This is a Refrigerator Door detector alarm, it will detect light of lamp in the fridge and alert with buzzer.
This projects is small size, easy to make and cheapest.
It will alarm when Small child secretly eating candy or medicine stored in the refrigerator or sometimes forget to close the door is not closed.
Which it Consumes electricity and the refrigerator’s lifespan shorter. Stored food may be spoiled, too.
This problem, we try to create a Refrigerator Door detector alarm.
How does it work.
While we close the refrigerator. Light bulb in the refrigerator is off. The resistance of LDR1 is very high, cause voltage across both R1 and VR1 is less, cause not enough will bias to transistor-Q1 worked then not have current flow to a buzzer-BZ1 thus no sound.
Figure 1 The circuit diagram
When we open door of refrigerator to make the light bulb glow, cause resistance of LDR1 reduce, voltage across at R1 and VR1 rises until makes transistor-Q1 working, have current flow to BZ1, make BZ1 work have alarm sound at output.
The potentiometer-VR1 is adjusted sensitivity of the circuit.
The component list
LDR1- Photo resistors
Q1____CS9013___0.8A 40V NPN transistor
R1____5K 0.25W resistors
R2____1K 0.25W resistors
C1____100uF 25V Electrolytic capacitors
PCB,9V battery, wires, etc.
How to builds and testing
This projects is a few parts we can assemble them on perforated board as Figure 2 we use KIT for my son.
Figure 2 The Refrigerator Door Detector Alarm KIT
Then we test it in cool box, it work well my daughter like and happy.