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Redundant Pull-Ups?

 
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victorf



Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
Posted: 02 July 2006, 10:36 AM    Post subject: Redundant Pull-Ups? Reply with quote
I found this on the BasicX forum and wondered about it:
Quote:

After about 2 or 3 thousand hours of use, I'm finding that the BX24p
internal pull-ups are going bad. So far, 3 of them have gone south.
The circuit is only a pushbutton switch to ground, so I don't think
that the resistors are getting destroyed from that. I'm having this
problem with only 1 chip so far.

I'm wondering if my next batch of boards should have provisions for
external pull-ups. Redundancy is a good thing, I suppose, and adding
one more 0603 or 0402 chip to the board really isn't a big deal.

Has anyone else experienced this kind of failure only after long term use?


There seemed to be mixed opinions about this on that forum. However, the postings on it were few.

Is this a potential problem with the ZX-24?

Any enlightenment will be appreciated.

Vic
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stevech



Joined: 23 Feb 2006
Posts: 657
Posted: 02 July 2006, 16:22 PM    Post subject: Reply with quote
are the push buttons connected by a long length of wire or without a good common ground, such that static electricity or other transients could be getting imposed on the lines to the switches? Or the button-pusher at times has a static charge? If so, some snuffer components may be needed.

Those pull-ups are high value as I recall and they're inside of the AVR chip.
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spamiam



Joined: 13 Nov 2005
Posts: 665
Posted: 03 July 2006, 2:27 AM    Post subject: Reply with quote
stevech wrote:
are the push buttons connected by a long length of wire or without a good common ground, such that static electricity or other transients could be getting imposed on the lines to the switches? Or the button-pusher at times has a static charge? If so, some snuffer components may be needed.

Those pull-ups are high value as I recall and they're inside of the AVR chip.


ISTR that the internal AVR pull ups are about 100K. Nothing wrong with external ones (too).

But I wonder how transient voltages would blow a pull-up before (instead of) the AVR port input itself??? OR is it a crap shoot?

-Tony
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