Main Documentation

PERSISTENCE OF VISION DISPLAY

ESWAR COLLEGE OF ENGINEERING Page 1

CHAPTER ONE

INTRODUCTION

Overview

Background

Objective

Thesis outline



1. INTRODUCTION

The purpose of this project is to design and to create a persistence of vision(POV)

display. This display will allow users to upload an image to be displayed through wireless

communication. A persistence of vision (POV) refers to the phenomenon of the human eye in

which an after image exits for a brief time(10ms). A POV display exploits this phenomena by

spinning a one dimensional row of LEDs through a two dimensional space at such a high

frequency that a two dimensional display is visible.

1.1. Overview

Our project uses two standards, serial peripheral interface(SPI) and IEEE 802.11 for

our wireless radio communication. The standard for SPI consists of a 4-wire serial bus that

allows a master/slave communication mode. The wires are the following:

SCLK : serial clock (output from master)

MOSI : master output, slave input (output from master)

MISO : master input, slave output (output from slave)

SS : slave select (output from master)

The IEEE 802.11 standard is for the wireless radio which is controlled by the FCC

regulations for radio frequency devices. This regulation can be found in title 47 part 15

section 243. Since our radio transceiver was designed within the FCC regulations, it meets all

the specifications noted in the section, especially the 500 microvolts/meter at 30 meters.

Our project does not include any exiting patents, copyrights or trademarks. Weve

designed all the hardware from scratch and all the software is our original work with some

assistance from classmates and professor land.

1.2. Background

The original idea for this project came from the brilliant mind of David Bjanes who has

many projects in his project queue. The inspiration came when david saw a video of a similar

POV display on youtube.com. Next we started brainstorming about the orientation of our

POV display. Some ideas we had seen oriented the display on a propeller or circular clock



while others spun the display around a cylinder. We choose to build column style POV

display in order to reduce the complexity of mapping a Cartesian coordinate system (found in

most rectangular display) to a polar coordinate system.

1.3. Objective

The overall design of this project can be grouped in the following three categories:

electrical design, mechanical design and software design. The most labour intensive portion

of this project was the mechanical design. While the electrical schematics and software

design appear trivial, intregating the hardware with an adept firmware proved to the biggest

challenge of all. Mounting the electrical components onto the mechanical structure- i.e. the

spinning arm- was also quite a challenge. As one can forsee, the nature of our mechanical

design introduced various safety issues that we also had to take into consideration.

1.4. Organization of the Thesis:

In view of the proposed thesis work explanation of theoretical aspects and algorithms

used in this work are presented as per the sequence described below.

Chapter 1 : Describes a brief review of the objectives and goals of the work.

Chapter 2: Discusses the existing technologies and the study of various technologies in

detail.

Chapter 3: Describes the Block diagram, Circuit diagram of the project and its description.

The construction and description of various modules used for the application are described in

detail.

Chapter 4: Explains the Software tools required for the project, the Code developed for the

design.

Chapter 5: Presents the results, overall conclusions of the study and proposes possible

improvements and directions of future research work.

Chapter 6: Presents references.



CHAPTER TWO

Overview of the

Technologies Used

Embedded system

Bluetooth technology



2. OVERVIEW OF TECHNOLOGIES USED

Embedded systems are the technology which has lot of scope to develop at any time.

Here it is very much required since this project had wide range of applications wherever there

is a need to display. Embedded system is nothing but a targeted application or a targeting a

single application by using a program.

2.1 Embedded Systems

An embedded system can be defined as a computing device that does a specific

focused job. Appliances such as the air-conditioner, VCD player, DVD player, printer, fax

machine, mobile phone etc. are examples of embedded systems. Each of these appliances will

have a processor and special hardware to meet the specific requirement of the application

along with the embedded software that is executed by the processor for meeting that specific

requirement.

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. Embedded systems span all aspects of modern life

and there are many examples of their use. Telecommunications systems employ numerous

embedded systems from telephone switches for the network to mobile phones at the end-user.

Computer networking uses dedicated routers and network bridges to route data.

2.1.1. Advantages of Embedded Systems:

1) They are designed to do a specific task and have real time performance constraints

which must be met.

2) They allow the system hardware to be simplified so costs are reduced.

3) They are usually in the form of small computerized parts in larger devices which

serve a general purpose.

4) The program instructions for embedded systems run with limited computer hardware

resources, little memory and small or even non-existent keyboard or screen.



2.1.2. Tools

As for other software, embedded system designers use compilers, assemblers, and

debuggers to develop embedded system software. However, they may also use some more

specific tools:

In circuit debuggers or emulators

Utilities to add a checksum or CRC to a program, so the embedded system can

check if the program is valid.

For systems using digital signal processing, developers may use a math workbench

such as MATLAB, Simulink, MathCad, or Mathematica to simulate the mathematics.

They might also use libraries for both the host and target which eliminates developing

DSP routines as done in DSPnano RTOS and Unison Operating System.

Custom compilers and linkers may be used to improve optimization for the

particular hardware.

An embedded system may have its own special language or design tool, or add

enhancements to an existing language such as Forth or Basic.

Another alternative is to add a Real-time operating system or Embedded operating

system, which may have DSP capabilities like DSP nano RTOS.

2.1.3 Software tools can come from several sources:

Software companies that specialize in the embedded market.

Ported from the GNU software development tools.

Sometimes, development tools for a personal computer can be used if the

embedded processor is a close relative to a common PC processor.

As the complexity of embedded systems grows, higher level tools and operating

systems are migrating into machinery where it makes sense. For example, cell phones,

personal digital assistants and other consumer computers often need significant software that

is purchased or provided by a person other than the manufacturer of the electronics. In these

systems, an open programming environment such as Linux, NetBSD, OSGi or Embedded

Java is required so that the third-party software provider can sell to a large market.



2.2 Bluetooth Technology

Bluetooth is an open specification that enables low-bandwidth, short-range wireless

connections between computers and peripherals, such as mice, cell phones, and personal data

assistants (PDAs).

2.2.1 What Is Bluetooth?

The appeal of the Bluetooth model lies in its convenience for wirelessly transferring

information and small data files between devices. Bluetooth is not a networking solution, so it

is not a competitor of AirPort, Apples wireless networking technology. Nor is it a

replacement for the cables needed by high-bandwidth peripherals, such as FireWire. Rather,

Bluetooth offers a replacement for IrDA (Infrared Data Association) technology, because it is

not constrained by IrDAs shorter range and line-of-sight requirements.

2.2.2 Bluetooth overview:

Bluetooth is a cable-replacement technology designed to wirelessly connect

peripherals, such as mice and mobile phones, to your desktop or laptop computer and to each

other. An inexpensive, low-power, short-range radio-based technology, Bluetooth is not a

wireless networking solution, such as AirPort. Rather, it is an alternative to the IrDA

(Infrared Data Association) standard. Although the IrDA standard, too, supports wireless

communication between peripherals and computers, it has two limiting requirements. First,

IrDA devices must be very close, no more than about 1 meter apart. Second, the

communicating devices must have a direct line of sight to each other. Because it relies on

radio waves, however, Bluetooth communication overcomes these strict.

2.2.3 Requirements:

Bluetooth devices can communicate at ranges of up to 10 meters.

Bluetooth devices do not need to be in direct sight of each other.

This makes Bluetooth communication much more flexible and robust. Its also

important to note that because Bluetooth excels at low-bandwidth data transfer, it is not



intended as a replacement for high-bandwidth cabled peripherals. For high-bandwidth

devices, such as external hard drives or video cameras, cables are still the best option.

