Help designing a Freezer Door Open Alarm

[Someone Electro]

An PIC and an I2C temperature sesor.


It shod use wery litle curent of about 0.1mA (shod run for more than 1 year on an 1000mA/h batery) (if run on 32kHz ufcurce)

It wod simply detect an suden rise in temperature.An piezo buzer wod do too make the beep

 

[Halogrunt1234]

again, for such a simple problem with a simple solution, you all have to extreme complexities like PIC and temperature sensors and magnetic sensors and all that crap. there is no need to go that for just to have a simple piezo buzzer sound when the door is open too long. its like constructing a Rube Goldberg contraption just to open a door when the door handle is pulled. by just putting a small 555 timer circuit that pulses to trigger a transistor leading to a transistor oscillator circuit that will drive the piezo buzzer, if you assemble the circuit correctly you can get an alarm that buzzes when you leave your freezer, or any door for that matter, open for more than the time you give for the circuit.

estimated cost: $3.00 to $9.00 using parts from Radioshack. using surplus stores will drive the price down even more.

Just think about it, even though its too simple for you to want to consider, and then think about how much it would cost to get temperature sensors, PIC chips, and complex control circuits just to make an alarm buzz because the fridge was open too long.

what also works is a second occupant complaining that you left the fridge open. then, you may get out of the habit of leaving it open.

 

[Nigel Goodwin]

again, for such a simple problem with a simple solution, you all have to extreme complexities like PIC and temperature sensors and magnetic sensors and all that crap. there is no need to go that for just to have a simple piezo buzzer sound when the door is open too long. its like constructing a Rube Goldberg contraption just to open a door when the door handle is pulled. by just putting a small 555 timer circuit that pulses to trigger a transistor leading to a transistor oscillator circuit that will drive the piezo buzzer, if you assemble the circuit correctly you can get an alarm that buzzes when you leave your freezer, or any door for that matter, open for more than the time you give for the circuit.

estimated cost: $3.00 to $9.00 using parts from Radioshack. using surplus stores will drive the price down even more.

Just think about it, even though its too simple for you to want to consider, and then think about how much it would cost to get temperature sensors, PIC chips, and complex control circuits just to make an alarm buzz because the fridge was open too long.

Your solution probably costs MORE than a PIC temperature sensing solution, and requires many more parts - also you have the problem of actually generating a signal when the door is open?.

If you're adding a mechanical switch to the door, why not sure connect it straight to a buzzer?, so it buzzes until you shut the door?.

But the idea (as far as I'm aware?) was NOT to modify the freezer.

 

[Someone Electro]

I sometimes like to complicate stuff a bit.

 

[bryan1]

Hi Guy's,
Here's a schematic and overlay of a fridge door alarm and I can't see any reason why you can't use it on a freezer as the parts are rated for - 20 degrees C. Using just 1 IC it's a pretty simple but efficient circuit.

Cheers Bryan

 

[eblc1388]

Interesting stuff.

Anyone knows would a electrolytic capacitor still works(i.e. have some reasonable capacitance) when it is frozen solid in the freezer?

After posting the above I searched the net for an answer. I found, from the following webpage:

http://www.extremetemperatureelectronics.com/tutorial2.html

Quote:
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Electrolytic capacitors typically lose capacitance rapidly upon cooling, and at cryogenic temperatures (below about −150°C) may have perhaps 10% of their room-temperature capacitance.
=====
Unquote:

 

[Someone Electro]

Thats -150°C but a frezer is about -10°C.