Joerg wrote:

Hello Jim,

Good idea, Joerg. Where do I get onesie-twosie IR sensors that will
trigger at 3 meters or better?


No idea but one source might be remote controls and the corresponding
receiver diode in the set or from a stereo. I bet that Radio Shack will
have something if there still is one in your area (our became a cell
phone store). You'd need a crude reflector on the other side, piece of
metal or white board.

Another source might be if someone replaces their garage door opener.
They usually come complete with the child protect barrier and most
people will throw out the old one.

Thing is, you need at least two sets. The LEDs could be running all the
time and you just have to sense the receive elements.

There is yet one more method: Two coils next to the road, each with
oscillator. On fence posts, wherever. A car will de-tune it or, if set
on the edge of the stable feedback range, would stop the oscillator
momentarily. In contrast to the IR method and the Doppler method this
can be made pretty weather proof from cheap wire.

Regards, Joerg

http://www.analogconsultants.com
Actually inductive loop detectors (buried or not) require fairly good wire
to last more than a year. Plus you have to provide a roadside cabinet and
detection electronics, and power therefore. of course you can space them
carefully and detect speed that way also.
--
JosephKK