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'[PIC:] want to make a LC meter with pic.'
2004\01\15@120041 by paul x

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f sweeping, serialing and comparing with a R, is a excurate method.
any exprience to share, by using PIC?

Or, any other method to do it? lots of multimeter has C or CL meter.
what method do they use?




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2004\01\15@125014 by Harold Hallikainen

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Some of the inexpensive C meters I've seen have a wien bridge oscillator
generating a sine wave. This drives one of the capacitor terminals. The
other capacitor terminal drives an op-amp current to voltage converter (op
amp with resistor from inverting input to output, non-inverting input
grounded, input applied to inverting input directly). Capacitor current
with known voltage and known frequency is proportional to capacity. So,
they just use their AC voltage measurement capability to measure the
voltage at the output of the current to voltage converter.

They can't tell if it's a capacitor, a resistor, or an inductor, but it's
a simple way of measuring a capacitor if it is indeed a capacitor.

If you want to get fancy, you could generate a sine wave with a lookup
table and D/A to drive the capacitor. Then, instead of just measuring the
RMS current, do fast D/A samples of the current (as indicated by the
current to voltage converter). Do a complex number division (using either
polar or rectangular notation, whichever works out best), to get Z=V/I . Z
can then be represented as R+jX . Knowing the frequency, you can convert
from X to inducatance or capacitance and model the unknown impedance as
L/C in series with R or L/C in parallel with a different R.

Another approach for use at RF that I think would be fun to try would be
to use a reflectometer and measure the voltage ratio and phase between the
forward and reverse samples. I believe these could then place the load
impedance on a Smith chart where the impedance could be read directly.

Harold

> f sweeping, serialing and comparing with a R, is a excurate method.
>
> any exprience to share, by using PIC?
>
> Or, any other method to do it? lots of multimeter has C or CL meter.
> what method do they use?
>


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2004\01\15@133415 by Mark

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       Try these PIC links:

       http://www.freddospage.nl/

       http://www.antrak.org.tr/gazete/111998/barbar.htm

       http://www.aade.com/lcm2binst/LC2Binst.htm

       http://www.elektroda.pl/eboard/ftopic37668-0-asc-30.html

       http://www.spettel.de/ralf/projekte/lc-meter/index.html



       And these ones using an ATMEL processor:

       http://xavier.fenard.free.fr/LCMeter.htm

       http://www.hw.cz/constrc/lc_metr/


       Mark PY3SS

On 15 Jan 2004 at 12:02, paul x wrote:

{Quote hidden}

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2004\01\15@134917 by Steve Smith

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Check out practical electronics there is one in the feb issue

Steve...

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[EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU] On Behalf Of paul x
Sent: 15 January 2004 17:02
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Subject: [PIC:] want to make a LC meter with pic.

f sweeping, serialing and comparing with a R, is a excurate method.

any exprience to share, by using PIC?

Or, any other method to do it? lots of multimeter has C or CL meter.
what method do they use?




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2004\01\16@163148 by John N. Power

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{Quote hidden}

An analog method would be to generate sine and cosine waves with
an analog oscillator which had quadrature outputs. Mixing the current output
with samples of both input phases will give you DC voltages which tell you
the real and imaginary parts of the impedance (actually the admittance).

John Power

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2004\01\16@164017 by Wouter van Ooijen

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The last EPE magazine contains a 16F628-based LCF meter. Uses an LC
oscillator and measures the frequency.

Wouter van Ooijen

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2004\01\16@164018 by Harold Hallikainen

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>
> An analog method would be to generate sine and cosine waves with
> an analog oscillator which had quadrature outputs. Mixing the current
> output
> with samples of both input phases will give you DC voltages which tell you
> the real and imaginary parts of the impedance (actually the admittance).
>
> John Power
>

Nice solution! It should be pointed out that "mixing" is analog
multiplication followed by a low pass filter to yield the DC component of
the product.

A quadrature output oscillator can be constructed with (as I recall) three
op amps and a bunch of resistors and capacitors. I dont' think it's very
easy to change the frequency, though. Direct Digital Sysnthesis is a nice
way to generate the quadrature signals, though not especially cheap
(unless you use a couple D/As on a PIC with a lookup table, which would be
somewhat frequency limted).

Harold


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2004\01\16@224531 by Techsavy

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Here's one, pic based.  The construction was detailed in an older Radio and
Electronics issue.  I 'think' he has the schematic somewhere on his website.

http://www.aade.com/lcmeter.htm

Dave

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2004\01\17@182934 by Diego Sierra

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Hi!

There is one on the latest (February) issue of EPE magazine.

   http://www.epemag.com

Cheers,
Diego.

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