Light Pens ...

From: Pete Turnbull <pete_at_dunnington.u-net.com>
Date: Wed Jul 18 01:43:02 2001

On Jul 18, 0:45, Tony Duell wrote:

> > Yes, but the schmitt-triggered one has a different problem -- it's too
> > slow! It's a long time ago, and the articles and my notes are buried
near
>
> Right... It's generally recomend for BBC lightpens (See, for example,
> the Advanced User Guide page 369). Are you saying none of these designs
> work properly?

Well, mine ended up having more in it than the one on p.369 (which has just
a Sweet Spot phototransistor mounted in the barrel) - it had a transistor
and bias resistor in there too, along with a CMOS chip to make a
touch-sensitive switch. I can't remember what the Sweet Spot part number
in the AUG is (schmitt or plain) so I can't tell you if that's the one I
used. I bought both types, and one other photodiode (or phototransistor?)
from the RS cat.

I see that page also refers to a fudge factor to be subtracted from the
register contents -- I remember having to do that too.

-- 
Pete						Peter Turnbull
						Network Manager
						University of York
Received on Wed Jul 18 2001 - 01:43:02 BST

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