Touch Switch Circuit using 555 Timer


Anjali Sethiya
The modern mechanic switches are improved concern of old technology. We however need to check current greater than the durability of certain switches or simply we need something with modern appearance. The project for ON and OFF switch is build around a 555 timer configured in such a way that latch is on one state and some action is required to change that state. Image below details with a conventional touch switch sensor :


In this project,  when power is supplied to the touch switch circuit, the devices connected to it remain ideal as voltage at pin2 is zero. When the switch is turned ON, trigger pin (pin2) receives trigger signal. The output pin (pin 3) receives a high output due to which transistor gets turned ON. Simultaneously relay connected to it also receives high signal due to this the device connected to it gets turned ON. Voltage at pin6 should be zero at this stage. When the switch is turned OFF similar action takes place. In this type of switches, relays are latched ON with push of a button and with another push, latch is released. The working is similar to flip flop.


Touch pad can also be used on place of switches. As soon as the switch is pressed ON, the device gets turned on and as the switch is pressed OFF the device gets turned off. When looked at the touch plates of the old toys it was found that some are light touch buttons. They consist of small carbon block which is mounted in silicon rubber. As the button is pressed, it touches the pad and resistance gets reduced between the two interleaved tracks. These pads are already protected against corrosion and have a good design for detecting finger. When finger is applied, the resistance between the tracks changes between 150K to 850K depending upon the pressure applied and the moisture of the finger.

Circuit Diagram


Resistor Image

Resistor is a passive component used to control current in a circuit. Its resistance is given by the ratio of voltage applied across its terminals to the current passing through it. Thus a particular value of resistor, for fixed voltage, limits the current through it. They are omnipresent in electronic circuits.

Relay Switch Image
Relay Switch

Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate....

555 Timer | IC 555 | NE555
555 Timer IC

555 is a very commonly used IC for generating accurate timing pulses. It is an 8pin timer IC and has mainly two modes of operation: monostable and astable. In monostable mode time delay of the pulses can be precisely controlled by an external resistor and a capacitor whereas in astable mode the frequency & duty cycle are controlled by two external resistors and a...

TI Innovation Challenge

WEBENCH Design Center

WEBENCH Design Environments are unique and powerful software tools that deliver customized power, lighting, filtering, clocking and sensing designs in seconds. These easy-to-use tools help you generate, optimize and simulate designs that conform to your unique specifications. They allow you to make value-based tradeoffs at a design, system and supply chain level before your design is committed to production.

Design & Simulation Tools

Power Design


Sensors, Filter, Clock and Amplifier Design

Download Tools, Models and Symbols