New System Design: Distance between DS18B20s, Data Logging

Hello, Am designing a new project and want to collect data from a number of sensors, then log it to analyze patterns.

Would be grateful if I can get some design review / critique on a couple things.

  • Using an Arduino Mega1280
  • Collecting temperature, time, and unique sensor ID from DS18B20 sensors
  • Twelve (12) DS18B20s will be clustered in one area
  • Approximately 33 metres away, a second group of four (4) DS18B20 sensors.
  • Connecting the two groups via Cat6e underground cable.

  • ?Where should or can the Arduino be located?
  • Can it be located at either end without loss in reliability or complicating setup?
  • We are thinking about using Cat 6 underground cable to 'daisy chain' all sixteen (16) sensors together since much of this will be outdoor and the two groups of sensors will be separated by an outdoor distance of roughly 30 metres.

Any hints? recommendations? or flat out problems with this?

Is this possible or highly probable?

Am grateful for suggestions or highlights of anything that appears out of sorts (won't work.)

Thank you for your input and help.

Clinton

Hi Clinton,

The distances seem OK. I would suggest you run the DS18B20's in "powered" configuration, not "Parasitic Power".

How are you planning to group the sensors to Arduino pins?

It is often suggested to decrease the typical Pullup (4.7k) to less, like 2.7K or so, on longer runs.

Here's a guy running 20 of them: http://rik94566.wordpress.com/ http://rik94566.wordpress.com/2012/04/06/ds18b20-external-power-5-probes-working

I'd run DS18B20 ground and signal on one twisted pair, and 5V and ground on another.

Aquaponics / Aquarium guys do a lot of this..

I'd get all this working on the bench before burying the wire :) Let us know how it goes...

Info on the DS18B20 on the Arduino-Info WIKI here: http://arduino-info.wikispaces.com/Brick-Temperature-DS18B20

Thank you for the quick reply, terryking228.
"The distances seem OK. I would suggest you run the DS18B20’s in “powered” configuration, not “Parasitic Power”. "
This was/is the plan. We are guessing that it’s more likely to drive signals further and cleaner when separating out power from data. Is this why you recommend twisting each of them with their own ground wire, in order to drive signal further and cleaner?

“How are you planning to group the sensors to Arduino pins?”
Not exactly sure what you mean here, but we are thinking about soldering a cat 6e pigtail to the Arduino digital, power, and ground pins, then putting an RJ-45 jack on the pigtail to connect to the DS18B20 chain (cable.)

“I’d get all this working on the bench before burying the wire/…”
Yeppers! haha… good point.

Thank you for the links, look forward to your confirmation answers.
Clinton

Is this why you recommend twisting each of them with their own ground wire, in order to drive signal further and cleaner?

Yes.. Like both transmit and receive data in Ethernet are on their own twisted pair..

"How are you planning to group the sensors to Arduino pins?" ... Not exactly sure what you mean here,

Multiple DS18B20's can be run on the same wires (The software library is somewhat more complex, to address each sensor separately).. So you have choices of how many DS18B20's you connect on "1 wire" and then to an Arduino pin. Each sensor COULD go to it's own pin (with a LOT more cabling). Some sub-grouping may make sense...

Let us know how you make out!