If I remember, it is not weight that triggers, it's a large coil and ferrous 
metal interacts with it, changing some frequency in the controller. Probably 
the same with the system in the link shown.

You could probably find a cheap metal detector and mount the coil at the edge 
of the drive. I've found cheap ones that do detect ferrous stuff at gross 
sensitivities for less than $10. Get one with a light as well and you'll have a 
binary interface already set to go. ;)

Even if the side of the driveway isn't good enough, you could bury it just 
under the surface and that would guarantee detection...


Marcel Birthelmer wrote:
> Brad,
> have you thought about those drive-over detectors that they use to
> count traffic sometimes? It seems to be just a cable that reacts to
> being compressed by the weight of a car. It's not as "magicky" as what
> you're proposing, but seems much simpler.
> Also, an acquaintance of mine once had a radar setup in his office,
> pointed out the window, and he could get a decent tracking of what
> cars were driving by.
> Just some thoughts.
>  - Marcel
> 
> On 10/15/07, Brad Stockdale <brad_lists@greenepa.net> wrote:
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