DS18B20 One Wire Temp Sensor Long Cable Run

I know there is a need to put a pullup resistor on the Dallas one wire temp sensor. My questions is where do I put it on a long cable run, near the temp sensor or near the Arduino? Does it matter?

Also, any other suggestions or ideas for placing a temperature sensor about 75 ft. from the Arduino is appreciated.

Adjust the value of the pullup resistor to create a stronger pullup. IE; if you are using 4.7K with a short, I would change it to 2.7K with a longer cable.

I'm currently doing this.

Maxim has an app note specifically about long cables: http://www.maxim-ic.com/appnotes.cfm/appnote_number/148

Google also turned up #132: http://pdfserv.maxim-ic.com/en/an/app132.pdf

There may be others.


what is the limit for short vs. long, and how long is too long?

Does the resistor goe near the sensor or where it connects to the arduino?

Are you using it with or without dedicated power ? The data sheet kind of implies 25 metres with a 5v supply (ie not phantom power) and cat5 twisted pair cabling without couplers is OK.

Personally, I’d suck it and see with the pull up resistor at the arduino end.