Remote sensing and control of an irrigation system using a distributed wireless sensor network

Remote sensing and control of an irrigation system using a distributed wireless sensor network

UNIT-1
INTRODUCTION

The project report describes the design Development and Fabrication of One demo unit
of the project work “ Remote sensing and control of an irrigation system using a distributed
wireless sensor network” using embedded systems.

The purpose of this project is Efficient energy yield is a major concern in photovoltaic
systems in solar energy supply. Smart photovoltaic modules offer a potential solution to
allow solar generators to maximize their productivity.

And this paper describes details of the design and instrumentation of smart
photovoltaic modules, a wireless sensor network, and software for real-time sensing and
control of a photovoltaic system with maximum power point tracking at module level.

Now a day, with the advancement technology, particularly in the field of
Microcontrollers, all the activities in our daily living have become a part of Information
technology and we find microcontrollers in each and every application. Thus, trend is directing
towards Microcontrollers based project works. However, in this project the data is communicated
by using GSM.

The microcontroller block is playing a major role in this project work. The micro
controller chip used in this project work is PIC 16F877A and this is like heart of the project. The
PIC 16F877A microcontroller is a 40-pin IC.

1.1 RELATED WORK:

To complete our project we studied about embedded systems basics and system design
cycle to know how to develop the Microcontroller and Microprocessor based projects. Further
we analyzed some of latest controllers’ architecture available in the market. Finally we selected
PIC 16f877A controller because of its features (it is discussed in hardware requirements). For
our successful completion of this project obviously we utilized howstuffworks.com,
www.microchip.com, www.google.com, en.wikipedia.org.

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1.2 SCOPE OF THE PROJECT:

The scope of the project is the Efficient energy yield is a major concern in
photovoltaic systems in solar energy supply. Smart photovoltaic modules offer a potential
solution to allow solar generators to maximize their productivity. And this paper describes
details of the design and instrumentation of smart photovoltaic modules, a wireless sensor
network, and software for real-time sensing and control of a photovoltaic system with
maximum power point tracking at module level.

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UNIT-2
INTRODUCTION TO EMBEDDED SYSTEMS

2.1 EMBEDDED SYSTEM:

Embedded System is a combination of hardware and software used to achieve a single
specific task. An embedded system is a microcontroller-based, software driven, reliable, real-
time control system, autonomous, or human or network interactive, operating on diverse physical
variables and in diverse environments and sold into a competitive and cost conscious market.

An embedded system is not a computer system that is used primarily for processing, not
a software system on PC or UNIX, not a traditional business or scientific application. High-end
embedded & lower end embedded systems. High-end embedded system - Generally 32, 64 Bit
Controllers used with OS. Examples Personal Digital Assistant and Mobile phones etc .Lower
end embedded systems - Generally 8,16 Bit Controllers used with an minimal operating systems
and hardware layout designed for the specific purpose. Examples Small controllers and devices
in our everyday life like Washing Machine, Microwave Ovens, where they are embedded in.

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SYSTEM DESIGN CALLS:

2.1.1 EMBEDDED SYSTEM DESIGN CYCLE

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“V Diagram”

In this place we need to discuss the role of simulation software, real-time systems and
data acquisition in dynamic test applications. Traditional testing is referred to as “static” testing
where functionality of components is tested by providing known inputs and measuring outputs.
Today there is more pressure to get products to market faster and reduce design cycle times.
This has led to a need for “dynamic” testing where components are tested while in use with the
entire system – either real or simulated. Because of cost and safety concerns, simulating the rest
of the system with real-time hardware is preferred to testing components in the actual real
system.

The diagram shown on this slide is the “V Diagram” that is often used to describe the
development cycle. Originally developed to encapsulate the design process of software
applications, many different versions of this diagram can be found to describe different product
design cycles. Here we have shown one example of such a diagram representing the design
cycle of embedded control applications common to automotive, aerospace and defense
applications.

In this diagram the general progression in time of the development stages is shown from
left to right. Note however that this is often an iterative process and the actual development will
not proceed linearly through these steps. The goal of rapid development is to make this cycle as
efficient as possible by minimizing the iterations required for a design. If the x-axis of the

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diagram is thought of as time, the goal is to narrow the “V” as much as possible and thereby
reduce development time.

The y-axis of this diagram can be thought of as the level at which the system components
are considered. Early on in the development, the requirements of the overall system must be
considered. As the system is divided into sub-systems and components, the process becomes
very low-level down to the point of loading code onto individual processors. Afterwards
components are integrated and tested together until such time that the entire system can enter
final production testing. Therefore the top of the diagram represents the high-level system view
and the bottom of the diagram represents a very low-level view.

Notes:
• V diagram describes lots of applications—derived from software development.
• Reason for shape, every phase of design requires a complimentary test phase. High-level
to low-level view of application.
• This is a simplified version.
• Loop Back/Iterative process, X-axis is time (sum up).

2.1.2 CHARACTERISTICS OF EMBEDDED SYSTEM

• An embedded system is any computer system hidden inside a product other than a
computer.

• There will encounter a number of difficulties when writing embedded system software in
addition to those we encounter when we write applications

– Throughput – Our system may need to handle a lot of data in a short period of
time.
– Response–Our system may need to react to events quickly
– Testability–Setting up equipment to test embedded software can be difficult
– Debugability–Without a screen or a keyboard, finding out what the software is
doing wrong (other than not working) is a troublesome problem
– Reliability – embedded systems must be able to handle any situation without
human intervention

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– Memory space – Memory is limited on embedded systems, and you must make
the software and the data fit into whatever memory exists
– Program installation – you will need special tools to get your software into
embedded systems
– Power consumption – Portable systems must run on battery power, and the
software in these systems must conserve power
– Processor hogs – computing that requires large amounts of CPU time can
complicate the response problem
– Cost – Reducing the cost of the hardware is a concern in many embedded system
projects; software often operates on hardware that is barely adequate for the job.
• Embedded systems have a microprocessor/ microcontroller and a memory. Some have a
serial port or a network connection. They usually do not have keyboards, screens or disk
drives.
2.2 APPLICATIONS
1. MILITARY AND AEROSPACE EMBEDDED SOFTWARE APPLICATIONS
2. COMMUNICATION APPLICATIONS
3. INDUSTRIAL AUTOMATION AND PROCESS CONTROL SOFTWARE

2.3 CLASSIFICATION

1. Real Time Systems.
2. RTS is one which has to respond to events within a specified deadline.
3. A right answer after the dead line is a wrong answer
2.3.1 RTS CLASSIFICATION

1. Hard Real Time Systems
2. Soft Real Time System

2.3.1.1 HARD REAL TIME SYSTEM
• "Hard" real-time systems have very narrow response time.
• Example: Nuclear power system, Cardiac pacemaker.

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2.3.1.2 SOFT REAL TIME SYSTEM
• "Soft" real-time systems have reduced constrains on "lateness"
but still must operate very quickly and repeatable.
• Example: Railway reservation system – takes a few extra
seconds the data remains valid.

LANGUAGES USED

• C
• C++
• Java
• Linux
• Ada
• Assembly

2.4 MPLAB FEATURES

MPLAB Integrated Development Environment (IDE) is a free, integrated toolset for the
development of embedded applications employing Microchip's PIC® and dsPIC®
microcontrollers.

development of embedded applications employing Microchip's PIC® and dsPIC®
microcontrollers.

MPLAB IDE runs as a 32-bit application on MS Windows®, is easy to use and includes
a host of free software components for fast application development and super-charged
debugging.

