Main Documentation

1.1 INTRODUCTION

Embedded systems are designed to do some specific tasks, rather than be a general

purpose computer for multiple tasks. Some also have real time performance

constraints that must be met, for reasons such as safety and usability, others may have

low or no performance requirements, allowing the system hardware to be specified to

reduce the cost.

With the growing use of computers the quality of our lives and even

the whole society are dramatically changed. Owing to the rapidly increasing ability of

computers to process information, we are going to presented with computer-based

world. For able-bodies people, access to computers can be taken for granted because

conventional computer interfaces (e.g. a keyboard and a mouse) are designed with the

able bodies in mind. Unfortunately, people with physical disabilities cannot enjoy the

benefits provided by computers on equal term. Therefore, how to lower or even tear

down the barriers between computers and users with disabilities is a very demanding

task. Users with disabilities should be able to equally access standard computers and

applications. We propose an accelerometer-based mouse which allows the user to use

head movements to access computers.

1

Human interacting section:

Computer Application Interface section:

Fig: 1.1 BLOCK DIAGRAM\

2

Microcontroller Unit

Eye Blink sensorSignal

conditioning section

3-axis MEMS Accelerometer

Encoder Device

WirelessTransmitter

1.2 AIM OF THE PROJECT

The aim of the project is to design a system of human computer mouse interface using

mems technology for physically challenged people.

1.3 METHODOLOGY

We use mems technology that keeps control of the whole system of human

computer mouse interface. The system uses accelerometers to detect the user's head

tilt in order to direct mouse movement on the monitor. The clicking of the mouse is

activated by the user's eye blinking through an IR sensor. The keyboard function is

implemented by allowing the user to scroll through letters with head tilt and with eye

blinking as the selection mechanism.

1.3.1 HARDWARE REQUIREMENTS

1. PIC micro-controller

2. 3-axis accelerometer

3. Encoder and Decoder

4. IR sensor

5. Wireless transmitter and receiver

6. Microphone

7. RS-232 cable

1.3.2 SOFTWARE REQUIREMENTS

1. Compiler (MP Lab)

2. Design Tools (Orcad)

3. Languages: Visual Basic and Embedded C

3

1.4 SIGNIFICANCE OF WORK

To lower or tear down the barriers between computers and users with disabilities is a

very demanding task. We have chosen mems technology because of its various

advantages such as low power consumption and low noise. We constructed an

interface system that would allow a similarly paralyzed user to interact with a

computer with almost full functional capability. That is, the system operates as a

mouse initially, but the user has the ability to toggle in and out of a keyboard mode

allowing the entry of text, and using blinking as an input. We built an accelerometer

based tilt detector to determine head motion.

1.5 ORGANISATION OF THE REPORT

Chapter 1 deals with the introduction of the project

Chapter 2 deals with the description of the hardware components used in our project

Chapter 3 deals with the description of the circuit employed

Chapter 4 gives the Final Result and Conclusion

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2.1 INTRODUCTION

In this chapter, all the hardware components that are used including the

microcontroller are explained elaborately. All the specifications and the internal

circuitry of the microcontroller including the functional features are explained in

detail so that the coding can be done accordingly.

2.2 MICRO-CONTROLLER ( PIC16F877A)

The PIC16F877A CMOS FLASH-based 8-bit microcontroller is upward compatible

with the PIC16C5x, PIC12Cxxx and PIC16C7x devices. It features 200 ns instruction

execution, 256 bytes of EEPROM data memory, self programming, an ICD, 2

Comparators, 8 channels of 10-bit Analog-to-Digital (A/D) converter, 2

capture/compare/PWM functions, a synchronous serial port that can be configured as

either 3-wire SPI or 2-wire I2C bus, a USART, and a Parallel Slave Port.

• PIC16F877A microcontroller is used for this project

• It is 8-bit Microcontroller

• System is RISC Architecture

• It has Small set of Instruction set

• It has 35-Instructions only

• Compatibility: avail 28/40 Pin ICs

• Operating Speed Max 20 MHz, Voltage-(2-5.5)v

• Memory:

Flash Program 8Kx14Words

RAM 368Bytes

EEPROM Data Memory 256Bytes

• Low power, High speed Flash/EEPROM Technology

2.2.1 FEATURES

1. It has 5 Ports for Internal and External usage

2. It has on chip Timers. 3 Timers are avail

3. It has in built Analog to Digital Converter

4. In built Multiplexer availability for signal Selection

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5. It has serial as well as Parallel Communication facilities

6. In built Capture, Compare and Pulse width modulation

7. Lead-free; RoHS-compliant

8. Operating speed: 20 MHz, 200 ns instruction cycle

9. Operating voltage: 4.0-5.5V

10. Industrial temperature range (-40° to +85°C)

11. 15 Interrupt Sources

12. 35 single-word instructions

13. All single-cycle instructions except for program branches (two-cycle)

2.2.2PINDIAGRAM

FIG 2.1 PIN DIAGRAM OF PIC16F877A

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2.2.3BLOCKDIAGRAM

V D D

M C L R

R XTX

R A 0

R B 7R B 6R B 5R B 4R B 3R B 2R B 1R B 0

R D 7R D 6R D 5R D 4R D 3R D 2R D 1R D 0

R C 2R C 3R C 4R C 5R C 6R C 7

R E 2R E 1R E 0R A 5R A 4R A 3R A 2R A 1

R C 0R C 1

R A 0

C 92 7 p F

C 82 7 p F

C 1 00 . 1 u F

P I C 1 6 F 8 7 7U 3

123456

11

32

12

31

789

1 0

1 31 4

1 51 61 71 8

1 92 0

3 33 43 53 63 73 83 94 0

2 82 93 0

2 12 2

2 42 52 6

2 7

2 3

M C L R / V p pR A 0 / A N 0R A 1 / A N 1R A 2 / A N 2 / V re f -R A 3 / A N 3 / V re f +R A 4 / T0 C K I

