What types of sensor(s)

Jack3

Folks drive way fast up my street. I would like to be able to make my own little speed trap that will tell me how fast these puppies are going. I can buy a hand held for just under $100, so I don't want to spend oodles. Already have dev boards, one in Propeller, one in Arduino mega. I would prefer to use C but what I really need is to know what types of sensors I should use, I will need to have them at the sides of the street, most cars go up the middle they are going so fast. Maybe 20 feet wide total.

I assume if I can get a signal at point A, then time to point B I can calculate the speed from there...with help on the math....but anyhow. What sensor(s) would work for this?
Is there already a program out there for this? I haven't found one in my searches. I could even record the data on my proto board with the SD card, but I don't know sensors.

Franklin

IR or lasers would work for what you describe.

GordonMcComb

Radar is the way to go. Ultrasonic doesn't have the distance, IR would need expensive optics to collimate the light, and there are no laser sensors you could use that would be legal in this instance, as they would not be certified for the application. It is not legal in this country to use a laser in a public space in a way not certified and intended. The reasons here should be obvious -- you'd effectively be shining a laser into the eyes of oncoming traffic.

Maybe you could look around for a cheap sports radar gun you could adapt to microcontroller input.

Publison

Timing systems are not cheap. Even Infra-Red.

The one we use in my Sports Car Club are $250 a Head, and you need two.

RaceAmerica.

Beau Schwabe

A simple video camera and knowing your frame rate (~24fps) in combination of knowing how far apart at least two strategically placed obstacles in your cameras field of view are all you need.

Jack3

Well that is what I was trying to figure out. Not at all feasible, except for the video camera one...Thanks