MUSICAL BURGLAR ALARM

This circuit generates a sweet melody for two minutes when it detects the shadow of a moving person. It uses the ROM IC UM66 to produce the melody. The music stops automatically.

LDR is used as the light sensor. In day light, its resistance is low and conducts. This keeps the base of T1 high and it remains off. When the shadow of the moving person falls on the LDR, its resistance increases and the current flowing through it decrease. T1 then conducts and C1 charges. This provides power to IC UM66. Zener diode ZD is used to regulate the supply voltage to UM66 to 3 volts. When UM 66 gets 3 volts supply, it oscillates and the music tone from it will be amplified by T2 which can be heard through the speaker.

Adjust VR1 to set the sensitivity of LDR at the particular light level in the room. Adjust VR1 till the music stops at the particular light level. Move hand over the LDR. Music should hear from the speaker.

Note

If component removal is required for re assembling, do not bend the excess leads of components before soldering. Cut the excess lead close to the PCB and apply some flux. Apply little solder at the contact point. Do not apply, excess solder or over heat the solder points. PCB tracks will detach. Clean the surface with kerosene, or PCB cleaning fluid to remove flux and dirt.