Post by thread:Trying to get 32KHz crystal to spin up!

Hello, I'm working on my PIC "Power Manager" which is set up much like the circuit shown in AN582, with a fast main crystal between OSC1 and OSC2, and then the watch crystal between T1OSI and T1OSO. This is a pretty neat thing that the PIC can do - allowing a sleeping PIC to sleep, but continue to keep time via the Timer1 and the 32KHz crystal. I have much of my firmware done. The problem is - I can't get the 32KHz crystal to oscillate reliably. My boards don't come in for another week, so, I'm prototyping on a vector board. I'm not an analog guru, but I've tried keeping the wires short, etc. If I lick my pinky and touch around the circuit (seriously...) I can get a few hundred ticks into Timer1 but nothing sustained. I have two 30pF caps across the crystal to ground. I've tried some large value resistors (e.g. 500K to 10M) across the crystal, and can often get several dozen ticks. No nets are greater than, say, 1/2 inch. I'm surprised this is all *that* sensitive. Am I doing something wrong? Tom Coonan spam_OUTThomas.CoonanTakeThisOuTSciatl.com http://www.mindspring.com/~tcoonan

Hi, I don't know if you do somethink wrong, but in many times with prototype board I have experience problem with quartz and timing. The better and quicker solution I have find is to build a oscillator, without PIC (perhaps with a 74HC4060), and then to connect the clock to the PIC (T1OSI). Didier ---------- > From: Tom Coonan <.....tcoonanKILLspam@spam@MINDSPRING.COM> > To: PICLISTKILLspamMITVMA.MIT.EDU > Subject: Trying to get 32KHz crystal to spin up! > Date: lundi 7 juillet 1997 19:52 > > Hello, > > I'm working on my PIC "Power Manager" which is set up much like the circuit > shown in AN582, with a fast main crystal between OSC1 and OSC2, and then > the watch crystal between T1OSI and T1OSO. This is a pretty neat thing > that the PIC can do - allowing a sleeping PIC to sleep, but continue to > keep time via the Timer1 and the 32KHz crystal. I have much of my firmware > done. The problem is - I can't get the 32KHz crystal to oscillate reliably. > My boards don't come in for another week, so, I'm prototyping on a vector > board. > > I'm not an analog guru, but I've tried keeping the wires short, etc. If I > lick my pinky and touch around the circuit (seriously...) I can get a few > hundred ticks into Timer1 but nothing sustained. > > I have two 30pF caps across the crystal to ground. I've tried some large value > resistors (e.g. 500K to 10M) across the crystal, and can often get > several dozen ticks. No nets are greater than, say, 1/2 inch. > > I'm surprised this is all *that* sensitive. Am I doing something wrong? > > Tom Coonan > .....Thomas.CoonanKILLspam.....Sciatl.com > http://www.mindspring.com/~tcoonan

I've often found that connecting the crystal can to ground will get an oscillator to function Steve {Quote hidden}> >I'm working on my PIC "Power Manager" which is set up much like the circuit >shown in AN582, with a fast main crystal between OSC1 and OSC2, and then >the watch crystal between T1OSI and T1OSO. This is a pretty neat thing >that the PIC can do - allowing a sleeping PIC to sleep, but continue to >keep time via the Timer1 and the 32KHz crystal. I have much of my firmware >done. The problem is - I can't get the 32KHz crystal to oscillate reliably. >My boards don't come in for another week, so, I'm prototyping on a vector >board. > >I'm not an analog guru, but I've tried keeping the wires short, etc. If I >lick my pinky and touch around the circuit (seriously...) I can get a few >hundred ticks into Timer1 but nothing sustained. > >I have two 30pF caps across the crystal to ground. I've tried some large value >resistors (e.g. 500K to 10M) across the crystal, and can often get >several dozen ticks. No nets are greater than, say, 1/2 inch. > >I'm surprised this is all *that* sensitive. Am I doing something wrong? >

Get rid of the 30 pF capacitors. The normal loading on "watch" type crystals is 6 pF or 12.5 pF depending on what type you have. Your circuit will supply enough stray capacitance to properly load these crystals. Joe ---------- From: Stephen Birchall (Stephen Birchall)[SMTP:EraseMEN.S.Birchallspam_OUTTakeThisOuTLBORO.AC.UK] Sent: Tuesday, July 08, 1997 4:44 AM To: PICLISTspam_OUTMITVMA.MIT.EDU Subject: Re: Trying to get 32KHz crystal to spin up! I've often found that connecting the crystal can to ground will get an oscillator to function Steve {Quote hidden}> >I'm working on my PIC "Power Manager" which is set up much like the circuit >shown in AN582, with a fast main crystal between OSC1 and OSC2, and then >the watch crystal between T1OSI and T1OSO. This is a pretty neat thing >that the PIC can do - allowing a sleeping PIC to sleep, but continue to >keep time via the Timer1 and the 32KHz crystal. I have much of my firmware >done. The problem is - I can't get the 32KHz crystal to oscillate reliably. >My boards don't come in for another week, so, I'm prototyping on a vector >board. > >I'm not an analog guru, but I've tried keeping the wires short, etc. If I >lick my pinky and touch around the circuit (seriously...) I can get a few >hundred ticks into Timer1 but nothing sustained. > >I have two 30pF caps across the crystal to ground. I've tried some large value >resistors (e.g. 500K to 10M) across the crystal, and can often get >several dozen ticks. No nets are greater than, say, 1/2 inch. > >I'm surprised this is all *that* sensitive. Am I doing something wrong? >

At 12:52 PM 7/7/97 -0500, you wrote: >Hello, > >I'm working on my PIC "Power Manager" which is set up much like the circuit >shown in AN582, with a fast main crystal between OSC1 and OSC2, and then >the watch crystal between T1OSI and T1OSO. This is a pretty neat thing >that the PIC can do - allowing a sleeping PIC to sleep, but continue to >keep time via the Timer1 and the 32KHz crystal. I have much of my firmware >done. The problem is - I can't get the 32KHz crystal to oscillate reliably. >My boards don't come in for another week, so, I'm prototyping on a vector >board. Its probably not the problem with a vector board prototype, but I have had trouble with board contamination with PICs with low frequency crystals. The problem was solved by carefully cleaning the area around the crystal with alcohol. Good luck! - Gary ------------------------------------------------------------------------ Gary Sutcliffe, W9XT Unified Microsystems @spam@ppvvppKILLspammixcom.com PO Box 133 Slinger, WI 53086 http://www.qth.com/w9xt 414-644-9036