VD

D

VD

D

VS

S

VS

S

R A 5 / A N 4 / S SR E 0 / A N 5 / R DR E 1 / A N 6 / W RR E 2 / A N 7 / C S

O S C 1 / C L K I NO S C 2 / C L K O U T

R C 0 / T1 O S O / T1 C K IR C 1 / T1 O S I / C C P 2R C 2 / C C P 1R C 3 / S C K / S C L

R D 0 / P S P 0R D 1 / P S P 1

R B 0 / I N TR B 1R B 2

R B 3 / P G MR B 4R B 5

R B 6 / P G CR B 7 / P G D

R D 5 / P S P 5R D 6 / P S P 6R D 7 / P S P 7

R D 2 / P S P 2R D 3 / P S P 3

R C 5 / S D OR C 6 / TX/ C KR C 7 / R X/ D T

R D 4 / P S P 4

R C 4 / S D I / S D A

Y 1

4 M h z

R 61 k

R 52 2 0 o h m

S W 2

R E S E T

FIG: 2.2 BLOCK DIAGRAM OF CONTROLLER

2.3 3-AXIS MEMS ACCELEROMETER

The MMA7260QT low cost capacitive micro machined accelerometer features

signal conditioning, a 1-pole low pass filter, temperature compensation and g-Select

which allows for the selection among 4 sensitivities. Zero-g offset full scale span and

filter cut-off are factory set and require no external devices. Includes a Sleep Mode

that makes it ideal for handheld battery powered electronics. An accelerometer

measures proper acceleration, which is the acceleration it experiences relative to

freefall, and is the acceleration that is felt by people and objects. Such accelerations

are popularly measured in terms of g-force.

2.3.1 FEATURES

1. Selectable Sensitivity (1.5g/2g/4g/6g)

2. Low Current Consumption: 500 µA

3. Sleep Mode: 3µ A

4. Low Voltage Operation: 2.2 V – 3.6 V

5. 6mm x 6mm x 1.45mm QFN

6. High Sensitivity (800 mV/g @ 1.5g)

7. Fast Turn On Time7

8. Integral Signal Conditioning with Low Pass Filter

9. Robust Design, High Shocks Survivability

10. Pb-Free Terminations

11. Environmentally Preferred Package

12. Low Cost

2.3.2 BLOCK DIAGRAM

FIG 2.3 BLOCK DIAGRAM OF 3-AXIS ACCELEROMETER

2.3.3PRINCIPLE OF OPERATION

The Free scale accelerometer is a surface-micro machined integrated-

circuit accelerometer. The device consists of two surface micro machined capacitive

sensing cells (g-cell) and a signal conditioning ASIC contained in a single integrated

circuit package. The sensing elements are sealed hermetically at the wafer level using

a bulk micro machined cap wafer. The g-cell is a mechanical structure formed from

semiconductor materials (polysilicon) using semiconductor processes (masking and

etching). It can be modeled as a setoff beams attached to a movable central mass that

move between fixed beams.

The movable beams can be deflected from their rest position by

subjecting the system to an acceleration ( as in Figure).As the beams attached to the

central mass move, the distance from them to the fixed beams on one side will

increase by the same amount that the distance to the fixed beams on the other side

decreases. The g-cell beams form two back-to-back capacitors ( as in Figure). As the

center beam moves with acceleration, the distance between the beams changes and 8

each capacitor’s value will change, (C = Aε/D). Where At the area of the beam, å is

the dielectric constant and D is the distance between the beams.. The ASIC also signal

conditions and filters (switched capacitor) the signal, providing a high level output

voltage that is ratio metric and proportional to acceleration.

FIG 2.4 WORKING OF ACCELEROMETER

2.3.4 SPECIAL FEATURES

g-Select

The g-Select feature allows for the selection among 4 sensitivities present in the

device. Depending on the logic input placed on pins 1 and 2, the device internal gain

will be changed allowing it to function with a 1.5g, 2g, 4g, or 6gsensitivity .This

feature is ideal when a product has applications requiring different sensitivities for

optimum performance. The g-Select1 andg-Select2 pins can be left unconnected for

applications requiring only a 1.5g sensitivity as the device has an internal pull-down

to keep it at that sensitivity (800mV/g).

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g-Select2 g-Select1 g-Range Sensitivity

0 0 1.5 g 800mv/g

1 1 2g 600mv/g

1 0 4g 300mv/g

1 1 6g 200mv/g

TABLE 2.1 SENSITIVITY VALUES OF ACCELEROMETER

2.3.5 TYPICAL APPLICATIONS

1. HDD MP3 Player: Freefall Detection

2. Cell Phone: Image Stability, Text Scroll, Motion Dialing, E-Compass

3. Pedometer: Motion Sensing

4. Navigation and Dead Reckoning: E-Compass Tilt Compensation

5. Gaming: Tilt and Motion Sensing, Event Recorder

6. Robotics: Motion Sensing

2.4EYE BLINK SENSOR

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FIG 2.5 EYE BLINK SENSOR

This switch is activated when the user blinks their eye. It allows individuals to operate

electronic equipment like communication aids and environmental controls hands-free.