Apple's Bluetooth support is integrated into Mac OS X, version 10.2 and later, and is

based on the Bluetooth Special Interest Group (SIG) specification (discussed in Bluetooth

Architecture). Apple also provides some high-level bridges between Mac OS X functionality

and the Bluetooth protocol stack. This means that many Bluetooth devices work transparently

with computers running Mac OS X version 10.2 and later. The Mac OS X HID Manager, for

example, handles a Bluetooth mouse just as it does a cabled mouse. In many cases, such

high-level bridges allow your application to handle Bluetooth devices without including any

Bluetooth-specific code.

2.2.4 Bluetooth Technology Basics:

Other applications may need to access Bluetooth-specific attributes and messages. For

them, Apple provides a comprehensive API that allows you to take advantage of Bluetooths

unique features. Be sure to read Bluetooth on Mac OS X for a description of the Bluetooth

API available in Mac OS X version 10.2 and later. For concrete examples showing how to

use Apples Bluetooth API, see Developing Bluetooth Applications

2.2.5 What Bluetooth Does Best

The characteristics of Bluetooth technology low cost, low power, and radio based

encouraged the concept of a personal area network (PAN). A PAN envelops the user in a

small, mobile bubble of connectivity that is effortlessly available at any time. Bluetooths

freedom from cables and potential ubiquity make it ideal for carrying your personal network

around with you. With a PAN, the possibilities are limitless:

Imagine being able to connect to the Internet on a dial-up connection you access

through your mobile phone. Surfing the Internet then becomes possible anywhere

your mobile phone can connect to your internet service provider.

Perhaps you prefer to use a traditional mouse with your laptop. Choose a Bluetooth

enabled mouse and you wont have to keep track of a mouse cable.



If you have a Bluetooth-enabled mobile phone that stores your business information in

the Vcard format, you can easily share this information with your colleagues. Swap

your Vcard with theirs, by wirelessly connecting to their Bluetooth-enabled mobile

phones.

2.2.6 Future Directions for Bluetooth

Industry analysts predict the growing popularity and availability of Bluetooth-enabled

devices. This in turn raises consumer expectations for mobile PANs and provides many

opportunities for vendors to create new products. At the end of 2003, the Bluetooth SIG

released the second version (version 1.2) of the Bluetooth specification. This successor to

version 1.1 provides a number of improvements, including:

Enhanced quality of service (QOS). This guarantees that your human-interface (and

other QOS) devices will get the time to transfer data when they need it.

A more adaptive frequency-hopping algorithm. The new algorithm increases

communication reliability and decreases interference from other wireless emitters

operating the same frequency range. Apples ongoing support for Bluetooth

communication is evidenced by frequent Bluetooth software updates and up-to-date

SDKs. Using the software frameworks and built-in support Apple provides, you can

bring your Bluetooth applications to Mac OS X with ease. Apple is committed to

helping you find ways to provide your customers with the wireless connectivity they

need.

2.2.7 How Bluetooth Works

This section seeks to give you an overview of the technology and specification that

will provide context for the Bluetooth implementation on Mac OS X. If youre already

familiar with the Bluetooth specification and how Bluetooth devices work, you might choose

to skip ahead to Bluetooth on Mac OS X.

Bluetooth devices operate at 2.4 GHz in the license-free, globally available ISM

(Industrial, Scientific, and Medical) radio band. The advantage of operating in this band is

worldwide availability and compatibility. A potential disadvantage is that Bluetooth devices



must share this band with many other RF emitters. These include automobile security

systems, other wireless communications standards (such as 802.11), and ordinary noise

sources (such as microwave ovens). To overcome this challenge, Bluetooth employs a fast

frequency-hopping scheme and uses shorter packets than other standards in the ISM band.

This scheme makes Bluetooth communication more robust and more secure.

2.2.8 Frequency Hopping

Frequency hopping is literally jumping from frequency to frequency within the ISM

band. After a Bluetooth device sends or receives a packet, it and the Bluetooth device or

devices it is communicating with hop to another frequency before the next packet is sent.

2.2.9 ADVANTAGES:

It allows Bluetooth devices to use the entirety of the available ISM band, while never

transmitting from a fixed frequency for more than a very short time This ensures that

Bluetooth conforms to the ISM restrictions on transmission quantity per frequency.

It ensures that any interference will be short-lived. Any packet that doesn't arrive

safely at its destination can be resent at the next frequency.

It provides a base level of security because it's very difficult for an eavesdropping

device to predict which frequency the Bluetooth devices will use next. Of course, the

connected devices must agree upon the next frequency to use. The Bluetooth

specification. ensures this in two ways. First, it defines a master-slave relationship

between Bluetooth devices. Second, it specifies an algorithm that uses device-specific

information to calculate frequency-hop sequences.

A Bluetooth device operating in master mode can communicate with up to seven

slave devices. To each of its slaves, the master Bluetooth device sends its own unique device

address (similar to an ethernet address) and the value of its internal clock. This information is

used to calculate the frequency-hop sequence. Because the master device and all its slaves

use the same algorithm with the same initial input, the connected devices always arrive

together at the next frequency.



2.2.10 Power Consumption

As a cable-replacement technology, its not surprising that Bluetooth devices are

usually battery-powered devices, such as wireless mice and mobile phones. To conserve

power, most Bluetooth devices operate as low-power, 1 mW radios (Class 3 radio power).

This gives Bluetooth devices a range of about 510 meters. This range is far enough for

comfortable wireless peripheral communication but close enough to avoid drawing too much

power from the devices power source.

2.2.11 Security

Security is a challenge faced by every communications standard. Wireless

communications present special security challenges. Bluetooth builds security into its model

on several different levels, beginning with the security inherent in its frequency-hopping

scheme (described in Frequency Hopping). At the lowest levels of the protocol stack,

Bluetooth uses the publicly available cipher algorithm known as SAFER+ to authenticate a

devices identity. The generic-access profile depends on this authentication for its device-

pairing process. This process involves creating a special link to create and exchange a link

key. Once verified, the link key is used to negotiate an encryption mode the devices will use

for their communication. The topic of Bluetooth security is beyond the scope of this

document. For references that contain more information on Bluetooths encryption and

authentication processes.

2.2.12 Bluetooth Architecture

Bluetooth is both a hardware-based radio system and a software stack that specifies

the linkages between layers. This supports flexibility in implementation across different

devices and platforms. It also provides robust guidelines for maximum interoperability and

compatibility. In this section, youll learn about:

The Bluetooth protocol stack: The protocol stack is the core of the Bluetooth

specification that defines how the technology works.

The Bluetooth profiles: The profiles define how to use Bluetooth technology to

accomplish specific tasks.



2.2.13 The Bluetooth Protocol Stack

The heart of the Bluetooth specification is the Bluetooth protocol stack. By providing

well-defined layers of functionality, the Bluetooth specification ensures interoperability of

Bluetooth devices and encourages adoption of Bluetooth technology. these layers range from

the low-level radio link to the profiles.

Lower Layers

At the base of the Bluetooth protocol stack is the radio layer. The radio module in a

Bluetooth device is responsible for the modulation and demodulation of data into RF signals

for transmission in the air. The radio layer describes the physical characteristics a Bluetooth

devices receiver-transmitter component must have. These include modulation characteristics,

radio frequency tolerance, and sensitivity level.

Above the radio layer is the baseband and link controller layer. The Bluetooth

specification doesnt establish a clear distinction between the responsibilities of the baseband

and those of the link controller. The best way to think about it is that the baseband portion of

the layer is responsible for properly formatting data for transmission to and from the radio

layer. In addition, it handles the synchronization of links. The link controller portion of this

layer is responsible for carrying out the link managers commands and establishing and

maintaining the link stipulated by the link manager.

