Interesting idea. The remote control is probably much cheaper
than our sensors but most likely it is too big for us to use. 
We are using as small as possible components here. For example,
we are using tiny QFN parts more and more. In case of
inductive sensors, the sensor is often smaller than the
cable connectors. In case of optic sensors, it is still not
that bad but the trend is getting smaller.

I have not measured the pulsing current of these remote controls,
I guess that they are not high enough to fully utilize the 
IR emitters. We are pulsing them at the limit in order to
achieve longer sensing distance yet keep the current consumption
low. If the emitter is allowing 750mA then we will probably 
pulse them at 700mA (a bit of safety margin). Therefore
we may not be able to send two pulse with too small pause.
The sensing distance of an optic sensor ranges from several
millimeter to 10s of meters (visible light or infrared) or even
higher (using laser diode). The other thing is the relative
fast switching frequency required (the higher the better).

Anyway I see your point and will consider it in future
applications. This is also applicable to all kinds of
sensors: level sensors, capacitive sensors, ultrasonic
sensors, etc.


Regards,
Xiaofan

-----Original Message-----
From: olin_piclist@embedinc.com [mailto:olin_piclist@embedinc.com]
Sent: Tuesday, June 28, 2005 10:32 AM
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] generating different pseudo random sequence using the
s ame firmware


The more you taylor the detection algorithm to the expected pulse the
better.  You have a minimum and maximum valid pulse duration, so it's
probably a good idea to use that.  You could also send specially coded pulse
sequences so that it's virtually impossible for random noise look like a
real signal.

Even just sending the "pulse" as a burst of a known frequency will help a
great deal with signal to noise ratio.  If you can send a burst of 10 cycles
at 35-50 KHz, then you can use a standard IR remote detector like is built
into VCRs, TVs, and lots of other things.  These do all the IR receiving,
gain adjustments, and carrier detection for you.  You give them +5V and GND,
and they return a digital signal indicating presence of carrier.  They
usually require minimum bursts of 10 carrier cycles.

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