Re: Private baby GPS

Ico wrote:

A basic (and maybe naive) setup could be to combine RF and audio: your
device-to-track transmits an audio and RF burst at the same time, a few
times per second. These signals are picked up by 3 microphones and a
radio receiver in the field. Calculating the time between the incoming
RF and audio signals should give you enough information for making a 2D
fix of the position.

That would be rather wasteful. It's certainly easier to install a 4th audio receiver to resolve time on top of distance than to bother with a RF transmitter/receiver system on top of the ultrasonic gear. If this is going to be a wannabe GPS, it should mimic the original as close as possible, i.e. use only one signal channel.

A more useful variation of the original principle might be to invert it: have the tracked device send 'pings' at arbitrary times, and collect arrival times from 4 sensors spanning a 3D space. Then break out the maths textbook to find out how to turn that into a positional fix.
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