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From: raan@hp-pcd.UUCP (raan)
Newsgroups: net.video
Subject: Re: Infrared remotes
Message-ID: <20600023@hpcvry.UUCP>
Date: Wed, 8-Jan-86 16:33:00 EST
Article-I.D.: hpcvry.20600023
Posted: Wed Jan  8 16:33:00 1986
Date-Received: Tue, 14-Jan-86 03:49:43 EST
References: <2453@ukma.UUCP>
Organization: Hewlett-Packard - Corvallis, OR
Lines: 47
Nf-ID: #R:ukma:-245300:hpcvry:20600023:000:2523
Nf-From: hpcvry!raan    Jan  8 13:33:00 1986


>>	Can someone out there give a simple explaination of how infrared
>>remote controls work? How hard would it be to build your own? Is there
>>a "programmable, one unit imitates anything" one of these on the market?
>>(Hmmmm, new product idea....)

In fact, there is already such a device on the market.  It is made by GE
and is called the Control Central (model RC-100 I think).  It can be 
programmed with at least 4 (and if your lucky and creative, maybe more)
remote control units.  It comes with built in commands for the GE line of
TVs, VCRs, etc.  I have programmed mine to control 5 different units from
4 different manufacturers and still have not exceeded its capacity.  

It is about 3x7 inches, has about 20 keys (all programmable) plus an LCD
with labelled functions and 3 keys to activate the selected function.
It is programmed by "playing" the original remote into the Control Central
which analyzes the signal and then duplicates it.  The only unit I found
it could not duplicate was the remote for the AR stereo remote control.
It sells for about $120 mail order.

As to how they work:  
  Most remotes transmit a digitally coded signal on a IR carrier.  The
  IR light is modulated with a carrier frequency (the Control Central
  can handle any frequency between 33 and 70 Khz).  This carrier frequency
  is further modulated with the digital code.  There are ICs available
  to do both the modulating and demodulating, requiring only a few 
  simple outboard parts.  Coding is done with square pulses, where the
  width indicates a 1 or a 0.  Most of my units use pulse spacing on the
  order of 5-10 mS, and codes of about 10 bits.  The AR uses a 4 bit code
  and pulse spacing more like 100 mS.  This seems to be beyond the limits
  of the Control Central to duplicate accurately and the AR tolerates no
  instability -- hence no go.

  Some units transmit the same code over and over as long as the button
  is held, others transmit a function code and then switch to a repeat
  code.  I find this annoying since it can generate false behaviour.
  I managed to convince the Control Central to always transmit the 
  function code by pressing and releasing the original unit's button
  rapidly while programming the Control Central.

---  Raan Young 

Unix mail:  [hplabs|uoregon|orstcs|harpo|microsoft|tekronix]->!hp-pcd!raan
HPMAIL:     Raan YOUNG / HP3900/50
US mail:    Raan Young | Hewlett-Packard | 1000 NE Circle | Corvallis, OR  97330
Phone:      (503) 757-2000 X2506
TELNET      81-757-2506