The scenario
This circuit uses a soil moisture sensor (resistive) in a voltage divider, compared against a reference to drive a relay for irrigation control. The op-amp provides hysteresis-free threshold detection.
What is in this drawing
Read the decisions behind it.
01
Using an op-amp comparator for accurate threshold detection
02
Flyback diode protects transistor from relay inductive kickback
03
Resistive sensor with fixed resistor forms potential divider
Suitable for DIY automatic plant watering systems, smart garden projects, and educational demonstrations of sensor-based control.
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