The LED Display System is used at the colleges and schools for displaying day-to-day information continuously or at regular intervals during the working hours. Being a WIRELESS transceiver system, it offers flexibility to display flash news or announcements faster than the programmable system. The wireless-based display system can also be used at other public places like schools, hospitals, railway stations, gardens etc. without affecting the surrounding environment. The LED display system mainly consists of a WIRELESS transceiver and a display toolkit which can be programmed from an Arduino. It consists of the main purpose is to convey the information through the LED. It can serve as the information passing in as an electronic display board and display the important displays instantaneously this avoiding the latency. Being wireless, the WIRELESS based LED display is easy to expand and allows the user to add more and more display units at any time and at any location in the campus depending on the requirement of the institute.

1. A Project Report
On
“WIRELESS ELECTRONIC DISPLAY BOARD USING”
Submitted in partial fulfillment for the requirements of the degree of
BACHELOR OF TECHNOLOGY IN
ELECTRONICS AND COMMUNICATION ENGINEERING
Submitted By:-
ABHISHEK ANAND 14BTECE014
NAISHADH MAURYA 14BTECE016
VINIT UPADHYAY 14BTECE018
VAIBHAV PANDEY 14BTECE031
PROJECT ADVISOR PROJECT COORDINATOR
Dr. ANIL KUMAR Er. NEELESH AGARWAL
(ASSISTANT PROFESSOR) (ASSISTANT PROFESSOR)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SHEPHERD INSTITUTE OF ENGINEERING AND TECHNOLOGY
SAM HIGGINBOTTOM UNIVERSITY OF AGRICULTURE, TECHNOLOGY AND SCIENCES
ALLAHABAD-211 007, (U.P) INDIA
Batch: 2014-2018

2. CERTIFICATE
This is to certify that the project work entitled “WIRELESS ELECTRONIC DISPLAY BOARD”
is a bonafied piece of project work carried out by Mr. ABHISHEK ANAND, Mr. NAISHADH
MAURYA, Mr. VINIT UPADHYAY and Mr. VAIBHAV PANDEY in partial fulfilment for the
award of Degree of Bachelor of Technology in Electronics and Communication Engineering,
Shepherd Institute of Engineering and Technology, Sam Higginbottom University of Agriculture,
Technology and Sciences.
Project Advisor Project Co-ordinator
Dr. Anil Kumar Er. Neelesh Agarwal
(Assistant Professor) (Assistant Professor)
___________________________
Head of Department
Prof. A. K. Jaiswal
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
SHEPHERD INSTITUTE OF ENGINEERING AND TECHNOLOGY
SAM HIGGINBOTTOM UNIVERSITY OF AGRICULTURE, TECHNOLOGY AND SCIENCES
ALLAHABAD-211 007, (U.P) INDIA

3. ACKNOWLEDGEMENT
We feel profound in bringing out this project report for which we had to go from pillar to pillar
post and make it a reality. This project work contribution of many people with whom we had long
discussion and without which it would not have been possible. We must first of all, express our
heartiest gratitude to respected Dr. Anil Kumar (project advisor) for providing us all guidance
required by us to complete the project.
We should also like to thank our Head of Department, Prof. A.K. Jaiswal for his encouragement,
motivation and support throughout the project.
Last but not least we express our sincerity, thanks to the institute of Shepherd Institute Of
Engineering And Technology, Allahabad for providing such a platform for implementing the idea
in our mind and allowing us to grow as budding engineering’s.
NAME OF STUDENTS IN GROUP ID. No.
ABHISHEK ANAND 14BTECE014
NAISHADH MAURYA 14BTECE016
VINIT UPADHYAY 14BTECE018
VAIBHAV PANDEY 14BTECE031

4. CONTENTS
Chapter Topic Page No.
LIST OF FIGURE i-ii
LIST OF TABLE iii
LIST OF ABBREVIATION iv
1. INTRODUCTION 1-2
1.1. Application of the project module 2
2. THEORY OF OPERATION 2-6
2.1. Working Principle 3
2.2. Block Diagram of Project Model Designed 3
2.2.1. Block Diagram Description 4
2.3 Circuit Diagram 5
2.3.1. Circuit Description 6
3. PCB LAYLOUT OF THE MAIN CIRCUIT 8-19
3.1. PCB Layout 8
3.2. Printed Circuit Board (PCB) 8
3.2.1 Express PCB 9
3.3. Beginning a New Layout 9
3.3.1. Placing the Component 9
3.3.2. Placing the Pad 10
3.3.3. Component Placement 10
3.3.4. Working with Traces 10
3.3.5. Placing Filled Plane 11
3.3.6. Making Custom Component 11
3.4. PCB designing and Fabrication 12
3.5. Flow Chart for Step of PCB Design 13
3.5.1. Processing 14
3.5.2. Cleaning 15
3.5.3. Etching 15
3.5.4. Drilling 16
3.5.4.1. Component Placement 17
3.5.5. Soldering 17
3.5.5.1. The Soldering Kit 17

5. 3.5.5.2. Way of Soldering 18
3.5.5.3. Tips of Soldering 18
3.5.5.4. Precautions 19
3.5.6. Masking 19
4. PROBLEM FACED AND REMEDIAL ACTION 20-21
4.1. Problem Faced 20
4.1.1. Over Etching 20
4.1.2. Short Circuit in Layout 20
4.2. Remedial Action 21
5. LIST OF COMPONENT USED 22-59
5.1. Components Description 23
5.1.1. Microcontroller Description 23
5.1.2. Features 27
5.1.3. Pin and Diagram Description 27
5.1.4. Introduction to AVR Microcontroller 30
5.1.4.1. Architecture of AVR 30
5.1.5. LED Display Board 34
5.1.5.1. Preparing the Matrix Display Board 34
5.1.5.1.1. 74595 IC 37
5.1.5.2. Connection between 8*8 LED Matrices 38
5.1.5.2.1. Connection b/w LED Matrix IST 74595 39
5.1.5.2.2. Connection b/w LED Matrix 2
and 2nd
74595 40
5.1.5.2.3. Connection between LED MATRIX 1 and
1st 74595, LED MATRIX 2 and 2nd 74595,
74595 ICs and Arduino Mega 41
5.1.6. Arduino Uno 46
5.1.6.1. Pins of Arduino UNO Board 47
5.1.7. Wireless Transceiver 49
5.1.8. Capacitors 50
5.1.9. Diode 51
5.1.10. Resistor 52
5.1.11. Crystal Oscillator 54
5.1.12. LM7805 56
5.1.12.1. Description 56
5.1.13. LM358 Op-Amp 57
5.1.13.1. Features 58
5.1.14. Accessories 58

6. 5.1.14.1. Adapter 58
5.1.14.2. Connector 59
5.1.14.3. Switch 59
6. EMBEDDED SYSTEM 62-63
7. APPLICATIONS 64
APPENDIX

7. [i]
LIST OF FIGURE
S. NO. Figure Name Page No.
1. 2.1. Block Diagram of Electronics Display Board 4
2. 2.2. Circuit Diagram of Display Board 6
3. 3.1. PCB Layout of Electronic Display Board 8
4. 3.2. Flow Chart for Step of PCB Design 14
5. 3.3. Flow Chart for Step of Cleaning Process 15
6. 4.1. Over Etching PCB 20
7. 4.2. Short Circuited Layout 20
8. 5.1. 8051 Microcontroller Pin Diagram 27
9. 5.2. Block Diagram of AVR Microcontroller 30
10. 5.3. AVR Architecture 32
11. 5.4. LED Matrix 35
12. 5.5. Detailed view of LED Matrix 36
13. 5.6. Circuit of LED Matrix 36
14. 5.7. 74595 IC 37
15. 5.8. Connection between 2 LED Matrices 38
16. 5.9. Connection between LED matrix 1 and 74595 IC 39
17. 5.10. Connection between LED matrix 2 and 74595 IC 40
18. 5.11. Connection between LED MATRIXES
1 and 1st 74595, LED MATRIX 2 and 2nd 74595, 41
74595 ICs and Arduino Mega
19. 5.12. Display the word "HE" in the 8*8 LED matrix 42
20. 5.13. a, b, c, d, e, f & g Adjustment of Row & Column of
Letter ‘HE’ on LED Board 45
21. 5.14. Arduino Uno Board 47
22. 5.15. Arduino Uno Board Pin Diagram 48
23. 5.16. Wireless Transceiver 49
24. 5.17. Capacitor 50
25. 5.18. Diode 51
26. 5.19. Resistor 52
27. 5.20. Crystal Oscillator 54
28. 5.21. LM7805 56
29. 5.22. Voltage Output from the LM7805 57
30. 5.23. LM358 Op-Amp 57
31. 5.24. Internal Block Diagram of Op-amp 58
32. 5.25. Connector wire 59