MPLAB IDE also serves as a single, unified graphical user interface for additional
Microchip and third party software and hardware development tools. Moving between tools is a
snap, and upgrading from the free software simulator to hardware debug and programming tools
is done in a flash because MPLAB IDE has the same user interface for all tools.

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MPLAB IDE’s SIM, high speed software simulator for PIC and dsPIC (Digital Signal
Processing PIC Microcontroller) devices with peripheral simulation, complex stimulus injection
and register logging

UNIT-3
BLOCK DIAGRAM

3.1 TRANSMITTER:

PIC RF Tx

16F877A
LCD

KEYPAD

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3.2 RECEIVER:

SOLAR
BATTERY

PANEL
UNIT

UNIT

RELAY

PIC UNIT WITH
DRIVER
CONTROLLER

SOLINOID

VALVE

WATER

RF Rx TANK

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3.3 DESCRIPTION OF THE BLOCK DIAGRAM

The major components of this project are PIC micro controller and Power supply, Relay
& driver unit, RF MODULE, Motor, Sensor, Inverter circuit.

Field condition is monitored by voltage, current, irradiance, and temperature
sensors distributed across the photovoltaic field. The sensory data are periodically sampled
and transmitted to a base station. The power point is controlled by a integrated DC-DC
converter. The output voltage in the converter is regulated by a digital controller. The
reference voltage is calculated based on a neural network model, which is used to identify
maximum power point. The communication data for remote monitoring and distributed control
are successfully transmitted using a low-cost RF MODULE wireless network. The web-based
software developed in this paper offers stable remote access to field conditions and real-time
control of the power points in the smart photovoltaic system.

Power supply:

The Entire Project (both TX and RX side) needs power for its operation. However, from
the study of this project it comes to know that we supposed to design 5v and 12v dc power
supply. So by utilizing the following power supply components required power has been gained.
(230/12v (1A and 500mA) – Step down transformers, Bridge rectifier to converter ac to dc,
booster capacitor and +5v (7805) and +12v (7812) regulator to maintain constant 5v & 12 supply
for the controller circuit and driver circuit).

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UNIT-4
PIC MICROCONTROLLER

The major heart of this project is PIC16F877A microcontroller, the reasons why we
selected this in our project?, it has more features like 16bit timer, 10-bit ADC, USART, SPI, I2C,
256 bytes of EEPROM memory, and 8kbytes of flash program memory, then at last its speed of
program execution is about to 1 microsecond or 10 MIPS (10 Million Instructions per second),
etc. However, compare to other microcontroller it is fast and very ease to program in C language
because of huge support can gain from the manufacturer (Microchip Corporation)for
programming. The special IDE offered by the manufacture, it is named as MPLAB IDE for it
code generation purpose. Then one more thing is several cheapest programming tools to dump
the coding in to the controller are available, for example: Pro PIC, PIC Flash, Pro MATE, and
Pro Universal.

4.1 CIRCUIT DIAGRAM

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4.1.1 RECEIVER SECTION

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4.1.2 TRANSMITTER SECTION

4.2 CIRCUIT DESCRIPTION

POWER SUPPLY:

Power supply unit consists of Step down transformer, Rectifier, Input filter, Regulator
unit, Output filter.

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The Step down Transformer is used to step down the main supply voltage from 230V AC
to lower value. This 230 AC voltage cannot be used directly, thus it is stepped down. The
Transformer consists of primary and secondary coils. To reduce or step down the voltage, the
transformer is designed to contain less number of turns in its secondary core. The output from
the secondary coil is also AC waveform. Thus the conversion from AC to DC is essential. This
conversion is achieved by using the Rectifier Circuit/Unit.

The Rectifier circuit is used to convert the AC voltage into its corresponding DC voltage.
There are Half-Wave, Full-Wave and bridge Rectifiers available for this specific function. The
most important and simple device used in Rectifier circuit is the diode. The simple function of
the diode is to conduct when forward biased and not to conduct in reverse bias.

Capacitors are used as filter. The ripples from the DC voltage are removed and pure DC
voltage is obtained. And also these capacitors are used to reduce the harmonics of the input
voltage. The primary action performed by capacitor is charging and discharging. It charges in
positive half cycle of the AC voltage and it will discharge in negative half cycle. Here we used
1000µF capacitor. So it allows only AC voltage and does not allow the DC voltage. This filter is
fixed before the regulator. Thus the output is free from ripples.

Regulator regulates the output voltage to be always constant. The output voltage is
maintained irrespective of the fluctuations in the input AC voltage. As and then the AC voltage
changes, the DC voltage also changes. Thus to avoid this Regulators are used. Also when the
internal resistance of the power supply is greater than 30 ohms, the output gets affected. Thus
this can be successfully reduced here. The regulators are mainly classified for low voltage and
for high voltage. Here we used 7805 & 7812 positive regulators. 7805 it reduces the 12V dc
voltage to 5V dc Voltage and 7812 it will maintain constant 12.

The Filter circuit is often fixed after the Regulator circuit. Capacitor is most often
used as filter. The principle of the capacitor is to charge and discharge. It charges during the
positive half cycle of the AC voltage and discharges during the negative half cycle. So it allows
only AC voltage and does not allow the DC voltage. This filter is fixed after the Regulator circuit
to filter any of the possibly found ripples in the output received finally. Here we used 0.1µF
capacitor.

MICCONTROLLER CIRCUIT:

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The PIC 16f877A microcontroller is a 40-pin IC. The first pin of the controller is MCLR
pin and the 5V dc supply is given to this pin through 10KΩ resistor. This supply is also given to
11th pin directly. The 12th pin of the controller is grounded. A tank circuit consists of a 4 MHZ
crystal oscillator and two 22pf capacitors are connected to 13th and 14th pins of the PIC.

4.3 SENSORS

A sensor (also called detectors) is a converter that measures a physical quantity and
converts it into a signal which can be read by an observer or by an (today mostly electronic)
instrument. For example, a mercury-in-glass thermometer converts the measured temperature
into expansion and contraction of a liquid which can be read on a calibrated glass tube. A thermo
couple converts temperature to an output voltage which can be read by a voltmeter. For
accuracy, most sensors are calibrated against known standards.

Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor) and
lamps which dim or brighten by touching the base. There are also innumerable applications for
sensors of which most people are never aware. Applications include cars, machines, aerospace,
medicine, manufacturing and robotics.

4.3.1 TEMPERATURE SENSOR:
Temperature Sensor converts the sensed temperature quantity into an easily
measurable quantity such as Voltage or Current. Big difference exist between different
temperature sensor or temperature measurement device types. Using one perspective, they can be
simply classified into two groups, contact and non-contact.

Contact temperature sensors measure their own temperature. One infers the temperature
of the object to which the sensor is in contact by assuming or knowing that the two are in thermal
equilibrium, that is, there is no heat flow between them. Examples: Thermo couples,
Thermistors.

Most commercial and scientific noncontact temperature sensors measure the
thermal radiant power of the Infrared or Optical radiation that they receive from a known or

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calculated area on its surface, or a known or calculated volume within it. Examples: Radiation
Thermometers, Fiber optic temperature sensors.

Temperature sensor is an equipment used to sense the temperature of the particular
area. Thermometer is the simple temperature sensor which is used to measure the temperature of
a human being in medical field.

There are different types of temperature sensors. some of them are

• Clinical thermometer one used to determine the temperature of the human body.
• Oral thermometer a clinical thermometer that is placed under the tongue.
• Recording thermometer a temperature-sensitive instrument by which the temperature to
which it is exposed is continuously recorded.

Rectal thermometer a clinical thermometer that is inserted into the rectum.

