Subject:
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[MindStorms FAQ 4.2 How do I use more than three sensors?]
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Newsgroups:
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lugnet.faq
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Date:
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Tue, 13 Jul 1999 21:36:38 GMT
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Viewed:
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2397 times
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Subject: 4.2 How do I use more than three sensors?
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>There are several approaches. </p>
<p>The simplest is to connect the sensors to the same input.
This is most useful for two sensors one of which is a touch
sensor. When the touch sensor is off (untouched) it has
infinite resistance and allows you to read the other sensor value.
When the touch sensor is on you cannot read the other sensor's
value. Sometimes this is acceptable, it depends on your design. </p>
<p>Two touch sensors on the same input can be connected in two different
ways. The obvious way makes tham act like an OR function: if either of
the touch sensors is touched the RCX will see it. However, you can
also connect the sensors so they work like an AND function. This approach is
called "wiring in series". </p>
<p>To wire two sensors in series, you have to connect the two sensors and
the RCX in a "ring" with three 9V connecting cables. Each device (RCX
and sensors) has a 2 x 2 pad where you connect the leads. Connect one
lead to contact half of the pad and the other lead to contact the
other half. Note that on each 9V lead, only one of the two conductors
is being used, and note also that when you connect the 2 x 2
connectors to the 2 x 2 contacts, if it's rotated 90 degrees it won't
make contact at all. Look carefully at the pads and connectors to
determine the proper orientation. On the RCX this is tricky on inputs
1 and 3 because your 2x2 connectors ends up pressing the View or Prgm
button. To avoid this, use a fourth 9V connecting cable to raise it up
a bit (or of course you can connect the "loop" to the other end of
that fourth cable) </p>
<p>A similar wiring scheme can be used to connect a touch sensor in
series with another type of sensor, so that that sensor is only
connected to the RCX when the touch sensor is pressed. Conbining two
or more sets of sensors would allow you to share multiple sensors on
the same input, using the touch sensors to control which sensor is
connected. Depending on your robot design, this could be useful. For
example, you could have one light sensor that's connected only when
the front bumper hits something, and other that's connected only when
the back bumper hits something. </p>
<p>Multiple touch sensors can be connected to one input with resistors,
either in series or parallel, and the input can be read in raw mode
(or as a temperature or light input if you're using RCX Code). If the
resistors have different values, different combinations of touch
sensors will create different input values. Here's an example of that
method implemented by modifying a 2 x 8 conducting plate: </p>
<blockquote>
<a href="http://www.plazaearth.com/usr/gasperi/3rmux.htm">
http://www.plazaearth.com/usr/gasperi/3rmux.htm </a></blockquote>
<p>and here is another: </p>
<blockquote>
<a href="http://www.akasa.bc.ca/tfm/lego_resistor.html">
http://www.akasa.bc.ca/tfm/lego_resistor.html </a></blockquote>
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