On Thu, Dec 15, 2011 at 09:21:32PM +0000, Colin Law wrote: > On 15 December 2011 15:44, Nick <[email protected]> wrote: > > ... > > After fiddling a little and getting nowhere, I brought in my laptop, LA and > > some other kit to the office to explore more. Curiously, with my Dell laptop > > (and same LinkUSB master), the network was now 100% reliable. Plugged into a > > different Dell desktop in the office, again a disaster. > > This has got to be a big clue. One possibility that occurs to me is > that the 0v on the desktop may be connected to the PC chassis and > therefore earthed, whereas on the laptop it may not be earthed. Is it > possible that that there is another earth connection somewhere on the > bus so that you are getting an earth loop. this is possibly born out > by the other points you note below. It is absolutely imperative that > if you have an actual earth connection then that is at one and only > one point.
This is good electrical engineering advice. I'll add that my laptop, when plugged into the mains, produces a lot of high frequency noise, presumably capacitively coupled through the switchmode power brick. Laptops in general are a challenging thing to connect to electrically because they tend to float all over the place, reaching sufficiently high voltages to draw small sparks in some cases. I'm not sold on the different pairs having different predictable properties, they are all made the same way. I think this is just a function of the specific cable used. njh > > Colin > > > Default wiring was > > orange power, white/orange earth, blue data. Others unconnected but wired in > > the RJ45. > > > > I started experimenting. Here are some of the outcomes that improved things, > > and that may go against advice given from Maxim. > > > > * Attaching just the earth wire from my Saleae LA made the network 100% > > reliable (i.e. 50 to 95% failures reduced to 0 failures) > > * Using white/blue for earth rather than white/orange, plus a 10K pullup for > > the dataline, 95% to 99% reliability. > > * Adding a PIC 1-wire slave without or without connecting the data line, > > 100% reliable (now attaching LA ground reduced reliability) > > * As above but with white/blue for ground gave 100% reliability and no > > change if LA ground was attached. > > * On different PC, worse problems and the pullup was not so effective. > > > > I did some other tests, and the final route to near enough 100% reliability > > with a single sensor on the end of the run was: > > > > * Use orange for power > > * Blue for data > > * Blue/white for earth > > * Connect the other earths from the LinkUSB for the length of the run but > > not to the slaves > > * Add a 10K pullup, though this can be removed with my PIC slaves added. > > * It's possible that more slaves will also increase reliability but unknown > > at the moment. > > > > I'm assuming that this boils down to capacitance issues, and that the > > changes I made such as choice of what wires to connect for earth etc. simply > > affected this, but found it very surprising that the same setup would be > > fine with the laptop and yet a failure with other PC's (they are connected > > to UPS's in case that's relevant). Effects such as attaching the ground wire > > from the LA I found odd too. > > > > What I took from this is that changing what wires are used for earth in the > > cat 5 (or which earth from the master if there's more than one), and how > > many earths are used, could be critical and worth doing for anyone with a > > similarly misbehaving network. Guidance I'd read said not to connect other > > wires to earth, but this was wrong in my case. I would add that in contrast, > > the house network uses just orange and white/orange for power, and > > green+green/white for data and is fine as I said. > > > > I would welcome any views about why the experiments made a difference, such > > as different PC's, why laptop is fine and not PCs, connecting the LA earth > > etc. > > > > Nick > > > > > > > > ------------------------------------------------------------------------------ > > 10 Tips for Better Server Consolidation > > Server virtualization is being driven by many needs. > > But none more important than the need to reduce IT complexity > > while improving strategic productivity. ??Learn More! > > http://www.accelacomm.com/jaw/sdnl/114/51507609/ > > _______________________________________________ > > Owfs-developers mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/owfs-developers ------------------------------------------------------------------------------ Learn Windows Azure Live! Tuesday, Dec 13, 2011 Microsoft is holding a special Learn Windows Azure training event for developers. It will provide a great way to learn Windows Azure and what it provides. You can attend the event by watching it streamed LIVE online. Learn more at http://p.sf.net/sfu/ms-windowsazure _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
