BLOCK

PIC Micro

Controller

LCD 16X2

KEYS

RS 232

PC

R E L A Y

D R I V E R

RELAY RELAY RELAY RELAY RELAY

BUZZER

CT

Power Supply PCBPCB for Relay Driver and RelaysLCDPCB for MicrocontrollerPush Buttons AssemblyPCB for Serial CommunicationIndicatorsBuzzerConnecting wires

A transformer of 0-12V rating is used. It provides a 12 volt supply to the Bridge rectifier.

Bridge rectifier produces a pulsating DC. This rectifier if followed by a filter to smooth

out the ripples present in the output voltage of rectifier.

A fixed positive voltage regulator follows the filter. It outputs +5 volt DC supply to two parallel capacitors.

POWER SUPPLY CIRCUIT

It works as an interface between relays and microcontroller.

Relay driver IC ULN2003 is used.It have 7 switching transistors channels.All transistors are of common emitter type.It have 16 pins• 7 pins for input from microcontroller.• 7 pins for output to relays.• 1 pin for input supply.• 1 pin for GND.

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

Relay is able to control an output circuit of higher power than the input circuit i.e. circuit of 220v ac is controlled by 5v dc.

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact.

When the current to the coil is switched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed position. Usually this is a spring, but gravity is also used. 

A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is prized by engineers because it uses very small amounts of electric power, and is therefore suitable for use in battery-powered electronic devices

LCD can show numbers, letters, words and symbols.

It is more versatile than 7-segment LED display.

It operates on +5v dc supply.It is ideally suited with PIC microcontroller.LCD module have 14 pins• 8 for data lines.• 3 for control lines.• 3 for power lines.

Microcontroller works as the processing and controlling unit of the load manager.

It takes a pre specified value of max. loading condition.

Gets the command from key to turn on a load.Compares the total load connected to the

max. load value.Gives command to relay driver to turn on or

off the relay depending on the comparison.Generally a PIC microcontroller is used for

the purpose of controlling a relay driver.

Here, we are using a PIC16F877A microcontroller.

It is an 8 - Bit microcontroller with operating clock speed of 20 MHz

A crystal oscillator of frequency 20 MHz is used for tuning of microcontroller.

It have 40 pins.Operating clock cycle of

microcontroller is 200ns.

For the communication of microcontroller with PC, we are using a serial communication via RS-232.

RS232 is the most known serial port used in transmitting the data in communication and interface.

This is the most effective method in which the data transmission requires less wires that yields to the less cost.

The RS232 is the communication line which enables the data transmission by only using three wire links that provides ‘transmit’, ‘receive’ and common ground.

RS232 can not be directly connected to the TTL/CMOS based devices. This is done by RS-232 Level Converters.

MAX 232 IC is used as level converter.

MAX 232MAX 232