Mick, The problem with 1-wire is that it is has "single ended" data communications signaling vs. "differential" in rs485 or ethernet over cat5. If you have the differential on a single twisted pair, the signal will be very resistant to external noise. With single ended systems, noise is always a problem. The more wire and the worse the environment, the greater the problem (think of it as a giant antenna.)
I attempt to mitigate the noise situation by wiring my sensors in a star configuration with the out to sensor and return from sensor on the same pair. The problem is that even with this, noise can occur on the ground. My wiring trades longer total length and capacitive loading to the master for less noise and easier wiring / debugging. I run a line out from the hub to the center of the star and then cat 5 to each sensor that is more than a couple feet from the start. There is also the issue with the amount of current you can push down the wire from the master to the last sensor (as well as the power drive capability of master itself) that can lead to unreliable sensor operation, especially in parasitic mode. You need to be careful of terminology. Hubs are things where all the devices see all the messages but there is some form of electrical separation from different sensor chains. Switches are things that choose which chain is attached to the master and only that chain hears the master commands. Hubs take no software support but switches take some software footwork, especially during search. OWFS does all the footwork for you. Maxim has made a 8 port switch forever. Ibuttonlink makes adapters with 4 port hubs built in. I use the ibuttonlink hubs, they work really well with my sensor networks. They separate the pullup for passive devices and allow me to have a stable network with sensors all over my home. I mostly have powered 18B20s, but also have a number of passive things as well. hope that helps, jerry On 01/25/2012 08:31 AM, Mick Sulley wrote: > I have noticed in other threads that many people use hubs in their > network. What is the advantage of splitting a network with hubs? I > currently have a single network with 25 DS1820's and a couple of > DS2406. I plan to extend this in the near future, so if there are > advantages to splitting it this would be a good time to plan it. > > Thanks > Mick > > ------------------------------------------------------------------------------ > Keep Your Developer Skills Current with LearnDevNow! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnow-d2d > _______________________________________________ > Owfs-developers mailing list > Owfs-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------------ Keep Your Developer Skills Current with LearnDevNow! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-d2d _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
