The proposed device allows you to enable or disable a variety appliances one touch of the sensor E1 - metal plate (see figure). It is simple in design and can be used in devices with battery voltage 3…15 V.
How does the switch? When a finger touches the sensor trigger DD1.1 forms the output pulse, which translates the trigger DD1.2 in another state. If, say, after the first touch sensor on pin 12 of the trigger was a logical 1, after the second touch on this conclusion appears logical 0.
This signal controls the electronic switch, which is made on the VT1 transistor and relay K1. If the trigger output logic 1, transistor open, relay and its closing contacts (not shown) supplies power to the load. When the trigger output logical 0, the relay contacts open, de-energizing the load.
The chip can be used similar to other series, the transistor is specified series with possible large current transfer ratio base, relay - RES-15, passport RS4.591.003 or RS4.591.004 (at power supply voltage more than 10 V). Current the load should not exceed the maximum allowable current through the relay contacts.
The reliability of the device is higher if the diode VD1 to replace a resistor of about 100 ohms, and between the sensor and the common wire to include a resistor of 10 megohms. The first one protects the input circuit from static electricity, and through the second the incoming level logic 0, it is also possible to dispense with the resistor R2 and to connect the input R chip DD1.2 with the common wire.
Author: M. Kutsev, S. Volcano-Burla Altai territory