The NPN transistor is used as a switch. When the capacitor charges or discharges to a certain level, it biases the transistor accordingly.
Resistor (R1):
R1 is connected between the positive voltage rail and the base of the NPN transistor. It is used for biasing the transistor.
Resistor (R2):
R2 is connected between the base of the NPN transistor and the discharge point. It is used for discharging the capacitor.
Capacitor (C1):
C1 is connected between the collector of the NPN transistor and the discharge point. It is used for timing the circuit.
LED:
The LED is connected in series with a current-limiting resistor (not shown in the diagram) between the collector of the NPN transistor and the positive voltage rail.
When power is applied, the capacitor (C1) begins to charge through the resistor (R1) towards the positive voltage rail.
The charging process biases the NPN transistor’s base, allowing current to flow from the collector to the emitter.
As the capacitor charges, the voltage at the base of the NPN transistor increases. When it reaches a certain level, the transistor turns on.
When the transistor turns on, the capacitor begins to discharge through the resistor (R2), creating a timed delay.
The LED lights up during the discharge phase, providing a flashing effect.
Once the capacitor discharges sufficiently, the transistor turns off, and the process repeats.
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