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LINEAR_SCALE

2017-03-02 20:32  
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LINEAR_SCALE
Wide frequency range and high output current of 555 timer contribute to linearity of operation as capacitance meter.Timer is connected as astable MVBR with frequency determined by values used for RA, RB, and C1. When timer output is high, unknown capacitance C1, is charged almost to VCC. When timer goes low, Cx discharges through D1. Use 100 kHz for 100-pF full-scale reading, 10kHz for 1 nF, 1 kHz for 10 nF, and down to 1 Hz for 10μF. Use regulated supply.-R. Horton, 555 Timer Makes Simple Capacitance Meter, EDN Magazine, Nov. 5, 1973, p 81.