Post by thread:[PIC:] want to make a LC meter with pic.

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? > -- FCC Rules Online at http://www.hallikainen.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

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}> 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? > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Check out practical electronics there is one in the feb issue Steve... -----Original Message----- From: pic microcontroller discussion list [EraseMEPICLISTspam_OUTTakeThisOuTMITVMA.MIT.EDU] On Behalf Of paul x Sent: 15 January 2004 17:02 To: PICLISTspam_OUTMITVMA.MIT.EDU 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? -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

{Quote hidden}> From: Harold Hallikainen[SMTP:RemoveMEharoldTakeThisOuTHALLIKAINEN.COM] > Sent: Thursday, January 15, 2004 12:48 PM > To: spamBeGonePICLISTspamBeGoneMITVMA.MIT.EDU > Subject: Re: [PIC:] want to make a LC meter with pic. > 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. > Harold 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 -- http://www.piclist.com hint: To leave the PICList TakeThisOuTpiclist-unsubscribe-requestEraseMEspam_OUTmitvma.mit.edu

> > 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 -- FCC Rules Online at http://www.hallikainen.com -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestEraseME.....mitvma.mit.edu