Fridge door alarm circuit

[Guest r816wsd]

could anyone explain how the fridge door alarm circuit works in technical terms. How does the 6040 IC work

Project Link: http://www.electronics-lab.com/projects/sensors/011/index.html

[mixos]

The above circuit uses the CD4060 IC which is a binary counter. I attach you the datasheet.

CD4060BC.pdf

[mixos]

Fridge door Alarm
http://www.electronics-lab.com/projects/sensors/011/index.html



Explanation (based on the existing explanation):

With the door closed the interior of the fridge is in the dark, the photo resistor R2 has a high resistance (>200K) thus clamping IC1 by holding pin 12 which is the RESET PIN at high logical state (logical 1) so the internal counters don't count and all output pins (Qx) are at logical 0.

Pin 12 has a voltage [R2/(R1+R2)]*VDD where VDD is the battery voltage. The result is a volatge close to VDD which is a logical 1 and clamping 4060 to reset state.

When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance (<2K), pin 12 goes low (0 logical state) and IC1 starts counting.

IC1 starts counting means that the internal oscillator goes ON and it is producing a square wave with a frequency which is set by R3, C1 and give out from the form (depending on datasheet):

f=1/(2,2*C1*R3) => f=454 Hz

This square wave is taken out from Q14 with a result frequency

f/(2^14)

and from Q7 with f/(2^7)

So the output waves Q14 and Q7 look like this:



after a preset delay (around 20 seconds in this case) the piezo sounder beeps for 20 sec because the low output of Q14 makes D1 ON =>Q1 ON. Then stops for the same lapse of time (Q14 is in high state and D1 is OFF => Q1 is OFF) and the cycle repeats until the fridge door closes.

D2 connected to pin 6 of IC1 makes the piezo sounder beeping 3 times per second.

[irabot]

I have completed the fridge alarm circuit and i have problems. The buzzer keeps sounding even with r2 in or out can someone help me??

Ivan

[audioguru]

Hi Ivan,
Welcome to out forum. ;D
Are the diodes installed backwards?
Are the pins of the transistor wired properly?

[logan_dslasher]

excuse me, may i butt in? audioguru? you have just showed a BC337 pin configuration. that's the same transistor i am using in the whistle responder right? all this time i thought that the first pin is the emitter... this could be the reason why i can;t get the project to work..

[audioguru]

Transistors operate much better when they are wired correctly.

[ZaZo4EvEr]

Hey every body i've tried to build this circuit but the problem that i faced is that the sound of beeping is too low can someone help me to fix this error

[audioguru]

If you use brand new alkaline battery cells then the supply voltage is only 3.0V and the beeper gets only about 2.2V from the emitter-follower transistor. A beeper barely works with only 2.2V.
Use a 6V, 9V or a 12V battery and it will be much louder.

[ZaZo4EvEr]

I used a 9V battery but I still have this problem.
Can you pist to me a picture of Piezo Sounder may the problem in it.I may bought a wrong device..Can you send your replay via e-mail plz....
[email protected]

[audioguru]

It is a piezo beeper with a built-in oscillator. When the circuit applies a voltage to it then it beeps. The circuit makes a delay then makes the piezo beep 3 times per second.
With only a 3V battery it will not be loud.
With a 9V battery then it should be much louder. if the transistor is connected backwards then it will not be loud. Look on the datasheet for the transistor to see which pin does what.

A piezo speaker looks similar but doesn't have a built-in osccillator so it would just make a faint clicking sound in this circuit.