Wagner, At the risk of exposing my misconceptions about Dopple Shift, here goes: Doppler Shift occurs because the transmitter adds it's relative velocity to the speed of the 'energy' that it's transmitting, and that increased velocity is perceived by the receiver as a frequency shift in the 'energy'. So...if a car is traveling between 0 and 100mph (approx 0 - 150 fps), and the speed of light emitted from it is 186,000 miles/second (186,000 x 5280 feet/mile = approx 900,000,000 fps) it appears that the PIC will be attempting to mearsure a frequency shift (or color change in the case of light) of approximately 1 part per 6 million. The speed of light here is for a vacuum, I don't have a figure for air, but it represents the worst case scenario since the speed of light in air is slower. Sound travels approximate 1000 fps in air, so the Doppler Shift for sound would be about 1 part in 6-7. Sounds to me like measuring the Doppler Shift in light is going to be extremely difficult with or without a PIC chip, however, sound doesn't look too bad! You could even time the returning sound waves. Mike. P.S. If this doesn't start a thread about Doppler Shift I'll be amazed :^) On Fri, 21 Jan 2000 18:52:18 -0500 Wagner Lipnharski writes: > Think about this situation: > > a) A device is installed under the car. > > b) Forget how dirty the device will be, and the distance car x floor > doesn't change. > > c) The device pulses a fast narrow light beam 450 towards the > direction > of movement (ahead of the car). > > d) An opto sensor is also pointing to 450 (same spot of the > emitter), > will be receiving the light pulse bounced at the floor. > > Question: It will have a doppler effect in the light beam frequency > received related to the car speed? > It will be possible to use a PIC to calculate this effect? > (Of course sound waves could also be used) > > Wagner ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: http://dl.www.juno.com/get/tagj.