01-02-2013, 01:02 PM
PROJECT REPORT ON TOUCH SWITCH
TOUCH.pptx (Size: 191.67 KB / Downloads: 80)
INTRODUCTION
It is an electronic switch that enables us to control a circuit by simply touching , and the switch automatically turns off a short time later .As you will see you can determine how much later less than a second to over one minute – just by changing the value of one resistor . The kit uses 12V relay to do switching .
Working principle
The circuit is based around an mos 555 timer IC . This is usually marked NE 555 or LM 555 .
The 555 is connected as a pulse generator , i.e a monostable multivibrator . The ‘mono’ gives a clue as to how it works it produces just one pulse when it is triggered.
When the power is first switched on current flows through R1 and charges C1 until the voltage across c1 equals one third of the supply voltage.
In this circuit if the supply voltage is 12V the capacitor is charged to 4V .
Pins 1 & 7 are shorted together by an internal resistor in the 555 so , current flows through R1 to ground .
Nothing more happens until the IC is triggered . This is done by putting a low voltage input on pin 2 , the trigger input.
When this happens an internal resistor turns of & the current flow from pin 7 to pin 1 is stopped . This causes C1 to charge
At the same time the voltage of output of pin 3 which had been at zero rises quickly to 9V . This is the beginning of the output pulse .
Charging of C2 is contineous until it reaches two third of the supply voltage , 8V .
As soon as it reaches 8V two things happen:
The output voltage on pin 3 drops almost instantly to zero ending the pulse .
Secondly the internal resistor turns back on & the path between pins 1 & 7 opens up again .
CONCLUSION:-
We can turn on almost any electrical device with this switch & the switch automatically turns off a short time later. It is used in various applications because of its quicker response. It is very simple.