One of the water and electricity saving faucet circuits

The circuit of one of the water- saving and energy-saving faucet circuits is shown in the figure. In the figure, H is the 12V indicator light, VTi is the phototransistor (it can be replaced by a 3DG6 tube with the top of the tube filed off, and the top of the tube faces the lens ), and Y is the solenoid valve installed on the water pipe . When washing hands, cover the light source with your hands, Y is attracted and water is supplied; when your hands are removed from the light source, Y is released and water supply is stopped.