1. Initial Condition and LDR Control:
The LDR is in parallel with a 100kΩ resistor. In bright light, the LDR has a low resistance, effectively shorting out the base of the first transistor (PNP), preventing the circuit from working.
In darkness, the LDR's resistance increases significantly, allowing the 100kΩ resistor to take over and supply enough bias to the PNP transistor to turn on the circuit.
2. Charging the Capacitors:
The 470µF capacitor charges through the 100kΩ resistor. As it charges, it builds a voltage across the base of the PNP transistor.
Once this voltage reaches a certain threshold, it forward-biases the PNP transistor, allowing current to flow from its emitter to collector.
3. Transistor Switching and LED Flashing:
When the PNP transistor turns on, it triggers the NPN transistor by providing it with base current.
As the NPN transistor conducts, it allows current to flow through the LED and the 100Ω resistor. This 100Ω resistor controls the discharge rate of the 470µF capacitor, determining the LED’s flash duration.
4. Discharge Phase:
Once the 470µF capacitor discharges, the PNP transistor no longer receives sufficient base current, turning it off.
This stops the current through the NPN transistor, turning off the LED.
5. Cycle Reset and Repetition:
After the capacitors discharge, the circuit resets, and the cycle begins again with the 470µF capacitor charging.
The circuit will repeat this cycle as long as it remains in the dark.
The LDR controls the circuit’s operation based on ambient light, only allowing it to flash in darkness.
The 470µF capacitor sets the flash timing, while the 100Ω resistor affects the LED’s flash duration.
The PNP-NPN transistor pair works together to control the LED flashing.
Blue light, especially if it’s flashing, can deter bats. Bats are highly sensitive to blue and UV light, which can disrupt their natural behavior and navigation. Flashing blue lights are even more disturbing due to the changing intensity, which can make them avoid areas where such lights are present. However, excessive light may also stress them, so it’s best to use it sparingly if trying to prevent bats from entering a specific area.
