A bit of 1-wire wire help please.

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  • Collectors
    Automated Home Jr Member
    • Mar 2009
    • 19

    A bit of 1-wire wire help please.

    I will be wiring the house with many 1-wire points for monitoring various sensors. (Mainly heat) I hope to do this with using rj45 outlets with a plug-in lead to each of the sensors.
    Am i ok to just come from each rj45 outlet with a 1 or 2 meter lead & just using 3 cores of cable to monitor the sensor? Or would i be better making the leads up as a 6 core lead so i can still keep the sensor next to the main run of cable.
    Naturally if i used the 2nd method i would make up a bridge for any rj45 outlets if no sensors where used.

    Thanks

    Chris.
    Regards Chris.
    Barnet Walks
    Collectors-info
  • tabath
    Automated Home Jr Member
    • Apr 2008
    • 12

    #2
    From what I read of one-wire you only need 2 cores, one for data and one as ground. I also think it works on a bus and not star topology.

    Comment

    • toscal
      Moderator
      • Oct 2005
      • 2061

      #3
      You actually need 3 wires one for ground, one for data and one for power. 4 core is normally used just to provide a return for the ground.
      More information here http://www.maxim-ic.com/products/1-wire/
      If you ask them nicely you can often get a sample of one or two temp sensors or similar, just click on the sample link on the left hand side.
      Another link is http://www.audon.co.uk/1-wire_index.html

      Also on the audon site http://www.audon.co.uk/1-wire_weather.html almost near the bottom is an RJ45 connection diagram. This may help you.
      IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
      Renovation Spain Blog

      Comment

      • tabath
        Automated Home Jr Member
        • Apr 2008
        • 12

        #4
        Originally posted by toscal View Post
        You actually need 3 wires one for ground, one for data and one for power. 4 core is normally used just to provide a return for the ground.
        More information here http://www.maxim-ic.com/products/1-wire/
        If you ask them nicely you can often get a sample of one or two temp sensors or similar, just click on the sample link on the left hand side.
        Another link is http://www.audon.co.uk/1-wire_index.html

        Also on the audon site http://www.audon.co.uk/1-wire_weather.html almost near the bottom is an RJ45 connection diagram. This may help you.
        No , they only use 2, the data and power use the same wire, data is sent by pulling down the voltage on that wire.

        Comment

        • toscal
          Moderator
          • Oct 2005
          • 2061

          #5
          Your not quite correct there. As it all depends on what mode you want to run the sensor in. If you have only one sensor then parasitic mode will indeed use only the ground and data line, but you have to ground the power line (Vdd). If you are running them on a bus topology, so using more than one sensor it is recommended to use an external supply connected to the Vdd pin. Maxim also recommend the use of an external supply. When using parasitic power data transmission and timing become much more of an issue as does high temperatures if the sensor is a temperature one.
          So that is why I said three wires.
          Have a look here
          Last edited by toscal; 20 November 2009, 02:03 PM.
          IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
          Renovation Spain Blog

          Comment

          • TimH
            Automated Home Legend
            • Feb 2004
            • 509

            #6
            Originally posted by toscal View Post
            Your not quite correct there. As it all depends on what mode you want to run the sensor in. If you have only one sensor then parasitic mode will indeed use only the ground and data line, but you have to ground the power line (Vdd). If you are running them on a bus topology, so using more than one sensor it is recommended to use an external supply connected to the Vdd pin. Maxim also recommend the use of an external supply. When using parasitic power data transmission and timing become much more of an issue as does high temperatures.
            So that is why I said three wires.
            Have a look here
            http://datasheets.maxim-ic.com/en/ds/DS1822.pdf
            Yup, two or three wires for "1-wire"
            IIRC it's around 80degC temps that the 3rd (power) wire is needed.

            I'm still figuring out the best way to wire mine up. There were some commerial enclosures with either RJ11 or RJ45 sockets to allow bus loop-through, but when the sensors are really tiny, a large matchbox-sized box look sreally out of place

            Cheers,

            Tim.
            My Flickr Photos

            Comment

            • Quinten
              Automated Home Sr Member
              • May 2004
              • 85

              #7
              Just rehouse them?

              Mine look like these:







              More here
              Awooga!!!

              Comment

              • Collectors
                Automated Home Jr Member
                • Mar 2009
                • 19

                #8
                Thanks guys, but the room temp i should be able to sort in a similar way to Quinten has done. But there will be about 8 points that may have temperatures up to 100c & wont be able to run the cat 5 near this. This is where i wanted to make up some 2 meter fly leads with silicon heat proof cable with a DS1822 on the end. But wasn't sure if i should run 3 core only down the lead or 3 in & 3 out from the DS1822.
                Last edited by Collectors; 20 November 2009, 07:40 PM.
                Regards Chris.
                Barnet Walks
                Collectors-info

                Comment

                • toscal
                  Moderator
                  • Oct 2005
                  • 2061

                  #9
                  Always run more wires than you need, you never know when you will need the extra wires.
                  IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
                  Renovation Spain Blog

                  Comment

                  • Simon300
                    Automated Home Jr Member
                    • Apr 2010
                    • 34

                    #10
                    Originally posted by Collectors View Post
                    Thanks guys, but the room temp i should be able to sort in a similar way to Quinten has done. But there will be about 8 points that may have temperatures up to 100c & wont be able to run the cat 5 near this. This is where i wanted to make up some 2 meter fly leads with silicon heat proof cable with a DS1822 on the end. But wasn't sure if i should run 3 core only down the lead or 3 in & 3 out from the DS1822.
                    Sorry to dig-up an old thread but this is exactly the same question as I have now...
                    I am using 1-wire for CH zone control so am looking to put temp sensors (DS18B20) in several rooms. An initial thought is to drop the sensor plus cable down an existing conduit (to get them to a more representative height in the room) and join it to the 1-wire bus above the ceiling.

