Date: Thu, 2 Jun 2016 00:19:21 +0200 From: Jan Kandziora <j...@gmx.de> Subject: Re: [Owfs-developers] Concurrency issues? (Jan Kandziora)
>> Wouldn't parasitic power onewire be symmetrical? >> > Colin Law asked the same in > <CAL=0glsp6xab4p-1vsyso-kehbwc9-fkxgr29hyaiaodudy...@mail.gmail.com>. > > I drew a circuit with noise sources in response. Here's how I'd think about the added cable capacitance of twisted pair: Host Pullup Cable... 1W Device ____/\ /\ /\ ____________________________________________... | \/ \/ \/ | | | | | | O = = = = = | | |____________________|______|______|______|______|______|____... It is evenly distributed along the entire cable. For noise originating at the host adapter, I agree the effect is limited by the pullup. But for noise originating along the cable, which I assume to be the problem in my environment, where DC power to relays and motors runs in the same conduits as the 1-Wire bus, it seems to me the cable capacitance is entirely symmetric. If the noise is reduced along the cable, it won't propagate back through the pullup to the 1-Wire host. But it seems to me like you've drawn cable capacitance from the two active conductors to some separate ground which connects back to the host independently, maybe other grounded conductors in the same cable. Even in that case, I'd think twisted pair would reduce the coupling between adjacent pairs, reducing the assymmetry. (All my documentation sources say unused conductors should not be grounded.) Maybe you're assuming the noise originates inside the host adapter, and thus on the other side of the pullup from the majority of the cable capacitance? > Mobile phone is the most likely culprit. Only one carrier has service here, and they're ~8 miles away, under -90 dBm. And they're CDMA, typically invisible even to intentional "bug detectors". My phone can be anywhere in the house, makes no difference. But there is a US "Military Operations Area" over the next ridge... I just searched my collection of 1-wire documentation. All of these specifically recommend twisted pair: Maxim 132 1-wire requirements Quick Guide.pdf Maxim 148 1-wire guidelines.pdf Maxim 244 Advanced 1-Wire Network Driver.pdf Maxim tb1 1-wire hdwre interface.pdf The last one, "Tech Brief 1", has a deep discussion of cable parameters, with great graphs of the relevant effects. "Figure 6 Electrical Equivalent Circuit of the 1-Wire net" is way more complete than my drawing. This document also recommends twisted pair, and provides many interesting clues: <http://www.108relays.ca/dl/1_Wire_Design_Guide_v1.0.pdf> "... examine the twist count for each pair and use the pair that has the most twists per inch." They show that the "Silver Satin" flat phone cable previously used for 1-wire is actually worse for capacitance than CAT5. "Note that the capacitance figures are lower in the twisted pair cable, both in the wires [pairs] and in between wires. This is very important, as wire lengths get longer." (I guess an untwisted cable with bigger wire and thicker insulation might change those numbers.) How's this for detail - it matters exactly where on a daisy cable you attach your slaves! "FIGURE 3 - Any discontinuity on the line, including slaves can cause reflections. Locations that are at integer fractions of the line length are particularly problematic as they can resonant." Probably irrelevant for most installations, but here's my setup. Primarily from "Maxim 132 1-wire requirements Quick Guide.pdf", P.6, Fig.7. Uses active pull-up and pull-down, and of course 5V. (The 100 ohm resistor is supposed to be 88 ohms, to add to 100 in series with either of the 22 ohm resistors, but I didn't have one and never got around to replacing it.) (To sensors) (End termination) Gnd|---||--|1-Wire Net Gnd| |1-Wire Net | 0.02 | | ___ | | ___| |-| >||-| 1N5711 Schottky | | | | | | / | | __\ | | \1 | |-| >||-| 1.5KE20A-T TVS | /0 | \ | \0 | | / | | \ | | | | ----------- |gnd|1-W|net| | o | o | o | ----------- 4b 5b 6b 1.33K ______________________| | __/\/\/\/\______ | / | | | PN _____________|_______| _______ 2N | | 2222 | | | | | 2906 | | (NPN) \|_ | 22 \ 22 | _|/ (PNP) | | /| | |\/\/\/\|/\/\/\/| | |\ _____| | | | | | | | |/ | ----------------------------------- | |emt|bas|col|spd|1-W|spu|col|bas|emt| PV_T9, | | o | o | o | o | o | o | o | o | o | left of PV_T6 | ----------------------------------- | 1 2 3 4 5 6 7 8 9 |_________/| | | | | | | | | \/\/\/\| | |/\/\/\/ | | Gnd 3.3K | | | 120 +5V ---(TVS) (PV_T7:28) | | | (PV_T6:1) | | | | | === (pulldn out)H5:7___| | |___H5:6(strong pull-up out) +|__________________________|_______T1:9(1-W signal input) (Yes, my whole house control system is documented in ASCII. This started back in the CP/M era, and has outlived ten different computers with different operating systems and incompatible apps.) OK, enough distraction for today. Thanks for making me look! Loren | Loren Amelang | lo...@pacific.net | ------------------------------------------------------------------------------ What NetFlow Analyzer can do for you? Monitors network bandwidth and traffic patterns at an interface-level. Reveals which users, apps, and protocols are consuming the most bandwidth. Provides multi-vendor support for NetFlow, J-Flow, sFlow and other flows. Make informed decisions using capacity planning reports. https://ad.doubleclick.net/ddm/clk/305295220;132659582;e _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
