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Redmond, WA
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The project I'm working on needs to monitor temperature in two places. One, at the location of the Arduino.  Two, about 70 feet (20+ meters) away.

Can I just solder reeeeealy long lead wires onto that temperature sensor, or will goofy electronics effects I know nothing about come into play to mess me up?  And if long lead wires aren't going to work, what should I do?

Any and all advice greatly appreciated.
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Georgina Ontario
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Which sensors? Which interface style? What sampling rate etc.


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or will goofy electronics effects I know nothing about come into play to mess me up?

Yes.

It depends on the sensors. The best bet generally is to convert the temperature to something that can be transmitted down a long wire. Like a temperature to frequency conversion, then long wire, then measure the frequency.
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Well, the sensors I happen to have on hand (well, at home) are Phidgets sensors; I don't know specifically what part numbers they are.  But, they come with an easy-disconnect connector, giving access to the sensor board's raw analog +/-/ground lines.  I was planning on plugging these straight into the Arduino's analog inputs.  I'm certainly willing to buy something else if it's affordable and is in some way just the thing for the job.  Basically, I'm open to anything that will help me just get the job done.

I would, ideally, like as few wires as possible running over that 70 foot span.  I would DEFINITELY like to avoid the complexities of separate power et cetera for the remote location.

Given that I haven't the slightest idea how to do voltage/frequency conversion but am willing to learn, can somebody point me towards specific parts, schematics, tutorials, or whatever that can at least get me started down the right road of research?  At the moment, I know little enough that I feel like I'm fumbling around in the dark.  Thanks!
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Manchester (England England)
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I don't know specifically what part numbers they are.

That's the important bit.

No plugging 70 ft of wire into the analogue input is not going to cut it. It will pick up all sorts of electrical crap and give you erratic and unreliable readings.

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I would DEFINITELY like to avoid the complexities of separate power et cetera for the remote location.
But you could run this power over the lead that connects the sensor to the arduino. Three core cable should do it.
 Look at:-
http://www.analog.com/en/analog-to-digital-converters/voltage-to-frequency-converters/ad537/products/product.html
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Georgina Ontario
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Best thing is to go to the specs and other people who claim to know them... smiley

http://www.i2cchip.com/i2c_connector.html

Find the Phillips specification for the I2C bus -- sometimes Called Two Wire Interface or TWI.

It can be pretty tolerant.

Forgot -- I saw 10 Meters and I am running two meter cables now...
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It can be pretty tolerant.

Come on you are not going to get 20+ meters from I2C are you!!!
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Thanks, Grumpy_Mike.  The AD537 looks like a good option.  The datasheet even includes a helpful two-wire schematic with frequency-to-voltage conversion on the receiving end!  Looks like that, plus some experimenting, calibration, and a bit of software will do the job.
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I have done the 20 meter length with LM35 and CAT3 (i would guess that CAT 5 maybe better). 0.1uf caps and all is good.  This has been working for 3 years sensing the temp of my solar collector for my pool. The caps are necessary in this config. For higher accuracy, other solution are superior.You could try it and monitor with a scope or dvm
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The Dallas 1-Wire chips that are popular for all sorts of reasons might be a good alternative. 70' is pushing things a bit... but not terribly. (Try the set up first with shorter runs, then extend.

They have the advantage of turning the temperature sensed into a digital signal before it is sent off to the monitoring silicon intelligence across the long wires. Checksums are included, if the importance of the data is such that you can be bothered to check the checksum. With LM35s, you have an analog signal, and it will pick up artifacts along the way.

What wire you use will make a big difference. For 1-Wire work, Cat-5 seems to be a good choice.
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field road, jupiter creek
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I'm using SHT15 temperature and humidity sensors in my "Barnduino" project.
In the data sheet they recommend leads no longer than 8cm!!
I'm going to us an ATMEGA328 at each sensor point, 4 per barn and then run RS232 back to a Seeedstudio mega clone, then transmit the data via XBee to the house, the office, my desk and my portable terminal thing.

If that sounds like overkill, bear in mind the ATMEGA328's in the barn will also have 2 Seeedstudio water flow sensors attached as well.


Probably still overkill, but hey, it's fun and there is not much else to do here in them thar hills!
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I'm using SHT15 temperature and humidity sensors in my "Barnduino" project.
In the data sheet they recommend leads no longer than 8cm!!
I'm going to us an ATMEGA328 at each sensor point, 4 per barn and then run RS232 back to a Seeedstudio mega clone, then transmit the data via XBee to the house, the office, my desk and my portable terminal thing.

If that sounds like overkill, bear in mind the ATMEGA328's in the barn will also have 2 Seeedstudio water flow sensors attached as well.


Probably still overkill, but hey, it's fun and there is not much else to do here in them thar hills!

You may want to consider using ATTiny's for the remote locations.

A couple days ago, a bunch of blogs posted about the Arduino IDE getting board definition files for the ATTiny's used in the BLinkM "Smart LED"'s

Here's the project site,
http://code.google.com/p/blinkm-projects/wiki/BlinkMuino

I only heard of this recently and haven't had a chance to come up with any projects let alone order parts/try it, but I don't see why you couldn't just run SoftwareSerial to achieve what you want.


This solution really isn't going to make much of a difference cost-wise (maybe $5 total), but personally, I'd feel really peeved about using a whole 328 to read 2 sensors and transmit to a host arduino. smiley
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Georgina Ontario
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And read up on I2C -- you may want to set up remote sensors with battery power.


On these questions always go back to the specs

http://www.nxp.com/acrobat_download2/literature/9398/39340011.pdf

http://ics.nxp.com/products/i2chubs/

Long Distance I2C or SMBus
The P82B715, P82B96, and PCA9600 are specifically designed to extend the reach of the I2C or SMBus over long distances, in the range of kilometers, depending on the maximum bus speed. This allows the designer to use I2C to interconnect equipment cabinets or for large area systems such as warehouse pick and place systems.
The P82B96 and improved PCA9600 use a static level offset on the slave side to isolate noise and loadings on either side of the device, allowing 4000pF on the high drive side. The nominal offset is 0.8V. That VOL level may create worst-case design tolerance problems with slave devices that do not use I2C switching levels, for example TTL levels. It also precludes operation with other bus buffers using special non-compliant I2C levels. A lower VOL level (<0.4V), combined with the ability to operate with any master, slave, or bus buffer, is the primary advantage of using the P82B715 for long-distance buses, but it doesn't isolate bus capacitance the way the P82B96 and the improved PCA9600 do, so the total system loading must be less than 3000pF.


You just need to use the search engines...
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