8. [ii]
33. 5.26. Toggle Switch 60
34. 5.27. Pushbutton Switch 60
35. 5.28. Selector Switch 61
36. 5.29. Joystick Switch 61
37. 5.30. Level Actuator Limit Switch 61
38. 5.31. Proximity Switch 62
39. 6.1. Embedded System 63

9. [iii]
LIST OF TABLES
S. NO. Table Name Page No.
1. 5.1. Component List 22
2. 5.2. Member of AVR Family 34
3. 5.3. The value of resistor and tolerance value 53

10. [iv]
LIST OF ABBREVIATION
µF - Micro-Farad
A/D - Analog to Digital
AC - Alternating Current
DC - Direct Current
Volt - Voltage
Amp - Ampere
mA - milli-ampere
mV - milli-volt
PEROM - Programmable and erasable read only memory
RST - Reset
ALE - Address Latch Enable
LED - Light Emitting Diode
PCB - Printed Circuit Board
DSP - Digital Signal Processor
DTPR - Data Pointer Register
PC - Program Counter
Tx/Rx - Transmitter/ Receiver

11. 1
1. INTRODUCTION
In this world everyone needs a comfort living life. Man has researched different technology for his sake
of his life. In today’s world of connectedness, people are becoming accustomed to easy access to
information. Whether it’s through the Internet or television, people want to be informed and up-to-date
with the latest events happening around the world.
Wired network connection such as Ethernet has many limitations depending on the need and type of
connection one has. Ethernet is established using single cable, which is shared by all other devices. But
the biggest limitation of establishing wired connection is the extensive cabling. To overcome from it
the technology switches to wireless communication. People prefer wireless connections because they
can interact with their peers and friends wherever they are.
The main objective of this project is to develop a wireless display board that displays messages sent
from the user. Display Board is primary thing in any institution/ organization or public utility places
like bus stations, railway stations and parks. But sticking various displays day-to-day is a difficult
process. A separate person is required to take care of this displays display. This project deals about an
advanced hi-tech wireless display board.
In past years, the WIRELESS transceiver system has used from a many areas in terms of mobile phones,
personal computers, laptops are to be commonly used by the rich to something so it can be major used.it
already owns by many area networks are available. This is amazing when
We look at the fact that our country in a developing one with almost half our population living below
the poverty line. This continuously growing popularity of the WIRELESS Connection has been used
to the growth of the country’s area network infrastructure has developed much more.
The LED used as the information are to be displayed. It specifies the characters and to display it
whenever type to show the text in to the user language. All major urban areas are currently covered by
both WIRELESS network providers, and soon every single corner of the peoples has used in mobiles
in a very poor villages to call away. The method to need for constant communication with family and
friends, coupled with the relatively cheap method of sending short text messages to them, has
information a WIRELESS revolution in the country. In fact, rarely will a used this method use his cell
phone to make a phone call, Preferring to anything and everything. All mobile phones has available in
WIRELESS network. Then WIRELESS network has been used to provide wide area network allows

12. 2
as to communicate with the information into text message through LCD display to move the display
board. Information can passing through for a specific service
Provide as chatting and to transmit and receive the information. News/traffic reports, and downloading
of ring tones for their phones. These services all themselves with one or more network ranges providers
will give them a special code number that can receive and monitor.
The information that their display board send to them. This many-to-one network of information
transmission has become quite popular and many a business has entered into this model with mixed
results. However, as of this writing, the vast majority of businesses that revolve around the WIRELESS
system have been targeted to consumers. This paper aims to propose industrial applications that will
utilize the distinct advantages of the WIRELESS. This system over other possible technologies in the
industrial process.
1.1 APPLICATION OF THE PROJECT MODULE
 To display the Room Rents, Available rooms
 and to AC or NON-AC rooms details in hotels
 It is used to colleges to display the placement news, circulars, daily events, schedules etc.
 Used in hotels to display the food items and menu offers etc.
 By using railway stations scheduling time to be displayed and platforms the service offered by the
railways.
 To display the nursing homes using the staff attendance availability of the doctors, list of the
specialized doctors and no of patients etc.
2. THEORY OF OPERATION
The design of accident prevention using eye blink sensor detector based on following assumption.
1. Push Button Message Box.
2. Arduino UNO board is used.
3. LED Display board is used to display message.

13. 3
2.1. WORKING PRINCIPLE
The LED Display System is used at the colleges and schools for displaying day-to-day information
continuously or at regular intervals during the working hours. Being WIRELESS transceiver system,
it offers flexibility to display flash news or announcements faster than the programmable system.
WIRELESS-based display system can also be used at other public places like schools, hospitals,
railway stations, gardens etc. without affecting the surrounding environment. The LED display system
mainly consists of a WIRELESS transceiver and a display toolkit which can be programmed from an
Arduino. It consists of the main purpose is to convey the information through the LED. It can serve as
the information passing in as an electronic display board and display the important displays
instantaneously this avoiding the latency. Being wireless, the WIRELESS based LED display is easy
to expand and allows the user to add more and more display units at any time and at any location in the
campus depending on the requirement of the institute.
2.2. BLOCK DIAGRAM
Transmitter Section
Keypad Wireless
Transceiver
Atmega 8
Power
supply

14. 4
Receiver Section
Figure 2.1: Block Diagram of Electronic Display Board
2.2.1. BLOCK DIAGRAM DSCRIPTION
Push button is an important part of a circuit.it is mainly used to all purposes. Because it has been used
to all works are to be implemented. It is basically used to transmit the message to the display board by
pressing the button. There are maximum four button, each button store a particular message when press
the button its shows the message on the display. There is the memory which store the message for each
memory. The processor and other devices get power supply from the vcc pins, 5 volts to give the
connection. The Arduino UNO board can be connected to the push button message box and Wireless
router. The push button message box has been used as to any information to be send and receive by
using WIRELESS transceiver. The Arduino UNO can be powered via the USB connection or with an
external power supply. The power source is selected automatically. External (non-USB) power can
come either from an AC-to-DC adapter (wallwart) or battery. The adapter can be connected by plugging
a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the
Gnd. and Vin pin headers of the Power connector. The board can operate on an external supply of 6 to
20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the
board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the
board. The recommended range is 7 to 12 volts. The LED display system mainly consists of a
WIRELESS transceiver and a display toolkit which can be programmed from an Arduino UNO board.
It consists of the main purpose is to convey the information through the LED. It can serve as the

15. 5
information passing in as an electronic notice board and display the important notices instantaneously
this avoiding the latency. Being wireless, the WIRELESS based LED display is easy to expand and
allows the user to add more and more display units at any time and at any location in the campus
depending on the requirement of the institute. WIRELESS transceiver is used to implement this
method.it has been implemented to transmit and receive the information at a time. Then it can transmit
the information has been very fasting the range. The WIRELESS has been to use as to information
passing and send is large distances. The WIRELESS coverage distance has been used to area has up to
100 meter available. Information passing and send is large distances. The WIRELESS coverage
distance has been used to area has up to 100 meter available.
This application has been used in any information has to been send notification using paperless to a
group of students in campus requirements and class cancellation, Test announcement and class
postponements without moving information through paper. The advantages of the work includes that
the information could be received very fast and it reduces the number of non-notified students. This
presents a new way of online communications through personal computer to notice board to helps
students and lecturers to be always aware of appointments no matter where they are. Among the
advantages of the system include reduced time lag problem.
2.3. CIRCUIT DIAGRAM
(A) TRANSMISTER SECTION

16. 6
(B) RECEIVER SECTION
Figure 2.3. Circuit Diagram of Electronic Display Board; a) Transmitter Section, b) Receiver Section
2.3.1. CIRCUIT DESCRIPTION
A monochrome (single colour) LED dot matrix display is used for displaying the Characters and
Symbols which is interface with a microcontroller. This project will deliberate on displaying a scrolling
text message on a 48×8 LED dot matrix display. The microcontroller used is Arduino Uno which is
open source prototype Electronic platform. The 48 columns of the LED matrix are driven individually
by six shift registers (74HC595), whereas the eight combined rows are also driven by the Shift register.
Here we will be scanning across the rows and feed the column lines with appropriate logic levels. The
program in the microcontroller is to determine the speed of the scrolling message as well as Message
what we are going to display. The technique will be demonstrated for right to left scroll, but can be
easily implemented for scrolling in other directions. The Sketch program for Arduino Uno is developed
with Arduino Software.
The more important of this project is microcontroller, LED Display Board and Arduino Board.
The above circuit of the Wireless Electronic Display Board using ESP8266 WIRELESS MODULE of
Arduino Uno, WIRELESS Transceiver Module (Modem) and LED. Here, the LED is used to display

