> > 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 mailto:piclist-unsubscribe-request@mitvma.mit.edu