Square wave frequency to voltage converter

[sudil99]

how can I convert square wave frequency (of around 20kHz) to voltage without using F-V converter ICs or MCU ?

 

[BradtheRad]

There is a method called a charge bucket. Each pulse adds a little bit of charge on a capacitor.

The more rapidly the pulses arrive, the more the charge builds. A resistor is in parallel, to make the charge reach an equilibrium state.

The pulses must be equal in length. I believe your signal must go through a one-shot, to generate identical pulses.

I've seen it used in a project for an automotive tachometer. It does the same job as a F-V converter.