Newsgroups: comp.robotics
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From: sarge@Rational.COM (Matthew C. Sargent)
Subject: Re: Getting Range with IR LEDs - HOW?
Message-ID: <1993Oct4.132932.777@rational.com>
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Date: Mon, 4 Oct 1993 13:29:32 GMT
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wallace.r.blackburn (wrb@cbnews.cb.att.com) wrote:
: OK, I've got the Sharp receiver working with the IR LED driven by a 555
: circuit.  Problem is, it only has a direct range of about an inch or two.
: I mean, holding it directly in front of the LED.

: I have reduced the duty cycle of the waveform to get more "instantaneous"
: power from the LED, but it doesn't help much.  Am I missing something?  How
: do TV remotes get so much range?  Thanks for any info.
: -- 
The Sharp recv. is very sensitive to the freq. you are putting out. If you
are not modulating between 39 and 41 kilohertz(for the 40k one), y
our range will be reduced
to inches. Also the waveform that you are driving the IR Led can effect your
range. I have spoken to some who know on why TV remotes can get so much
range - they let the 1.5 cells drive the IR led with only a little resistor 
in the circuit. They guy said the IR LED was running at like 5 Amps with a
10% duty cycle. I have found a trick that sometimes helps when working with 
IR leds. If you have a video camera, use it to look at the IR led while you 
are modulating it. On some cameras (mine is a cannon 8mm) you can see the IR Led
glow. I think that the IR can be picked up by the CCD elements and show it on
your camera as a glow spot. 

Good luck.


:    Wally Blackburn		   Clinton-Gore - Socialist Leadership
:    wrb@ccsitn.att.com			          for the 90s!
:    Amateur Radio Station AA8DX

--
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| Matthew C. Sargent         |  My opinions are my own. Any |
| sarge@rational.com         |  similarity between them and |
|                            |  other opinions, living or   |
|                            |  dead, is accidental.        |
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