The link manager itself translates the host controller interface (HCI) commands it

receives into baseband-level operations. It is responsible for establishing and configuring

links and managing power-change requests, among other tasks. Youve noticed links

mentioned numerous times in the preceding paragraphs. The Bluetooth specification defines

two types of links between Bluetooth devices:

Synchronous, Connection-Oriented (SCO), for isochronous and voice

communication using, for example, headsets

Asynchronous, Connectionless (ACL), for data communication, such as the

exchange of vCards Each link type is associated with a specific packet type. A SCO

link provides reserved channel bandwidth for communication between a master and a

slave, and supports regular, periodic exchange of data with no retransmission of SCO



packets. An ACL link exists between a master and a slave the moment a connection is

established. The data packets Bluetooth uses for ACL links all have 142 bits of

encoding information in addition to a payload that can be as large as 2712 bits. The

extra amount of data encoding heightens transmission security. It also helps to

maintain a robust communication link in an environment filled with other devices and

common noise.

The HCI (host controller interface) layer acts as a boundary between the lower

layers of the Bluetooth protocol stack and the upper layers. The Bluetooth

specification defines a standard HCI to support Bluetooth systems that are

implemented across two separate processors. For example, a Bluetooth system on a

computer might use a Bluetooth modules processor to implement the lower layers of

the stack (radio, baseband, link controller, and link manager). It might then use its

own processor to implement the upper layers (L2CAP, RFCOMM, OBEX, and

selected profiles). In this scheme, the lower portion is known as the Bluetooth module

and the upper portion as the Bluetooth host. Of course, its not required to partition the

Bluetooth stack in this way. Bluetooth headsets, for example combine the module and

host portions of the stack on one processor because they need to be small and self-

contained. In such devices, the HCI may not be implemented at all unless device

testing is required.

Because the Bluetooth HCI is well defined, you can write drivers that handle different

Bluetooth modules from different manufacturers. Apple provides an HCI controller object

that supports a USB implementation of the HCI layer.

Upper layers

Above the HCI layer are the upper layers of the protocol stack. The first of these is the

L2CAP (logical link control and adaptation protocol) layer. The L2CAP is primarily

responsible for:

Establishing connections across existing ACL links or requesting an ACL link if one

does not already exist

Multiplexing between different higher layer protocols, such as RFCOMM and SDP, to

allow many different applications to use a single ACL link



Repackaging the data packets it receives from the higher layers into the form expected

by the lower layers. The L2CAP employs the concept of channels to keep track of

where data packets come from and where they should go. You can think of a channel

as a logical representation of the data flow between the L2CAP layers in remote

devices. Because it plays such a central role in the communication between the upper

and lower layers of the Bluetooth protocol stack, the L2CAP layer is a required part of

every Bluetooth system.

Above the L2CAP layer, the remaining layers of the Bluetooth protocol stack arent

quite so linearly ordered. However, it makes sense to discuss the service discovery protocol

next, because it exists independently of other higher-level protocol layers. In addition, it is

common to every Bluetooth device.

The SDP (service discovery protocol) defines actions for both servers and clients of

Bluetooth services. The specification defines a service as any feature that is usable by another

(remote) Bluetooth device. A single Bluetooth device can be both a server and a client of

services. An example of this is the Macintosh computer itself. Using the file transfer profile a

Macintosh computer can browse the files on another device and allow other devices to

browse its files.

An SDP client communicates with an SDP server using a reserved channel on an

L2CAP link to find out what services are available. When the client finds the desired service,

it requests a separate connection to use the service. The reserved channel is dedicated to SDP

communication so that a device always knows how to connect to the SDP service on any

other device. An SDP server maintains its own SDP database, which is a set of service

records that describe the services the server offers.

Along with information describing how a client can connect to the service, the service

record contains the services UUID, or universally unique identifier.

Also above the L2CAP layer is the RFCOMM layer. The RFCOMM protocol

emulates the serial cable line settings and status of an RS-232 serial port. By providing serial-

port emulation, RFCOMM supports legacy serial-port applications. It also supports the

OBEX protocol and several of the Bluetooth profiles.



OBEX (object exchange) is a transfer protocol that defines data objects and a

communication protocol two devices can use to easily exchange those objects. Bluetooth

adopted OBEX from the IrDA IrOBEX specification because the lower layers of the IrOBEX

protocol are very similar to the lower layers of the Bluetooth protocol stack. In addition, the

IrOBEX protocol is already widely accepted and therefore a good choice for the Bluetooth

SIG, which strives to promote adoption by using existing technologies. A Bluetooth device

wanting to set up an OBEX communication session with another device is considered to be

the client device.

1. The client first sends SDP requests to make sure the other device can act as a server

of OBEX services.

2. If the server device can provide OBEX services, it responds with its OBEX service

record. This record contains the RFCOMM channel number the client should use to establish

an RFCOMM channel.

3. Further communication between the two devices is conveyed in packets, which

contain requests and responses, and data. The format of the packet is defined by the OBEX

session protocol.

Although OBEX can be supported over TCP/IP, this document does not discuss this

option (nor is it described in the Bluetooth specification).



CHAPTER THREE

HARDWARE

IMPLEMENTATION OF

PROJECT

High Level Design

Electrical Design

AT89S52

Dc motors

Led

Max232

Switches



3.HARDWARE IMPLEMENTATION OF PROJECT

A persistent of vision display is able to receive images wirelessly to display in a two

dimensional grid. The purpose of this project is to design and to create a persistence of vision

(POV) display. This display will allow users to upload an image to be displayed through

wireless communication. A persistence of vision (POV) refers to the phenomenon of the

human eye in which an after image exists for a brief time (10 ms). A POV display exploits

this phenomena by spinning a one dimensional row of LED's through a two dimensional

space at such a high frequency that a two dimensional display is visible. In our case, we

created a cylindrical display by spinning a column of LED's around a central motor shaft .

The rotational speed of the LED's is fast enough such that the human eye perceives a two

dimensional image.

3.1 High Level Design

The overall design of this project can be grouped in the following three categories:

electrical design, mechanical design, and software design.

Fig1. Hardware setup of POV display

The most labor intensive portion of this project was the mechanical design. While the

electrical schematics and software design appear trivial, integrating the hardware with an

adept firmware proved to the biggest challenge of all. Mounting the electrical components



onto the mechanical structure - i.e. the spinning arm - was also quite a challenge. As one can

foresee, the nature of our mechanical design introduced various safety issues that we also had

to take into consideration.

Fig 2: Block diagram of POV

3.2 Electrical Design

The electrical components used are:

On-board AT89S52 microcontroller

MAX232

8 RED LEDs

1-9V battery

Bluetooth wireless module

LM7805 Linear Regulator

Various Resistors and capacitors

Various wires and header pins



3.3 AT89S52 Micro Controller

3.3.1 Features:

Compatible with MCS-51 Products

8K Bytes of In-System Programmable (ISP) Flash Memory

Endurance: 1000 Write/Erase Cycles

4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256K Internal RAM

Programmable I/O Lines

3 16-bit Timer/Counters

Eight Interrupt Sources

Full Duplex UART Serial Channel

Low-power Idle and Power-down Modes

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

3.3.2 Description Of Microcontroller 89S52:

The AT89S52 is a low-power, high-performance CMOS 8-bit micro controller with

8Kbytes of in-system programmable Flash memory. The device is manufactured using

Atmels high-density nonvolatile memory technology and is compatible with the industry-

standard 80C51 micro controller. The on-chip Flash allows the program memory to be

reprogrammed in-system or by a conventional nonvolatile memory programmer. By

combining a versatile 8-bit CPU with in-system programmable flash one monolithic chip; the

Atmel AT89S52 is a powerful micro controller, which provides a highly flexible and cost-

effective solution to many embedded control applications.

The device is manufactured using Atmels high-density nonvolatile memory

technology and is compatible with the industry-standard 80C51 micro controller.



