A soil moisture sensor or two metal probes are inserted into the soil. The conductivity of the soil affects the resistance between the probes.
NPN Transistor (BC547):
The NPN transistor is used as a switch. When the soil moisture level changes, affecting the conductivity, the transistor is biased accordingly.
Resistor (R1):
A resistor is connected between the base of the NPN transistor and the positive voltage rail. This resistor is used for biasing the transistor.
LED (Indicator):
An LED is connected to the collector of the NPN transistor. When the soil moisture level drops (or rises, depending on the configuration), the transistor turns on, allowing current to flow to the LED.
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