Post by thread:[PIC]:18F1320 INTOSC temp stability

I can't find any info in the data sheets about the behaviour of the internal oscillator of the 18F1320 with respect to temperature. I'm using the internal osc at 4 mHz for a project, and it appears to be reasonably accurate - about 0.2 percent at room temperature. The project involves resetting some counters and computing some averages at midnight (more or less). My time-of-day clock code can easily be calibrated to compensate for the error, but I've no idea how the osc freq will change with temperature. The environment will vary from perhaps 5 degrees Celsius to 35 degrees Celsius. If the freq doesn't change by too much, I can get away with using the internal osc, as I don't really need to be too close to midnight - I can reset the clock manually every few days if necessary. Does anyone have any ideas as to the oscillator's behavior in this regard? Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Larry Bradley wrote : > I can't find any info in the data sheets about the behaviour of the > internal oscillator of the 18F1320 with respect to temperature. The errate sheet DS80160B has some updated figures on this matter on page 5. Jan-Erik. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Larry Bradley wrote: > If the freq doesn't > change by too much, I can get away with using the internal osc, as I > don't really need to be too close to midnight - I can reset the clock > manually every few days if necessary. Is is really worth all that to save a 50 cent crystal? ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Yeah, I saw that, but it really doesn't say much. What I was looking for was something that would say that the osc deviates by x parts per million per degree temp change, like they do for xtals. The only reason for not using an xtal is I/O pin count, but I can multiplex and LCD pin with something else if necessary At 02:39 PM 1/3/2004 +0100, you wrote: {Quote hidden}>Larry Bradley wrote : > > > I can't find any info in the data sheets about the behaviour of the > > internal oscillator of the 18F1320 with respect to temperature. > >The errate sheet DS80160B has some updated figures >on this matter on page 5. > >Jan-Erik. > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Of course not. It is an interesting experiment, if nothing else. The PICs have an internal osc - why not use it if it will do what you want? If it won't, I'll use an xtal - I have a bunch of them. I'd like to use the OSC pins as I/O ports for this project, but it isn't necessary, since I can multiplex a couple of other pins if I have to. At 09:49 AM 1/3/2004 -0500, you wrote: {Quote hidden}>Larry Bradley wrote: > > If the freq doesn't > > change by too much, I can get away with using the internal osc, as I > > don't really need to be too close to midnight - I can reset the clock > > manually every few days if necessary. > >Is is really worth all that to save a 50 cent crystal? > >***************************************************************** >Embed Inc, embedded system specialists in Littleton Massachusetts >(978) 742-9014, http://www.embedinc.com > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics Larry Bradley Orleans (Ottawa), Ontario, CANADA -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 10:07 AM 1/3/2004 -0500, you wrote: >Of course not. It is an interesting experiment, if nothing else. The PICs >have an internal osc - why not use it if it will do what you want? If it >won't, I'll use an xtal - I have a bunch of them. I'd like to use the OSC >pins as I/O ports for this project, but it isn't necessary, since I can >multiplex a couple of other pins if I have to. Or use a 30 cent resonator with built-in capacitors. A good compromise for many situations (0.5% accuracy). Best regards, Spehro Pefhany --"it's the network..." "The Journey is the reward" spam_OUTspeffTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Saturday, Jan 3, 2004, at 06:49 US/Pacific, Olin Lathrop wrote: > Is is really worth all that to save a 50 cent crystal? > It's more often useful to save two pins. I've noticed that a lot of things I contemplate will fit in an 18 pin pic, but NOT one of the old ones with only 13 IOs. And of course the 8-pin PICS are a LOT more useful with 6 I/Os (as atmel found out the hard way...) > Or use a 30 cent resonator with built-in capacitors. A good compromise > for many situations (0.5% accuracy). Where do i get these cheap resonators? I didn't get any responses to my last flame to the effect that cheap crystals were far more common than cheap resonators. (again, it's an ease-of-use thing. I want built-in caps! (and how come no one seems to make cystal modules with built-in caps, anyway?) BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Digikey started carrying Murata brand resonators with built in caps. Under $0.30/ea in 100's Dave > Where do i get these cheap resonators? I didn't get any responses -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Saturday, Jan 3, 2004, at 18:49 US/Pacific, David Schmidt wrote: > Digikey started carrying Murata brand resonators with built in caps. > Under $0.30/ea in 100's And not much more than that even in 1's. Thanks: it's tough to keep up with digikey's additions... BillW -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > Or use a 30 cent resonator with built-in capacitors. A good > compromise > > for many situations (0.5% accuracy). > > Where do i get these cheap resonators? [AD] I have 6, 10 and 20 MHz resonators, US$ .36, .36 and .42 each (singles, pay by PayPal). 0.25 for 25+ (mixing allowed). $8.40 S/H per order. See website for prices in Euro and/or for other payment options. [/AD] Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.