Online Device Controller[1]

MMIINNII PPRROOJJEECCTT RREEPPOORRTT

oonn

OONNLLIINNEE DDEEVVIICCEE CCOONNTTRROOLLLLEERR

Submitted in partial fulfillment of the requirements for the award of the degree of

BACHELOR OF TECHNOLOGY in

ELECTRONICS ENGINEERING

of the

COCHIN UNIVERSITY OF SCIENCE AND TECHNOLOGY

by

AGIL FRANCIS HARRY JOSE M JIM CHERIAN

under the guidance of

Mr. LIJU PHILIP Lecturer, Electronics Engineering,

College of Engineering Chengannur

DEPARTMENT OF ELECTRONICS ENGINEERING,

COLLEGE OF ENGINEERING,

CHENGANNUR, KERALA - 689121.

September 2001

Online Device Controller

1

ACKNOWLEDGEMENT

This is the age of the Internet and the World Wide Web is becoming a part of the

life of the common man of our country. In this scenario, we have tried to implement the

control of hardware through Internet, a really challenging project. This project would not

have been successfully materialized had it not been for the several people who have

directly and indirectly helped us. We are extremely indebted to all of them and we whole-

heartedly thank everyone for their valuable support.

We are extremely grateful to Mr. P Prathapachandran Nair, our Principal for

providing us with good facilities and a proper environment for developing our project.

We thank Mr. Jyothiraj V P, Head of the Department, Department of Electronics

Engineering for the support and appreciation. We are also grateful to Mr. C V

AnilKumar, our Project Co-ordinator for all the guidance.

Our guide Mr. Liju Philip has been a real help to us during the entire course of

our project and we are highly obliged to him for his valuable suggestions, appraisal and

guidance. We also thank Mr.Gopakumar C, Lecturer and Project Lab In Charge, and

Mr. Sudhin Jacob, Lecturer for the constant support and encouragement for our project.

We are also greatly indebted to Mr. Riyas A, Electronics Engineer, Rubber Board

of India, Kottayam for his critical suggestions and technical advice.

And several of our seniors for their wonderful help rendered and powerful

suggestions in the initial phase of our project, and all our friends, both of Electronics and

Computer Engineering branches, who have been a great help.

We are also very thankful to all those unknown and unseen people who helped us

with valuable information through several discussion boards over the Internet.

We truly admire our parents for their constant encouragement and enduring

support which was inevitable for the success of our ventures.

Last, but not the least, we are thankful to each other in this project group for being

cooperative, patient and hardworking for the successful completion of this project.

Above all, we thank God Almighty for the ever-abiding kind blessings.


2

ABSTRACT

The ‘Online Device Controller (ODC) is a multi-channel hardware administration

system that has been developed to enable the control of equipments and appliances from

any part of the world, through the Internet. The concept of ODC is a relatively new one,

and makes use of Common Gateway interface (CGI), a very powerful technique that was

hitherto used solely for e-mail, database access and other ‘soft’ purposes involving

dynamic web page content. But, through this project we have made an attempt to bring a

very powerful but often unknown and underutilised aspect of CGI; the same technique

used to manipulate our e-mail accounts can equally well be applied to access the parallel

port of the web server, and control hardware through it.

Our project, the ‘Online Device Controller’ allows a remote user to login to the

Web server and control the devices connected to the server. Also provided is the feature

to control the same devices locally, through a Cordless Telephone.

The present product offers the facility to remotely control an ON/OFF device and

an Intensity Variable load, through the Internet, and locally through a Cordless telephone

and is a product of paramount significance in office, industrial and household

applications.


3

CONTENTS

INTRODUCTION 4

REVIEW 5

The World Wide Web 6

Common Gateway Interface 9

Parallel Port Basics 15

DTMF Dialing System 22

Microcontrollers 24

The Triac 26

THE PROJECT 29

Block Diagram 30

Hardware details 31

Software details 34

Flow Charts 35

Working of the System 41

Result and Discussion 42

CONCLUSION AND FUTURE SCOPE 43

REFERENCES 44


4

INTRODUCTION

With the advent of technology, the world has shrunk to a global village. Man has

been looking forward to realise the automation of every process, taking place around him.

But his dream, to extend his control to devices from anywhere in the world still remains

unfulfilled.

Our project envisages the control of equipments from a remote location through

the Internet, or an Intranet. Local control is also available through a dedicated PC and a

Cordless Phone Unit.

This project is suited for Office Automation and Home Automation. The concept

can equally well be extended to Industrial applications where direct human access is

restricted.

Through this project, we strive to make this dream come true…

Salient Features

� Remote access to dedicated devices from anywhere in the world through the Internet.

� Wide application in industrial, office and domestic automation.

� Secure and reliable.

� Remote control from local station is available.

� Power regulation � Facility to read the current status of the device is incorporated


5

Review


6

The World Wide Web

The World Wide Web is the collection of all browsers, servers, files, and browser-

accessible services available through the Internet. Conceived in 1989 by a computer

scientist named Tim Berners-Lee, its original purpose was to facilitate communication

between research scientists. The Web was designed in such a way that documents located

on one computer on the Internet could provide links to documents located on other

computer on the Internet.

A browser is the user’s window to the Web, providing the capability to view Web

documents and access Web-based services and applications. The most popular browsers

are Netscape’s Navigator and Microsoft’s Internet Explorer. Both browsers are

descendants of the Mosaic browser developed at the National Center for Supercomputing

Applications (NCSA). Mosaic’s slick graphical user interface (GUI) transformed the

Web from a research tool to the global publishing medium that it has become today.

