Refrigerator open door alarm

[Sam Fisher]

Refrigerator's open door alarm

Hi there,
If in a period of 20 seconds refrigerator's door be left open, the circuit will activate and will be warn you by hooting.
There is a light bulb in the refrigerators, When the refrigerator's door is open , light is on and the circuit photoresistor detects that the door is open...Circuit alarm period is 20 seconds.If you connect D2 to pin2 of Ic1 it will causes the delay time reduce by half.Time delay will be changed if you change the value of C1 and resistance of R3 .
Any photoresistor can be used.
Resistance calculated for the circuit is negligible, so you can remove the SW from the circuit .
Always put the circuit near the light bulb and never put it in thr frazer.

Parts list:


R1____________10K 1/4W Resistor

R2___________Any kind of Photoresistor

R3,R4________100K 1/4W Resistor

C1____________10nF 63V Polyester Capacitor

C2___________100µF 25V Electrolytic capacitor

D1,D2_______1N4148 75V 150mA Diode

IC1___________4060 14 stage ripple counter and oscillator IC

Q1___________BC337 45V 800mA NPN Transistor.

BZ1__________Piezo sounder (incorporating 3KHz oscillator)

SW1__________Miniature SPST slide Switch

B1___________3V Battery (2 AA 1.5V Cells in series)

Note: This is not my project and i cant help you if you have questions...
Thanks.

 

[Boncuk]

ํYou might find a lot of interested people in Scotland. They remove the fridge light to make sure it is turned off (may be the operator forgets turning it off) when the door is closed.

Just modify your circuit so it will alarm when the door is open.

 

[Hero999]

Make R2 a thermistor, it's far more useful to have it triggered by high temperature than light, in a fridge.

 

[ericgibbs]

Make R2 a thermistor, it's far more useful to have it triggered by high temperature than light, in a fridge.

hi,
So you are saying its better to have high tempr alarm that goes off, after the food has defrosted.

 

[kchriste]

Plus the high temp alarm would be hard to hear when the fridge door is closed anyway.
You could make a circuit which monitors the temperature of the condenser coils on the back of the fridge and sound an alarm if the coil temp has not risen enough above ambient with in a set time frame. This would indicate a compressor or power failure. It wouldn't help with the door being left open. You'd need a circuit like Sam's for that.

 

[Hero999]

hi,
So you are saying its better to have high tempr alarm that goes off, after the food has defrosted.

It's a fridge do it doesn't freeze.

Point taken though, remove the timer and replace it with an LM311.

Plus the high temp alarm would be hard to hear when the fridge door is closed anyway.

True, but an LDR wouldn't be any better, it wouldn't tell you if the compressor broke down and if the door was left open the food would already be too warm by the time the alarm has sounded.

 

[tinkerunique]

Just a simple thought from a simple mind - why not use a switch like an auto door switch / buzzer instead of a dome light. - There are 110v. switches & buzzers used on doors/safes/etc.

 

[kchriste]

While that would work, the idea of a project like this is it's simplicity of use and installation. Simply put your battery powered project in the fridge and the LDR will detect when the door is open due to the fridge light coming on. No modifications to the fridge required. No angry wife.

 

[Boncuk]

Why would somebody put a complete battery operated circuit into a fridge?

A fridge normally contains moist air which means trouble for any PCB. Batteries deplete faster at low temperatures. Additionally the circuit requires some space in the fridge and being covered by food it would certainly not work at all with the LDR "sitting" in the dark.

Triggering an alarm circuit as soon as the door is open you might get trouble with your wife as well.

This is my suggestion: Use a temperature sensor or a varistor cast in a reasonably big block of epoxy. (Instant alarm when opening the door is not desired, since the temperature inside the fridge will rise slightly with the door open.) The expoxy block will slowly transfer the temperature increase to the sensor, thus triggering the alarm circuit delayed.

For my freezer I cast the varistor in a block of 5X3X2cm (including the cable) and had the entire circuit (except for the sensor)on top of the freezer with a big loudspeaker and AF-amplifier. The temperature setting of the freezer was set to -22deg/C while the temperature setting of the alarm circuit was set to -20deg/C.

Those two degrees difference give enough time to open the door and remove or put in food without triggering an alarm, still safe enough to keep the food well frozen.

Boncuk

 

[mneary]

A simple NO window/door switch (and magnet) from an alarm system could replace the LDR. Then the alarm could sit on top of the fridge.

 

[KMoffett]

Another, similar circuit: EDN PDF

ken

 

[Hero999]

I agree with Boncuk, this is a silly circuit and there are much better ways of solving the problem.

