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1.INTRODUCTION TO DEVICE CONTROLLING USING PARALLEL PORTOur project aim is to control turning on and off any device or machinery using pc. The

device is electrically isolated from the PC using optocouplers. So, any variation in the load

circuit does not affect the controlling circuit. Hence, it is a safe way to control the output. As ther

are 8 bits, 8 devices can be controlled easily however with decoding 128 devices can be

controlled.

Parallel port communication is used to control the devices. A parallel port is a type of

interface found on computers (personal and otherwise) for connecting various peripherals. In

computing, a parallel port is a parallel communication physical interface. It is also known as a

printer port or Centronics port. The IEEE 1284 standard defines the bi-directional version of the

port, which allows the transmission and reception of data bits at the same time. Generally

parallel port is used for Printers. The same protocol is used here to send command from the PC.

An easy to use VB6 (Visual BASIC 6) program with a GUI (Graphical User Interface) is

provided for controlling the devices. BASIC stands for Beginners All purpose Symbolic

Instruction Code. A DLL (Dynamic Linked Library) is used for accessing the parallel port from

the software.

To control the device relays are used. The relays in our project have a rating of 250V AC

and 5 Amps current. So the devices connected must not exceed these rating.

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2. INTRODUCTION TO PARALLEL PORT LPT1The parallel port or line printer terminal (LPT) port is a 25-pin D-type female connector available at

the back of your PC. A basic IBM PC usually comes with one or two LPT ports. The original parallel

port, called standard parallel port (SPP), is a bundle of three ports (or registers), namely, data port, status

port, and control port. Pins 2 through 9 form the 8-bit data port. This port is purely a write-only port. This

means it can be used only to output some data through it. Pins I, 14, 16, and 17 form the control port,

which is capable of reading/writing. Pins 10 through 13 and pin 15 together form the status port. The

status port is a read-only port. The details of 25-pin parallel port are given in following table.

The base address of the first parallel port (LPT1) is 0378 in hexadecimal (hex) notation (or 888 in decimal

notation). The base address of the second parallel port (LPT2) is 0278 in hex. In this project, weve used

only LPT1.

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The pin outs of LPT1 connector is shown below:-

The lines of DB25 connector are divided into three groups:-

1) Data Lines (Data bus)

2) Status Lines

3) Control Lines

As the name refers, data is transferred over data lines, Control lines are used to control the

peripheral and the peripheral returns status signals back to the computer through Status lines.

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3. BLOCK DIAGRAM OF SYSTEM

The block diagram shown below shows the main components of the system for switching

multiple devices using a personal computer. The control command to switch the devices

on/off is given through the keyboard. The software program which can be developed in any

programming language such as VB6, C, C++, VB.net etc. scans the input and, as per the

input command, the data is available at the parallel port.

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4. CIRCUIT DESCRIPTION:

The basic circuit comprises of a Relay, an Opto-coupler IC numbered MCT2E, .

The commands for hardware functioning are given through the keyboard. The commands

after being scanned by the software program result into an appropriate voltage generation for

hardware. In the hardware there are 2 stages mutually connected to each other through the Opto-

coupler. The other end of the Opto-coupler is the output end, which is connected to

ULN2803. This ULN2803 drives relay to control applications.

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5. COMPONENTS

The components used in the hardware circuit are as follows:-

5.1) Opto-Coupler

The Opto-Coupler is an Integrated Circuit. The number of the IC used is MCT2E.

Basically an optocoupler is a combination of a light source and a photosensitive detector. In the

optocoupler, or photon coupled pair, the coupling is achieved by light being generated on

one side of a transparent insulating gap and being detected on the other side of the gap without

an electrical connection between the two sides (except for a minor amount of coupling

capacitance).

The particular MCT2E Opto-Coupler IC is used in this circuit is a 6 pin IC. The ICconsists of a diode at the input side by the pin no. 1 as the anode and the pin no. as the cathode

of the diode. The pin no. 3 is not used and represents no internal interconnection. The other 3

pins of the IC represent the output side of the IC which is a transistor. The pin nos. 4, 5, and 6

represent the emitter, collector, and the base respectively of the transistor. Diagrammatically, the

IC can be viewed as :-

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The Pin-numbering and the corresponding

functions are as follows:

1As an Anode of the diode.

2As a Cathode of the diode.

3No internal connection (not used).

4As an Emitter of the phototransistor.

5As a Collector of the phototransistor.

6As a Base of the phototransistor

Characteristics:

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5.2) Octal High Voltage, High Current Darlington Transistor Arrays

The eight NPN Darlington connected transistors in this family of arrays are ideally suited for

interfacing between low logic level digital circuitry (such as TTL, CMOS or PMOS/NMOS) and

the higher current/voltage requirements of lamps, relays, printer hammers or other similar loads

for a broad range of computer, industrial, and consumer applications. All devices feature open

collector outputs and freewheeling clamp diodes for transient

Suppression.

The ULN2803 is designed to be compatible with standard TTL families while the ULN2804 is

optimized for 6 to 15 volt high level CMOS or PMOS

These Darlington arrays are furnished in 18-pin dual in-line plastic

packages (suffix A) or 18-lead small-outline plastic packages (suffix

LW). All devices are pinned with outputs opposite inputs to

facilitate ease of circuit board layout. Prefix ULN devices are rated

for operation over the temperature range of -20C to +85C; prefixULQ devices are rated for operation to -40C.