Today’s Web browsers extend Mosaic’s GUI features with multimedia

capabilities and with browser programming languages such as Java and JavaScript. In

order to publish a document on the Web, it must be made available to a Web server. Web

servers retrieve Web documents in response to browser requests and forward the

documents to the requesting browsers via the Internet. Web servers also provide

gateways that enable browsers to access Web-related applications as well as other

Internet services, such as Gopher and Wide Area Information Search (WAIS).

The earliest Web servers were developed by CERN and NCSA. These servers

were the mainstay of the Web throughout its earlier years. Lately, Commercial Web

servers, developed by Netscape, Microsoft, and other companies, have become

increasingly popular on the Web. These servers are designed for higher performance and

to facilitate the development of complex Web applications.


7

Because the Web uses the Internet as its communication medium, it must follow

Internet communication protocols. The Internet’s Transmission Control Protocol (TCP)

and Internet Protocol (IP) enable worldwide connectivity between browsers and servers.

In addition to using the TCP/IP protocols for communication across the Internet, the Web

also uses its own protocol, called the HyperText Transfer Protocol (HTTP), for

exchanges between browsers and servers.

The HyperText Transfer Protocol (HTTP)

HTTP is the protocol used for communication between browsers and web servers.

HTTP uses a request/response model of communication. A browser establishes a

connection with a server and sends URL requests to the server. The server processes the

browser’s request and sends a response back to the browser.

A browser connects with the Web server by establishing a TCP connection at port

80 of the server. (This is the default port until another is specified in the URL) This port

is the default address at which web servers “listen” for browser requests. Once a

connection has been established a browser sends a request to the server. This request

specifies a request method, the URL of the document, program or other resource being

requested, the HTTP version being used by the browser, and other information related to

the request.

Several request methods are available. GET, HEAD, and POST are the most

commonly used ones.

The GET method is used to retrieve the information contained at the specified

URL. This method may also be used to submit data collected in an HTML form or to

invoke a Common Gateway Interface (CGI) program. When the server processes a GET

request, it delivers the requested information (if it can be found). The server inserts at the


8

front of the information an HTTP header that provides data about the server, identifies

any errors that occurred in processing the request, and describes the type of information

being returned as a result.

The HEAD method is similar to the GET method except that when a Web server

processes a HEAD request, it only returns the HTTP header data and not the information

that was the object of the request. The HEAD method is used to retrieve the information

about a URL without actually obtaining the information addressed by the URL.

The POST method is used to inform the server that the information appended to

the request is to be sent to the specified URL. The POST method is typically used to send

form data and other information to Common Gateway Interface (CGI) programs. The

Web server responds to a POST request by sending back header data followed by any

information generated by the CGI program as the result of processing the request.

The current version of HTTP is HTTP 1.1. It incorporates performance, security

and other improvements to the original HTTP 1. A new version of HTTP, referred to as

HTTP-NG, is currently being defined. (The NG stands for “Next Generation”.) The goal

of HTTP-NG is to simplify the HTTP protocol and make it more extensible.

Hyper Text Markup Language

The Hyper Text Markup Language, or HTML, originally developed by Tim

Berners Lee at CERN is the lingua franca of the Web. It is used to create Web pages and

uses ordinary ASCII text files to represent Web pages. The files consist of the text to be

displayed and the tags that specify how the text is to be displayed.

The use of tags to define the elements of a Web document is referred to as

markup. A tag is usually enclosed in angle brackets, and most tags come in pairs, with an

opening and a closing tag. The closing tag is the same as the opening tag but starts with a


9

forward slash. For example, the following line from an HTML file shows the text of a

title between the appropriate title tags.

<TITLE>Welcome to the Control Menu of Online Device Controller</TITLE>

A browser interprets these tags and displays only the text within the tags

appropriately. There are different tags used to identify headings, paragraphs or hyperlinks

and also, to insert images, forms, multimedia objects etc.

Common Gateway Interface (CGI)

The Common Gateway Interface (CGI) is a standard that specifies how external

programs may be used by Web servers. Programs that adhere to the Common Gateway

Interface standard are referred to as CGI programs. CGI programs may be used to process

data submitted with forms, to perform database searches, and to support other types of

Web applications such as clickable image maps.

Where HTML gives the World Wide Web its look, CGI makes it functional. It is

a ‘Common Gateway” between the web server and applications that can be useful to the

server, but doesn’t run as a part of it. In technical terms, a gateway is an interface or an

application that allows two systems to pass information between them. The CGI does the

same function in the context of a Web server and Web client (Web browser). The server

does not know Perl or C. But by means of CGI, it can handle requests from “clients” or

visitors to the Web page, allow execution of the required application programs and pass

the results back. In fact, CGI is the only way the server can communicate with these other

applications, such as a database or even the parallel port of the machine.

A browser request for the URL of a CGI program comes about as the result of a

user clicking a link or submitted a form. The browser uses HTTP to make the request.

When a Web server receives the request, the Web server executes the CGI program and


10

also passes it any data that was submitted by the browser. When the CGI program

performs its processing, it usually generates data in the form a Web page, which it returns

via the Web server to the requesting browser.

The CGI standard specifies how data may be passed from Web servers to CGI

programs and how data should be returned from CGI programs to the web server.

Working of CGI

CGI programs also referred to as CGI scripts are the external programs, which are

a standard interface for communication between Web servers and external programs. The

CGI specification identifies how data is to be passed from a Web server to a CGI

program and back.

The following points summarise how CGI works

� A browser requests a CGI program by specifying the CGI program’s URL. The

request arises as the result of the user submitting a form or clicking a link. The browser

may insert into the URL a query string or extra path information

� When a Web server receives a URL request it determines whether the URL refers

to CGI program, Most Web servers identify CGI programs by the path in which they are


11

located or by the file name extensions. For example, all files in the path /cgi-bin/ or with

the extensions .CGI or .PL could be CGI programs.

