79637RE: [Electronics_101] OPI-ONE cables again...
- Dec 13, 2012Chuck, 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.
[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?
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:
> 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:
> 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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