hi guys,
thanks for the inputs.

the 100,00rpm is just an arbitary number.
actually 65536 (2^16 = 2 byte ) seems like a good enuff upper limit to start with.
and, the thingy is to measure the rpm of a jet turbine project i am working on.(no big deal, am using a turbo charger based system).

next, i went thru the sites mentioned alredy, no details about the limits of the device (max rpm etc.) also, inadequate docs regarding the electronic sensor module.
i would be glad if someone can help me design a laser based relected light sensor module.even passing thoughts are welcome.

thx again.