On Fri, Feb 03, 2006 at 04:27:17PM -0800, Peter van Hoof wrote:
> I bought a package of the simple "Home Alert" door alarms $10 for 4
> And modified one with a 12f675 and a n channel fet to switch on the
> old electronics if the reed contact was not closed within 1 minute
> While the door is opened it will chirp every 10 seconds to remind
> you to close the door (this also works as a battery test)
>  
> After screaming for a couple seconds it takes a break for a half minute
> and the process repeats.
>  
> The pic sleeps most of the time the reed contact operates the INT input
> all very simple.

Out of curiosity... Any reason why you didn't simply run the PICs power
through the reed switch itself? Or use a transistor operated by the reed
switch to turn on the PIC? Running in sleep mode seems kinda wastefull
to me rather than just totally turning the PIC off.


Incidentally your project kinda reminds me of one I want to do with my
fridge... It's a tiny "bar-fridge" sized model, sutable for my equally
tiny apartment. Works fine except that if the temperature is set such
that ice-cream stays solid in the freezer compartment, the rest of the
fridge ends up below zero! The two compartments aren't seperated, and
cooling for the fridge is provided by falling air from the freezer. (at
top) At worst if set to maximum the freezer part ends up at -30C (!) and
my milk is a solid -10C block...

My looney scheme was to put a small heater at the very bottom controlled
by a PIC with some temperature sensors. I'd have the heater add heat to
the fridge portion based on the temp sensor reading to keep it above
freezing so that the overall temperature differential would be greater.
Power would be supplied by thin insulated copper strips sneaking past
the door seal.  I suspect that the manufacture assumed in the design
that the door would be opened more often than it is, I'm practically
never home.

Fortunately my apartment has unmetered electricity...

-- 
pete@petertodd.ca http://www.petertodd.ca
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