Capacitive switching circuit based on 555 chip

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Memory chip

As shown, the switching circuit consists of a capacitive oscillator, an integrating network, a comparison circuit, and a relay control circuit. When the human body approaches the induction metal plate, the sensing capacitance to the ground increases, causing the 555-organized astable multivibrator to oscillate or change the oscillation frequency. The alternating square wave of the output is added to the IC2 through the three-stage integration network. (LM324) The non-inverting terminal of the comparator, compared with the set reference voltage, outputs a negative pulse of transition, VT1 is turned on, K is pulled, and the load circuit is turned on. On the contrary, disconnected. The size of the sensing board should be chosen such that the oscillation frequency is not less than several thousand kHz.