Each blink of the eye is detected by an infrared sensor, which is mounted on dummy

spectacle frames.The eye blink switch can be set up to operate on either eye and may

be worn over normal glasses. The sensitivity of the switch can be adjusted to the users

needs and involuntary blinks are ignored. The sensor is connected to a hand-held

control unit with a rechargeable battery

2.4.1 IR SENSOR

• IR LED at 900nm

-GaAlAs Infrared Light Emitting Diode

-Shines invisible IR light on the user’s eye

• IR 900nm sensor

-Light Detector

-Detects reflected IR light

we decided to use blinking as we wanted the device to be functional for

non-vocal or ventilated users (blowing or sucking was another option). Our first idea,

and the one we implemented, was to use a led/photodiode pair to reflect light off the

eye. We found that Optek Inc. makes a round receiver, consisting of a LED and a

phototransistor mounted on the same unit. This detected a strong increase in signal 11

upon blinking. We were worried about detecting the difference between normal and

intentional blinks, but we found that for most users the intentional blinks produced a

much stronger signal, and they were always much longer the ~300ms normal blink

duration.

2.5 SIGNAL CONDITIONER

A signal conditioner is a device that converts one type of electronic signal into a

another type of signal. Its primary use is to convert a signal that may be difficult to

read by conventional instrumentation into a more easily read format. In performing

this conversion a number of functions may take place. They include:

Amplification

When a signal is amplified, the overall magnitude of the signal is increased.

Converting a 0-10mV signal to a 0 -10V signal is an example of amplification.

Electrical Isolation

Electrical isolation breaks the galvanic path between the input and output signal. That

is, there is no physical wiring between the input and output. The input is normally

tranferred to the output by converting it to an optical or magnetic signal then it is

reconstructed on the output. By breaking the galvanic path between input and output,

unwanted signals on the input line are prevented from passing through to the output.

Isolation is required when a measurement must be made on a surface with a voltage

potential far above ground. Isolation is also used to prevent ground loops.

Linearization

Converting a non-linear input signal to a linear output signal. This is common for

thermocouple signals.

Excitation

Many sensors require some form of excitation for them to operate. Strain gages and

RTDs are two common examples.

The signal conditioning unit accepts input signals from the analog

sensors and gives a conditioned output of 0-5V DC corresponding to the entire range

of each parameter.  This unit also accepts the digital sensor inputs and gives outputs in

10 bit binary with a positive logic level of +5V.  The calibration voltages* (0, 2.5 and

5V) and the health bits are also generated in this unit.  The unit is powered through

DCSTS unit.

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The  DCSTS unit controls the entire operation of a DCP field station.  It consists of

power supply regulator,  timing generator,  control logic circuit,  multiplexer-cum-

A/D  converter,  health monitor circuit,   memory,   pseudo-random burst sequence

generator and a UHF transmitter. It operates on +12V  uninterrupted power.  The

hourly sequence of operations performed by DCSTS is as given below:  

a. Provides +12V switched power to signal conditioner 3 minutes and 30 sec 

prior to full hour.

b. Converts the calibration voltages and sensor data  (outputs of signal

conditioner) into digital form and stores in  memory.

c. Generates one pseudo random burst command in each three minutes 3-sub-slot

during the allotted ten minutes transmission window of a particular AWS, to enable

the random transmission of stored data three times.  These data along with station

identification code, start and end signals are transmitted to INSAT / Kalpana   at

carrier frequency 402.75 MHz @4800 bits/second

2.6 ENCODER -HT12E

2.6.1 BLOCK DIAGRAM

FIG 2.6 ENCODER BLOCK DIAGRAM

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2.6.2 FEATURES

1. Low power and high noise immunity CMOS technology

2. Operating voltage – 2.4V to 12V

3. Low standby current 0.1µA (typ.) at VDD=5V.

4. Minimal external components.

5. 18 pin DIP or 20pin SOP package.

6. Pair with Holtek’s 212 series of decoders.

7. Built in oscillator needs only 5% resister.

FIG 2.7 ENCODER PIN DIAGRAM

2.6.3 PIN DESCRIPTION

A0 – A7 Input pins for address A0-A7 setting.

AD8 – AD11input pins for address/data setting.

DOUT Encoder data serial transmission output.

L/M Latch/Momentary transmission format Latch – floating or VDD Momentary –

Vss

TE (active low) Transmission Enable.

OSC1 oscillator input pin.

OSC2 oscillator output pin.

VSS Negative power supply, Ground.

VDD Positive power supply.

2.6.4 ENCODER DESCRIPTION

For proper operation, a pair of encoder/decoder with the same number of addresses

and data format should be chosen. The decoders receive serial addresses and data

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from a programmed 2 12 series of encoders that are transmitted by a carrier using an

RF or an IR transmission medium. They compare the serial input data three times

continuously with their local addresses. If no error or unmatched codes are found, the

input data codes are decoded and then transferred to the output pins. The VT pin also

goes high to indicate a valid transmission. The 212 series of decoders are capable of

decoding information that consist of N bits of address and 12_N bits of data. Of this

series, the HT12D is arranged to provide 8 address bits and 4 data bits, and HT12F is

used to decode 12 bits of address information.

