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MICRO CONTROLLER BASED AUTOMATIC GARDEN IRRIGATION SYSTEM

ABSTRACT

The main aim of this paper is to provide automatic irrigation to the plants which

helps in saving money and water. The entire system is controlled using PIC micro

controller which is programmed as giving the interrupt signal to the sprinkler.

Temperature sensor are connected to internal ports of micro controller, Whenever

there are a change in temperature of the surroundings these sensors senses the

change in temperature and gives an interrupt signal to the micro-controller and thus

the sprinkler is activated.

BLOCK DIAGRAM:

MICRO-CONTROLLER

LCD DISPLAY

LCD

MOTOR DRIVERS

POWERSUPPLY

WATERPUM

PS

TEMPERATURESENSOR

WATER LEVEL SENSOR

HARDWARE USED:

Micro Controller

Motor

Power supply

LCD

Temperature sensor

Water level sensor

CIRCUIT

BR1

C122PF

VI1 VO 3

GN

D2

U17805TR1

12-0-12/1AMPS

D1

LED

R11K

C2

104

RA0/AN02

RA1/AN13

RA2/AN2/VREF-4

RA4/T0CKI6

RA5/AN4/SS7

RE0/AN5/RD8

RE1/AN6/WR9

RE2/AN7/CS10

OSC1/CLKIN13

OSC2/CLKOUT14

RC1/T1OSI/CCP2 16

RC2/CCP1 17

RC3/SCK/SCL 18

RD0/PSP0 19

RD1/PSP1 20

RB7/PGD 40RB6/PGC 39

RB5 38RB4 37

RB3/PGM 36RB2 35RB1 34

RB0/INT 33

RD7/PSP7 30RD6/PSP6 29RD5/PSP5 28RD4/PSP4 27RD3/PSP3 22RD2/PSP2 21

RC7/RX/DT 26RC6/TX/CK 25

RC5/SDO 24RC4/SDI/SDA 23

RA3/AN3/VREF+5

RC0/T1OSO/T1CKI 15

MCLR/Vpp/THV1

U2

PIC16F877

D7

14D

613

D5

12D

411

D3

10D

29

D1

8D

07

E6

RW

5R

S4

VS

S1

VD

D2

VE

E3

LCD1LM016L

10K

PRESET

Q1BC547

R2

1k

R31K

12v

X14MHZ

C5

22PF

C6

22PF

+88.

8

kRPM

C122PF

RV110K

+5V

PROBE

.

27.0

3

1

VOUT 2

U3

LM35

+5V

V1VSINE

POWER SUPPLY

The power supply unit is used to provide a constant 5V of DC supply from a 230V

of AC supply. These 5V DC will acts as power to different standard circuits. It mainly

uses 3 devices

1. Bridge wave rectifier

2. Voltage regulator

Figure 3.1: Block Diagram Of Power Supply

BRIDGE WAVE RECTIFIER

A rectifier is an electrical device that converts alternating current (AC) to direct

current (DC), a process known as rectification. The term rectifier describes a diode that is

being used to convert AC to DC.

A bridge-wave rectifier converts the whole of the input waveform to one of

constant polarity (positive or negative) at its output. Bridge-wave rectifier converts both

polarities of the input waveform to DC (direct current), and is more efficient. However,

in a circuit with a center tapped transformer (9-0-9) is used.

Figure 3.2: Bridge Wave Rectifier

For single-phase AC, if the transformer is center-tapped, then two diodes back-to-

back(i.e. anodes-to-anode or cathode-to-cathode) can form a full-wave rectifier. Many

windings are required on the transformer secondary to obtain the same output voltage.

In this only two diodes are activated at a time i.e. D1 and D3 activate for positive

cycle and D2 and D4 activates for negative half cycle. D2 and D4 convert negative cycle

to positive cycle as it as negative supply and negative cycle as positive cycle at its output.

VOLTAGE REGULATOR

This is most common voltage regulator that is still used in embedded designs. LM7805

voltage regulator is a linear regulator. With proper heat sink these LM78xx types can

handle even more than 1A current. They also have Thermal overload protection, Short

circuit protection.

This will connect at the output of rectifier to get constant Dc supply instead of ripple

voltages. It mainly consists of 3 pins

1. Input voltage

2. Output voltage

3. Ground

The capacitor C2 is used to get thee ripple voltage as input to regulator instead of

full positive cycles.

Vr = I load/Xc

Figure 3.3: Voltage Regulator

For some devices we require 12V/9V/4V Dc supply at that time we go for

7812/7809/7804 regulator instead of 7805 regulator. It also have same feature and pins

has 7805 regulator except output is of 12V/9V/4V instead of 5V.

The general circuit diagram for total power supply to any embedded device is as

shown below.

Figure 3.4: Circuit Diagram Of Power Supply

MICROCONTROLLER

A micro controller is a true computer on a chip. The design incorporates all

the features found in a microprocessor such as CPU, ALU,PC,SP and registers. It

also has some added features needed to make a complete computer ROM, RAM,

parallel I/o, serial I/o, counters and clock circuit.

