Temperature Probe, long distance

Forum 2005-2010 (read only) Hardware Interfacing
1

Hy,
i would like to take the temperature outside of my house and inside and make a difference between those two.
To climate the house.
In summer, if it is cooler outside then inside then start the air exchange to get that cool air (let say at night)

But i got a issue for the probe, if i use a DS18B20+ then i cannot bet to far from the sensor, and if i use a analog type i am scare that i will get i drop in a long run of wire.

I would like to put the Arduino inside so i am probably taking about a 20-30 feet wire run.
i was thinking of using a differential transmitter (rs-485) locally at the sensor (with another arduino) to send the temp
Any suggestion?
Anything simpler but stable and precise?

Thanks
Pat Gadget

2

did you consider a thermocouple?

http://isefaq.com/ActiveKB/questions.php?questionid=27

3

Well... Thermocouple don't interface easily with Arduino.
but Nice Idea. i will look into that also

Thank

4

I have several one-wire runs that are close to 40 feet. I use 4 wire alarm wire. The only issue that I had was if I mixed parasite mode power - so now I just run 3-wires to each 18b20 and it's been working great for over 6 months.

as a note on with the playground example I used (anyways that's what I think I used): it was set up for the 18s20 - so it couldn't find mine until I killed the device checking part of the code. It was also set up for parasite mode it worked with 3-wires as well but after the fact I was able to change the power up flag and remove charging delays that are needed if you use parasite power option.

5

i am scare that i will get i drop

Huh? What?

6

Use a 10k NTC thermistor. You can run the wire for a long way (~200ft).

7

For this reason: The accuracy will be worse rhan 1% anyhow, which gives you round about 100 Ohms to play with. If you want better accuracy you have to calibrate the specimen anyhow; doing this "in-situ" will calibrate it including any wire. There are some ways to do the calibration....

There is a difference whether you drive it with constant current or use a voltage devider. In the latter case the software has to handle some non-linearities when you want to get +/-1K.

8

I've used a DS18B20 on a long run of wire for a Cloud Sensor from my garden. The wire is about 20 metres long and it works fine.

9

.. and it will also work with a 300m wire with highest precision :slight_smile:

10

Just another idea to throw into the mix; I've used Analog Devices' AD590 temperature transducer. It's output is a current that is proportional to absolute temperature.

It won't care how long your run is.

11

good idea for the current one.

Perfect i have a bunch of 18B20 in stock so i will use them.
i was worry because i did a project with a bunch of 18b20 in parallel and after a few connection it failed.
i did connect them in a star fashion though.

Thanks you all guys, i will keep you inform of my ventilation project.

Pat Gadget