2.6.5 APPLICATIONS

1. Burglar alarm system.

2. Smoke and fire alarm system.

3. Car door controllers.

4. Cordless telephones.

2.7 DECODER-HT12D

2.7.1 FEATURES

1. Low power and high noise immunity CMOS technology

2. Operating voltage – 2.4V to 12V

3. Low standby current.

4. Minimal external components.

5. Capable of decoding 12 bits of information.

6. Binary address setting.

7. Valid transmission indicator.

8. Easy interface with an RF and infrared transmission medium.

9. 18 pin DIP or 20pin SOP package.

10. Pair with Holtek’s 212 series of encoders.

11. Built in oscillator needs only 5% resistor

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FIG 2.8 DECODER PIN DIAGRAM

2.7.2 PIN DESCRIPTION

A0 – A7 Input pins for address setting.

D8 – D11 Output data pins, power on status is low.

DIN Serial data input pin.

OSC1 Oscillator input pin.

OSC2 Oscillator output pin.

VSS Negative power supply, ground.

VDD Positive power supply.

2.7.3 APPLICATIONS

1. Smoke and fire alarm system.

2. Car door controllers.

3. Cordless telephones.

4. Burglar alarm

2.7.4 GENERAL ENCODER AND DECODER OPERATIONS

The Holtek HT-12E IC encodes 12-bits of information and serially transmits

this data on receipt of a Transmit Enable, or a LOW signal on pin-14 /TE.  Pin-17 the

D_OUT pin of the HT-12E serially transmits whatever data is available on pins

10,11,12 and 13, or D0,D1,D2 and D3. Data is transmitted at a frequency selected by

the external oscillator resistor. Note that if we use anything other than 5V on both

encoder/decoder circuits, we will need to change these oscillator resistor values.By

using the switches attached to the data pins on the HT-12E, as shown in the

schematic, we can select the information in binary format to send to the receiver. The

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receiver section consists of the HT-12D decoder IC. The DATA_IN pin-14 of the HT-

12D reads the 12-bit binary information sent by the HT-12E and then places this data

on its output pins. Pins 10,11,12 and 13 are the data out pins of the HT-12D,

D0,D1,D2 and D3.

The HT-12D receives the 12-bit word and interprets the first 8-bits as address

and the last 4-bits as data. Pins 1-8 of the HT-12E are the address pins. Using the

address pins of the HT-12E, we can select different addresses for up to 256 receivers.

The address is determined by setting pins 1-8 on the HT-12E to ground, or just

leaving them open.  The address selected on the HT-12E circuit must match the

address selected on the HT-12D circuit (exactly), or the information will be ignored

by the receiving circuit

2.8. RF MODULE (Radio Frequency)

Radio Frequency, is the frequency within the electromagnetic spectrum associated

with radio wave propagation. When an RF current is supplied to an antenna, an

electromagnetic field is created that then is able to propagate through space. Many

wireless technologies are based on RF field propagation.

FIG 2.9 Receiver Module FIG 2.10 Transmitter

Module

Radio Frequency. The 10 kHz to 300 GHz frequency range that can be used for

wireless communication

Radio Frequency. Also used generally to refer to the radio signal generated by the

system transmitter, or to energy present from other sources that may be picked up by a

wireless receiver.

Wireless mouse, keyboard

Wireless data communication

Alarm and security systems

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Home Automation, Remote control

Automotive Telemetry

Intelligent sports equipment

Handheld terminals, Data loggers

Industrial telemetry and tele-communications

In-building environmental monitoring and control

High-end security and fire alarms

2.8.1 - TRANSMITTER

The TWS-434 extremely small, and are excellent for applications requiring short-

range RF remote controls.  The transmitter module is only 1/3 the size of a standard

postage stamp, and can easily be placed inside a small plastic enclosure.

TWS-434:  The transmitter output is up to 8mW at 433.92MHz with a range of

approximately 400 foot (open area) outdoors.  Indoors, the range is approximately 200

foot, and will go through most walls.

FIG 2.11 TRANSMITTER MODULE

The TWS-434 transmitter accepts both linear and digital inputs, can operate from 1.5

to 12 Volts-DC, and makes building a miniature hand-held RF transmitter very easy. 

The TWS-434 is approximately 1/3 the size of a standard postage stamp.

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FIG 2.12 TWS-434 PIN DIAGRAM

FIG 2.13 - Transmitter Application Circuit

2.8.2- RECEIVER

RWS-434:  The receiver also operates at 433.92MHz, and has a sensitivity of 3uV. 

The WS-434 receiver operates from 4.5 to 5.5 volts-DC, and has both linear and

digital outputs.

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FIG 2.14 PIN DIAGRAM OF RECEIVER MODULE

2.8.3 - TRANSMIT AND RECEIVE DATA

The TWS-434 modules do not incorporate internal encoding. If you want to send

simple control or status signals such as button presses or switch colsures, consider

using an encoder and decoder IC set that takes care of all encoding, error checking,

and decoding functions. These chips are made by Motorola and Holtek. They are an

excellent way to implement basic wireless transmission control.

