Fridge Door Alarm
SummaryIt is very important that you should keep close your fridge door all the time. If they are left open they will no longer do their job. Sometimes it happens we forget to close the door properly in that condition it will give you an alarm that you have not close it. This alarm circuit will allow you to open and close the door without sounding the buzzer but if it has been left open more than the pre-set time it will give an audio visual alarm.
CD4011 is the most commonly used Complementary Metal Oxide Semiconductor (CMOS) chip. It comes in a 14 pin Dual Inline Package (DIP). It has small notch on one side which identifies as pin 1.It consists of 4 independent NAND gate in a single chip. Each gate has 2 inputs and 1 output. Working voltage range of IC is from 5V to 16V. It can deliver approx.10mA at 12V but this can be reduce as power supply voltage reduces.
IC consist of 14 pin in this pin 7 and 14 is connected to battery or DC power supply. Negative is connected to pin 7 and pin 14 is connected to power supply. As we know it has four gates we call it NI1, NI2, NI3, NI4. In first gate NI1 pin 1 and 2 are for inputs and pin 3 is for output. As you can see in the circuit below.
As we can see in the truth table it will provide the output equal to one when any one of the input is low. In another words we will receive the high output when any of the signals goes low. And if both the inputs are high we will receive the low output.
Description
Working of circuit is very simple in standby mode switch SW1 is closed and the current flowing through R1 is grounded through switch. This mean that pin 1 is low and C1 is discharged. As pin 1 is low pin 3 should be high as you can have a look in truth table (we will get output when any of the signal go low). If pin 3 is high pin 5 and 6 is also high and pin 4 remains low. The buzzer will not sound.
When SW1 is open the current flowing through R1 is not grounded now. It is now used to charge C1 as a result voltage on pin 1 begin to rise as capacitor charges. The period of charging depends on the value of C1 and R1 used in our circuit it may take approx. 1 minute after that pin 1 goes high. When it goes high automatically pin 3 becomes low and pin 4 becomes high and alarm start sounding. It will sound until we will close the door again.
Here we have use reed switch with magnet but you can use any switch that suits your requirement.
| Components | |
| IC | |
| IC1(CD4011) |
1
|
| Resistor | |
| R1(2.2ME) |
1
|
| R2.R3,R4(4.7K) |
3
|
| Capacitor | |
| C2(.1uF) |
1
|
| C1(1uF) |
1
|
| Miscellaneous | |
| Reed Switch |
1
|
| T1(BC547) |
1
|
| Buzzer |
1
|
| LED |
1
|
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