1. INTRODUCTION

1.1 Introduction to project

The Scope of the project is power management for shopping malls with bidirectional visitors counting.

The project provides a method for automatic control of devices (lights, fans, or AC s)

throughout a shopping mall. A unique architecture of occupancy sensors includes entry/exit

sensors for detecting movement through doorways. The bidirectional sensors are used to sense

the entry and exit.

This project is designed around a microcontroller which forms the control unit of the

project. The central embedded controller controls the devices according to the no.of persons

entered into the shopping mall in response to the entry/exit sensors. The present project provides

a system for saving power of a shopping mall. The hall of the mall is provided with bidirectional

entry and exit way sensors.

All the input devices such as sensors and output devices such as relays are interfaced to

microcontroller. The microcontroller controls the devices according to the inputs from the IR

sensors.

Block diagram:

Fig 1.1 Block diagram

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Regulated power supply

MICRO

CONTROLLER

Hyper Terminal

Hall with IR Sensors

Devices

1.2 Project Overview

This Project “Power management for shopping mall with bidirectional visitors counting”

using Microcontroller is a reliable circuit that takes over the task of controlling the room lights as

well us counting number of persons/ visitors in the room very accurately. When somebody enters

into the room then the counter is incremented by one and the light in the room will be switched

ON and when any one leaves the room then the counter is decremented by one. The light will be

only switched OFF until all the persons in the room go out. The total number of persons inside

the room is also displayed on the seven segment displays.

The microcontroller does the above job. It receives the signals from the sensors, and this

signal is operated under the control of software which is stored in ROM. Microcontroller

AT89S52 continuously monitor the Infrared Receivers, When any object pass through the IR

Receiver’s then the IR Rays falling on the receiver are obstructed , this obstruction is sensed by

the Microcontroller.

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2. INTRODUCTION TO EMBEDDED SYSTEMS

An embedded system is a special-purpose computer system designed to perform one or a

few dedicated functions, sometimes with real-time computing constraints. It is usually embedded

as part of a complete device including hardware and mechanical parts. In contrast, a general-

purpose computer, such as a personal computer, can do many different tasks depending on

programming. Embedded systems have become very important today as they control many of the

common devices we use.

Since the embedded system is dedicated to specific tasks, design engineers can optimize

it, reducing the size and cost of the product, or increasing the reliability and performance. Some

embedded systems are mass-produced, benefiting from economies of scale.

Physically, embedded systems range from portable devices such as digital watches and

MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems

controlling nuclear power plants.Complexity varies from low, with a single microcontroller chip,

to very high with multiple units, peripherals and networks mounted inside a large chassis or

enclosure.

In general, "embedded system" is not an exactly defined term, as many systems have

some element of programmability. For example, Handheld computers share some elements with

embedded systems such as the operating systems and microprocessors which power them — but

are not truly embedded systems, because they allow different applications to be loaded and

peripherals to be connected.

An embedded system is some combination of computer hardware and software, either

fixed in capability or programmable, that is specifically designed for a particular kind of

application device. Industrial machines, automobiles, medical equipment, cameras, household

appliances, airplanes, vending machines, and toys (as well as the more obvious cellular phone

and PDA) are among the myriad possible hosts of an embedded system. Embedded systems that

are programmable are provided with a programming interface, and embedded systems

programming is a specialized occupation.

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Certain operating systems or language platforms are tailored for the embedded market,

such as Embedded Java and Windows XP Embedded. However, some low-end consumer

products use very inexpensive microprocessors and limited storage, with the application and

operating system both part of a single program. The program is written permanently into the

system's memory in this case, rather than being loaded into RAM (random access memory), as

programs on a personal computer are.

2.1 APPLICATIONS OF EMBEDDED SYSTEM

We are living in the Embedded World. You are surrounded with many embedded

products and your daily life largely depends on the proper functioning of these gadgets.

Television, Radio, CD player of your living room, Washing Machine or Microwave Oven in

your kitchen, Card readers, Access Controllers, Palm devices of your work space enable you to

do many of your tasks very effectively. Apart from all these, many controllers embedded in your

car take care of car operations between the bumpers and most of the times you tend to ignore all

these controllers.

In recent days, you are showered with variety of information about these embedded

controllers in many places. All kinds of magazines and journals regularly dish out details about

latest technologies, new devices; fast applications which make you believe that your basic

survival is controlled by these embedded products. Now you can agree to the fact that these

embedded products have successfully invaded into our world. You must be wondering about

these embedded controllers or systems. What is this Embedded System?

The computer you use to compose your mails, or create a document or analyze the

database is known as the standard desktop computer. These desktop computers are manufactured

to serve many purposes and applications.

You need to install the relevant software to get the required processing facility. So, these

desktop computers can do many things. In contrast, embedded controllers carryout a specific

work for which they are designed. Most of the time, engineers design these embedded controllers

with a specific goal in mind. So these controllers cannot be used in any other place.

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Theoretically, an embedded controller is a combination of a piece of microprocessor based

hardware and the suitable software to undertake a specific task.

These days designers have many choices in microprocessors/microcontrollers. Especially,

in 8 bit and 32 bit, the available variety really may overwhelm even an experienced designer.

Selecting a right microprocessor may turn out as a most difficult first step and it is getting

complicated as new devices continue to pop-up very often.

In the 8 bit segment, the most popular and used architecture is Intel's 8031. Market

acceptance of this particular family has driven many semiconductor manufacturers to develop

something new based on this particular architecture. Even after 25 years of existence,

semiconductor manufacturers still come out with some kind of device using this 8031 core.

Military and aerospace software applications

From in-orbit embedded systems to jumbo jets to vital battlefield networks, designers of

mission-critical aerospace and defense systems requiring real-time performance, scalability, and

high-availability facilities consistently turn to the Linux OS RTOS and the LynxOS-178 RTOS

for software certification to DO-178B.

Rich in system resources and networking services, Linux OS provides an off-the-shelf

software platform with hard real-time response backed by powerful distributed computing

(CORBA), high reliability, software certification, and long-term support options. The LynxOS-

178 RTOS for software certification, based on the RTCA DO-178B standard, assists developers

in gaining certification for their mission- and safety-critical systems. Real-time systems

programmers get a boost with Linux Works' DO-178B RTOS training courses.LynxOS-178 is

the first DO-178B and EUROCAE/ED-12B certifiable, POSIX compatible RTOS solution.

Communications applications

"Five-nines" availability, Compact PCI hot swap support, and hard real-time response

Linux OS delivers on these key requirements and more for today's carrier-class systems. Scalable

kernel configurations, distributed computing capabilities, integrated communications stacks, and

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fault-management facilities make Linux OS the ideal choice for companies looking for

a single operating system for all embedded telecommunications applications from complex

central controllers to simple line/trunk cards.

Linux Works Jumpstarts for Communications package enables OEMs to rapidly develop

mission-critical communications equipment, with pre-integrated, state-of-the-art,datanetworking

and porting software components including source code for easy customization.

The Lynx Certifiable Stack (LCS) is a secure TCP/IP protocol stack designed especially

for applications where standards certification is required.

Electronics applications and consumer devices

As the number of powerful embedded processors in consumer devices continues to rise,

the Blue Cat® Linux® operating system provides a highly reliable and royalty-free option for

systems designers.

And as the wireless appliance revolution rolls on, web-enabled navigation systems,

radios, personal communication devices, phones and PDAs all benefit from the cost-effective

dependability, proven stability and full product life-cycle support opportunities associated with

Blue Cat embedded Linux. Blue Cat has teamed up with industry leaders to make it easier to

build Linux mobile phones with Java integration.

For makers of low-cost consumer electronic devices who wish to integrate the Linux OS

real-time operating system into their products, we offer special MSRP-based pricing to reduce

royalty fees to a negligible portion of the device's MSRP.