2.8.4 RECEIVER DATA OUTPUT

A 0 volt to Vcc data output is available on pins. This output is normally used to drive

a digital decoder IC or a microprocessor which is performing the data decoding. The

receiver’s output will only transition when valid data is present. In instances when no

carrier is present the output will remain low

2.8.5 DECODING DATA

The RWS-434 modules do not incorporate internal decoding. If you want to receive

Simple control or status signals such as button presses or switch colsures, you can use

the encoder and decoder IC set described above. Decoders with momentary and

latched outputs are available.

2.8.6- TRANSMITTING AND RECEIVING

Full duplex or simultaneous two-way operation is not possible with these modules.

If a transmit and receive module are in close proximity and data is sent to a

remote receive module while attempting to simultaneously receive data from a

remote transmit module, the receiver will be overloaded by its close proximity

transmitter. This will happen even if encoders and decoders are used with

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different address settings for each transmitter and receiver pair. If two way

communication is required, only half duplex operation is allowed.

2.9 INTRODUCTION TO RS232 SERIAL COMMUNICATION

Serial communication is basically the transmission or reception of data one bit at a

time. Today's computers generally address data in bytes or some multiple thereof. A

byte contains 8 bits. A bit is basically either a logical 1 or zero. Every character on this

page is actually expressed internally as one byte. The serial port is used to convert each

byte to a stream of ones and zeroes as well as to convert a streams of ones and zeroes

to bytes. The serial port contains a electronic chip called a Universal Asynchronous

Receiver/Transmitter (UART) that actually does the conversion.

The serial port has many pins. We will discuss the transmit and receive pin first.

Electrically speaking, whenever the serial port sends a logical one (1) a negative

voltage is effected on the transmit pin. Whenever the serial port sends a logical zero (0)

a positive voltage is effected. When no data is being sent, the serial port's transmit pin's

voltage is negative (1) and is said to be in a MARK state. Note that the serial port can

also be forced to keep the transmit pin at a positive voltage (0) and is said to be the

SPACE or BREAK state. (The terms MARK and SPACE are also used to simply

denote a negative voltage (1) or a positive voltage(0) at the transmit pin respectively)

When transmitting a byte, the UART (serial port) first sends a START BIT which is a

positive voltage (0), followed by the data (general 8 bits, but could be 5, 6, 7, or 8 bits)

followed by one or two STOP BITs which is a negative(1) voltage. The sequence is

repeated for each byte sent. Figure 1 shows a diagram of a what a byte transmission

would look like.

At this point you may want to know what is the duration of a bit. In other words, how

long does the signal stay in a particular state to define a bit. The answer is simple. It is

dependent on the baud rate. The baud rate is the number of times the signal can switch

states in one second. Therefore, if the line is operating at 9600 baud, the line can

switch states 9,600 times per second. This means each bit has the duration of 1/9600 of

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a second or about 100 µsec.

When transmitting a character there are other characteristics other than the baud rate

that must be known or that must be setup. These characteristics define the entire

interpretation of the data stream.The first characteristic is the length of the byte that

will be transmitted. This length in general can be anywhere from 5 to 8 bits.

The second characteristic is parity. The parity characteristic can be even, odd, mark,

space, or none. If even parity, then the last data bit transmitted will be a logical 1 if the

data transmitted had an even amount of 0 bits. If odd parity, then the last data bit

transmitted will be a logical 1 if the data transmitted had an odd amount of 0 bits. If

MARK parity, then the last transmitted data bit will always be a logical 1. If SPACE

parity, then the last transmitted data bit will always be a logical 0. If no parity then

there is no parity bit transmitted.The third characteristic is the amount of stop bits. This

value in general is 1 or 2.Assume we want to send the letter 'A' over the serial port. The

binary representation of the letter 'A' is 01000001. Remembering that bits are

transmitted from least significant bit (LSB) to most significant bit (MSB), the bit

stream transmitted would be as follows for the line characteristics 8 bits, no parity, 1

stop bit, 9600 baud

LSB (0 1 0 0 0 0 0 1 0 1) MSB

The above represents (Start Bit) (Data Bits) (Stop Bit)

To calculate the actual byte transfer rate simply divide the baud rate by the number of

bits that must be transferred for each byte of data. In the case of the above example,

each character requires 10 bits to be transmitted for each character. As such, at 9600

baud, up to 960 bytes can be transferred in one second.The above discussion was

concerned with the "electrical/logical" characteristics of the data stream. We will

expand the discussion to line protocol.

Serial communication can be half duplex or full duplex. Full duplex communication

means that a device can receive and transmit data at the same time. Half duplex means

that the device cannot send and receive at the same time. It can do them both, but not at

the same time. Half duplex communication is all but outdated except for a very small

focused set of applications.

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Half duplex serial communication needs at a minimum two wires, signal ground and

the data line. Full duplex serial communication needs at a minimum three wires, signal

ground, transmit data line, and receive data line. The RS232 specification governs the

physical and electrical characteristics of serial communications. This specification

defines several additional signals that are asserted (set to logical 1) for information and

control beyond the data signals and signal ground.

These signals are the Carrier Detect Signal (CD), asserted by modems to

signal a successful connection to another modem, Ring Indicator (RI), asserted by

modems to signal the phone ringing, Data Set Ready (DSR), asserted by modems to

show their presence, Clear To Send (CTS), asserted by modems if they can receive

data, Data Terminal Ready (DTR), asserted by terminals to show their presence,

Request To Send (RTS), asserted by terminals if they can receive data. The section

RS232 Cabling describes these signals and how they are connected.