The prime use of a micro controller is to control the operation of a machine

using a fixed program that is stored in ROM and that does not change over the life

time of the system. The architecture and instruction set of the micro controller are

optimized to handled data in bit and byte size.

The areas if applications of micro controllers include control process,

manufacturing process, medicine, instrumentation etc.

PIC

PIC stands for peripheral interface controller as coined by microchip

technology inc., USA

PIC is a very popular microcontroller world wide

Microchip is the first manufacturer of 8 pin RISC MCU. Microchip is the

world’s second largest chip manufacturer.

Focus on high performance cost-effective, field programmable embedded

control solutions.

Variety of end-user applications-specific standard products(ASSP)

&application specific integrated circuits.

Global network of manufacturing and customer support facilities.

PIN DIAGRAM

ARCHITECTURE

High-Performance RISC CPU:

• Only 35 single-word instructions to learn

• All single-cycle instructions except for program branches, which are

two-cycle

• Operating speed: DC – 20 MHz clock input DC – 200 ns instruction cycle

• Up to 8K x 14 words of Flash Program Memory, Up to 368 x 8 bytes of

Data Memory (RAM), Up to 256 x 8 bytes of EEPROM Data Memory

• Pinout compatible to other 28-pin or 40/44-pin PIC16CXXX and

PIC16FXXX microcontrollers

Analog Features:

• 10-bit, up to 8-channel Analog-to-Digital Converter (A/D)

• Brown-out Reset (BOR)

• Analog Comparator module with:

- Two analog comparators

- Programmable on-chip voltage reference (VREF) module

- Programmable input multiplexing from device inputs and internal voltage

reference

- Comparator outputs are externally accessible

Peripheral Features:

• Timer0: 8-bit timer/counter with 8-bit prescaler

• Timer1: 16-bit timer/counter with prescaler, can be incremented during

Sleep via external crystal/clock

• Timer2: 8-bit timer/counter with 8-bit period register, prescaler and

postscaler

• Two Capture, Compare, PWM modules

- Capture is 16-bit, max. resolution is 12.5 ns

- Compare is 16-bit, max. resolution is 200 ns

- PWM max. resolution is 10-bit

• Synchronous Serial Port (SSP) with SPI™ (Master mode) and I2C™

(Master/Slave)

• Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI)

with 9-bit address detection

• Parallel Slave Port (PSP) – 8 bits wide with external RD, WR and CS

controls (40/44-pin only)

• Brown-out detection circuitry for Brown-out Reset (BOR)

Special Microcontroller Features:

• 100,000 erase/write cycle Enhanced Flash program memory typical

• 1,000,000 erase/write cycle Data EEPROM memory typical

• Data EEPROM Retention > 40 years

• Self-reprogrammable under software control

• In-Circuit Serial Programming™ (ICSP™) via two pins

• Single-supply 5V In-Circuit Serial Programming

• Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable

operation

• Programmable code protection

• Power saving Sleep mode

• Selectable oscillator options

• In-Circuit Debug (ICD) via two pins

CMOS Technology:

• Low-power, high-speed Flash/EEPROM technology

• Fully static design

• Wide operating voltage range (2.0V to 5.5V)

• Commercial and Industrial temperature ranges

• Low-power consumption

I/O PORTS

Some pins for these I/O ports are multiplexed with an alternate function for

the peripheral features on the device. In general, when a peripheral is enabled, that

pin may not be used as a general purpose I/O pin. Additional information on I/O

ports may be found in the PICmicro™ Mid-Range.

PORTA and the TRISA Register

PORTA is a 6-bit wide, bidirectional port. The corresponding data direction

register is TRISA. Setting a TRISA bit (= 1) will make the corresponding PORTA

pin an input (i.e., put the corresponding output driver in a High-Impedance mode).

Clearing a TRISA bit (= 0) will make the corresponding PORTA pin an output

(i.e., put the contents of the output latch on the selected pin). Reading the PORTA

register reads the status of the pins, whereas writing to it will write to the port

latch. All write operations are read-modify-write operations. Therefore, a write to a

port implies that the port pins are read; the value is modified and then written to

the port data latch.

Pin RA4 is multiplexed with the Timer0 module clock input to become the

RA4/T0CKI pin. The RA4/T0CKI pin is a Schmitt Trigger input and an open-drain

output. All other PORTA pins have TTL input levels and full CMOS output

drivers. Other PORTA pins are multiplexed with analog inputs and the analog

VREF input for both the A/D converters and the comparators. The operation of

each pin is selected by clearing/setting the appropriate control bits in the ADCON1

and/or CMCON registers.

PORTB and the TRISB Register

PORTB is an 8-bit wide, bidirectional port. The corresponding data direction

register is TRISB. Setting a TRISB bit (= 1) will make the corresponding PORTB

pin an input (i.e., put the corresponding output driver in a High-Impedance mode).

Clearing a TRISB bit (= 0) will make the corresponding PORTB pin an output

(i.e., put the contents of the output latch on the selected pin). Three pins of PORTB

are multiplexed with the In-Circuit Debugger and Low-Voltage Programming

function: RB3/PGM, RB6/PGC and RB7/PGD. Each of the PORTB pins has a

weak internal pull-up. A single control bit can turn on all the pull-ups. This is

performed by clearing bit RBPU (OPTION_REG<7>). The weak pull-up is

automatically turned off when the port pin is configured as an output. The pull-ups

are disabled on a Power-on Reset.

