build an LC Meter

An open source LC-Meter, which is very accurate and easy to build. All the documentation included.

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This is an open source project. You may use, modify and distribute both software and hardware as long as you give credit.

All the project's files are available here:

This project is based on an original idea shared by Neil Hecht back in the mid 90's.
"Thanks for sharing your work Neil !"

Watch the Youtube series on how it works, how I built it and tested it here:

# LC-Meter
Open Source LC-Meter. All documentation included.

This LC Meter Project is open source. All the documentation both hardware and software is provided without any warranty.
If you build one I would be glad to get a picture of your finished device. Subscribe to my Youtube channel and post your comments and questions about this project in the comment section of the series.

The video series is a full tutorial on how it works, how to build it and how to test it.
You can watch it here:

Give this project a thumbs up if you liked it and subscribe, 'cause so much more is yet to come ;-)

About this project:

This design is based on Neil Hecht's idea. It uses an oscillator (LM311) to generate a frequency which can be then modified by adding a capacitance or an inductance on the measuring terminals. The frequency is measured by the microcontroller (ATMEGA328p) which then also does all the math in order to extract the value of the added capacitance or inductance. The value is then adjusted in engineering units and displayed on a graphical LCD.

I designed the PCB using through-hole-terminal components only. That makes it really easy solder for everyone. There's room for improvements in the schematic. A second version would probably include these changes:
    - make use of a rechargeable Li Ion battery
    - add a usb connector on board     - add charging circuitry for the battery
    - add UART - USB translation circuitry on board
    - add a voltage step up to boost the battery voltage to 5V
    - increase the frequency of the AVR

The LC Meter PC application was written in C# and it's very useful when a lot of measurements have to be done. It includes a catalog function for the measured components and UART logging for debug purposes.

The firmware for the microcontroller is written in BASCOM. I shared the source files are too. You can modify and improve on them. You can easily port it the firmware to other languages. There's a readme file in the firmware's folder with the FUSES Configuration for the AVR if you decide to use the precompiled firmware.

PART 1: Needed materials and tools for this project, the operation principle behind the LC Meter, writing the algorithm on which the firmware will be based.

PART 2: Drawing the schematic and PCB for this project, soldering the components and a short explanation of the firmware.

PART 3: 3D Modeling the case for the LC Meter and assembling.

PART 4: Testing the LC Meter and the PC Application.

Enjoy making it and send me a photo of your finished LC METER !

coreWeaver / ioCONNECTED  - 2021

Updated Firmware (May 3rd, 2021).zip

There's a small typing error in the original fw's UART debug function ("F4 for C_det") should've been ("F4 for L_det). It's now corrected.

x-zip-compressed - 30.64 kB - 05/03/2021 at 10:48


LC Meter Case - STL (UPDATED May 3rd, 2021).zip

This is the updated version of the LC Meter's Case. See the "UPDATE Readme 1st.txt" for the details. May 3rd, 2021 coreWeaver / ioCONNECTED

x-zip-compressed - 595.28 kB - 05/03/2021 at 09:50


(UPDATED Apr.08,2021) LC

Last Updated on Apr. 8, 2021. I would like to thank Mike Doty who discovered some errors in the original files archive and helped me improve the LC Meters case. This archive contains the schematic, PCB, Gerber files, Bill of Materials, Firmware - source and precompiled, UART PC API, STL files for the 3D Printed case.

x-zip-compressed - 2.91 MB - 04/08/2021 at 16:06



a list of the used connectors and probes for this project.

plain - 1.30 kB - 03/28/2021 at 12:17


  • Updated STL files for the LC Meter's CASE

    core weaver05/03/2021 at 09:56 0 comments

    The new STL files (updated version of the case) are now available as a standalone .zip archive.

  • Apr. 08, UPDATE

    core weaver04/08/2021 at 16:21 0 comments

    I've corrected some mistakes on the original schematic and updated the whole files archive.

    The R14 in the schematic was reported as too low. Together with R12 this resistor forms a voltage divider for the LCD's reset line. I must've accidentally switched the values of R12 with R14's. Although the old value (1k2) was ok on my board (and that's why I didn't detected the typo), a higher value (3k9) for the R14 resistor is preferable.

    I also redesigned three parts of the LC Meter's case. The new version will use 4 additional screws which will hold the bottom side and the mid section together. This will ensure a tighter fit of the case parts. I also slightly modified the battery cover to provide better access. I didn't manage to test print the new parts and that's why I still didn't include the updated STL files in the Apr. 08 UPDATE. As soon as the new parts will pass the test I will make them public and re-update the archive.

View all 2 project logs

Enjoy this project?



cmshelton2010 wrote 03/12/2024 at 00:12 point

I almost finished this LC meter, waiting on a 82uh inductor and the display. . I used a OKI-78SR-5/1.5-W36H-C in place of the 7805 and rechargeable 9 volt battery and modified the case and battery cover to accommodate it. 

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AI66IA65 wrote 02/11/2024 at 12:16 point

L.C meter ??

inductor ? nH.....mH

capacitor ? qF.....mF

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Omid wrote 02/14/2023 at 20:58 point

Thank you for sharing your experiences with us
I have a question
I got the parts and connected them but the values it shows me are not accurate.
I made all the parts exactly like the schematic except the inductor which was 82uH but I couldn't find  it and used 100 uH.
However, what should I change in the program code?
thank you

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core weaver wrote 05/03/2021 at 09:55 point

I've uploaded the UPDATED Case (STL Files) for the LC Meter. Happy printing !