� When a Web server identifies a request for a CGI program it executes the CGI

program as a separate process and passes any data included in the URL of the program.

� The CGI program performs its processing and then returns its output to the Web

server. The conventions defined by the CGI specification determine how CGI programs

receive data from and return data to Web servers.

Getting Data from the Web Server

When a CGI program is executed, one of its first tasks is to determine what data

was passed to it by the Web Server. This data may be passed in the following ways:

� Command-line Arguments

� Environment Variables

� The program’s standard input stream

Command-line arguments and the standard input stream are supported by almost

all programming languages. Environment variables are less commonly used outside the

Web applications.


12

Environment Variables

Environment Variables are the primary mechanism by which web servers

communicate with CGI programs. All CGI programs can receive data from Web Servers

via environment variables.

Environment variables are variables that are external to a program’s execution.

They are used to define the environment in which a program executes. The following

table identifies some commonly used environment variables defined by CGI version 1.1.

Environment Variable Description

AUTH_TYPE The authentication scheme used to validate the user

requesting access to a Web page.

CONTENT_LENGTH The number of characters that have been passed via

standard input.

CONTENT_TYPE The MIME type associated with the data variable via

standard input

PATH_INFO The extra path information added to the URL of the

CGI program


13

PATH_TRANSLATED The full path name that was translated from the URL

by the Web server.

QUERY_STRING The query string portion of the URL.

REMOTE_ADDR The IP address of the host associated with the

requesting browser

REMOTE_HOST The name of the host associated with the requesting

browser.

REMOTE_USER The name of the user associated with the requesting

browser.

REQUEST_METHOD The method associated with the browser request:

GET, POST, HEAD and so on.

SCRIPT_NAME The path and name of the CGI program.

SERVER_NAME The name of the Web server host.

SERVER_PORT The HTTP port number (usually 80) used by the

Web server.

SERVER_PROTOCOL The name and version of the protocol used by the

requesting browser to submit the request.

These environment variables are available to all CGI programs regardless of

whether the CGI program was executed as the result of a command line argument based

query, a form submission, or the clicking of a hyperlink. Many programming languages

provide special mechanisms for accessing environment variables. For example, C

provides the getenv( ) library function and Perl provides the $ENV array.

Reading Query String Data

When data is passed to a CGI program via the QUERY_STRING environment

variable, the data is encoded using the following conventions. These coding conventions

are referred to as URL coding.


14

� Spaces are replaced by plus (+) signs.

� Other characters may be replaced by character codes of the form %xx (with the

xx being replaced by two hexadecimal digits). For example, %2a is used to encode a plus

sign.

CGI programs must decode the data passed via the QUERY_STRING variable.

This is accomplished by replacing plus signs with spaces, and sequences of the form %xx

with their character equivalent. This decoding is known as URL decoding.

Sending Data back to the Web Server

A CGI program returns data to the requesting browser via the Web server. In all

cases, it returns the data by writing it to the standard output stream. The output of the

CGI program must begin with a header line, followed by a blank line, and ten by the data

to be displayed by the browser. The header line usually consists of a Content-type

header that specifies the MIME type of the data returned by the CGI program. In most

cases, the MIME type will be text/html, as shown in the following example.

Content type: text/html

<HTML>

<HEAD>

<TITLE>Online Device Controller-- Request Confirmation

</TITLE>

</HEAD>

<BODY>

<H1>Hi Your request has been processed. Please wait for the Control Menu

to load in a few seconds….

</H1>

</BODY>

</HTML>


15

Parallel Port Basics

A PC Parallel Port (Printer Port) is an inexpensive and yet powerful platform for

implementing projects dealing with the control of real world peripherals. The printer

port provides eight TTL outputs, five inputs and four bidirectional leads and it provides a

very simple means to use the PC interrupt structure.

The Parallel Port is the most commonly used port for interfacing home made

projects. This port will allow the input of up to 9 bits or the output of 12 bits at any one

given time, thus requiring minimal external circuitry to implement many simpler tasks.

The port is composed of 4 control lines, 5 status lines and 8 data lines. It's found

commonly on the back of the PC as a D-Type 25 Pin female connector. There may also

be a D-Type 25 pin male connector. This will be a serial RS-232 port and thus, is a totally

incompatible port.

Newer Parallel Port’s are standardized under the IEEE 1284 standard first

released in 1994. This standard defines 5 modes of operation, which are as follows,

1. Compatibility Mode.

2. Nibble Mode.

3. Byte Mode.

4. EPP Mode (Enhanced Parallel Port).

5. ECP Mode (Extended Capabilities Port).

The most widely used mode is the Compatibility mode or "Centronics Mode" as it

is commonly known, which can only send data in the forward direction at a typical speed

of 50 Kbytes per second but can be as high as 150+ Kbytes a second.


16

Port Assignments

Each printer port consists of three port addresses; Data, Status and Control port.

These addresses are in sequential order. That is, if the Data port is at address 0x0378, the

corresponding Status port is at 0x0379 and the Control port is at 0x037A.

Address Notes

3BCh – 3BFh

Used for parallel ports which were incorporated into video cards and now, commonly an option for Ports controlled by BIOS. – Doesn’t support ECP addresses.

378h – 37Fh Usual Address for LPT 1 278h – 27Fh Usual Address for LPT 2

Port Addresses

Please refer to the figures titled Pin Assignments and Port Assignments. These

two figures illustrate the pin assignments on the 25-pin connector and the bit assignments

on the three ports.

Hardware Properties

The "Pin Outs" of the D-Type 25 Pin connector and the Centronics 34 Pin

connector are as shown in the table. The D-Type 25 pin connector is the most common

connector found on the Parallel Port of the computer, while the Centronics Connector is

commonly found on printers.

