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79655Re: [Electronics_101] OPI-ONE cables again...

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  • chuck merja
    Dec 14, 2012
      I'm not sure I understand your comments. There are a maximum of 8
      sensor wires and one ground wire in the cable. I'm not sure how this
      all occurs, but I guess that each of the sensor leads has a diode at the
      end of it and the other side of each diode is then tapped into the
      common ground cable. If this is true, then I definitely need to read
      these cables one at a time.

      But given that wiring, does your comment still apply, or do I just need
      up a single 8 channel mux?

      And can I dump the output of that 8 channel mux into one analog port on
      the arduino and read it there? We are talking about low end reading 0.4
      ish to 0.6 volts high end so a "full range" of 0.2 volts, is that going
      to be a problem in the arduino?


      On 12/14/2012 9:35 AM, Howard Hansen wrote:
      > On 12/12/2012 10:43 PM, chuck merja wrote:
      > >
      > > I got a better multimeter and checked the cable, which again contains
      > > sensors every 4 feet so we can see if there is any stratification in a
      > > grain bin. The diode function on the multimeter revealed a "OL" on one
      > > polarity and an 0.698 with the other polarity, when measured to the
      > > white (gnd) lead. So we have a diode on each of the lines in a
      > > cable...every 4 ft. These sensors and a 1/8 diameter steel cable are
      > > molded into a heavy HDPE coating that has allowed these cables to 30
      > > years. So I am not looking to replace the existing sensors in this
      > > tough cable with the digital DS18B20.
      > >
      > > In the existing data reader the lines come in and straight to a
      > > MC74HC4051N an analog multiplexer. No resistor, just straight in.
      > >
      > > So I think this leaves me hoping I can create a constant current source,
      > > and read the cables into the analog ports of an arduino. A poster on
      > > arduinohome thinks this might be too much for a limited electronics guy
      > > like me. Are there other votes about this?
      > >
      > > thanks, Chuck
      > >
      > One thing that may not be apparent is that you need to switch two signal
      > lines, use two multiplexers and a differential amplifier to convert the
      > diode signal to a single ended signal for use with a microprocessor like
      > an Arduido UNO.
      > Or you could use an Arduino compatible microprocessor that has a
      > differential A to D. This would eliminate the need for a differential
      > amplifier. But with 8 diodes per cable you still need two
      > multiplexers. A low cost Arduino compatible microprocessor with 8
      > differential inputs is a lot harder to find.
      > The other Howard.
      > [Non-text portions of this message have been removed]

      [Non-text portions of this message have been removed]
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