Industrial automation and process control software

Designers of industrial and process control systems know from experience that Linux

Works operating systems provide the security and reliability that their industrial applications

require. From ISO 9001 certification to fault-tolerance, POSIX conformance, secure partitioning

and high availability, we've got it all. Take advantage of our 20 years of experience.

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3. CONTROLLER DATA

MICROCONTROLLER Vs MICROPROCESSOR:

What is the difference between a Microprocessor and Microcontroller? By

microprocessor is meant the general purpose Microprocessors such as Intel's X86 family (8086,

80286, 80386, 80486, and the Pentium) or Motorola's 680X0 family (68000, 68010, 68020,

68030, 68040, etc). These microprocessors contain no RAM, no ROM, and no I/O ports on the

chip itself. For this reason, they are commonly referred to as general-purpose Microprocessors.

A system designer using a general-purpose microprocessor such as the Pentium or the

68040 must add RAM, ROM, I/O ports, and timers externally to make them functional. Although

the addition of external RAM, ROM, and I/O ports makes these systems bulkier and much more

expensive, they have the advantage of versatility such that the designer can decide on the amount

of RAM, ROM and I/O ports needed to fit the task at hand. This is not the case with

Microcontrollers.

A Microcontroller has a CPU (a microprocessor) in addition to a fixed amount of RAM,

ROM, I/O ports, and a timer all on a single chip. In other words, the processor, the RAM, ROM,

I/O ports and the timer are all embedded together on one chip. In many applications, for example

a TV remote control, there is no need for the computing power of a 486 or even an 8086

microprocessor. These applications most often require some I/O operations to read signals and

turn on and off certain bits.

3.1 MICROCONTROLLERS FOR EMBEDDED SYSTEMS

In the Literature discussing microprocessors, we often see the term Embedded System.

Microprocessors and Microcontrollers are widely used in embedded system products. An

embedded system product uses a microprocessor (or Microcontroller) to do one task only. A

printer is an example of embedded system since the processor inside it performs one task only;

namely getting the data and printing it. Contrast this with a Pentium based PC. A PC can be used

for any number of applications such as word processor, print-server, bank teller terminal, Video

game, network server, or Internet terminal. Software for a variety of applications can be loaded

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and run. Of course the reason a pc can perform myriad tasks is that it has RAM memory and an

operating system that loads the application software into RAM memory and lets the CPU run it.

In an Embedded system, there is only one application software that is typically burned

into ROM. An x86 PC contains or is connected to various embedded products such as keyboard,

printer, modem, disk controller, sound card, CD-ROM drives, mouse, and so on. Each one of

these peripherals has a Microcontroller inside it that performs only one task. For example, inside

every mouse there is a Microcontroller to perform the task of finding the mouse position and

sending it to the PC. Table 1-1 lists some embedded products.

3.2 Microcontroller Architecture and Features

The basic internal designs of microcontrollers are pretty similar. Figure1 shows the block

diagram of a typical microcontroller. All components are connected via an internal bus and are

all integrated on one chip. The modules are connected to the outside world via I/O pins.

Fig 3.2.1: Basic Layout of Microcontroller

The following list contains the modules typically found in a microcontroller. You can

find a more detailed description of these components in later sections.

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Processor Core: The CPU of the controller. It contains the arithmetic logic unit, the control unit,

and the registers (stack pointer, program counter, accumulator register, register file . . .).

Memory: The memory is sometimes split into program memory and data memory. In larger

controllers, a DMA controller handles data transfers between peripheral components and the

memory.

Interrupt Controller: Interrupts are useful for interrupting the normal program flow in case of

(important) external or internal events. In conjunction with sleep modes, they help to conserve

power.

Timer/Counter: Most controllers have at least one and more likely 2-3 Timer/Counters, which

can be used to timestamp events, measure intervals, or count events. Many controllers also

contain PWM (pulse width modulation) outputs, which can be used to drive motors or for safe

breaking (antilock brake system, ABS). Furthermore the PWM output can, in conjunction with

an external filter, be used to realize a cheap digital/analog converter.

Digital I/O: Parallel digital I/O ports are one of the main features of microcontrollers. The

number of I/O pins varies from 3-4 to over 90, depending on the controller family and the

controller type.

Analog I/O: Apart from a few small controllers, most microcontrollers have integrated

analog/digital converters, which differ in the number of channels (2-16) and their resolution (8-

12 bits). The analog module also generally features an analog comparator. In some cases, the

microcontroller includes digital/analog converters.

3.3 The UART

The Universal Asynchronous Receiver/Transmitter (UART) controller is the key

component of the serial communications subsystem of a computer. The UART takes bytes of

data and transmits the individual bits in a sequential fashion. At the destination, a second UART

re-assembles the bits into complete bytes.

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Serial transmission is commonly used with modems and for non-networked

communication between computers, terminals and other devices. There are two primary forms of

serial transmission: Synchronous and Asynchronous. Depending on the modes that are supported

by the hardware, the name of the communication sub-system will usually include a A if it

supports Asynchronous communications, and a S if it supports Synchronous communications.

Both forms are described below.

3.4 Synchronous Serial Transmission

Synchronous serial transmission requires that the sender and receiver share a clock with

one another, or that the sender provide a strobe or other timing signal so that the receiver knows

when to “read” the next bit of the data. In most forms of serial Synchronous communication, if

there is no data available at a given instant to transmit, a fill character must be sent instead so

that data is always being transmitted. Synchronous communication is usually more efficient

because only data bits are transmitted between sender and receiver, and synchronous

communication can be more costly if extra wiring and circuits are required to share a clock

signal between the sender and receiver.

A form of Synchronous transmission is used with printers and fixed disk devices in that

the data is sent on one set of wires while a clock or strobe is sent on a different wire. Printers and

fixed disk devices are not normally serial devices because most fixed disk interface standards

send an entire word of data for each clock or strobe signal by using a separate wire for each bit of

the word. In the PC industry, these are known as Parallel devices. The standard serial

communications hardware in the PC does not support Synchronous operations. This mode is

described here for comparison purposes only

3.5 Asynchronous Serial Transmission

Asynchronous transmission allows data to be transmitted without the sender having to

send a clock signal to the receiver. Instead, the sender and receiver must agree on timing

parameters in advance and special bits are added to each word which are used to synchronize the

sending and receiving units.

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When a word is given to the UART for Asynchronous transmissions, a bit called the

"Start Bit" is added to the beginning of each word that is to be transmitted. The Start Bit is used

to alert the receiver that a word of data is about to be sent, and to force the clock in the receiver

into synchronization with the clock in the transmitter. These two clocks must be accurate enough

to not have the frequency drift by more than 10% during the transmission of the remaining bits in

the word. (This requirement was set in the days of mechanical teleprinters and is easily met by

modern electronic equipment.)

After the Start Bit, the individual bits of the word of data are sent, with the Least

Significant Bit (LSB) being sent first. Each bit in the transmission is transmitted for exactly the

same amount of time as all of the other bits, and the receiver “looks” at the wire at approximately

halfway through the period assigned to each bit to determine if the bit is a 1 or a 0. For example,

if it takes two seconds to send each bit, the receiver will examine the signal to determine if it is a

1 or a 0 after one second has passed, then it will wait two seconds and then examine the value of

the next bit, and so on.

The sender does not know when the receiver has “looked” at the value of the bit. The

sender only knows when the clock says to begin transmitting the next bit of the word.When the

entire data word has been sent, the transmitter may add a Parity Bit that the transmitter generates.

The Parity Bit may be used by the receiver to perform simple error checking. Then at least one

Stop Bit is sent by the transmitter.