The IEEE 1284 standard however specifies 3 different connectors for use with the

Parallel Port. The first one, 1284 Type A is the D-Type 25 connector found on the back

of most computers. The 2nd is the 1284 Type B which is the 36 pin Centronics Connector

found on most printers. IEEE 1284 Type C however, is a 36 conductor connector like the

Centronics, but smaller. This connector is claimed to have a better clip latch, better


17

electrical properties and is easier to assemble. 1284 Type C connectors are yet to be

implemented in present day applications.

Pin No (D-Type 25)

Pin No (Centronics)

SPP Signal Direction In/Out

Register Hardware Inverted

1 1 nStrobe In/Out Control Yes 2 2 Data 0 Out Data 3 3 Data 1 Out Data 4 4 Data 2 Out Data 5 5 Data 3 Out Data 6 6 Data 4 Out Data 7 7 Data 5 Out Data 8 8 Data 6 Out Data 9 9 Data 7 Out Data 10 10 nAck In Status 11 11 Busy In Status Yes 12 12 Paper-Out

Paper End In Status

13 13 Select In Status 14 14 nAuto-Linefeed In/Out Control Yes 15 32 nError/ nFault In Status 16 31 nInitialise In/Out Control 17 36 nSelect-Printer

nSelect-In In/Out Control Yes

18 - 25 19 - 30 Ground GND

Pin Assignments of the D-Type 25 Pin Parallel Port Connector Software Registers - Standard Parallel Port (SPP)

Port Assignments


18

The base address, usually called the Data Port or Data Register is simply used for

outputting data on the Parallel Port's data lines (Pins 2-9). This register is normally a

write only port. If we read from the port, we should get the last byte sent. However if the

port is bi-directional, then Read and Write Operations can be performed on the Data

Register and we can receive data on this address.

The Status Port (Base address + 1) is a read only port. Any data written to this

port will be ignored. The Status Port is made up of 5 input lines (Pins 10,11,12,13 & 15),

an IRQ status bit and two reserved bits. There are five status leads from the printer.

(BUSY, /ACK, PE (Paper Empty), SELECT, /ERROR). These are available at the 5 most

significant bits of the Status port. Of these, the BUSY pin is hardware-inverted and

typically this bit is inverted in the software application program to comply with the “True

Positive Logic”.

The Control Port (Base address + 2) was intended as a write only port. When a

printer is attached to the Parallel Port, four "controls" are used. These are Strobe, Auto

Linefeed, Initialize and Select Printer, all of which are inverted except Initialize.

However these four outputs can also be used for inputs. If the computer has placed a pin

high (e.g. +5v) and the device wanted to take it low, we would effectively short out the

port, causing a conflict on that pin. Therefore these lines are "open collector" outputs (or

open drain for CMOS devices). This means that it has two states: - a low state (0 V) and a

high impedance state (open circuit).

Normally the Printer Card will have internal pull-up resistors, but as we expect,

not all will. Some may just have open collector outputs, while others may even have

normal totem pole outputs. In order to make the device work correctly on as many Printer

Ports as possible, we can use an external resistor as well. If there is already an internal

resistor, then it will act in Parallel with it, or if they are Totem pole outputs, the resistor

will act as a load. An external 4.7k resistor can be used to pull the pin high.


19

The 4 pins of the Control Port can be used for bi-directional data transfer.

However the Control Port must be set to xxxx0100 to be able to read data, that is all pins

to be +5v at the port so that it can be pulled down to GND (logic 0). Bits 4 & 5 are

internal controls. Bit 4 will enable the IRQ. In the Standard & Bi-directional (SPP) Mode

of the Parallel port, Bit 5 will enable the Bi-directional port. In this case, we can use the 8

Data bits (DATA0-7) for input also. This mode is only possible if the card of the PC

supports the feature. Bits 6 & 7 are reserved.

At a minimum, there are 12 outputs; eight on the Data Port and four on the lower

nibble of the Control Port. There are five inputs, on the highest five bits of the Status

Port. Three output bits on the Control Port and one input on the Status Port are inverted

by the hardware, but this is easily handled by using the Exclusive-OR function to

selectively invert bits.

Using the Parallel Port's IRQ

A hardware interrupt is a capability where a hardware event causes the software

to stop whatever it is doing and to be redirected to a function to handle the interrupt.

When done, the program picks up where it left off. Aside from losing time in executing

the interrupt service routine, the operation of the main program remains unaffected by the

interrupt. Interrupts are good when interfacing monitoring devices where we don't know

when it is going to be activated. Indeed, it's more efficient to have an interrupt request

rather than have the software poll the ports regularly to see if something has changed.

The same technique may be adapted to exerting interrupts directly on the ISA bus.

The Parallel Port's interrupt request is normally IRQ5 or IRQ7 but may be

something else if these are in use. It may also be possible that the interrupts are totally

disabled on the card, if the card was only used for printing. The Parallel Port interrupt can

be disabled and enabled using bit 4 of the control register, Enable IRQ Via Ack Line.


20

Once enabled, an interrupt will occur upon a low to high transition (rising edge) of the

/ACK.

Interrupt Handler Table

The original 8088 PC design provided for up to 256 interrupts (0x00 - 0xff). This

includes both hardware and software interrupts. Each of these 256 interrupt types has four

bytes in a table beginning at memory location 0x00000. These 1024 bytes (256x4)

constitute the Interrupt Vector Table. These four bytes contain the address of where the

PC is to go to when an interrupt occurs. Most of the table is loaded when we boot up the

machine. The table may be added to or entries modified when various applications are

run.

The eight hardware interrupts beginning at INT 0x08 were reserved by IBM for

interrupt expansion, commonly known as IRQ0 - IRQ7; IRQ 0 corresponds to INT 8;

IRQ 1 corresponds to INT 9, etc. Typically, the Parallel Port uses the Interrupt Request

IRQ7.

