Refrigerator open door alarm

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The battery inside the fridge is powering a CMOS circuit, not cranking an engine. The battery Ah capacity, or loss of current delivery capacity is not really the issue is it?. The mention of "capacity" depletion is silly isn't it? If I remember correctly, a suggestion was made that "The battery depleted quicker in the fridge". Many people keep unuused batteries in the fridge (rightly or wrongly) to extend their shelf life.

Call it as you like. Nevertheless unusable capacity is not what you want, do you?
Yes, for the most part I agree with you and if I was cranking an engine inside the fridge, capacity and capacity mean the same to me. But I thought we we talking about a battery powering a CMOS circuit "depleting" ?

And about the "delay". In a typical alarm, it is desirable for the alarm condition (beeper) to cease as soon as the trigger causing the alarm has been removed, after being 'cancelled' by the person taking responsibility for the situation (closing the door). I was merely pointing out that thermally lagging the trigger sensor will have a delay both ways, but a light sensor + on timer will not. After all, the OP was a 'door left open alarm', not a 'temperature alarm'.

This has made me think. Given the choice, I would choose your lagged sensor scheme, rather than a 'door open alarm', since yours reacts when the food is actually increasing temperature unknowingly, and that it should be made known with an alarm. Arguably, someone causing the alarm by leaving the door open deserves to be punished by a few minutes of beeping after the door is reclosed, in the same manner as someone was cooking breakfast under a smoke detector has to endure hearing damage for a while or remove the battery.

When I was project responsible for development and manufacture of a toxic gas alarm, the alarm unit had an 'alarm mute' button, which turned off the sounder only, but the alarm condition was still there until 1. the trigger was removed and 2. the cancel switch operated. If the customer wanted a response delay, they were responsible for the amount of seconds delay they programmed, since they owned that risk, not us.
 
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I did that too, for our blood bank refrigerators, after a disastrous loss of one full of autologous blood. And for multiple IV pumps in isolation rooms that were connected to the nurse call system. On both you could pause the alarm, but not cancel it until the alarming condition was corrected.

Ken
 
Question related to this post, i built a similar circuit with a photo resistor it works fine if there is a light in the fridge, but in low light from the fridge door being cracked open it wont set off the circuit, how could i make the circuit more sensitive. Use a smaller resistor for R1?

Thanks
 
Some one I know has a pig in the fridge which oinks when the door is open, it is battery operated and has worked for the last 10 year that I know of and they only change batteries occasionly.
 
Some one I know has a pig in the fridge which oinks when the door is open, it is battery operated and has worked for the last 10 year that I know of and they only change batteries occasionally.
I'd like to know this circuit

However sometimes , children left fridge door almost closed (no completely colsed) , so the inside light is off. How this problem can be solved?
 
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