When the receiver has received all of the bits in the data word, it may check for the Parity

Bits (both sender and receiver must agree on whether a Parity Bit is to be used), and then the

receiver looks for a Stop Bit. If the Stop Bit does not appear when it is supposed to, the UART

considers the entire word to be garbled and will report a Framing Error to the host processor

when the data word is read. The usual cause of a Framing Error is that the sender and receiver

clocks were not running at the same speed, or that the signal was interrupted.Regardless of

whether the data was received correctly or not, the UART automatically discards the Start,

Parityand Stop bits. If the sender and receiver are configured identically, these bits are not passed

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to the host.If another word is ready for transmission, the Start Bit for the new word can be sent as

soon as the Stop Bit for the previous word has been sent.

Because asynchronous data is “self synchronizing”, if there is no data to transmit, the

transmission line can be idle.

3.6 MICROCONTROLLER

ATmega8

The ATmega8 is a low-power CMOS 8-bit microcontroller, based on the AVR

enhanced RISC architecture. By executing powerful instructions in a single clock cycle, the

ATmega8 achieves throughputs approaching 1 MIPS per MHz allowing the system designer to

optimize power consumption versus processing speed.

Fig. 3.6.1 Pin Out of ATmega8

AVR core combines a rich instruction set with 32 general-purpose working registers. All

the 32 registers are directly connected to the Arithmetic Logic Unit (ALU), allowing two

independent registers to be accessed in one single instruction executed in one clock cycle. The

resulting architecture is more code efficient while achieving throughputs up to ten times faster

than conventional CISC microcontrollers.

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3.6.1 ATmega8 features

• High-performance, Low-power AVR 8-bit Microcontroller

• Advanced RISC Architecture

130 Powerful Instructions – Most Single-clock Cycle Execution

32 x 8 General Purpose Working Registers

Fully Static Operation

Up to 16 MIPS Throughput at 16 MHz

On-chip 2-cycle Multiplier

• High Endurance Non-volatile Memory segments

8K Bytes of In-System Self-programmable Flash program memory

512 Bytes EEPROM

1K Byte Internal SRAM

Write/Erase Cycles: 10,000 Flash/100,000 EEPROM

Data retention: 20 years at 85°C/100 years at 25°C

Optional Boot Code Section with Independent Lock Bits

In-System Programming by On-chip Boot Program

True Read-While-Write Operation

Programming Lock for Software Security

• Peripheral Features

Two 8-bit Timer/Counters with Separate Prescaler, one Compare Mode

One 16-bit Timer/Counter with Separate Prescaler, Compare Mode, and Capture

Mode

Real Time Counter with Separate Oscillator

Three PWM Channels

8-channel ADC in TQFP and QFN/MLF package

Eight Channels 10-bit Accuracy

6-channel ADC in PDIP package

Six Channels 10-bit Accuracy

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Byte-oriented Two-wire Serial Interface

Programmable Serial USART

Master/Slave SPI Serial Interface

Programmable Watchdog Timer with Separate On-chip Oscillator

On-chip Analog Comparator

• Special Microcontroller Features

Power-on Reset and Programmable Brown-out Detection

Internal Calibrated RC Oscillator

External and Internal Interrupt Sources

Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, and Standby

• I/O and Packages

23 Programmable I/O Lines

28-lead PDIP, 32-lead TQFP, and 32-pad QFN/MLF

• Operating Voltages

2.7 - 5.5V (ATmega8L)

4.5 - 5.5V (ATmega8)

• Speed Grades

0 - 8 MHz (ATmega8L)

0 - 16 MHz (ATmega8)

• Power Consumption at 4 Mhz, 3V, 25°C

Active: 3.6 mA

Idle Mode: 1.0 mA

Power-down Mode: 0.5 μA

The Idle mode stops the CPU while allowing the USART, Two-wire interface, A/D

Converter, SRAM, Timer/Counters, SPI port, and interrupt system to continue functioning. The

Power-down mode saves the register contents but freezes the Oscillator, disabling all other chip

functions until the next External Interrupt or Hardware Reset.

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In Power-save mode, the Asynchronous Timer continues to run, allowing the user to

maintain a timer base while the rest of the device is sleeping. The ADC Noise Reduction mode

stops the CPU and all I/O modules except Asynchronous Timer and ADC, to minimize switching

noise during ADC conversions.

By combining an 8-bit RISC CPU with In-System Self-Programmable Flash on a

monolithic chip, the Atmel ATmega8 is a powerful microcontroller that provides a highly

flexible and cost-effective solution to many embedded control applications.

3.6.2 Pin Descriptions

VCC- Digital supply voltage.

GND- Ground.

Port B (PB7-PB0) XTAL1/XTAL2/TOSC1/TOSC2

Port B is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

bit). The Port B output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port B pins that are externally pulled low will source current if the

pull-up resistors are activated. The Port B pins are tri-stated when a reset condition becomes

active, even if the clock is not running. Depending on the clock selection fuse settings, PB6 can

be used as input to the inverting Oscillator amplifier and input to the internal clock operating

circuit. Depending on the clock selection fuse settings, PB7 can be used as output from the

inverting Oscillator amplifier. If the Internal Calibrated RC Oscillator is used as chip clock

source, PB7..6 is used as TOSC2..1 input for the Asynchronous Timer/Counter2 if the AS2 bit in

ASSR is set.

Port C (PC5-PC0)

Port C is an 7-bit bi-directional I/O port with internal pull-up resistors (selected for each

bit). The Port C output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port C pins that are externally pulled low will source current if the

pull-up resistors are activated. The Port C pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

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PC6/RESET

If the RSTDISBL Fuse is programmed, PC6 is used as an I/O pin. Note that the electrical

characteristics of PC6 differ from those of the other pins of Port C. If the RSTDISBL Fuse is

unprogrammed, PC6 is used as a Reset input. A low level on this pin for longer than the

minimum pulse length will generate a Reset, even if the clock is not running

Port D (PD7-PD0)

Port D is an 8-bit bi-directional I/O port with internal pull-up resistors (selected for each

bit). The Port D output buffers have symmetrical drive characteristics with both high sink and

source capability. As inputs, Port D pins that are externally pulled low will source current if the

pull-up resistors are activated. The Port D pins are tri-stated when a reset condition becomes

active, even if the clock is not running.

RESET

Reset input. A low level on this pin for longer than the minimum pulse length will

generate a reset, even if the clock is not running. Shorter pulses are not guaranteed to generate a

reset.

AVCC

AVCC is the supply voltage pin for the A/D Converter, Port C (3.0), and ADC (7.6). It

should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it

should be connected to VCC through a low-pass filter. Note that Port C (5.4) use digital supply

voltage, VCC.

AREF

AREF is the analog reference pin for the A/D Converter.

ADC7.6 (TQFP and QFN/MLF Package Only)

In the TQFP and QFN/MLF package, ADC7.6 serve as analog inputs to the A/D

converter. These pins are powered from the analog supply and serve as 10-bit ADC channels.

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Fig 3.6.2.1 BLOCK DIAGRAM OF AT mega 8

The ATmega8 AVR is supported with a full suite of program and system development

tools including: C compilers, macro assemblers, program debugger/simulators, in-circuit

emulators, and evaluation kits.

A flexible interrupt module has its control registers in the I/O space with an additional

global interrupt enable bit in the Status Register. All interrupts have a separate interrupt vector in

the interrupt vector table. The interrupts have priority in accordance with their interrupt vector

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position. The lower the interrupt vector address, the higher the priority. The I/O Memory can be

accessed directly, or as the Data Space locations following those of the Register File, 20h - 5Fh

3.6.3 I/O PORTS

All AVR ports have true Read-Modify-Write functionality when used as general digital

I/O ports. This means that the direction of one port pin can be changed without unintentionally

changing the direction of any other pin with the SBI and CBI instructions. The same applies

when changing drive value (if configured as output) or enabling/disabling of pull-up resistors (if

configured as input). Each output buffer has symmetrical drive characteristics with both high

sink and source capability. The pin driver is strong enough to drive LED displays directly. All

port pins have individually selectable pull-up resistors with a supply-voltage invariant resistance.

