This document describes a mini project report on a sensitive switch circuit. The circuit uses a 555 timer in monostable mode that is triggered by a touch plate. When triggered, the 555 output drives a relay for a fixed time to switch on a load. The circuit was built by four students for their Bachelor of Engineering degree in Electronics and Communication Engineering under the guidance of their professor. The circuit design, components, working, advantages, PCB design, and results are documented in the report.

1. SRI ESHWAR COLLEGE OF ENGINEERING
KINATHUKADAVU, COIMBATORE-641202
MINI PROJECT REPORT
ON
SENSITIVE SWITCH
S.SONA ANTONY 722813106149
R.SUGANYA 722813106156
S.SUGANYA 722813106157
S.VEENA SREE 722813106167
In Partial fulfillment for the award of degree
of
BACHELOR OF ENGINEERING
in
ELECTRONICS AND COMMUNICATION ENGINEERING
Guided by:
Mr.YOGESWARAN
(Department of ECE)

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CERTIFICATE
It is certified that the work contained in the thesis titled “SENSITIVE SWITCH” by S.SONAANTONY(722813106149),R.SUGANYA(722813106156),S.SUGANYA(722813106157),S.VEENA SREE(722813106167) has been carried out in under my supervision and that this work has not been submitted elsewhere for a degree.
Head of the Department Mini-project Co-ordinator Project Supervisor

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ACKNOWLEDGEMENT
At the outset we express our gratitude to the ALMIGHTY who has been with us during each and every step that we have taken towards the completion of this project.
We feel great pleasure to acknowledge all those involved in the process of our education and research. In the first place we would like to record our deep and sincere gratitude to our in charge, Mr.YOGESWARAN for his supervision, advice, guidance, and crucial contribution, which made him a backbone of this project. His understanding, encouraging and personal guidance have provided a good basis for the present project. His involvement with his originality has triggered and nourished our intellectual maturity that we will benefit from, for a long time to come.
We wish to express our gratitude towards our all teachers, who helped us throughout our course work. We extend our acknowledgement to our lab mates, lab staff, who are directly or indirectly involved in carrying out the project work.
On a personal note, we submit our thanks to our beloved parents and friends. Without their generous sacrifice this project would not see light of the day.

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ABSTRACT
The project is designed to develop a touch sensitive switch to control any load. A 555 timer is used in mono stable mode to drive a relay to switch ON a load for fixed time duration.
The 555 timer is triggered by a touch plate connected to its trigger pin. The output of 555 delivers logic high for a fixed time interval as decided by the RC time constant connected to the timer. This output drives a relay which in turn switches ON the load for that duration after which is switches OFF automatically. Human body induced mains supply develops a voltage on the touch plate to trigger the timer.

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CONTENTS
TITLE PAGE NO
ABSTRACT………………………………………………. 4
INTRODUCTION………………………………………… 6
BLOCK DIAGRAM……………………………………… 7
DESCRIPTION OF BLOCK DIAGRAM………………... 8
555 Timer
Relay
Transformer
Rectifier
CIRCUIT COMPONENTS………………………………… 10
Resistors
Capacitors
Battery
Transistor
Diode
CIRCUIT DIAGRAM………………………………………. 12
WORKING OF THE CIRCUIT…………………………….. 13
ADVANTAGE……………………………………………… 14
PCB DESIGN………………………………………………. 15
Schematics Diagram
PCB Layout
RESULT…………………………………………………….. 16
CONCLUSION………………………………………………. 17
BIBILOGRAPHY……………………………………………. 18

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INTRODUCTION:
This is a project on SENSITIVE SWITCH which can switch on/off any electrical circuit by the user touching a metal plate. The operation of the circuit is simple. It is designed to directly switch a relay to allow it to be used with large loads. As it uses only a few commonly available transistors and a 12V supply, it is ideal for hostile environments where mechanical switches would be damaged. Using a latching relay and two of these circuits, a simple pad "touch on/touch off" arrangement can be made.
This circuit is constructed using basic electronic components like resistors, transistors, relay, transformer, capacitors. This circuit turns ‘ON’ light for the first touch. The light turns ON till the next touch. For the next touch the light turns OFF. This circuit works with 12V voltage. Therefore a step-down transformer 12V/300mA is employed. This working of this circuit is based on transistor switch relay as an electronic switch

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BLOCK DIAGRAM:

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DESCRIPTION OF BLOCK DIAGRAM:
555 TIMER
The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications.
The 555 has three operating modes:
• Monostable mode: In this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, switches, touch
switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc.
• Astable - free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.
• Bistable mode or Schmitt trigger: the 555 can operate as a flip- flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc.
RELAY :
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor . Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are