Modifying the Interrupt Handler Table

Assume, we are going to use IRQ 7. When an IRQ 7 interrupt occurs, our

program must proceed to our Interrupt Service Routine, a function that we define. For

this, we must first modify the interrupt handler table. Initially we must read the present

value in the table, save it, perform the required operations and restore the original value

when our ISR terminates.

Masking

The programmer can mask or temporarily disable specific interrupts. In the

present context, we must set the interrupt mask such that IRQ 7 is enabled. Port 0x21 is

associated with the interrupt mask. To enable a particular IRQ (say, IRQ 7), write a zero

to that bit location. However, the other bits must not be altered. Prior to exiting from the


21

program, the user should return the system to its original state; by setting the altered bit

(bit 7) of the interrupt mask to logic one and restoring the interrupt vector.

If the IRQ Enable output is at logic one, an interrupt occurs on a negative going

transition on the /ACK input. Thus, in addition to setting the mask to entertain interrupts

from IRQ 7, we must also set IRQ Enable to a logic one.

Interrupt Service Routine

� Disable any further interrupts.

� Set Interrupt Mask to disable IRQ 7 interrupts.

� Set a variable such that in returning to the main program there is an indication that an interrupt has occurred.

� Indicate to the PC that the interrupt was processed

� Enable all interrupts.

� Execute the required tasks of the ISR

� Disable all interrupts

� Set Interrupt Mask to enable IRQ 7 interrupts.

� Enable all interrupts.


22

DTMF Dialing System

To speed up the dialing procedure and to make it more reliable, the DTMF dialing

system is used. In this system, digits are transmitted as two tones simultaneously. This

explains the name "Dual Tone Multi Frequency". It is also known as DTMF dialing or mf

dialing. The tone frequencies are selected to avoid harmonic interference from speech

signals. There are eight frequencies defined in the DTMF system: four in a low frequency

group (679-941 Hz) and four in a high frequency group (1209-1633Hz).

A valid digit is defined as one of the low frequency group together with one tone

out of the high frequency group. In total, there are sixteen combinations possible but we

use only the digits 0-9. The maximum dialing speed with a DTMF system is typically 7

digits per second, i.e., a tone burst of 70 ms. With the pulse dialing system, the speed

varies between 1.1 to 0.56 digits per second. The DTMF is therefore ten times faster. The

major application for DTMF is low speed data transfer.

Generation of DTMF

1209 Hz 1336 Hz 1477 Hz 1633 Hz

697 Hz

1 2 3 A

770 Hz 4 5 6 B

852 Hz 7 8 9 C

941 Hz * 0 # D


23

Two tunable oscillators, one for the low frequency group and one for the high

frequency group can be used to generate DTMF tones as shown in the figure above.

However, due to accurate frequency demand, ICs were put together with a crystal

oscillator and two synthesisers, which generate the DTMF tone digitally. Although, it

cannot synthesize the exact DTMF frequency, an inexpensive crystal has turned out to be

the most popular type of DTMF synthesizer clock that generates a frequency of

3579545Hz and can be divided down to the DTMF frequencies with only a small error.

Tone Details The exchange will use standard DTMF frequencies for the calling number on the

line. The duration of the digit shall be 50 ms each.

Interface to the Telephone Line

The DTMF tones generated by the DTMF dialer must applied to the telephone

line respecting the AAC and DC requirements of the PTT. Most bipolar DTMF dialers

incorporate an on chip line interface. This approach results in very simple and efficient

circuit designs. The DTMF dialer is powered from the speech circuit peripheral supply

point. The DTMF tones are transmitted to the telephone line via the speech circuit line

interface. The mute signal generated by the DTMF dialer, controls the speech circuit and

determines when to transmit speech and DTMF signals. The switch over from speech

mode to dialing mode can be realized without noticeable audible clicks.

If the speech circuit passes part of the signals on its DTMF input to the earpiece

output, a confidence tone will be introduced. This approach is called the common line

interface architecture because both the speech and dialing parts of telephone are

connected to the by the same interface. If an appropriate speech circuit is not available for

interfacing the CMOS DTMF dialer to the telephone line, a separate line interface for the

dialer must be used. This requires a large number of discrete components.


24

Microcontrollers

The Microcontroller is another branch in the evolution of microprocessor

technology. Instead of focusing upon larger word widths & address space, the emphasis

here has been upon exceedingly fast real-time control. It has focused upon the integration

of the facilities needed to support fast control into a single chip. Its on chip resources

provide an integrated approach to a variety of real-time control tasks.

Features

The MCS51 architecture consists, of the following features:

� Eight-bit CPU with registers A (Accumulator) and B

� Sixteen-bit Program Counter (PC) and Data Pointer (DPTR)

� Eight-bit Program Status Word (PSW)

� Eight-bit Stack Pointer (SP)

� Internal ROM (8051) or EPROM (8751) or EEPROM (8951)

� Internal RAM of 128 bytes

o Four Register Banks each containing eight registers

o Sixteen bytes, which may be addressed at the bit level

o Eighty bytes of general-purpose data memory

� Thirty-two input/output pins arranged as four 8-bit Ports: P0-P3

� Two 16-bit Timer/Counters: T0 and T1

� Full duplex Serial Data Receiver/Transmitter: SBUF

� Control registers: TCON, TMOD, SCON, PCON, IP, and IE

� Two external and three Interrupt sources

� Oscillator and Clock circuits


25

Programming Model

The programming model of the MCS51 shows the MCS51 as a

collection of 8 bit and 16 bit registers and 8 bit memory locations. These registers and

memory locations can be made to operate using the software instructions that are

incorporated as part of the design. The program instructions have to do with the control

of the registers and digital data paths that are physically contained inside the

Microcontroller, as well as memory locations that are physically outside the

Microcontroller. To make a Microcomputer a Microcontroller, several special function

registers must be present. Each register, with the exception of the Program Counter, has

an internal 1-byte address assigned to it. Some registers are both byte addressable and bit

addressable. That is, the entire byte of data at such register addresses may be read or

altered, or individual bits may be read or altered. Software instructions are generally able

to specify a register by its address, its symbolic name, or both.

