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[DPRG] reading a Cds via Port E on a HC11

Subject: [DPRG] reading a Cds via Port E on a HC11
From: Ralph Tenny rten at metronet.com
Date: Sat Jun 23 14:39:42 CDT 2001

I was surprised to hear of Cds cells with such extremely low resistance. I
agree, they would be MUCH faster at low resistance. Have I been away from
instrumentation too long?

On Sat, 23 Jun 2001, Rodent wrote:

> I would imagine the photoresistive cells that are lower resistance and don't
> have much swing would be faster. I know the ones I got are about 15 meg in
> dark and about 20k in light.
> If it were me, I would use an I/R emitter / detector pair. The ones I use
> work really well provided they are mounted less than 1/8" from the surface
> of the arena. Two resistors and you connect them right to the Stamp pin --
> should work the same on any other processor with TTL level inputs. An op-amp
> circuit of some sort would get you more distance.
> ----- Original Message -----
> > > Are you getting acceptable line recognition using an LED with a Cds
> > > sensor? My impression of Cds devices has been (relatively) low
> sensitivity
> > > and slow operation.
> >
> > using my multimeter, i get 6 Ohms over a white line, 50 over a black
> > surface, and 15 over my medium shade fake wood desk. the Cds/LED are
> > just over a 1/4 inch over the surface.
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