Subject:
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Re: Multiplexing Input Circuit
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 12 Nov 1998 15:59:07 GMT
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Original-From:
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Larry Coffin <lcoffin@pointinfinity.SPAMLESScom>
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Viewed:
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2334 times
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> I think Sven thought of this first. Anyway I threw a circuit together
> last night that uses the SetSensorType to switch between 4 inputs. I put
> it on a page at:
> http://ourworld.compuserve.com/homepages/Michael_Gasperi/mux.htm
> It seems to work well, but startup is a problem. It starts out on input
> 1 but if you stop the program it can get lost. I need to add a reset
> circuit. Any suggestions?
Looks good!
How about using the third input port to assert the reset line and
set the counter back to zero?
Is your counter set up as a binary counter? From your diagram it
looks like there are times that more than one sensor would be active -- say
on count 3 both O0 and O1 would be active, right?
Do you need to have bit 5 connected to the reset line? I would
think you could simply continue counting -- the other lines might go high
but the four lines you are using should just wrap back around.
I've been using the MAX337 and the MAX336 CMOS MUXs -- the 337 is a
dual 8 channel mux, the 336 is a single 16 channel mux. See the specs at
http://209.1.238.250/arpdf/1704.pdf (from
http://www.maxim-ic.com/efp/AnalogSM.htm). They cost about $6.50 each
through Arrow electronics (http://www.arrowamericas.com). With the counter
in binary mode you could run these MUXes to cycle through 8 or 16 sensors
(or more with multiple muxes).
From your diagram it looks like your sensors are sharing a direct
connection to the RCX input port. Did you have any trouble with orientation
of the contact on the RCX? When I tried the same setup (through my MUX
though) I found that I would get bad sensor readings when it was connected
in one orientation and good readings when rotated 180 degrees. I assumed
that there was something going on that had one sensor continue to feed a
signal back to the RCX even after it was not supposed to be selected.
---Larry
+-----------------------------------------------------------------------+
Larry Coffin lcoffin@PointInfinity.com
Point Infinity http://www.PointInfinity.com
Nantucket, Massachusetts 508-325-6677 * fax: 325-6676
+-----------------------------------------------------------------------+
Micro Credo:
Never trust a computer bigger than you can lift.
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Message has 2 Replies:
 | | Re: Multiplexing Input Circuit
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| (...) The counter is a CMOS decade counter that has only one output high for each count. There is only one analog switch on at a time. The counter is reset when it hits the value 5 so it jumps back to 0 to start over. The analog switch is (...) (26 years ago, 12-Nov-98, to lugnet.robotics)
| | | Re: Multiplexing Input Circuit
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| (...) The setup I was using was bi-directional too, I'm not sure exactly why I was seeing it, but I remember getting a high reading for a non-pressed touch sensor when the next one over (the previous one in the cycle?) was pressed. If I reversed the (...) (26 years ago, 12-Nov-98, to lugnet.robotics)
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Message is in Reply To:
| | Multiplexing Input Circuit
|
| I think Sven thought of this first. Anyway I threw a circuit together last night that uses the SetSensorType to switch between 4 inputs. I put it on a page at: (URL) seems to work well, but startup is a problem. It starts out on input 1 but if you (...) (26 years ago, 12-Nov-98, to lugnet.robotics)
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