A simple and low-cost light alarm circuit sharing

This is a simple and low cost light alarm circuit using timer IC555 as a sound generator and LDR to sense the ambient light. This alarm gets activated when the light beam on the LDR photocell is interrupted (You can use the light from a flashlight which will give you a power source to keep it on, this could be 3 volts either AC or DC).

Components List:

capacitance:

C1：0.1uF

resistance:

R1: 100K (potentiometer)

R2: 1K

R3:47K

R4：100K

R5: 27 ohm

R6: 220 ohm

semiconductor:

IC1：555

TR1: 2N3055, C1060 or C1226

D1：1N4002

other:

Speaker 8 or 16 ohms

1LDR/Phototube

When the LDR/phototube receives light, the resistance is low, thus blocking the positive voltage supplied by R4 to IC555 terminal 4, keeping the multivibrator off and the speaker silent. When the phototube stops receiving light, its resistance increases within a fraction of a second, causing it to reach the positive voltage at the above terminal, activating the alarm.

Circuit Note: The LDR should not receive any light other than that used for activation.