4.3.2 HUMIDITY SENSOR:
Humidity sensors detect the relative humidity of the immediate environments in which
they are placed. They measure both the moisture and temperature in the air and express
relative humidity as a percentage of the ratio of moisture in the air to the maximum amount
that can be held in the air at the current temperature. As air becomes hotter, it holds more
moisture, so the relative humidity changes with the temperature.
Most humidity sensors use capacitive measurement to determine the amount of moisture
in the air. This type of measurement relies on two electrical conductors with a non-
conductive polymer film laying between them to create an electrical field between them.
Moisture from the air collects on the film and causes changes in the voltage levels between
the two plates. This change is then converted into a digital measurement of the air’s relative
humidity after taking the air temperature into account.

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UNIT-5
RF MODULE
RF MODULE is the only standards-based wireless technology designed to address the
unique needs of low-cost, low-power wireless sensor and control networks in just about any
market. Since RF MODULE can be used almost anywhere, is easy to implement and needs little
power to operate, the opportunity for growth into new markets, as well as innovation in existing
markets, is limitless. Here are some facts about RF MODULE:

 With hundreds of members around the globe, RF MODULE uses the 2.4 GHz radio
frequency to deliver a variety of reliable and easy-to-use standards anywhere in the
world.
 Consumer, business, government and industrial users rely on a variety of smart and easy-
to-use RF MODULE standards to gain greater control of everyday activities.

 With reliable wireless performance and battery operation, RF MODULE gives you the
freedom and flexibility to do more.

 RF MODULE offers a variety of innovative standards smartly designed to help you be
green and save money.

5.1 RELAY:

A relay is usually an electromechanical device that is actuated by an electrical current.
The current flowing in one circuit causes the opening or closing of another circuit. Relays are
like remote control switches and are used in many applications because of their relative

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simplicity, long life, and proven high reliability. Relays are used in a wide variety of applications
throughout industry, such as in telephone exchanges, digital computers and automation systems.
Highly sophisticated relays are utilized to protect electric power systems against trouble and
power blackouts as well as to regulate and control the generation and distribution of power. In
the home, relays are used in refrigerators, washing machines and dishwashers, and heating and
air-conditioning controls. Although relays are generally associated with electrical circuitry, there
are many other types, such as pneumatic and hydraulic. Input may be electrical and output
directly mechanical, or vice versa.

All relays contain a sensing unit, the electric coil, which is powered by AC or DC
current. When the applied current or voltage exceeds a threshold value, the coil activates the
armature, which operates either to close the open contacts or to open the closed contacts. When a
power is supplied to the coil, it generates a magnetic force that actuates the switch mechanism.
The magnetic force is, in effect, relaying the action from one circuit to another. The first circuit
is called the control circuit; the second is called the load circuit.

On/Off Control: Example: Air conditioning control, used to limit and control a “high
power” load, such as a compressor Limit Control:

Example: Motor Speed Control, used to disconnect a motor if it runs slower or faster than the
desired speed

Logic Operation: Example: Test Equipment, used to connect the instrument to a number
of testing points on the device under test.

Electromechanical Relays:

In our project we will be using an electromechanical relay, which will be a 5 pin relay
and the working of the relay will be like as. The general-purpose relay is rated by the amount of
current its switch contacts can handle. Most versions of the general-purpose relay have one to
eight poles and can be single or double throw. These are found in computers, copy machines, and
other consumer electronic equipment and appliances.

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Load Types:

Load parameters include the maximum permissible voltage and the maximum permissible
current. The relay can handle both volts and amps. Both the size of the load and its type are
important. There are four types of loads:

1.) Resistive, 2.) Inductive, 3.) AC or DC, and 4.) High or Low Inrush.

1.) Resistive Load is one that primarily offers resistance to the flow of current. Examples of
resistive loads include electric heaters, ranges and ovens, toasters and irons.

2.) Inductive Loads include power drills, electric mixers, fans, sewing machines and vacuum
cleaners. Relays that are going to be subjected to high-inrush inductive loads, such as an AC
motor, will often be rated in horsepower, rather than in volts and amps. This rating reflects the
amount of power the relay contacts can handle at the moment the device is turned on (or
switched).

3.) AC or DC – This affects the contacts circuit of the relay (due to EMF) and the timing
sequencing. And may result in performance issues in the switching capacity of the relay for
different load types (I.e. resistive, inductive, etc.).

4.) High or Low Inrush - Some load types draw significantly higher amounts of current
(amperage) when first turned then they do when the circuit later stabilizes (loads may also
pulsate as the circuit continues operating, thus increasing and decreasing the current). An

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example of a high inrush load is a light bulb, which may draw 10 or more times its normal
operating current when first turned on (some manufacturers refer to this as lamp load).

5.2 INTERNAL OPERATION OF MECHANICAL RELAYS

Standard: Single Side Stable with any of the following three different methods for closing
contacts:

1. Flexure Type: The armature actuates the contact spring directly, and the contact is driven into
a stationary contact, closing the circuit.

2. Lift-off Type: The moveable piece is energized by the armature, and the contact closes

3. Plunger Type: The lever action caused by the energization of the armature produces a long
stroke action. Reed: A Single Side Stable Contact that involves low contact pressure and a
simple contact point.

4. Polarized: Can be either a single side stable or dual-winding. A permanent magnet is used to
either attract or repel the armature that controls the contact. A definite polarity (+ or -) is required

By the relay coil. The latching option makes a polarized relay dual-winding, meaning it remains
in the current state after the coil is de-energized.

5.3 RELAY DRIVER (ULN2003):

The ULN2001A, ULN2002A, ULN2003 and ULN2004Aare high Voltage, high current
Darlington arrays each containing seven open collector Darlington pairs with common emitters.
Each channel rated at 500mAand can withstand peak currents of 600mA.Suppressiondiodesare
included for inductive load driving and the inputs are pinned opposite the outputs to simplify
board layout.

These versatile devices are useful for driving a wide range of loads including solenoids,
relays DC motors; LED displays filament lamps, thermal printheads and high power buffers. The
ULN2001A/2002A/2003A and 2004A are supplied in 16 pin plastic DIP packages with a copper
lead frame to reduce thermal resistance. They are available also in small outline package (SO-16)
as ULN2001D/2002D/2003D/2004D.

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FEATURES OF DRIVER:

• SEVENDARLINGTONS PER PACKAGE.
• OUTPUT CURRENT 500mA PER DRIVER (600mA PEAK)
• OUTPUT VOLTAGE 50V.
• INTEGRATED SUPPRESSION DIODES FOR INDUCTIVE LOADS.
• OUTPUTS CAN BE PARALLELED FOR HIGHER CURRENT.
• TTL/CMOS/PMOS/DTLCOMPATIBLE INPUTS.
• INPUTS PINNED OPPOSITE OUTPUTS TO SIMPLIFY LAYOUT

PIN CONNECTION:

5.4 SERIAL COMMUNICATION

A serial port sends and receives data one bit at a time over one wire. While it takes eight
times as long as to transfer each byte of data this way, only a few wires are required. In fact,

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two-way (full duplex) communications is possible with only three separate wires- one to send,
one to receive, and a common signal ground wire.

 Bi-directional communications
 Communicating by wires
 The Parity Bit
 Cable lengths
 MAX-232C
 DCE And DTE devices
 Synchronous and Asynchronous Communications

5.4.1 Bi-directional Communications

The serial port on your PC is a full-duplex device meaning that it can send and receive
data at the same time. In order to be able to do this, it uses separate lines for transmitting and
receiving data. Some types of serial devices support only one-way communications and
therefore use only two-wires in the cable – the transmit line and the signal ground.

