Sender: [email protected]
Newsgroups: comp.arch.hobbyist
Subject: Re: fast light sensors
References: 
From: Tomi Holger Engdahl 
Organization: Helsinki University of Technology, Finland
Lines: 29
X-Newsreader: Gnus v5.3/Emacs 19.34
Date: 09 Mar 1999 10:42:03 +0200
Message-ID: 
[email protected] writes:
 
> I am looking for a fast light sensor to be used in a light pen. It should
> give a pulse each time it senses the screen raster ray. I need a pixel
> resolution which means about 30 nS precision. Does anybody know wether it's
> better to use an LDR, a photodiode, a phototransistor or a photodarlington.
> Which particular component is suitable? 

LDR is definately too slow for this kind of application.
Phototransistor might be usable for low resolution light pen, but
will not give the resolution you need (I think). I woudl expect
photodarlington to be even slower than normal phototransistor.

The fastest one of those sensors you mentioned is photodiode, so
give it a try.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web pages at http://www.hut.fi/Misc/Electronics/