Wiring 1-wire to ethernet break out.

5 replies [Last post]
London, United Kingdom
Joined: 10 Jun 2010

Can anyone give me some pointers on this...I keep reading different material suggesting the use of different wires.

I'm now in a spin.

Glasgow, United Kingdom
Joined: 26 Oct 2009
No real 'standard'

Unless you intend to use pre-built sensors from a third party supplier, it doesn't really matter too much how you wire the RJ45 breakouts. The wiring standard shown at http://www.hobby-boards.com/catalog/howto_wiring_diagram.php?referer=howto_connecting.php is as good as any.


Lincolnshire, United Kingdom
Joined: 24 May 2010
There was a proposed 1WRJ45

There was a proposed 1WRJ45 standard available from here:-

http://www.1wire.org/en-us/dept_22.html  (page 13)

Not sure that this went anywhere, but the hobby boards pcbs and others (stuart poulton and Sheepwalk) use this.

Don't get confused by the T568A and T568B wiring standards. Use the T568A colour scheme as shown in both diagrams and stick with that standard

On a practical note, I have noticed that if you get the wires the wrong way round, the DS18B20 gets hot quickly, so when you plug it in, do so holding on to the sensor, unplug quickly if it gets hot to the touch. I have found they are normaly still functional even after this mistreatment 


London, United Kingdom
Joined: 10 Jun 2010
I don't know why I found this

I don't know why I found this so difficult, once done it all seems very straight forward...looking back.  Nevertheless, in an attempt to simplify, for others like me, here's the monkey version:

For details on the Dallas Sensors, go here.

You'll need some ethernet cable, I think any will do so long as it's cat5.  I also needed several RJ45 connectors, an RJ45 splitter for every sensor location and an ethernet breakout board.

I used the T568A standard to wire my "in-between" cable as suggested:

1 White/Green
2 Green
3 White/Orange
4 Blue
5 White/Blue
6 Orange
7 White/Brown
8 Brown

The table below describes how to wire from the HAH to the break out board as well as the RJ45 connector for the sensor end.

NOTE: On the breakout board, pin 1 is on the left as you look at the front of the socket.

NOTE: On the RJ45 connector, pin 1 is on the left looking at the aperture of the socket with the clip at the bottom.


My sensor was one of the sealed external sensors rather than the ones provided by Derek.  This had a 1/2 meter long tail on it with White, Red and an unshielded wire (I assumed Gnd).  It was a bit tricky to make sure the 3 wires went into the right 'slots' in the RJ45 connector but it was doable.

Pin Sensor Wire
1 Black Gnd White/Green
2 Red Vdd Green
3 empty
4 White Data (DQ)
5 empty  
6 empty  
7 empty  
8 empty  

SUGGESTION: If you are using the sensor provided by Derek, you could just simply solder the feet of the sensor to the appropriate coloured wire of the ethernet cable, using some heat shrink on each leg to prevent contact.  If the run is short enough, you could pull the ethernet cable sleeve back over the sensor so it sits covered snuggly at the end.

I have plugged the ethernet splitters between the sensors and the "in-between" cable so that I can add other sensors onto my 1-wire bus:

Hope that clarifies it a little.

United Kingdom
Joined: 11 Jun 2010
Be Careful

If you are only using your CAT5 cabling for 1-wire devices then there is nothing wrong with this, in fact it doesn't matter which wires you use.  

The pins/wires you're suggesting people use WOULD be dangerous if you had anything else connected in a CAT5 network.  Pins 1 and 2 are normally used for data, pin 4 isn't used in a 10/100Mb network.

I have made up a suitable connector for using CAT5 and connecting to the HAH PCB, I'm happy to write this up on the wiki if people are interested.

I'm not saying your wrong Gary, as long as the wiring you use isn't used for anything else.  A lot of people are now starting to put CAT5 around their houses and the information you've provided could lead to problems if shared with normal ethernet devices.

London, United Kingdom
Joined: 10 Jun 2010
Wow, it hadn't even occured

Wow, it hadn't even occured to me that people might mix the two together.  I only wired my "in-between" cables fully because I thought they might get re-used at a later date.


Did I misinterpret the the spec then with my wiring?

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