Diagram Guide

The Figure shows a linear frequency to voltage converter which works by charging a capacitor up once for every input cycle, the charge to do so being passed by a MOSFET into a summing amplifier.
The component values given are based on an approximate five volt output for the given frequency. The resistor R1 should be made a 100kQ preset if it is required to set a range exactly. The capacitor C2 "smooths" the output and need not be changed from 10pF if fast- response on the upper ranges is not needed. The linearity achieved on the top range will depend on the particular "741" used and if reliable operation is required a higher speed op- amp should be used.