PORTC and the TRISC Register

PORT C is an 8-bit wide, bidirectional port. The corresponding data

direction register is TRISC. Setting a TRISC bit (= 1) will make the corresponding

PORTC pin an input (i.e., put the corresponding output driver in a High-Impedance

mode). Clearing a TRISC bit (= 0) will make the corresponding PORTC pin an

output (i.e., put the contents of the output latch on the selected pin). PORTC is

multiplexed with several peripheral functions. PORTC pins have Schmitt Trigger

input buffers. When the I2C module is enabled, the PORTC<4:3> pins can be

configured with normal I2C levels, or with SM Bus levels, by using the CKE bit

(SSPSTAT<6>). When enabling peripheral functions, care should be taken in

defining TRIS bits for each PORTC pin. Some peripherals override the TRIS bit to

make a pin an output, while other peripherals override the TRIS bit to make a pin

an input. Since the TRIS bit override is in effect while the peripheral is enabled,

read-modify write instructions (BSF, BCF, XORWF) with TRISC as the

destination, should be avoided. The user should refer to the corresponding

peripheral section for the correct TRIS bit settings.

PORT-D PIN DETAILS

PORTD is an 8-bit port with Schmitt Trigger input buffers. Each pin is

individually configurable as an input or output. PORTD can be configured as an 8-

bit wide microprocessor port (Parallel Slave Port) by setting control bit,

PSPMODE (TRISE<4>). In this mode, the input buffers are TTL.

PORTE PIN DETAILS

PORT D has three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7)

which are individually configurable as inputs or outputs. These pins have Schmitt

Trigger input buffers. The PORTE pins become the I/O control inputs for the

microprocessor port when bit PSPMODE (TRISE<4>) is set. In this mode, the user

must make certain that the TRISE<2:0> bits are set and that the pins are configured

as digital inputs. Also, ensure that ADCON1 is configured for digital I/O. In this

mode, the input buffers are TTL. Register 4-1 shows the TRISE register which also

controls the Parallel Slave Port operation. PORTE pins are multiplexed with

analog inputs. When selected for analog input, these pins will read as ‘0’s. TRISE

controls the direction of the RE pins, even when they are being used as analog

inputs. The user must make sure to keep the pins configured as inputs when using

them as analog inputs.

TIMER-0 MODULE

The Timer0 module timer/counter has the following features:

• 8-bit timer/counter

• Readable and writable

• 8-bit software programmable prescaler

• Internal or external clock select

• Interrupt on overflow from FFh to 00h

• Edge select for external clock

In block diagram of the Timer0 module and the prescaler shared with the WDT.

Additional information on the Timer0 module is available in the PICmicro® Mid-

Range MCU Family Reference Manual (DS33023). Timer mode is selected by

clearing bit T0CS (OPTION_REG<5>). In Timer mode, the Timer0 module will

increment every instruction cycle (without prescaler). If the TMR0 register is

written, the Increment is inhibited for the following two instruction cycles. The

user can work around this by writing an adjusted value to the TMR0 register.

Counter mode is selected by setting bit T0CS (OPTION_REG<5>). In

Counter mode, Timer0 will increment either on every rising or falling edge of pin

RA4/T0CKI. The incrementing edge is determined by the Timer0 Source Edge

Select bit, T0SE (OPTION_REG<4>). Clearing bit T0SE selects the rising edge.

The prescaler is mutually exclusively shared between the Timer0 module and the

Watchdog Timer. The prescaler is not readable or writable.

TIMER 0 BLOCKDIAGRAM

TIMER 1 MODULE

The Timer1 module is a 16-bit timer/counter consisting of two 8-bit registers

(TMR1H and TMR1L) which are readable and writable. The TMR1 register pair

(TMR1H:TMR1L) increments from 0000h to FFFFh and rolls over to 0000h. The

TMR1 interrupt, if enabled, is generated on overflow which is latched in interrupt

flag bit, TMR1IF (PIR1<0>). This interrupt can be enabled/disabled by

setting/clearing TMR1 interrupt enable bit, TMR1IE (PIE1<0>). Timer1 can

operate in one of two modes:

• As a Timer

• As a Counter

The operating mode is determined by the clock select bit, TMR1CS (T1CON<1>).

In Timer mode, Timer1 increments every instruction cycle. In Counter mode, it

increments on every rising edge of the external clock input. Timer1 can be

enabled/disabled by setting/clearing control bit, TMR1ON (T1CON<0>). Timer1

also has an internal “Reset input”. This Reset can be generated by either of the two

CCP modules (Section 8.0 “Capture/Compare/PWM Modules”).

