Touch Switch Circuits

A great collection of touch switch circuits. A touch switch is an electronic device that enables us to control a circuit by simply touching a sensor. The circuit as you can see from its diagram is very simple and only uses 8 components. The heart of the circuit is the IC CD 4011 that is connected as a FLIP-FLOP. Pins 9 and 13 of the IC are
Touch Switch Circuits - schematic

the «SET » and «RESET » contacts of the FLIP-FLOP. The IC is of the CMOS type and requires a very low current to in its gates to control it. This high sensitivity of the circuit makes the touch operation possible. The two gates are held at logic state «1 » continuously by means of the two resistors R1 and R3 that connect them to the positive supply rail. These resistors have a very large resistance of 10 Mohm. If we now touch a set of contacts the skin resistance closes the circuit between the corresponding gate and the negative supply rail. The skin resistance for small areas of the skin is normally much lower than 10 Mohm and the gate is effectively brought to logic condition «0 » which makes the FLIP-FLOP change state. For any given state of the FLIP-FLOP touching the corresponding set of contacts will make the circuit to reverse its state of balance and in effect toggle the switch. As a switch is used a relay driven by a transistor which is driven from the out put of the FLIP-FLOP. A touch switch is a switch that is turned on and off by touching a wire contact, instead of flicking a lever like a regular switch. Touch switches have no mechanical parts to wear out, so they last a lot longer than regular switches. Touch switches can be used in places where regular switches would not last, such as wet or very dusty areas. This circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in...

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