Bathroom automatic hand dryer circuit

Bathroom automatic hand dryer circuit. In the figure, LED is a light-emitting diode; VT is a photosensitive transistor. LED and VT
form an infrared optocoupler, which serves as a signal sensor, and the 1WH8778 switch integrated circuit serves as a control component.
    When the hand reaches under the photocoupler, the potential of pin ⑤ of the TWH8778 switch integrated circuit is higher than 1.6V and is turned on. The current flows through R, triggering the
bidirectional transistor VTH to turn on, and the far-red line is heated. Turn on the EH and dry your hands. After the hand leaves, the switch circuit automatically cuts off and the EH stops
working.