TIMER2 MODULE

Timer2 is an 8-bit timer with a prescaler and a postscaler. It can be used as

the PWM time base for the PWM mode of the CCP module(s). The TMR2 register

is readable and writable and is cleared on any device Reset. The input clock

(FOSC/4) has a prescale option of 1:1, 1:4 or 1:16, selected by control bits

T2CKPS1:T2CKPS0 (T2CON<1:0>). The Timer2 module has an 8-bit period

register, PR2. Timer2 increments from 00h until it matches PR2 and then resets to

00h on the next increment cycle. PR2 is a readable and writable register. The PR2

register is initialized to FFh upon Reset. The match output of TMR2 goes through

a 4-bit postscaler (which gives a 1:1 to 1:16 scaling inclusive) to generate a TMR2

interrupt (latched in flag bit, TMR2IF (PIR1<1>)).

Timer2 can be shut-off by clearing control bit, TMR2ON (T2CON<2>), to

minimize power consumption.

INSTRUCTION SET SUMMARY

The PIC16 instruction set is highly orthogonal and is comprised of three

basic categories:

• Byte-oriented operations

• Bit-oriented operations

• Literal and control operations

Each PIC16 instruction is a 14-bit word divided into an opcode which specifies the

instruction type and one or more operands which further specify the operation of

the instruction. For byte-oriented instructions, ‘f’ represents a file register

designator and ‘d’ represents a destination designator. The file register designator

specifies which file register is to be used by the instruction.

The destination designator specifies where the result of the operation is to be

placed. If ‘d’ is zero, the result is placed in the W register. If ‘d’ is one, the result is

placed in the file register specified in the instruction.

For bit-oriented instructions, ‘b’ represents a bit field designator which

selects the bit affected by the operation, while ‘f’ represents the address of the file

in which the bit is located.

For literal and control operations, ‘k’ represents an eight or eleven-bit

constant or literal value One instruction cycle consists of four oscillator periods;

for an oscillator frequency of 4 MHz, this gives a normal instruction execution

time of 1and 0s. All instructions are executed within a single instruction cycle,

unless a conditional test is true, or the program counter is changed as a result of an

instruction. When this occurs, the execution takes two instruction cycles with the

second cycle executed as a NOP. Any instruction that specifies a file register as

part of the instruction performs a Read-Modify-Write (R-M-W) operation. The

register is read, the data is modified, and the result is stored according to either the

instruction or the destination designator‘d’. A read operation is performed on a

register even if the instruction writes to that register.

GENERAL FORMAT FOR INSTRUCTIONS

Liquid Crystal Display [LCD]

We examine an intelligent LCD display of two lines, 16 characters per line that is

interfaced to the 8051.The protocol (handshaking) for the display is as shown. The

display contains two internal byte-wide registers, one for commands (instructions)

(RS=0) and the second for characters (data) to be displayed (RS=1).It also contains a

user-programmed RAM area (the character RAM) that can be programmed to generate

any desired character that can be formed using a dot matrix. To distinguish between these

two data areas, the hex command byte 80 will be used to signify that the display RAM

address 00h will be chosen Port1 is used to furnish the command or data type, and ports

3.2 to 3.4 furnish register select and read/write levels.

The display takes varying amounts of time to accomplish the functions as listed.

LCD bit 7 is monitored for logic high (busy) to ensure the display is overwritten. A

slightly more complicated LCD display (4 lines*40 characters) is currently being used in

medical diagnostic systems to run a very similar program.

Liquid Crystal Display

Figure: 10.1 Liquid Crystal Display

Pins Description

1 Ground 2 Vcc

3 Contrast Voltage 4"R/S"_Instruction(0)/data(1) Select

5 "R/W" Read(1)/Write(0) LCD Registers 6 "E" Clock

7 - 14 Data I/O Pins 8 A(anode) back light power supply 5V

9 K(cathode) back light power supply GND

RELAY

Introduction:-

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

form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was

invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the

input circuit, it can be considered, in a broad sense, to be a form of an electrical amplifier.

Operation:-

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

Gn +5v Vd A K

1 2 3 15 16

4 5 6 7 8 9 10 11 12 13 14

16x2 Liquid Crystal Display

RS R/W En D0 0D6

0

D2 D3 D5 D7D6D4D1

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 commonly in industrial

motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce

noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the

collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause

damage to circuit components. If the coil is designed to be energized with AC, a small copper ring can be

crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases

the minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor

or other solid-state switching device. To achieve electrical isolation, a light-emitting diode (LED) is used with a

photo transistor.

Types of relay :-

Figure: 11.1: latching relay

1) Latching relay:-

A latching relay has two relaxed states (bistable). These are also called 'keep' relays. When the current is

switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam

mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the

armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam

example, the first pulse to the coil turns the relay on and the second pulse turns it off.

In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay

off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched,

and it retains its last setting across a power outage.

2) Reed relay:-

A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts

against atmospheric corrosion. The contacts are closed by a magnetic field generated when current passes

through a coil around the glass tube. Reed relays are capable of faster switching speeds than conventional

relays. See also reed switch.

2.1) Mercury-wetted relay:-

A mercury-wetted relay is a form of reed relay in which the contacts are wetted with mercury. Such relays

are used to switch low-voltage signals (one volt or less) because of its low contact resistance, or for high-speed

counting and timing applications where the mercury eliminated contact bounce. Mercury wetted relays are

position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of

liquid mercury, these relays are rarely specified for new equipment. See also mercury switch.

