I never saw the original post.  I have one of these in
my driveway -
http://www.sureaction.com/directionalprobe.htm

It works quite well - can detect in-bound or out-bound
traffic.  Has a relay for each direction.  I built a
PIC board to generate logging information, fire an
annunciator and operate a camera. 

Phil

--- Herbert Graf <mailinglist2@farcite.net> wrote:
> On Wed, 2005-05-18 at 15:42 +1000, Tony Smith wrote:
> > Yep, you can usually see where the coil is, fairly
> big loop.
> > 
> > Tend not to work for motorcycles though, which is
> a pain if you're riding
> > one.
> > 
> > Parking garages use them too, you usually see them
> on the 'in' entrance.
> > Years ago, a friend of mine determined that there
> was enough metal in the
> > average toolbox to trigger them.  He'd send the
> apprentice off to trigger
> > the gate, then drive out the in entrance, thus
> saving the parking fee.
> 
> My buildings, a LONG time ago, used to have one for
> the main parking
> area gate.
> 
> Discovered while riding my bike that if you drove
> your bike ALONG where
> the coil was buried you'd trigger the gate! Worked
> flawlessly. TTYL
> 
> 
> -----------------------------
> Herbert's PIC Stuff:
> http://repatch.dyndns.org:8383/pic_stuff/
> 
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