5.4.2 Communicating by bits

Once the start bit has been sent, the transmitter sends the actual data bits. There may
either be 5, 6, 7 or 8 data bits, depending on the number you have selected. Both receiver and
the transmitter must agree on the number of data bits, as well as the baud rate. Almost all
devices transmit data using either 7 or 8 data bits. Notice that when only 7 data bits are
employed, you cannot send ASCII values greater than 127. Likewise, using 5 bits limits the
highest possible value to 31. After the data has been transmitted, a stop bit is sent. A stop bit
has a value of 1- or a mark state- and it can be detected correctly even if the previous data bit
also had a value of 1. This is accomplished by the stop bit’s duration.

5.4.3 The Parity Bit

Besides the synchronization provided by the use of start and stop bits, an additional bit
called a parity bit may optionally be transmitted along with the data. A parity bit affords a

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small amount of error checking, to help detect data corruption that might occur during
transmission.

5.4.4 Cable Lengths

The MAX-232 standard imposes a cable length limit of 50 feet. You can usually ignore
this “standard”, since a cable can be as long as 10000 feet at baud rates up to 19200 if you use
a high quality, well shielded cable. The external environment has a large effect on lengths for
unshielded cables.

5.4.5 MAX232 (Voltage Converter)

Since the RS232 is not compatible with today microprocessors and micro controller,
we need line driver to convert the RS232 signals to TTL voltage levels that will be acceptable
to the 8051’s TXD and RXD pins. One example of such a converter is MAX 232 from maxim
corp. The MAX 232 converts from RS232 voltage levels to TTL voltage levels, and vice versa.
One advantage of MAX232 chip is that it uses a +5V power source, which is the same as the
source voltage for the at89s52 micro controller. In other words, with a single +5v power supply
we can power both the PIC and MAX 232, with no need of for the dual power supplies that are
common in many older systems. The MAX 232 requires four capacitors ranging from 1 to 22
microfarad. The most widely used value for this capacitor is 22microfarad.

The MAX232 is a dual driver/receiver that includes a capacitive voltage generator to
supply TIA/EIA-232-Fvoltage levels from a single 5-V supply. Each receiver converts
TIA/EIA-232-F inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of
1.3 V, a typical hysterias is of 0.5 V, and can accept ±30-V inputs. Each driver converts
TTL/CMOS input levels into TIA/EIA-232-F levels.

PIN DIAGRAM OF MAX232

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Fig 4.5 max232 pin diagram

5.4.6 DCE and DTE devices

Two terms you should be familiar with are DTE and DCE. DTE stands for Data
Terminal Equipment, and DCE stands for Data Communication Equipment. These terms are
used to indicate the pin-out for the connectors on a device and the direction of the signals on
the pins. Your computer is a DTE device, while most other devices are usually DCE devices. If
you have trouble keeping the two straight then replace the term “DTE device” with your PC
and the term DCE device with “remote Device” in the following discussion. The RS-232
standard states that DTE devices use a 25-pin male connector, and DCE devices use a 25-pin
female connector. You can therefore connect a DTE device to a DCE using a straight pin-for-
pin connection. However, to connect two like devices, you must instead use a null modem
cable. Null modem cables cross the transmit and receive lines in the cable.

The DTE device puts this line in a mark condition to tell the remote device that it is
ready and able to receive data. If the DTE device is not able to receive data (typically because
its receive buffer is almost full), it will put this line in the space condition as a signal to the
DCE to stop sending data. When the DTE device is ready to receive more data it will place this
line back in the mark condition. The complement of the RTS wire is CTS, which stands for
Clear to Send. The DCE device puts this line in a mark condition to tell the DTE device that it
is ready to receive the data. Likewise, if the DCE device is unable to receive data, it will place
this line in the space condition. Together, these two lines make up what is called RTS/CTS or
“hardware” flow control. The software wedge supports this type of flow control as well as

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Xon/Xoff or “software” flow control. Software flow control uses special control characters
transmitted from one device to another to tell the other device to stop or start sending data.
With software flow control the RTS and CTS lines are not used.

DTR stands for Data Terminal Ready. Its intended function is very similar to the
RTS line. DSR (Data Set Ready) is the companion to DTR in the same way that CTS is to
RTS. Some serial devices use DTR and DSR as signals to simplify confirm that a device is
connected and turned on. The software wedge sets DTR to the mark state when the serial port
is opened and leaves it in that state until the port is closed. The DTR and DSR lines were
originally designed to provide an alternate method of hardware handshaking. It would be
pointless to use both RTS/CTS and DTR/DSR for flow control signals at the same time.
Because of this DTR and DSR are rarely used for flow control.

5.4.7 Synchronous and Asynchronous Communications

There are two basic types of serial communications, synchronous and asynchronous.
With synchronous communications, the two devices initially synchronize themselves to each
other, and then continually send characters to stay in sync. Even when the data is not really
being sent, a constant flow of bits allows each device to know where the other is at any given
time. That is, each character that is sent is either actual data or an idle character. Synchronous
communications allows faster data transfer rates than asynchronous methods, because
additional bits to mark the beginning and end of each data byte are not required. The serial
ports on IBM style PCs are asynchronous devices and therefore only support asynchronous
serial communications. Asynchronous means no “synchronization”, and thus does not require
sending and receiving idle characters. However, the beginning and end of each byte of data
must be identified by start and stop bits. The start bit indicates when the data byte is about to
begin and the stop bit signals when it ends.

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UNIT-6
HARDWARE REQUIREMENTS

6.1 MICROCONTROLLER
Introduction to microcontroller:
A computer-on-a-chip is a variation of a microprocessor which combines the processor
core (CPU), some memory, and I/O (input/output) lines, all on one chip. The computer-on-a-chip
is called the microcomputer whose proper meaning is a computer using a (number of)
microprocessor(s) as its CPUs, while the concept of the microcomputer is known to be a
microcontroller. A microcontroller can be viewed as a set of digital logic circuits integrated on a
single silicon chip. This chip is used for only specific applications.

Most microcontrollers do not require a substantial amount of time to learn how to
efficiently program them, although many of them, which have quirks, which you will have to
understand before you, attempt to develop your first application.
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Along with microcontrollers getting faster, smaller and more power efficient they are also
getting more and more features. Often, the first version of microcontroller will just have memory
and digital I/O, but as the device family matures, more and more pat numbers with varying
features will be available.

In this project we used PIC 16f877A microcontroller. For most applications, we will be
able to find a device within the family that meets our specifications with a minimum of external
devices, or an external but which will make attaching external devices easier, both in terms of
wiring and programming.

For many microcontrollers, programmers can built very cheaply, or even built in to the
final application circuit eliminating the need for a separate circuit. Also simplifying this
requirement is the availability of micro-controllers wit SRAM and EEPROM for control store,
which will allow program development without having to remove the micro controller fro the
application circuit.

6.2 PIC MICROCONTROLLER CORE FEATURES:

• 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.
• Pin out compatible to the PIC16C73B/74B/76/77
• Interrupt capability (up to 14 sources)
• Eight level deep hardware stack
• Direct, indirect and relative addressing modes.
• Power-on Reset (POR).

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• Power-up Timer (PWRT) and Oscillator Start-up Timer (OST).
• Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable operation.
• Programmable code-protection.
• Power saving SLEEP mode.
• Selectable oscillator options.
• Low-power, high-speed CMOS FLASH/EEPROM technology.
• Fully static design.
• In-Circuit Serial Programming (ICSP) .
• Single 5V In-Circuit Serial Programming capability.
• In-Circuit Debugging via two pins.
• Processor read/write access to program memory.
• Wide operating voltage range: 2.0V to 5.5V.
• High Sink/Source Current: 25 mA.
• Commercial and Industrial temperature ranges.
• Low-power consumption.

