[akosednar]

How does this work with other noises and interference?

[RogerL]

I'm sitting outside on my deck. Birds are chirping, dogs are barking. There was a clear 20kHz band, but the resizing rectangle was just randomly jumping around, and when I turned on the hands free scrolling the webpage started jumping up and down randomly and rapidly.

But hey, this is an excellent project! Love it.

[mjb]

This simple demo wouldn't be very good at noise rejection, but the general idea could be extended to reject noise very well. One option is to use a wider-band signal, like a pulse or a chirp. Signal processing techniques could then be used to extract the doppler while strongly rejecting noise. Another option, especially if you want multiple devices using this technique to work near eachother, is to use code division pulses (the same approach as CDMA). These kinds of pulses aren't that good at rejecting noise, but can be made very effective at rejecting other devices using different codes.

[vessenes]

If they're up around 20khz probably not well.

[colechristensen]

Because something fairly specific is being searched for, the signal should stick out from the noise fairly well.

One could also use a pseudo-random code instead of a steady signal to further distinguish the signal from the noise (in the style of GPS).