Well, I know for a fact that its not 85C outside right now and not inside either, and I know that the DS18S20-PAR is fault free as they work with other software.
/Thomas Roberto Spadim skrev: > i have some problems with pic16f877a reading 85 degree, what i do? > read again, if it's 85 degree ok (maybe ds1820 are burning) if i'm > sure that it isn't at 85 degree i change the ds1820 and every thing go ok > > Thomas Berg escreveu: >> Mostle hardware related tips, as other software works without any prblem >> redaing temperatures from the same hardware-setup I strongly beleave >> that this 85C problem is related to owfs somehow. >> >> Well, here is the schematics of the 1-wire master hub >> http://www.hobby-boards.com/catalog/links/6cmh1-r1/6%20Channel%20Master%20Hub%20v1.1%20Schematic.pdf, >> >> if you se any consturction errors it would be nice to know. >> >> /Thomas >> >> David Lissiuk skrev: >> >>> Hi all, >>> >>> As I have done fairly extensive testing of various 1-wire issues I can >>> maybe help shed some light on possible hardware causes of seeing 85.0C >>> errors for those new to these issues. >>> >>> In general a 85.0C reading indicates that a POR has occurred in the >>> chip: >>> >>> The following issues are common, note that not all are things that >>> software alone can correct. >>> >>> 1) Poor 1-wire line levels >>> A). If the chip is wired for parasitic operation, the VDD line must be >>> grounded. Otherwise unknown parasitic results may occur. (This is not >>> required with -PAR devices, which are internally grounded inside the >>> chip). >>> >>> B). While operating under powered mode of operation, the power supply >>> has to have a reasonably fast rise time, else the chip may enter an >>> internal test mode. The voltage should ideally be 5 volts to insure >>> maximum signal headroom for the 1-wire signal. Line losses through the >>> cable need to be considered. >>> >>> C). The slave device (the DS18B20) may not have enough >>> power/current to >>> complete the temperature conversion and this may cause a POR to >>> occur in >>> the chip instead (Generating the 85.0C reading). This may be caused by >>> the following: >>> >>> 2). Insufficient weak-pull-up current on simple 1-wire bus master >>> designs >>> I've seen issues when the weak-pull up current is insufficient, causing >>> the chip to do a POR during the temp conversion time. Generally a value >>> between 1.1K and 2.5K for the weak pull-up resistor is what I >>> recommend. >>> I've often seen this problem on bus master designs using a 4.7K or >>> greater weaker pull-up resistors. >>> >>> 3) Insufficient conversion time/current. Parasitic driven devices >>> take considerably longer to do their conversion >>> than a powered device does (for this reason I generally recommend >>> powered sensors (See 1WRJ45 for one way how to supply power through a >>> cable). You will get a 85.0 result if the conversion has not completed >>> and a POR had occurred previously. >>> A powered device temperature conversion is typically around 650ms at >>> 12bits (750ms max). The DS18B20 uses a relatively crude internal >>> timing >>> oscillator. And variations from both, temperature and internal chip >>> composition, etc. may effect the duration needed for a successful >>> temperature conversion cycle to complete, and the chip may draw as much >>> as 1.5ma during the conversion processes. This may be why one chip >>> works and the other doesn't if you're just marginal with the timings. >>> (generally a good time to redesign your network to fix the fundamental >>> problems). I have heard of one batch of DS18X20's working in a circuit >>> and another not due to these slight internal differences on marginal >>> designed networks. This is not a failure of the parts, just of poor >>> network design and is generally corrected by insuring sufficient >>> conversion current is received by the temperature device for the entire >>> temperature conversion cycle. Powered temperature sensors may also be >>> polled for when the temperature conversion is complete (thus saving >>> time). See the datasheet for more information on this. >>> >>> Another source of errors is too long delays in providing a strong >>> pull-up current for parasitic device. The sensor is issued a conversion >>> command, but a strong pull-up current is not applied for one reason or >>> another and the device loses power. This is only an issue with >>> parasitic >>> operated devices obviously. It is generally a poor bus master design or >>> improper programming of the strong pull-up of the bus master. >>> >>> 4), Current supply limitations: >>> Since during a temperature conversion current use in the device can be >>> fairly high, (1.5ma max by spec) limitation of the network design may >>> affect this supplied current. >>> A). Limitations of the Bus master to supply conversion current. >>> A LINK based design bus master can supply more current than a DS2480B >>> design (DS9097U-S09). A DS2490 (USB) can supply slightly more current >>> than a DS2480B unit. The Impedance matching line filter on the bus >>> master must also be considered if added to a DS9097U-S) or USB unit >>> (Generally a highly recommended practice to add the filter for signal >>> reflection issues). If the bus master is also parasiticlly powered this >>> may also be an issue or limitation. >>> >>> B). Any additional bus line resistance. >>> The use of a DS2409 adds additional current limiting to what can be >>> supplied to downstream devices. Each channel of a DS2409 has a >>> different >>> resistance. So channel use may also effect operation. In addition the >>> DS2409 chip package sets the maximum pass-gate current to 20ma max. >>> according to Dallas (info not in data sheet) This can be a >>> limitation in >>> any attempt to do bulk temperature conversions of parasitic downstream >>> devices. >>> >>> C) Time delays generated by inline devices >>> A DS2409 can also cause a POR to occur on a temperature sensor after >>> switching channels using a smart-on command. (There are several errors >>> in the DS2409 data sheet that I've notified Dallas about, including the >>> flow diagram. Dallas has verified them and is correcting them in a new >>> revision of the data sheet. Though I am not sure if all of them will be >>> corrected by then). >>> >>> Much of this information has been developed in my efforts on basic >>> research for a hardware book on 1-wire I am developing in my free time >>> (Still in early stages of writing, as I have very little of that. I do >>> however welcome suggestions and reports of problems that need to be >>> researched (contact me off list)). >>> >>> I hope this information can be of help by the software writers in >>> understanding some of the possible conditions that can cause the >>> reporting of a 85.0C error in the software that should be >>> considered. As >>> you can see when reporting an 85.0C error it might also be useful to >>> others to report the bus master used, any line filter, the number and >>> channels used in any hubs (and the hub design being used), along with >>> the temperature sensor wiring (powered or parasitic), the delivered >>> power voltage and the chip revision if known. >>> >>> Hope this helps the software efforts, >>> Cheers >>> >>> David Lissiuk >>> Sr. Computer Scientist >>> Springbok Digitronics >>> >>> >>> ------------------------------------------------------------------------- >>> >>> Take Surveys. Earn Cash. Influence the Future of IT >>> Join SourceForge.net's Techsay panel and you'll get the chance to >>> share your >>> opinions on IT & business topics through brief surveys-and earn cash >>> http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV >>> >>> _______________________________________________ >>> Owfs-developers mailing list >>> Owfs-developers@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/owfs-developers >>> >> >> >> ------------------------------------------------------------------------- >> >> Take Surveys. Earn Cash. Influence the Future of IT >> Join SourceForge.net's Techsay panel and you'll get the chance to >> share your >> opinions on IT & business topics through brief surveys-and earn cash >> http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV >> >> _______________________________________________ >> Owfs-developers mailing list >> Owfs-developers@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/owfs-developers >> >> Esta mensagem foi verificada pelo E-mail Protegido Terra. >> Scan engine: McAfee VirusScan / Atualizado em 21/02/2007 / Versão: >> 5.1.00/4968 >> Proteja o seu e-mail Terra: http://mail.terra.com.br/ >> >> >> >> > > ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