The above paragraph eluded to hardware flow control. Hardware flow

control is a method that two connected devices use to tell each other electronically

when to send or when not to send data. A modem in general drops (logical 0) its CTS

line when it can no longer receive characters. It re-asserts it when it can receive again.

A terminal does the same thing instead with the RTS signal. Another method of

hardware flow control in practice is to perform the same procedure in the previous

paragraph except that the DSR and DTR signals are used for the handshake.

Note that hardware flow control requires the use of additional wires. The

benefit to this however is crisp and reliable flow control. Another method of flow

control used is known as software flow control. This method requires a simple 3 wire

serial communication link, transmit data, receive data, and signal ground. If using this

method, when a device can no longer receive, it will transmit a character that the two

devices agreed on. This character is known as the XOFF character. This character is

generally a hexadecimal 13. When a device can receive again it transmits an XON

character that both devices agreed to. This character is generally a hexadecimal 11.

2.9.1NULL MODEM, AN INTRODUCTION

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Serial communications with RS232. One of the oldest and most widely spread

communication methods in computer world. The way this type of communication can

be performed is pretty well defined in standards. I.e. with one exception. The standards

show the use of DTE/DCE communication, the way a computer should communicate

with a peripheral device like a modem. For your information, DTE means data

terminal equipment (computers etc.) where DCE is the abbreviation of data

communication equipment (modems). One of the main uses of serial communication

today where no modem is involved—a serial null modem configuration with

DTE/DTE communication—is not so well defined, especially when it comes to flow

control. The terminology null modem for the situation where two computers

communicate directly is so often used nowadays, that most people don't realize

anymore the origin of the phrase and that a null modem connection is an exception, not

the rule.

In history, practical solutions were developed to let two computers talk

with each other using a null modem serial communication line. In most situations, the

original modem signal lines are reused to perform some sort of handshaking.

Handshaking can increase the maximum allowed communication speed because it

gives the computers the ability to control the flow of information. High amounts of

incomming data is allowed if the computer is capable to handle it, but not if it is busy

performing other tasks. If no flow control is implemented in the null modem

connection, communication is only possible at speeds at which it is sure the receiving

side can handle the amount information even under worst case conditions.

2.9.2 ORIGINAL USE OF RS232

When we look at the connector pinout of the RS232 port, we see two pins which are

certainly used for flow control. These two pins are RTS, request to send and CTS, clear

to send. With DTE/DCE communication (i.e. a computer communicating with a

modem device) RTS is an output on the DTE and input on the DCE. CTS is the

answering signal comming from the DCE.

Before sending a character, the DTE asks permission by setting its RTS output. No

information will be sent until the DCE grants permission by using the CTS line. If the

DCE cannot handle new requests, the CTS signal will go low. A simple but useful

mechanism allowing flow control in one direction. The assumption is, that the DTE

can always handle incomming information faster than the DCE can send it. In the past,

24

this was true. Modem speeds of 300 baud were common and 1200 baud was seen as a

high speed connection.

For further control of the information flow, both devices have the ability to signal their

status to the other side. For this purpose, the DTR data terminal ready and DSR data

set ready signals are present. The DTE uses the DTR signal to signal that it is ready to

accept information, whereas the DCE uses the DSR signal for the same purpose. Using

these signals involves not a small protocol of requesting and answering as with the

RTS/CTS handshaking. These signals are in one direction only. The last flow control

signal present in DTE/DCE communication is the CD carrier detect. It is not used

directly for flow control, but mainly an indication of the ability of the modem device to

communicate with its counter part. This signal indicates the existence of a

communication link between two modem devices.

2.9.3 Null modem without handshaking

How to use the handshaking lines in a null modem configuration? The simplest way is

to don't use them at all. In that situation, only the data lines and signal ground are cross

connected in the null modem communication cable. All other pins have no connection.

An example of such a null modem cable without handshaking can be seen in the figure

below.

Connector 1 Connector 2 Function

2 3 Rx Tx

3 2 Tx Rx

5 5 Signal ground

FIG 2.15 Simple null modem without handshaking

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2.9.4 COMPATIBILITY ISSSUES

If you read about null modems, this three wire null modem cable is often talked about.

Yes, it is simple but can we use it in all circumstances? There is a problem, if either of

the two devices checks the DSR or CD inputs. These signals normaly define the ability

of the other side to communicate. As they are not connected, their signal level will

never go high. This might cause a problem.

The same holds for the RTS/CTS handshaking sequence. If the software on both sides

is well structured, the RTS output is set high and then a waiting cycle is started until a

ready signal is received on the CTS line. This causes the software to hang because no

physical connection is present to either CTS line to make this possible. The only type

of communication which is allowed on such a null modem line is data-only traffic on

the cross connected Rx/Tx lines.

This does however not mean, that this null modem cable is useless. Communication

links like present in the Norton Commander program can use this null modem cable.

This null modem cable can also be used when communicating with devices which do

not have modem control signals like electronic measuring equipment etc. As you can

imagine, with this simple null modem cable no hardware flow control can be

implemented. The only way to perform flow control is with software flow control

using the XOFF and XON characters.

2.10 MAX 232

2.10.1 INTRODUCTION

MAX-232 is primary used for people building electronics with an RS-232 interface.

Serial RS-232 communication works with voltages (-15V ... -3V for high) and +3V ...

