[sdiy] Three Leg Photocell Hunt

[Kyle Stephens]

Tony, Mark and Tim,

Thanks for the responses!

Here's what I'm building: http://forum.deviever.com/download/file.php?id=859&t=1

In addition to the eye on/off, I wanted an inverted response as well, thus my inquiry.

I though about the two cell idea, and recon yeah, I'll just have to find two equivalent enough (in resistance/on-off time) cells to use, one that goes up in resistance to light, the other the opposite. Those two and an on-off-on DPST switch will be my ticket then.

I otherwise thought about using a switch to swap the (variable) cell between one divider network to another, each respectively making up the input and feedback resistances of a non-inverting configured op amp, though I wanted to keep things passive/cheap/simple (even as I'm complicating things now, heh).

If you look at page 52 here...

http://www.datasheetcatalog.com/datasheets_pdf/V/T/L/5/VTL5C3_2.shtml

...the diagram for the dual Vactrol has a schem symbol that's a modified pot, with the wiper as the middle leg, hence my idea that it was a "light pot" in effect. I haven't checked anything with my meter though, doh, though I'll take your word for it Mark :)


Thanks again all for the input!


_Kyle
(Hold tight, I'll have a new question for everyone in a bit...)



--- On Tue, 3/30/10, Tony Rolando <tony at makenoisemusic.com> wrote:

> From: Tony Rolando <tony at makenoisemusic.com>
> Subject: Re: [sdiy] Three Leg Photocell Hunt
> To: "Kyle Stephens" <lightburnx at yahoo.com>
> Cc: synth-diy at dropmix.xs4all.nl
> Date: Tuesday, March 30, 2010, 5:39 PM
> You could build one from two standard
> photocells, right.
> 
> T
> 
> 
> Kyle Stephens wrote:
> > Ahoy...
> >
> > I'm looking for a three terminal photocell with
> potentiometeric response (the exact log/linearity isn't
> important) - like what's in a three legged Vactrol.
> >
> > I suppose I could try and pop one of those open to get
> what I have in mind, but it'd be a waste of a good Vactrol,
> assuming it's even possible to saw through and chip away all
> the potting.
> >
> > A max resistance of ~10M would be grand, as would a
> turn on time less than ~50ms.
> >
> > Any leads anywhere? This is the best I got so far, the
> "MI (TH Series)":
> >
> > http://www.macron.com.hk/productlist.htm
> >
> > The exact terminology seems to part of my problem
> finding one - what to call it, a (dual?) optocell,
> photocell, photoresistor, optoresistor, CdS cell, "Cadmium
> sulfide" spelled out in full, etc.?
> >
> >
> > _Kyle
> >
> >
> >       
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> > Synth-diy at dropmix.xs4all.nl
> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> >
> >   
> 
>