All I/O pins have protection diodes to both VCC and Ground.

All registers and bit references in this section are written in general form. Three I/O

memory address locations are allocated for each port, one each for the Data Register PORTx,

Data Direction Register DDRx, and the Port Input Pins PINx. The Port Input Pins I/O location is

read only, while the Data Register and the Data Direction Register are read/write. In addition, the

Pull-up Disable PUD bit in SFIOR disables the pull-up function for all pins in all ports when set.

Most port pins are multiplexed with alternate functions for the peripheral features on the

device. Enabling the alternate function of some of the port pins does not affect the use of the

other pins in the port as general digital I/O.

3.6.3.1 Ports as general purpose I/O:

The ports are bi-directional I/O ports with optional internal pull-ups. Each port pin

consists of three register bits: DDxn, PORTxn, and PINxn. The DDxn bits are accessed at the

DDRx I/O address, the PORTxn bits at the PORTx I/O address, and the PINxn bits at the

PINxI/O address. The DDxn bit in the DDRx Register selects the direction of this pin. If DDxn is

written logic one, Pxn is configured as an output pin. If DDxn is written logic zero, Pxn is

configured as an input pin. If PORTxn is written logic one when the pin is configured as an input

pin, the pull-up resistor is activated. To switch the pull-up resistor off, PORTxn has to be written

logic zero or the pin has to be configured as an output pin. The port pins are tri-stated when a

reset condition becomes active, even if no clocks are running. If PORTxn is written logic one

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when the pin is configured as an output pin, the port pin is driven high (one). If PORTxn is

written logic zero when the pin is configured as an output pin, the port pin is driven low (zero).

Normally, the pull-up enabled state is fully acceptable, as a high-impedance environment will

not notice the difference between a strong high driver and a pull-up. If this is not the case, the

PUD bit in the SFIOR Register can be set to disable all pull-ups in all ports.

Table 3.6.3.1 Selection Table

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Fig 3.6.3.1 General I/O Block diagram

Independent of the setting of Data Direction bit DDxn, the port pin can be read through the

PINxn Register bit. The PINxn Register bit and the preceding latch constitute a synchronizer.

This is needed to avoid meta stability if the physical pin changes value near the edge of the

internal clock, but it also introduces a delay. The maximum and minimum propagation delays are

denoted tpd, max and tpd, min respectively.

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Fig 3.6.3.2 Timing Diagram while Reading an 1

Consider the clock period starting shortly after the first falling edge of the system clock.

The latch is closed when the clock is low, and goes transparent when the clock is high, as

indicated by the shaded region of the “SYNC LATCH” signal. The signal value is latched when

the system clock goes low. It is clocked into the PINxn Register at the succeeding positive clock

edge. As indicated by the two arrows tpd, max and tpd, min, a single signal transition on the pin will be

delayed between ½ and 1½ system clock period depending upon the time of assertion.When

reading back a software assigned pin value, a nop instruction must be inserted. The out

instruction sets the “SYNC LATCH” signal at the positive edge of the clock. In this case, the

delay tpd through the synchronizer is one system clock period.

3.7 8-bit Timer/Counter Register Description

Timer/Counter Control Register – TCCR2

Fig 3.7.1 TCCR 1

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Bit 7 – FOC2: Force Output Compare

The FOC2 bit is only active when the WGM bits specify a non-PWM mode. However,

for ensuring compatibility with future devices, this bit must be set to zero when TCCR2 is

written when operating in PWM mode. When writing a logical one to the FOC2 bit, an

immediate Compare Match is forced on the waveform generation unit. The OC2 output is

changed according to its COM21:0 bits setting. Note that the FOC2 bit is implemented as a

strobe. Therefore it is the value present in the COM21:0 bits that determines the effect of the

forced compare. A FOC2 strobe will not generate any interrupt, nor will it clear the timer in CTC

mode using OCR2 as TOP. The FOC2 bit is always read as zero.

• Bit 6,3 – WGM21:0: Waveform Generation Mode

These bits control the counting sequence of the counter, the source for the maximum

(TOP) counter value, and what type of waveform generation to be used. Modes of operation

supported by the Timer/Counter unit are: Normal mode, Clear Timer on Compare Match (CTC)

mode, and two types of Pulse Width Modulation (PWM) modes

table 3.7.1 TCCR modes

• Bit 5:4 – COM21:0: Compare Match Output Mode

These bits control the Output Compare Pin (OC2) behavior. If one or both of the

COM21:0 bits are set, the OC2 output overrides the normal port functionality of the I/O pin it is

22

connected to.However, note that the Data Direction Register (DDR) bit

corresponding to OC2 pin must be setin order to enable the output driver. When OC2 is

connected to the pin, the function of the COM21:0 bits depends on the WGM21:0 bit setting.

Timer/Counter Register – TCNT2

Fig 3.7.2 TCNT

The Timer/Counter Register gives direct access, both for read and write operations, to the

Timer/Counter unit 8-bit counter. Writing to the TCNT2 Register blocks (removes) the Compare

Match on the following timer clock. Modifying the counter (TCNT2) while the counter is

running, introduces a risk of missing a Compare Match between TCNT2 and the OCR2 Register.

Output Compare Register – OCR2

Fig 3.7.3 OCR2

The Output Compare Register contains an 8-bit value that is continuously compared with

the counter value (TCNT2). A match can be used to generate an Output Compare interrupt, or to

generate a waveform output on the OC2 pin.

3.8 8-bit Timer/Counter0

Timer/Counter0 is a general purpose, single channel, 8-bit Timer/Counter module. The

main features are:

23

• Single Channel Counter

• Frequency Generator

• External Event Counter

• 10-bit Clock Prescaler

Overview

A simplified block diagram of the 8-bit Timer/Counter is shown in Fig 3.8.1. For the

actual placement of I/O pins CPU accessible I/O Registers, including I/O bits and I/O pins, are

shown in bold. The device-specific I/O Register and bit locations are listed in the “8-bit

Timer/Counter Register Description”.

Fig 3.8.1 8-bit Timer/Counter

Registers

The Timer/Counter (TCNT0) is an 8-bit register. Interrupt request (abbreviated to Int.

Req. in the figure) signals are all visible in the Timer Interrupt Flag Register (TIFR). All

interrupts are individually masked with the Timer Interrupt Mask Register (TIMSK). TIFR and

TIMSK are not shown in the figure since these registers are shared by other timer units. The

24

Timer/Counter can be clocked internally or via the prescaler, or by an external clock source on

the T0 pin. The Clock Select logic block controls which clock source and edge the

Timer/Counter uses to increment its value. The Timer/Counter is inactive when no clock source

is selected. The output from the clock select logic is referred to as the timer clock (clkT0).

Definitions

Many register and bit references in this document are written in general form. A lower

case “n” replaces the Timer/Counter number, in this case 0. However, when using the register or

bit defines in a program, the precise form must be used i.e. TCNT0 for accessing

Timer/Counter0 counter value and so on.

Timer/Counter Clock Sources

The Timer/Counter can be clocked by an internal or an external clock source. The clock

source is selected by the clock select logic which is controlled by the clock select (CS02:0) bits

located in the Timer/Counter Control Register (TCCR0).

Counter Unit

Fig 3.8.2 Counter Unit Block Diagram

25

Operation

The counting direction is always up (incrementing), and no counter clear is performed.

The counter simply overruns when it passes its maximum 8-bit value (MAX = 0xFF) and then

restarts from the bottom (0x00). In normal operation the Timer/Counter Overflow Flag (TOV0)

will be set in the same timer clock cycle as the TCNT0 becomes zero. The TOV0 Flag in this

case behaves like a ninth bit, except that it is only set, not cleared. However, combined with the

timer overflow interrupt that automatically clears the TOV0 Flag, the timer resolution can be

increased by software. A new counter value can be written anytime.