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core weaver wrote 04/22/2021 at 09:53 point

the STL files for the second version of the case are ready and tested.

@mikedoty assisted me, by printing, assembling and making valuable suggestions. Thanks Mike. In the new version, the screws used to hold the PCB in place are slightly longer. They also hold all the parts ensuring a tighter fit. There will be 2 different mid sections for the case, for 2 different PCB thicknesses (1.6mm or 1mm), and the battery access cover has been modified. I will zip and upload the archive with the files, probably the next days. Stay tuned !

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core weaver wrote 03/30/2021 at 11:14 point

Help needed !  (Beta testing an UPDATED version of the case)

@mikedoty or anyone else who would like to get involved in testing an updated version of the case.

I redesigned some of the geometry for 3 parts of the case. The main purpose was to change the position of the screws which hold the pcb in place. They're now accessible from outside the case, beneath the white (bottom) part, just like the screws for the battery cover. The screws will need to be longer. They go from the bottom side of the case through the pcb's mounting holes, and into the middle part of the case (red part). I did this as an improvement and not to correct a mistake !

Like Mikedoty said (and this could happen to others too) sometimes the case shells won't have the same tight fit as the parts that I printed myself. This is a printer settings related thing, as I was talking in the video, that offset between the parts, which I always take into consideration when modelling parts, is proportional with the quality of the print job. On my printer quality affects not only the speed but a lot of other parameters too, which ultimately affects the results.

In the UPDATED version there's also a modified battery cover.. I thought this will provide better access to the battery.

I can't test these changes because I ran out of filament. So if anyone wants to beta test the parts, just send me a message and I will send you the STL files per email.

I don't wanna make the changes available to the public before testing them.

Thanks a lot

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mikedoty wrote 03/30/2021 at 20:45 point

Fox - I'll test them if you to email me the STL files.

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core weaver wrote 03/31/2021 at 15:32 point

Hey, thanks. Can you give your email address ? here or per pm

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mikedoty wrote 03/28/2021 at 18:53 point

Thanks for the response.  I've printed a couple of the enclosures and they are not a tight fit so I'll look for a good place to put a couple of screws.  And, I found one mistake on your layout PDF that you may want to correct.  There are two R19's.  The one that sits below the LM311 on the layout should be R21.  Thanks again.  I knew Neil Hecht and he passed away in 2015.  I'm sure he would be pleased with your version of his design!!

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core weaver wrote 03/28/2021 at 20:47 point

Thank you. That's R18 and it's corrected now. I've updated the FilesArchive again.

You knew Neil Hecht ?

man I wish he could've seen this.

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core weaver wrote 03/28/2021 at 20:54 point

About the case.. I don't have the same problem when I print on my Flashforge Finder using Standard Quality. If I use the best quality then that small offset between the parts becomes a little bigger and the parts don't fit so tight anymore.

if you don't mind waiting a few days, I can try redesign the case and add some holes for another 4 screws which will be then used to hold the two parts of the case together.

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mikedoty wrote 03/27/2021 at 16:49 point

Nice job.  I'm curious as to how you secure the top and bottom of the enclosure?  The only screws I see are for the battery box cover.  Also, as a heads up, the layout shown in your PDF file does not match the pc board.  The row of resistors in the layout shows 9 resistors and the pc board has only 8 shown with different component numbers.

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core weaver wrote 03/28/2021 at 12:27 point

thanks. Watch the geometry of the top side (red) of the case. It has a small profile which goes about 3 mm into the bottom (white) part of the case. This profile is present on about 70% of the outer perimeter of the top shell. It's designed and printed in such a matter that you have to exert a little bit of force to assemble the parts. They not only fit and stick together very well, but it also takes a small amount of force to take'em apart. I used this .."trick" in other cases too. You still need a small offset between the parts. Otherwise they won't fit. The hard part is always to find the right balance between that offset and the printing quality (3d printer's settings). When printing in higher quality I usually increase those offsets.

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core weaver wrote 03/28/2021 at 12:34 point

You're a very perceptive person. I've updated the BOM and Layout. Those resistors under the LCD's header are the voltage divider for the LCD's SPI. MISO doesn't need a level translation. It's wasn't affecting the functionality, but I removed it anyway in v.1.2.

the layout.pdf was based on the first version of the schematic and I didn't realized that when I uploaded the archive. Thanks for pointing this out


if you watch the end of the last part of the youtube series, you can see the PCBs for the giveaway. They're ver1.2, as well as all the other files in the archive, .sch, .brd, and gerbers. I checked this again just to make sure.

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core weaver wrote 03/18/2021 at 11:24 point

Thanks for all the interest in this project. All the tutorial's parts are now available on Youtube here:

If you have questions about building this wonderful tool, I hope you'll find all the answers in the video series.

And if you need assistance or you still have some unanswered questions on this topic, post them on my Youtube channel in the comments section or here, and I will try to guide you though it.

Happy soldering everyone and stay safe !

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Cat wrote 03/17/2021 at 21:38 point

Very nice; thank you.

Can I buy a PCB?

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core weaver wrote 03/17/2021 at 22:03 point

yes you can. private message me

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Joseph Tannenbaum wrote 03/17/2021 at 16:01 point

Cool.  Useful tool.

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