In this project we used PIC 16f877A microcontroller. PIC means Peripheral Interface
Controller. The PIC family having different series. The series are 12- Series, 14- Series, 16-
Series, 18- Series, and 24- Series. We used 16 Series PIC microcontrollers.

6.3 ADVANTAGES OF USING A MICROCONTROLLER OVER MICROPROCESSOR:

A designer will use a Microcontroller to
• Gather input from various sensors
• Process this input into a set of actions
• Use the output mechanisms on the Microcontroller to do something useful
• RAM and ROM are inbuilt in the MC.
• Cheap compared to MP.
• Multi machine control is possible simultaneously.

Examples 8051 (ATMEL), PIC (Microchip), Motorola (Motorola), ARM Processor.

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APPLICATIONS:

• Cell phones.

• Computers.

• Robots.

• Interfacing to two PC’s.

6.4 PIN DIAGRAM PIC 16 F874A/877A:

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6.5 FUNCTIONAL BLOCK DIAGRAM OF PIC 16F877A:

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PIN DESCRIPTION:

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OSC1/CLKI:

Oscillator crystal or external clock input. Oscillator crystal input or external clock source
input. ST buffer when configured in RC mode; otherwise CMOS. External clock source input.
Always associated with pin function OSC1 (see OSC1/CLKI, OSC2/CLKO pins).

OSC2/CLKO:

Oscillator crystal or clock output. Oscillator crystal output. Connects to The crystal or
resonator in Crystal Oscillator mode. In RC mode, OSC2 pin outputs CLKO, which has 1/4 the
frequency of OSC1 and denotes the instruction cycle rate.

MCLR/VPP:

Master Clear (input) or programming voltage (output). Master Clear (Reset) input. This
pin is an active low Reset to the device. Programming voltage input.

• RA0/AN0.
• RA1/AN1.
• RA2/AN2/VREF-/CVREF.
• VREFCVREF.
• RA3/AN3/VREF+.
• VREF+.
• RA4/T0CKI/C1OUT.
• T0CKI.
• C1OUT.
• RA5/AN4/SS/C2OUT/SS/C2OUT.
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.

PORT A AND TRIS A REGISTER:

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PORT A is a 6-bit wide, bidirectional port. The corresponding data direction register is
TRIS A. Setting a TRIS A bit (= 1) will make the corresponding PORT A pin an input (i.e., put
the corresponding output driver in a High – Impedance mode). Clearing a TRIS A bit (= 0) will
make the corresponding PORT A pin an output (i.e., put the contents of the output latch on the
selected pin). Reading the PORT A 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 PORT A
pins have TTL input levels and full CMOS output drivers. Other PORT A 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. The TRIS A register controls the direction of the port pins
even when they are being used as analog inputs. The user must ensure the bits in the TRIS A
register are maintained set when using them as analog inputs.

Note: On a Power-on Reset, these pins are configured as analog inputs and read as ‘0’. The
comparators are in the off (digital).

PORT B AND TRIS B REGISTER:

PORT B is an 8-bit wide, bidirectional port. The corresponding data direction register is
TRIS B. Setting a TRIS B bit (= 1) will make the corresponding PORT B pin an input (i.e., put
the corresponding output driver in a High-Impedance mode). Clearing a TRIS B bit (= 0) will
make the corresponding PORT B pin an output (i.e., put the contents of the output latch on the
selected pin). Three pins of PORT B are multiplexed with the In-Circuit Debugger and Low-
Voltage Programming function: RB3/PGM, RB6/PGC and RB7/PGD.

Four of the PORT B pins, RB7:RB4, have an interruption- change feature. Only pins
configured as inputs can cause this interrupt to occur (i.e., any RB7:RB4 pin configured as an
output is excluded from the interruption- change comparison). The input pins (of RB7:RB4) are
compared with the old value latched on the last read of PORTB. The “mismatch” outputs of

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RB7:RB4 are OR’ed together to generate the RB port change interrupt with flag bit RBIF
(INTCON<0>).

This interrupt can wake the device from Sleep. The user, in the Interrupt Service
Routine, can clear the interrupt in the following manner:

a) Any read or write of PORT B. This will end the mismatch condition.

b) Clear flag bit RBIF.

A mismatch condition will continue to set flag bit RBIF. Reading PORT B will end
the mismatch condition and allow flag bit RBIF to be cleared. The interrupt-on-change feature is
recommended for wake-up on key depression operation and operations where PORT B is only
used for the interrupt-on-change feature. Polling of PORT B is not recommended while using the
interrupt-on- change feature. This interrupt-on-mismatch feature, together with software
configurable pull-ups on these four pins, allow easy interface to a keypad and make it possible
for wake-up on key depression.

PORT C AND TRIS C REGISTER:

PORT C is an 8-bit wide, bidirectional port. The corresponding data direction register is
TRIS C. Setting a TRIS C bit (= 1) will make the corresponding PORT C pin an input (i.e., put
the corresponding output driver in a High- Impedance mode). Clearing a TRIS C bit (= 0) will
make the corresponding PORT C pin an output (i.e., put the contents of the output latch on the
selected pin). PORT C is multiplexed with several peripheral functions (Table 4-5). PORT C
pins have Schmitt Trigger input buffers. When the I2C module is enabled, the PORT C<4:3>
pins can be configured with normal I2C levels, or with SMBus levels, by using the CKE bit
(SSPSTAT<6>). When enabling peripheral functions, care should be taken in defining TRIS bits
for each PORT C 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
TRIS C as the destination, should be avoided. The user should refer to the corresponding
peripheral section for the correct TRIS bit settings.

PORT D AND TRIS D REGISTERS:

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PORT D is an 8-bit port with Schmitt Trigger input buffers. Each pin is individually
configurable as an input or output. PORT D can be configured as an 8-bit wide microprocessor
port (Parallel Slave Port) by setting control bit, PSP MODE (TRISE<4>). In this mode, the input
buffers are TTL.

PORT E AND TRIS E REGISTER:

PORT E 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 PORT E 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 TRIS E<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 TRIS
E register which also controls the Parallel Slave Port operation. PORT E pins are multiplexed
with analog inputs.

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

MEMORY ORGANIZATION:

There are three memory blocks in each of the PIC16F87XA devices. The program
memory and data memory have separate buses so that concurrent access can occur and is
detailed in this section. The EEPROM data memory block is detailed in.

PROGRAM MEMORY ORGANIZATION:

The PIC16F87XA devices have a 13-bit program counter capable of addressing an 8K
word x 14 bit program memory space. The PIC16F876A/877A devices have 8K words x 14 bits
of Flash program memory, while PIC16F873A/874A devices have 4K words x 14 bits.
Accessing a location above the physically implemented address will cause a wraparound. The
Reset vector is at 0000h and the interrupt vector is at 0004h.

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The data memory is partitioned into multiple banks which contain the General Purpose
Registers and the Special Function Registers. Bits RP1 (Status<6>) and RP0 (Status<5>) are the
bank select bits. Each bank extends up to 7Fh (128 bytes). The lower locations of each bank are
reserved for the Special Function Registers. Above the Special Function Registers are General
Purpose Registers, implemented as static RAM. All implemented banks contain Special Function
Registers. Some frequently used Special Function Registers from one bank may be mirrored in
another bank for code reduction and quicker access.

