Building Automatic Touchless Water Tap without Microcontroller

This touchless water tap system operates purely on analog and discrete logic, completely omitting the need for a programmable microcontroller or digital code. The core sensing is handled by the RCWL-0516 microwave radar sensor, which uses Doppler radar technology to detect movement within its adjustable range. When a user approaches the tap and places their hands near the sensor, the microwave module detects the motion and outputs a high DC trigger signal. This output signal is routed to a relay module, which acts as an electrically operated switch. Because the low-voltage sensor output cannot directly drive high-power inductive loads, the relay energizes using power supplied by the 12V DC adapter. When the relay triggers, it completes the circuit for the 12V DC solenoid valve, opening the internal valve mechanism to allow pressurized water to flow through the hoses, pipes, and tap assembly. Once the user removes their hands and motion ceases, the radar sensor drops its output signal, the relay disengages, and the solenoid valve snaps shut to immediately cut off the water supply. Independent power supplies, including a separate 5V DC adapter where needed, ensure stable voltage separation across the sensing and actuation stages.