Single touch switch circuit

This article introduces a single-button touch switch composed of CD4017. The switch is controlled by a single touch electrode. Every time the electrode is touched, the switch will act (on or off) once. It has the same function as an ordinary mechanical switch and is very convenient to use. The circuit principle is shown in the attached figure, in which HD is a tubular neon bulb, which forms a "self-made photocoupler" with the photoresistor RG, and forms a touch signal input path with the touch electrodes M and R1. The odd-numbered output terminals of CD4017 such as Q1, Q3, Q5, Q7 and Q9 are respectively connected to diodes V2~V6. When one of them outputs a high level, V8 is turned on and triggers the triac VT to turn on. The load connected to the socket is At this time, Q2, Q4... the even-numbered output terminals are floating; on the contrary, when one of the even-numbered output terminals is high level, both V8 and VT are cut off, and the socket load is powered off. When the touch switch is just powered on, due to C1 and R4 Differential action, CD4017 automatically resets to zero, and the socket is in a power-off state. After touching M for the first time, HD starts to glow, the RG resistance decreases, the CL terminal of CD4017 becomes high level, and Q1 outputs high level; after touching M again, CD4017 counts once, and Q1 becomes low level. Q2 outputs a high level, and so on, thereby realizing the touch switch function. The two mains input lines are connected to the touch path through R7 and R8 respectively, so there is no need for a phase line or a neutral line to ensure the normal operation of the circuit. Component selection: The withstand voltage of C2 and VT should be greater than 400V, and the specifications of VT can be determined according to the power of the load. The starting voltage of HD should be lower than 100V, V8 can use 9013, β≥60 is enough, the light resistance of RG should be no less than 20K, and the dark resistance should be greater than 2MΩ. The remaining components can be selected according to the diagram data. As long as the components are in good condition and the welding is correct, the switch can work normally without debugging. The entire circuit can be installed in a 100mm × 70mm × 50mm plastic box and fixed at an appropriate location on the indoor wall. The touch electrodes can be made from 10mm × 10mm copper sheets or scraps of printed boards.