TIMER0 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
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.
TIMER0 INTERRUPT:

The TMR0 interrupt is generated when the TMR0 register overflows from FFh to 00h.
This overflow sets bit TMR0IF (INTCON<2>). The interrupt can be masked by clearing bit
TMR0IE (INTCON<5>). Bit TMR0IF must be cleared in software by the Timer0 module
Interrupt Service Routine before re-enabling this interrupt. The TMR0 interrupt cannot awaken
the processor from Sleep since the timer is shut-off during Sleep.

TIMER1 MODULE:

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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 or 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. Shows the Timer1 Control register. When the

Timer1 oscillator is enabled (T1OSCEN is set), the RC1/T1OSI/CCP2 and
RC0/T1OSO/T1CKI pins become inputs. That is, the TRISC<1:0> value is ignored and these
pins read as ‘0’.

TIMER2 MODULE:

Timer2 is an 8-bit timer with a pre scaler and a post scaler. 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.

IN-CIRCUIT DEBUGGER:

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PIC16F87XA devices have a Watchdog Timer which can be shut-off only through
configuration bits. It runs off its own RC oscillator for added reliability. There are two timers
that offer necessary delays on power-up. One is the Oscillator Start-up Timer (OST), intended to
keep the chip in Reset until the crystal oscillator is stable. The other is the Power-up Timer
(PWRT), which provides a fixed delay of 72 ms (nominal) on power-up only. It is designed to
keep the part in Reset while the power supply stabilizes. With these two timers on-chip, most
applications need no external Reset circuitry. Sleep mode is designed to offer a very low current
power-down mode. The user can wake-up from Sleep through external Reset, Watchdog Timer
wake-up or through an interrupt. Several oscillator options are also made available to allow the
part to fit the application. The RC oscillator option saves system cost while the LP crystal option
saves power. A set of configuration bits is used to select various options.

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UNIT-7
POWER SUPPLY UNIT

Power supply unit consists of following units:

1) Step down transformer
2) Rectifier unit
3) Input filter
4) Regulator unit
5) Output filter
7.1 STEPDOWN TRANSFORMER:
The Step down Transformer is used to step down the main supply voltage from 230V AC
to lower value. This 230 AC voltage cannot be used directly, thus it is stepped down. The
Transformer consists of primary and secondary coils. To reduce or step down the voltage, the
transformer is designed to contain less number of turns in its secondary core. The output from
the secondary coil is also AC waveform. Thus the conversion from AC to DC is essential. This
conversion is achieved by using the Rectifier Circuit/Unit.
Step down transformers can step down incoming voltage, which enables you to have the
correct voltage input for your electrical needs. For example, if our equipment has been specified
for input voltage of 12 volts, and the main power supply is 230 volts, we will need a step down
transformer, which decreases the incoming electrical voltage to be compatible with your 12 volt
equipment.

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7.2 RECTIFIER UNIT:
The Rectifier circuit is used to convert the AC voltage into its corresponding DC voltage.
The most important and simple device used in Rectifier circuit is the diode. The simple function
of the diode is to conduct when forward biased and not to conduct in reverse bias. Now we are
using three types of rectifiers. They are
1. Half-wave rectifier
2. Full-wave rectifier
3. Bridge rectifier

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7.2.1 Half-wave rectifier: In half wave rectification, either the positive or negative half of the
AC wave is passed, while the other half is blocked. Because only one half of the input waveform
reaches the output, it is very inefficient if used for power transfer. Half-wave rectification can be
achieved with a single diode in a one phase supply, or with three diodes in a three-phase supply.

7.2.2 Full-wave rectifier: A full-wave rectifier converts the whole of the input waveform to one
of constant polarity (positive or negative) at its output. Full-wave rectification converts both
polarities of the input waveform to DC (direct current), and is more efficient. However, in a
circuit with a non-center tapped transformer, four diodes are required instead of the one needed
for half-wave rectification. A full-wave rectifier uses a diode bridge, made of four diodes, like
this

At first, this may look just as confusing as the one-way streets of Boston. The thing to realize is
that the diodes work in pairs. As the voltage of the signal flips back and forth, the diodes shepard
the current to always flow in the same direction for the output.

Here's what the circuit looks like to the signal as it alternates:

So, if we feed our AC signal into a full wave rectifier, we'll see both halves of the wave above 0
Volts. Since the signal passes through two diodes, the voltage out will be lower by two diode
drops, or 1.2 Volts.

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7.2.3 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.

A diode bridge or bridge rectifier is an arrangement of four diodes in a bridge configuration
that provides the same polarity of output voltage for either polarity of input voltage. When used
in its most common application, for conversion of alternating current (AC) input into direct
current (DC) output, it is known as a bridge rectifier. A bridge rectifier provides full-wave
rectification from a two-wire AC input, resulting in lower cost and weight as compared to a
center-tapped transformer design.

The Forward Bias is achieved by connecting the diode’s positive with positive of the
battery and negative with battery’s negative. The efficient circuit used is the Full wave Bridge
rectifier circuit. The output voltage of the rectifier is in rippled form, the ripples from the
obtained DC voltage are removed using other circuits available. The circuit used for removing
the ripples is called Filter circuit.

7.3 INPUT FILTER
Capacitors are used as filter. The ripples from the DC voltage are removed and pure DC
voltage is obtained. And also these capacitors are used to reduce the harmonics of the input
voltage. The primary action performed by capacitor is charging and discharging. It charges in
positive half cycle of the AC voltage and it will discharge in negative half cycle. So it allows
only AC voltage and does not allow the DC voltage. This filter is fixed before the regulator.
Thus the output is free from ripples.

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There are two types of filters. They are

1. Low pass filter
2. High pass filter
7.3.1 Low pass filter:

One simple electrical circuit that will serve as a low-pass filter consists of a resistor in
series with a load, and a capacitor in parallel with the load. The capacitor exhibits reactance, and
blocks low-frequency signals, causing them to go through the load instead. At higher frequencies
the reactance drops, and the capacitor effectively functions as a short circuit. The combination of
resistance and capacitance gives you the time constant of the filter τ = RC (represented by the
Greek letter tau). The break frequency, also called the turnover frequency or cutoff frequency (in
hertz), is determined by the time constant: or equivalently (in radians per second):

One way to understand this circuit is to focus on the time the capacitor takes to charge. It
takes time to charge or discharge the capacitor through that resistor:

• At low frequencies, there is plenty of time for the capacitor to charge up to
practically the same voltage as the input voltage.

• At high frequencies, the capacitor only has time to charge up a small amount
before the input switches direction. The output goes up and down only a small fraction of the
amount the input goes up and down. At double the frequency, there's only time for it to charge
up half the amount.

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Another way to understand this circuit is with the idea of reactance at a particular
frequency:

• Since DC cannot flow through the capacitor, DC input must "flow out" the path
marked Vout (analogous to removing the capacitor).

• Since AC flows very well through the capacitor — almost as well as it flows
through solid wire — AC input "flows out" through the capacitor, effectively short circuiting to
ground (analogous to replacing the capacitor with just a wire).

It should be noted that the capacitor is not an "on/off" object (like the block or pass fluidic
explanation above). The capacitor will variably act between these two extremes. It is the Bode
plot and frequency response that show this variability.

7.3.2 High pass filter:

The above circuit diagram illustrates a simple 'RC' high-pass filter. we should find that the circuit
passes 'high' frequencies fairly well, but attenuates 'low' frequencies. Hence it is useful as a filter
to block any unwanted low frequency components of a complex signal whilst passing higher
frequencies. Circuits like this are used quite a lot in electronics as a 'D.C. Block' - i.e. to pass a.c.
signals but prevent any D.C. voltages from getting through.

