Hosfelt electronics (http://www.hosfelt.com/) has hand-held laser pointers for as little as $10.95 USD, you could adapt one to a "wall wart" power source, I'd guess. Some decent prices on other goodies for PICers, too, there. White LED's pricing looked pretty OK, for one. Inquiring Minds wanna know: What in the world's that projectile? Are you making a "Poor Man's Howitzer" here or something? Mike Chaloupka wrote: > > Thanks Peter for the tip. Any suggest regarding the light source. I though o f using an EGG laser diode / receiver but total component cost are toooo high. > > Regarding the photoresistor - any particular kind? > > Did I mention the projectile my be travelling upto 100mph and has a width 4-5 inch circular & 19 inch long... > > Have you or anyone else listening hear dir MIR Mircropower Inpulse Radar tech nolgy. FCC doesn't like it yet buy companies have spend a lot for the license t o use the technology. I understand it will revolutionize speed & object sensin g since the entire circuit (transmitter /receiver) is possible under $50 > > Mike > > >>> "Peter L. Peres" 11/13 5:34 AM >>> > On Thu, 12 Nov 1998, Mike Chaloupka wrote: > > > I need to detect the speed of an object 2 - 5 feet from the sensor mount. > > > > Sensor is mounted upward looking at the sky. > > The optical way is easy, using a CW light source in the night and the sun > in the day, but one uses more than one sensor (more like a matrix - > minimum size 2 x 2) connected to a micro. This eliminates dirt etc sensing > and can tell which way the object is passing, also has an early failure > indicator built-in (sensors won't fail together unless someone paints > them over very quickly ). > > I did something similar for a protection device on an exhaust chimney and > I used 4 Al. tubes of different lengths in a pipe-organ style mount with > glass windows and CdS photoresistors at the bottom connected to a LM324. > The LM324 was connected as adaptive AC amplifier (to remove DC bias). The > light was a parlight and was on all the time with a current sense resistor > in one of the return wires. Outputs went to a Z80 based controller that > also did other things. > > hope this helps, > > Peter