17. 7
message and is used in 8 – bit mode. Means, we need 8 data lines to display the data. The data lines of
the LED Display are connected to PORT1 Pins. The control pins RS, RW, and E pins are connected to
P3.6, GND and P3.7 pins respectively.
The WIRELESS Transceiver Module is directly connected to the Arduino Uno as the logic levels of
both the WIRELESS Transceiver Module Modem and Arduino Uno are already matched in the
WIRELESS Module Board. If there is no level converter on the board, then we need to use MAX232
level converter as a mediator between Controller and WIRELESS Transceiver Module to transfer the
data.
In order to communicate with the WIRELESS Transceiver Module Modem, we need to send some AT
commands using serial communication (UART protocol). Here, WIRELESS Transceiver Module is
used. This module requires 9600 baud rate. Matrix wiring each matrix has 64 LEDs. Instead the LEDs
are wired into a matrix. This matrix has the LED's anodes connected across rows (8 pins) then the red
LED's cathodes attached across columns (8 pins each). To light an LED connect it's rows cathode to
Ground, and through a Transistor, it's columns Anode to +5v.
Displaying Images (Scanning) Now that we can light any LED we choose it's time to move on to
displaying a (small) image. To do this we will use a scan pattern. In the example code we define a
bitmap image (an array of 8 bytes, each bit representing one LED). Next we scan through this array
one byte at a time, displaying one column then the next. If we do this fast enough (about 1000 times a
second) it appears as an image. It sounds complex but if you download the code and play around it
should quickly become clear
Here, we will cascade two 74595 ICs for controlling two 8*8 LED matrices. LED matrices are
arranged in such a way that control pins of LED matrices should be at the top and bottom of the LED
matrix as shown in the following image. To avoid confusion in fixing LED matrices, note the position
of wedges at the middle of sides of each LED matrices.

18. 8
3. PCB LAYOUT AND DESIGNING
3.1. PCB LAYOUT
Figure 3.1: PCB with component layout from bottom view.
3.2. PRINTED CIRCUIT BOARD (PCB)
A PCB layout is required to place component on the PCB so that the component area can be minimized
and components can be placed in an efficient manner. The component can be placed in two ways, either
manually or by software. The manual procedure is quiet cumbersome and very inefficient. The other
method is by the use of computer software. The method is advantageous as it saves time and valuable
copper area. There are various software’s available for this purpose are:-
 Express PCB
 Porte2pad
 Proteus ISIS 7
 PCB design etc.
Many of them loaded with auto routing and auto placement facility. The software that we have used
here is Express PCB. This software has a good interface, easy editing options and wide range of
component.

19. 9
3.2.1. EXPRESS PCB
Express PCB is a very easy to use Windows application for laying out printed circuit boards. There are
two parts to Express PCB, Express PCB, and Express SCH for drawing schematics and Express PCB
for designing circuit boards. We downloaded the software from the website www.expresspcb.com.
There are lots of functions available in the software. This software is free of cost and it is very easy to
use. The different layers of the PCB can be viewed by just a click of a button on the interface. And we
easily get its print on paper which is utilized for further processing. We can design single sided PCB
as well as double sided PCB with software.
3.3. BEGINNING A NEW LAYOUT
1. Begin a new layout by running Express PCB.
2. In the main window, the yellow rectangle defines the perimeter of the PC board. Set the size of
your board by moving three of its four corners (upper left corner is fixed at 0, 0). Move the corners
by dragging them with the mouse. Or by double- clicking them and entering coordinates.
3. Zooming and panning: the easiest way to move around your with the scroll wheel on the mouse.
Turning the wheel zooms in and out. Pressing the wheel and dragging the mouse pans.
3.3.1. PLACING THE COMPONENT
The easiest way to place components in your board layout is to use the component manager.
Tip: Use the find button to search for a PCB footprint by its name. To place a component:
1. Click the button located on the top toolbar to display the component manager.
2. Select one of these categories: Library components – Components that included with the
programme – Custom components – Components that you have drawn – Favourite
components – Components or symbols that you have book marked.
3. From the list box, choose the item to insert them select the component’s orientation (rotated
up. Left, down, or right) by clicking one of these buttons.
4. Press the insert component into PCB button, then drag the component to the desired location.

20. 10
5. Assign the component’s Part ID (such as R1 or U2). To do this, select then double click on
the component to display its component properties dialog box.
3.3.2. PLACING THE PAD
Individual pads are used both to build new components and as via. To insert a pad:
1. From the side toolbar, select or press the P shortcut key.
2. Select the pad size from the drop down list box on the top toolbar. These are several pad types:
round, square, surface mount and are used to pass traces between layers. Regular pads differ
from via pads in that express PCB may eliminate via. If the traces connecting to it are all on
the same layer.
3. To place the pad, click on your layout at the desired location.
3.3.3. COMPONENT PLACEMENT
These are the steps to add traces to your layout. If you have drawn a schematic for your circuit, be
sure to read the section linking the schematic and PCB before you begin.
a. From the side toolbar, select or press the T shortcut key.
b. Select the trace width from the drop down list box on the top toolbar. A width of 0.010” is a
good default for digital and analog signals. For power lines, use traces 0.05” or wider.
c. Select the layer by clicking or by pressing the L shortcut key.
d. Move the mouse to trace’s first end point and click. Drag the trace to the second end point,
and then click again. Continue placing trace segment (use the L key to change layers) until
you have reached the final point end point.
e. Tip: keep an eye on the status bar when connecting traces to components. It will display the
pin and part number to which the trace is connected.
f. As you drag he trace, the L key changes layers, the Del key deletes the previous segment, the
+ and – keys zoom in ad out, the G key toggles the snap to grid on and off. The spacebar sets
the trace, and press the Esc key cancels it.
g. To complete the operation, press the spacebar or click right.
3.3.4. WORKING WITH TRACES

21. 11
Traces themselves cannot be remove. The path of the trace is determined by the straight line between
its two connections. Therefore, to move, you need connect it to something different o to move what
it is connected to. Corners in traces allow them to bend. They are displayed as small square blocks at
the ends of traces. In your final PC board layout, the corners will not be included.
Corners can be ragged, inserted or deleted to change the trace’s path. To insert a corner, select the
required tab then click to choose the layer on which the corner will be placed then click on the trace
at the point where you want to insert the corner. To disconnect a trace and reconnect it elsewhere,
select desired tab from the side toolbar. Next, click on the trace near the point you want disconnect,
and then drag the trace to new pin.
3.3.5. PLACING FILLED PLANE
Filled planes are used to add ground or power to circuit, usually on double-sided boards. They can be
placed on the top or bottom layers. The parameter can have the shape of nay polygon and the interior
is automatically insulted from traces and pads.
To place a filled plane, select the proper tab, then on the on the top toolbar choose the draw filed plane
option, along with layer. Next use the mouse to draw the perimeter. Do this by clicking the mouse
button at each corner, then clicking right after you have placed the last corner. Connect a pad to pad
to plane clicking on the pad. In the popup menu, select one of the top layer pad shape or bottom layer
pad shape options.
3.3.6. MAKING CUSTOM COMPONENT
Express PCB includes many component that you can use to create your PCB. However if you need a
footprint not in our library, you can easily build your own.
Here is how:
1. First add the pads by selecting and choosing a pad type on the top toolbar. Carefully position
the pads with the correct spacing. It may be helpful to change the snap-to-grid spacing in the
options dialog. Tip: if u cannot find a pad size you need, create a custom pad.

22. 12
2. Assign each pad a pin number. This must be done if you link your PCB to its schematic.
Assign pin numbers by selecting and then double clicking on each pad to display its pad
properties dialog box. In the pin number field, enter the pin number.
3. Draw the component outline for the new part on the silkscreen layer. Draw straight lines by
selecting or circles and arcs using. Be sure to select the silkscreen layer before drawing the
outline by clicking. The recommended line width drawing component outlines is 0.012”.
Check the concerned tab in the toolbar.
4. Group everything together to combine it into a single component as follows. Select all of the
objects in your new part by clicking and then dragging the mouse to enclose them. From the
component menu, choose the command group to make PCB component. Next, double click
the new component to assign its Part ID (i.e. U12).
5. Save the component to add it to the custom component list. Do this by selecting the part with
the mouse and then choosing save custom component from the component menu.
3.4. PCB DESINGING AND FARBICATION
1. What is PCB?
Printed Circuit Board are used for housing components to make a circuit for compactness, simplicity
of servicing and case of interconnection. Thus we can also define as the Printed Circuit Boards is
actually a sheet of Bakelite (an insulating material) on the one side of which copper patterns are made
with holes and from another side, leads of electronic components are inserted in the proper holes and
soldered to the copper points on the back. Thus leads of electronic components terminals are joined
to make electronic circuit.
A PCB populated with electronic components is called a printed circuit assembly (PCA),
Printed circuit board assembly or PCB assembly (PCBA). In informal use the term “PCB” is used
both for bare and assembly boards, the context clarifying the meaning. Alternatives to PCB’s include
wire wrap and point to point construction.
PCB’s must initially be designed and laid out, but become cheaper, faster to make and potentially
more reliable for high volume production since production and soldering of PCB’s can be automated.