 

[marcbarker]

A fridge normally contains moist air which means trouble for any PCB.

What inside a sealed enclosure? The light bulb is in a cold moist air.


Batteries deplete faster at low temperatures.

Do they?


Additionally the circuit requires some space in the fridge and being covered by food it would certainly not work at all with the LDR "sitting" in the dark.

Granted


Triggering an alarm circuit as soon as the door is open you might get trouble with your wife as well.

The OP circuit has a delay-on timer.


varistor cast in a reasonably big block of epoxy. <..> , thus triggering the alarm circuit delayed.

Delayed on timer again.

OK, but when you come down to the kitchen in the morning and the fridge door is ajar, you say "What's happened to the alarm?", Wife replies "Oh, while you were at the pub, I threw it in the garage, because it was still making a beeping noise, even after I shut the door. I tried opening and shutting the door and it wouldn't stop"

 

[Boncuk]

Hi Marc,

Knowing about refrigerators you should know that it contains lots of moist air, caused by evaporation of ice while the door is open. The light bulbs are normally mounted behind a glass plate, sometimes (cheaper type fridges) under a plastic hood.

Batteries don't really deplete faster at low temperatures, but their capacity reduces considerably (with the effect of a depleted battery).

If you own a car you will have noticed that the starter cranks the engine much slower at temperatures well below 32deg/F (0deg/C).

When it comes to real frosty weather (-32deg/C) and the diesel fuel becomes kind of solid, the engine oil is almost the same as the fuel and the engine won't crank at all. (Tougher oil + reduced battery power)

If a circuit has a delay for "ON" it should also have been taken care of "OFF"

Boncuk

 

[marcbarker]

The light bulbs are normally mounted behind a glass plate, sometimes (cheaper type fridges) under a plastic hood.

Not on mine, it's broke!


Batteries don't really deplete faster at low temperatures, but their capacity reduces considerably (with the effect of a depleted battery).

What about the capacity when warmed back up, being out of the fridge?


If you own a car you will have noticed that the starter cranks the engine much slower at temperatures well below 32deg/F (0deg/C).

That's internal resistance (current delivery capacity), not "capacity", you spoke of. Besides, the "capacity" returns when it warms back up doesn't it?


When it comes to real frosty weather (-32deg/C) and the diesel fuel becomes kind of solid, the engine oil is almost the same as the fuel and the engine won't crank at all. (Tougher oil + reduced battery power)

That's not "capacity", that's current capacity & increased friction


If a circuit has a delay for "ON" it should also have been taken care of "OFF"

The OP has a 20 sec delay-on and no delay-off. An lagged thermal sensor has equal delay on and off.

 

[aljamri]

Another, similar circuit: EDN PDF

ken

Thanks for the link,I was looking for 4 - 20 ma circuit

 

[aljamri]

I need this circuits idea as my children keep the fridge open for no reason except they don't know why they opened it.

I prefer using small 12FXXX PIC to do this circuit, may be I'll combine all the above sensors is inputs .

 

[Boncuk]

What about the capacity when warmed back up, being out of the fridge?

Are we getting silly now? Would you take the cirucit out of the fridge to bring the battery back to life?

That's internal resistance (current delivery capacity), not "capacity", you spoke of. Besides, the "capacity" returns when it warms back up doesn't it?

Call it as you like. Nevertheless unusable capacity is not what you want, do you?


When it comes to real frosty weather (-32deg/C) and the diesel fuel becomes kind of solid, the engine oil is almost the same as the fuel and the engine won't crank at all. (Tougher oil + reduced battery power)

That's not "capacity", that's current capacity & increased friction

Where did you find the word "capacity" in that sentence?


If a circuit has a delay for "ON" it should also have been taken care of "OFF"

The OP has a 20 sec delay-on and no delay-off. An lagged thermal sensor has equal delay on and off.

I didn't say to have a delayed "off". I did say to have an "off". If it won't work it's no "off"

And now, please get off my back, will you?

 

[KMoffett]

Why would you put the electronics and battery inside the refrigerator? All you would need are two fine (32AWG) wires, connecting the photo-detector on the inside to the electronics on the outside, covered with tape and running under the door seal.

But this is all silly anyway...right?

Ken

 

[Boncuk]

Why would you put the electronics and battery inside the refrigerator? All you would need are two fine (32AWG) wires, connecting the photo-detector on the inside to the electronics on the outside, covered with tape and running under the door seal.

Ken

That's exactly what I did for the freezer alarm. No supercooled batteries and always working properly.

Boncuk