Posted on Aug 7, 2012

U1a is an oscillator and U1b tbe measurement part of tbe circuit. It converts unknown capacity into a pulse-width modulated signal the same way an·automotive dwell meter works. The meteris linear so tbe fraction or percentage of time that tbe output is high is directly proportional to the unknown capacitance (CXin the schematic).

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Meter M1 r€ads the average voltage of those pulses since its mechanical frequency response is low compared to tbe oscillator frequency of U1a.

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