Products > Test Equipment
XJW01 Auto LCR meter review ($120 bench top LCR meter)
Yansi:
There have been a few threads about these chinese meters, or the principles of their functionality. I have also kindly asked a member Blueskull to make a translation. If you find the thread, there is the translated schematic. Might be interesting for you interested guys :-)
Yansi:
Sorry, I haven't refreshed the thread, when I was writing.
nctnico:
--- Quote from: dannyf on June 04, 2016, 11:19:58 am ---
--- Quote ---Are they so difficult beasts.
--- End quote ---
With a build-in 24bit adc, it can be done fairly easily with a mcu (C8051F350 for example).
Using discrete parts, external adcs, it is beyond most people's capabilities if you want to go over 20-22 bits.
--- End quote ---
You don't need that kind of ADC resolution. The input frequency is fixed so crank up the gain of the measured signal enough to get to a reasonable ADC resolution. IIRC I used 500x in my circuit to measure in the tens of milli Ohms range using a 10 bit ADC in a microcontroller. At some point noise and non-linearities bite you in the ass.
dannyf:
--- Quote ---The schematics (2 versions) were translated, and posted here.
https://www.eevblog.com/forum/projects/chinese-lcr-meter-schematic-with-stm32-questions-can-someone-translate-please/msg832297/#msg832297
--- End quote ---
This version, built around a 8051, differs from the STM32 version posted earlier.
1) the 8051 version uses a square wave + filter to generate the excitation signal; the STM32 version uses a dedicated DDS chip;
2) the 8051 version has a dedicated AFE, the STM32 version reuses the AFE for V and I;
3) the 8051 version has a different way of shorting the input signal in the phase detector.
Overall, I think I like the STM32 version better. I do wish it had the AFE of the 8051 version.
I suspect the STM32 version is newer.
nctnico:
I would like to have the newer version as well since it can go to 100kHz. Having the source code would be excellent; I assume it will be easy to let it make frequency sweeps so you can also use it as some kind of impedance analyser.
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