555 Touch Sensor

How to make a touch sensor? Here is a simple DIY touch sensor circuit diagram using 555 timer monostable mode. Touch switch is only a conducting metal sheet that acts as touch sensor. The 555 touch switch is not a touch capacitive sensor; it is only a metal touch sensor button. Using this you can turn on and off devices by single touch. Here we are using a JK flip flop IC 7476 that is connected as T-flip flop. The output of T-flip flop is connected to the base of transistor to turn ON the relay so as to control high current electrical devices such as fan, motor, lamps etc.

Circuit diagram of 555 touch switch

touch new 555 Touch Sensor

Components

  1. IC 555
  2. IC 7476
  3. Transistor BC 548
  4. LED
  5. Resistor (1M,1K,330)
  6. Capacitor (0.1uF)
  7. Touch pad (Any conducting sheet)
  8. Relay 12V,10A

Working

  • The 555 timer IC is connected in monostable mode, i.e. 6th and 7th pins are shorted, a capacitor is connected to ground and a resister is connected to Vcc.
  • Working of this circuit is same as that of a monostable multivibrator.
  • When we touch on the touch pad, a negative voltage is produced on the trigger pin (2nd pin) of 555 IC. Then monostable output goes high.
  • Touch pad is only a conducting metal sheet.
  • If your circuit is not working then you have to connect a 1M resistor from the 2nd pin of 555 to Vcc (+5V).
  • Output of 555 is connected to the clock of JK flip flop IC 7476.
  • Here JK flip flop is connected as a T flip flop (toggling mode) depending on the clock.
  • Its state will change by applying clock signal, i.e. if the output of JK flip flop is high, it changes to low else it will change to high.
  • Output of T flip flop is connected to the base of transistor BC 548 through a 1K resistor.
  • A positive voltage on the base of transistor will forward bias the transistor, then relay gets negative and it switches the device.

Components Layout

TSR top image 555 Touch Sensor

Download Component Layout PDF

PCB Layout

TSR bottom image 555 Touch Sensor

Download PCB Layout PDF

Components Pin out

555 timer internal diagram  555 Touch SensorBC 548 pin 555 Touch Sensor

                             555

Relay Pin out 555 Touch Sensor

                 Relay

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