상황
Designing a simple water level controller using an NPN transistor as a switch to drive a pump motor, with a high-level probe to detect water level.
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01
Using an NPN transistor (Q1) as a switch instead of a relay for simplicity and low cost.
02
A pull-up resistor (R1) keeps the transistor on when water drops below the high probe.
03
A second resistor (R2) limits current when the probe is submerged, protecting the transistor base.
04
A flyback diode (D1) protects against voltage spikes from the pump motor.
05Two probe terminals
common grounded probe and high-level sense probe.
Suitable for automatic water tank filling in residential or agricultural settings where a low-cost, reliable electronic control is needed without complex logic.