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INTRODUCTION
This project can be used for the controlling of various appliances using PC. It consist a circuit for using the printer port of a PC, for control application using software and some interface hardware. The interface circuit along with the given software can be used with the printer port of any PC for controlling up to eight equipment. Parallel port is a simple and inexpensive tool for building computer controlled devices and projects. The simplicity and ease of programming makes parallel port popular.
SCOPE OF PROJECT
This project can be used in industries as well as in houses to control the various appliances through PC. Devices can be controlled from the desktop while working on it.
DESRIPTION OF PROJECT
BASIC COMPONENTS REQUIRED
1. Personal Computer
2. Optocoupler
3. ULN 2803
4. Electro-mechanical Relay(SPDT)
5. Transformer(15v)
6. Voltage Regulator 78XX
7. Diode(IN4007), Resistors, capacitors
BRIEF INTRODUCTION TO PARALLEL PORT
Hardware
The pin outs of DB25 connector is shown in the picture below:
The lines in DB25 connector are divided into three groups, they are:
1. Data lines (data bus)
2. Control lines
3. Status lines.
As the name refers, data is transferred over data lines. Control lines are used to control the peripheral, and of course, the peripheral returns status signals back to the computer through Status lines. These lines are connected to Data, Control and Status registers internally.
Parallel port registers
The Data, Control and Status lines are connected to there corresponding registers inside the computer. So, by manipulating these registers in program, one can easily read or write to parallel port with programming languages like 'C' and BASIC.
The registers found in a standard parallel port are:
1. Data register
2. Status register
3. Control register
POWER SUPPLY
REGULATOR IC (78XX)
It is a three pin IC used as a voltage regulator. It converts unregulated DC current into regulated DC current.
BRIDGE RECTIFIER
A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.
CIRCUIT DIAGRAM OF POWER SUPPLY
OPTOCOUPLER
There are many situations where signals and data need to be transferred from one subsystem to another within a piece of electronics equipment, or from one piece of
equipment to another, without making a direct ohmic contact electrical connection. Often this is because the source and destination are (or may be at times) at very different voltage levels, like a microprocessor which is operating from 5V DC but being used to control a triac which is switching 240V AC. In such situations the page link between the two must be an isolated one, to protect the microprocessor from over-voltage damage.
HIGH VOLTAGE HIGH CURRENT DARLINGTON TRANSISTOR ARRAY (ULN2803):
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 free wheeling 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