79655Re: [Electronics_101] OPI-ONE cables again...
- Dec 14, 2012I'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]
- << Previous post in topic Next post in topic >>