DS18B20 One Wire Temp Sensor Long Cable Run

Forum 2005-2010 (read only) Hardware Interfacing
#1

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.

#2

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.

#3

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.

Ran

#4

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

#5

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

#6

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.

.

#7