Tamas Rudnai wrote:
> Thanks everyone for the answers. It is a really small item, an airplane
> model propeller. Basically I just wanted to make a simple rotation speed
> measurement device and thought I just can put something together with my
> existing components I have at home at the moment -- and also to learn
> something from it.

I've fooled around with making optical "buttons" out of LEDs.  My 
experience is that, while LEDs can be used as optical sensors, 
phototransistors and photodiodes are more sensitive.  So, for a one-off 
project, they'll be easier to get up and running, and the increased cost 
is negligible.
-- 
Timothy J. Weber
http://timothyweber.org
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