A very interesting project of a light activated alarm or morning alarm circuit. The circuit will produce a beautiful melody when it will detect light. You can use this circuit as a morning alarm, for this purpose first select a permanent place in your home which gets morning light and then adjust the
500K variable resistor to produce melody on the desired amount of light, after adjusting the desired light level, this circuit will produce melody on the same amount of light every day. You can also use this circuit as light activated alarm for other sources of lights, for this purpose also you have to adjust the 500K variable resistor to produce the melody on the desired amount of light. The melody circuit is built around the UM66 IC, which is a CMOS IC comes in TO-92 transistor package.
Working of Circuit:
Working of the circuit is simple the transistor BC 547 is working as a switch when the LDR detects light its resistance will decrease which will switch on the BC547 transistor and as a result 3 volts start passing through the transistor which will power on the UM66 melody circuit. The transistor 2N3904 is used to amplify the sound of the melody to drive an 8 Ohms speaker.