+15V for low) which are not compatible with normal computer logic voltages. To

receive serial data from an RS-232 interface the voltage has to be reduced, and the low

and high voltage level inverted. In the other direction (sending data from some logic

over RS-232) the low logic voltage has to be "bumped up", and a negative voltage has

to be generated, too.

26

2.10.2 PINDIAGRAM

FIG 2.16 Pin Diagram Of Max 232

27

RS232 COMMUNICATION

Fig 2.17 Circuit Diagram Of Serial Communication

28

3.1 INTRODUCTION

In this chapter the entire circuitry of the project is shown. The design parameters kept

in mind while the circuits are being designed are clearly explained. Also the chapter

includes the main important part of any hardware project i.e power supply, it’s circuit

and it’s internal circuit components. On the whole this chapter gives the circuits

employed in the whole project and their interfacing.

3.2 POWER SUPPLY

3.2.1 BLOCK DIAGRAM

The ac voltage, typically 220V rms, is connected to a transformer, which steps that ac

voltage down to the level of the desired dc output. A diode rectifier then provides a

full-wave rectified voltage that is initially filtered by a simple capacitor filter to

produce a dc voltage. This resulting dc voltage usually has some ripple or ac voltage

variation.

A regulator circuit removes the ripples and also remains the same dc value even if the

input dc voltage varies, or the load connected to the output dc voltage changes. This

voltage regulation is usually obtained using one of the popular voltage regulator IC

units.

Fig 3.1 Block Diagram of Power supply

3.3 WORKING PRINCIPLE

3.3.1 TRANSFORMER

The potential transformer will step down the power supply voltage (0-230V) to (0-6V)

level. Then the secondary of the potential transformer will be connected to the

precision rectifier, which is constructed with the help of op–amp. The advantages of

using precision rectifier are it will give peak voltage output as DC, rest of the circuits

will give only RMS output.

3.3.2 BRIDGE RECTIFIER

29

TRANSFORMER RECTIFIER FILTER IC REGULATOR LOAD

When four diodes are connected as shown in figure, the circuit is called as bridge

rectifier. The input to the circuit is applied to the diagonally opposite corners of the

network, and the output is taken from the remaining two corners.

Let us assume that the transformer is working properly and there is a positive potential,

at point A and a negative potential at point B. the positive potential at point A will

forward bias D3 and reverse bias D4.

The negative potential at point B will forward bias D1 and reverse D2.

At this time D3 and D1 are forward biased and will allow current flow to pass through

them; D4 and D2 are reverse biased and will block current flow. The path for current

flow is from point B through D1, up through RL, through D3, through the secondary of

the transformer back to point B. this path is indicated by the solid arrows. Waveforms

(1) and (2) can be observed across D1 and D3.

One-half cycle later the polarity across the secondary of the transformer

reverse, forward biasing D2 and D4 and reverse biasing D1 and D3. Current flow will

now be from point A through D4, up through RL, through D2, through the secondary

of T1, and back to point A. This path is indicated by the broken arrows. Waveforms (3)

and (4) can be observed across D2 and D4. The current flow through RL is always in

the same direction. In flowing through RL this current develops a voltage

corresponding to that shown waveform (5). Since current flows through the load (RL)

during both half cycles of the applied voltage, this bridge rectifier is a full-wave

rectifier.

One advantage of a bridge rectifier over a conventional full-wave

rectifier is that with a given transformer the bridge rectifier produces a voltage output

that is nearly twice that of the conventional full-wave circuit.

This may be shown by assigning values to some of the components shown in

views A and B. assume that the same transformer is used in both circuits. The peak

voltage developed between points X and y is 1000 volts in both circuits. In the

conventional full-wave circuit shown—in view A, the peak voltage from the center tap

to either X or Y is 500 volts. Since only one diode can conduct at any instant, the

maximum voltage that can be rectified at any instant is 500 volts.

The maximum voltage that appears across the load resistor is nearly-but never

exceeds-500 v0lts, as result of the small voltage drop across the diode. In the bridge

rectifier shown in view B, the maximum voltage that can be rectified is the full

30

secondary voltage, which is 1000 volts. Therefore, the peak output voltage across the

load resistor is nearly 1000 volts. With both circuits using the same transformer, the

bridge rectifier circuit produces a higher output voltage than the conventional full-

wave rectifier circuit.

3.3.3 IC VOLTAGE REGULATORS

Voltage regulators comprise a class of widely used ICs. Regulator IC units contain the

circuitry for reference source, comparator amplifier, control device, and overload

protection all in a single IC. IC units provide regulation of either a fixed positive

voltage, a fixed negative voltage, or an adjustably set voltage. The regulators can be

selected for operation with load currents from hundreds of milli amperes to tens of

amperes, corresponding to power ratings from milli watts to tens of watts.

FIG 3.2 Circuit Diagram Of voltage regulator

A fixed three-terminal voltage regulator has an unregulated dc input voltage, Vi,

applied to one input terminal, a regulated dc output voltage, Vo, from a second

terminal, with the third terminal connected to ground. The series 78 regulators provide

fixed positive regulated voltages from 5 to 24volts. Similarly, the series 79 regulators

provide fixed negative regulated voltages from 5 to 24 volts.

