Night Security LightCircuit

This simple circuit activates a light approximately two hours after midnight, a time when many robberies occur. The circuit is based on a CMOS IC 4060 to achieve the necessary timing. During the daytime, the light-dependent resistor (LDR) has low resistance, keeping pin 12 of the IC high and preventing it from oscillating. In darkness, the resistance of the LDR increases, causing pin 12 of the IC to go low and enabling oscillation, indicated by the flashing of LED D3. The timing components R1, R2, and C4 are selected so that the output at pin 3 of the IC goes high after 8 hours, which in turn activates a triac to switch on the lamp around 2:00 AM. In the morning, the LDR's resistance decreases, returning pin 12 of the IC to high and stopping the oscillation, which turns off the lamp. The switch S1 allows for manual activation of the lamp, while capacitor C2 prevents false triggering.

The circuit employs a CMOS IC 4060, which functions as an oscillator and timer. The operational principle relies on the interaction between the LDR and the timing components. The LDR is a critical component that changes its resistance based on ambient light levels. During the day, when light levels are high, the LDR maintains a low resistance, which keeps pin 12 of the IC high, effectively disabling the oscillator function of the IC.

As night falls and light levels drop, the resistance of the LDR increases, resulting in a low signal at pin 12. This change enables the IC to oscillate, generating a square wave output at pin 3. The frequency of oscillation is determined by the values of resistors R1 and R2, and capacitor C4, which are chosen to create a timing delay that results in the output going high approximately 8 hours after the circuit is activated, aligning with the desired time of 2:00 AM.

When pin 3 goes high, it triggers a triac, which is a semiconductor device capable of controlling power to the lamp. The triac allows for the lamp to be turned on at the specified time, providing illumination when it is most needed for security purposes. The manual switch S1 offers a convenient way to override the automatic function, allowing the user to turn the lamp on at any time.

Capacitor C2 is included in the design to suppress any transient signals that might inadvertently trigger the circuit, ensuring reliable operation. This feature is particularly important in environments where electrical noise may be present, as it helps maintain the integrity of the timing function and prevents false activation of the lamp. Overall, this circuit provides an effective solution for enhancing security through timed lighting.This simple circuit switches on a light around 2 hours after midnight, the time at which most of the robberies taking place. This simple circuit is build around a CMOS IC 4060 to obtain the required timing. During day time the LDR has low resistance and keeps the pin 12 of the IC1 high, preventing the IC1 from oscillating.

When it is dark the LDR r esistance becomes high and the pin 12 of IC1 becomes low and the IC starts oscillating, which indicated by the flashing of LED D3. The values of the timing components R1, R2, C4 are so selected that the out put pin3 of IC1 goes high after 8 hours.

That means the high output drives the triac to switch on the lamp around 2`O clock. At morning, the LDR resistance drops and the pin 12 of IC1 goes high and stops the oscillation, making the lamp OFF. The switch S1 can be used to manually ON the lamp. The capacitor C2 prevents false triggering. 🔗 External reference