Newsgroups: comp.robotics
Path: brunix!uunet!gatech!emory!sol.ctr.columbia.edu!The-Star.honeywell.com!umn.edu!csus.edu!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: It must be simple, make robot home on LED, but how?
Message-ID: <1993Jan20.071149.9310@netcom.com>
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
References: <9161@lee.SEAS.UCLA.EDU>
Distribution: usa
Date: Wed, 20 Jan 1993 07:11:49 GMT
Lines: 17

yee@edison.seas.ucla.edu (John Yee) writes:
>Hey robot experts, you all must have done this a zillion times, so could
>you please relate a cheap way to make a robot home in on an LED, say from
>4 feet away inand using ich we prefer to keep lit.  

       Not too clear what the last line above means, but what you want
to do should be straightforward enough.  Blink the LED at some 
convenient frequency (probably not 40KHz, because most infrared remote
controls are on the frequency.)  Receive the signal with two photocells,
and run the signals through active filters at the indicated frequency.  See
"The Art of Electronics" for oscillator and filter circuits.  Result
should be two analog signals.  Feed to op-amp and difference; the
result is which way to turn.  This shouldn't take more than $25 or
so in parts; it's all audio frequency stuff, so layout is no problem.
Build it up on a solderless breadboard first, for debugging.

					John Nagle