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The basic quantities which describe this circuit are similar to those used for the Low Pass Filter.
In effect, this circuit is just a simple low-pass filter with the components swapped over.

The action of the circuit can also be described in terms of a related quantity, the Turn over
Frequency, f0, which has a value

As with the low-pass filter, the circuit's behavior we can be understood as arising due to the time
taken to change the capacitor's charge when we alter the applied input voltage. It always takes a
finite (i.e. non-zero) time to change the amount of charge stored by the capacitor. Hence it takes
time to change the potential difference across the capacitor. As a result, any sudden change in the
input voltage produces a similar sudden change on the other side of the capacitor. This produces
a voltage across the resistor and causes a current to flow thorough it, charging the capacitor until
all the voltage falls across it instead of the resistor. The result is that steady (or slowly varying)
voltages appear mostly across the capacitor and quick changes appear mostly across the resistor.
Since we're using the voltage across the resistor as out output the main properties of the circuit
are
Therefore

The Voltage Gain:

The Phase Delay:

Try using the above experimental system to collect results and plot a graph of how the voltage
gain, Av, (and the phase change) depend upon the input frequency and if we check result agrees
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with the above formulae. Compare this with a low-pass filter that uses the same component
values and you should see that they give 'opposite' results. In the high-pass filter, the output
waveform 'leads' the input waveform - i.e. it peaks before the input.

7.4 REGULATOR UNIT

7805 Regulator
Regulator regulates the output voltage to be always constant. The output voltage is
maintained irrespective of the fluctuations in the input AC voltage. As and then the AC voltage
changes, the DC voltage also changes. Thus to avoid this Regulators are used. Also when the
internal resistance of the power supply is greater than 30 ohms, the output gets affected. Thus
this can be successfully reduced here. The regulators are mainly classified for low voltage and
for high voltage. Further they can also be classified as:

i) Positive regulator
1---> input pin
2---> ground pin
3---> output pin
It regulates the positive voltage.
ii) Negative regulator
1---> ground pin
2---> input pin
3---> output pin
It regulates the negative voltage.

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Fixed regulators

An assortment of 78xx series ICs
"Fixed" three-terminal linear regulators are commonly available to generate fixed voltages of
plus 3 V, and plus or minus 5 V, 9 V, 12 V, or 15 V when the load is less than about 7 amperes.

7805 VOLTAGE REGULATOR:

The 7805 provides circuit designers with an easy way to regulate DC voltages to 5v.
Encapsulated in a single chip/package (IC), the 7805 is a positive voltage DC regulator that has
only 3 terminals. They are: Input voltage, Ground, Output Voltage.
General Features:
• Output Current up to 1A
• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

• Thermal Overload Protection

• Short Circuit Protection

• Output Transistor Safe Operating Area Protection

7812 12V Integrated Circuit3-Terminal Positive Voltage Regulator:
• The 7812 fixed voltage regulator is a monolithic integrated circuit in a TO220
type package designed for use in a wide variety of applications including
local, onboard regulation. This regulator employs internal current limiting,
thermal shutdown, and safe area compensation.

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• With adequate heat-sinking it can deliver output currents in excess of 1.0
ampere. Although designed primarily as a fixed voltage regulator, this device
can be used with external components to obtain adjustable voltages and
currents.

7.5 OUTPUT FILTER
The Filter circuit is often fixed after the Regulator circuit. Capacitor is most often used
as filter. The principle of the capacitor is to charge and discharge. It charges during the positive
half cycle of the AC voltage and discharges during the negative half cycle. So it allows only AC
voltage and does not allow the DC voltage. This filter is fixed after the Regulator circuit to filter
any of the possibly found ripples in the output received finally. Here we used 0.1µF capacitor.
The output at this stage is 5V and is given to the Microcontroller. The output voltage overshoots
when the load is removed or a short clears. When the load is removing from a switching mode
power supply with a LC low-pass output filter, the only thing the control loop can do is stop the
switching action so no more energy is taken from the source. The energy that is stored in the
output filter inductor is dumped into the output capacitor causing a voltage overshoot.
The magnitude of the overshoot is the vector sum of two orthogonal voltages, the output voltage
before the load is removed and the current through the inductor times the characteristic
impedance of the output filter, Zo = (L/C)^1/2. This can be derived from conservation of energy
considerations.
The initial energy, Ei, is:
Ei = 1/2*(L*Ii^2 + C*Vi^2)

The final energy, Ef, is:

Ef = 1/2*(L*If^2 = C*Vf^2)

The two energies are equal when the load is removed, since the load is no longer taking energy
from the system. Equating the two energies, substituting zero current for the final inductor
current, then the solution for the final voltage Vf is:

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Vf = (Vi^2 + (Ii*Zo)^2)^1/2

This is the orthogonal vector sum of the output voltage and the load current times the
characteristic impedance and is illustrated in Figure 1.

Figure 1: Overshoot Voltage as Vector Sum

The problem becomes worse if the current in the inductor is established by a short circuit on the
output and the short circuit clears. In this case, the initial voltage is zero (short circuit) and the
overshoot is I*Zo, where I can be very large, resulting in a ruinous overshooot

7.6 RF MODULES

The relay subsystem is an electrically-operated switch. It
requires a separate electrical supply to provide power to
an output device. It is often used for reversing motors.

Like ordinary switches, relay switches are available as single-pole single-throw (SPST), single-
pole double-throw (SPDT), and double-pole double-throw (DPDT). The circuit diagram shows

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a DPDT relay.

The switching is done by a coil of wire (an electromagnet) that creates a magnetic field when a
current passes through it.
The switch contacts in the relay change over due to the force from the magnetic field when a
current passes through the coil.

The reverse biased diode is included because, when relays are switched off, they can generate a
‘back e.m.f.’ that can damage the driver. When the relay is switched off the diode conducts
current and prevents the damage.
The driver subsystem that provides the input signal to the relay must be able to supply enough
current for the coil.

A DPDT relay has three pairs of connections known as common (CO), normally open (NO) and

normally closed (NC).

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A DPDT relay is often used to reverse a motor. The circuit diagram on the left shows how the
motor is connected to the relay.

Relay circuit for reversing a motor

When the input signal to the relay is high there is no current in the relay coil (as on the left), the
positive side of the battery B1 is connected to the right-hand terminal of the motor, so the current
in the motor flows from right to left.
When the input signal to the relay is low there is current in the relay coil (as on the left) and the
switch contacts change over. So now the positive side of the battery is connected to the left-hand
terminal of the motor, the current in the motor flows from left to right and so the direction of
rotation of the motor reverses.

The circuit diagram shows the basic principles. If it is necessary to stop and start the motor this
can be done with a separate driver or a SPST relay.

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A few relays need relatively low currents and can be driven directly from a PIC, 555
Timer IC or LM324 op-amp. In these cases the relay coil is connected to the input signal and to
0V.

Possible applications
• Reversing a motor
• Providing electrical isolation between a noisy output device (such as a motor) and the
processing electronics.

• Controlling a low voltage a.c. output device, e.g. a low voltage halogen bulb (hotlink to
bulb data sheet, section that refers to halogen bulb)

Making:

Pins of the Rapid 60-0100 DPDT relay

The diagram shows the pin arrangements and numbering for the Rapid 60-0100 DPDT relay.
Note the unusual pin labelling system. The PCB shows the basic circuit. The separate power
supply and output device would be connected to the six upper pins.

Build and test the driver unit that will provide the input signal before building the relay.