23. 13
Much of the electronics industry’s PCB design, assembly and quality control needs are set by standard
published by IPC organisation. PCB are inexpensive and can be highly reliable. They required much
more layout effort and higher initial cost than either wire wrapped or point to point constructed
circuits, but are cheaper and faster for high volume production.
Much of the electronics industry’s PCB design, assembly and quality control needs are set by
standards that are published by the IPC organization. Printed circuit boards are primarily an insulating
material used as base, into which conductive strips are printed. The base material is generally fibre
glass and the conductive connection are generally copper and made through an etching process. The
main PCB board is called the motherboard; the smaller attachment PCB boards are daughter boards
or daughter cards.
2. What is PCB design?
The Design for Manufacturing step is where a PCB designer (slang: "layout guy" or "layout gal")
makes his contribution to that portion of the product that involves electronic circuits. For that part
of the product, an electrical engineer has done the engineering, or circuit design in the step just before
this. He has produced, among other sub-products, a diagram of the functionality of the circuit. This
diagram is called a "schematic." It contains symbols connected by lines. For example, a zig-zag line
is used to represent a resistor, a type of electrical component that reduces the voltage of a current that
passes through it.
PCB board design the electrical pathways between the components. It is derived from a schematic
representation of the circuit. When it is derived or imported from a schematic design, it translates the
schematic symbol and libraries into physical components and connections.
UNITS: PCB boards are primarily designed in imperial units (inches) as opposed to the metric units
(mm). A thousand of an inches is called mil (not to be confused with mm), where: 100mils =0.1 inch
= 2.54 mm. The reason for using imperial units in a PCB documents is because most of the component
were manufactured according to imperial pin spacing. The practice continues even today.
3.5. FLOW CHART FOR STEP OF PCB DESIGN
The layout of a PCB has to incorporate all the information on the bard before one can go on the art
work preparation. This means that a concept that clearly defines all the details of the circuit and partly

24. 14
also of the final equipment, is a prerequisite before the actual layout can start. The detail circuit
diagram is very important for the layout designer and he must also be familiar with the design concept
and with the philosophy behind the 0equipment. PCB Designing includes the following steps:
Figure 3.2: Flow Chart for step of PCB Design.
3.5.1. PROCESSING
The layout of a PCB has incorporate all the information on the board before one can go on to the art
work preparation. This means that a concept that clearly defines all the details of the circuit and partly
also of the final equipment, is a prerequisite before the actual layout can start. The detail circuit
diagram is very important for the layout designer and he must also be familiar with the design concept
and with the philosophy behind the equipment. The general considerations are-
1. PROCESSING
3. PRINTING
2. CLEANSING
4. ETCHING
5. DRILLING
6. SOLDERING
7. MASKING

25. 15
 LAYOUT SCALE: Depending upon the accuracy required, artwork should be produced at
a 1:1 or 2:1 or even 4:1 scale. The layout is the best prepared on the same scale as the artwork.
This prevents all the problem which might be caused by redrawing of layout to the art work
scale.
 GRID SYSTEM OR GRAPH PAPER: It is commonly accepted practice to use these for
designing.
 BOARD TYPES: There are two sides of a PCB board – Component side & older side.
Depending on these board are classified as-
 SINGLE SIDED BOARDS: These are used where costs have to be kept at a minimum & a
particular Circuit can be accommodated on such board. To jump over conductor tracks,
components have to be utilized. If this is not feasible, jumper wires are used. (Jumper wires
should be less otherwise double-sided PCB should be considered.
 DOUBLE- SIDED BOARDS: These are made with or without plated through holes. Plated
through holes are fairly expensive.
3.5.2. CLEANING
Figure 3.3: Flowchart for Steps of Cleaning Process.
Water Rinse
Acid dip
Final Rinse De-ionized Water
Tap Water
Tap Water
Scrubbing
Drying
Wet Brushing
Oven or Blowing Of
air
Hydrochloric Acid
HCL
Pumice/ Acid Slurry

26. 16
The cleaning of the copper surface prior to resist application is an essential step for any type of PCB
process using etches or plating resist. After scrubbing with the abrasive, a water rinse with remove
most of the remaining slurry.
3.5.2. ETCHING
It is of utmost importance to choose a suitable etchant systems. They are many factors to be
considered:-
 Etching speed
 Copper solving capacity
 Etchant price
 Pollution character
Operation characteristics of different etchants:-
We have uses (Conc. 120 g/l 0.1 M) for etching.
Reaction involved:-
 Fecl3 + 3H2O --------- Fe (OH)3 + 3HCl
 FeCl3 + Cu ----- CuCl + FeCl2
 FeCl3 + CuCl ----- FeCl2 +CuCl2
 CuCl2 + Cu ------ 2CuCl
3.5.2 DRILLING
Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross- section in
solid materials. The drill bit is a rotary cutting toll, often multipoint. The bit is pressed against the
work piece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the
cutting edge against the work- piece, cutting off chips from what will become the hole being drilled.

27. 17
1. Exceptionally, specially-shaped bits can cut holes of non-circular cross section; a square cross-
section is possible.
2. The importance of whole drilling into PCB’s has further gone with electronic component
miniaturization and its need for smaller holes diameters (diameters less than half the board
thickness) and higher package density.
The following hole diameter tolerances have been generally accepted wherever no other
specifications are mentioned.
Hole diameter (D) <= 1mm +/-0.05 mm
Hole diameter (D) > 3mm +/-0.1 mm
Drill bits are made up of high-speed steel (HSS), glass epoxy material, tungsten carbide.
3.5.2.1 COMPONENT PLACEMENT
1. Component placement is an extremely important function of the designer.
2. Component should be placed according to their connections to other components, thermal
considerations, mechanical requirement, as well as signal integrity and rout-ability.
3. Components which have connections to each other should be placed in the same vicinity.
4. For example, a processor should be placed very close to the RAM and flash ICs on which it
relies.
5. Component should also be placed on a grid, usually a 100 mil grid, in order to provide for a
symmetric flow of routing where tracks and components are lined up.
3.5.3 SOLDERING
Soldering is a process in which two or more metal items are joined together by melting and then flow
a filter metal (solder) into the joint. The filter metal having a lower melting point than the work of
piece. Soldering differs from welding in that soldering does not involve melting the work pieces. In
brazing, the filler metal at a higher temperature, but the work piece metal does not melt. Electronic
soldering connects electrical writing and electronic components to printed circuits boards. Soldering

28. 18
filter materials are available in many different alloys for differing applications. In electronics
assembly, the eutectic alloy of 63% tin and 37% lead has been the alloy of choice.
3.5.3.1 THE SOLDERING KIT
 SOLDERING IRON: As soldering is a process of joining together two metallic parts, the
instrument, which is used, for doing this job is known as soldering Iron. Thus it is meant for
melting the solder and to setup the metal parts being joined. Soldering Iron is rated according
to their wattage, which varies from 10- 200 watts.
 SOLDER: The raw material used for soldering is solder. It is composition of lead & tin. The
good quality solder (a type of flexible naked wire) is 60% Tin +40% Lead which will melt
between 180℃ to 200℃ .
 FLUXES OR SOLDERING PASTE: When the points to solder are heated, an oxide film
forms. This must be removed at once so that solder may get to the surface of the metal parts.
This is done by applying chemical substance called Flux, which boils under the heat of the
iron remove the oxide formation and enable the metal to receive the solder.
 BLADES OR KNIFE: To clean the surface & leads of components to be soldered is done
by this common instrument.
 SAND PAPER: The oxide formation may attack at the tip of your soldering iron & create
the problem. To prevent this, clean the tip with the help of sand paper time to time or you may
use blade for doing this job. Apart from all these tools, the working bench for soldering also
includes disoldering pump, wink wire (used for disoldering purpose), file etc.
3.5.3.2 WAY OF SOLDER
Mount components at their appropriate place; bend the leads slightly outwards to prevent them from
falling out when the board is turned over for soldering. No cut the leads so that you may solder them
easily. Apply a small amount of flux at these components leads with the help of a screwdriver. Now
fix the bit or iron with a small amount of solder and flow freely at the point and the P.C.B copper
track at the same time. A good solder joint will appear smooth & shiny. If all appear well, you may
continue to the next solder connections.
3.5.3.3 TIPS FOR SOLDERING

