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Looking for DIY LC meter

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carbonzit

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Anyone have a good design for an analog DIY LC meter? Either one using an external meter (VOM or DMM) or one with a dedicated meter would be fine. No problem having to do a little arithmetic to get the value.

Before replying, please keep in mind I'm looking for an analog meter. I'm not interested in PIC-based meters. (Funny how the same two circuits for PIC LC meters keep popping up all over the place on the web.) I have nothing against PIC-based meters; in fact, I'd love to have one. But I'm not set up to program PICs and don't see getting into that for some time now.
 
I expect it is a lot harder to make an analog LC meter then a uC based one. If you ask nice and have a hex file I expect someone will send you a programmed PIC.

That's good to know, and I'll keep it in mind. I guess it would be nice to have an auto-ranging device that showed you the value nice 'n neat on a LCD, as opposed to taking a meter reading and doing some calculations.

Still would like to pursue the analog route if any designs are forthcoming.
 
An analog Wien bridge will measure capacitance and an analog Maxwell bridge will do inductance. They both require stable sine wave sources which shouldn't be too hard to build depending upon the accuracy you require, as well as a null indicator which could be headphones or a meter movement. Waaaaay back in the day I built one that used a neon lamp for a null indicator. I don't recall much about it other than I built it in a discarded "portable" phonograph cabinet.
A really simple really cool LCR bridge utilizes a stereo PC sound card, a simple PC program, and a few op-amps. It is in a past issue of Elector magazine. If you were so inclined, you could skip the PC end of it and develop a hardware version of their sound card utilization and also the PC program.
Many PIC/AVR based units come as complete kits, Just the PCB alone, or Just the preprogrammed µC alone. Ham guys are big in this stuff.
 
Well, seeing as you're intent on an 'analogue' (which I take to mean just non-uC), there's an inductance meter adapter here: https://qrphomebrew.synthasite.com/inductance-meter-adapter-for-multimeter.php

It's currently only an L meter, the capacitance could be measured by connecting the unknown capacitor between pins 8 & 12, and the timing resistor (just use a pot) and diode from pin 12 to the positive supply rail. When you're measuring inductance, the connection for the cap is shorted; for capacitance, the connection for the inductor is left open.
 
I've seen analogue cap meters in the old days built with two 555 timers. The test cap sets the frequency of the first astable 555 timer, and the second 555 timer is a monostable with fixed ON period, so the average output voltage is exactly proportional to freq and goes to an analogue meter.
 
you may find Inductance and capacitance measuring adopters for DMM, in ARRL handbook, in chapter 25. I hope though the display is digital, it may not be classified as digital and the OPs need of non pic or non-software version , is met with.
However, due to modernization, you are likely to measure with a very high accuracy in Micro controller based instruments. I fail to understand the OPs restriction. Perhaps it is a school project spec, presumably. If the OP is now willing, perhaps he can make a cheap and accurate one with a design by Phil Rice of Australia. It is simple and working very well
thanks to Neil of US and Rice of Australia for the redesigned version.
 
Not as much fun a building your own, but here's what I did and it does a bunch of other stuff too and probably doesn't cost much more. https://cgi.ebay.com/New-MASTECH-19...ltDomain_0&hash=item3365494865#ht_4019wt_1168


I hope it works better than my DM4070 from ebay - I can get a more accurate result by guessing the value.

Actually doesn't seem to being too bad of a meter, cap measuring was a pain so I took the guts out 2 ez hooks and soldered wires & clips to them and pushed the into the cap slots and left them there, so now I have 4 test lead coming out of it.
 
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you may find Inductance and capacitance measuring adopters for DMM, in ARRL handbook, in chapter 25. I hope though the display is digital, it may not be classified as digital and the OPs need of non pic or non-software version , is met with.

Well, my edition of the ARRL Handbook (1991: I guess it's a few years out of date) does indeed have a complete analog L meter (no C meter, however). But it's needlessly complicated, at least for my limited purposes, and requires too much calibration. (It appears to be very accurate except for very small inductors.)

However, due to modernization, you are likely to measure with a very high accuracy in Micro controller based instruments. I fail to understand the OPs restriction. Perhaps it is a school project spec, presumably.

Wrong. I'm too old to be in school.

If the OP is now willing, perhaps he can make a cheap and accurate one with a design by Phil Rice of Australia. It is simple and working very well thanks to Neil of US and Rice of Australia for the redesigned version.

No, as I said, I don't want a microprocessor-based meter, for reasons of my own. Just because something is the current "latest and greatest" doesn't mean that everyone automatically should, or does, want it. I prefer a (less accurate, not as easy to use) multimeter attachment at this point, thank you very much.

Actually, the attachment that Dougy suggested above looks to be perfect for me.
 
No, as I said, I don't want a microprocessor-based meter, for reasons of my own. Just because something is the current "latest and greatest" doesn't mean that everyone automatically should, or does, want it. I prefer a (less accurate, not as easy to use) multimeter attachment at this point, thank you very much.

That is reason enough.
 
on DIY, do you own math, you may be able to something with the frequency of a PUT, and a njf, the njf provides a constant current charge for the cap and the put lets you set the charge to voltage.
 

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Newnes "Electronic Circuits" vol. 2 written by Ray Martson has a whole section on bridges with a circuit for an analog LCR unit on page 139. It also has a circuit for a 1kHz exciter for it.
You can get this book used from Amazon for a few dollars.
 
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