Post by thread:[PIC]: DAMP! Startup problems?

Dear all, I have a few circuits that are kept in water proof boxes, but while in storage (in not the most ideal place in the word) they seem to get damp. My question is not how to prevent this, as I have sealed the boxes as well as is humanly possible, and have put sachets of silica gel in the boxes also. My question is would a crystal or RC res circuit (in am currently using cheap resonator) startup more reliabily in these conditions? Has anyone come across this problem before? I know electronics should not be subjected to these environmments, but we all live in the real world don't we! Thanks for your valuble time and comments, Regards Graham North _________________________________________________________________________ Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com. Share information about yourself, create your own public profile at http://profiles.msn.com. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's

Graham North wrote: {Quote hidden}> > Dear all, > > I have a few circuits that are kept in water proof boxes, but while in > storage (in not the most ideal place in the word) they seem to get damp. > > My question is not how to prevent this, as I have sealed the boxes as well > as is humanly possible, and have put sachets of silica gel in the boxes > also. > > My question is would a crystal or RC res circuit (in am currently using > cheap resonator) startup more reliabily in these conditions? > > Has anyone come across this problem before? > > I know electronics should not be subjected to these environmments, but we > all live in the real world don't we! > > Thanks for your valuble time and comments, > > Regards > > Graham North Graham, one word; Encapsulate! Set up your hardware to use ICSP for upgrades, then set the whole lot in a chunk of plastic. If you do it right you can run the thing submerged in saltwater for years and it won't care. Microchip make it easy with the simple ICSP on the flash chips, and I have found you can use the PicstartPlus for ICSP with no probs, saving some bucks there if that is an issue for you. Most big hardware stores have cheap polyester (fibreglass) resin, play with this until you are comfortable with the whole thing and your molds etc, then order some higher quality electrical resin from anyone in the yellow pages. Normally you can "pot" the device in a cheap plastic hobby box with just the wires hanging out the top. I was trained in encapsulating elec devices many years ago in industry, it has numerous adantages including tamperproofing and mechanical strength. Our current product can be run-over repeatedly by a car with no affect on performance. Not many electronic products can claim that! :o) -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's

On Fri, 29 Sep 2000 11:24:12 GMT, you wrote: >Dear all, > >I have a few circuits that are kept in water proof boxes, but while in >storage (in not the most ideal place in the word) they seem to get damp. > >My question is not how to prevent this, as I have sealed the boxes as well >as is humanly possible, and have put sachets of silica gel in the boxes >also. > >My question is would a crystal or RC res circuit (in am currently using >cheap resonator) startup more reliabily in these conditions? > >Has anyone come across this problem before? > >I know electronics should not be subjected to these environmments, but we >all live in the real world don't we! > >Thanks for your valuble time and comments, If anything, a _little_ leakage can actually help resonator startup, but a lot would probably cause problems. Leakage will always have some effect on the frequency of an RC osc, but will probably not actually prevent operation unless R was high and you have a lot of leakage across the cap. If this is a major problem, conformal-coat the assembly. Remember that moisture on a _powered_ board can cause rapid corrosion. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's

----- Original Message ----- From: "Graham North" <spam_OUTgs_piclistTakeThisOuTHOTMAIL.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Friday, September 29, 2000 12:24 PM Subject: [PIC]: DAMP! Startup problems? > Dear all, > > I have a few circuits that are kept in water proof boxes, but while in > storage (in not the most ideal place in the word) they seem to get damp. > My question is not how to prevent this, as I have sealed the boxes as well > as is humanly possible, and have put sachets of silica gel in the boxes > also. Does the silica gel absorb much of the moisture? Enough to change colour? Is the silica gel on the inside of the waterproof box? > My question is would a crystal or RC res circuit (in am currently using > cheap resonator) startup more reliabily in these conditions? > Has anyone come across this problem before? Yes, I had a similar problem with equipment at a transmitter site atop a small mountain. The equipment was only used occasionally and suffered from internal condensation. We solved the problem by keeping it powered and fitting a net-like arrangement of resistors in the lid to keep the kit very slightly warmer than ambient. If your equipment is in storage then keeping it powered might not be practical but the principle of keeping it slightly warmer than the ambient air temp still holds good. Maybe lay along the shelves a run of that resistance wire which horticulturalists use for soil heating, you don't need much heat to keep the condensation at bay IME. Another option is to seal the kit along with _freshly baked_ silica gel packs in either heat-sealed plastic or if that's not available you could try those zip-topped bags sold in supermarkets for storing stuff in freezers. (Do this in a warm dry environment.) Once it's completely sealed there's only the small amount of moisture in the bag and case to be absorbed, which fresh gel should be able to handle pretty simply. I did once have a handy table for silica gel showing how much was recommended for a certain volume at a given RH but I can't find it just now. > I know electronics should not be subjected to these environmments, but we > all live in the real world don't we! Lance is yer man for waterproofing really. I'm sure he'll have some other suggestions... . -- http://www.piclist.com hint: PICList Posts must start with ONE topic: "[PIC]:" PIC only "[EE]:" engineering "[OT]:" off topic "[AD]:" ad's