DS18B20 1-Wire on noisy lines over CAT5E cables

Projects Networking, Protocols, and Devices
1

I have this 1-Wire issue I have been trying to solve for quite some time...

I'm running 2 or 3 DS18B20 temp sensors over a kitchen into the freezer, less than 20m, a very noisy environment, initially using UTP (unshielded twisted pair), first picture, and later using FTP (foiled twisted pair wrapped) but still cannot solve the problem on having more than one sensors on the same bus.

Laster I found out the wiring guy did not terminate the small conductor wires ( shown in pic4 ) and not using a metal RJ45 socket and therefore I did not get any grounding on both ends ...

The sensor end is stuffed and packed into the freezer near the compressor using a long 2m flat RJ45 cable (unshielded) ....

My circuit diagram is as follow ( last pic ) :-

  • 2.2K pullup to 3.3V
  • 3.6V zener protection diode
  • 1K on the wire
  • Jumper is soldered

I'm suspecting a "mismatched impedance" and lots of signal bouncing to and from both ends....

Can anyone please suggest how do I :-

Q1. Remove or reduced the impedance mismatch ?

Q2. How to further troubleshoot this ?

Q3. Reduce the noise or improve the SNR ?

Q4. Do I need to use a higher value resistors on R7 ( currently 2.2K ) ??

Thank you for your time to read this long post...

Stanley

Cable 1 UTP
UTP cable - noise level

Cable 1 FTP
FTP cable - noise level

Cable 1 - compare
Comparing UTP vs FTP noise level

Both end not connect to the RJ45 jacks/grounded

1-wire sch

2

Have you tried connecting the shield only at the arduino end? No shield ground to the shield at the sensor end.

3

Did you properly use the 4 pairs of twisted wires in the CAT-5 cable? One wire of each pair is for signal the other wire of the pair is ground.

Paul

4

I have successfully used cat5e utp with the same sensors at a distance of 25m.
Just make sure you use one pair for data/ground and Vcc/ ground on another pair.

5

A commercial solution

6

Thanks ...

I m looking for 1-Wire solutions, not I2C ... BUT the suggested solution is something I am also looking for in the future for extending long I2C connections ..

Good find ....

Stanley

7

Paul_KD7HB:
Did you properly use the 4 pairs of twisted wires in the CAT-5 cable? One wire of each pair is for signal the other wire of the pair is ground.

Paul

I use the following pinout for RJ45 :-
pin 1 - 1-wire
pin 2 - unconnected

pin3 - unconnected
pin6 - unconnected

pin4 - 5V
pin5 - Gnd

pin7 - 3.3V
pin8 - Gnd

8

1-wire still requires a ground to make a complete circuit. Try it.

Paul

9

I have 20 DS18B20 temperature sensors connected via 1-wire, I pulled up DB line to 5V via a 2.4K resistor to charge up the capacitor in the temperature sensor. I am only using one twisted pair wires. How are your sensors wired? I allow some time for the capacitor to charge up in-between communications. On your schematic SJ1 is shown as opened?