Newsgroups: comp.robotics
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From: browen@lyapunov.aoc.nrao.edu (Bruce Rowen)
Subject: Re: Q: IR - beacon
In-Reply-To: rick@ee.uwm.edu's message of 25 Aug 1993 11: 59:37 GMT
Message-ID: <BROWEN.93Aug25102759@lyapunov.aoc.nrao.edu>
Sender: news@nrao.edu
Organization: National Radio Astronomy Observatory, Socorro NM
References: <25f8r2$kop@theben.kapsch.co.at> <25fk79INN1pt@uwm.edu>
Date: Wed, 25 Aug 1993 16:27:59 GMT
Lines: 67


   frisch@zams.kapsch.co.at (Martin Frischherz) writes:

>>      I  just  did  my first trial in toy building. It is a modified R/C car
>>      which is searching a modified glass of jam (no jam inside but an IR
>>      transmitter).  On top of  the  car  an  IR  detector is mounted on a
>>      model servo looking left & right until the IR signal is detected. To
>>      get a narrow angle of view (about 5 degree) and  increase  sensitivity,
>>      the detector is mounted in a tube with a focussing lens in front.

>   Sounds pretty sofisticated.  Want to write about it for PERSONAL ROBOTICS?

>>      My  problem  is  to  get  it working at short AND long distances. The
>>      IR-led is directed to the ceiling to avoid different IR intensities for
>>      different directions.  Of course the most energy is sent to the ceiling
>>      and useless for the main purpose but the detector with its lens is very
>>      sensitive.

>   What you need, first, is a better beacon.  Let the IR-LED stay pointing
>   upwards, but put a reflective ball in its path.  A nice, shiny bearing
>   would fit the bill nicely.  Make sure it's centered over the LED, and

Don't forget you are dealing with IR light. You want a good IR
reflector, not a good visible reflector.

I found a Laser diode once and pondered using it as a transmitter that
would be so powerful, you could flash it in a room and the reflections
could be received *anywhere*. (did you ever look at a IR led with a
CCD camera with no IR filter? Damn bright!). Well (as R. Reagen would
say), I dug the diode out from my junk collection a while back (these
can be bought for about $5) and set up a power FET driver that would
send 10 amp pulses through the thing at a 1% duty cycle. The receiver
was a fat photo diode and low noise op amp circuit to test for the
signal.

I set the "transmitter" up in one room of my house and turned it on.
Then I walked around the house with the receiver to find places where I
could get a signal. The problem was finding a place where I could
*not* get a signal! The transmitter must look like a camera flash in
the IR band. I could get a reliable signal in every room, even though
it was not line-of-sight. I even got a signal behind a closed door via
leakage around and under the door. Heating vents also distribute the
signal quite well.

I am convinced this would make a neat way to command a mobile robot in
a house via IR with a single laser diode transmitter mounted near the
"control computer".

Another fun thing you can do with these laser diodes is to configure
them as an "amplifier" for your universal remote control and change
your neighbors tv channels from across the street and through the
their curtains. 8^}

>   a short distance away such that the LED's emissions cover at least two
>   thirds of the lower hemisphere.

>   RICK MILLER           <rick@ee.uwm.edu>            Voice:  +1 414 221-3403
>   P.O. BOX 1759                                        FAX:  +1 414 221-4744
>   MILWAUKEE, WI                      Send a postcard and I'll send one back.
>   53150-1759 USA                    Sendu bildkarton kaj mi retrosendos oni.
--
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Bruce Rowen 				National Radio Astronomy Observatory
Scientific Programmer				Array Operations Center
browen@aoc.nrao.edu			  P.O. Box O  Socorro, NM   87801
(505)385-7329					     (505)385-7000
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