The 8951 Microcontroller The 8951 is a second-generation Microcontroller belonging to the MCS51 family.

Compared to its predecessors, the 8951 provides a significantly more powerful

architecture, a more powerful instruction set, a full serial port and 4KB of internal

EEPROM. Some key product features include sophisticated I/O port capability, 4KB of

EEPROM, 128 bytes of internal RAM, two 16-bit Counter-Timers. Because all these I/O

devices are fabricated within the 8951, they form part of the programming model. The

8951 has an 8-bit ALU. It has 32 I/O lines organised as four 8-bit I/O ports. The 8951 can

also address external memory if there is not enough internal RAM or ROM. When used

to address external memory, two ports provide the memory addressing and data lines.


26

The Triac

The Triac is a three terminal, gated npnp device for controlling ac current in either

direction. Originally designated as a bi-directional triode thyristor, it is more commonly

referred to as Triode ac semiconductor (TRIAC).

Either positive or negative gate signals may be used to trigger the Triac into

conduction. This characteristic helps to simplify circuit design. The load or main current

terminals are designated as MT1 and MT2. Usually, MT1 is taken as the point of

reference for voltage and current measurements made and the gate terminal. Maximum

current and offset voltage ratings are of the order of 40 A and 800 V, respectively.

Theory of Operation

The n and p semiconductor sections between MT1 and MT2 can be considered as

parallel npnp and pnpn switches. The Triac is similar to connecting two SCRs in parallel

for bi-directional, or full wave, current conduction. The primary difference between

parallel SCRs and the equivalent switching sections of the Triac lies in the gate structure

and trigger methods.

The Triac can be switched to conduction either by gate triggering or by two other

operating conditions- exceeding the break over voltage rating, or a sharp rise in off-state

voltage. These methods of conduction are not employed in normal Triac operation but

they may be considered as limiting factors in circuit design. As a result, Triacs switched

to conduction by either of these mechanisms will not be damaged, since the Triac merely

switches to the on-state condition. In general, the Triac requires no external over voltage

protection.

However, a snubber network, consisting of a series resistor and capacitor

connected across the MT1 and MT2 terminals, can be used to protect a Triac from sharp


27

increases in the off-state voltage. The charging capacitor momentarily places the voltage

across the resistor and the energy contained in the sharply rising portion of the voltage

waveform is dissipated in the resistor. Snubber circuit can also protect the Triac against

voltage transients, which exceed the break over voltage level. The design of snubber

circuits must take into account peak line voltages, load characteristics, and time constant

of the RC network must be small when compared to the ac load conduction time.

Triac Turn On Methods

Triacs may be triggered into conduction by a variety if methods. The particular

application will generally dictate the method if triggering to be employed. The gate

circuits can be designed for static, zero voltage, or phase switching techniques. Each

method offers specific advantages and disadvantages.

Static Switching

Triacs employed in static switching circuits offer many advantages over

mechanical switching using relays or manually operated switches. This electronic

switching eliminates arcing and contact bounce, both of which are problems with moving

physical contacts. These factors result in more reliable operation and virtual elimination of

RFI. A resistor is connected to the gate circuit to limit the gate current and is about 100

ohms.

Zero-Voltage Switching During zero voltage switching, the Triac conducts for virtually 360° of each cycle,

and full power is delivered to the load. The Triac is triggered at approximately the 0 and

180 degree points in the ac cycle. During power off periods, the Triac is held in a non-

conducting state. The ratio of power-on to power-off intervals determines the average

power applied to the load. The power-control time base may consist of intervals of 30 ac


28

cycles (one half second). If the Triac is switched on for 15 full cycles during each one-

half-second interval, the average power being applied to the load is one-half of full power.

Triac zero crossing switching circuits are used in industrial control and related

applications. Like static switching, zero crossing power switching systems are virtually

free of radio frequency interference problems. Another important advantage is the inherent

differential control capability that exists when gradual changes in average power can be

applied to a load.

Phase Control Switching

Triac phase-controlled gate circuits allow conduction of load current during a

specified portion of each ac half cycle. Simple resistive gate switching circuits can be

employed to trigger the Triac for firing angles up to 90 degree in each half cycle.

Resistance-capacitance phase shifting networks are used to delay the firing angle up to

nearly 180-degree.

The performance of phase controlled gate trigger circuits can be greatly improved

by the use of a trigger device. For low voltage levels, the trigger device exhibits high

impedance. Except for a small leakage current, no gate signal is presented to the Triac

during this time. When the applied voltage is increased to the break over level, the trigger

device suddenly latches into conduction. This presents a fast rising trigger signal to the

Triac, resulting in reliable turn on of load current.

Common trigger devices in use today are the diac, unijunction transistors (UJTs)

and special two-transistor configurations usually fabricated as one integrated circuit.


29

The Project

The Project


30

Block Diagram


31

Hardware Details

The Hardware unit of the system includes the following sections:

1. Microcontroller Card

2. DTMF Decoder Card

3. Relay Based ON/OFF Control Card

4. Triac Based Intensity Control Card

5. Status Reading Card

6. Power Supply Card

Microcontroller Card The Microcontroller Card is the most important section of the ‘Online Device

Controller’ Hardware. This card is designed so as to provide the facility to control

ON/OFF devices and Intensity Variable loads. This Card is divided into the following

sub-sections: Parallel Port Input, DTMF Decoder Input, a 4-to-16 Decoder, NOT Gates

and Connector for interfacing different Loads.

