Subject:
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RE: What about multiplexing sensors?
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 11 Nov 1998 21:50:45 GMT
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Original-From:
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Larry Coffin <lcoffin@PointInfinity.com&ihatespam&>
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Viewed:
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2803 times
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At 4:07 PM -0500 11/11/98, Stephen Waits wrote:
> > Or rather than using each output port as an n-ary state
> > output you
> > could use it as a 'clock' (i.e. turning the output port on and off) to
> > increment an n-bit counter to cycle on every pulse through
> > however many
> > sensors you want.
>
>
> This seems like what I call a statistical multiplexor or "StatMux".
> Seems like it may be more difficult to implement (ie ROM decoding,
> writing drivers, etc.), but the advantage of freeing up an output port
> is really cool. The hardware to generate the clock signal, etc. could
> be a pain.
One idea is to just use the input port itself to generate the clock
signal under control of the RCX software. Otherwise, it is not too
difficult to generate a clock using external hardware -- an IC and a few
resitors and capacitors. But it gets complicated for the RCX to know which
of the sensors is currently active. I currently favor having the selection
under control of the RCX.
> On the topic of "using up output ports" I was wondering why the Mux idea
> couldn't be extended to Mux output channels as well as input channels?
I've thought about this and the only problem I see is that you need
to supply a constant current to the motors all the time. You can't MUX
between them and only supply current for the fraction of the cycle during
which any one motor is selected. So you can't drive the motors directly
from the RCX. (Well, you can ... but then the motor would either work in a
jerky fashion turning on and off continuously, or the motor would appear to
be running at a fraction of the power that you are applying depending on
how fast you cycle through them.)
But if you wanted to use an external power source, then you
probably could use the output ports as signals which the external hardware
would then use to set the power source that actually drives the motors. For
example, you could use one output port as a clock to cycle between the
motors, one port as an 'assert' that would tell the hardware to use the
value on the third output port as the power level and direction. Only when
the 'assert' port was on would the hardware use the signal from the third
output port.
---Larry
+-----------------------------------------------------------------------+
Larry Coffin lcoffin@PointInfinity.com
Point Infinity http://www.PointInfinity.com
Nantucket, Massachusetts 508-325-6677 * fax: 325-6676
+-----------------------------------------------------------------------+
Cold, adj.:
When the local flashers are handing out written descriptions.
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Message is in Reply To:
 | | RE: What about multiplexing sensors?
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| (...) This seems like what I call a statistical multiplexor or "StatMux". Seems like it may be more difficult to implement (ie ROM decoding, writing drivers, etc.), but the advantage of freeing up an output port is really cool. The hardware to (...) (26 years ago, 11-Nov-98, to lugnet.robotics)
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