A Surprisingly Accurate Digital LC Meter
An inductance / capacitance meter by Phil Rice VK3BHR, Almost as published in Amateur Radio magazine, April 2004. The AADE web site gave details of how their design worked and a circuit diagram. This led me to propose a design using their oscillator, but in a slightly different way. Like theirs, mine would measure the free running frequency of an LC oscillator, then successively apply a known capacitance then the unknown inductor (or capacitor).
A Surprisingly Accurate Digital LC Meter
Frank Winter VK4BLF has made a nice printed circuit board for this meter. (It’s much nicer than my unit which was constructed on “dot matrix” board.) See http://members.optusnet.com.au/frankwinter/ for details. Frank also has a nice Amp-Hour meter described on his site.
The oscillator design originally came from the AADE LC meter web page. It uses an LM311 comparator with positive feedback to make a parallel LC oscillator with digital output. It seems to oscillate readily over a wide range of L and C values. Hopefully, it follows the “well known formula for resonant frequency”.
Amateur Radio Magazine
Selected articles from issues of AR have been made
A 16F628 PIC is used. This has internal comparator, which means the LM311 is no longer needed. Software calibration is used. The finished meter can be calibrated against “any” accurate capacitor within the range 100pF to about 10000pF.
