Newsgroups: comp.robotics
Path: brunix!cat.cis.Brown.EDU!noc.near.net!MathWorks.Com!europa.eng.gtefsd.com!howland.reston.ans.net!usc!nic-nac.CSU.net!charnel.ecst.csuchico.edu!olivea!news.hal.COM!decwrl!enews.sgi.com!wdl1!mail!cps201!dombrows
From: dombrows@lds.loral.com (Brian Dombrowski, 5424)
Subject: Re: Fun with sensors - Light Tracking
Message-ID: <1994Aug18.001823.6723@lds.loral.com>
Sender: news@lds.loral.com
Reply-To: dombrows@lds.loral.com
Organization: LORAL Data Systems
References: <32r46l$3ra@handler.Eng.Sun.COM>
Date: Thu, 18 Aug 1994 00:18:23 GMT
Lines: 34

> : A couple of years ago, I made light tracker from a gear head motor from
> : a cordless screw driver and two IR photo-transistors.  The transistors,
> : Q1 & Q2, were mounted on a 0.5 x 2" piece of perf-board and the perf-board
> : was mounted perpendicular to the motor shaft to form a T shaped assembly:
> 
> Sounds cool, how did you bias the photo transistors? and did you use a
> darlington arrangement or just the straight output ? I found my junk

Tied the collector to Vcc via a 10K resistor: 

		^  Vcc
		|
		<
		>  10K ohm
		<
		|   C
	       /
	    B -|             
	       \
		|   E
		|
		V  Gnd
		

The voltage at C will drop proportionaly as light intensity increases.
I fed this voltage to OP AMP to increase the voltage swing.  This is
what you'll have to do to if your going to feed an A/D on the 6811.

Good Luck 

Brian D.



