Logging temperatures from remote positions

I'd like to build an Arduino base project that can log data from thermometers. The thermometers would be placed at various places in a hall building, sub floor, slab (with hydronic heating elements), air, roof cavity and roof exterior (ideally).

The data would be logged to an SD card or some other at regular intervals. Purpose is to study ESD characteristics of the building and monitor effect mechanical air flow directed from sub-floor rooms to hall. May later be used to control processes but that's not important at present.

The distance of the sensors would vary from a few meters to perhaps 15m max but through materials like a 250mm bond-deck reinforced concrete slab and roofing metal. I'm expecting that rules out Wireless but I would have the faintest idea what I'm talking about.

Can I reasonable expect to get data across wires for those distances?

What kind of options are available for sensor devices that would suit say a 0-70 degC range. accurate to 1 dp would be great but 0dp adequate I guess. Anybody made a project like this before?

I'm totally new to Ardunio but in the 80s made a few things including a 7 PCB monophonic synth with thousands of solder joins so I'm game to go digital. ;)

The distance of the sensors would vary from a few meters to perhaps 15m max

Is this distance from the sensor to the Arduino? Or will you have multiple Arduinos with sensors on them?

Wireless communication between Arduinos with sensors and a central Arduino to log the data (or send it to a PC to store in a database) should be possible. If you can listen to a radio inside the building, or access a wireless router from a PC, you can communicate wirelessly between the Arduinos.

If you can string wires between the Arduinos, you could make them communicate using wires. Search the forum (or web) for RS485 (I think).

Google thermistors. There are a wide variety of them available, with different sensitivities and accuracies.

As was suggested you may not need to rule out wireless. The XBee's run at 2.4GHz. Unless you surround the radio with metal I would be surprised if you have a problem. A mesh of rebar is unlikely to be a problem. This is an easy test to perform

The XBees have an A/D converter so you would not need an Arduino. You would condition your sensors, program the XBee to transmit to an XBee attached to your PC. This is exactly the type of application XBee's (and the Zigbee protocol) were designed for.

If you decide you need or want a uC attached to the XBee checkout the boards I make -- http://www.wiblocks.com I make an Arduino compatible board with and XBee radio. I am also in the process of making some XBee standalone boards (some with battery power).

(* jcl *)

www: http://www.wiblocks.com twitter: http://twitter.com/wiblocks blog: http://luciani.org

Thanks jcl,

As well as the rebar, as it is a suspended slab on bondeck, the slab is poured into a steel tray (it's a bit like a clip-lock sheet metal roof). Not sure the thickness a few mm is my guess. I just thought wires would save dramas and reduce cost. No?

I'll check out these XBee devices. What's a uC? I'm new to all this stuff.

Thanks PaulS
“Is this distance from the sensor to the Arduino? Or will you have multiple Arduinos with sensors on them?”

Yeah I figured I could use one Arduino to log multiple sensors. Wired connects seemed to be A) cheap B) not likely to interfere with each other and C) one Arduino could talk to them all if it had enough pins.

I guess disadvantage may be that over longer wires, impedance may effect sensor output and much calibrating may be required for each thermometer/sensor. Also running wires is okay because the building isn;t built yet but moving them could be a hassle.

Hmm, project is starting to sound like a big undertaking, should I start with a beginners kit and get my hands dirty first?

Would a serial connection over wire to the sensors be possible without a micro-controller at each sensor, ie. a sensor with serial protocol chip sold as a premade (or kit) entity?

Yes. Please purchase a beginners kit.

Remember to only bite off as much as you can chew, but take big bites while you're at it.

Unless the radio is completely surrounded by metal I would be surprised if you would have a reception problem. It is something that you can easily test. The indoor reception distances are lower than the outdoor values.

For long wires I would use temperature sensors with a current output and twisted pair wires. These will be less sensitive to noise. A shielded twisted pair would be even better.

(* jcl *)