EDR project help

hi guys
i`m working on a project called
edr(event data recorder)
it is the same as the black box of
eroplanes but it gathers data about the
car`s engine speed in rpm,speed of the car,and
temperature of the engine
i used lm35 for measuring temperature
i used a photo sensor for measuring speed in rpm
but i don`t know how to measure the speed of the car
plz help

Your could, of course, measure the speed of a wheel using the anti-lock wheel speed sensors on most cars, but then you have to account for the different wheel sizes to determine the speed.

An off-the-wall thought is to use the sensor from an optical mouse focused on the roadway. According to this site **broken link removed** a mouse optical chip takes "pictures" at 6000 per second or 167µs per picture. In that time a car going at 60mph moves less than 0.2 inches, thus the sensor should be able to detect the speed directly from roadway, similar to the way it detects the motion of the mouse.

You would need optics to focus the image of the roadway unto the sensor wherever it's located (perhaps from 8-12 inches above the road). That probably is the most difficult part of the task.

You would also need a strong source of light such as one or more of the IR lasers used in a laser mouse, or a single stronger laser.

thanks
crutschow
thank you for your reply