3) Polarized relay:-

A Polarized Relay placed the armature between the poles of a permanent magnet to increase sensitivity.

Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and correct

telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum

sensitivity and then apply a bias spring to set the critical current that would operate the relay.

4) Machine tool relay:-

A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and

other sequential control. They are characterized by a large number of contacts (sometimes extendable in the

field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a

form factor that allows compactly installing many relays in a control panel. Although such relays once were the

backbone of automation in such industries as automobile assembly, the programmable logic controller mostly

displaced the machine tool relay from sequential control applications.

5) Contactor relay:-

A contactor is a very heavy-duty relay used for switching electric motors and lighting loads. With high

current, the contacts are made with pure silver. The unavoidable arcing causes the contacts to oxidize and

silver oxide is still a good conductor. Such devices are often used for motor starters. A motor starter is a

contactor with an overload protection devices attached. The overload sensing devices are a form of heat

operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate

auxiliary contacts. These auxiliary contacts are in series with the coil. If the overload senses excess current in

the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for

use where noise is a chief concern.

Pole & Throw:-

Circuit symbols of relays. "C" denotes the common terminal in SPDT and DPDT types. Since relays are

switches, the terminology applied to switches is also applied to relays. According to this classification, relays

can be of the following types:

* SPST - Single Pole Single Throw. These have two terminals which can be switched on/off. In total, four

terminals when the coil is also included.

* SPDT - Single Pole Double Throw. These have one row of three terminals. One terminal (common) switches

between the other two poles. It is the same as a single change-over switch. In total, five terminals when the

coil is also included.

* DPST - Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or

relays actuated by a single coil. In total, six terminals when the coil is also included. This configuration may also

be referred to as DPNO.

* DPDT - Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two

SPDT switches or relays actuated by a single coil. In total, eight terminals when the coil is also included.

* QPDT - Quadruple Pole Double Throw. Often referred to as Quad Pole Double Throw, or 4PDT. These have

four rows of change-over terminals. Equivalent to four SPDT switches or relays actuated by a single coil or two

DPDT relays. In total, fourteen terminals when the coil is also included.

The contacts can be either Normally Open (NO), Normally Closed (NC), or change-over (CO) contacts.

* Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when

the relay is inactive. It is also called Form A contact or "make" contact. Form A contact is ideal for applications

that require to switch a high-current power source from a remote device.

* Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when

the relay is inactive. It is also called Form B contact or "break" contact. Form B contact is ideal for applications

that require the circuit to remain closed until the relay is activated.

* Change-over contacts control two circuits: one normally-open contact and one normally-closed contact

with a common terminal. It is also called Form C contact or "transfer" contact.

Applications:-

Relays are used:-

* To control a high-voltage circuit with a low-voltage signal, as in some types of modems,

* To control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,

* To detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers

(protection relays),

* To isolate the controlling circuit from the controlled circuit when the two are at different potentials, for

example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to

control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as

needs change.

* To perform logic functions. For example, the Boolean AND function is realized by connecting NO relay

contacts in series, the OR function by connecting NO contacts in parallel. The change-over or Form C contacts

perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using NC

contacts. Due to the failure modes of a relay compared with a semiconductor, they are widely used in safety

critical logic, such as the control panels of radioactive waste handling machinery.

* To perform time delay functions. Relays can be modified to delay opening or delay closing a set of

contacts. A very shorts (a fraction of a second) delay would use a copper disk between the armature and

moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening

release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with

fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate.

For longer time periods, a mechanical clockwork timer is installed.

Protective relay:-

A protective relay is a complex electromechanical apparatus, often with more than one coil, designed to

calculate operating conditions on an electrical circuit and trip circuit breakers when a fault was found. Unlike

switching type relays with fixed and usually ill-defined operating voltage thresholds and operating times,

protective relays had well-established, selectable, time/current (or other operating parameter) curves.

Such relays were very elaborate, using arrays of induction disks, shaded-pole magnets, operating and

restraint coils, solenoid-type operators, telephone-relay style contacts, and phase-shifting networks to allow

the relay to respond to such conditions as over-current, over-voltage, reverse power flow, over- and under-

frequency, and even distance relays that would trip for faults up to a certain distance away from a substation

but not beyond that point. An important transmission line or generator unit would have had cubicles

dedicated to protection, with a score of individual electromechanical devices.

Each of the protective functions available on a given relay is denoted by standard ANSI Device Numbers. For

example, a relay including function 51 would be a timed over current protective relay.

Design and theory of these protective devices is an important part of the education of an electrical engineer

who specializes in power systems. Today these devices are nearly entirely replaced (in new designs) with

microprocessor-based instruments (numerical relays) that emulate their electromechanical ancestors with

great precision and convenience in application. By combining several functions in one case, numerical relays

also save capital cost and maintenance cost over electromechanical relays. However, due to their very long life

span, tens of thousands of these "silent sentinels" are still protecting transmission lines and electrical

apparatus all over the world.