29. 19
1. Use right type of soldering iron. A small efficient soldering iron (about 10-25 watts with 1/8
or 1/4 inch tip) is ideal for this work.
2. Keep the hot tip of the soldering iron on a piece of metal so that excess heat is dissipated.
3. Make sure that connection to the soldered is clean. Wax frayed insulation and other substances
cause poor soldering connection. Clean the leads, wires, tags etc. before soldering.
4. Use just enough solder to cover the lead to be soldered. Excess solder can cause a short circuit.
5. Use sufficient heat. This is the essence of good soldering. Apply enough heat to the component
lead. You are not using enough heat, if the solder barely melts and forms a ground ball of
rough flaky solder. A good solder joint will look smooth, shining and spread type. The
difference between good & bad soldering is just a few seconds extra with a hot iron applied
firmly.
3.5.3.4 PRECAUTIONS
1. Mount the components at the appropriate places before soldering. Follow the circuit
description and components details, leads identification etc. Do not start soldering before
making it confirm that all the components are mounted at the right place.
2. Do not use a spread solder on the board, it may cause short circuit.
3. Do not sit under the fan while soldering.
4. Position the board so that gravity tends to keep the solder where you want it.
5. Do not over heat the components at the board. Excess heat may damage the components or
board.
6. The board should not vibrate while soldering otherwise you have a dry or a cold joint.
7. Do not put the kit under or over voltage source. Be sure about the voltage either dc or ac while
operating the gadget.
8. Do spare the bare ends of the components leads otherwise it may short circuit with the other
components. To prevent this use sleeves at the component leads or use sleeved wire for
connections.
9. Do not use old dark colour solder, it may give dry joint. Be sure that all the joints are clean
and well shiny.
10. Do make loose wire connections especially with cell holder, speaker, probes etc. Put knots
while connections to the circuit board, otherwise it may get loose.

30. 20
3.5.4 MASKING
It is done for the protection of conductor track from oxidation. Solder mask or solder resist a lacquer-
like layer of polymer that provides a permanent protective coating for the copper traces of a printed
circuits board and prevents solder from bridging between conductions, thereby preventing shorts
circuits. Solder mask was created primarily to facilitate wave soldering used in mass assembly. Solder
mask is traditionally green but is now available in many colours. Solder mask comes in different
media depending upon the demands of the application. The lowest cost solder mask is epoxy liquid
that is silkscreened or sprayed on the PCB, exposed to the pattern onto the PCB. Other types are the
liquid photo image able solder mask (LPSM) inks and dry film photo image able solder mask
(DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to
provide openings in the pattern for parts to be soldered to copper pads. DFSM is vacuum laminated
on the PCB then exposed and developed. All three processes go through a thermal cure of some type
after the pattern is defined.
4. PROBLEM FACED AND REMEDIAL ACTION TAKEN
4.1 PROBLEM FACED
4.1.1 OVER ETCHING
Figure 4.1: Over etching PCB.
4.1.2 SHORT CIRCUIT IN LAYOUT

31. 21
Figure 4.2: Short circuited layout.
4.2 REMEDIAL ACTION
Urgently we change the PCB plate. And we made a new layout, etching the PCB plate again.

32. 22
5. LIST OF COMPONENT AND USAGE
TABLE 5.1: Component List
S.No. NAME SPECIFICATION QUANTITY COST
1 Microcontroller ATMEGA 8 1 Rs.150
2 LED Display Board 1024 LED Lights 1 Rs.1024
3 Frame To cover the LED Matrix 1 Rs.350
3 Battery 6F22, 9V and 0% mercury and
cadmium.
1 Rs.40
4 Arduino UNO Project Controlled by the board 1 Rs.550
5 PCB plate Copper coated board 1 Rs.140
6 Wireless Module Wireless Transceiver 2 Rs.450
7 Power Adapter 220V, 50Hz into 10V, 50Hz 1 Rs.450
8 Switch Used For ON or OFF remote
control
1 Rs.10
9 Micro Switch Push to send messages 4 Rs.20
11 Capacitor 10uf 2 Rs.20

33. 23
5.1 COMPONENT DESCRIPTION
5.1.1 MICROCONTOLLER DESCRIPTION
Microcontroller is a small computer on a single integrated circuit containing a processor core,
memory, and programmable input peripherals. Program memory in the form of Ferroelectric
RAM, NOR flash or OTP ROM is also often included on chip, as well as a typically small amount
of RAM. Microcontrollers are designed for embedded applications, in contrast to
the microprocessors used in personal or other general purpose applications consisting of various
discrete chips. A microcontroller is s a computer on a chip, or if you prefer a single chip
computer .Micro suggests that the device is small, and controller tells that the device might be used
to control objects, processes, or events. Another term to describe a microcontroller is embedded
controller; because the microcontroller and its support circuits are often built into, or embedded in,
the device they control.
Micro suggests that the device is small, and controller tells that the device might be used to control
objects, processes, or events. Another term to describe a microcontroller is embedded controller;
because the microcontroller and its support circuits are often built into, or embedded in, the device
they control. You can find microcontroller in all kinds of things these days, any device that measures,
stores, control, calculate or displays information is a candidate for putting a microcontroller inside.
The largest single use for microcontroller is in automobiles – just about every car manufactured today
include at least one microcontroller for engine control, and often more to control additional system in
the car. In desktop computers, you can find microcontrollers inside keyboards, modems, printers and
other peripherals. In test equipment’s, microcontroller make it easy toad features ability to add
features such as ability to store measurements, to create and store user routines, and to display
12 Resistance 10K±5% 2 Rs.2
220 Ohm 8 Rs.5
13 74595 IC Controlling Rows and Columns
of matrix
4 Rs.60
14 7805 IC 1 Rs.10
TOTAL Rs.3281

34. 24
message and waveforms. Consumer products that use microcontrollers includes cameras, video
recorders, compacts disk players, and ovens. And these are just few examples.
Microcontrollers are used in automatically controlled products and devices, such as automobile
engine control systems, implantable medical devices, remote controls, office machines, appliances,
power tools, toys and other embedded systems. By reducing the size and cost compared to a design
that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it
economical to digitally control even more devices and processes. Mixed signal microcontrollers are
common, integrating analog components needed to control non-digital electronic systems.
Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4
kHz, for low power consumption (single-digit milli watts or microwatts). They will generally have
the ability to retain functionality while waiting for an event such as a button press or other interrupt;
power consumption while sleeping (CPU clock and most peripherals off) may be just nano watts,
making many of them well suited for long lasting battery applications. Other microcontrollers may
serve performance-critical roles, where they may need to act more like a digital signal
processor (DSP), with higher clock speeds and power consumption
Micro-controllers may not implement an external address or data bus as they integrate RAM and non-
volatile memory on the same chip as the CPU. Using fewer pins, the chip can be placed in a much
smaller, cheaper package.
Integrating the memory and other peripherals on a single chip and testing them as a unit increases the
cost of that chip, but often results in decreased net cost of the embedded system as a whole. Even if
the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU and external
peripherals, having fewer chips typically allows a smaller and cheaper circuit board, and reduces the
labour required to assemble and test the circuit board, in addition to tending to decrease the defect
rate for the finished assembly.
A micro-controller is a single integrated circuit, commonly with the following features:
1. Central Processing Unit - Ranging from small and simple 4-bit processors to complex 32-
bit or 64-bit processors
2. Volatile memory (RAM) for data storage
3. ROM, EPROM, EEPROM or Flash memory for program and operating parameter storage

35. 25
4. Discrete input and output bits, allowing control or detection of the logic state of an individual
package pin
5. Serial input/output such as serial ports (UARTs)
6. Other serial communications interfaces like I²C, Serial Peripheral Interface and Controller
Area Network for system interconnect
7. Peripherals such as timers, event counters, PWM generators, and watchdog
8. Clock generator - often an oscillator for a quartz timing crystal, resonator or RC circuit
9. Many include analog-to-digital converters, some include digital-to-analog converters
10. In-circuit programming and in-circuit debugging support.
Microcontrollers are basically LSI chips with millions of logic gates constituting an Arithmetic and
Logic Unit (ALU), accompanying registers, bus control circuitry and an instruction decoder. This is
the definition in the strictest sense. Most modern microcontrollers usually have on chip RAM and
ROM and a few peripherals such as timers, serial interfaces such as a UART(Universal Asynchronous
Receiver Transmitter), ports and even ADC’s (Analog to Digital Converters). A wide variety of
microcontrollers is available today. Some are general purpose, while some are optimized for special
applications. A few well known microcontrollers are Intel’s 8051, 8085, Pentium, Motorola’s 68000
and 68008, Atmel’s AVR series, AMD’s Athlon, and the relatively new PSoC from Cypress.
A few important terms:
Word or Word size: It is smallest group of bits upon which normal arithmetic operations are carried
out (although there are instructions operating on individual bits). Memory units store bits in groups
called words. A word moves in and out of memory as a unit. A memory address is the location of a
word of the memory. Word size is usually a multiple of 8bits.
Arithmetic and Logic Unit: This unit performs basic arithmetic and logic functions like add, subtract
and AND, OR etc., on operands stored in memory or registers.
Register: Aregister is a collection of flip-flops, used to store limited amount of data (a flip-flop stores
one bit) such as status information, pointers etc.
Program and Data Memory: Program memory is that part of the memory where code written by
the user is stored. It also stores constants. This memory is usually the ROM and has to be programmed
using special hardware (although it can also be programmed in system). It also stores a program called

