--===============0941462002== Content-Type: text/plain; charset="gb2312" Content-Transfer-Encoding: quoted-printable X-MIME-Autoconverted: from 8bit to quoted-printable by pch.mit.edu id m2SHjbmt015351 Have you checked you PCB? We have seen similar problem and it turns out t= o be metal migration in PCB and it causes some stupid short circuit when = some ESD occurs. > Date: Fri, 28 Mar 2008 05:27:52 -0700> From: michael_r_monteith@yahoo.c= om> Subject: Re: [PIC] very slight ESD events wake up my sleeping PICs> T= o: piclist@mit.edu> > You should always make it a point for sensitive cir= cuits like these> to have a good ground. In this case since you have one = in a metal> case that's even better. But not tying it to the board ground= causes> a problem. When you have an arc the case has a difference of pot= ential> compared to the board. So more than likely some energy tranferred= to> the board. At least if it was ground you might still have a problem = but> not as bad. That and the next part is the PIC board itself. > > You = should make it a default design to put a decoupling capacitor from> Vdd t= o ground as close to the PIC as possible and one on Vdd to > ground on an= y chip on the board. > > Getting up out of your chair generates large amo= unts of static electricity.> But now that you can pretty much duplicate t= he test anyway you can then> go to trying to ground things, putting in decoupling capacitors and may have> to res= ort to ESD protection devices as an extra caution. The decoupling> capaci= tors if nothing else will reduce noise on the chip but might also act> to= absorb some of the energy. > > If nothing else grounding and shielding w= ith a metal case (tied to ground of> course) will go a long ways.> > Mich= ael> > ----- Original Message ----> > From: trossin > > To: piclist@mit.edu> > Sent: Thursday, March 27, 2008 1:55:43 PM> > = Subject: [PIC] very slight ESD events wake up my sleeping PICs> > > > > >= I've built a few "executive" (I'm just a grunt geek) toys and two of the= m> > have the same problem. That is when I get up from my chair, they tur= n on. > > Both of these toys have push buttons to activate them. When the= button is> > pushed they do their thing then go to sleep. I enable wake = up on port B> > change and use the internal pull up resistor. On my lates= t toy I added a 1K> > pull up to try to s top this problem from happening (it reduces the problem> > but does not = eliminate it). One toy uses the 16LF628A and the other uses a> > 16LF873A= . One runs on two AA cells while the other runs on 3 AA cells.> > > > On = the toy with the 1K pull up (the 16LF873A), I put the PIC in a metal case= > > but did not ground the case. The case is just "floating". On this dev= ice I> > once had an arc to the case and it required me to pop out the ba= ttery to> > reboot it. I think that grounding the case should solve the p= roblem but I'm> > not sure.> > > > The toy with the 16LF628A is just an e= xposed PC board but has a 5 inch> > twisted pair wire for the switch.> > = > > Has anyone else had problems like this? It only is a problem for me w= ith> > projects that use the wake from sleep on interrupt feature. Any id= eas on> > how to fix it. I guess I could use at 220 Ohm resistor but the = lower I go> > the more power that is wasted when the button is pushed.> >= -- > > View this message in context: > > http://www.nabble.com/very-slight-ESD-events-wake-up-my-sleeping-PICs-t= p16331156p16331156.html> > Sent from the PIC - [PIC] mailing list archive= at Nabble.com.> > > ____________________________________________________= ________________________________> Looking for last minute shopping deals?= > Find them fast with Yahoo! Search. http://tools.search.yahoo.com/newse= arch/category.php?category=3Dshopping> -- > http://www.piclist.com PIC/SX= FAQ & list archive> View/change your membership options at> http://mailm= an.mit.edu/mailman/listinfo/piclist _________________________________________________________________ =D0=C2=C4=EA=BB=BB=D0=C2=D1=D5=A3=AC=BF=EC=C0=B4=D7=B1=B0=E7=D7=D4=BC=BA=B5= =C4MSN=B8=F8=D0=C4=D2=C7=B5=C4TA=D2=BB=B8=F6=BE=AA=CF=B2=A3=A1 http://im.live.cn/emoticons/?ID=3D18 --===============0941462002== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: 7bit -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist --===============0941462002==--