IR Circuit Question
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Posts: 46,084
I've adapted the tachometer excercise from the StampsInClass
Industrial Control text to serve as a simple proximity detector. It
is wired exactly as the example in the text.
I can get the design to function, but the adjustment is *so*
sensitive that I don't think it would work once it leaves my bench.
I can only get it to work when the reference voltage into the op-amp
is exactly 4.88 volts. 1/100th up or down, and it does not work.
I'm using a radio-shack 10K pot as the voltage divider to provide
this reference voltage. The IR Detector is wired:
+5--/\/\/\----|
Coll Emit
Gnd
100K | B
OpAmp
Does this sound right?
Ideally, I'm trying to create a near-field motion sensor (about 12-
18") to serve as a trigger. It should not be impacted by day/night
operations (which is a problem with the IR application). Any other
suggestions would be appreciated.
Thanks,
Rob
Industrial Control text to serve as a simple proximity detector. It
is wired exactly as the example in the text.
I can get the design to function, but the adjustment is *so*
sensitive that I don't think it would work once it leaves my bench.
I can only get it to work when the reference voltage into the op-amp
is exactly 4.88 volts. 1/100th up or down, and it does not work.
I'm using a radio-shack 10K pot as the voltage divider to provide
this reference voltage. The IR Detector is wired:
+5--/\/\/\----|
Coll Emit
Gnd
100K | B
OpAmp
Does this sound right?
Ideally, I'm trying to create a near-field motion sensor (about 12-
18") to serve as a trigger. It should not be impacted by day/night
operations (which is a problem with the IR application). Any other
suggestions would be appreciated.
Thanks,
Rob
Comments
multiturn pot of the same value it shouldn't be so
sensitive then
--- rrothe64 <rrothe@m...> wrote:
> I've adapted the tachometer excercise from the
> StampsInClass
> Industrial Control text to serve as a simple
> proximity detector. It
> is wired exactly as the example in the text.
>
> I can get the design to function, but the adjustment
> is *so*
> sensitive that I don't think it would work once it
> leaves my bench.
>
> I can only get it to work when the reference voltage
> into the op-amp
> is exactly 4.88 volts. 1/100th up or down, and it
> does not work.
> I'm using a radio-shack 10K pot as the voltage
> divider to provide
> this reference voltage. The IR Detector is wired:
>
> +5--/\/\/\----|
Coll Emit
Gnd
> 100K | B
> OpAmp
>
>
> Does this sound right?
>
> Ideally, I'm trying to create a near-field motion
> sensor (about 12-
> 18") to serve as a trigger. It should not be
> impacted by day/night
> operations (which is a problem with the IR
> application). Any other
> suggestions would be appreciated.
>
> Thanks,
> Rob
>
>
>
>
>
>
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IF you don't need to adjust throughout the entire range of the 10K, then it'd
offer a bit of sensitivity....I'm guessing (didn't do the math..grr).
sb
Original Message
From: kenneth magers <kenneth_m_73149@y...>
Date: Thursday, July 24, 2003 7:21 am
Subject: Re: [noparse][[/noparse]basicstamps] IR Circuit Question
> just a idea i would replace the 10k pot with a
> multiturn pot of the same value it shouldn't be so
> sensitive then
> --- rrothe64 <rrothe@m...> wrote:
> > I've adapted the tachometer excercise from the
> > StampsInClass
> > Industrial Control text to serve as a simple
> > proximity detector. It
> > is wired exactly as the example in the text.
> >
> > I can get the design to function, but the adjustment
> > is *so*
> > sensitive that I don't think it would work once it
> > leaves my bench.
> >
> > I can only get it to work when the reference voltage
> > into the op-amp
> > is exactly 4.88 volts. 1/100th up or down, and it
> > does not work.
> > I'm using a radio-shack 10K pot as the voltage
> > divider to provide
> > this reference voltage. The IR Detector is wired:
> >
> > +5--/\/\/\----|
Coll Emit
Gnd
> > 100K | B
> > OpAmp
> >
> >
> > Does this sound right?
> >
> > Ideally, I'm trying to create a near-field motion
> > sensor (about 12-
> > 18") to serve as a trigger. It should not be
> > impacted by day/night
> > operations (which is a problem with the IR
> > application). Any other
> > suggestions would be appreciated.
> >
> > Thanks,
> > Rob
> >
> >
> >
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed.
> > Text in the Subject and Body of the message will be
> > ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
>
>
> __________________________________
> Do you Yahoo!?
> Yahoo! SiteBuilder - Free, easy-to-use web site design software
> http://sitebuilder.yahoo.com
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the
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>
>
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
--- In basicstamps@yahoogroups.com, buht_krak@s... wrote:
> Or what about putting a 20K pot in parallel with a 20K resistor.
> IF you don't need to adjust throughout the entire range of the 10K,
then it'd offer a bit of sensitivity....I'm guessing (didn't do the
math..grr).
>
> sb
>
>
Original Message
> From: kenneth magers <kenneth_m_73149@y...>
> Date: Thursday, July 24, 2003 7:21 am
> Subject: Re: [noparse][[/noparse]basicstamps] IR Circuit Question
>
> > just a idea i would replace the 10k pot with a
> > multiturn pot of the same value it shouldn't be so
> > sensitive then
> > --- rrothe64 <rrothe@m...> wrote:
> > > I've adapted the tachometer excercise from the
> > > StampsInClass
> > > Industrial Control text to serve as a simple
> > > proximity detector. It
> > > is wired exactly as the example in the text.
> > >
> > > I can get the design to function, but the adjustment
> > > is *so*
> > > sensitive that I don't think it would work once it
> > > leaves my bench.
> > >
> > > I can only get it to work when the reference voltage
> > > into the op-amp
> > > is exactly 4.88 volts. 1/100th up or down, and it
> > > does not work.
> > > I'm using a radio-shack 10K pot as the voltage
> > > divider to provide
> > > this reference voltage. The IR Detector is wired:
> > >
> > > +5--/\/\/\----|
Coll Emit
Gnd
> > > 100K | B
> > > OpAmp
> > >
> > >
> > > Does this sound right?
> > >
> > > Ideally, I'm trying to create a near-field motion
> > > sensor (about 12-
> > > 18") to serve as a trigger. It should not be
> > > impacted by day/night
> > > operations (which is a problem with the IR
> > > application). Any other
> > > suggestions would be appreciated.
> > >
> > > Thanks,
> > > Rob
> > >
> > >
> > >
> > >
> > >
> > >
> > > To UNSUBSCRIBE, just send mail to:
> > > basicstamps-unsubscribe@yahoogroups.com
> > > from the same email address that you subscribed.
> > > Text in the Subject and Body of the message will be
> > > ignored.
> > >
> > >
> > > Your use of Yahoo! Groups is subject to
> > > http://docs.yahoo.com/info/terms/
> > >
> > >
> >
> >
> > __________________________________
> > Do you Yahoo!?
> > Yahoo! SiteBuilder - Free, easy-to-use web site design software
> > http://sitebuilder.yahoo.com
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@yahoogroups.com
> > from the same email address that you subscribed. Text in the
> > Subject and Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
> > http://docs.yahoo.com/info/terms/
> >
> >
> >
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
> > > >
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
> > > > >