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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Mon, 3 Mar 1997 18:10:12 GMT
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Original-From:
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Chuck McManis <cmcmanis@&ihatespam&freegate.net>
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Reply-To:
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cmcmanis@freegate(spamcake).net
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Viewed:
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1744 times
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Richard Whitehead (I think) wrote:
> Why is everyone using a digital device to try to detect the (analogue)
> distance to an object? Especially one with AGC, it makes no sense!
The Sharp IR modules are not being used to detect distance, they are
being used simply as non-contact bumpers. This allows one to
inexpensively put an arbitrarily long 'whisker' on your robot.
The advantage to these things are that they are simple to attach
(only three wires) and pretty easy to use. The problem is that they
can be picky when used in this unconventional mode. Known things that
make these modules act up are:
1) Inadequate decoupling at the power pins. You MUST attach
a .1uF capacitor across power and ground at the case on
these things. Solding the ground side directly too the
case is important too.
2) The duty cycle of the input signal. The closer you are
to a 50% duty cycle, the more light energy is concentrated
in the 'center' frequency.
3) The frequency stability of the modulation frequency.
Drifts in the modulation freqency of only a few 100 hz
over short periods of time will cause a decrease in
sensitivity.
My reccomended way of using these is to decouple them, and use
a dedicated chip (like a crystal controlled PIC chip) to provide
the clock source.
Bill (the heretic :-) Richman's description of how these things work
is essentially correct except that we disagree on the frequency
response of the AGC and the operation of the AGC in the presence of
a valid signal. Of course "IR module" isn't a precise description of
the part under test. After talking with Bill privately about his
theories on why he was getting the behaviour he saw I tested the
seventeen IS1U60 (http://www.sharp.co.jp/ecg/unit/is1u60/is1u60.html)
parts in my stock bin and, under controlled conditions, (closed box
testing) the IS1U60 will produce an output as long as the lens
sees a 38Khz signal. However, I reccomend using a modulated output
because it aids in the discrimination against background noise that
is so essential. (Which means the discussion of the actual operation
is moot if all parties advocate a usage scheme that accomodates their
notion of the operational aspects of the part :-)
Using a modulated IR LED with a controlled current source is one
way of actually getting distance information out of an IR detector
scheme, but it incurs a significantly more complex circuit (relative
to the all-in-one module approach)
--Chuck
--
cmcmanis@netcom.com http://www.professionals.com/~cmcmanis
All opinions in the non-included text above are the sole opinions of
the author.
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Message has 1 Reply:
 | | Re: IR Collision avoidance
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| The part number on the device from Radio Shack is "GP1U52X". In our earlier discussions, I thought I made it clear that I was using "the Radio Shack IR detector module", although I may not have quoted the number. If Sharp makes a module without the (...) (28 years ago, 4-Mar-97, to lugnet.robotics.handyboard)
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