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[DPRG] FW: Any ideas?

Subject: [DPRG] FW: Any ideas?
From: bryan at visi.com bryan at visi.com
Date: Wed Oct 11 14:13:01 CDT 2000

If one isn't opposed to spending a bit of money, there are commonly
available laser modules that accept digital and/or analog inputs for
modulating them.  Usually this adds anywhere from $20 to $40 to the
price.  I have a few at home and can retreive the URL of the place I
bought them from later.  It was about $60 in quantity 1.

> > The standard method for increasing the range of photoelectric sensors for
> > this sort of application is to pulse the beam.  To do this first measure the
> > amount of returned light with the light turned off.  Then measure the amount
> > of returned light with the light turned on.
> > 
> > Subtracting the two values removes the effects of room lights, sun shine,
> > etc.  Because of the removal of the noise from any external lights the
> > signal to noise ratio is higher and the sensor works at longer distances.
> > 
> > The same technique can be used for a laser sensor also.  However not all
> > laser can be pulsed in this manner.  Most of the lasers used in laser
> > pointers need to be left on for longer then the standard 40kHz or they do
> > not emit any light.
> Some may be damaged by rapid pulsing. One possibility is not to use
> electronic but rather electromechanical means for modulating the light.
> One possibility (which works to the 10s of KHz at least) is to put the
> signal out to a small speaker with a reflector mounted on it, and
> bounce the light off of the reflector.

A problem with this is the vibrations your robot goes through as it
moves will add noise to your signal.

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