Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!apple!well!nagle
From: nagle@well.sf.ca.us (John Nagle)
Newsgroups: sci.electronics
Subject: Re: X-Y detection of moving metal ball?
Message-ID: <23982@well.sf.ca.us>
Date: 2 Apr 91 05:39:59 GMT
References: <1225@telesoft.com> <2642@sun13.scri.fsu.edu> <1991Apr1.003056.15878@colorado.edu>
Lines: 35


     Your first solution, LEDs and photosensors, will work if you modify it
slightly.  Touchscreens often use such a setup, and you may even be able to 
buy a touchscreen frame for a big monitor adn use it directly.  But they
don't work by using collimated beams.  They work by having only one LED on
at a time, and ignoring all but one photosensor at a time.  Cycle times
can be in the kilohertz range; LEDs turn on and off fast.

     Some commercial manufacturers of touchscreens are

	Mantex Corp (Rep: Westech sales, 415-961-1422)
	Tektronix (Rep: Ross Markeging, 408-988-8111)
	Transparent Devices Inc (Rep: Richards Assoc, 408-297-3010)

They may not use beam-interruption technology, but the reps will probably
know who does.

     The TV camera approach is of course feasible.  If you don't want to
bother with a computer and frame grabber, you could probably do the image
processing by building suitable circuits out of a sync extractor chip,
some comparators, and a few op-amps.  The National Semiconductor 
LM1881 is a cheap sync extractor.  You could also use the LM1880 
no-holds vertical/horizontal TV sync processor to generate H and
V ramps, and then use a comparator on the video signal to detect
the object.  When the object goes by, feed the appropriate ramps
to V and H sample-and-holds and thence (assuming the desired 
output is digital) to A/Ds.  See the National special-purpose
linear databook for specs on these parts.  For the op-amps and
comparators, I use MC34002 op-amps, LM311N comparators, and 
LM733CN video amps; one can do better, but these are easily
available jellybeans.

     Now tell us what you're building.

				John Nagle