Subject:
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Two piece light sensor.
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 30 Jan 1999 05:36:36 GMT
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Original-From:
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Pam Durham <pdurham1@ixAVOIDSPAM.netcom.com>
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Viewed:
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919 times
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Greetings,
Well I finally succeeded. I have created two piece light sensor emitter
pair. To do this I took the basic light sensor circuit of Malcolm S. Powell
(see http://www.umbra.demon.co.uk/sensor1.html) and broke it into two
pieces. I built the emitter in one brick and the detector in another brick.
In the emitter brick I directly wired in a lego wire connector for the
connection to the RCX. To connect to the emitter I cut a lego electric
plate in half and soldered the input wires to it and glued it to the top of
the detector brick. For the emitter brick I soldered the inputs to the
other half of the electric plate and glued it to the bottom of the brick.
In this way if I want to create an integrated emitter detector pair I simply
snap the emitter on to the detector. If I want to create a zero force bump
sensor I place the emitter and the detector bricks on either side of a gap
and connect them with a lego wire connector. Each brick has its own diode
bridge. For the detector I use a Darlington pair phototransistor. I get
responses almost as good at the detector shipped with Mindstorms.
Putting the emitter into its own brick gives you tremendous flexibility.
You can use the emitter with any passive sensor such as a CdS light sensor,
a themistor, whatever you'd like. Also you can use the detector by itself
without any interference from the emitter.
I would highly recommend this configuration to anyone interesting in
building your own light sensor. The key to building Malcolm's circuit is
the resistor that is attached to the emitter LED. The description says that
this is a current limiting resistor. While this is strictly true, more
importantly this resistor sets the time constant for the RC circuit. In
otherwords, it regulates how fast the capacitor discharges. If the value of
the resistor is too small the capacitor will discharge in less that the 10ms
window that the RCX does its light sensor measurement. If this happens the
LED will draw current during the measurement phase which will cause the
readings from your light sensor to be lost in the noise. One of the
problems I had with my circuit was that I had a bad resistor. It was a
recycled resistor that was supposed to be a 1k ohm resistor. In reality it
was about 1 ohm. That's what you get for using recycled parts.
So in any case that's my story. Its been fun. Maybe some day if I get the
ambition I'll put together a web page and put up some pictures.
Doug
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message has 1 Reply:
 | | Re: Two piece light sensor.
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| Hi Pam, (...) I am glad you got it working and your split design is a nice touch. I hope you spoke hashly to that dud resistor! Regards Malcolm (...) -- Did you check the web site first?: (URL) (26 years ago, 1-Feb-99, to lugnet.robotics)
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