Visitor Alarm Circuit Diagram Using IC 555

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Description

                  Figure shows the circuit diagram of the 'Visitor Alarm' . Here I have used a LDR and a mono stable Multi Vibrator for making this circuit . When who breaking the LED ray, the LDR has high resistance so the transistor will be OFF and the pin number two of the IC 555 is negative then the IC 555 will be triggering so the output is ON. When who don't breaking the LED ray, the LDR has low resistance so the transistor will be ON and the pin number two of the IC 555 is positive after that the IC 555 doesn't triggering so the output is OFF.

Circuit Idea

Making Of LDR and LED

           Cover both items with a black insulation tape. See the below images for further details.

LED	LDR

Arrangement Of LDR and LED




Parts List 

Component No:	Value
R1	10K
R2	10K
R3	680R
R4	10K
C1	10MF
C2	103pF
Q1	BC548
D1	White LED Or LASER
	LDR
U1	NE555
B1	6V Buzzer