Freezer door alarm

How about one of the window burglar alarms sensors that uses a magnet and reed switch?

No cancel button?

Don't be such a lazy B and buy "frost free" heaps of s**te then. The important thing *is* the temperature if that rises for any reason you need to know about it. Must admit if the frost free thing doesn't "know" it's doing a defrost cycle and can supress the alarm for the expected duration plus a bit it is poor design.

Actually I'd also like a to low temp alarm as well. When we bung 3 loaves of bread in the freezer it alarms due to the temp rise. Put it into "rapid freeze" mode but then forget about it until I spot the display showing

-31C...

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

If you cant do electonics... youre stuffed.

NT

Well, we've got it now. And it's attached to the fridge that we rather like. And it's a non-standard cabinet size that just happens to suit our kitchen rather well. So we're in no hurry to swap it.

Now there's a thought. I was about to counter that it's the temperature of the food that matters, whereas a short increase in air temperature (which is what the alarm is responding to) is of little consequence. It's an aftermarket alarm, which obviously doesn't know when the defrost cycle is.

Answer: wrap the sensor in a little insulation (e.g. put it in a food container) to shield it from short-lived temperature rises. I'll get onto that straight away. Thanks!

But an effective "door not closed properly" alarm would be much better.

Here's your answer...

Excellent idea - and not too conspicuous if mounted *under* the door. I can't imagine why I didn't think of that, because I recently designed some very effective LED drawer lights using exactly what you suggest. I even know where to get the right sort of switches, with contacts that

It might be a bit of a fiddle getting the range right but it's a very promising idea. Thanks.

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.

Its not a FIsher & Paykel one by any chance?!?

Matt

Some years ago (prolly about 20), I made one for Mum's freezer. I got the innards out of a musical birthday card, a miniature microswitch and a small piece of wood (as an actuator for the microswitch). I glued the card innards and the microswitch on the side of the freezer and the wooden block on the edge of the door. OK, you had to listen to the tune incessantly whilst the door was open, but the problem (of leaving the door slightly ajar) went away. The battery in the card outlasted the freezer!

Nowadays, of course, musical birthday cards are bases around digital samples, so they don't play annoying monophonic tunes that keep going indefinitely.

I think youre out of luck then. Sticking extraflex to the underneath edge of the door shouldnt be hard.

why would one run it off a battery?

If you want a simple switch in series with a beeper, you could do that but dont expect decent performance.

NT

I had one for a fridge which was a red plastic apple shape incorporating a light sensor. I don't know if the leakage around a freezer door slightly open would be enough for it to operate.

Chris

Give that man a cigar!

But there's the same problem with our other freezer (Zanussi) and its predecessor (Philips).

Hum, two things to ponder. What is the range like with the transmitters inside an earthed metal box, I notice that they mainly stress having the display on the fridge/freezer. Also what batteries do they use for the unit in the freezer, most batteries don't like much below 0C let alone the

-18C or more of a freezer.

I bought a Candy fridge freezer a few years back and cursed it more than one because the magnetic seals weren't very and the freezer door would bounce slightly open if you didn't pay attention.

The fix was easy but only realised it when I got my new fridge here. Just make sure that there is a slight rearward tilt thus making the door self closing. Not 100% re a drawer left open of course.

Two foils on the frame and one long enough to cover both frame foils on the door solves that one, that's 2 caps are in series then.

Your scepticism does you credit. :-)

Mine works through the front door of the freezer and then 2.5m across the kitchen to the side of the other freezer. I haven't experimented further.

ISTR they recommend lithium. Not many places stock lithium AA so I ordered some from CPC. While waiting for those to arrive I put in some ordinary Duracell alkalines (both sensors). That was at least a year or two ago and I haven't needed the lithiums yet.

In message , snipped-for-privacy@care2.com writes

Hall effect sensor, PIC Micro waking on interrupt, programmable delay so it only complains after a preset period and a low battery monitor..

Tiny current consumption when in sleep, hall effect should work with the door strip and you can make the sensing range adjustable in software. Parts cost probably under a fiver too. Anyone interested?

Or if it would work when the kitchen is in darkness.

I doubt many people are set up for PICs. A single hex invertor chip would probably do the lot.

NT

Did that with my Hotpoint once. I don't know how low it went, but it was below -40C where the mercury (or red stuff) went off the scale as it all went into the thermometer bulb.