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Topic: Distance Temperature Sensing (Read 640 times) previous topic - next topic

robstar

Hi guys,

I recently got the arduino and love it.. this is the development kit I've been looking for!

I have a small project where I need to sense the temperature in a couple of apartments from an electric closet in the hallway.

I bought a couple of Microchip 9701s and have them returning values to the A/D on board.

My big question is distance.  How far I can pull these thermistors and still get an accurate reading ?  50 feet? 100 feet? I also need to put them in some sort of enclosure and pull power to them..

is there some other solution / module I should be looking at for this type of application??

Thanks for your help.

Rob

Anachrocomputer

I'd say 5 feet is about the limit.  Sorry to disappoint!  I assumge you are referring to the Microchip MCP9701 Linear Active Thermistor:

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en022290

The trouble with long wires is that they not only have resistance, but they also pick up noise, particularly 50 or 60Hz power-line noise.  To make a longer cable, you might try using a screened type, and add a voltage regulator at the far end (near to the MCP9701).  The screening would shield the signal voltage coming back from the device.

robstar

I'm searching around and see people have interfaced the Dallas DS18B20 with the arduino.

This looks perfect as long as I can pull it with parasite power (1 wire) up to 100 feet .. will this work?

robstar

Upon more research it looks like this Dallas chip will do what I want .. and there's tons of info here!!

I'm just getting into hardware interfacing so I'm not sure which to order..   is the TO92 model the most popular?


Anachrocomputer

TO92 is a package specification, a small D-shaped plastic thing about 4mm long.  It's the same size as many popular plastic-packaged transistors.  So yes, it's probably the one to go for.

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