Fig 3. Pin configuration of 89S52

The on-chip Flash allows the program memory to be reprogrammed in-system or by a

conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with in-

system programmable flash one monolithic chip; the Atmel AT89S52 is a powerful micro

controller, which provides a highly flexible and cost-effective solution to many embedded

control applications.

The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes

of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, full

duplex serial port, on-chip oscillator, and clock circuitry. In addition, the AT89S52 is

designed with static logic for perationdown to zero frequency and supports two software

selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM

timer/counters, serial port, and interrupt system to continue functioning. The Power-down

mode saves the RAM contents but freezes the oscillator, disabling all other chip functions

until the next interrupt Or hardware reset.



fig 4. Block diagram of 89S52



3.3.3. Pin Description Of Microcontroller 89S52

VCC

Supply voltage.

GND

Ground

Port 0

Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can

sink eight TTL inputs. When 1sare written to port 0 pins, the pins can be used as high

impedance inputs. Port 0 can also be configured to be the multiplexed low order address/data

bus during accesses to external program and data memory. In this mode, P0 has internal pull-

ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes

during program verification. External pull-ups are required during program verification

Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 Output

buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled

high by the internal pull-ups and can be used as inputs. In addition, P1.0 and P1.1 can be

configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2

trigger input P1.1/T2EX), respectively, as shown in the following table. Port 1 also receives

the low-order address bytes during Flash programming and verification.

Port Pin Alternate Functions

P1.0 T2(External Count input to Timer/Counter 2), clock-out

P1.1 T2EX (Timer/ Counter 2 capture/reload trigger and direction control)

P1.5 MOSI (used for In-system Programming)

P1.6 MISO (used for In-system Programming)

P1.7 SCK (used for In-system Programming)

Table 1: Functions of Port1

Port 2

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output

buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled

high by the internal pull-ups and can be used as inputs. Port 2 emits the high-order address

byte during fetches from external program memory and during accesses to external data



memory that use 16-bit addresses (MOVX @DPTR). In this application, Port 2 uses strong

internal pull-ups when emitting 1s. During accesses to external data memory that use 8-bit

addresses (MOVX @ RI), Port 2emits the contents of the P2 Special Function Register. Port

2 also receives the high-order address bits and some control signals during Flash

programming and verification.

Port 3

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output

buffers can sink/source four TTL inputs. When 1s are writt 1s are written to Port 3 pins, they

are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that

are externally being pulled low will source current (IIL) because of the pull-ups. Port 3 also

serves the functions of various special features of the AT89S52, as shown in the following

table. Port 3 also receives some control signals for Flash programming and verification.

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

Table2: Functions of Port3

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running

resets the device.

ALE/PROG

Address Latch Enable (ALE) is an output pulse for latching the low byte of the

address during accesses to external memory. This pin is also the program pulse input (PROG)

during Flash programming. In normal operation, ALE is emitted at a constant rate of1/6 the

oscillator frequency and may be used for external timing or clocking purposes. Note,

however, that one ALE pulse is skipped during each access to external data Memory. If



desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set,

ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly

pulled high. Setting the ALE-disable bit has no effect if the micro controller is in external

execution mode.

PSEN

Program Store Enable (PSEN) is the read strobe to external program memory. When

the AT89S52 is executing code from external program memory, PSEN is activated twice

each machine cycle, except that two PSEN activations are skipped during each access to

external data memory.

EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to

fetch code from external program memory locations starting at 0000H up to FFFFH.Note,

however, that if lock bit 1 is programmed, EA will be internally latched on reset. A should be

strapped to VCC for internal program executions. This pin also receives the 12-

voltProgramming enables voltage (VPP) during Flash programming.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating

circuit.

XTAL2

Output from the inverting oscillator amplifier.

Oscillator Characteristics

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier

that can be configured for use as an on-chip oscillator, as shown in Figure 1. Either a quartz

crystal or ceramic resonator may be used. To drive the device from an External clock source,

XTAL2 should be left unconnected while XTAL1 is driven.



Fig 5. Oscillator Connections

Special Function Register (SFR) Memory:

Special Function Registers (SFR s) are areas of memory that control specific

functionality of the 8051 processor. For example, four SFRs permit access to the 8051s 32

input/output lines. Another SFR allows the user to set the serial baud rate, control and access

timers, and configure the 8051s interrupt system.

Accumulator:

The Accumulator, as its name suggests is used as a general register to accumulate the

results of a large number of instructions. It can hold 8-bit (1-byte) value and is the most

versatile register.

The R registers: The R registers are a set of eight registers that are named R0, R1.

Etc up to R7. These registers are used as auxiliary registers in many operations.

The B registers: The B register is very similar to the accumulator in the sense

that it may hold an 8-bit (1-byte) value. Two only uses the B register 8051 instructions:

MUL AB and DIV AB.

The Data Pointer: The Data pointer (DPTR) is the 8051s only user accessible 16-bit

(2Bytes) register. The accumulator, R registers are all 1-Byte values. DPTR, as the name

suggests, is used to point to data. It is used by a number of commands, which allow the 8051

to access external memory.



The program counter and stack pointer:

The program counter (PC) is a 2-byte address, which tells the 8051 where the next

instruction to execute is found in memory. The stack pointer like all registers except DPTR

and PC may hold an 8-bit (1-Byte) value

3.3.4. Addressing modes:

An addressing mode refers that you are addressing a given memory location. In

summary, the addressing modes are as follows, with an example of each:

Each of these addressing modes provides important flexibility.

Immediate Addressing MOV A, #20 H

Direct Addressing MOV A, 30 H

Indirect Addressing MOV A, @R0

Indexed Addressing

a. External Direct MOVX A, @DPTR

b. Code In direct MOVC A, @A+DPTR

Immediate Addressing:

Immediate addressing is so named because the value to be stored in memory

immediately follows the operation code in memory. That is to say, the instruction itself

dictates what value will be stored in memory. For example, the instruction:

MOV A, #20H

This instruction uses immediate Addressing because the accumulator will be loaded

with the value that immediately follows in this case 20(hexadecimal). Immediate addressing

is very fast since the value to be loaded is included in the instruction. However, since the

value to be loaded is fixed at compile-time it is not very flexible.

Direct Addressing:

Direct addressing is so named because the value to be stored in memory is obtained

by directly retrieving it from another memory location.

For example: MOV A, 30h



This instruction will read the data out of internal RAM address 30(hexadecimal) and

store it in the Accumulator. Direct addressing is generally fast since, although the value to be

loaded isnt included in the instruction, it is quickly accessible since it is stored in the 8051s

internal RAM. It is also much more flexible than Immediate Addressing since the value to be

loaded is whatever is found at the given address which may variable.

Also it is important to note that when using direct addressing any instruction that

refers to an address between 00h and 7Fh is referring to the SFR control registers that control

the 8051 micro controller itself.

Indirect Addressing:

Indirect addressing is a very powerful addressing mode, which in many cases

provides an exceptional level of flexibility. Indirect addressing is also the only way to access

the extra 128 bytes of internal RAM found on the 8052. Indirect addressing appears as

follows:

MOV A, @R0:

This instruction causes the 8051 to analyze Special Function Register (SFR) Memory:

Special Function Registers (SFRs) are areas of memory that control specific

functionality of the 8051 processor. For example, four SFRs permit access to the 8051s 32

input/output lines. Another SFR allows the user to set the serial baud rate, control and access

timers, and configure the 8051s interrupt system.

Timer 2 Registers:

Control and status bits are contained in registers T2CON and T2MOD for

Timer 2 . The register pair (RCAP2H , RCAP2L) are the Capture / Reload registers for

Timer 2 in 16-bit capture mode or 16-bit auto-reload mode .

