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From: tom@syssoft.com (Rodentia)
Newsgroups: sci.electronics
Subject: IR Reception - Modulation and Quality
Message-ID: <1991Mar13.193045.18623@syssoft.com>
Date: 13 Mar 91 19:30:45 GMT
Reply-To: tom@syssoft.com (Rodentia)
Organization: Systems & Software, Inc., Irvine, CA
Lines: 34

I have been playing with infra-red transmitters and receivers, and
seem to be having a lot of trouble with range.  I have an audio 
amplifier connected to an IR receiver (transistor) in the following
manner:
    +9---390ohm---audio input(+)---IR receiver---audio input(-)---gnd

With that, I can hear my remote from about four feet away (with a 
fast dropoff in amplitude).  In fact, I get similar results if I 
remove the power from the receiver.  My TV definitely can handle
eight feet plus, so what are they doing better?  What is cheap to
do with lensing, and what helps electronically?

I know the remote does some modulation.  What travels the best?
I was experimenting with pulse width modulated speech transmission, 
but it drops off as fast as the remote does.  I was trying to avoid
demodulation (as I could with PWM), but now I'm willing to add some
hardware to the receiver.

It appears that fast rise and fall times are characteristic of my
PWM signal.  Could a differenting op-amp going to a set-reset flip
flop give me the sort of gain control I need?  Or is frequency 
information more amplitude independent?  Any other tricks to get
better sensitivity out of the IR receiver?

BTW, I did read a Forest Mimms article out of Modern Electronics, 
but that was just a high (adjustable) gain amplifier, and I was
looking for something that wouldn't need adjustment based on 
distance.  Thanks in advance.

-- 
Thomas Roden                                      | tom@syssoft.com
Systems and Software, Inc.                        | Voice: (714) 833-1700 x454 
"If the Beagle had sailed here, Darwin would have | FAX:   (714) 833-1900
come up with a different theory altogether." - me |