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5.3) Relay:

Relay is a circuit used for tripping and switching purposes. Here we have used two types

of relays, which are as follows:-

1-relay (6v, 100ohm, and 1c/o):-Used for signal tripping.

2-relay (6v, 100ohm, and 2c/o):-used for double tripping.

The detection of a fault and disconnection of a fully section or apparatus can be achieved by

using fuses or relays in conjunction with circuit breakers. A fuse performs both detection

and interruption functions automatically but its use is limited for the protection of low voltage

circuits only, for high voltage circuits (say above 3.3kv), relays and circuit breakers are

employed to serve the desired function of the automatic protective gear.

Relay Classification:

Relays have the same subsystem and principles of operation regardless of whether they

are electromechanical or electronic, or designed to switch signal or high power loads.

These principle functions are as follows:

Conversion of an electrical input signal on primary side to an intermediate and non electric

physical signal.

Reconversion of this non electric physical signal to operate a switching element

(secondary side) such as contacts which switch and conduct electrical current (output,

load current).

The use of the non electric signal between primary and secondary side provides the

necessary galvanic separation between input and output circuits.

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6. PCB LAYOUT

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7. SOFTWARE

Before beginning the work on software, there are various points that should be considered. These

points are discussed as follow-

Methodology:To understand the concept of software development, the predefined phases of

the Software Engineering are to be followed. The phases included are as follows:

1). Requirements Analysis

2). Design

3). Coding

4). Testing

To develop software each of the phases of software development model is to be

implemented properly. The work done in various steps are :-

7.1) Requirements Analysis:In this phase the, the focus is basically on the requirements of the project. To

understand the nature of the programs to be built, the software engineer must understand

the information required for the software as well as the required function, behavior,

performance and interface. Firstly the information regarding the project is gathered such as why

the software is needed, how the software will be better than the previous existing one, what

technologies are needs for developing the software etc. The focus is specifically on the

software.

The requirements analysis also suggest that there should also exist some good

facilities for developing an attractive Graphical User Interface (GUI).Besides these things it is

also required that the functionality or the way to use the system should be simple so that a

layman having elementary knowledge can also use it.

For the project under consideration, it is obvious that the internal low-level

interaction with the hardware should be abstracted from the user so as to facilitate the user to

easily handle the system. The best programming language for achieving the hardware

interaction is TURBO C. On the contrary one of the marked languages for developing a good

user interface is the Visual Basic.

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DFD (Data Flow Diagrams)

The data Flow Diagrams

depict the Process Model of the

system. DFD are also known as

"Bubble Chart". They have the

purpose of clarifying system

requirements and identifying major

transformations that will become

programs in system Design.

Following Data Flow Diagrams for

controlling applications using pc:

7.2) Design:

Software design is actually a multi step process in itself. The design process translates

the requirements into a representation of the software that can be assessed for quality before

coding. In simple words the design phase aims at producing a model or representation of an

entity that will later be built.

For the system under consideration the physical specification obtained afteranalyzing the requirements indicate that there is a requirement of a program so as to deal with

the printer port and another program to interact with the user.

7.3) Coding:

The design must be translated into a machine-readable form. The code generation step

performs this task. This phase is the heart of the software development process.

For this project the code that interacts with the hardware that is the back end has been

designed using the programming language VB6.

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7.4) Testing:

This phase is the most important phase as it removes errors and bugs from the software

code. In this phase the tester tests the code listings for errors in order to make the

software error-free. This makes the software more maintainable. Testing is also done to check

whether the software fulfills the user requirements or not. This phase is also essential as

all possible extreme boundary conditions are checked and verified. That is tests are conducted

to uncover errors and ensure that defined input will produce actual results that agree with

required results.

The software to control the devices

from PC has been written in Visual

BASIC 6 (VB6). However, VB6 doesnot allow direct access t o the parallel

port. So, an external software library

which interacts with the parallel port

is used. This is called DLL as it has

already been compiled (i.e. the source

code is not available) and will be

loaded at runtime. It does not comes

with the program written in VB6 but

rather as a separate file. This file

should be present for the program to

run otherwise it will result in a runtime error.

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8. SYSTEM REQUIREMENTS

System Requirements defines the ideal resources required for the efficient working of the application. The system

requirement for this application can be broadly categorized under two headings namely, Hardware Requirements and

Software requirements.

Hardware Requirements:

Processor: Pentium 1/ Pentium II / Pentium III / Pentium IV/and above

Memory : 32 MB Ram (Minimum)

Resolution: 800 x 600 pixels and above

Software Requirements:

Platform : windows 95, 98, NT, Vista, 7

Version above windows 98 doesnt allow direct part access with the parallel port. So we have to

use third party drives, which opens the specific port.One such software is Userport. For software made in VB require inout32.dll file.

Language: VB, C or C++ or VC++.

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9. CONCLUSION

This project allows us to control the devices from PC. We use parallel port for this (also called

LPT1 which is the printer port).. In industries, there is a need for a secure way of controlling a

machine; this project achieves that by providing a PC based device control. In this system,

multiple devices can be controlled from a PC. The device can be anything and is isolated from

the PC and relays by Optocoupler.

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10. FUTURE DEVELOPMENT

The circuit can be extended to control 128 devices. By using micro-controller circuit can be used to control devices by using serial port. Feedback can be taken from the device and displayed. It can be used for industrial automation purpose.

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11. REFERENCES:

Books

Embedded SystemsRaj Kamal8051 Microcontroller and Embedded SystemMazidiMicrocontrollerKenneth Aayla

Websiteswww.8051projects.info

www.electro-tech-online.com