Refrigerator Alarm DIY HOME

Abstract

I made a refrigerator alarm because I forgot to close the door of the freezer in the peak of the summer heat and had a terrible experience.

	The manufacturing cost is	1,793 (jpy)
	Standby Power is	Below a limit of measurement. (power meter I own)

My small two-door fridge for students doesn't have an alarm function.

Large fridge nowadays have an alarm for prevent to leave the open door as a matter of course.

However, there is to be a fridge of a strange specification that a vegetable compartment does only not have it for some reason.

Therefore this article may be useful for something.

I have set up slightly lifting the front side of the fridge, so the door closes automatically, even if I forgot to close the door.

But, in this failure, because I had put the food in sloppily, it was caught in the door. And I didn't notice that.......

Conclusion

The finished is like this.

I used the AC adapter to the power, stuck the main body of the alarm to the fridge with the double-sided tape.

Reed switch sensor is.

The photo is the side of the fridge, the drawer part of the freezer.

Structure

• I have put the reed switch in the case.

• The universal circuit board is processed.

Circuit

I made the circuit like this.

I decided to use the two general-purpose ICs without using a microcomputer.

Because don't have to worry about unnecessary radiation or download especially cumbersome on a Mac .

And, if you can solder, you can make it.

• As the specification, the one "pip" sound is set to when you close the door, and the intermittent "peep, peep, peep ..." sound is set to when remain open for about 20 seconds or more.

• The timer IC raises an intermittent sound, and the monostable multivibrator IC have set the time for control.

• Control of the alarm sound is done directly on the power of the timer IC.

There is a time constant, it might be some worry of the latch up.......

Buzzer is directly driven by the timer IC.

• Only monostable multivibrator IC is connected to the power source at all times.

Standby power is below the limit of measurement according to my power meter (TAP-TST5 of Sanwa Supply).

In the calculation, it's about 13.2μW. However, it doesn't contain the efficiency of the AC adapter.

Parts Specification

Link to the specifications of the timer IC - LMC555

Link to the specifications of the monostable multivibrator IC - 74HC123AP

Other Circuits

The simpler circuit and cost, please click here.

Parts Processing

Circuit Board Processing

• Cut the 2.54mm pitch, 1.6mm thickness universal circuit board.

• Circuit board size is 75.2 * 44mm. The size of the notches 10.16 * 10.16mm.

As work, cut off the horizontal 30th hole position, the vertical 18th from the end of the board, and detach at the 4 * 4th hole position.

Then, shave it with a file so that the width is less than 44mm, and further shave about 1mm the DC jack side.

• After having cut a horizontal direction with a metal-handsaw, make a cut in both sides with a box cutter to the vertical direction and break the notch part of the corner by hand.

• 3.5mm diameter is only one place for the DC jack, the other holes is 3.2mm diameter.

Case Processing

• Open the square hole in the case for the DC jack.

• Stick the paper pattern to the case with the tape, fit the tip of the drill diameter of 2mm along the lines of the inner square, drill holes at an appropriate interval.

• cut between holes with nippers.

• Shave it with a file along the lines of the outer square of the paper pattern.

The paper pattern was created in OpenOffice.

Circuit Board

I did this arrangement to make a space for the reed switch at the top of the component side.

The following is a state in which the components are mounted. Soldering ..... I am badly.

• Transistor is bent by hand after soldering.

• When you mount the component with a direction, you need to pay attention to the direction of parts (e.g. ICs, transistors, diodes, chemical capacitors, buzzer).

• Finally, check that it's not short-circuited by the tester.

Assembly

Reed Switch Position

• The reed switch can be placed on either side.

Assembly

• Fix the circuit board with four tapping screws (M3, 5mm in length).

• Stuck the reed switch with double-sided tape to the lid of the case.

This time, because I plan to put it on the left side of the fridge, I stuck it in the position shown in the picture below.

The lid side of the main body of the alarm is stuck on the fridge with the double-side tape.

If you have fixed it to the fridge to this direction, the back side of the case becomes on the surface.

But, it's convenient. it's able to open the case without peeling off the double-sided tape in the case of repair.

• Finally, the lid is fixed with the screws supplied with the case.

Output Cost

The price of the AC adapter is high. The power consumption is small, so you might be able to make it cheaper if you use the battery.

Also, if you use the case which is sold in a 100-yen shop, I think you can create a little more cheaply.

