In uk.d-i-y, wrote:
Mike Barnes wrote:
I've had several freezers with "door open" alarms but they've been all
been f***ing useless. Door wide open when I'm rearranging stuff? Beep
beep bloody beep, yes, thank you, but it's obvious the door's open isn't
it? Door half an inch open because one of the drawers isn't quite
pushed home? Silence.

Thermometer-based alarms are useless because they routinely go off
during the automatic defrost cycle.

The problem with the makers' "door open" alarms are that they work on
the hinge side so they're spectacularly inaccurate. What's needed,
*obviously*, is a switch at the opening edge of the door. But it seems
to be beyond the wit of the manufacturers to understand that or to put
it into practice.

end rant

I did try making my own "door open" alarm many years ago, using a timer
operated by a microswitch stuck on the side of the cabinet with a lever
between the cabinet edge and the door seal. I can't remember why but it
wasn't very successful, probably not robust enough for a kitchen
environment.

I wonder if some sort of magnetic detector might work better - there
are, after all, magnets in the door seal. Or perhaps a low-profile
keyboard-type switch between the cabinet edge and the seal? Or any other
ideas?


Its simple enough if you can do some electronics. A metal foil contact
on each face, but not used as a swtich, rather used as a detecting
capacitor. An oscillator uses those contacts as its frequency
determining capacitor. Door closed, C higher, f higher. Output from
osc goes thru cap and is threshold detected. You also need the circuit
to detect correctly if the foils connect, so provide a dc path for
that condition too.

Now, with door open/closed reliably detected, its up to you to add
whatever suppression you want, eg timer, cancel etc, and whatever
output you want, eg LED while not closed, and beeper if not closed for
3 minutes or more.

If you cant do electonics... youre stuffed.

I can do the electronics at a pinch, but I was hoping for something
simpler, that didn't involve running a wire to the door or a constant
battery drain. Thanks for the thought.

--
Mike Barnes