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Frequency Detector


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Hi Dody

What you intend to do is extremely complex and difficult!
First, in order to detect simultaneously several frequencies in real time, you have to use some form of convolution process: a Fourier transform, f.e.. But , that's not enough, because each single vehicle will produce multiple frequencies, mainly harmonics of the motor's rpm. Therefore, in the mass of frequencies that are collected and identified, you have to find groups of harmonically related frequencies (that is frequencies whose respective phases remain stable in time). Once you've sorted all the frequencies present in groups, you're able to determine the number of vehicles by counting the number of groups.
It's a computation intensive application for a DSP circuit...
Good luck anyway!

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I think it is not that easy to build in just using bandpass filters.

And the sound frequency generated by the vehicles are not always the same and you have to take care of the "sound" generated by other sources, these are the most critical points!

May be you have to analyze the sound frequency spectrum in realtime and look for some peaks..... but will that be working..... I don't know.

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You can't count cars by their sounds, unless you funnel them into a single lane with spaces between them. Besides, the doppler shift from the cars quickly coming and going would make bandpass filters count many more frequencies.

Maybe you could bounce ultrasonic waves off the cars and detect the reflection (it is almost sound). If you beam the ultrasonics in 3 different directions, a computer could triangulate their exact positions and accurately count them.
If your teacher says you must detect real]/b] sound, use 20KHz. If your teacher says that the 21KHz reflection of cars approaching isn't sound, tell him that the average frequency of the reflections are real 20KHz sound because the reflections will be 19KHz when the cars are leaving.

We aren't scientists. We're just fooling around here. Lotsa fun! ;D

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