"Please Step Away From the Vehicle" - Sensors?

xanatos

Thinking about a car project got me to wondering about how cars with proximity sensing manage to do that - I'm thinking specifically of those cars that will tell you to step back/away from the vehicle. Without having hundreds of individual Sharp or similar Proximity Sensors mounted all over a car, how do those cars that can tell if a person has been standing a little too close to that car, manage to do that?

kwinn

Probably use the car body as a capacitive sensor. I built a couple of them many years ago using a circuit similar to that of a theremin. No need for that now though. Use the car body as the capacitor, and a small inductor to build an oscillator. Have a propeller counter monitor the frequency for changes that indicate someone in proximity and output the audio request "Please step away from the car."

xanatos

LOL... well, don't necessarily need the audio component But the idea of using the car's body as a capacitive sensor is interesting. Googling info on that now...

Thanks!

kwinn

xanatos wrote: »

LOL... well, don't necessarily need the audio component But the idea of using the car's body as a capacitive sensor is interesting. Googling info on that now...

Thanks!

You're welcome. Good luck with your application.

I rather liked the possibilities the audio capability of using a prop would add to such a project. I can imagine the output from it as an anti theft system.

First the polite "Please step away from the car"

Followed by a somewhat less polite "Warning, step away from the car or the theft deterrent system will be armed" if they continue to approach.

And finally "Warning, extreme danger! Theft deterrent system active! SURVIVORS WILL BE PROSECUTED!