Interrupt Registers:

The individual interrupt enable bits are in the IE register . Two priorities can

be set for each of the six interrupt sources in the IP register.

Timer 2 is a 16-bit Timer / Counter that can operate as either a timer or an

event counter. The type of operation is selected by bit C/T2 in the SFR T2CON .

Timer 2 has three operating Modes : capture , auto-reload ( up or down Counting ) , and

baud rate generator . The modes are selected by bits in T2CON . Timer 2 consists of



two 8-bit registers , TH2 and TL2 . In the Timer function , the TL2 register is

incremented every machine cycle . Since a machine cycle consists of 12 oscillator

periods, the count rate is 1/12 of the oscillator frequency.In the Counter function , the

register is incremented in response to a 1-to-0 transition at its corresponding external

input pin , T2 .When the samples show a high in one cycle and a low in the next

cycle, the count is incremented . Since two machine cycles (24 Oscillator periods ) are

required to recognize 1-to-0 transition , the maximum count rate is 1 / 24 of the

oscillator frequency . To ensure that a given level is sampled at least once before

it changes , the level should be held for atleast one full machine cycle .

Symbol Position Function

EA IE.7 Disables all interrupts. If EA=0, no interrupt is acknowledged. If

EA=1, each interrupt source is individually enabled or disabled by

setting or clearing its enable bit.

- IE.6 Reserved

ET2 IE.5 Timer2 interrupt enable bit

ES IE.4 Serial port interrupt enable bit


EX1 IE.2 External interrupt1 enable bit


EX0 IE.0 External interrupt0 enable bit

Table3: Interrupt Register Functions

Capture Mode

In the capture mode , two options are selected by bit EXEN2 in T2CON . If

EXEN2 = 0, Timer 2 is a 16-bit timer or counter which upon overflow sets bit TF2

in T2CON . This bit can then be used to generate an interrupt . If EXEN2 = 1 , Timer

2 performs the same operation , but a 1-to-0 transition at external input T2EX also

causes the current value in TH2 and TL2 to be captured into RCAP2H and

RCAP2L , respectively Auto-reload (Up or Down Counter).

Timer 2 can be programmed to count up or down when configured in its 16-

bit auto-reload mode. This feature is invoked by the DCEN (Down Counter Enable)

bit located in the SFR T2MOD . Upon reset , the DCEN bit is set to 0 so that

timer 2 will default to count up. When DCEN is set , Timer 2 can count up or down

, depending on the value of the T2EX pin . In this mode , two options are selected



by bit EXEN2 in T2CON . If EXEN2 = 0 , Timer 2 counts up to 0FFFFH and then

sets the TF2 bit upon overflow . If EXEN2 = 1 , a 16-bit reload can be triggered

either by an overflow or by a 1-to-0 transition at external input T2EX.

3.5. Baud Rate Generator

Timer 2 is selected as the baud rate generator by setting TCLK and/or

RCLK in T2CON . Note that the baud rates for transmit and receive can be different

if Timer 2 is used for the receiver or transmitter and Timer 1 is used for the other

function .The baud rates in Modes 1 and 3 aredetermined by Timer 2s overflow rate

according to the following equation .

Modes 1 and 3 Baud Rates =Timer 2 Overflow Rate16

The timer operation is different for Timer 2 when it is used as a baud rate

generator .Normally ,as a timer , it increments every machine cycle (at 1/12 the

oscillator frequency).As a baud rate generator , however, it increments every state time (

at 1/2 the oscillator frequency ) .

Timer 0

Timer 0 functions as either a timer or event counter in four modes of

operation . Timer 0 is controlled by the four lower bits of the TMOD register and

bits 0, 1, 4 and 5 of the TCON register

Mode 0 ( 13-bit Timer)

Mode 0 configures timer 0 as a 13-bit timer which is set up as an 8-bit

timer (TH0 register) with a modulo 32 prescaler implemented with the lower five

bits of the TL0 register . The upper three bits of TL0 register are indeterminate and

should be ignored . Prescaler overflow increments the TH0 register.

Mode 1 ( 16-bit Timer )

Mode 1 is the same as Mode 0, except that the Timer register is being

run with all 16 bits . Mode 1 configures timer 0 as a 16-bit timer with the TH0

and TL0 registers connected in cascade . The selected input increments the TL0

register .



Mode 2 (8-bit Timer with Auto-Reload)

Mode 2 configures timer 0 as an 8-bit timer ( TL0 register ) that

automatically reloads from the TH0 register . TL0 overflow sets TF0 flag in the

TCON register and reloads TL0 with the contents of TH0 , which is preset by

software .

Mode 3 ( Two 8-bit Timers )

Mode 3 configures timer 0 so that registers TL0 and TH0 operate as separate

8-bit timers. This mode is provided for applications requiring an additional 8-bit

timer or counter .

Timer 1

Timer 1 is identical to timer 0 , except for mode 3 , which is a hold-count

mode .

Mode 3 ( Halt )

Placing Timer 1 in mode 3 causes it to halt and hold its count . This can

be used to halt Timer 1 when TR1 run control bit is not available i.e. , when

Timer 0 is in mode 3 .

Baud Rates :

The baud rate in Mode 0 is fixed. The baud rate in Mode 2 depends

on the value of bit SMOD in Special Function Register PCON. If SMOD = 0

(which is its value on reset), the baud rate is 1/64 the oscillator frequency . If

SMOD = 1, the baud rate is 1/32 the oscillator frequency. In the 89S52 , the baud

rates in Modes 1 and 3 are determined by the Timer 1 overflow rate. In case of

Timer 2 , these baud rates can be determined by Timer 1 , or by Timer 2 , or by

both (one for transmit and the other for receive ).



TCON REGISTER : Timer/counter Control Register

7 6 5 4 3 2 1 0

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0

Table 4: TCON Register functions

Bit

number

Bit

Mnumonic

Description

7

TF1

Timer 1 Overflow flag

Cleared by hardware when processor vectors to interrupt routine

Set by hardware on timer/counter overflow, when the timer1

register overflows

6

TR1

Timer1 Run Control Bit

Clear to turn off timer/counter 1

Set to turn on timer/counter 1

5

TF0

Timer 0 overflow flag

Cleared by hardware when processor vectors to interrupt routine

Set by hardware on timer/counter overflow, when the timer0

register overflows

4

TR0

Timer 0 Run Control Bit

Clear to turn off timer/counter 0

Set tot urn on timer/counter 0

3

IE1

Interrupt1 Edge Flag

Cleared by hardware when interrupt is processed if edge-triggered

Set by hardware when external interrupt is detected on NT1#pin

2

IT1

Interrupt1 Type Control Bit

Clear to select low level active for external interrupt 1

Set to select falling edge active for external interrupt 1

1

IE0

Interrupt 0 edge flag

Cleared by hardware when interrupt is processed if edge-triggered

Set by hardware when external interrupt is detected on NT0#pin

0

IT0

Interrupt0 Type Control Bit

Clear to select low level active for external interrupt0

Set to select falling edge active for external interrupt0



TMOD REGISTER: Timer/Counter 0 and 1 Modes

7 6 5 4 3 2 1 0

GATE1 C/T1# M11 M01 GATE0 C/T0# M10 M00

Bit

Number

Bit

Mnumonic

Description

7

GATE1

Timer1 Gain Control Bit

Clear to enable timer1 whenever the TR1 bit is set

Set to enable timer1 only when the INT1#pin is high and TR1 bit is

set

6

C/T1#

Timer1 Counter/timer Select Bit

Clear for timer operation:Timer0 counts the divided-down system

clock

Set for counter operation:timer1 counts negative transitions on

external pin T1

5

4

M11

M01

Timer1 mode select bits M11 M01 Operating mode

0 0 Mode0:8-bit timer/counter(TH1) wuth 8-bit prescaler(TL1)

