For anyone who might be interested in the sort of thing:

Frequency Detector « Broken Remote

I wish I had the original schematic that I used to create this. Enjoy!

thinks freind

Hi,
Thanks for the link. I currently doing the project that detect the presence of electromagnetic waves which i think similar to frequency detection, since electromagnetic waves also have property of frequency. Am I right? For the frequency detector circuit provide by the link posted by bacterozoid..instead of audio input, can the circuit accepts radio frequency or electromagnetic waves as the input? if cannot, can anyone suggest some modification that i need to do on the circuit?
On the butterworth filter part, it is low frequency butterworth filter with cut off frequency of 400Hz right?It means, the filter will suppress other harmonics greater than 400Hz frequency..Am I right?If let say, I want to make my frequency detector circuit that have cut off frequency larger than 400Hz, I just need to calculate the new value of resistor and capacitor on the butterworth filter part. Is it? If I modify the butterworth filter part, is it necessary for me to modify the circuit at gain, envelope or comparator part?
Or I just can used the original one, just a modification on butterworth filter part?
Thanks for any idea and help.
Really appreciate it

My circuit is designed for frequencies in the audible range (under 2KHz). I doubt if you can use it for electromagnetic waves. Those are much higher in frequency - you would have to hook an antenna up to the input and even then I don't really think it would work...

I'm not really any sort of expert on that.

I don't recall exactly about that filter - what you said sounds about right. If this circuit would work for what you want, that filter needs to cut off at much higher frequencies. The reason for the butterworth filter is to knock out harmonics in the audio input. I don't know if that does any good for a wave though.

You probably want to create a new topic if you're looking to detect electromagnetic waves. I'm sure there are better ways of doing such a thing

Good luck!