Frequency to voltage converter Circuit

Converter circuits are widely used in all places and there are several types in it .Here is a simple Frequency to Voltage converter circuit uses a IC LM331 which is basically a precision voltage to frequency convertor.This IC has lot of applications with it here we are about to use it as a simple frequency to voltage convertor.Lets see how this circuit works.

WORKING OF CIRCUIT:

In this circuit the frequency conversion was attained by differentiating the input frequency by using Capacitor C3 and Resistor R7 and feeding  the resultant frequency to the pin6 of the IC which was the threshold of the IC(refer the below pin diagram).The negative going edge of the resultant pulse train at pin 6 makes the built in comparator circuit to trigger the timer circuit inbuild within it.

As you can see that pin 2 was given as the reference input  to the internal comparator so the pin was connected to the R6 and it was used for calibration.At any time instant the output current will be proportional to the input frequency and value of the timing components( C1 and R1).As a reslt voltage Vout is proportional to the input frequency.Thus by this way the frequency is converted to voltage.The output voltage depends on the equation

Vout= ((R4)/(R5+R6))*R1C1*2.09V*Fin