The Microcontroller used is Atmel 89C51. The connections to the various Port

pins of the Microcontroller are as mentioned below:

P1.0 to P1.7 – Input Port connected to the Data bits of the Parallel Port

P2.0 to P2.3 – Input Port connected to the BCD Output of DTMF Decoder

P3.2 – /INT0 Interrupt connected to /STROBE pin (Pin 1) of the PC Parallel Port

P3.3 – /INT1 Interrupt connected to the Zero Crossing Detector circuit Output

P0.4 to P0.7 – Outputs the 4-bit ON/OFF Device Code to the 4-to-16 Decoder

P3.1 –The gate firing pulse for the Triac.

The Delayed Steering Output (Pin 15) of the DTMF Decoder (MM 8870) is used

to Interrupt the PC (IRQ 7) through Pin 10 of the Parallel Port.


32

DTMF Decoder Card This Card makes possible the control of Load through the Cordless Phone. This

card includes the DTMF Decoder IC (MM 8870), and a Buffer IC (7407).

The DTMF Decoder IC receives the tone input from the Telephone Line

connected to the Telephone Exchange from the Base Unit of the Cordless Phone. For

each key pressed, the DTMF tone produced is decoded to the corresponding 4-bit BCD

Code by IC MM 8870. The reception of a valid DTMF tone generates a pulse at the Pin

15 of this IC, which is used to interrupt the PC through the Parallel Port pin 10 (/ACK).

Pin 11-14: 4-bit BCD Output

Pin 15: Delayed Steering Output

A 7407 Buffer IC is also used to drive the Decoder output before sending it to the

Microcontroller Input Port.

Relay Based ON/OFF Control Card This Card includes a D Flip-Flop (CD 4013), Optocoupler (MCT2E), Relay

Driver Circuit and a 12 V single-pole Relay.

The D Flip-Flop is wired as a Toggle Flip-Flop, the output of which toggles for

every rising edge of its Clock input received from the Microcontroller Card. The MCT2E

provides electrical isolation. Each time the device is selected by the Microcontroller, the

Load (say, a Bulb) connected to the Relay toggles between ON and OFF states.

Triac Based Intensity Control Card The Triac Based Intensity Control Card consists of the Zero Crossing Detector

Circuit and the Triac Based Intensity Control circuit. The Zero Crossing circuit provides

the reference signal for the MCU for generating firing pulses. It includes an Opamp

Comparator receiving 12 V AC supply and a 555 Timer IC wired as a Monoshot. The

Triac circuit makes use of MOC 3021, an opto-isolated Triac Driver IC which is

connected to the gate of the Triac. The variation in Firing Pulses generated by the MCU,


33

at the Triac Gate results in proportional Intensity variation at the Load connected to the

Triac.

Status Reading Card

The Status Reading Circuit consists of a Current Transformer, which senses the

current through the Load circuit. The CT produces a very low voltage which is amplified

using an Opamp amplifier (µA 741) and after opto isolation through an MCT2E, is fed to

the PC parallel port input pin. This circuit can sense whether the Load is On or OFF.

Power Supply Card The Power Supply Card provides the necessary DC voltages +5V, +12V and -12V

required to power the various Cards used in the entire Hardware. This uses a Centre-

Tapped Transformer (230/12-0-12). The Power Supply Card uses 7805, 7812 and 7912

Voltage Regulator ICs for proper regulation.

To ensure extremely good electrical isolation by the Opto couplers used, the

Hardware unit comprises of two similar Power Supply Cards fed by the two secondary of

the Transformer.


34

Software Details

The ‘Online Device Controller’ software section mainly comprises the Web

Server Interface software (using CGI) and the Microcontroller programs.

Web Interface

This includes the interface between the hardware to the Internet. This is accomplished by

running a Web Server in a dedicated computer, the parallel port of which is connected to

the ‘Online Device Controller’ Hardware unit. The Web server running is used to execute

CGI programs. The Web server serves the homepage of the ‘Online Device Controller’

Website, when a remote browser requests the homepage at the given URL or IP address.

Initially, a username-password check is done and on success, the present status of devices

is available on the Web page as a Control Menu. In the Control Menu, the user can

change the status of the appliances as desired. The new control information is sent to the

Web server using a GET method, the Web Server passes this information to the CGI

program in the CGI-BIN directory, which checks the present status of devices read

through the Parallel port with the new control signal received, and outputs an appropriate

byte at the Parallel port, after interrupting the 8951 MCU. After a short delay, the new

status of devices is again read and the response is sent back to the Web Browser.

At present, we are offering the Web Interface software that runs on Windows 9x

platform. For this, we used Xitami, a commonly available Web Server for Windows

platform. The CGI programs were coded in the ‘C’ language and the Web pages were

designed using an HTML authoring tool.

Microcontroller Programs

The Microcontroller programs are used to manage the Hardware unit of the

‘Online Device Controller’. Written in the 8051 Assembly language, this includes the

programs to initiliase the Microcontroller, External Interrupt Service Routines, and

programs for timing and firing pulse generation.