Timing Diagrams

The Timer/Counter is a synchronous design and the timer clock (clkT0) is therefore

shown as a clock enable signal in the following figures. The figures include information on when

Interrupt Flags are set. Figure contains timing data for basic Timer/Counter operation. The figure

shows the count sequence close to the MAX value.

Fig 3.8.3 Timing diagrams 1

26

Shows the same timing data,but with the prescalar enabled

Fig 3.8.4 Timing diagrams 2

27

4. SPECIFIC TECHNOLOGY

4.1 Introduction

As next-generation electronic information systems evolve, it is critical that all people

have access to the information available via these systems. Examples of developing and future

information systems include interactive television, touch screen-based information kiosks, and

advanced Internet programs. Infrared technology, increasingly present in mainstream

applications, holds great potential for enabling people with a variety of disabilities to access a

growing list of information resources. Already commonly used in remote control of TVs, VCRs

and CD players, infrared technology is also being used and developed for remote control of

environmental control systems, personal computers, and talking signs.

For individuals with mobility impairments, the use of infrared or other wireless

technology can facilitate the operation of information kiosks, environmental control systems,

personal computers and associated peripheral devices. For individuals with visual impairments,

infrared or other wireless communication technology can enable users to locate and access

talking building directories, street signs, or other assistive navigation devices. For individuals

using augmentative and alternative communication (AAC) devices, infrared or other wireless

technology can provide an alternate, more portable, more independent means of accessing

computers and other electronic information systems.

In this presentation/paper, an introduction to wireless communication in general is first

presented. A discussion specific to infrared technology then follows, with advantages and

disadvantages of the technology presented along with security, health and safety issues. The

importance of establishing a standard is also discussed with relevance to the disability field, and

future uses of infrared technology are presented.

4.2 Wireless Communication

Wireless communication, as the term implies, allows information to be exchanged

between two devices without the use of wire or cable. A wireless keyboard sends information to

the computer without the use of a keyboard cable; a cellular telephone sends information to

another telephone without the use of a telephone cable. Changing television channels, opening

28

and closing a garage door, and transferring a file from one computer to another can all be

accomplished using wireless technology. In all such cases, information is being transmitted and

received using electromagnetic energy, also referred to as electromagnetic radiation. One of the

most familiar sources of electromagnetic radiation is the sun; other common sources include TV

and radio signals, light bulbs and microwaves. To provide background information in

understanding wireless technology, the electromagnetic spectrum is first presented and some

basic terminology defined.

The electromagnetic spectrum classifies electromagnetic energy according to frequency

or wavelength (both described below). As shown in Figure 1, the electromagnetic spectrum

ranges from energy waves having extremely low frequency (ELF) to energy waves having much

higher frequency, such as x-rays.

Fig4.2.1 The electromagnetic spectrum

[Figure 4.2.1 description: The electromagnetic spectrum is depicted in Figure 4.2.1. A

horizontal bar represents a range of frequencies from 10 Hertz(cycles per second) to 10 to the

18th power Hertz. Some familiar allocated frequency bands are labeled on the spectrum.

Approximate locations are as follows. (Exponential powers of 10 are abbreviated as 10exp.)

10 Hertz: extremely low frequency or ELF.

10exp5 Hertz: AM radio.

10exp8 Hertz: FM radio.

10exp10 Hertz: Television.

10exp11 Hertz: Microwave.

10exp16 Hertz: Infrared (frequency range is below the visible light spectrum).

29

10exp16 Hertz: Visible Light.

10exp16 Hertz: Ultraviolet (frequency range is above the visible light spectrum).

10exp18 Hertz: X-rays.

A typical electromagnetic wave is depicted in Figure 2, where the vertical axis represents

the amplitude or strength of the wave, and the horizontal axis represents time. In relation to

electromagnetic energy, frequency is:

1. the number of cycles a wave completes (or the number of times a wave repeats itself) in

one second

2. expressed as Hertz (Hz), which equals once cycle per second

3. commonly indicated by prefixes such as

a. Kilo (KHz) one thousand

b. Mega (MHz) one million

c. Giga (GHz) one billion

4. directly related to the amount of information that can be transmitted on the wave

Fig4.2.2: sine wave

[Figure 4.2.2 description: A sine wave is depicted in the graph in Figure 4.2.2. The

horizontal axis of the graph represents time, and the vertical axis of the graph represents

amplitude. One cycle (or one complete sine wave) is labeled on the graph.]

30

Fig4.2.3: Graphs of three different sine waves

[Figure 4.2.3 description: Graphs of three different sine waves are depicted in Figure

4.2.3. The horizontal axis, with values ranging from 0 to 1, represents time in seconds. The

vertical axis, with values ranging from -1 to 1, represents arbitrary amplitude. The first graph in

the figure depicts a sine wave with a frequency of 1 cycle per second. As shown, the energy

wave makes a complete cycle from 0 to its maximum positive value, then through to its

maximum negative value, then back to 0. The second graph in the figure depicts a sine wave

with a frequency of 2 cycles per second. The sine wave therefore makes 2 complete cycles of

moving from 0 to its maximum positive value, through to its maximum negative value, and back

to 0, in the same time that the wave in the first graph completes 1 cycle. The third graph in the

figure depicts a sine wave with a frequency of 3 cycles per second. The sine wave therefore

completes 3 full cycles in the same amount of time that the wave in the first graph completes 1

cycle.]

Figure 4.2.3 illustrates energy waves completing one cycle, two cycles and three cycles

per second. Generally, the higher the range of frequencies (or bandwidth), the more information

can be carried per unit of time.

The term wavelength is used almost interchangeably with frequency. In relation to

electromagnetic energy, wavelength is:

31

the shortest distance at which the wave pattern fully repeats itself

1. expressed as meters

2. commonly indicated by prefixes such as

3. a. Kilo (km) 10exp3

b. Milli (mm) 10exp-3

c. Nano (nm) 10exp-9

4. inversely proportional to frequency

Figure 4.2.4 depicts an infrared energy wave and a radio energy wave, and illustrates the

two different energy wavelengths. As is expected based on the electromagnetic spectrum, the

infrared wave is higher frequency and therefore shorter wavelength than the radio wave.

Conversely, the radio wave is lower frequency and therefore longer wavelength than the infrared

wave. Anyone who has listened to the radio while driving long distances can appreciate that

longer wavelength AM radio waves carry further than the shorter wavelength FM radio waves.

Fig4.2.4: A radio frequency energy wave

[Figure 4.2.4 description: Figure 4.2.4 depicts a radio frequency energy wave

superimposed upon an infrared energy wave, and illustrates the inverse relationship between

frequency and wavelength. The infrared energy wave completes nearly 5 and a half cycles in the

time that the radio frequency wave completes 2 cycles. The wavelengths of the infrared wave

and the radio wave are labeled, and the infrared wavelength is less than half the wavelength of

the radio wave.]

32

Other terms commonly used in describing wireless communication include transmitter,

receiver, and transceiver. In any type of wireless technology, information must be sent (or

transmitted) by one device and captured (or received) by another device. The transmitter takes its

input - a voice or stream of data bits for example, creates an energy wave that contains the

information, and sends the wave using an appropriate output device. As an example, a radio

transmitter outputs its energy waves using an antenna, while an infrared transmitter uses an

infrared light- emitting diode (LED) or laser diode. The electromagnetic energy waves are

captured by the receiver, which then processes the waves to retrieve and output the information

in its original form. Any wireless device having the circuitry to both transmit and receive energy

signals is referred to as a transceiver. Depending on the communication protocol being used, a

device may be capable of only transmitting or receiving information at one time, or it may be

capable of both transmitting and receiving information at the same time.

