IR LED Emitter Problem Solved - Thanks
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I figured out the problem to my IR LED not working. Radio Shack does not
label their Infared Emitter / Detector pair as to which one is the Emitter
and which is the Detector. I swithed the two, and my Emitter works. By the
way, the Emitter is the colored one, and the Detector is the clear one. (
Cat No. 276-142 )
I do have three another questions though.
On my test circuit for the detector, I put the detector, a resistor, and a
capacitor in series, but nothing would happen. When I took out the
capacitor, things started working. Why was the capacitor limiting my
voltage ? I thought that the capacitor would charge, then discharge, and
cycle back again.
My detector has two leads. How would I connect my two lead detector to my
stamp ? What I've tried so far is having the detector lead( anode ) in (+),
the other lead going to a small resistor ( 15 ohm ), to a normal LED, then
to the (-). Do I need to put a capacitor in with the resistor and do a
RCTIME, or can I attach my BS II pin9 to the resistor and check IN09?
Currently, I have to have the emitter very close to the detector for it to
pick up on the signal. What can I do to increase the distance?
Thanks,
Bryan Smith
label their Infared Emitter / Detector pair as to which one is the Emitter
and which is the Detector. I swithed the two, and my Emitter works. By the
way, the Emitter is the colored one, and the Detector is the clear one. (
Cat No. 276-142 )
I do have three another questions though.
On my test circuit for the detector, I put the detector, a resistor, and a
capacitor in series, but nothing would happen. When I took out the
capacitor, things started working. Why was the capacitor limiting my
voltage ? I thought that the capacitor would charge, then discharge, and
cycle back again.
My detector has two leads. How would I connect my two lead detector to my
stamp ? What I've tried so far is having the detector lead( anode ) in (+),
the other lead going to a small resistor ( 15 ohm ), to a normal LED, then
to the (-). Do I need to put a capacitor in with the resistor and do a
RCTIME, or can I attach my BS II pin9 to the resistor and check IN09?
Currently, I have to have the emitter very close to the detector for it to
pick up on the signal. What can I do to increase the distance?
Thanks,
Bryan Smith
Comments
enough current. If you are not, the I/R source will be "dim" and not work at
any real distance. The other thing, if you have to modulate the emitter, is
to confirm the frequency you are modulating it at is close to 37,500 or
38,000 hertz. The detector loses alot of range when the frequency of the I/R
is off.
As for the detector, which I assume is an NPN phototransisitor, you should
test it with a meter before connecting it to the stamp. Here is what works
for me on the Fairchild sensors I use for line following:
Connect one leg of a 10k resistor to +5 volts. Connect the other end to the
collector (straight line in the diagram) of the phototransistor. Connect the
emitter (arrow line in the diagram) to ground. Hook a meter between ground
and the collector of the transistor. With no I/R light, the meter should
read about 5 volts. When I/R light is present, the voltage should drop --
how far depends on the characteristics of the phototransistor.
If the detector works like you want, connect the collector of the
phototransistor to the stamp pin. The stamp pin should go low when the
detector is triggered.
I went with the FREQOUT example in the Stamps App document and it works
quite well. I mounted the LED's in a brass tube and made a small aluminum
housing for the detector to decrease the field of view. The detector looks
through a narrow slot, which makes it more directional.
Original Message
> I figured out the problem to my IR LED not working. Radio Shack does not
> label their Infared Emitter / Detector pair as to which one is the Emitter
> and which is the Detector. I swithed the two, and my Emitter works. By
the
> way, the Emitter is the colored one, and the Detector is the clear one. (
> Cat No. 276-142 )
>
> I do have three another questions though.
>
> On my test circuit for the detector, I put the detector, a resistor, and a
> capacitor in series, but nothing would happen. When I took out the
> capacitor, things started working. Why was the capacitor limiting my
> voltage ? I thought that the capacitor would charge, then discharge, and
> cycle back again.
>
> My detector has two leads. How would I connect my two lead detector to my
> stamp ? What I've tried so far is having the detector lead( anode ) in
(+),
> the other lead going to a small resistor ( 15 ohm ), to a normal LED, then
> to the (-). Do I need to put a capacitor in with the resistor and do a
> RCTIME, or can I attach my BS II pin9 to the resistor and check IN09?
>
> Currently, I have to have the emitter very close to the detector for it to
> pick up on the signal. What can I do to increase the distance?
>
>
> Thanks,
>
> Bryan Smith
>
>
>
>
>
>
>
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>
>You need to insult the specs on the emitter to see if you are supplying
>enough current. If you are not, the I/R source will be "dim" and not work at
>any real distance. The other thing, if you have to modulate the emitter, is
>to confirm the frequency you are modulating it at is close to 37,500 or
>38,000 hertz. The detector loses alot of range when the frequency of the I/R
>is off.
Note, as you do later, that the detector seems to be a simple photo
transistor that doesn't care what the modulating frequency is. No need to
add this complexity unless a Sharp (or similar) detector is
used. Switching to a Sharp detector instead of a simple photo transistor
will *greatly* extend the range and the performance.
>As for the detector, which I assume is an NPN phototransisitor, you should
>test it with a meter before connecting it to the stamp. Here is what works
>for me on the Fairchild sensors I use for line following:
>
>Connect one leg of a 10k resistor to +5 volts. Connect the other end to the
>collector (straight line in the diagram) of the phototransistor. Connect the
>emitter (arrow line in the diagram) to ground. Hook a meter between ground
>and the collector of the transistor. With no I/R light, the meter should
>read about 5 volts. When I/R light is present, the voltage should drop --
>how far depends on the characteristics of the phototransistor.
>
>If the detector works like you want, connect the collector of the
>phototransistor to the stamp pin. The stamp pin should go low when the
>detector is triggered.
Or when ambient light exceeds some given value unless the detector is
insensitive to all but IR. I doubt this is the case.
>I went with the FREQOUT example in the Stamps App document and it works
>quite well. I mounted the LED's in a brass tube and made a small aluminum
>housing for the detector to decrease the field of view. The detector looks
>through a narrow slot, which makes it more directional.
And eliminates a lot of ambient light. Good approach. An IR filter
(passes IR, blocks visible light) in front of the detector arrangement you
describe could help a bit more if ambient light levels are high.
>
Original Message
>
> > I do have three another questions though.
> >
> > On my test circuit for the detector, I put the detector, a resistor, and a
> > capacitor in series, but nothing would happen. When I took out the
> > capacitor, things started working. Why was the capacitor limiting my
> > voltage ? I thought that the capacitor would charge, then discharge, and
> > cycle back again.
Capacitors do not pass DC current apart from the amount required to charge
them initially - after that they just sit there fully charged. Even
assuming you are modulating the IR beam, the voltage induced in the
detecting circuit only has one polarity - the polarity of its DC power
supply, thus no current flowed even when it was illuminated by IR, so there
was nothing to detect.
Jim H