PDP-8 /e/f/m memory

Chuck Guzis cclist at sydex.com
Tue Aug 15 00:19:08 CDT 2006

On 8/14/2006 at 9:35 PM Don wrote:

>Unless you can make a battery application last A VERY LONG TIME
>(not just a LONG time since those are the cases where you get
>screwed because you have forgotten about the battery that
>you replaced 1 or 2 years ago... *but*, if you replaced it
>*10* years ago you don't mind -- as much -- when it dies
>after that long of a service life) it will frustrate users.

Well, consider the Dallas battery-inside-the-chip clock-calendar circuits.
7 years sounded like forever--and it may well have been to the original
owners of the equipment.  But now, they're starting to fade and finding
replacements can be a bit of a hassle.  In 20 years, it'll probably be
nearly impossible.

For this particular application, any keep-alive power source needs only to
last as long the longest power-off interval.  If, as Don, says a supercap
will last several months, that should be good enough--and it's a permanent
solution.  Heck, I wonder if you could trickle-charge the battery with
ambient light via a solar cell.    That should extend the keep-alive period

I just don't like chemical reactions in my equipment--it's sort of like
bird's nest soup.  It might taste good, but I don't like the idea of eating
bird spit..


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