Use a 16-pin Dual In Line (DIL) socket for the relay. Before inserting the relay, connect the
power supply and use a voltmeter to check that:

• the voltage on pin ‘b’ is high (the supply voltage);
• the voltage on pin ‘a’ (the blue PCB track) goes high and low in response to the driver
unit that provides the input signal.

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Insert the relay the right way round.

7.7 TESTING

Use a multimeter to test the resistance between the switch contacts and make sure that
their resistance changes from high to low when the coil is switched on and off.

Fault finding

If there is a fault, check that:

• The voltage on pin ‘b’ is high
• The relay has been correctly inserted

If there is a fault, check the tracks and solder joints.

Alternatives
• Pair of SPDT relays can be used to provide forward, reverse, stop and start for a motor –
this has the advantage of providing a better ‘brake’ for a motor but is more expensive.
• A L293D IC can also be used to provide forward, reverse, stop and start for two motors –
this has the advantage of providing a better ‘brake’ for a motor, but is more expensive.

• If the relay is being used to provide electrical isolation from noise, an alternative is the
opto-isolator.

HUMIDITY SENSOR:

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Humidity sensitive resistor is used a new type of organic polymer materials, the humidity
sensing element, with a sense of wet-range, fast response, strong anti-pollution, no heat cleaning
and performance is stable and reliable long-term use and many other features. Humidity Sensor:
Our professional agents of the product, the series is complete, fast delivery. This product is
widely used in: air conditioning, refrigerator, water heater, radio clock, electronic calendar,
microwave ovens, cars, granaries, medical equipment, fire alarm devices, small appliances and
other fields.
Sensor type: humidity sensor
Operating temperature: 0...60°C
Measuring range: 20%...95% RH
Output configuration: analogue voltage
Tolerance: ±5% RH
Features:
- Highly marketable product - Small and light
- Long history - Mass production
Application
Weather station, Humidifier & dehumidifier, Air-conditioner, Refrigerator and so on

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A humidity sensor also called a hygrometer, measures and regularly reports the relative
humidity in the air. They may be used in homes for people with illnesses affected by humidity;
as part of home heating, ventilating, and air conditioning (HVAC) systems; and in humidors or
wine cellars. Humidity sensors can also be used in cars, office and industrial HVAC systems, and
in meteorology stations to report and predict weather.

A humidity sensor senses relative humidity. This means that it measures both air
temperature and moisture. Relative humidity, expressed as a percent, is the ratio of actual
moisture in the air to the highest amount of moisture air at that temperature can hold. The
warmer the air is, the more moisture it can hold, so relative humidity changes with fluctuations in
temperature.

The most common type of humidity sensor uses what is called “capacitive measurement.”
This system relies on electrical capacitance, or the ability of two nearby electrical conductors to
create an electrical field between them. The sensor itself is composed of two metal plates with a
non-conductive polymer film between them. The film collects moisture from the air, and the
moisture causes minute changes in the voltage between the two plates. The changes in voltage
are converted into digital readings showing the amount of moisture in the air.

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7.8 INVETER:

So how can an inverter give us a high voltage alternating current from a low voltage
direct current?
Let's first consider how an alternator produces an alternating current. In its simplest form, an
alternator would have a coil of wire with a rotating magnet close to it. As one pole of the
magnet approaches the coil, a current will be produced in the coil. This current will grow to a
maximum as the magnet passes close to the coil, dying down as the magnetic pole moves
further away. However when the opposite pole of the magnet approaches the coil, the current
induced in the coil will flow in the opposite direction.
As this process is repeated by the continual rotation of the magnet, an alternating current is
produced.

Now let’s consider what a transformer does. A transformer also causes an electric current to be
induced in a coil, but this time, the changing magnetic field is produced by another coil having
an alternating current flowing through it. Any coil with an electric current flowing through it
will act like a magnet and produce a magnetic field. If the direction of the current changes then
the polarity of the field changes.

Now, the handy thing about a transformer is that, the voltage produced in the secondary coil is
not necessarily the same as that applied to the primary coil. If the secondary coil is twice the
size (has twice the number of turns) of the primary coil, the secondary voltage will be twice
that of the voltage applied to the primary coil. We can effectively produce whatever voltage we
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want by varying the size of the coils.

If we connected a direct current from a battery to the primary coil it would not induce a current
in the secondary as the magnetic field would not be changing. However, if we can make that
direct current effectively change direction repeatedly, then we have a very basic inverter. This
inverter would produce a square wave output as the current would be changing direction
suddenly.

This type of inverter might have been used in early car radios that needed to take 12 volts
available in the car and produce the higher voltages required to run radio valves (known as
tubes in America) in the days before transistors were widely used.

100Watt Inverter 24VDC to 220VAC II

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This is another 100watt inverter circuit diagram. Built based on IC CD4047 and Mosfet IRF540,
this inverter have ability to supply electronic device -which require 220VAC- up to 100w from
2-3A transformer..

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UNIT-8
SOFTWARE REQUIREMENTS

8.1 SOFTWARE TOOLS
• Development tool – MPLAB IDE v7.42

• Hardware Compiler - HI-Tech PIC C

• Programmer - PIC Flash

• Hardware Simulation tool - Proteus v7.6Sp0

8.2 INTRODUCTION TO EMBEDDED ‘C’:

Ex: Hitec – c, Keil – c

HI-TECH Software makes industrial-strength software development tools and C
compilers that help software developers write compact, efficient embedded processor code.

For over two decades HI-TECH Software has delivered the industry's most reliable
embedded software development tools and compilers for writing efficient and compact code to
run on the most popular embedded processors. Used by tens of thousands of customers including
General Motors, Whirlpool, Qualcomm, John Deere and many others, HI-TECH's reliable
development tools and C compilers, combined with world-class support have helped serious
embedded software programmers to create hundreds of breakthrough new solutions.

Whichever embedded processor family you are targeting with your software, whether it is
the ARM, PICC or 8051 series, HI-TECH tools and C compilers can help you write better code
and bring it to market faster.

HI-TECH PICC is a high-performance C compiler for the Microchip PIC micro
10/12/14/16/17 series of microcontrollers. HI-TECH PICC is an industrial-strength ANSI C

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compiler - not a subset implementation like some other PIC compilers. The PICC compiler
implements full ISO/ANSI C, with the exception of recursion. All data types are supported
including 24 and 32 bit IEEE standard floating point. HI-TECH PICC makes full use of specific
PIC features and using an intelligent optimizer, can generate high-quality code easily rivaling
hand-written assembler. Automatic handling of page and bank selection frees the programmer
from the trivial details of assembler code.

8.3 EMBEDDED “C” COMPILER

• ANSIC - full featured and portable
• Reliable - mature, field-proven technology
• Multiple C optimization levels
• An optimizing assembler
• Full linker, with overlaying of local variables to minimize RAM usage
• Comprehensive C library with all source code provided
• Includes support for 24-bit and 32-bit IEEE floating point and 32-bit long data types
• Mixed C and assembler programming
• Unlimited number of source files
• Listings showing generated assembler
• Compatible - integrates into the MPLAB IDE, MPLAB ICD and most 3rd-party
development tools
• Runs on multiple platforms: Windows, Linux, UNIX, Mac OS X, Solaris

8.4 MPLAB INTEGRATION

development of embedded applications employing Microchip's PIC micro and dsPIC
microcontrollers. MPLAB IDE runs as a 32-bit application on MS Windows, is easy to use
and includes a host of free software components for fast application development and super-
charged debugging. MPLAB IDE also serves as a single, unified graphical user interface for
additional Microchip and third party software and hardware development tools. Moving

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