Introduction A touchpad (also track pad) is a pointing

device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. 

Operation & Development Touchpad’s operate in one of several ways

including capacitance and conductance sensing.

we prefer the resistance touch pad in some respect as compared to other touchpad.

Hotspots are the main configuration of the touch pad.

Applications

Touchpad’s are primarily used in portable laptop computers.

ATM machine . Washing Machine. Photostat Machine.

Main Component Of OTEA Touch pad LM358 Microcontroller Voltage Regulator Transceiver LCD Electromechanical Relays 8 ULN 2803APG

Touch Pad

Resistance touch is most commonly used because of its relatively low price and ability to use a range of input means.

LM358 (Low Power Dual Operational Amplifier) The LM358 series consists of two

independent, high gains; internally frequency compensated operational amplifiers which were designed specifically to operate from a single power supply over a wide range of voltages.

Connection Diagram

Features

Internally frequency compensated for unity gain.

Large dc voltage gain: 100 dB. Wide power supply range:

Single supply: 3V to 32V

dual supplies : ±1.5V to ±16V Large output voltage swing.

Microcontroller The AT89C52 is a low-power, high-

performance CMOS 8-bit microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM).

The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pin out.

PIN DIAGRAM

Features Compatible with MCS-51™ Products. 4K Bytes of In-System Reprogrammable

Flash Memory- Endurance: 1,000 Write/Erase cycles .

Fully Static Operation: 0 Hz to 24 MHz. Three-level Program Memory Lock. 128 x 8-bit Internal RAM. 32 Programmable I/O Lines. Two 16-bit Timer/Counters. Six Interrupt Sources.

Voltage Regulator (LM7805c) A voltage regulator is an electrical regulator

designed to automatically maintain a constant voltage level.

The LM78XX series of three terminal positive regulator.

Each type employs internal current limiting, thermal shut down and safe operating area protection.

Features Output Current up to 1A. Output Voltage of 5. Thermal Overload Protection. Short Circuit Protection. Output Transistor Safe Operating Area

Protection.

TRANSCEIVER(MAX 232) A transceiver is a device that has both a

transmitter and a receiver which are combined and share common circuitry or a single housing.

If no circuitry is common between transmit and receive functions, the device is a transmitter-receiver.

An electronic switch allows the transmitter and receiver to be connected to the same antenna and prevents the transmitter output from damaging the receiver.

Pin Diagram MAX232

FEATURES 120kbits/sec data rate. Low power shutdown current: 1µA. Designed for RS-232 and V.28 Applications. Three state TTL/CMOS receiver outputs. 0.1µF to 10µF external capacitors.

LCD(LIQUID CRYSTAL DISPLAY) A liquid crystal display (LCD) is an

electronically-modulated optical device shaped into a thin.

flat panel made up of any number of color or monochrome pixels filled with liquid crystals and arrayed in front of a light source or reflector.

It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power.

D0-D7 is the bi-directional data bus. R/W determines if we read from or write

to the LCD. RS stands for "register select” RS=0

means that the instruction register is selected.

RS=1 means that the data register is selected.

E pin enables or disables the LCD module. When Enable is low the LCD is disabled and When Enable pin is high the LCD is enabled.

Vo pin is for adjusting the contrast of the display.

Vdd and Vss are the power supply pins.

 

Electromechanical Relays A simple electromagnetic relay is an

adaptation of an electromagnets and It consists of a coil of wire surrounding a soft iron core.

An iron yoke provides a low reluctance path for magnetic flux, a moveable iron armature and a set of contacts.

The armature is hinged to the yoke and mechanically linked to a moving contact or contacts.

It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit.

electromechanical relay Small relay as used in electronics

Type Of Relays Latching relay Reed relay Mercury-wetted relay Polarized relay Machine tool relay Solid-state relay Overload protection relay

Applications Control a high-voltage circuit with a low-

voltage signal, as in some types of modems or audio amplifiers.

Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile. Detect and isolate faults on transmission and distribution lines by opening and closing circuit breaker (protection relays).

Isolate the controlling circuit from the controlled circuit when the two are at different potentials.

ULN 2803APG

The ULN2803APG / AFWG Series are high voltage, high current Darlington drivers comprised of eight NPN Darlington pairs.

All units feature integral clamp diodes for switching inductive loads. Applications include relay, hammer, lamp and display (LED) drivers. The suffix (G) appended to the part number represents a Lead(Pb)-Free product.

Features Output current (single output) - 500 mA

(Max.) High sustaining voltage output -50 V (Min.) Output clamp diodes Inputs compatible with various types of

logic. Package Type−APG: DIP−18pin

Pin Digram

Model Digram

Circuit Digram

Conclusion

The OTEA is operating on the resitivity of the hand and is easy to operate and process the required function.

The OTEA functioning is controlled by the microcontroller AT89C51 for the required controlled function at the output so that we can get the desired result.

most widely used application of the touch pad is in a laptop in the case where we can not have a mouse all the time in our bag.

REFERENCES

Ritchie W.K., “Different Display Device” British Telecommunication Engg.1(4), PP. 205-210; 1983.

Smith D.R., “Different Microcontroller IC’s IEEE Comm. Mag. 24(1), PP. 9-15; 1986.

Trischitta P.R. & Chen D.T.S., “Opto Electronics Devices”, IEEE Comm. Mag., PP.16-21; May 1989

D.F. Stout Handbook of Operational Amplifier Circuit Design (McGraw-Hill, 1976, ISBN 007061797X).

The Encyclopedia of Electronic Circuits - Volume 1 to 7. Rudolf Graf's.