Subject:
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Re: photocell arrangement
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 19 Jun 1996 19:20:25 GMT
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Original-From:
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GoRK <gork@SAYNOTOSPAMarn.net>
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Viewed:
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2634 times
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At 01:58 AM 6/19/96 -0700, you wrote:
> I'm experimenting with photocells, and I'm looking for some feedback
> from anyone who's got some insight or experience with this sort of thing.
> Essentially, I have two photocells, both facing forward, on the left and
> right side of my robot. I'd like to use them to track light sources, such
> as a flashlight, LED, anything like that. I'm trying to figure out the best
> way to shield unwanted light away from the sensors, and right now I have
> about an inch of heatshrink tubing extending from the sensors. However, I
> have a feeling that this might be too long to yield any sensible results
> from the sensors, since the field of view of the sensors is extremely
> narrow. Does anyone know the best way to do this? My next step will
> probably be to chop some length off of the heat shrink tubing, but I'm not
> sure quite how long to make them...
It seems as if your unwanted light is mostly going to be coming from above
your bot. It also seems that the tubing that you have around the photocells
has made the light detection too directional. (Is that what you want?) With
the two cells on the left and right, it's as if you want to be able to tell
if the light is brighter on the left or the right, so you should probably
build some sort of a hood apparatus that shields light from above and from
the direction opposite the photocell. (That sounds confusing. I shall
illustrate.)
Plastic
Front of robot: _____ | ______
| <---^---> |
( ) | | ( ) <-- Photocell
That way, you have the two photocells mounted like headlights and they
get rid of the unwanted light. You can then detect if light is brighter to
the left or to the right. If you are really looking for a directional
approach, a neat way to accomplish it is to get one of your photocells, and
leave about 3/8 inches of tubing extending from it, then mount it on top of
a servo, like a little light-sensing radar on top of the bot. Have the
program rotate the servo and take light readings, that way you can find
the brightest or darkest spot anywhere around the robot. Of course, you
might want to keep the arrangement that you have now, but get some more
sensitive photocells.
John
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