The patch tact switch can be used to control low-power household appliances such as lights and exhaust fans. The electronic switch is actively turned off after the mains power failure, and will not be turned on by itself when the power is turned on again (you need to press the control button to turn on), which can prevent electrical energy consumption or accidents caused by long-time electrical power on. Each time the waterproof light-touch switch is powered off, the YO terminal of the IC outputs a high level, the Yl terminal is a low level, V is non-conducting, K is in an open state, and the electronic switch is in an off state. As long as S is pressed once, V is turned on and K is closed, and the electronic switch can be turned on. Component selection, Rl selects 1-2W metal film resistors; R2-R5 selects 1/4W carbon film resistors or metal film resistors. Cl selects a polyester capacitor or CBB capacitor with a withstand voltage of 400V; C2 selects an aluminum electrolytic capacitor with a withstand voltage of 25V; C3 selects an aluminum electrolytic capacitor with a withstand voltage of 16V. When it is pressed again, the above action is repeated, the bistable circuit condition is reversed again, UD outputs a high level again to make Q1 cut off, and OUT stops output. If SW-PB is spread out when C2 has not been charged to the UB threshold, the UA output will turn to low level, and C2 will quickly discharge to UA through D1, because C2 will discharge through D1 before it is charged to the UB threshold. , The output status of UB is still high level, the bistable circuit has no trigger signal, and the waterproof tact switch is invalid.