35

Flow Charts

CGI Program N y

Read the CGI Environment

Read the Present Status of Devices

from Parallel Port

Store the requested lamp and Fan Modes

Decode Query-String

Interrupt the 8951 MCU and output the

new Fan Mode through Parallel Port

Is Lamp mode

requested = Status Read

Interrupt 8951 MCU and O/P Data

through Parallel Port

C


36

MCU Main Program

Read the Present Status of Devices

C

Send valid HTTP Response Header and new Device Status to

the Web Browser

End

Insert Delay

Start

Initialize SP Timers, Interrupt Fan Mode Register

8951 Enters into a wait loop, ready to accept interrupts


37

Parallel Port Interrupt Service Routine (/INT 0)


38

N N N N N Y Y Y Y Y

Phone

Initialize Port 2 and Read 4 Bit BCD Code from DTMF Decoder

Store 4 Bit BCD Code in R5

Is R5=1

Output Data to Port 0

Is R5=4

Is R5=3

Is R5=2

Is R5=5

Set Fan Mode to 0

Set Fan Mode to 1

Set Fan Mode to 2

Set Fan Mode to 3

Reti


39

N N N N

Y Y Y Y Timer 0 Interrupt Service Routine

Fan

Select Lower 3 bits for Mode

Selection

Is A=00h

Is A=01h

Is A=03h

Is A=02h

Set Fan Mode (R6) to 0




Reti

Timer 0

Clear P3.1

Stop Timer 0

Reti


40

Zero Crossing Detector Interrupt Service Routine (/INT 1) N N N N Y Y Y Y

Y

ZCD

Is Fan

Mode =0

Is Fan

Mode =1

Is Fan

Mode =2

Is Fan

Mode =3

Set P3.1 Set P3.1 Set P3.1

Initialize Timer 0 to Mode 1



Loads Count EC78h for a delay of 5ms

Loads Count D120h for a

delay of 12ms

Loads Count BFC8h for a delay of 19ms

Clears Overflow Flag, Start Timer



Reti

Clear P3.1


41

Working of the System

A typical scheme of the working of the system can be described as follows.

A remote user can log in from any location in the world to the homepage of the

Web server through the Internet/Intranet via a Web Browser. This request is processed by

the CGI and after security check, the user is presented with the current status of

equipments. Now he can control the equipments as required and he can send the

information through a form or menu. According to the control information received, the

CGI executes the required programs to read/write data to the parallel port (LPT1).

Local control is made possible with a Cordless telephone. The PC and phone

produces their own interrupts. When a key on the keypad is pressed, the arrival of a new

valid DTMF tone will interrupt the PC using the PC Parallel port (using IRQ 7). The

DTMF tone generated from the telephone line is decoded by the DTMF Decoder which

produces the corresponding 4 bit BCD code output which is read by the Microcontroller.

The Microcontroller 89C51 reads the appropriate control signal when interrupted by the

PC (through /INT0 pin of the Microcontroller). This is processed and is sent to the output

port, and to the devices. ON/OFF devices are controlled through the Relay Based Control

circuit and Intensity Variable Loads are controlled via the Triac Based Circuit. The firing

pulse for the Triac is generated by the 8951. To synchronize the firing pulse with the AC

cycle, a Zero Crossing Detector circuit is also used which is connected to another

interrupt pin (/INT1) of the Microcontroller.

After executing the control signals, the actual status of the equipments are read by

sensing the load current by means of a Current Transformer, is fed back through Status

Reading circuit and is read through the input pins of the PC Parallel Port.

Finally, the remote user will receive back the confirmation message that the status

of the devices has been changed as per the control signal sent by him. This completes the

cycle of events.


42

Result and Discussion

Through this project, the ‘Online Device Controller’ we are sure that we have

been able to accomplish a good task, something which will be useful to the society as a

whole. In fact, right from the design to the final implementation, we had gone through

several steps, and each of these was completed satisfactorily. After the initial design of

the circuits, these were assembled on the Breadboard and verified at the labs. The

Microcontroller program was developed using a software simulator, the Acebus 8051

IDE and the program was loaded into the Microcontroller EPROM. The Web Interface

software and DTMF Interrupt Service software were coded in C and were thoroughly

verified. The PCBs for the circuits were designed and etched. A user friendly and

pleasing Front Panel and Cabinet was designed and obtained. The entire hardware was

assembled. The software was checked on real time and the entire system was again

verified. The final product the ‘Online Device Controller’ is thus made available as a

finished product. The approximate cost of the entire product (on developmental stage) is

Rs.3000/-.


43

Conclusion and Future Scope Thus, the ‘Online Device Controller (ODC) as implemented through our project

has emerged as a valuable product useful for several applications, ranging from Industrial

Control applications to Office Administration and even for domestic purposes. In this

world of Convergence, where everything from Cell phones to Palmtops meet the Internet,

we feel proud that our project has added a small drop to a big ocean.

The present system is presented as a general purpose one and can be enhanced by

adding several other features specific and relevant to the environment where it is to be

installed. This will bring greater and efficient utilization of the system. The project can be

very well implemented in Industrial applications if slightly more complicated Status

Reading Circuit and Automatic Control Loop is added. A Telephone based control from

Remote locations is also feasible with slight additions in hardware and software.

The possibilities offered by this system for the future, is limited only by one’s

imagination. The day is not a distant one, when all devices around us will get linked to

the Internet and that’s exactly what we are trying to prove through this project. Imagine

controlling all the gadgets of your home from any corner of the world, or switching off

the fan above your Office desk, even while you are on a flight to New York….


44

References

Books

[1] Perl, CGI, and JavaScript Complete, BPB Publications, New Delhi, 2000 [2] Manger, Jason J., The World Wide Web, Mosaic and More, 1994 [3] Ayala, Kenneth J., The 8051 Microcontroller: Architecture, Programming

& Applications, Penram International Publishing (India), Mumbai, 1996 Websites

[1] http://www.us-epanorama.net [2] http://www.8052.com [3] http://www.w3.org [4] http://www.apache.org [5] http://www.intel.com [6] http://www.acebus.com [7] http://www.google.com

Online Device Controller[1]

Documents

Transcript of Online Device Controller[1]