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79637RE: [Electronics_101] OPI-ONE cables again...

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  • Larry Beaty
    Dec 13, 2012
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      Chuck, nothing is ever too much for you to handle. You can research any
      topic you want and learn.

      Don't give up. I didn't.


      From: Electronics_101@yahoogroups.com
      [mailto:Electronics_101@yahoogroups.com] On Behalf Of chuck merja
      Sent: Wednesday, December 12, 2012 11:43 PM
      To: Stefan Trethan; Electronics_101@yahoogroups.com
      Subject: Re: [Electronics_101] OPI-ONE cables again...

      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

      On 12/12/2012 1:36 PM, Stefan Trethan wrote:
      > I haven't myself used a diode as temperature sensor.
      > There is some basic information here, or anywhere on the web really:
      > <http://www.tij.co.jp/jp/lit/an/sboa019/sboa019.pdf>
      > For the electronics, you could go the old fashioned way with an A/D
      > converter (10 bit internal to the microcontroller would suffice) and
      > some analog conditioning electronics. But there are more elegant ways now.
      > Turns out temperature measurement via a P/N junction is still very
      > relevant, like in computer CPUs and such. They make ICs that take a
      > diode input, and provide the data via digital interface like I2C. This
      > one for example, but there are also multiple input types:
      > <http://www.ti.com/product/lm82>
      > ST
      > On Wed, Dec 12, 2012 at 6:51 PM, chuck merja <chuckm@...
      > <mailto:chuckm@... <mailto:chuckm%403rivers.net> >> wrote:
      > Thanks Stefan,
      > And that Flaman pdf is a good find. I hadn't seen that. I already
      > have the old (DB9) cables in all my bins, but need to go to each
      > bin with a $150 cable reader that hooks to the DB9 cable end and
      > then allows me to cycle through the sensors on that cable and
      > record (WITH A PENCIL) the temps. I contacted the company about
      > getting an appliance that stayed connected to the bin, read the
      > temps a few times a day, (every hour ish??) recorded that data
      > and/or transmitted data over my farm wide WIFI to a location that
      > I could access from anywhere (internet). The company said I'd
      > have to REPLACE all cables with their new digital (2wire) system.
      > So I asked for a quote...I have 2 bin sites and thought I'd have
      > them do the easy one first... 7 bins... US$28,000! That's US$4k
      > per bin. So now you see my motivation to use the existing cables,
      > even if I have to have a microcontroller on each bin. And if done
      > correctly, I could add an in bin humidity sensor as well as one
      > outside with an outside temp sensor and I'd have enough info to
      > add automatic control to my bin fans and optimizing grain quality.
      > I've had some success with Arduino and DS18B20 and a generic
      > humidity sensor, so I'm looking for a way to read these existing
      > OPI-ONE (DB9) cables with an arduino (since I have several) or
      > similar unit. I'm thinking I could do the interpreting of old
      > cables, plus new humidity and temp for maybe $200 per bin, and
      > another couple hundred for motor starters and I'd literally have
      > something like $500 per bin in a data logging and fan controlling
      > (money saving and grain quality optimizing) system...a savings of
      > $3500 per bin times 20 total bins is like $70,000. And I "think"
      > it's within reach for me technically, so I'm motivated to get it
      > done before the $70,000 payback period, which is maybe 15 years:o))
      > So back to the cables...I just used auto ranging ohms to measure
      > the unenergized cables. Maybe that wasn't appropriate - another
      > poster on [arduinohome yahoo group] mentioned that ohms setting
      > might not have enough oomph to measure the diodes. I've got a
      > meter with diode tester and will go do that today.
      > The open circuit voltage referenced is on the cable reader with
      > the cable not attached (DB9 unplugged). I took apart the cable
      > reader to measure the voltages with the cable attached. The cable
      > attached voltages (0.6ish) are with the cable attached to the
      > cable reader and probed where the cables come onto the PC board.
      > Inside the OPI-ONE cable reader, the main chip is a 40 pin 3.5
      > digit A/D converter TC7106CPL 9641BC. There are 3 other 16 pin
      > chips and 2 14 pin chips that I haven't tracked down yet...
      > MC74HC4051W (8 channel multiplexer), MC74HC00N, MC14588CP,
      > MC145438CP, MC14070BCP. There are a few resistors - mostly 4 band,
      > but a few 6 band ones, a diode, a transistor or two along with an
      > LCD to display sensor # and temp. Looks pretty simple, except I
      > haven't found a couple of the chips. But this cable reader is 30
      > years old - seriously.
      > But can I do something like create this constant current source
      > (not sure how to do or how to say), multiplex that to the cables
      > and use an analog input of arduino to measure the voltage, then
      > use some math (calibration) or a lookup table to convert to
      > temp...? For bigger cables (up to 8 leads) I'd have to use a mega
      > (16?) or a multiplexer? Actually, after saying this, for testing,
      > I think I could just make a breakout of the DB9 connection and
      > plug those pins into an analog port of the Arduino to see what I
      > can see. How good is the A/D converter on the Arduino? might I
      > need better resolution? I noticed last night that 1 degree F was
      > roughly 0.00x Volts DC. Can I get resolution of 0.000x Volts DC
      > without going to a high cost A/D?
      > Thanks Again, C

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