LM331 voltage to frequency converter

If  we  use  a single  input RC  filter  the output square wave voltage  frequency is  [math]F=\frac{V_{in}}{2.09} \frac{R_2+R_7}{R_4} \frac{1}{R_1 C_1}=0.08134 \frac{V_{in}}{R_{1n}C_{1n}}[/math]  with  n possible values are  0,1,2 and  3.

To change the Frequency range we use the  two switches  to aligne  each resistor with each  corresponding  capacitor.

To maintain stability over time and temperature, observe the following guidelines:
– Use an NPO ceramic, Teflon, or polystyrene capacitor for C1.
– Ensure resistors R1 and R2 are 1% tolerance metal film resistors.
– Choose a cermet type for the RV1 adjustable potentiometer.