The above described terminology is relevant in all forms of wireless communication,

regardless of the band of electromagnetic energy (radio, infrared, etc.) being used. Although

radio and ultrasound waves have frequent application in wireless communication, the remainder

of the presentation/paper is devoted more specifically to infrared (IR) technology. Infrared

technology is highlighted because of its increasing presence in mainstream applications, its

current and potential usage in disability-related applications, and its advantages over other forms

of wireless communication.

4.3 Infrared Technology

As depicted in Fig. 4.2.1, infrared radiation is the region of the electromagnetic spectrum

between microwaves and visible light. In infrared communication an LED transmits the infrared

signal as bursts of non-visible light. At the receiving end a photodiode or photoreceptor detects

and captures the light pulses, which are then processed to retrieve the information they contain.

Some common applications of infrared technology are listed below.

1. Augmentative communication devices

2. Car locking systems

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3. Computers

a. Mouse

b. Keyboards

c. Floppy disk drives

d. Printers

4. Emergency response systems

5. Environmental control systems

a. Windows

b. Doors

c. Lights

d. Curtains

e. Beds

f. Radios

6. Headphones

7. Home security systems

8. Signage

9. Telephones

10. TVs, VCRs, CD players, stereos

11. Toys

Infrared technology offers several important advantages as a form of wireless

communication. Advantages and disadvantages of IR are first presented, followed by a

comparative listing of radio frequency (RF) advantages and disadvantages.

IR Advantages:

1. Low power requirements: therefore ideal for laptops, telephones, personal digital

assistants

2. Low circuitry costs: $2-$5 for the entire coding/decoding circuitry

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3. Simple circuitry: no special or proprietary hardware is required, can be incorporated into

the integrated circuit of a product

4. Higher security: directionality of the beam helps ensure that data isn't leaked or spilled to

nearby devices as it's transmitted

5. Portable

6. Few international regulatory constraints: IrDA (Infrared Data Association) functional

devices will ideally be usable by international travelers, no matter where they may be

7. High noise immunity: not as likely to have interference from signals from other devices

IR Disadvantages:

1. Line of sight: transmitters and receivers must be almost directly aligned (i.e. able to see

each other) to communicate

2. Blocked by common materials: people, walls, plants, etc. can block transmission

3. Short range: performance drops off with longer distances

4. Light, weather sensitive: direct sunlight, rain, fog, dust, pollution can affect transmission

5. Speed: data rate transmission is lower than typical wired transmission

Health Risks

Imagine for a moment going about your daily routine without electricity. You probably

awoke to an electric clock radio/alarm, showered under warm water supplied via an electric hot

water heater, drank a couple of cups of coffee from your automatic electric coffee maker,

listened to the weather on the electric powered TV or radio and the list goes on and on. We live

in an electrical environment.

Electricity is all around you and while you cannot see electricity, you can certainly

appreciate the results. However, any time electric current travels through a wire, the air, or runs

an appliance, it produces an electromagnetic field. It is important to remember that

35

electromagnetic fields are found everywhere that electricity is in use. While researchers have not

established an ironclad link between the exposure to electromagnetic fields and ailments such as

leukemia, the circumstantial evidence concerns many people.

The evidence also suggests that we need to use some common sense when dealing with

electricity. In scientific terms, your body can act as an antenna, as it has a higher conductivity for

electricity than does air. Therefore, when conditions are right you may have experienced a small

"tingle" of electric current from a poorly grounded electric appliance. As long as these currents

are very small there isn't much danger from electric fields, except for potential shocks. Your

body, however, also has a permeability almost equal to air, thus allowing a magnetic field to

easily enter the body. Unfortunately your body cannot detect the presence of a strong magnetic

field, which could potentially do much more harm.

In terms of wireless technology, there are no confirmed health risks or scientific dangers

from infrared or radio frequency, with two known exceptions:

1. point-to-point lasers which can cause burns or blindness

2. prolonged microwave exposure which has been linked to cancer and leukemia

Therefore, most health concerns related to electromagnetic fields are due to electricity in

our day-to-day use, such as computer monitors and TVs. These dangers, if any, are already in the

home and work place, and the addition of wireless technology should not be seen as an

exceptional risk. We might be rightfully worried or concerned about the electric power grid two

blocks from our home or school, but at the same time, we sleep each night with our head only a

few feet from an AC powered clock radio, which may be far worse due simply to proximity. We

might be also be worried about the magnetic radiation or magnetically induced electrical fields

which surround us from the fluorescent light fixtures and high voltage, high frequency lighting

we sit under at work and at home. The real danger, however, is that we normally position

ourselves too close to the electromagnetic field source (computer monitor, TV, etc.). Remember

that the strength of the electromagnetic field (EMF) decreases as the square of the distance from

the field source. Therefore, if we are 2 meters away from the source, the EMF strength is reduced

36

to 1/4, but if we move 8 meters away from the source, the EMF strength is reduced to 1/64 of its

original strength.

Safety

There are a few things you can do to make your home and work environment a safer

"electronic" place. The first thing to consider when possible is to buy Federal Communications

Commission (FCC) Class B rated equipment. The FCC classifies computer equipment for its

potential to generate radio frequency pollution. Class B emits less radio frequency pollution than

Class A, and is more suitable for the residential environment. Unfortunately, while Class B emits

less radio frequency pollution, there is nothing in the FCC classes regarding magnitude or level

of the pollution.

Other potential risks exist in high voltage (e.g. power) components such as display

monitors, computer power supplies, etc. If possible select low power units, shielded units, etc.

and operate them at lower resolutions. For example, VGA resolution has a lower refresh scan

rate than SVGA, and thus lower magnetic field pollution. If you are adding internal cards to your

computers, don't tamper with the computer by removing any internal shielding, covers, etc. Any

metal shielding inside your computer was probably put there for a purpose, although to you it

may look like a harmless spacer.

If you are really concerned, you can purchase formal safety testing tools or hire a

consultant to do formal testing for EMF. There are also cheap tools you can utilize to test for the

presence of strong radio or magnetic fields. For example, the presence of a strong magnetic field

will deflect a compass needle from pointing north, or the presence of a strong radio frequency

field will distort an AM radio's ability to clearly tune in a station. Simple tools like these can be

used to screen for strong EMF.

Security

37

Electromagnetic frequencies currently have little legal status for protection and as such,

can be freely intercepted by motivated individuals. This doesn't mean wireless transmission is

easily breached, as security varies by the type of wireless transmission method. As presented

earlier in the advantages and disadvantages of infrared versus radio frequency transmission, what

might be considered an advantage to one method for transmission could turn out to be a

disadvantage for security. For example, because infrared is line-of-sight

it has less transmission range but is also more difficult to intercept when compared to radio

frequency. Radio frequency can penetrate walls, making it much easier to transmit a message,

but also more susceptible to tapping.

A possible solution to security issues will likely be some form of data encryption. Data

encryption standards (DES) are also being quickly developed for the exchange of information

over the Internet, and many of these same DES will be applied to wireless technology.

Importance of Standards

Several of the wireless devices demonstrated during the presentation (see Appendix A)

have benefited to some degree from standardization. For example, a universal IR remote was

once priced at roughly $100.00. It is now possible, for under $15.00, to purchase a universal

remote that will learn the IR codes for all of your electronic appliances - not just the TV or VCR.

Another example of a device that has benefited from standardization is the Macintosh IR mouse.

The compatibility of this mouse to the Apple Desktop Bus (ADB) Standard has certainly

contributed to its inexpensive price and availability. As you look around the exhibit hall, think of

all the assistive devices that have proliferated due to the ADB (IntelliKeys, Ke:nx, etc.).

Additionally, the X10 devices that were demonstrated in the presentation not only rely on but

have benefited from the 60 HZ AC standard which applies to most of North America. As a result

these devices are now numerous and inexpensive. One final example demonstrating the

importance of standards is the relationship of augmentative alternative communication (AAC)

devices to the General Input Device Emulating Interface (GIDEI) standard. Any AAC device

programmed to use the GIDEI protocol can access any PC or Macintosh running either the DOS,

Windows, or Macintosh version of Serial Keys. The collaboration of the rehabilitation field to

38

create the GIDEI standard has allowed AAC users to access multiple computers without the need

to reprogram their devices or purchase expensive, proprietary hardware.

