Distance Temperature Sensing

Forum 2005-2010 (read only) Hardware Interfacing
1

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

2

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.

3

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?

4

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?

5

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.