C_WITH_VOM

Published:2009/7/5 22:47:00 Author:May | From:SeekIC

TTL-derived square-wave gen-erator U1 charges unknown capacitor CX to about 3.5 V at 285 kHz when using 150-μA scale of Heath MM-1 volt-ohm-milliammeter, to give 150-pF full-scale range. Larger values of capacitance are read by decreasing frequency with 7490 decade dividers. Use Mallory PTC401 for CR1-CR4. T1 is 6.3-VAC filament transformer. S2 restores normal VOM functions. Article gives design equations.-K. H. Cavcey, Read Capacitance with Your VOM,QST,Dec. 1975, p 36-37.



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