Temperature sensor

The LM35 series are precision integrated-circuit temperature sensors, whose

output voltage is linearly proportional to the Celsius (Centigrade) temperature. The

LM35 thus has an advantage over linear temperature sensors calibrated in ° Kelvin,

as the user is not required to subtract a large constant voltage from its output to

obtain convenient Centigrade scaling.

The LM35 does not require any external calibration or trimming to provide

typical accuracies of ±1/4°C at room temperature and ±3/4°C over a full -55 to

+150°C temperature range. Low cost is assured by trimming and calibration at the

wafer level. The LM35’s low output impedance, linear output, and precise inherent

calibration make interfacing to readout or control circuitry especially easy. It can

be used with single power supplies, or with plus and minus supplies. As it draws

only 60 μA from its supply, it has very low self-heating, less than 0.1°C in still air.

The LM35 is rated to operate over a -55° to +150°C temperature range, while the

LM35C is rated for a -40° to +110°C range (-10° with improved accuracy). The

LM35 series is available packaged in hermetic TO-46 transistor packages, while

the LM35C, LM35CA, and LM35D are also available in the plastic TO-92

transistor package. The LM35D is also available in an 8-lead surface mount small

outline package and a plastic TO-220 package.

Features

Calibrated directly in ° Celsius (Centigrade).

Linear + 10.0 mV/°C scale factor.

0.5°C accuracy guarantee able (at +25°C).

Rated for full -55° to +150°C range.

Suitable for remote applications.

Low cost due to wafer-level trimming.

Operates from 4 to 30 volts.

Less than 60 μA current drain.

Low self-heating, 0.08°C in still air.

Nonlinearity only ±1/4°C typical one.

The LM35 can be applied easily in the same way as other integrated-circuit

temperature sensors. It can be glued or cemented to a surface and its temperature

will be within about 0.01°C of the surface temperature. These devices are

Sometimes soldered to a small light-weight heat fin, to decrease the thermal time

Constant and speed up the response in slowly-moving air. On the other hand, a

Small thermal mass may be added to the sensor, to give the steadiest reading

Despite small deviations in the air temperature. This is especially true if the circuit

May operate at cold temperatures where condensation can occur.

SOIL SENSOR CIRCUIT

C122PF

RV110K

+5V

PROBE

OUT

PCB DESIGN AND FABRICATION

Designing of a PCB is a major slip in the production of PCBs. It forms a

distinct factor n electronic performance and reliability. The productivity of a PCB

with assembly and serviceability also depends on design.

STEPS INVOLVED

1. Prepare the required circuit diagram

2. List out the components, their sizes etc.

3. Draft it onto a graph sheet

4. Place all pads and finish thin tracks

5. Put it on the mylor sheet and then on the graph sheet

6. Place parts including screw holes with the help of knife.

7. Fix all the tracks.

8. Keep one component as the key.

CONVERSION OF CIRCUIT DIAGRAM

1. Cutting lines, mounting lines are done

2. List all the components their length diameter thickness code names etc.

3. Keep one component as key component

4. Keep key component first and their supporting tools

5. All tracks are straight lines

6. In between ICs no signal lines should be passed

7. Mark the pin number of IC on the lay out for avoiding dislocations

8. The length of the conductor should be as low as possible

9. Place all the components, resistors, diodes etc. parallel to each other

LAY OUT APPROACHES

              First the board outlines and the connectors are marked on a sheet of paper

followed by sketching of the component outlines with connecting point and

conductor patterns. Prepare the layout as viewed from the component side first, so

as to avoid any confusion. The layout is developed in the direction of signal flow

as far as possible. Among the components the larger ones are filled first and the

space between is filled with smaller ones. Components, rewiring input, output

connections came near the connectors. All the components are placed in such a

manner that de-soldering of the component is not is not necessary, if they have to

be re placed. While designing the conductors, the minimum spacing requirement

for the final network should be known. Transforming the lay out to copper. The lay

out made on the graph sheet should be redrawn on the copper clad using paint or

nail polish.

ETCHING

The final copper pattern is formed by selective removal of the unwanted

copper which is not protected by an electric rebist. FeCl3 solution is popularly

used etching solution. FeCl3 powder is made into a solution using water and kept

in a plastic tray. Immerse the marked copper clad in this solution for two or three

hours. Due to the reaction solution will became weak and it is not recommended

for further etching process. Take out the etched sheet from the tray and dry out for

in sunlight for an hour.

ETCHANTS

Many factors have to be considered to choose the most suitable etchant

system for a PCB process. Some commonly used etchants are FeCl3, Cupric

chloride, Chromic acid etc. After etching FeCl3 is washed from the board and

cleaned dry. Paint is removed using suitable from the component insertion. Holes

are drilled into appropriate position and the components are soldered into PCB

carefully.

Take a copper clad of the required dimensions. Transfer the circuit layout to

the copper clad using cotton paper. The layout area should be marked with nail

polish. Put the copper clad into FeCl3 solution and warm it. Stage by stage

transformation of the copper clad occurs. Warm the solution intermittently

according to the requirement. After about 4 hours etching will be completed. Wash

the board using soap solution to remove the remaining of FeCl3 solution. Scrap off

the nail polish and drill holes wherever required using appropriate drill bits. PCB is

fabricated.