0 1 Mode 1: 16-bit timer/counter

1 0 Mode2:8bit auto reload timer/countert(TL1). 1 1 Mode 3: Timer1 hacked. Retains count

3

GATE0

Timer1 gain Control Bit

Clear to enable timer0 whenever the TR0 bit is set

Set to enable timer/counter0 only when the INT0#pin is high and

the TR0 pin is set

2

C/T0#

Timer0 Counter/timer select bit

Clear for timer operation: timer0 counts the divided-down system

clock

Set for counter operation:Timer 0 counts negative transitions on

external pin T0

1

0

M10

M00

Timer0 Mode Select Bit M10 M00 Operating mode

0 0 Mode0:8 bit timer/counter(TH0) with 8bit prescaler

0 1 Mode1:16-bit timer/counter

1 0 Mode2:8bit auto reload timer/counter(TL0)

1 1 Mode3:TL0 is an 8bit timer/counter

TH0 is an 8bit timer using timer1s TR0 and TF0 bits

Table 5: TMOD Register Functions



3.4. DC MOTORS

Industrial applications use dc motors because the speed-torque relationship can be

varied to almost any useful form for both dc motor and regeneration applications in either

direction of rotation. Continuous operation of dc motors is commonly available over a speed

range of 8:1. Infinite range (smooth control down to zero speed) for short durations or

reduced load is also common. Dc motors are often applied where they momentarily deliver

three or more times their rated torque. In emergency situations, dc motors can supply over

five times rated torque without stalling (power supply permitting). Dynamic braking (dc

motor-generated energy is fed to a resistor grid) or regenerative braking (dc motor-generated

energy is fed back into the dc motor supply) can be obtained with dc motors on applications

requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical

brake. Dc motors feature a speed, which can be controlled smoothly down to zero,

immediately followed by acceleration in the opposite direction without power circuit

switching. And dc motors respond quickly to changes in control signals due to the dc motor's

high ratio of torque to inertia. In any electric motor, operation is based on simple

electromagnetism. A current carrying conductor generates a magnetic field; when this is then

placed in an external magnetic field, it will experience a force proportional to the current in

the conductor, and to the strength of the external magnetic field. As you are well aware of

from playing with magnets as a kid, opposite (North and South) polarities attract, while like

polarities (North and North, South and South) repel. The internal configuration of a DC

motor is designed to harness the magnetic interaction between a current carrying conductor

and an external magnetic field to generate rotational motion. Let's start by looking at a simple

2-pole DC electric motor (here red represents a magnet or winding with a "North"

polarization, while green represents a magnet or winding with a "South" polarization).

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator,

commentator, field magnet(s), and brushes. In most common DC motors (and all that

BEAMers will see), the external magnetic field is produced by high-strength permanent

magnets1. The stator is the stationary part of the motor this includes the motor casing, as well

as two or more permanent magnet pole pieces. The rotors (together with the axle and attached

commentator) rotate with respect to the stator. The rotor consists of windings (generally on a

core), the windings being electrically connected to the commentator. The above diagram

shows a common motor layout -- with the rotor inside the stator (field) magnets.



Fig 6. 2-pole DC electric motor

Theory of DC motor speed control:

The speed controller works by varying the average voltage sent to the motor. It could

do this by simply adjusting the voltage sent to the motor, but this is quite inefficient to do. A

better way is to switch the motor's supply on and off very quickly. If the switching is fast

enough, the motor doesn't notice it, it only notices the average effect. When you watch a film

in the cinema, or the television, what you are actually seeing is a series of fixed pictures,

which change rapidly enough that your eyes just see the average effect movement.

Your brain fills in the gaps to give an average effect. Now imagine a light bulb with a

switch. When you close the switch, the bulb goes on and is at full brightness, say 100 Watts.

When you open the switch it goes off (0 Watts). Now if you close the switch for a fraction of

a second, and then open it for the same amount of time, the filament won't have time to cool

down and heat up, and you will just get an average glow of 50 Watts.

This is how lamp dimmers work, and the same principle is used by speed controllers

to drive a motor. When the switch is closed, the motor sees 12 Volts, and when it is open it

sees 0 Volts. If the switch is open for the same amount of time as it is closed, the motor will

see an average of 6 Volts, and will run more slowly accordingly. As the amount of time that

the voltage is on increases compared with the amount of time that it is off, the average speed

of the motor increases.

This on-off switching is performed by power MOSFETs. A MOSFET (Metal-Oxide-

Semiconductor Field Effect Transistor) is a device that can turn very large currents on and off



under the control of a low signal level voltage. For more detailed information, see the

dedicated chapter on MOSFETs) .The time that it takes a motor to speed up and slow down

under switching conditions is dependent on the inertia of the rotor (basically how heavy it is),

and how much friction and load torque there is. The graph below shows the speed of a motor

that is being turned on and off fairly slowly:

Fig 7. Speed of the motor



3.5. LED (LIGHT EMITTING DIODE)

A light-emitting diode (LED) is a semiconductor diode that emits light when an

electrical current is applied in the forward direction of the device, as in the simple LED

circuit. The effect is a form of electroluminescence. where incoherent and narrow-spectrum

light is emitted from the p-n junction..

LEDs are widely used as indicator lights on electronic devices and increasingly in

higher power applications such as flashlights and area lighting. An LED is usually a small

area (less than 1 mm2) light source, often with optics added to the chip to shape its radiation

pattern and assist in reflection. The color of the emitted light depends on the composition and

condition of the semi conducting material used, and can be infrared, visible, or ultraviolet.

Besides lighting, interesting applications include using UV-LEDs for sterilization of water

and disinfection of devices, and as a grow light to enhance photosynthesis in plants.

Basic principle:

Like a normal diode, the LED consists of a chip of semi conducting material

impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current

flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse

direction. Charge-carriers electrons and holes flow into the junction from electrodes with

different voltages. When an electron meets a hole, it falls into a lower energy level, and

releases energy in the form of a photon.

The wavelength of the light emitted, and therefore its color, depends on the band gap

energy of the materials forming the p-n junction. In silicon or germanium diodes, the

electrons and holes recombine by a non-radioactive transition which produces no optical

emission, because these are indirect band gap materials.

The materials used for the LED have a direct band gap with energies corresponding to

near-infrared, visible or near-ultraviolet light. LED development began with infrared and red

devices made with gallium arsenide. Advances in materials science have made possible the

production of devices with ever-shorter wavelengths, producing light in a variety of colors.

LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer



deposited on its surface. P-type substrates, while less common, occur as well. Many

commercial LEDs, especially GaN/InGaN, also use sapphire substrate.

Fig 8. Working of LED

3.5.1 LED Display types:

Bar graph

Seven segment

Star burst

Dot matrix

3.5.2 Basic LED types:

Miniature LEDs

Fig 9. Miniature LEDs



Different sized LEDs. 8 mm, 5mm and 3 mm. These are mostly single-die LEDs used as

indicators, and they come in various-size packages:

Surface mount

2 mm.

3 mm (T1).

5 mm(T1).

10 mm.

Other sizes are also available, but less common.

Common package shapes:

Round, dome top.

Round, flat top.

Rectangular, flat top (often seen in LED bar-graph displays)

Triangular or square, flat top

The encapsulation may also be clear or semi opaque to improve contrast and viewing angle.

There are three main categories of miniature single die LEDs:

Low current typically rated for 2mA at around 2V (approximately 4mW

consumption).

Standard 20 mA LEDs at around 2 V (approximately 40mW) for red, orange, yellow

& green, and 20 mA at 45 V (approximately 100mW) for blue, violet and white.

Ultra-high output 20 mA at approximately 2 V or 45 V, designed for viewing in

direct sunlight.