Likewise, there is an urgent need to develop standards regarding the use of wireless

technology in accessing electronic appliances of all kinds. Without such a standard, it may be

difficult if not impossible for those using assistive devices to communicate with

all available information systems. Examples of current or developing appliances which can or

may potentially be accessed via wireless technology include:

1. ATMs

2. Information Kiosks

3. Building Directories

4. TV Set Top Boxes

5. Bus Stops (Electronic Interactive)

6. Fare Machines (ticket machines, etc.)

7. Home Appliances (especially touch screens)

8. Informational Telephones, Screen Based Telephones

9. POS (point of sale) equipment

10. Home environmental controls

11. Home security systems

12. Whiteboards, for classroom / interactive office use

13. Games and entertainment

4.4 Relays

A relay is an electrical switch that opens and closes under the control of another

electronic circuit. In the original form, the switch is operated by an electro magnet to open or

39

close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is

able to control an output circuit of higher power than the input circuit, it can be considered to be,

in a broad sense, a form of an electrical amplifier.

Operation

When a current flows through the coil, the resulting magnetic field attracts an armature

that is mechanically linked to a moving contact. The movement either makes or breaks a

connection with a fixed contact. When the current to the coil is switched off, the armature is

returned by a force approximately half as strong as the magnetic force to its relaxed position.

Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most

relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise.

In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate

the energy from the collapsing magnetic field at deactivation, which would otherwise generate a

with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring"

creates a small out-of-phase current, which increases the minimum pull on the armature during

the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state relay is

made with a thyristor or other solid-state switching device. To achieve electrical isolation an

optocoupler can be used which is a light-emitting diode (LED) coupled with a photo transistor

Fig4.4.1 Circuit symbol for a relay

40

Fig 4.4.2 Relays

(Courtesy: Rapid Electronics)

In the above diagram pin 3 is connected to pin 5, by default. By sending +12V between

pin 1 and pin 2, you will turn on a switch. Pin 1 and pin 2 will disconnect, and pin 5 and pin 4

will connect.

Relays more Info:

A relay is an electrically operated switch. Current flowing through the coil of the relay

creates a magnetic field which attracts a lever and changes the switch contacts. The coil current

can be on or off so relays have two switch positions and they are double throw (changeover)

switches.

Relays allow one circuit to switch a second circuit which can be completely separate

from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC

41

mains circuit. There is no electrical connection inside the relay between the two circuits, the link

is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it

can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips)

cannot provide this current and transistor is usually used to amplify the small IC current to the

larger value required for the relay coil. The maximum output current for the popular 555 timer

IC is 200mA so these devices can supply relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts,

for example relays with 4 sets of changeover contacts are readily available. For further

information about switch contacts and the terms used to describe them please see the page on

switches.

Most relays are designed for PCB mounting but you can solder wires directly to the pins

providing you take care to avoid melting the plastic case of the relay.

The supplier's catalogue should show you the relay's connections. The coil will be

obvious and it may be connected either way round. Relay coils produce brief high voltage

'spikes' when they are switched off and this can destroy transistors and ICs in the circuit. To

prevent damage you must connect a protection diode across the relay coil.

The relay's switch connections are usually labelled COM, NC and NO:

COM = Common, always connect to this, it is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the relay coil is

on.

Connect to COM and NC if you want the switched circuit to be on when the relay coil is

off.

42

Choosing a relay

You need to consider several features when choosing a relay:

Physical size and pin arrangement

If you are choosing a relay for an existing PCB you will need to ensure that its dimensions and

pin arrangement are suitable. You should find this information in the supplier's catalogue.

1. Coil voltage

The relay's coil voltage rating and resistance must suit the circuit powering the relay coil.

Many relays have a coil rated for a 12V supply but 5V and 24V relays are also readily

available. Some relays operate perfectly well with a supply voltage which is a little lower

than their rated value.

2. Coil resistance

The circuit must be able to supply the current required by the relay coil. You can use

Ohm's law to calculate the current:

3. For example: A 12V supply relay with a coil resistance of 400 passes a current of 30mA.

This is OK for a 555 timer IC (maximum output current 200mA), but it is too much for most

ICs and they will require a transistor to amplify the current.

4. Switch ratings (voltage and current)

The relay's switch contacts must be suitable for the circuit they are to control. You will need

to check the voltage and current ratings. Note that the voltage rating is usually higher for AC,

for example: "5A at 24V DC or 125V AC".

5. Switch contact arrangement (SPDT, DPDT etc)

Most relays are SPDT or DPDT which are often described as "single pole changeover"

(SPCO) or "double pole changeover" (DPCO). For further information please see the page on

switches.

43

Protection diodes for relays

Transistors and ICs must be protected from the brief high voltage produced when a relay

coil is switched off. The diagram shows how a signal diode (eg:1N4148) is connected

'backwards' across the relay coil to provide this protection.

Current flowing through a relay coil creates a magnetic field which collapses suddenly

when the current is switched off. The sudden collapse of the magnetic field induces a brief high

voltage across the relay coil which is very likely to damage transistors and ICs. The protection

diode allows the induced voltage to drive a brief current through the coil (and diode) so the

magnetic field dies away quickly rather than instantly. This prevents the induced voltage

becoming high enough to cause damage to transistors and ICs.

Reed relays

Reed relays consist of a coil surrounding a reed switch. Reed switches are normally

operated with a magnet, but in a reed relay current flows through the coil to create a magnetic

field and close the reed switch.

Fig4.4.3 Reed relay

Reed relays generally have higher coil resistances than standard relays (1000 for

example) and a wide range of supply voltages (9-20V for example). They are capable of

switching much more rapidly than standard relays, up to several hundred times per second; but

they can only switch low currents (500mA maximum for example).

The reed relay shown in the photograph will plug into a standard 14-pin DIL socket ('IC

holder'). For further information about reed switches please see the page on switches.

44

Relays and transistors compared

Like relays, transistors can be used as an electrically operated switch. For switching small

DC currents (< 1A) at low voltage they are usually a better choice than a relay. However

transistors cannot switch AC or high voltages (such as mains electricity) and they are not usually

a good choice for switching large currents (> 5A). In these cases a relay will be needed, but note

that a low power transistor may still be needed to switch the current for the relay's coil.The main

advantages and disadvantages of relays are listed below:

Advantages of relays:

Relays can switch AC and DC, transistors can only switch DC.

Relays can switch high voltages, transistors cannot.

Relays are a better choice for switching large currents (> 5A).

Relays can switch many contacts at once.

Disadvantages of relays:

Relays are bulkier than transistors for switching small currents.

Relays cannot switch rapidly (except reed relays), transistors can switch many times per

second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many ICs can provide, so a low power transistor may be

needed to switch the current for the relay's coil.

4.5 POWER SUPPLY

A variable regulated power supply, also called a variable bench power supply, is

one where you can continuously adjust the output voltage to your requirements. Varying

45

the output of the power supply is the recommended way to test a project after having

double checked parts placement against circuit drawings and the parts placement guide.

This type of regulation is ideal for having a simple variable bench power supply.

Actually this is quite important because one of the first projects a hobbyist should

undertake is the construction of a variable regulated power supply. While a dedicated

supply is quite handy e.g. 5V or 12V, it's much handier to have a variable supply on hand,

especially for testing.

Most digital logic circuits and processors need a 5 volt power supply. To use these

parts we need to build a regulated 5 volt source. Usually you start with an unregulated

power To make a 5 volt power supply, we use a LM7805 voltage regulator IC (Integrated

Circuit). The IC is shown below.

