Subject:
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Re: light sensor multiplexer
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Newsgroups:
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lugnet.robotics.rcx
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Date:
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Thu, 22 Mar 2001 14:18:17 GMT
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Viewed:
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1876 times
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"Nitin Patil" <gn1721@lycos.com> wrote in message
news:GALoKA.Eto@lugnet.com...
> In lugnet.robotics.rcx, Michael Gasperi writes:
> Ok I agree what you say about time constant of your RC
> But still by using such low resistance you are wasting power. almost 1.5 • mA
> is flowing through this 4.7K.
> you can keep RC constant and increase R that should improve performance.
> what I do is I have 5.2V zener in series with 120Kand 10pF this takes
> current of 40MicroAmp.
If you use my simple approach, you need 4.7k and around 0.1uF. You need a
low enough resistance to guarantee that the voltage drops to CMOS logic
level 0 for the clock on the 4017 to work. Even during the passive mode the
RCX is trying to pull the sensor up to 5V through a 10K. My way does take a
little power, but you don't need the zener. The 1.5mA is essentially the
whole power requirement of the mux and since it is designed for resistance
or voltage type sensors it doesn't matter how much power it uses anyway.
The important thing is it doesn't effect the reading.
Depending on how you write the RCX software, my mux design is just as
"random access" as yours. My mux sequences through the channels in order,
but you don't need to stop to take a reading if you aren't interested in
that channel's value. It's just a matter of keeping track of the channel
number the mux in on in the RCX and not the mux itself.
The total parts cost of my mux using Mouser prices is only $2 w/o a pc
board. You probably pay $5 just for the micro in yours. Your design has
the capabiliity of driving multiple powered sensors like the LEGO light
sensor but my design does not. It is a cost/functionality tradeoff.
I'm not criticizing your work, I think it is amazing that you can build such
a mux and sell it packaged for only $30. I'm sure we all look forward to
seeing how you did it. I just want to set the record straight about the
incorrect statements you have made about my mux design.
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Message is in Reply To:
 | | Re: light sensor multiplexer
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| In lugnet.robotics.rcx, Michael Gasperi writes: Ok I agree what you say about time constant of your RC But still by using such low resistance you are wasting power. almost 1.5 mA is flowing through this 4.7K. you can keep RC constant and increase R (...) (24 years ago, 22-Mar-01, to lugnet.robotics.rcx)
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