Five- and twelve-volt LEDs

These are miniature LEDs incorporating a series resistor, and may be connected

directly to a 5 V or 12 V supply.

Flashing LEDs

Flashing LEDs are used as attention seeking indicators where it is desired to avoid the

complexity of external electronics. Flashing LEDs resemble standard LEDs but they contain

an integrated multivibrator circuit inside which causes the LED to flash with a typical period

of one second. In diffused lens LEDs this is visible as a small black dot. Most flashing LEDs



emit light of a single color, but more sophisticated devices can flash between multiple colors

and even fade through a color sequence using RGB color mixing.

High power LEDs

High power LEDs from limitless mounted on a star shaped heat sink High power

LEDs (HPLED) can be driven at more than one ampere of current and give out large amounts

of light. Since overheating destroys any LED the HPLEDs must be highly efficient to

minimize excess heat, furthermore they are often mounted on a heat sink to allow for heat

dissipation. If the heat from a HPLED is not removed the device will burn out in seconds.

A single HPLED can often replace an incandescent bulb in a flashlight or be set in an

array to form a powerful LED lamp. LEDs have been developed that can run directly from

mains power without the need for a DC converter. For each half cycle part of the LED diode

emits light and part is dark, and this is reversed during the next half cycle. Current efficiency

is 80 lm/W..

Multi-color LEDs

A bi-color LED is actually two different LEDs in one case. It consists of two dies

connected to the same two leads but in opposite directions. Current flow in one direction

produces one color, and current in the opposite direction produces the other color. Alternating

the two colors with sufficient frequency causes the appearance of a third color. A tri-color

LED is also two LEDs in one case, but the two LEDs are connected to separate leads so that

the two LEDs can be controlled independently and lit simultaneously.RGB LEDs contain red,

green and blue emitters, generally using a four-wire connection with one common (anode or

cathode). The Taiwanese LED manufacturer. Ever light has introduced a 3 watt RGB

package capable of driving each die at 1 watt.

Alphanumeric LEDs

LED displays are available in seven-segment and starburst format. Seven-segment

displays handle all numbers and a limited set of letters. Starburst displays can display all

letters. Seven-segment LED displays were in widespread use in the 1970s and 1980s, but

increasing use of liquid crystal displays, with their lower power consumption and greater

display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.



3.5.3 Applications:

Automotive applications with LEDS

Instrument Panels & Switches, Courtesy Lighting, CHMSL, Rear Stop/Turn/Tai,

Retrofits, New Turn/Tail/Marker Lights.

Consumer electronics & general indication

Household appliances, VCR/DVD/ tereo/Audio/Video devices, Toys/Games

Instrumentation, Security Equipment, Switches.

Illumination with LEDs

Architectural Lighting, Signage (Channel Letters), Machine Vision, Retail Displays,

Emergency Lighting (Exit Signs), Neon and bulb Replacement, Flashlights, Accent Lighting

- Pathways, Marker Lights.

Sign applications with LEDs

Full Color Video, Monochrome Message Boards, Traffic/VMS, Transportation

Passenger Information.

Signal application with LEDs

Traffic, Rail, Aviation, Tower Lights, Runway Lights, Emergency/Police Vehicle

Lighting.

Mobile applications with LEDs

Mobile Phone, PDA's, Digital Cameras, Lap Tops, General Backlighting.

Photo sensor applications with LEDs

Medical Instrumentation, Bar Code Readers, Color & Money Sensors, Encoders,

Optical Switches, Fiber Optic Communication.



3.6 MAX 232

A standard serial interface for PC, RS232C, requires negative logic, i.e., logic 1 is -

3V to -12V and logic 0 is +3V to +12V. To convert TTL logic, say, TxD and RxD pins of the

microcontroller thus need a converter chip. A MAX232 chip has long been using in many

microcontrollers boards. It is a dual RS232 receiver / transmitter that meets all RS232

specifications while using only +5V power supply. It has two onboard charge pump voltage

converters which generate +10V to -10V power supplies from a single 5V supply. It has four

level translators, two of which are RS232 transmitters that convert TTL/CMOS input levels

into +9V RS232 outputs. The other two level translators are RS232 receivers that convert

RS232 input to 5V. Typical MAX232 circuit is shown below.

Fig 10. Pin configuration of MAX232



Features:

Operates With Single 5-V Power Supply

LinBiCMOSE Process Technology

Two Drivers and Two Receivers

30-V Input Levels

Low Supply Current 8 mA Typical

Meets or Exceeds TIA/EIA-232-F and ITU Recommendation V.28

Designed to be Interchangeable With Maxim MAX232

Applications

TIA/EIA-232-F

Battery-Powered Systems

Terminals

Modems

Computers

ESD Protection Exceeds 2000 V Per MIL-STD-883, Method 3015

Package Options Include Plastic

Small-Outline (D, DW) Packages and

Standard Plastic (N) DIPs

Circuit connections:

A standard serial interfacing for PC, RS232C, requires negative logic, i.e., logic '1' is -

3V to -12V and logic '0' is +3V to +12V. To convert a TTL logic, say, TxD and RxD pins of

the uC chips, thus need a converter chip. A MAX232 chip has long been using in many uC

boards. It provides 2-channel RS232C port and requires external 10uF capacitors.

Fig 9. MAX232



Fig 10. Pin configuration of MAX232

3.7 SWITCHES

A switch is a mechanical device used to connect and disconnect an electric circuit at

will. Switches cover a wide range of types, from subminiature up to industrial plant switching

megawatts of power on high voltage distribution lines. In applications where multiple

switching options are required (e.g., a telephone service).

The switch is referred to as a "gate" when abstracted to mathematical form. In the

philosophy of logic, operational arguments are represented as logic gates. The use of

electronic gates to function as a system of logical gates is the fundamental basis for the

computer i.e. a computer is a system of electronic switches which function as logical gates.

Fig 11. Switches



3.7.1 Types of switches

A pair of contacts is said to be 'closed' when there is no space between them, allowing

electricity to flow from one to the other. When the contacts are separated by an insulating air

gap, an air space, they are said to be 'open', and no electricity can flow at typical voltages.

Switches can be and are classified according to the arrangement of their contacts in

electronics field, but electricians in the electrical wiring service business and their electrical

supplier industries use different nomenclature, such as "one-way", "two-way", "three-way"

and "four-way" switches. We have types of switches also

SPST (single pole single through),

SPDT (single pole double through),

DPST (double pole single through),

DPDT (double pole double through).

In a multi-throw switch, there are two possible transient behaviors as you move from

one position to another. In some switch designs, the new contact is made before the old

contact is broken. This is known as make-before-break, and ensures that the moving contact

never sees an open circuit (also referred to as a shorting switch). The alternative is break-

before-make, where the old contact is broken before the new one is made. This ensures that

the two fixed contacts are never shorted to each other. Both types of design are in common

use, for different applications.

Biased switches

The momentary push-button switch is a type of biased switch. In this contact is made

by spring. The most common type is a push-to-make switch, which makes contact when the

button is pressed and breaks when the button is released. A push-to-break switch, on the other

hand, breaks contact when the button is pressed and makes contact when it is released. An

example of a push-to-break switch is a button used to release a door held open by an

electromagnet. Changeover push button switches do exist but are even less common.

Mercury tilt switch

The mercury switch consists of a drop of mercury inside a glass bulb with 2 contacts.

The two contacts pass through the glass, and are connected by the mercury when the bulb is

tilted to make the mercury roll on to them. This type of switch performs much better than the



ball tilt switch, as the liquid metal connection is unaffected by dirt, debris and oxidation, it

wets the contacts ensuring a very low resistance bounce free connection, and movement and

vibration do not produce a poor contact.

