Direct Coupled On/Off Touch Switch

The following touch switch circuit uses a CA3240 dual BiMOS op amp to sense small currents flowing between the contact points on a touch plate. Since this circuit is directly coupled with line voltage, a 1 M resistors in series with the touch plates is employed  to ensure user safety, avoiding hazardous high voltage shock. This high resistor values is allowed without decreasing the effectiveness of its function the since the op-amp CA3240 has high input impedance. The CA3059 zero voltage switch is actuated by a positive output on either pin 7 (ON) or pin 1 (OFF) of the CA3240. The internal power supply of the CA3059 powers the CA3240. Here is the schematic diagram of the touch switch circuit:

ON OFF TOUCH SWITCH1 circuit schematic diagram

[Circuit’s schematic diagram source: seekic.com]

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