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Capacitive Switch Circuit

2015-01-01 00:15  
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Capacitive Switch Circuit
As shown in the figure, the switch circuit is composed of capacitive oscillator, integrating network, comparative circuit and relay control circuit. When the human body gets close to the metal plate, inductive capacitance over the ground will increase, so that the astable multivibrator formed of 555 will start oscillation or have its oscillation frequency changed. The output alternating square wave will be added to the inphase end of comparator IC2 (LM324) after going through the three-level integrating network to be compared with the reference voltage which has been set. Then it will output a transitioning negative pulse, VT1 will break over, and K will actuate to connect the load circuit. Conversely, the load circuit will be disconnected. Selection of the induction plate should make oscillation frequency be no less than several thousand kHz.