For ICs, microcontroller, LCD --------- 5 volts

For alarm circuit, op-amp, relay circuits ---------- 12 volt

31

3.4 COMPLETE CIRCUIT DIAGRAM EMPLOYED

32

33

4.1 INTRODUCTION

This chapter gives the advantages and disadvantages of the project. The various

applications in which the project can be utilized and implemented are furnished in

this chapter. Finally the chapter is ended with conclusion.

4.2 ADVANTAGES

1. High reliability and performance

2. Low cost and low complexity

3. Unwanted additional devices

4. Easiest way to interface with computer

4.3 APPLICATIONS

1. Easy to operate for patient or fit able person

2. Automobile and commercial applications

3. Inertial measurement systems

4. Emerging military systems

34

4.4 FUTURE SCOPE

1. Usage of Bluetooth technology for wireless transmission instead of Radio

Frequency transmission.

2. Usage of laser sensors in place of IR sensors

4.5 CONCLUSION

The advantages and disadvantages explained earlier in this chapter justify the

significance of wireless mouse. The application areas are also vast with the simplest

of modifications.

1. Help the disabled benefit from advances in computer and electronics

technologies

2. Speech input for operating a computer

3. User-friendly features such as, LED indication

4. Plugged into any IBM compatible personal computers running either

Windows 98/LinuX

35

REFERENCES:

[1] David E.Simon, An Embedded Software Primer,12 edition, Addison-

Wesley,1999

[2] Interfacing PIC Controllers by Martin Bates

[3] <http://www.mitelbook.com>

36

APPENDIX

CODE FOR INPUT SECTION

#include <pic.h>

__CONFIG(0x3f72);

#define TE RC0

#define Eye RC7

unsigned char GetX();

unsigned char GetY();

unsigned char GetZ();

void delay1(int);

void delay2(int);

unsigned char ch1,ch2,ch3,ch4,chL,chM;

unsigned char X,Y,Z;

void DelayMs(int n)

{

int i,j;

for(i=0;i<n;i++)

{

for(j=0;j<1000;j++);

}

}

unsigned char GetX()

{

ADCON0=0x41;

DelayMs(1);

ADGO=1;

while(ADGO==1);

X = ADRESH;

return(X);

}

unsigned char GetY()

37

{

ADCON0=0x49;

DelayMs(1);

ADGO=1;

while(ADGO==1);

Y = ADRESH;

return(Y);

}

unsigned char GetZ()

{

ADCON0=0x51;

DelayMs(1);

ADGO=1;

while(ADGO==1);

Z = ADRESH;

return(Z);

}

void wireless_send(unsigned char ch)

{

PORTD = ~ch & 0x0F;

TE = 0;

delay2(7);

TE = 1;

delay2(7);

}

void main()

{

char hor,ver,inc;

TRISA = 0xff;

ADCON1 = 0x00;

TRISD = 0x00;

TRISC = 0xF0;

PORTC = 0xF0;

38

Eye = 0;

TE=1;

while(1)

{

while(1)

{

hor = GetX();

ver = GetY();

inc = GetZ();

ch1 = 0xA1;

chL = ch1 & 0x0F;

chM =(ch1 >> 4);

wireless_send(chL);

wireless_send(chM);

ch1 = hor;

chL = ch1 & 0x0F;

chM =(ch1 >> 4);

wireless_send(chL);

wireless_send(chM);

ch1 = 0xA2;

chL = ch1 & 0x0F;

chM =(ch1 >> 4);

wireless_send(chL);

wireless_send(chM);

ch1 = ver;

chL = ch1 & 0x0F;

chM =(ch1 >> 4);

wireless_send(chL);

wireless_send(chM);

if(Eye == 1)

{

ch1 = 0xA3;

39

chL = ch1 & 0x0F;

chM =(ch1 >> 4);

wireless_send(chL);

wireless_send(chM);

}

}

}

}

void delay1(int n)

{

int i;

for(i=0;i<n;i++);

}

void delay2(int n)

{

int i;

for(i=0;i<n;i++)

{

delay1(1000);

}

}

CODE FOR COMPUTER SECTION

#include<pic.h>

__CONFIG(0x3f72);

#define recB RC0

unsigned char ch,chM,chL,ch_buf,chL1,chM1;

void delay1(int n)

{

40

int i;

for(i=0;i<n;i++);

}

void delay2(int n)

{

int i;

for(i=0;i<n;i++)

{

delay1(1000);

}

}

void main()

{

char ch;

int i;

int t=1,z=1;

TRISC = 0xff;

TRISD = 0xff;

TRISB = 0xff;

PORTB = 0xff;

RBPU = 0;

TXSTA = 0x24;

RCSTA = 0x90;

SPBRG = 64;

PORTC = 0x0f;

PORTD = 0x00;

while(1)

{

41

if(recB == 0)

{

recB = 1;

ch_buf = 0xF & ~PORTD; // 0000 1111

while(t == 1)

{

chL = ch_buf;

t = 2;

}

while(t == 5)

{

chM = ch_buf;

ch = chL + (chM * 0x10);

TXREG = ch;

delay2(8);

t = 0;

}

delay2(3);

t++;

if(PORTB == 0x01)

{

TXREG = 'G';

delay2(1);

}

if(PORTB == 0x02)

{

TXREG = 'H';

delay2(1);

42

}

if(PORTB == 0x04)

{

TXREG = 'I';

delay2(1);

}

if(PORTB == 0x08)

{

TXREG = 'J';

delay2(1);

}

} }}

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