     |
Touch Switch/Contact Switch Free Electronic Circuits
The main part of the Touch Switch Free Electronic Circuits are the two NAND gates of the 4011 Integrated Circuit which are connected as a flip-flop. Pins 9 and 13 are the ON and OFF contacts. The two gates are connected to the positive rail by the two 10M resistors. Shorting one of the gates with the ground rail by touching it (this is equivalent to connecting about 50K between the gate and ground) FLIPs the output to that state. Shorting out the other contact FLOPs it back. The output of the flip-flop drives a transistor connected as a switch. It switches an LED and a relay. The relay is a 12V relay and commonly available SPDT type 240VAC can be used to switch ON or OFF a lamp or other electrical appliances. However, make sure that the current and voltage of the device are within the contact relay specifications. Connecting the two 1K resistors connects the other two NAND gates of the IC into the flip-flop and makes it much more sensitive to touch. The touch plate may in fact work with only the first two gates connected. But it will be much more sensitive with all four gates connected as a flip-flop. Ensure that an isolating transformer is used when the power supply comes from the mains before being rectified to 12V DC for
safety purposes. The schematic diagram of the circuit is as shown below. 
Parts List
Free Electronic Circuits Home Page
|
