Help me detect a car

[Unregistered]

I want to make a sensor like the ones used on traffic lights to detect the presence/absence of cars. Im having a hard time finding information on how 2 do this, and I sure would apreciate the help. Where should I start? Is there anyone who knows a existing desing that do the trick? any Ideas?
Thanks for the help
Alex

[Carl-NC]

I responded to a similar question on TNet... I suspect most traffic light sensors are PI. That's certainly an easy way to do it, or a fluxgate sensor would work.

- Carl

[jimmyjiver]

How To Detect A Car

There are all sorts of technologies for detecting cars -- everything from lasers to rubber hoses filled with air! By far the most common technique is the inductive loop. An inductive loop is simply a coil of wire embedded in the road's surface. To install the loop, they lay the asphalt and then come back and cut a groove in the asphalt with a saw. The wire is placed in the groove and sealed with a rubbery compound. You can often see these big rectangular loops cut in the pavement because the compound is obvious.

[Jim]

Check with any automatic gate opener vendor for available options. You can go with loop, electric eye or magnetic sensors. The possibilities are endless; it all depends on how deep your pockets are.

Good luck, Jim

[Atul Asthana]

Easier : sense the vibrations using piezo-ceramic elements (used as speakers).

I guess, it will be better to use a simple piezo-ceramic sensor to sense vibrations, BPF | detect using TL084 and powered and data transmission on a current loop.

Receiver side, detect and send commands to open gate etc.