36. 26
the “bootstrap loader”, which gets the microcontroller started when power is first turned on. Some
popular types of ROM are EPROM, EEPROM and more recently flash. Data memory is that part of
the memory hierarchy which is used to store variables defined by the user and values generated during
program execution. This memory is the RAM.
Program Counter: As mentioned previously the user’s code is stored in the ROM. While executing
the program a special register called the Program Counter keeps track of the next instruction in the
program to be fetched. At the start of a program’s execution the Program Counter stores the address
of the first instruction of the program and as each instruction is executed, it is incremented. This helps
the microcontroller in knowing what location to fetch the next instruction from. The Program Counter
is not always incremented. For example when a “jump to location A” kind of instruction is
encountered, the Program Counter stores the address of “location A”.
Stack Pointer: In simple words a stack is a method of storing data in a particular manner. The data
element that is first to go into a stack is the last to come out of it. The “top” of the stack is the only
place in a stack where addition or deletion can take place. In most microcontrollers the stack is stored
starting from a special location in the memory. One of the uses of the stack is to store the contents of
the Program Counter when a subroutine is encountered. The Stack Pointer is a register containing the
address of the “top” of the stack.
Addressing Modes: Most of the instructions in a program will mention its operands and their location
i.e. addresses in memory or register space. An address may not always be specified in absolute terms,
i.e. the address may not be the address of the operand. In such cases the mode of addressing used in
the instruction tells the microcontroller how to interpret the address and calculate the operand’s
address. This is done to provide the user flexibility, to shorten the instruction size (not having to
specify the whole address, but only a part of it) etc. For example the indirect addressing mode is used
to specify a memory location where not the operand but its address is stored.
Interrupts: An interrupt is a way of asking the microcontroller to stop what it is doing and attend to
the source of the interrupt. An example is that of I/O systems in microcontrollers. These I/O systems
issue an interrupt when they receive some data or have completed transmitting some data. This helps
in saving processing time as the microcontroller doesn’t have to keep checking the I/O systems for
an arrival of data or completion of transfer of data. There can be many other sources of interrupts.

37. 27
Ports: They are basically gateways through which I/O transfers of a microcontroller take place.
Usually a port has several pins of the microcontroller dedicated to it. In memory terms a port occupies
several bits, usually multiples of 8. There are port registers through which data is transferred in and
out of ports. Ports might be bi-directional or unidirectional.
Oscillator: The microcontroller needs various clocking signals to operate its registers and other
peripherals like the UART. The main clocking signal is provided with the help of an oscillator and
associated circuitry.
5.1.2. FEATURES
1. 4K Bytes of In-System Reprogrammable Flash Memory & Endurance: 1,000 Write/Erase
Cycles.
2. Fully Static Operation: 0 Hz to 24 MHz
3. Three-Level Program Memory Lock
4. 128 x 8-Bit Internal RAM
5. 32 Programmable I/O Lines
6. Two 16-Bit Timer/Counters
7. Six Interrupt Sources
8. Programmable Serial Channel
9. Low Power Idle and Power Down Modes
5.1.3. PIN DESCRIPTION AND DIAGRAM OF 8051

38. 28
Figure 5.1: 8051 Microcontroller Pin Diagram
VCC Digital supply voltage
GND (VSS) Ground
Port 0; is a dual-purpose port on pins 32-39 of the 8051 1C. In minimum – component designs, it is
used as a general purpose I/O Port. For larger designs with external memory, it becomes a multiplexed
address and data bus.
Port 1; is a dedicated I/O port on pins 1-8. The pins, designated as P1.0. P1.1. P1.2 etc. are available
for interfacing to external devices as required. No alternate functions are as signed for Port 1 pins;
thus they are used solely for interfacing to external devices. Exceptions are the 8032/8052 ICs. Which
use P1.0 and P1.1 either as I/O lines or as external in outs to the third timer.
Port 2; (pints 21-28) is a dual – purpose port serving as general purpose I/O, or as the high byte of
the address bus for designs with external code memory or more than 256 bytes of external data
memory.
Port 3; is a dual – purpose port on pins 10-17. As well as general – purpose I/O, these pins are
multifunctional with each having an alternate purpose related to special features of the 8051).
Now coming to the other pin functions.
PSEN; this is an output pin. PSEN stands for “program store enable.” In an 8031-based system in
which an external ROM holds the program code, this pin is connected to the OE pin of the ROM. Pin
40 provides supply voltage to the chip. The voltage source is +5V.
XTAL1 and XTAL2; the 8051 has an on-chip oscillator but requires an external clock to run it. Most
often a quartz crystal oscillator is connected to inputs XTALI (pin 19) and XTAL2 (pin 18). The
quartz crystal oscillator connected to XTAL1 AND XTAL2 also needs two capacitors of 30 pF value.

39. 29
One side of each capacitor is connected to the ground
EA; the 8051 family members, such as the 8751, 89C51, or DS5000. All come with on-chip ROM to
store programs. In such cases, the EA pin is connected to VCC for giving power to save and erase
program from the memory.
RST (RESET); The RST input on pin 9 is the master rest for the 8051. When this signal is brought
high for a least two machine cycles, the 8051 internal registers are loaded with appropriate values for
an orderly system start-up. For normal operation, RST is low. Figure shows permanent connections
of Reset Pin.
ALE; (address latch enable) is an output pin and is active high. When connecting an 8031 to external
memory, port 0 provides both address and data. In other words, the 8031 multiplexes address and data
through port 0 to save pins. The ALE pin is used for de-multiplexing the address and data by
connecting to the G pin of the 74LS373 chip. Now we will talk about what other things are inside an
AT89C51 MCU;
Registers; IN the CPU, registers are used to store information temporarily. That information could
be a byte of data to be processed, or an address pointing to the data to be fetched. The vast majority
of 89C51 register an address pointing to the data to be fetched. The vast majority of 89C51 registers
are 8-bit registers. In the 8051 there is only one data type: 8 bits. The 8 bits of a register are shown in
the diagram from the MSB (most significant bit) D7 to the LSB (least significant bit) D0. With an 8-
bit data type, any data larger than 8 bits must be broken into 8-bit chunks before it is processed. The
most widely used registers of the 89C51 are A (accumulator), B, R0, R1, R2, R3, R4, R5, R6, R7,
DPTR (data pointer), and PC (program counter). All of the above registers are 8-bits, except
DPTR and the program counter. The accumulator, register A, is used for all arithmetic and logic
instructions.
Timers; Both timer 0 and timer 1 are 16 bits wide. Since the 89C51 has an 8-bit architecture, each
16-bit timer is accessed as two separate registers of low byte and high byte. Each timer is discussed
separately.
Timer 0 Register; The 16-bit register of time 0 is accesses as low byte and high byte. The low byte
register is called TL0 (timer 0 low byte) and the high byte register is referred to as th0 (timer 0 high
byte). These registers can be accessed like any other register, such as A, B, R0, R1, R2 etc. For

40. 30
example, the instruction “TLO= 20” moves the value 500 into TL0, the low byte of timer 0. These
registers can also be read like any other register.
Timer 1 Register; Timer 1 is also 16 bits, and its 16- bit register is split into two bytes, referred to as
TL1 (timer 1 low byte) and TH1 (timer 1 high byte). These registers are accessible in the same way
as the registers of timer 0.
5.1.4. INTRODUCTION TO AVR MICROCONTROLLER
Microcontroller: Microcontroller can be termed as a single on chip computer which includes number
of peripherals like RAM, EEPROM, Timers etc., required to perform some predefined task.
Figure 5.2: Block Diagram of AVR microcontroller
Does this mean that the microcontroller is another name for a computer…? The answer is NO!
The computer on one hand is designed to perform all the general purpose tasks on a single machine
like you can use a computer to run a software to perform calculations or you can use a computer to
store some multimedia file or to access internet through the browser, whereas the microcontrollers
are meant to perform only the specific tasks, for e.g., switching the AC off automatically when room
temperature drops to a certain defined limit and again turning it ON when temperature rises above the
defined limit.