SOFTWARE USED:

Embedded C

MPLAB IDE

PROTUES

PIC KIT2

SOFTWARE TOOLS

1. MPLAB

MPLAB IDE is an integrated development environment that provides

development engineers with the flexibility to develop and debug firmware for

various Microchip devices

MPLAB IDE is a Windows-based Integrated Development Environment for the

Microchip Technology Incorporated PICmicrocontroller (MCU) and dsPIC digital

signal controller (DSC) families. In the MPLAB IDE, you can:

Create source code using the built-in editor.

Assemble, compile and link source code using various language tools. An

assembler, linker and librarian come with MPLAB IDE. C compilers are

available from Microchip and other third party vendors.

Debug the executable logic by watching program flow with a simulator,

such as MPLAB SIM, or in real time with an emulator, such as MPLAB

ICE. Third party emulators that work with MPLAB IDE are also available.

Make timing measurements.

View variables in Watch windows.

Program firmware into devices with programmers such as PICSTART Plus

or PRO MATE II.

Find quick answers to questions from the MPLAB IDE on-line Help.

2. MPLAB SIMULATOR

MPLAB SIM is a discrete-event simulator for the PIC microcontroller (MCU)

families.  It is integrated into MPLAB IDE integrated development environment.

The MPLAB SIM debugging tool is designed to model operation of Microchip

Technology's PIC microcontrollers to assist users in debugging software for these

devices

4. COMPILER-HIGH TECH C

A program written in the high level language called C; which will be converted

into PICmicro MCU machine code by a compiler. Machine code is suitable for use

by a PICmicro MCU or Microchip development system product like MPLAB IDE.

PIC SIMULATION QUICK TUTORIAL  

THE CIRCUIT

The circuit to be simulated is shown here, consisting of a PIC 16F877A

microcontroller unit (MCU)

THE SCHEMATIC

The ISIS user interface is shown here, consisting of edit, overview and object

select windows, with edit toolbars. Components are added to the object list from

the libraries provided, dropped onto the schematic, and connected up using virtual

wiring. Components can be labelled and their simulation properties

SELECT COMPONENTS

Components are found in the libraries accessed via the ‘pick’ button P in the object

select window. The MCU is selected from ‘Microprocessors ICs’ category, ‘PIC16

Family’ sub-category. The other components are added to the pick list from the

appropriate categories. These are then selected and dropped on the schematic

within the blue border.

4 WRITE PROGRAM

The MCU needs a program to work as required. From the ‘Source’ menu, select

‘add source file’, ‘new’ and open the source file GPS.C in folder GPS. Select code

generation tool MPASM. Open the source edit window by selecting the new file

from the source menu, and enter the source code listed here Save the source file

code file GPS.C in the project folder.

ASSEMBLE PROGRAM

Save the source code when complete. From the Source menu, select Build All. The

message window should confirm build OK. If not, correct syntax errors in the

source code by reference to PIC programming rules. A hex file is produced as

shown, GPS.HEX, which contains the MCU machine code.The machine code

program GPS.HEX is stored automatically in the project folder with the source

code.

ATTACH PROGRAM

This hex file must be attached to the MCU in the schematic. Right click, then left

click on the PIC chip to open the Edit Component dialogue. Click on the Program

File folder tab and select the GPS.HEX file from the project folder. Set the

Processor Clock Frequency to 4MHz. Note that the external components do not

affect the simulation clock frequency. The Port B output LEDs should operate

when the run/step/pause/stop controls are clicked (the buttons on the schematic

have no effect with this program). Save the completed design file.

TEST PROGRAM

Pause the program and from the Debug menu check the PIC CPU Source Code

option to display the program with the execution point highlighted. Use the ‘Step

Into’ button in the source code window to single step the program. Note that the

initialisation instructions are executed once, and the loop then repeats endlessly –

this is the usual program operating sequence for control applications. The source

code window has buttons to run, single step (into, over and out of subroutines) and

set breakpoints.Correct any logical program errors detected.

DEBUG PROGRAM

To monitor program progress, the MCU registers can be displayed, and other

changes monitored, using:

· Special function register display

· RAM register display

· Register watch window

· Execution clock

· Simulation logs

The effect of the program on the registers and status flags, and program timing can

thus be checked.

Save the test window arrangement using ‘save preferences’.

DOWNLOAD PROGRAM

When all logical errors have been resolved, the program can be downloaded to the

real hardware using the programming tools in MPLAB, for example, using the

PICKIT2 programmer unit. Alternatively, the ICD system allows in-circuit

programming and debugging, requiring the purchase of the MPLAB ICD2 module.

PIC SIMULATIOR IDE SOFTWARE WORKING STEPS

1. Write and compile programme in MPLAB IDE

2. Start PIC Simulator IDE.

3. Click on Options\Select Microcontroller.

4. Select 'PIC16F8xxA' and click on Select button.

5. Click on File\Load Program.

6. Select project.hex file and click on Open. That will load the program into

PIC program memory.

7. Click on Tools\LCD Displays Panel. That will open the window with 1 LCD

Display.

