AVR Inductance / Capacitance meter 


Posted on Jun 2, 2012 11368
This instrument requires two precision components: A precision capacitor and a precision inductor. You only need to start with one precision component, either the reference capacitor or the reference inductor, and using this meter, you can select or adjust the other precision component. Calculates and displays L and C from oscillation frequency using reference components. No relays, no range switching, a minimum of controls. And it is pretty accurate too!
The basis of this project is several similar projects on the world wide web and some magazine articles before the world wide web was a common means of information interchange. Unfortunately, I am not able to determine the originator(s) of the concept, but I suspect that it is as old as radio. Another project on my web site, LC Determination by Resonant Frequency Measurement, measures the resonant frequency of an L/C circuit, but the hardware stops at the frequency measurement. It does not proceed to calculate the unknown inductance or capacitance.
To convert from frequency to inductance or capacitance requires a pocket calculator or spreadsheet, and is fine if only taking a few measurements per day. Beyond that, the manual labor seems a bit much, and the time to complete a measurement and calculation becomes burdensome. As I found myself spending more time winding transformers in my Thailand lab for various power supplies that I longed for a meter that would read out directly in inductance and capacitance, such as I had in my lab in Arizona.
An LC oscillator oscillates at the resonant frequency of a parallel LC resonant circuit. When measuring an inductor, a precision capacitor is switched in to the circuit. When measuring a capacitor, a precision inductor is switched into the circuit.
If the Q of the resonant circuit is about 10 or greater, the measurement error contributed by this factor will be less than 1%. Q...
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