Detecting the metal in a car... how??

[NightHawk_099]

As a university project, I want to develop a sensor that knows if a car is right on top of it or if its not. The sensor should respond only to cars, and I was thinking, since cars are made of metal, how about a inductive sensor. Problem is, I dont know a lot about metal detectors, and I need the sensor to be SMALL, have a interface with a microcontroller, and be as cheap as posible. Would a cheap do it yourself metal detector do the thrick, or would it have to be bigger than that? Any ideas or links? thanks a lot.
alex

 

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[Carl-NC]

Induction sensors are used at traffic lights; those oblong octagonal slots you see cut into the pavement hold the loop. Not sure what circuitry is used but I suspect it's pulse induction.

You could also use a fluxgate sensor which is quite small, about the size of your index finger. See www.fatquarterssoftware.com.

- Carl

 

[NightHawk_099]

I notice that the size of the loop is big, is it to help it detect motorcicles and other small vehicles, or its just a requirment for detecting cars at that range?.
Also, know where can I get a schematic for a simple metal detector that will detect cars?
Thanks.

 

[Carl-NC]

I don't know why they make the loops so big, even a 12-inch loop would be sufficient. I do know that my motorcycle sometimes will not trip a sensor. See www.thunting.com/geotech for lots of detector schematics.

- Carl