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T R OUCH

ESPONSIVE

A

S

PPLICATION

WITCHING

S

Why Press When the Touch Works? TM Design by: Muhammad Fahd Waseem

©

YSTEM


TRASS – A Touch Plate Switch … …

Touch Responsive Application Switching System Operation: p A Touch Plate responds p to human touch and performs the functions of a normal mechanical switch


Advantages of Touch Switching … … … …

No moving parts = Much greater life Better Aesthetic Appearance pp and Feel Switch interface area can be very, very small C Comparatively ti l noiseless i l


Disadvantages of Touch Switching …

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Powered: Draws a very small amount of current even when switched off – to keep itself alive Comparatively complicated, and thus more expensive p Cannot normally work in very extreme conditions of temperature, temperature humidity, humidity and particularly where there is strong static charge in the ambient


TRASS Design Schematic A conducting Any d ti touch t h plate l t goes hhere


Working Principle – I 1. 2.

3 3.

4.

Humans are conductors Humans’ nerves g generate a small varying y g voltages that control the muscles Moreover the presence of radio waves around us Moreover, means that humans also act as very weak radio antennas These things combine to generate a small noise signal i l at the h hhuman touchh


Working Principle – II 5.

6.

7.

8.

The noise / AC signal so generated has a P-P value of about 0.1 V depending on where and h the how th touch t h is i made d This is amplified many times over, rectified and smoothed h d to create a smallll DC signal i l that h then h feeds into a comparator Th comparator simply The l converts the h DC signall into a sharply varying logic level signal, 1 or 0 This is fed into a 1-bit memory device as a clock for switching purposes


TRASS vs. other touch methods … …

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Muchh simpler M l – just three h ICs C involved l d Very cheap – just $0.5 for all the components of the circuit i it combined bi d Can be switched on/off only once every second Does not depend on borderline principles, thus more reliable in rough environments C be triggered by the touch off any large conductor, Can not just humans C be Can b expanded d d using i standard t d d 5V R Reed d Relays R l without extra adaptation


Part List Q Quantity i

Description i i

1

OPAMP; LM741CN

5

RESISTOR 1k立 RESISTOR;

1

RESISTOR; 100k立

1

DIODE;; 1N4007

1

CAP_ELECTROLIT; 1袖F

1

RESISTOR; 4.7M立

1

COMPARATOR; LM339N

1

JK_FLIPFLOP; 74STD, 7476N


Complementary

Internal Diagram of JK Flip Flop

Internal Construction of a NAND


TRASS