Touch Switch Circuit 

This Touch Switch circuit uses a 555 timer as its core component. The timer operation is configured as a monostable or one shot multivibrator in that once it is triggered, it will output a fixed pulse and remain there for a period which is a function of the time constant t= R2 X E1. In this circuit, the pulse width generated is about 4-4.5 seconds. The trigger is activated by touching the touch terminal.





In this circuit, the output from pin 3 of 555 timer is used to turn ON the NPN transistor Q1. Q1 will in turn activate a buzzer for about 4-4.5 seconds after which it will go OFF. If you need a longer delay, increase the values of R2 and E1. Similarly if a shorter duration is required, reduce the values of R2 and E1.



The Vcc used is 9V from a battery. For safety reason, it is important that you do not use any power supply from mains unless the power supply is designed with isolating transformer that comforms to the safety standard such as UL. Improperly designed power supply may cause shock to you when you touch the terminal hence it is always better to use a dry cell battery for this project.

Besides the buzzer, you can modify the circuit to on a series of light emitting diodes once the terminal is touched.


Touch Switch Parts List



Label Description
R1 10K ohm 1% 1/4W Metal Film Resistor
R2 520K ohm 1% 1/4W Metal Film Resistor
R3 4.7K ohm 1% 1/4W Metal Film Resistor
C1 39pF/25V Ceramic Capacitor
E1 4.7uF/25V Electrolytic Capacitor
E2 220uF/25V Electrolytic Capacitor
SW1 SPST switch
Q1 2SC2002 NPN Transistor
BZ 9V Buzzer
U1 555 Timer
D1 Diode 1N4003
Terminal Touch Terminal





Back To Touch Switch Circuit Home Page



Recent Articles

  1. Electronics Design Contest

    oin electronics design contest and win prizes. Test your hardware and software skills against the best designers from the rest of the world.

    Read More

  2. Electronics Events

    Join the electronics events to enhance your knowledge and network with other professionals in this industry.

    Read More

  3. Engineering Free Magazine

    Some engineering free magazine available for you to subscribe today

    Read More

New! Comments

Have your say about what you just read! Leave us a comment in the box below.


Digital Dice 
Project

Explore the use of 7-Segment Display, 555 Timer, Decade Counter and Binary Adder. Get the circuit.

Battery Tester 
Project

Design and build a battery tester to test dry cell and rechargeable battery with a voltage of less than 2V. Check here


Door Bell

Construct this simple door bell chime and have fun. Find out more here



Electronic Kits

If you are looking for electronic kits, electronic gadgets or robotic kits, get them here


Home Alarm 
Project

Build this simple home alarm to protect your house from intruders. See the schematic circuit