillation visible which even drives the output voltage below 0V(!), but this does not concern me so much at the moment.
  • What concerns me more is that when removing the short, the output volage overshoots quite a lot, it goes up to 7V, after which it takes 1.5ms to recover to the programmed 1V.
From my understanding of the DIY-SMU circuit, a voltage overshoot after removing a short on the output is hard or even impossible to avoid due to the fact that the circuit has to deal with the voltage drop on the current sense resistor. As I had set the current sense resistor to 500 Ohms, the voltage drop on that resistor is 5V when the instrument is in compliance, and these 5V plus some additional voltage will end up on the output when the load current suddenly drops from 10mA to a few microamperes due to removing the short.

Looking at the Keithley 236 schematics, I was looking for some circuitry to deal with this situation and reduce the overshoot, but so far I have not found anything that looks like doing so. So, what I am curious of is whether such overshoot is also encountered on other SMUs, such as the Keithley 236?

Thanks and kind regards,

Stephan.
 
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