41. 31
There are number of popular families of microcontrollers which are used in different applications as
per their capability and feasibility to perform the desired task, most common of these are 8051, AVR
and PIC microcontrollers. In this article we will introduce you with AVR family of microcontrollers.
5.1.4.1. ARCHITECTURE OF AVR
The AVR microcontrollers are based on the advanced RISC architecture and consist of 32 x 8-bit
general purpose working registers. Within one single clock cycle, AVR can take inputs from two
general purpose registers and put them to ALU for carrying out the requested operation, and transfer
back the result to an arbitrary register. The ALU can perform arithmetic as well as logical operations
over the inputs from the register or between the register and a constant. Single register operations like
taking a complement can also be executed in ALU. We can see that AVR does not have any register
like accumulator as in 8051 family of microcontrollers; the operations can be performed between any
of the registers and can be stored in either of them.
AVR follows Harvard Architecture format in which the processor is equipped with separate memories
and buses for Program and the Data information. Here while an instruction is being executed, the next
instruction is pre-fetched from the program memory.
Since AVR can perform single cycle execution, it means that AVR can execute 1 million instructions
per second if cycle frequency is 1MHz. The higher is the operating frequency of the controller, the
higher will be its processing speed. We need to optimize the power consumption with processing
speed and hence need to select the operating frequency accordingly.
There are two flavours for Atmega8 microcontroller:
1. Atmega8:- Operating frequency range is 0 – 8 MHz
2. Atmega8L:- Operating frequency range is 0 – 8 MHz
If we are using a crystal of 8 MHz = 8 x 106 Hertz = 8 Million cycles, then AVR can execute 8 million
instructions.
Naming Convention - The AT refers to Atmel the manufacturer, Mega means that the
microcontroller belong to Mega AVR category, 8 signifies the memory of the controller, which is
8KB.
Architecture Diagram: Atmega 8

42. 32
Following points explain the building blocks of Atmega8 architecture:
I/O Ports: Atmega8 has four (PORTA, PORTB, PORTC and PORTD) 8-bit input-output ports.
Internal Calibrated Oscillator: Atmega8 is equipped with an internal oscillator for driving its clock.
By default Atmega8 is set to operate at internal calibrated oscillator of 1 MHz The maximum
frequency of internal oscillator is 8Mhz. Alternatively, ATmega8 can be operated using an external
crystal oscillator with a maximum frequency of 8MHz. In this case you need to modify the fuse bits.
(Fuse Bits will be explained in a separate tutorial).
Figure 5.3: AVR Architecture
ADC Interface: Atmega8 is equipped with an 8 channel ADC (Analog to Digital Converter) with a
resolution of 10-bits. ADC reads the analog input for e.g., a sensor input and converts it into digital
information which is understandable by the microcontroller.
Timers/Counters: Atmega8 consists of two 8-bit and one 8-bit timer/counter. Timers are useful for
generating precision actions for e.g., creating time delays between two operations.
Watchdog Timer: Watchdog timer is present with internal oscillator. Watchdog timer continuously
monitors and resets the controller if the code gets stuck at any execution action for more than a defined
time interval.
Interrupts: Atmega8 consists of 21 interrupt sources out of which four are external. The remaining

43. 33
are internal interrupts which support the peripherals like USART, ADC, and Timers etc.
USART: Universal Synchronous and Asynchronous Receiver and Transmitter interface is available
for interfacing with external device capable of communicating serially (data transmission bit by bit).
General Purpose Registers: Atmega8 is equipped with 32 general purpose registers which are
coupled directly with the Arithmetic Logical Unit (ALU) of CPU.
Memory: Atmega8 consist of three different memory sections:
1. Flash EEPROM: Flash EEPROM or simple flash memory is used to store the program dumped
or burnt by the user on to the microcontroller. It can be easily erased electrically as a single unit. Flash
memory is non-volatile i.e., it retains the program even if the power is cut-off. Atmega8 is available
with 8KB of in system programmable Flash EEPROM.
2. Byte Addressable EEPROM: This is also a non-volatile memory used to store data like values of
certain variables. Atmega8 has 512 bytes of EEPROM, this memory can be useful for storing the lock
code if we are designing an application like electronic door lock.
3. SRAM: Static Random Access Memory, this is the volatile memory of microcontroller i.e., data is
lost as soon as power is turned off. Atmega8 is equipped with 1KB of internal SRAM. Asmall portion
of SRAM is set aside for general purpose registers used by CPU and some for the peripheral
subsystems of the microcontroller.
ISP: AVR family of controllers have In System Programmable Flash Memory which can be
programmed without removing the IC from the circuit, ISP allows to reprogram the controller while
it is in the application circuit.
SPI: Serial Peripheral Interface, SPI port is used for serial communication between two devices on a
common clock source. The data transmission rate of SPI is more than that of USART.
TWI: Two Wire Interface (TWI) can be used to set up a network of devices, many devices can be
connected over TWI interface forming a network, the devices can simultaneously transmit and receive
and have their own unique address.
DAC: Atmega8 is also equipped with a Digital to Analog Converter (DAC) interface which can be
used for reverse action performed by ADC. DAC can be used when there is a need of converting a
digital signal to analog signal.

44. 34
Various microcontroller of Mega AVR series: ATmega8 and Atmega32 are other members of Mega
AVR series controllers. They are quite similar to ATmega8 in architecture. Low power version Mega
AVR controllers are also available in markets. The following table shows the comparison between
different members of Mega AVR family:
TABLE 5.2: Members of AVR family
Part Name RO
M
RA
M
EEPRO
M
I/0
Pin
s
Time
r
Interrup
ts
Operatio
n
Voltage
Operatin
g
frequenc
y
Packagin
g
ATmega8 8KB 1KB 512B 23 3 19 4.5-5.5 V 0-8 MHz 28
ATmega8
L
8KB 1KB 512B 23 3 19 2.7-5.5 V 0-8 MHz 28
ATmega8 8KB 1KB 512B 32 3 21 4.5-5.5 V 0-8 MHz 40
ATmega8
L
8KB 1KB 512B 32 3 21 2.7-5.5 V 0-8 MHz 40
ATmega32 32K
B
2KB 1KB 32 3 21 4.5-5.5 V 0-8 MHz 40
ATmega32
L
32K
B
2KB 1KB 32 3 21 2.7-5.5 V 0-8 MHz 40
5.1.5. LED DISPLAY BOARD
A monochrome (single colour) LED dot matrix display is used for displaying the Characters and
Symbols which is interface with a microcontroller. This project will deliberate on displaying a
scrolling text message on a 48×8 LED dot matrix display. The microcontroller used is Arduino Uno
which is open source prototype Electronic platform. The 48 columns of the LED matrix are driven
individually by six shift registers (74HC595), whereas the eight combined rows are also driven by the

45. 35
Shift register. Here we will be scanning across the rows and feed the column lines with appropriate
logic levels. The program in the microcontroller is to determine the speed of the scrolling message as
well as Message what we are going to display. The technique will be demonstrated for right to left
scroll, but can be easily implemented for scrolling in other directions. The Sketch program for
Arduino Uno is developed with Arduino Software.
5.1.5.1. PREPAIRING THE MATRIX DISPLAY BOARD
Matrix wiring each matrix has 64 LEDs. Instead the LEDs are wired into a matrix. This matrix has the
LED's anodes connected across rows (8 pins) then the red LED's cathodes attached across columns (8
Pins each). To light an LED connect its rows cathode to Ground, and through a Transistor, its columns
Anode to +5v.
Displaying Images (Scanning) Now that we can light any LED we choose it's time to move on to
displaying a (small) image. To do this we will use a scan pattern. In the example code we define a
bitmap image (an array of 8 bytes, each bit representing one LED). Next we scan through this array
one byte at a time, displaying one column then the next. If we do this fast enough (about 1000 times a
second) it appears as an image. It sounds complex but if you download the code and play around it
should quickly become clear.
Here, we will cascade two 74595 ICs for controlling two 8*8 LED matrices. LED matrices are arranged
in such a way that control pins of LED matrices should be at the top and bottom of the LED matrix as
shown in the following image. To avoid confusion in fixing LED matrices, note the position of wedges
at the middle of sides of each LED matrices.

46. 36
Figure 5.4: LED Matrix
An individual LED matrix is shown below. Each LED matrix have 8 control pins of which eight are
anode pins (8, 15, 11, 3, 10, 5, 6 and 13) and remaining are cathode pins (4, 7, 2, 8, 12, 1, 14, 9).
Figure 5.5: Detailed View of LED Matrix
Internal circuit of an 8*8 LED matrix is given below. 64 LEDs are arranged to form 8 rows and 8
columns. One anode pin will be common for eight LEDs. Similarly, one cathode pin will be common
for eight LEDs.

