IR Circuit Question (Solved)
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Well, it was wrong. Swapping the IR transistor so the long lead went
to ground (ie, the long lead was the emitter which was opposite the
flat spot) fixed the problem. I now get full range deflection in
varying light conditions.
Isn't the flat spot side supposed to be the emitter?
--- In basicstamps@yahoogroups.com, "rrothe64" <rrothe@m...> wrote:
> Thanks, Tracy. I will try it with room light and take some
> measurements.
>
> Since I'm very new to this, I was careful to follow the
schematic...
> However, I will say that some of the documentation for the
components
> wasn't very good (ie, RShack). In particular, the IR tranistor
> lacked meaningful documentation (to me) --- so I went with "long
lead
> to positive" which is what the StampsInClass docs say. Now if
this
> is wrong, that might explain it.
>
> I'll keep plugging along.... Thanks again.
>
> Rob
>
>
> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > That circuit at the junction of the 100k and the Coll should
> > transition pretty rapidly from 5 volts down to less than one volt
> as
> > light intensity increases past a certain level. What happens if
> you
> > expose it to a 100w light bulb or sunlight? If it doesn't go
down
> > to less than one volt, there is something wired wrong. Did it
work
> > okay in the Industrial Control experiment?
> >
> > Detection of a weak light source against a strong background is a
> > problem. Depending on the situation, it might take shielding the
> > receiver in a tube, an IR filter over it to block ambient,
> modulation
> > of the source and AC amplification in the detector, and a
> photodiode
> > instead of a transistor for wider dynamic range.
> >
> > If the object to be detected is moving, you might be able to
check
> > better for *change* in level, by coupling the signal from the
> > photo-transistor through a capacitor to the comparator. Passive
> > infrared (PIR) might also be an option.
> >
> > -- Tracy
> >
> >
> >
> > >I can certainly try this. However, I think my question really
is:
> > >
> > >Why is the detection of IR by the transistor only amounting to
> > >1/100th of a voltage change being fed to the OP-AMP? No matter
> how
> > >strong/weak the IR source is, the most change I can induce is
> 1/100th
> > >of a volt... This is the part that is too sensitive, I think,
since
> > >the reference voltage has no buffer zone.
> > >
> > >If the IR intensity resulted in a larger range, then the op-amp
> could
> > >be better tuned as a comparator. No?
> > >
> > >Tx,
> > >Rob
> > > > > >
> > >> > > +5--/\/\/\----|
Coll Emit
Gnd
> > >> > > 100K | B
> > >> > > OpAmp
> > > > > >
to ground (ie, the long lead was the emitter which was opposite the
flat spot) fixed the problem. I now get full range deflection in
varying light conditions.
Isn't the flat spot side supposed to be the emitter?
--- In basicstamps@yahoogroups.com, "rrothe64" <rrothe@m...> wrote:
> Thanks, Tracy. I will try it with room light and take some
> measurements.
>
> Since I'm very new to this, I was careful to follow the
schematic...
> However, I will say that some of the documentation for the
components
> wasn't very good (ie, RShack). In particular, the IR tranistor
> lacked meaningful documentation (to me) --- so I went with "long
lead
> to positive" which is what the StampsInClass docs say. Now if
this
> is wrong, that might explain it.
>
> I'll keep plugging along.... Thanks again.
>
> Rob
>
>
> --- In basicstamps@yahoogroups.com, Tracy Allen <tracy@e...> wrote:
> > That circuit at the junction of the 100k and the Coll should
> > transition pretty rapidly from 5 volts down to less than one volt
> as
> > light intensity increases past a certain level. What happens if
> you
> > expose it to a 100w light bulb or sunlight? If it doesn't go
down
> > to less than one volt, there is something wired wrong. Did it
work
> > okay in the Industrial Control experiment?
> >
> > Detection of a weak light source against a strong background is a
> > problem. Depending on the situation, it might take shielding the
> > receiver in a tube, an IR filter over it to block ambient,
> modulation
> > of the source and AC amplification in the detector, and a
> photodiode
> > instead of a transistor for wider dynamic range.
> >
> > If the object to be detected is moving, you might be able to
check
> > better for *change* in level, by coupling the signal from the
> > photo-transistor through a capacitor to the comparator. Passive
> > infrared (PIR) might also be an option.
> >
> > -- Tracy
> >
> >
> >
> > >I can certainly try this. However, I think my question really
is:
> > >
> > >Why is the detection of IR by the transistor only amounting to
> > >1/100th of a voltage change being fed to the OP-AMP? No matter
> how
> > >strong/weak the IR source is, the most change I can induce is
> 1/100th
> > >of a volt... This is the part that is too sensitive, I think,
since
> > >the reference voltage has no buffer zone.
> > >
> > >If the IR intensity resulted in a larger range, then the op-amp
> could
> > >be better tuned as a comparator. No?
> > >
> > >Tx,
> > >Rob
> > > > > >
> > >> > > +5--/\/\/\----|
Coll Emit
Gnd
> > >> > > 100K | B
> > >> > > OpAmp
> > > > > >