All, I don't know what the difference is between the 1822 and the 1822+, but I have the 1822, not the plus version. But, in the application I have in mind, it doesn't need to be parasite powered. It was just a convenience that I would like to have implemented. Jim ----- Original Message ----- From: "Marc Nicholas" To: "Microcontroller discussion list - Public." Sent: Tuesday, August 11, 2009 6:19 PM Subject: Re: [PIC]: One Wire Temp Sensor Question I'd agree with Bob - they really worked out the kinks of the earlier devices. I wouldn't dream of using any other device for remote temperature monitoring and logging! -marc On 8/11/09, Bob Axtell wrote: > We've had perfect results with the DS1822+, even when using it in > parasitic (no VCC) mode. > > > > On Mon, Aug 10, 2009 at 6:33 AM, Marc Nicholas > wrote: >> At a guess, I'd say that you have it set to higher than 9-bit resolution? >> AFAIK, the DS1822 has user configurable 9 to 12-bit resolution. >> >> -marc >> >> On Mon, Aug 10, 2009 at 9:23 AM, jim wrote: >> >>> All, >>> >>> I worked yesterday getting my one wire routines working, which I >>> accomplished. >>> The 1822 One Wire Temp Sensor is a 9 bit sensor. It has a range of -55C >>> to >>> +125C. >>> It uses 2's complement math for the negative temps. It's temperature >>> measurement is >>> contained in 2 bytes. The LSB is the temp reading in .5C increments. >>> The >>> MSB is the >>> sign bit. All 8 positions in the MSB are sign bits. So, I gather that >>> if >>> the temp is negative, >>> all 8 bits of the MSB would be set. However, when the PIC reads the >>> Temp >>> sensor, I get >>> the correct (approximately) reading in the LSB, but the MSB has 1 or 2 >>> bits >>> set. It's not >>> clear to me from the datasheet whether all 8 bits should be set for >>> negative temps, or if it can >>> be any number of bits set for negative temps. >>> >>> Does anyone have any experience with one wire comms, especially with >>> this >>> temp sensor? >>> If so, do you have any idea about the MSB and how the sign bit is >>> supposed >>> to work? >>> Or any other insight that may give me an idea if I'm doing anything >>> wrong. >>> >>> BTW, I've tried powering this sensor from Vdd and using parasite power, >>> and >>> it acts the same either way. >>> Also, I opowered it from 5 volts and from 3 volts, and that doesn't >>> change >>> anything either. >>> >>> Please advise. >>> >>> >>> Thanks >>> and Regards, >>> >>> >>> Jim >>> -- >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- Sent from my mobile device -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist