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PICList Thread
'IR Remote control emitter'
1998\01\04@140549 by Aaron Hickman

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Does anyone know what the requirements for infra red LEDs are when using
a Sharp GPiU52X demodulator.  I just finished some code that allows a
12c509 to turn on/off and adjust the volume of my Kenwood receiver using
IR.  Everything looks good on the scope, but when I stick a plain old IR
LED in, the signal looks like crap!  Any suggestions would be appreciated.

Aaron

1998\01\04@175503 by Martin McCormick

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       The case of the Sharp module must be _WELL_ grounded for one thing.
If not, it tends to false trigger frequently.  Unless we are talking about
different modules, the Sharp modules I have experimented with were very
forgiving as long as they saw the near infrared light from the kind of
LED's commonly used in remotes and the carrier frequency was
within a KHZ or so of 32,767 HZ.  The range and quality of the received
data go right down to nothing if the carrier frequency is off.  If it is
way off such as 40 or 50 KHZ, you may get brief triggers from the Sharp
module, but it won't follow the carrier.

       In one case, I took a 33 KHZ generator I had built and gated it with
a square-wave signal generator and began raising the frequency of the
generator.  The output of the IR module tracked the square wave pretty well
until I reached about 2,000 HZ at which time the Sharp receiver began to
falter.  I must admit that this test was not very scientific in that I
simply listened to the output on a speaker as I cranked up the frequency
and noted the point when it got rough and noisy which occurred rather quickly
above about 2 KHZ.

       Most IR remotes we had lying around the house made the Sharp module
respond with the kind of range typical of such things, so it shouldn't be
too tricky to get it to work as long as the carrier frequency is right.

Martin McCormick

1998\01\04@180120 by Andrew Mayo

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It is extremely important to gate the 38KHz modulation synchronously i.e
you always transmit whole cycles of modulation. Otherwise you will get
nasty jitter on the recovered signal.

{Quote hidden}

1998\01\05@013543 by Mike Keitz

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On Sun, 4 Jan 1998 14:01:39 -0500 Aaron Hickman
<hickmaabspamKILLspamDUNX1.OCS.DREXEL.EDU> writes:
>Does anyone know what the requirements for infra red LEDs are when
>using
>a Sharp GPiU52X demodulator.

The wavelength of the LED must be suitable to pass through the filter
plastic on the receiver's photodiode.  And the intensity of the LED must
be enough to cover the desired transmission range.  If the maximum range
isn't a problem, a plain old IR LED will work fine.  In fact, a plain old
*red* LED usually works fine at pointblank range.  I think the filter
plastic and the photodiode are optimized for 950 nm.  The spec sheet for
the receiver should say so.  A few dim cheap LEDs in series or parallel
can replace a bright expensive one.  If the transmitter is to be placed
stationary close to the receiver, LED choice isn't important at all.

> Everything looks good on the scope, but when I stick a plain old
>IR
>LED in, the signal looks like crap!  Any suggestions would be
>appreciated.

Use the commercial remote transmitter to test your receiver module, power
supply, grounding, etc.  Sometimes the receiver modules can be overloaded
by having the transmitter very close (less than a few feet).  If that
looks good, then the problem is obviously in your homemade transmitter.
Make sure the current for the LED isn't overloading the PIC power supply
or port pin (which may affect read-modify-write operations on the port).
In order to reach the rated peak drive current for the LED (to get
maximum range), an external driver transistor or several port pins in
parallel may be needed.  Always obey the PIC current specs.  Check with a
scope at the LED and make sure the drive waveform is still OK with the
LED in circuit.

The carrier frequency must be correct of course (You are driving the LED
with pulses of 40 KHz, not pulses of baseband, right?)  Someone else said
the carrier phase has to be coherent as well.  I'm not sure about that, I
thought the receiver was just a bandpass filter and envelope detector but
maybe they are more sophisticated than that.

1998\01\05@075253 by jrmont

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Mike Keitz wrote:
>
> On Sun, 4 Jan 1998 14:01:39 -0500 Aaron Hickman
> <.....hickmaabKILLspamspam.....DUNX1.OCS.DREXEL.EDU> writes:
> >Does anyone know what the requirements for infra red LEDs are when
> >using
> >a Sharp GPiU52X demodulator.
>


With regards to the Sharp detector. I had a problem with this device
falsely triggering this week. The project was on a vector board. Turns
out that a 22uF cap and 0.1 uF cap right at VCC of the module cleaned it
up.

1998\01\05@154541 by Griffith Wm. Kadnier

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Hi John,

Could you diagram your fix pls? What kind of caps did you use (and were they
parallel to GND or what?)

thx,
Griffith Wm. Kadnier
Algorithmics Inc.
(425)775-1010

{Original Message removed}

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