Subject:
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Re: IR Collision avoidance
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 13 Mar 1997 15:41:47 GMT
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Original-From:
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Richard Vannoy <RICHARDV@ABAC.ihatespamCOM>
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Reply-To:
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richardv@abac.SPAMLESScom
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Viewed:
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1626 times
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> My question is...in the first diagram (below) the resistance is 220
> ohm ie 0.2KOhm
> But in the second diagram the resistances are 2.2KOhm
> Which is the correct one?
Resistors in series with LEDs are generally current limiters, meaning
that the LED is very low resistance when conducting, so the resistor is
the determinant of current flow. With the little colored LEDs I teach
my students to hook up a 1K pot (set at max or 1K with a 5 volt supply)
in series with the LED, and then slowly turn the pot until they get the
LED to go from dim to "just bright enough", but not so bright thad the
LED gets burned out. In this case, turns out 220 ohms is usually a
pretty good value.
For robot/IR LEDs, the size of the resistor can be used to control
current and therefore range. We put a pot in series, (6 volt supply in
this case) slowly lowered it until we got a range of a few inches,
measured the current & resistance, then continued until we got six feet
range and remeasured. In this example about 1 milliamp through a Radio
Shack LED transmit/receiver pair gave us a solid two foot range which is
what we needed.
Also check the spec sheet which usually supplies operating or maximum
current. Use ohms law with the voltage of your power supply to get an
approximate current.
Short answer: It depends.
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Message is in Reply To:
 | | Re: IR Collision avoidance
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| (...) My question is...in the first diagram (below) the resistance is 220 ohm ie 0.2KOhm But in the second diagram the resistances are 2.2KOhm Which is the correct one? ---...--- (...) (28 years ago, 12-Mar-97, to lugnet.robotics.handyboard)
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