                    Looking at Maxim's Reliable Long 1-wire Networks doc (http://pdfserv.maxim-ic.com/en/an/AN148.pdf) they call these drops to the sensors "stubs". They call the network a "linear topology" (page 2) if the stubs are shorter than 3m or a "stubbed topology" (page 3) if longer.

                    It would appear that the linear topology will give the most reliability, and possibly the 3m value is fairly arbitrary.

                    The standard 1-wire RJ45 wiring seems to be:
                    1=GND (power)
                    2=Vdd 5V
                    3=? GND or not connected?
                    4=DQ
                    5=GND (data)
                    6=not connected
                    7=unregulated 12-24V
                    8=GND unreg

                    So, like Collector, I was also thinking should I drop the DQ and GND down to the sensor and then "back up" again - in other words, passing the network via the sensor so that there is no stub?

                    The advantage of this is that you reduce the number of stubs. The disadvantage is that you increase the length of the network ("radius" in Dallas/Maxim terminology) by, say 3-4m, per drop.

                    Assuming I only want to drop one, not two, CAT5 cables to the sensor (I'm using the Clipsal pink cable which isn't too big) is this a good idea? If so, what pins/cores do people use? You'd want DQ/GND on another pair so "incoming" could be 4+5 and "outgoing" could be 3+6? Then the ceiling/void bus connector would have 3 RJ45s with 2 "bus" sockets and one "sensor" socket. All would have 2, 7 & 8 connected. "Bus" A would have 4 connected to "sensor" 4 and 5 connected to "sensor" 5. "Bus" B would have 4 connected to "sensor" 6 and 5 connected to "sensor" 3. The sensor end, or a bridge made from an RJ45 plug if no sensor fitted, would connect 3 to 5 (GND) and 4 to 6 (DQ).

                    Of course if you put sensors in the ceiling, like Quinten has, this is a non-issue . However there may still be situations where you really want to branch off the 1-wire network only running one cable where this technique would be better.

                    By the way, where did you get your little PCBs from Quinten?


                    Simon

                    Comment

                    • Quinten
                      Automated Home Sr Member
                      • May 2004
                      • 85

                      #11
                      I got mine made by a member on the ukha_d yahoo group/#ukha irc group called Stuart/Gadget. Pretty sure he's a member on the forums too.

                      My 1wire network consists of one long chain of modules, going from the center of the garage (where my node0 lives) through the outside wall, into the bathroom (hard to explain, but it's the easiest way to get cables up in the loft), through the airing cupboard in the middle of the house, into the loft and then from room to room. All in all, I think it's about 30-50m of cat5 cable. And although I'm still running in parasitic power mode, I've yet to experience any problems with sensors falling of the network. It is surprisingly reliable!

                      Future plans involve a sensor in the living room and kitch, but they aren't easy to reach without major refurbishment
                      Awooga!!!

                      Comment

                      • KW1816
                        Automated Home Jr Member
                        • Feb 2004
                        • 28

                        #12
                        Timely discussion as I've just re-run my own 1-wire network. Previously I had a bit of a mix of cables (though all cat 5e) and the odd long stub where I'd decided to add an extra sensor later. Although it worked It did suffer from the odd sensor going missing and slow updates sometimes.

                        I've replaced all the existing cabling with a new run of Cat 5e that loops in and out of each sensor location. I decided to go external powered due partly to the number of sensors (25) and partly to future proof it in case I decide to add any devices that require power. It's not actually powered at the moment but the option is there.

                        I see you can get pre made modules from ebay (http://cgi.ebay.co.uk/SWE1-DS18S20-T...item1e5e1cd2f7)

                        I took a slightly different route that's a bit more heath Robinson - I didn't fancy terminating each cable in a RJ45 plug twice at each location so I used keystone RJ45 sockets, double punched with the 'In' and 'Out' cables, heat shrinked and cable tied to provide some mechanical support. I know double punching IDC connectors is frowned upon but in my experience, as long as the cables are identical, you can get away with 2. I then soldered the temp sensors onto a short length of premade patch cable (about 1") protoected with a bit of heat shrink. These then simply plug into the keystone sockets and are housed in the same enclosures as earlier in the thread - I got mine from CPC and sprayed them white to match the ceilings.

                        Got all the 1-wire parts from Hobby Boards who I would recommend:


                        Nice guide from Maxim on long networks and loads:


                        Cheers
                        Kevin W.

                        Comment

                        • Simon300
                          Automated Home Jr Member
                          • Apr 2010
                          • 34

                          #13
                          Thanks Quentin & Kevin W for your updates. It's nice to hear that 1-wire can be very reliable - sometimes it's easy to get bogged down reading about problems.

                          I like Kevin's idea for just using one RJ45 socket per junction - the 1-wire cabling is fixed and the socket is only allowing for easy sensor installation/replacement so 3 sockets could be overkill. I don't suppose there's much to worry about from having two cores installed in one slot - the blades are parallel for a mm or two anyway. Plus if I go for this idea of having pins 4-5 going to the sensor and 6-3 coming back the only pin doubled up would be 2/Vdd (unless I looped through 1 and 7 & 8 - I can't really see the need at the moment though).

                          BTW: I've got my eye on http://www.hobby-boards.com/catalog/...oducts_id=1554 so will probably get one shipped over from the US. Thanks for the recommendation.

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