> Someone of you mentioned that an ordinary led can be used as 
> a light sensor. How sensitive is that? 

It generates a small voltage - you can measure it with a multimeter.

> How fast is it

AFAIK quite fast, compareable to an opto-transistor.

> can be it > used as a test
> measurement device for a really fast movements (sometimes 
> nearly as fast as the speed of sound).

Unity error: you try to compare distance/time with time.

> And finally as far as I know it 
> gives a very
> small signal you can measure, so would you use a simple 
> analogue amplifier
> to attach it to the PIC?

comparator? (some PICs have one build-in) or use the bias-trick, check
ultrasound distance measurement with a PIC, there is some circuit out
there that does that without an amplifier.

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu
 

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