T&L Publications

Vehicle detectors: Placed a 5' diam. coil (5 loops) 4-6" under pavement on front road. Object to have the
50 km/hr (31 mph) traffic turn the lights on a xmas tree. Need advice on what to look for in a vehicle
detector and what to avoid.

Hi,


One way to do this would be to make the coil part of an oscillator circuit that depended on
inductance, with the coil of course being the inductor. The circuit would oscillate at a
given frequency with no ferromagnetic material close by but as soon as some material
did come in close proximity to the coil the frequency would change because the
inductance would change. Detecting the frequency change would be all that is required.

In a more modern design, you would probably employ a small camera aimed at the location
to monitor and use motion detection software. That way you could even have a pic taken
when the software detects motion of something like an automobile, bike, or even animal.

Maybe employ and modify a basic metal detector circuit which works as Mr. Al points out? A Google of Metal Detector Circuits had no shortage of circuits that looked like they could be modified.

Ron

i have access to vehicle detectors, they run off of 120vac, have relay contacts, adjustable delay / extend ( only few seconds tho ) you might wanna use a seperate timer tho..
make your own coils, the unit has a wide range.. 6x6 5t or 6x60 3t / figure 8 style coils are typical..let me know if interested..