Fig 4.5.1 LM7805 voltage regulator

The LM7805 is simple to use. You simply connect the positive lead of your

unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin, connect

the negative lead to the

4.5.1 CIRCUIT FEATURES

Brief description of operation: Gives out well regulated +5V output, output current

capability of 100 mA

46

Circuit protection: Built-in overheating protection shuts down output when

regulator IC gets too hot

Circuit complexity: Very simple and easy to build

Circuit performance: Very stable +5V output voltage, reliable operation

Availability of components: Easy to get, uses only very common basic components

Design testing: Based on datasheet example circuit, I have used this circuit

successfully as part of many electronics projects

Applications: Part of electronics devices, small laboratory power supply

Power supply voltage: Unregulated DC 8-18V power supply

Power supply current: Needed output current + 5 mA

Component costs: Few dollars for the electronics components + the input

transformer cost

4.5.2 BLOCK DIAGRAM

Fig 4.5.2.1 BLOCK DIAGRAM of Power supply

4.5.3 EXAMPLE CIRCUIT DIAGRAM

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Fig 4.5.3.1 Circuit diagram of Power supply

5. RESULT ANALYSIS

The project is Automatic power saving system for an shopping mall is a method for

automatic control of devices (lights, fans, AC s). A unique architecture of occupancy sensor

includes entry/exit sensors for detecting movements through doorways. Shopping mall room

motion sensor for detecting room occupancy. A central embedded controlled communicates with

the sensors and controls the device

The present project provides a system for saving power of an shopping mall. This project

is designed around a microcontroller which forms the control unit of the project.

According to this project, the number of visitors entering into and exiting from the

shopping mall is calculated and displayed. A part from this, the appliances are made ON and

OFF according to number of persons present in the shopping mall by which power can be

utilized with great efficiency. This is realized using IR sensors.

This project finds its place in places where the things wanted to be done automatically

with utilization of power in efficient and effective manner.

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The programming language used for developing the software to the microcontroller is

embedded/assembly. The KEIL cross compiler is used to edit, compile and debug this program.

Here in our application we are using ATmega8 microcontroller which is flash programmable IC.

AT represents Atmel corporation represents CMOS technology is used for designing the IC.

HARDWARE

For desigining of this project we are using some hardware components. The list of the

hardware components are, Stepdown transformer, bridge rectifier, capacitive filter, IR sensors,

ATmega8 microcontroller, klystron, relays.

5.1 STEPDOWN TRANSFORMER

Step down transformer is one whose secondary voltage is less than its primary voltage. It

is designed to reduce the voltage from the primary winding to the secondary winding. This kind

of transformer “steps down” the voltage applied to it.

Here we are taking a 12-0-12 volts stepdown transformer, a 12 volts transformer input

will be given to the rectifier circuit.

As a step-down unit, the transformer converts high-voltage, low-current power into low-

voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary

due to the increase in current. The primary winding, which doesn’t have to conduct as much

current, may be made of smaller-gauge wire.

5.1.1 STEP-DOWN TRANFORMER CONSIDERATIONS

Fig5.1.1 Stepdown transformer

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It is possible to operate either of these transformer types backwards (powering the

secondary winding with an AC source and letting the primary winding power a load) to perform

the opposite function a step-up can function as a step-down and vice-versa.

One convention used in the electric power industry is the use of “H” designations for the

higher-voltage winding (the primary winding in a step-down unit the secondary winding in a

step-up) and “X” designations for the lower-voltage winding.

One of the most important considerations to increase transformer efficiency and reduce

heat is choosing the metal type of the windings. Copper windings are much more efficient than

aluminum and many other winding metal choices, but it also costs more. Transformers with

copper windings cost more to purchase initially, but save on electrical cost over time as the

efficiency more than makes up for the initial cost.

Step-down transformers are commonly used to convert the 220 volt electricity found in

most parts of the world to the 110 volts required by North American equipment.

5.2 BRIDGE RECTIFIER

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave

rectification. This is a widely used configuration, both with individual diodes wired as shown

and with single component bridges where the diode bridge is wired internally.

Fig 5.2 Bridge rectifier

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The rectifier can converts an AC voltage into DC voltage. This DC voltage will be

filtered by a capacitor filter, by this capacitor filter a pure DC output will be obtain.

5.2.1 CURRENT FLOW IN THE BRIDGE RECTIFIER

For both positive and negative swings of the transformer, there is a forward path through

the diode bridge. Both conduction paths cause current to flow in the same direction through the

load resistor, accomplishing full-wave rectification.

Fig5.2.1

Fig5.2.2

While one set of diodes is forward biased, the other set is reverse biased and effectively

eliminated from the circuit.

This circuit output will be a dc output and this is given to the microcontroller. Vcc and

ground will be connected to the port PADC. The first pin is the Vcc and second pin is the

ground.

5.3 INPUT

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The input is taken by the IR sensor. Two sensors will be taken, one is for entrance and

and another is for exit. when the visitors are entered into the mall the IR sensors will be detecting

the movements of the doorways. This input will be given to the port PD. PD0, PD1 will be the

one input and PD4,PD5 will be the another input given by the sensors.

5.4 OUTPUT

The output will be taken by the port PB. PB2,PB3,PB4 pins are the output pins in the

microcontroller section. A 12V DC output will be obtained in the port PB. This output will be

given to the relays.

5.5 RELAY

A relay is an electrical switch that opens and closes under the control of another

electronic circuit. In the original form, the switch is operated by an electro magnet to open or

close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is

able to control an output circuit of higher power than the input circuit, it can be considered to be,

in a broad sense, a form of an electrical amplifier.

Operation

When a current flows through the coil, the resulting magnetic field attracts an armature

that is mechanically linked to a moving contact. The movement either makes or breaks a

connection with a fixed contact. When the current to the coil is switched off, the armature is

returned by a force approximately half as strong as the magnetic force to its relaxed position.

Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most

relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise.

In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate

the energy from the collapsing magnetic field at deactivation, which would otherwise generate a

with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring"

creates a small out-of-phase current, which increases the minimum pull on the armature during

the AC cycle.

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SNAP SHOT

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CONCLUSION

Thus the project entitled “Power management for shopping malls with

Bidirectional Visitor Counting” helps to measure the visitor entering and exiting a

particular passage or way. The circuit counts both entering and exiting visitors and displays the

number of visitors present inside the hall. Visitor counting is not limited to the entry/exit point of

a company but has a wide range of applications that provide information to management on the

volume and flow of people throughout a location. The visitor helps to maximize the

efficiency and effectiveness of employees, floor area and sales potential of an

organization. It can also be enhanced for long and accurate sensing range using a laser

torch instead of IR transmission circuit. Thus the circuit can be used to monitor visitor flow in

effective manner, where the visitors have to counted and controlled.

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FUTURE SCOPE

Our project is applicable to shopping malls and hotels to save power consumption as well

as man power. In future we can work out to implement same application in wireless by

interfacing wireless modules like ASK-RF and ZIGBEE.

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REFERENCE

1. Avtar Singh-"8086 Micro Processor”-4th edition -Published by

Prentice Hall of India-2003

2. Das .J-"Principles of Digital Communication"-1st edition-Published by

New Age International Publication 1986

3. Muhammad Ali Mazidi-"The 8051 Microcontroller and Embedded System

Using Assemble C"-2nd edition-Published by Pearson Education 2006

4. Rajiv Kapadia-"8051 Micro Controllers and Embedded System"-

1st edition-Published by Jaico Books 2004

5. RAY.A.K -"Advanced Micro Processors and Peripherals"-2nd edition-

Published by TATA McGraw-Hill 2006-07

6. Simon Hawkins-"Digital Communication"-1st edition-Published by Wiley India 2009

7. www.chetanasprojects.com

8. www.1000projects.com

9. www.microcontrollers.com

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