Knife switch

Knife switches are unique, because rather than employing an enclosed circuit

connection area with a rubber- or plastic-insulated section for the user, the contacts and

bridge are fully exposed. The "knife", a flat metal swinging arm, oscillates via user operation

between a set of two or more contact areas. The knife and contacts are typically formed of

copper, steel, or brass, depending on the application. Although knife switches are inferior to

traditional switches in applications where user safety are paramount, knife switches are still

commonly employed in everyday high-voltage applcations such as building transformers,

large power relays, air-conditioning units, etc.

Changeover switch

A changeover switch provides two distinct events, the making of one contact and the

breaking of the other. These can be used to feed the inputs of a flip-flop. This way the press

will only be detected when the pressed contact is made and the release will only be detected

when the released contact is made. When the switch is bouncing around in the middle no

change is detected. To get a single logic signal from such a setup a simple SR latch can be

used.

Toggle switches are actuated by a lever angled in one of two or more positions. The

common light switch used in household wiring is an example of a toggle switch. Most toggle

switches will come to rest in any of their lever positions, while others have an internal spring

mechanism returning the lever to a certain normal position, allowing for what is called

"momentary" operation.



Pushbutton switches are two-position devices actuated with a button that is pressed

and released. Most pushbutton switches have an internal spring mechanism returning the

button to its "out," or "unpressed," position, for momentary operation. Some pushbutton

switches will latch alternately on or off with every push of the button. Other pushbutton

switches will stay in their "in," or "pressed," position until the button is pulled back out. This

last type of pushbutton switches usually have a mushroom-shaped button for easy push-pull

action.

Selector switches are actuated with a rotary knob or lever of some sort to select one of

two or more positions. Like the toggle switch, selector switches can either rest in any of their

positions or contain spring-return mechanisms for momentary operation.

A joystick switch is actuated by a lever free to move in more than one axis of motion.

One or more of several switch contact mechanisms are actuated depending on which way the

lever is pushed, and sometimes by how far it is pushed. The circle-and-dot notation on the



switch symbol represents the direction of joystick lever motion required to actuate the

contact. Joystick hand switches are commonly used for crane and robot control.

Some switches are specifically designed to be operated by the motion of a machine rather

than by the hand of a human operator. These motion-operated switches are commonly called

limit switches, because they are often used to limit the motion of a machine by turning off the

actuating power to a component if it moves too far. As with hand switches, limit switches

come in several varieties.

These limit switches closely resemble rugged toggle or selector hand switches fitted

with a lever pushed by the machine part. Often, the levers are tipped with a small roller

bearing, preventing the lever from being worn off by repeated contact with the machine part.

Proximity switches sense the approach of a metallic machine part either by a magnetic

or high-frequency electromagnetic field. Simple proximity switches use a permanent magnet

to actuate a sealed switch mechanism whenever the machine part gets close (typically 1 inch

or less). More complex proximity switches work like a metal detector, energizing a coil of

wire with a high-frequency current, and electronically monitoring the magnitude of that

current. If a metallic part (not necessarily magnetic) gets close enough to the coil, the current

will increase, and trip the monitoring circuit. The symbol shown here for the proximity

switch is of the electronic variety, as indicated by the diamond-shaped box surrounding the



switch. A non-electronic proximity switch would use the same symbol as the lever-actuated

limit switch. Another form of proximity switch is the optical switch, comprised of a light

source and photocell. Machine position is detected by either the interruption or reflection of a

light beam. Optical switches are also useful in safety applications, where beams of light can

be used to detect personnel entry into a dangerous area.

In many industrial processes, it is necessary to monitor various physical quantities

with switches. Such switches can be used to sound alarms, indicating that a process variable

has exceeded normal parameters, or they can be used to shut down processes or equipment if

those variables have reached dangerous or destructive levels. There are many different types

of process switches.

These switches sense the rotary speed of a shaft either by a centrifugal weight

mechanism mounted on the shaft, or by some kind of non-contact detection of shaft motion

such as optical or magnetic.

Gas or liquid pressure can be used to actuate a switch mechanism if that pressure is

applied to a piston, diaphragm, or bellows, which converts pressure to mechanical force.



An inexpensive temperature-sensing mechanism is the "bimetallic strip:" a thin strip

of two metals, joined back-to-back, each metal having a different rate of thermal expansion.

When the strip heats or cools, differing rates of thermal expansion between the two metals

causes it to bend. The bending of the strip can then be used to actuate a switch contact

mechanism. Other temperature switches use a brass bulb filled with either a liquid or gas,

with a tiny tube connecting the bulb to a pressure-sensing switch. As the bulb is heated, the

gas or liquid expands, generating a pressure increase which then actuates the switch

mechanism.

Voltage regulator:

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this

project, power supply of 5V and 12V are required. In order to obtain these voltage levels,

7805 and 7812 voltage regulators are to be used.



CHAPTER FOUR

Firmware

Implementation of the

Project

Software Tools Required

Keil Compiler

Proload



4. FIRMWARE IMPLEMENTATION OF THE PROJECT

This chapter briefly explains about the firmware implementation of the project. The

required software tools are discussed in section 4.2. Section 4.3 shows the flow diagram of

the project design. Section 4.4 presents the firmware implementation of the project design.

4.1 Software Tools Required

Keil v3, Proload are the two software tools used to program microcontroller. The

working of each software tool is explained below in detail.

4.1.1 Programming Microcontroller

A compiler for a high level language helps to reduce production time. To program the

AT89S52 microcontroller the Keil v3 is used. The programming is done strictly in the

embedded C language. Keil v3 is a suite of executable, open source software development

tools for the microcontrollers hosted on the Windows platform.

The compilation of the C program converts it into machine language file (.hex). This

is the only language the microcontroller will understand, because it contains the original

program code converted into a hexadecimal format. During this step there are some warnings

about eventual errors in the program. This is shown in Fig 4.1. If there are no errors and

warnings then run the program, the system performs all the required tasks and behaves as

expected the software developed. If not, the whole procedure will have to be repeated again.

Fig 4.2 shows expected outputs for given inputs when run compiled program.

One of the difficulties of programming microcontrollers is the limited amount of

resources the programmer has to deal with. In personal computers resources such as RAM

and processing speed are basically limitless when compared to microcontrollers. In contrast,

the code on microcontrollers should be as low on resources as possible.

4.2. Keil Software:

Installing the Keil software on a Windows PC

1. Insert the CD-ROM in your computers CD drive

2. On most computers, the CD will auto run, and you will see the Keil installation

menu. If the menu does not appear, manually double click on the Setup icon, in

the root directory: you will then see the Keil menu.



3. On the Keil menu, please select Install Evaluation Software. (You will not

require a license number to install this software).

4. Follow the installation instructions as they appear.

4.2.1. Loading the Projects:

The example projects for this book are NOT loaded automatically when you install

the Keil compiler.These files are stored on the CD in a directory /Pont. The files are

arranged by chapter: for example, the project discussed in Chapter 3 is in the directory

/Pont/Ch03_00-Hello.

Rather than using the projects on the CD (where changes cannot be saved), please

copy the files from CD onto an appropriate directory on your hard disk.

Note: you will need to change the file properties after copying: file transferred from the CD

will be read only.

4.2.2. Steps for loading a project and getting resultant:

Configuring the Simulator

Open the Keil Vision2

Fig12. Opening a new Project



Fig13. Selecting Device for Target Target1

Fig 14. Selecting 8052(all variants) and click OK



Fig15. Make sure that the oscillator frequency is 12MHz

Fig 16. Building the Target



Running the Simulation

Having successfully built the target, we are now ready to start the debug session and

run the simulator.

Fig 17. Starting debug session

After debugging the program then RUN the program to get the required result which

we want

4.

Main Documentation

Documents

Transcript of Main Documentation