Designing Digital Circuit to Determine Frequency of Incoming Signals

[formulajoe]

Need to design a digital circuit that determines the frequency of incoming signals. Incoming signals will vary, but all will be converted to a 0-5 V square wave before going to the digital portion of the circuit. The current idea is to have a counter to count the edges for a certain period of time, store that number, clear the counter and start all over again. Just curious as to whether anybody else has some different takes on a circuit like this.

thanks

 

[chroot]

That circuit will definitely work -- the counter is clocked by the signal being measured, and is cleared by a fixed reference clock of known period.

- Warren

 

[berkeman]

I agree with chroot. Just to add a couple of details if they matter, think about how regular frequency counter instruments work. They'll have buttons on the front for averaging period, or for resolution (which is directly related). At a minimum, you need to specify what the counting period is, and preferably make that a variable. There is a big difference between counting frequencies around 1MHz and around 1kHz and around 1Hz. Make your circuit easily re-configurable between those ranges, and have the display/output be meaningful for them. And if you really want to get creative and fancy, you can design a 2-input circuit that can take the ratio of two different inputs, and display that as a frequency as well.

Quiz question -- when would you want to be able to display the frequency ratio of two input signals? Hint, network physical layer design...