BOM

Part name	Type	Part NO.	Quantity	Unit Cost (jpy)	Minor Total (jpy)	Comment
Total					1,793
IC	CMOS Timer	LMC555 (NS)	1	20	20	[shop] akizuki-denshi 100(jpy)/5pcs
IC	Dual Retriggerable Monostable Multivibrator	TC74HC123AP (Toshiba)	1	78	78	[shop] marutsu-parts
SW	reed switch w/magnet	MC-14AG	1	250	250	[shop] akizuki-denshi
Buzzer	piezobuzzer 3.6KHz(12V)	PKB24SPCH3601 (Murata)	1	150	150	[shop] akizuki-denshi
Transistor		2SC1815Y	1	8	8	[cost] akizuki-denshi 80(jpy)/10pcs
Diode	general diode	e.g.1N4148	5	2	10	[cost] akizuki-denshi 100(jpy)/50pcs
Resistor	1k (~1/4W)		1	1	1	[cost] akizuki-denshi 100(jpy)/100pcs
Resistor	10k (~1/4W)		5	1	5	[cost] akizuki-denshi 100(jpy)/100pcs
Resistor	220k (~1/4W)		1	1	1	[cost] akizuki-denshi 100(jpy)/100pcs
Resistor	330k (~1/4W)		1	1	1	[cost] akizuki-denshi 100(jpy)/100pcs
Capacitor	1uF, film or chemical W7xH8xD6.5mm	e.g.ECQV1H105JL2(W) (film)	1	63	63	[cost] marutsu-parts
Capacitor	0.01uF, ceramic	e.g.CCDC50V103	2	5.2	10.4	[cost] marutsu-parts 52(jpy)/10pcs
Capacitor	10uF (6.3V~), chemical		1	10	10	[cost] akizuki-denshi
Capacitor	100uF (6.3V~), chemical		1	10	10	[cost] akizuki-denshi
DC Jack	2.1mm standard internal diameter:2.1mm external diameter:5.5mm	2DC0005D100	1	25	25	[shop] akizuki-denshi 100(jpy)/4pcs
Circuit Board	universal type,2.54mm Paper base epoxy resin	e.g.95x72mm (or 72x48mm)	1	120	120	[cost] akizuki-denshi
Plastic Case	W50xH26xD90.3mm	SS-90A (Takachi)	1	283	283	[shop] marutsu-parts
AC Adapter	3.3V,2A	GF12-US03320	1	600	600	[shop] akizuki-denshi
Solder						small quantity
Screw	M3,l=5mm,self-tapping for circuit board	e.g.EM-3 (Takachi)	4	4.4	17.6	[cost] marutsu-parts 220(jpy)/50pcs
Double Sided Tape	280mm (90mmx2pcs+5mmx2pcs)	KPG−19 (3M)		130	130	[cost] amazon 697(jpy)/1.5m

[shop]： is the name of the shop where I purchased this time.

[cost]： is source of cost.（I used parts were previously purchased or my junk.）

Tools

• Metal handsaw

• Box cutter

• Drill

• Plus driver

• Soldering iron

• Solder Wick (Desoldering tool)

• Tweezers

• Nippers

• Radio pliers

• Scissors

• Metal file

• Tester

...... etc.

Setting

• At first, stick the magnet for the reed switch to the door side of the fridge with double-side tape.

• Keep close the fridge door. Bring close the main body of the alarm to the magnet. And, stick it with the double-sided tape to a position that is "pip".
  Because it's eye-catching, might be better to stick on the wall side .

• Vibration during opening and closing of the fridge is pretty big, so I use a super strong double-sided tape that seems good.

If you tear it off, I think that either which you warm it with a dryer or hangs down salad oil, but I don't want to do.

Attention

I didn't check the waveform. Because I didn't have any problem in the actual operation.

If you stuck the main body of the alarm to the fridge by the sheet-like magnets, there's a possibility of malfunction. Because using a reed switch.

I thought it's okay if it's weak magnet, and I tried with the magnet sheet for plumbers advertising that is put in the mailbox from time to time. However, although not malfunction, the magnetic force was too weak, it was fallen by vibration during opening and closing of the fridge door.

The alarm sound is smallish. Because the voltage is 3.3V and the buzzer is confined in the case.

The breakdown voltage of the monostable multivibrator IC is 7V, so I have tried a 5V AC adapter that was in the house, audibility was not much different.

I think that making holes in the side of the main body is effective in increasing the volume. But I don't try, personally just so good at present.

− About the contents of this page, I don't guarantee anything. Please judge in self-responsibility −

---

Copyright © 2012-2014 chococake All rights reserved.