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Subject: 2.4 How do I use the light sensor?
Content-Language: en
Topic-Level: 0
Revision: Robert Munafo, 1999-07-13
Location: /robotics/rcx/
Comment: Topic-level is inaccurate pending a reference for topic
levels
<p>The touch sensor is a 2 x 4 x 1 1/3 brick with an LED (light emitter)
and photodiode (light detector) on the smallest face (the "end" of the
brick) and a non-detachable 9V connecting cable. You connect the other
end of the cable to the RCX, and then (using your chosen programming
method, see section 3 answers below) tell the RCX to do something
based on a light level or range of light levels. You might want to
mount the sensor on an arm that rotates under motor control, so you
can "scan" the area ahead of you, or you may want to obstruct the
light emitter by placing a beam (a narrow brick with holes) in front
of it, so that the detector detects ambient light and doesn't see the
reflected light from the LED. You can use a fixed light sensor to
detect the presence of an object, such as a ping-pong ball on a
conveyor belt. </p>
<p>The printed instructions ("constructopedia"), CD-ROM idea area
("programmopedia") and various users online web sites give many
examples of specific applications of the light sensor. </p>
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Subject: 2.4 How do I use the light sensor?
Content-Language: en
Topic-Level: 0
Revision: Robert Munafo, 1999-07-14
Location: /robotics/rcx/
Comment: Topic-level is inaccurate pending a reference for topic
levels
<p>The light sensor is a 2 x 4 x 1 1/3 brick with an LED (light
emitter) and photodiode (light detector) on the smallest face (the
"end" of the brick) and a non-detachable 9V connecting cable. You
connect the other end of the cable to the RCX, and then (using your
chosen programming method, see section 3 answers below) tell the RCX
to do something based on a light level or range of light levels. You
might want to mount the sensor on an arm that rotates under motor
control, so you can "scan" the area ahead of you, or you may want to
use a fixed light sensor to detect the presence of an object, such as
a ping-pong ball on a conveyor belt. </p>
<p>The built-in LED makes it possible for the sensor to detect
proximity or to see in the dark, if the thing it's "seeing" is close
to the sensor. The LED also makes the sensor more reliable for
line-tracking, because it helps make the line tracker less sensitive
to ambient light. However, if you only want to detect ambient light,
you'll need to block the LED. To do this, place a black Technic beam
directly in front of the light sensor. The hole in the beam lines up
just right to allow light in to the photodiode while blocking the
LED. </p>
<p>To make your robot work well in different ambient light levels,
you'll probably have to make it measure the light level in some way
when it starts up. This could be as simple as taking one reading right
away when you start, or it could involve scanning in a circle and
keeping track of the lowest and highest readings it gets during the
scan. After you know what the average ambient level is, store it in a
variable to compare to in the future. You can also design it to adjust
to ambient light levels by repeating the scan from time to time.</p>
<p>The printed instructions ("constructopedia"), CD-ROM idea area
("programmopedia") and various users online web sites give many
examples of specific applications of the light sensor. </p>
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