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used to protect electrical circuits from overload or faults; in modern electric
power systems these functions are performed by digital instruments still called
"protective relays".
TRANSFORMER:
Usually, DC voltages are required to operate various
electronic equipment and these voltages are 5V, 9V
or 12V. But these voltages cannot be obtained
directly. Thus the a.c input available at the mains
supply i.e., 230V is to be brought down to the
required voltage level. This is done by a transformer.
Thus, a step down transformer is employed to
decrease the voltage to a required level.
RECTIFIER:
The output from the transformer is fed to the rectifier. It converts A.C. into
pulsating D.C. The rectifier may be a half wave or a full wave rectifier. In this
project, a bridge rectifier is used because of its merits like good stability and full
wave rectification.
The Bridge rectifier is a
circuit, which converts an ac voltage
to dc voltage using both half cycles
of the input ac voltage. The Bridge
rectifier circuit is shown in the
figure. The circuit has four diodes
connected to form a bridge. The ac input voltage is applied to the diagonally
opposite ends of the bridge. The load resistance is connected between the other
two ends of the bridge.
For the positive half cycle of the input ac voltage, diodes D1 and D3
conduct, whereas diodes D2 and D4 remain in the OFF state. The conducting
diodes will be in series with the load resistance RL and hence the load current
flows through RL. For the negative half cycle of the input ac voltage, diodes D2
and D4 conduct whereas, D1 and D3 remain OFF. The conducting diodes D2
and D4 will be in series with the load resistance RL and hence the current flows
through RL in the same direction as in the previous half cycle. Thus a bi-directional
wave is converted into a unidirectional wave.

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CIRCUIT COMPONENTS:
RESISTORS:
Resistors are the most common passive electronic component (one that does not
require power to operate). They are used to control voltages and currents. While a resistor is a very basic component, there are many ways to
manufacture them. Each style has its own characteristics that make it desirable in certain types of applications. Choosing the right type of resistor is important to making high-performance or precision circuits work well. This bonus chapter
covers the resistor types and helps with picking the right one for your project. All resistors are basically just a piece of conducting material with a specific
value of resistance. For that piece of conducting material to be made into a practical resistor, a pair of electrodes and leads are attached so current can flow. The resistor is then coated with an insulating material to protect the conducting material from the surrounding environment and vice versa. There are several different resistor construction methods and body styles (or packages) that are designed for a certain range of applied voltage, power dissipation, or other considerations. The construction of the resistor can affect its performance at high frequencies where it may act like a small inductor or capacitor has been
Added, called parasitic inductance or capacitance.
CAPACITORS:
Capacitor has ability to store charge and release them at a later time. Capacitance is the measure of the amount of charge that a capacitor can store for a given applied voltage. The unit of capacitance is the farad (F) or
microfarad. The capacitors used in the circuit are electrolytic-capacitor.
In the circuit the electrolytic capacitor is used as a bypass capacitor. Any noise variation in the circuit is removed by the capacitor.
BATTERY:
In electricity, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy.

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Since the invention of the first battery (or “voltaic pile") in 1800 by Alessandro Volta and especially since the technically improved Daniel cell in 1836, batteries have become a common power source for many household and industrial applications. According to a 2005 estimate, the worldwide battery 7 industry generates US$48 billion in sales each year, with 6% annual growth There are two types of batteries: primary batteries (disposable batteries), which are designed to be used once and discarded, and secondary batteries (rechargeable batteries), which are designed to be recharged and used multiple times. Batteries come in many sizes, from miniature cells used to power hearing aids and wristwatches to battery banks the size of rooms that provide standby power for telephone exchanges and computer data centres.
TRANSISTOR:
A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. It is composed of semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
DIODE:
A diode is a specialized electronic component with two electrodes called the anode and the cathode. Most diodes are made with semiconductor materials such as silicon, germanium, or selenium. Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure. Diodes can be used as rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers, signal demodulators, and oscillators.
The fundamental property of a diode is its tendency to conduct electric current in only one direction. When the cathode is negatively charged relative to the anode at a voltage greater than a certain minimum called forward break over, then current flows through the diode. If the cathode is positive with respect to the anode, is at the same voltage as the anode, or is negative by an amount less than the forward breakover voltage, then the diode does not conduct current. This is a simplistic view, but is true for diodes operating as rectifiers, switches, and limiters. The forward breakover voltage is approximately six tenths of a volt (0.6 V) for silicon devices, 0.3 V for germanium devices, and 1 V for selenium devices.

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CIRCUIT DIAGRAM:

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WORKING OF THE CIRCUIT: Assemble the circuit properly and apply power supply. To “ON” the connected device, put your finger between touch to “ON” point and to off the device put your finger between touch to OFF point. When power supply is provided to circuit device connected through relay remain ideal because voltage at pin2 (trigger pin) of IC is low but as soon as you touch the “ON” switch pin 2 of IC1gets the trigger signals and out pin3 receives high input and output pin 3 goes high which will make the transistor T1 into conduction and the relay connected through it energize and device connected across relay becomes “ON”. At this point voltage at pin 6 is zero. Similar action takes place when you touch the “OFF” switch. This circuit works by latching a relay to “ON” state with push of a button and with another push latch is released and device become “OFF”. It is working similar to a flip-flop states. If you are getting problem in getting touch pad then in place of touch pad you can also switch. In that case use push to on switch so that when you press the switch it will make the connection and “ON” and “OFF” the device according to the requirement.

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ADVANTAGES:
The touch security is cheap in cost.
This is used for house security at doors.
The touch switch is used for dusty conditions.
This is also useful in rainy conditions.

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SCHEMATIC DIAGRAM:
PCB LAYOUT DIAGRAM:

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RESULT:

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CONCLUSION:
The switch also contains an additional general function. By touching several surfaces simultaneously or within a pre-defined time, the additional function can be activated. This invention concerns a multiple touch switch for operating lighting. This is in contrast to the current systems in which only a single touch pad in a multiple switch can be used to turn lights on or off or in which a separate touch pad for each light circuit to be pressed.

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BIBILOGRAPHY:
www.electronicsforu.com
www.alldatasheets.com
www.scribd.com
www.extremecircuit.com