Power is reported by the chip, using the 0xB4 command. The datasheet is a little unclear: http://pdfserv.maxim-ic.com/en/ds/DS18B20.pdf page 12
READ POWER SUPPLY [B4h] The master device issues this command followed by a read time slot to determine if any DS18B20s on the bus are using parasite power. During the read time slot, parasite powered DS18B20s will pull the bus low, and externally powered DS18B20s will let the bus remain high. See the Powering the DS18B20 section for usage information for this command. I think this means that if we use the "Skip ROM" to select all the slaves, we can quickly see if all DS1820s are powered. I haven't experimented and it's not directly stated. Paul Alfille On Tue, Dec 7, 2010 at 3:58 AM, Martin Patzak (GMX) <[email protected]> wrote: > Hello to all owfs-developers, > > First of all I am very pleased with the all the work you must have put > in, to bring owfs to such a mature development state. > > I am using owfs, 1-wire, mblogic and self-written software for the > heating system of my house. There is a wood-burning oven, that heats > water, which gets pumped in a cycle into an 800l buffer for storing the > hot water. Parallel there are pumps and mixers providing the right > temperature of water for radiators and floor-heaters depending on the > current outside temperature. I am actively developing the system at the > moment step by step. The control unit can be switched from bus to manual > control via buttons and switches, as well as a semi-automatic mode in > which both is possible with manual setting overriding the bus. > > At the moment I have 15 DS18B20 and 3 DS2408S+ (controlling some relays > and switches) chained in one line of 15m length using regular > telephone-cable. All sensors are connected over the bus-cable to +5VDC > external power using my PC-power-supply. I poll the temperatures in > /uncached/28..../temperature10 twice a minute (at second 00 and second > 30) with a perl-programm via the file-system powered by owfs. There is > very little traffic to the DS2408S+ at the momement. > > When I then start owfs and check /power of each sensor, then some of > them claim to be parasitically powered (value = 0). No matter what I > try, the problem is persistent and consistent (always the same sensors > fail to report that they are externally powered). Since it looks like an > electrical problem, I measured of course those sensors at their pins, > just to find, that electrically they are indeed powered with 5VDC. There > is no pattern I can see which sensors claiming to be not powerd. The > first 4 are fine. No. 5 has a problem, No. 6 is fine, No. 7 has a > problem, No. 8-10 (the 3 DS2408S+) are fine, 11-15 problem, 16 fine, 17 > problem, 18 fine. > > I tested the cable itself beforehand in a 50m roll with one sensor > connected in the end and it worked without errors for days polling the > temperature twice a minute. > > It sounds like an electrical problem, since an upgrade to 2.8p4 did not > change the situation. I measured PC-power-supply GND to the LINK GND and > they are using the same GND, so it cant be a floating GND. > > I am using the LINK USB as bus-master running in ASCII-mode on Lenny Debian. > > Additionally I have some bus instability, which might have to with this > - I dont know. The bus spontaneously looses all the items on the bus, > but the bus-master itself. And the red LED on my LINK lights > continuously - as if there were a short on the bus, but there isnt (if > there were the 2A fuse would trigger). > > What does the red LED lighting continuously on the LINK mean other than > short between 1-wire-data-line and GND? > > I can only get the bus going again with manually take the external +5VDC > away and reapply it. All items appear back on the bus again. > > This happens from once a week, to twice a day. Again, not sure if this > problem is related. > > Maybe some of you came across something similar already. Please ask me > for more details, if I forgot to mention something. > > My best regards, > > Martin Patzak > > > > > ------------------------------------------------------------------------------ > What happens now with your Lotus Notes apps - do you make another costly > upgrade, or settle for being marooned without product support? Time to move > off Lotus Notes and onto the cloud with Force.com, apps are easier to build, > use, and manage than apps on traditional platforms. Sign up for the Lotus > Notes Migration Kit to learn more. http://p.sf.net/sfu/salesforce-d2d > _______________________________________________ > Owfs-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/owfs-developers > ------------------------------------------------------------------------------ What happens now with your Lotus Notes apps - do you make another costly upgrade, or settle for being marooned without product support? Time to move off Lotus Notes and onto the cloud with Force.com, apps are easier to build, use, and manage than apps on traditional platforms. Sign up for the Lotus Notes Migration Kit to learn more. http://p.sf.net/sfu/salesforce-d2d _______________________________________________ Owfs-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/owfs-developers