8. Click on Setup button to configure the PORT PINS.

9. Click on Tools\Microcontroller View. That will open the Microcontroller

View window.

10.Select the Rate\Extremely Fast simulation rate.

11.Click on Simulation\Start. The simulation will start immediately

12.The simulation can be stopped any time by clicking on Simulation\Stop.

DESIGNING A PCB USING PROTEUS

PCB stands for Printed Circuit Board. The naming convention will be clear once

steps for the design are understood. On a lower level of project, PCBs are usually

designed on a board whose one side is lined with copper. But on the industrial

scale or on a professional level, it is preferred to have a double sided PCB. This

also complexes the procedure through which PCBs are made. This document only

emphasizes on PCB designing in PROTEUS 7.10 sp0. Other versions of

PROTEUS may have similar steps but you might need to be cautious anyway.

Proteus ISIS:

Open the ‘ISIS Professional’ from PROTEUS. This is the application where the

simulations of the circuits can be tested. But the same file can be further processed

to transform it into a layout. Layout is the final design which is needed in order to

make the PCB of a circuit. To make the schematic, first we must have its raw

design. Below is the schematic, that this documents uses to explain the steps to

make the PCB.

Proteus ARES:

‘ARES Professional’ will open automatically once the previous step is done. This

is the application where the final layout will be made. Once the layout is made, the

work on the software will be finished. Proceed with the following steps to make

the PCB layout.

Introduction 

What is PICKIT 2?

The PICKIT 2 is a low-cost in-circuit debugger (ICD) and in-circuit serial

programmer (ICSP). PICKIT 2 is intended to be used as an evaluation, debugging

and programming aid in a laboratory environment. The PICKIT 2 offers these

features: Real-time and single-step code execution 

Breakpoints, Register and Variable Watch/Modify

In-circuit debugging

Target VDD monitor

Diagnostic LEDs

MPLAB IDE user interface

USB interface to a host PC / USB POWERED

40 Pin Target Board With FRC Cable

ICSP FRC connecter Easy to interface to all our boards

SOFTWARE CODE

#include "config.c"

#include "pic16f877a.c"

__CONFIG(0X1F72);

#define SOIL RA4

#define RL1 RC5

void newline();

unsigned char pc;

void main()

{

ADCON1=0x07; // All analog pins are used as digital

TRISA=0XFF;

TRISB=0X00;

TRISC=0X00;

TRISD=0X01;

TRISE=0X00;

PORTA=PORTB=0;

PORTC=PORTD=PORTE=0;

lcd_init();

usart_initialise();

while(1)

{

lcdcmd(0x80);

lcddatawrt(" Soil Moisture ");

if(SOIL==0)

{

lcdcmd(0xC0);

lcddatawrt(" Low - Pump-ON ");

RL1=1;

GSM();

GSM1();

}

else if(SOIL==1)

{

lcdcmd(0xC0);

lcddatawrt(" Normal-Pump-OFF");

RL1=0;

}

}

} // end of main

//-------------------------------------------------------------------------------------------

-------------------------------------------

static void interrupt isr()

{

if(RCIF==1)

{

if(RCREG=='%' || RCREG=='^') // system input

{

pc=RCREG;

RCIF=0;

}

}

}

//-------------------------------------------------------------------------------------------

-------------------------------------------

//

CONCLUSION

BIBILOGRAPHY

1. Sedra and Smith, Microelectronic Circuits, fourth edition , Oxford

University Press, 1998

2. R.S. Sedha, 2002. A Text Book of Applied Electronics, S. Chand and

Company Ltd., New Delhi

3. Theodore S. Rappaport, Wireless Communications, second edition, PHI.

New Delhi Draft EN (GSM 03.40) v6.0.0

WEBREFERENCES:

1. www.electronicstutorials.com

2. www.aimglobal.com

3. www.kernel.org

4. www.egtechprojects.com

5. www.microchip.com

6. www.google.com

CONCLUSION

The system provides with several benefits and can operate with less manpower.

The system supplies water only when the humidity in the soil goes below the

reference. Due to the direct transfer of water to the roots water conservation takes

place and also helps to maintain the moisture to soil ratio at the root zone constant

to some extend. Thus the system is efficient and compatible to changing

environment.

ADVANTAGES

1. Saves water - Studies show that drip irrigation systems use 30 - 50% less water

than conventional watering methods, suchas sprinklers.

2. Improves growth - Smaller amounts of water applied over a longer amount of

time provide ideal growing conditions. Drip irrigation extends watering times for

plants, and prevents soil

erosion and nutrient runoff. Also, because the flow is continuous, water penetrates

deeply into the soil to get well down into the root zone.

3. Discourages weeds - Water is only delivered where it's needed.

4. Saves time - Setting and moving sprinklers is not required. A timer delay as per

environment can be added to the system for automatic watering.

5. Helps control fungal diseases, which grow quickly under moist conditions. Also,

wet foliage can spread disease.

6. Adaptable - A drip irrigation system can be modified easily to adjust to the

changing needs of a garden or lawn.

7. Simplest Method - Start by drawing a map of your garden and yard, showing the

location of plantings. Measure the distances required for lengths of hose or plastic

tubing to reachthe desired areas.