morning light activated alarm circuit

This project involves a light-activated alarm or morning alarm circuit that produces a pleasant melody upon detecting light. To use this circuit as a morning alarm, it should be placed in a location that receives morning sunlight. A 500K variable resistor is used to adjust the sensitivity of the circuit to light levels, allowing the melody to trigger at a specific light intensity each day. The circuit can also function as a light-activated alarm for other light sources, requiring the same adjustment of the variable resistor. The melody generation is facilitated by the UM66 integrated circuit (IC), which is a CMOS IC housed in a TO-92 transistor package. The operation of the circuit is straightforward: the BC547 transistor acts as a switch. When the light-dependent resistor (LDR) detects light, its resistance decreases, activating the BC547 transistor. This, in turn, allows 3 volts to flow through the transistor, powering the UM66 melody circuit. Additionally, a 2N3904 transistor is employed to amplify the melody's sound, enabling it to drive an 8-ohm speaker.

The light-activated alarm circuit is designed to provide an auditory alert in response to ambient light levels. The core components include a light-dependent resistor (LDR), which serves as the primary sensor, and the UM66 melody IC, which generates the sound output. The LDR's resistance varies inversely with light intensity; as light increases, the resistance drops, leading to the activation of the BC547 transistor.

The circuit's configuration is as follows: the LDR is connected in a voltage divider arrangement with the 500K variable resistor. This setup allows for precise tuning of the light threshold at which the alarm will activate. The output from the voltage divider feeds into the base of the BC547 transistor, turning it on when the light level exceeds the set point. The collector of the BC547 is connected to the power supply, typically 3V, which is sufficient to power the UM66 IC. The UM66 is specifically designed for melody generation and will produce sound when supplied with the appropriate voltage.

To enhance the audio output, the 2N3904 transistor is used as a sound amplifier. The collector of the 2N3904 connects to the speaker, while its base receives the output signal from the UM66 IC. This configuration allows the circuit to drive an 8-ohm speaker effectively, producing a louder and clearer melody.

For installation, the circuit should be placed in a location where it can receive direct sunlight in the morning. The variable resistor should be adjusted according to the desired sensitivity to light, ensuring that the alarm activates at the preferred light level. This versatility allows the circuit to be adapted for various lighting conditions, making it suitable for different applications beyond just a morning alarm. Overall, this light-activated alarm circuit combines simple components to create an effective and engaging solution for sound-based alerts triggered by light.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 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. 🔗 External reference