Electronics > Open Source Hardware

µLCR Tweezers - Open source project

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Kleinstein:
The plan has not changed much over the years. I would definitely add a path to also have the option to measure the DC voltage (would be relatively easy with likely only 1 or 2 resistors to PA7). The first amplifier has a gain near 1 and seems to be mainly used for the added protection. So up to some 2 V may work.
Could still be enough to check a alkaline coin cell or the current through an isolating resistor in the supplys.

koendv:
There is also this Chinese open source project: https://oshwhub.com/moonyblue/dian-qiao-nie-zi.
Click on the "编辑器打开" button to open the project in the editor.
This is a complete project, schematic and pcb, production ready for jlcpcb assembly. STM32F071 processor, could program it in Arduino if you wish.
Schematic attached.

Kleinstein:
The chinese version is a more cost optimised version compared to the russian one.
There seem to be still a few mistakes in the attached schematics: R1 or R2 should be something like 10 K to have 2 different ranges and not 2 versions of the same. I think at U5 the inv and non inv inputs are swapped. At least the other way around would make sense and as shown I doubt it would work. There is also a chance that this part may oscillate - an added small capacitor around U5 may be a good idea, though it would somewhat limit the use with a higher frequency.
So this project may still be work in progress.


One could add a DC path, but with the only rudimentary protection one would have to be very careful an a powered PCB. Especially when fault finding there can be unexpected voltages.

croma641:

Hi, Kleinstein,  and thanks for your helpful comments.

But, are You referring to the chinese (last schematic posted uRLC)  or nRLC ? The nRLC is a russian  uRLC fork).

Kleinstein:
My last comments were about the Chinese version. It looks like an attempt to make it cheaper. Though this comes at the price of doing the voltage and current measurement one at a time and thus slower / more noisy.

A nice point in the software of the russian version is that they don't measure just simple RLC, but use mixed models like capacitor with ESR and thus the display of 2 values. It can be a bit confusing in a few cases (e.g. the large resistor showning extra capacitance - should be in series in the model).

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