Touch Switch Circuits

Here is 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.

1. Simple touch switch circuit with 4011 – source
   

   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 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.
   R1:………..10MOhm 1/4 W
   R2:………..10MOhm 1/4 W
   R3:……….. 1KOhm 1/4 W
   D1:……….. Led red
   D2:………..1N4148 diode
   TR1:………BC558 PNP Transistor – BC327
   IC1:……….CD4011 CMOS IC
   RL1:……….12V relay rated at 250 V / 2A

2. Simple Touch Switch Version 2 – source
   
   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.
   C1 – 10uF 16V Electrolytic Capacitor
   R1, R2 – 100K 1/4 Watt Resistor
   R3 – 10 Meg 1/4 Watt Resistor
   U1 – 4011 CMOS NAND Gate IC
3. Touch Switch with 555 – source
   
   This circuit uses a 555 timer as the bases of the touch switch. You can learn more about 555 timers in the Learning section on my site. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.
4. Touch switch activated relay – source
   
   A very simple touch switch circuit diagram can be constructed using this circuit schematic . This circuit will turn on /off an electronic relay using the same touch sensor . This touch switch circuit is composed from an current amplifier and a decimal counter circuit . the counter circuit is a CDB490 type and is capable to show at pin 12 states 1 and 0 that depends by the pulse applied of pin number 14 . Pulses applied to pin 14 are provided by the current amplifier formed by that two BC transistors . It requires a 5volts power supply and can be used to turn on /off any other electronic circuit.
5. Electronic touch switch – source
   
   This is a electronic touch switch ( on/off ) activated by skin resistance of finger . When the finger touch the on contact the a small current is delivered through skin to transistors to turn on the circuit . The circuit remains on until the finger touch the off contact . This electronic touch switch designed with transistors require a 6 volts power supply circuit . The electronic touch switch circuit require few external components ( four transistors and four resistors ) and is very simple do build even for beginners .
6. Very simple electronic touch switch – source
   
   A very simple electronic touch switch can be constructed using this circuit diagram . This electronic touch switch is based on two transistors an can activate a relay , when the touch sensor is pressed .
   The touch sensor can be constructed using a small piece of a printed circuit board ( two small tracks with a 2 mm distance between each other ) . This circuit is powered using a 12 volts DC power supply , so the relay used for this project must be a 12 volts relay . This circuit is working very simple , when both plates of the sensor are touched the skin resistance will activate the circuit.
7. On Off Touch Switch
   
   This is a easy to build on/off touch switch circuit with the well known IC 555. The modern mechanic switches are improved concerning of old technology. We need however many times to replacement some old switch or to check currents bigger than the durability of certain switches or simple we need something with modern appearance. For it and different reasons is essential the up circuit.