High impedance DC Voltmeter by IC CA3130
R1=8.2Mohms R7=1Kohms C2-3=10uF 25V
R2-3=820Kohms R9-10=10Kohms D1=1N4148
R4=82Kohms TR1=10Kohms trimmer IC1= CA3130
R5=100Kohms TR2=25Kohms trimmer VV1=100uA instrument
R6-8=47Kohms C1=1.5uF 25V
The MOSFET input of the CA3140 makes it ideally suited for use in a high impedance DC voltmeter. Switch S1 is the range selector. The input impedance is limited to 10M by the resistors used in the voltage divider, but this is still a very acceptable value.
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