47. 37
Figure 5.6: Circuit of LED Matrix
Three 74595 ICs are used in the circuit of which two ICs are cascade connected. Pin out diagram of
74595 is given below.
Figure 5.7: 74595IC
5.1.5.1.1. 74595 IC
 8-Bit Serial-In, Parallel-Out Shift
 Wide Operating Voltage Range of 2 V to 6 V
 High-Current 3-State Outputs Can Drive Up
 To 15 LSTTL Loads

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 Low Power Consumption, 80-μA Max ICC
 Typical t pd= 13 ns
 ±6-mA Output Drive at 5 V
 Low Input Current of 1 μA Max
 Shift Register Has Direct Clear
description/ordering information The ’HC595 devices contain an 8-bit serial-in, parallel-out shift
register that feeds an 8-bit D-type storage register. The storage register has parallel 3-state outputs.
Separate clocks are provided for both the shift and storage register. The shift register has a direct
overriding clear (SRCLR) input, serial (SER) input, and serial outputs for cascading. When the output-
enable (OE) input is high, the outputs are in the high-impedance state. Both the shift register clock
(SRCLK) and storage register clock (RCLK) are positive-edge triggered. If both clocks are connected
together, the shift register always is one clock pulse ahead of the storage register.
Circuit diagram to control two 8*8 LED matrix using Arduino mega and 74595 is given below. Cascade
connected ICs are used for controlling the anode pins of 8*8 LED matrices. Cathode pins of both LED
matrices are shorted. These shorted cathode pins are then connected to the Q0-Q7 pins of other 74595
as shown in the circuit diagram.
5.1.5.2. CONNECTION BETWEEN 8*8 LED MATRICES
Cathode pins of both LED matrices are shorted (at the middle of LED matrices). If the cathode pins are
shorted, only twenty four control pins will be remaining. They are sixteen anode pins (16, 15, 11, 3,
10, 5, 6 and 13) and eight cathode pins (4, 7, 2, 8, 12, 1, 14, and 9). Anode pins of LED MATRIX 1 is
connected to the Q0-Q7 pins of 1st 74595. Similarly, anode pins of LED MATRIX 2 is connected to
the Q0-Q7 pins of 2nd 74595. Cathode pins are connected to the Q0-Q7 pins of 3rd 74595. Current
limiting resistances of 100 ohm should be connected in series with the anode pins of LED matrices.

49. 39
Figure 5.8: Connection between 2 LED Matrices
5.1.5.2.1. CONNECTION BETWEEN LED MATRIX 1 AND 1ST 74595

50. 40
Figure 5.9: Connection between LED matrix 1 and 74595 IC
From the circuit, it is clear that anode terminals of LED MATRIX 1 is connected to the Q0-Q7 pins of
1st 74595 through current limiting resistors of 100 Ohm each.
5.1.5.2.2. CONNECTION BETWEEN LED MATRIX 2 AND 2ND 74595

51. 41
Figure 5.10: Connection between LED matrix 2 and 74595 IC
From the circuit, it is clear that anode terminals of LED MATRIX 2 is connected to the Q0-Q7 pins of
2nd 74595 through current limiting resistors of 100 Ohm each.
Step 1: From the circuit, it is clear that anode terminals of LED MATRIX 1 is connected to the Q0-Q7
pins of 1st 74595 through current limiting resistors of 100 Ohm each.
Step 2: From the circuit, it is clear that anode terminals of LED MATRIX 2 is connected to the Q0-Q7
pins of 2nd 74595 through current limiting resistors of 100 Ohm each.
Step 3: From the circuit, it is clear that cathode terminals of both LED MATRICES are connected to
the Q0-Q7 pins of 3rd 74595.
Step 4: Connection between 74595 ICs and Arduino mega is given below.
5.1.5.2.3. CONNECTION BETWEEN LED MATRIX 1 AND 1ST 74595, LED MATRIX 2 AND
2ND 74595, 74595 ICS AND ARDUINO MEGA

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Figure 5.11: Connection between LED MATRIX 1 and 1st 74595, LED MATRIX 2 and 2nd 74595,
74595 ICs and Arduino Mega
Connections can be summarized as:
DS (pin 14) of 1st 74595 is connected to the 13th digital pin of Arduino mega. SHCP (pin 11) of 1st and
2nd 74595 is connected to the 12th digital pin of Arduino mega. STCP (pin 12) of 1st and 2nd 74595
is connected to the 11th digital pin of Arduino mega. Q7' (pin 9) of 1st 74595 is connected to the DS
(pin 14) of 2nd 74595. DS (pin 14) of 3rd 74595 is connected to the 10th digital pin of Arduino mega.
SHCP (pin 11) of 3rd 74595 is connected to the 9th digital pin of Arduino mega. STCP (pin 12) of
3rd 74595 is connected to the 8th digital pin of Arduino mega. Gnd pin of 74595 ICs should be
connected to the Gnd pin of Arduino mega. OE (pin 13) of all 74595 ICs should be connected to ground.
MR (pin 10) of all 74595 ICs should be connected to Vcc.
We had completed the circuit for 8*8 LED display. Next is a step by step procedure to display the word
"HE" in the 8*8 LED matrix as shown in the following image.

53. 43
Figure 5.12: Display the word "HE" in the 8*8 LED matrix
LED matrix works based on the principle of persistence of vision. That is, when some frames are
displayed one after another at a high speed, our eyes will feel that all frames are displaying together
because of persistence of vision. Frames used to create "HE" display is given below.
(a)
. (b)

54. 44
(c)
(d)
(e)

55. 45
(f)
(g)

56. 46
Figure 5.13: a, b, c, d, e, f & g Adjustment of Row & Column of Letter ‘HE’ on LED Board
When these frames are displayed at a high speed eyes will get "HE" feeling. Next is to write an Arduino
program that will generate these frames and display one after another at a high speed.
5.1.6. ARDUINO UNO
Arduino is an open-source platform used for building electronics projects. Arduino consists of both a
physical programmable circuit board (often referred to as a microcontroller) and a piece of software,
or IDE (Integrated Development Environment) that runs on your computer, used to write and upload
computer code to the physical board.
The Arduino platform has become quite popular with people just starting out with electronics, and for
good reason. Unlike most previous programmable circuit boards, the Arduino does not need a separate
piece of hardware (called a programmer) in order to load new code onto the board – you can simply
use a USB cable. Additionally, the Arduino IDE uses a simplified version of C++, making it easier to
learn to program. Finally, Arduino provides a standard form factor that breaks out the functions of the
micro-controller into a more accessible package.
The Arduino UNO is a widely used open-source microcontroller board based on
the ATmega328P microcontroller and developed by Arduino.cc. The board is equipped with sets of
digital and analog input/output (I/O) pins that may be interfaced to various expansion boards (shields)

57. 47
and other circuits. The board features 14 Digital pins and 6 Analog pins. It is programmable with
the Arduino IDE (Integrated Development Environment) via a type B USB cable. It can be powered
by a USB cable or by an external 9 volt battery, though it accepts voltages between 7 and 20 volts. It
is also similar to the Arduino Nano and Leonardo. The hardware reference design is distributed under
a Creative Commons Attribution Share-Alike 2.5 license and is available on the Arduino website.
Layout and production files for some versions of the hardware are also available. "Uno" means one in
Italian and was chosen to mark the release of Arduino Software (IDE) 1.0.[1] The Uno board and
version 1.0 of Arduino Software (IDE) were the reference versions of Arduino, now evolved to newer
releases. The Uno board is the first in a series of USB Arduino boards, and the reference model for the
Arduino platform. The ATmega328 on the Arduino Uno comes preprogrammed with a bootloader that
allows to upload new code to it without the use of an external hardware programmer.[3] It
communicates using the original STK500 protocol. The Uno also differs from all preceding boards in
that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2
(Atmega8U2 up to version R2) programmed as a USB-to-serial converter. The Arduino UNO is
generally considered the most user-friendly and popular board, with boards being sold worldwide for
less than 5$.
Figure 5.14: Arduino Uno Board
5.1.6.1. PINS OF ARDUINO UNO BOARD

58. 48
 LED: There is a built-in LED driven by digital pin 13. When the pin is HIGH value, the LED
is on, when the pin is LOW, it's off.
 VIN: The input voltage to the Arduino/Genuino board when it's using an external power source
(as opposed to 5 volts from the USB connection or other regulated power source). You can
supply voltage through this pin, or, if supplying voltage via the power jack, access it through
this pin.
 5V: This pin outputs a regulated 5V from the regulator on the board. The board can be supplied
with power either from the DC power jack (7 - 20V), the USB connector (5V), or the VIN pin
of the board (7-20V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and
can damage the board.
 3V3: A 3.3 volt supply generated by the on-board regulator. Maximum current draw is 50 mA.
 GND: Ground pins.
 IOREF: This pin on the Arduino/Genuino board provides the voltage reference with which the
microcontroller operates. A properly configured shield can read the IOREF pin voltage and
select the appropriate power source or enable voltage translators on the outputs to work with
the 5V or 3.3V.
 Reset: Typically used to add a reset button to shields which block the one on the board.[7]
 Serial: pins 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data. These
pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL Serial chip.
 External Interrupts: pins 2 and 3. These pins can be configured to trigger an interrupt on a
low value, a rising or falling edge, or a change in value.
 PWM (Pulse Width Modulation) 3, 5, 6, 9, 10, and 11 Can provide 8-bit PWM output with
the analog Write () function.
 SPI (Serial Peripheral Interface): 10 (SS), 11 (MOSI), 12 (MISO), 13 (SCK). These pins
support SPI communication using the SPI library.
 TWI (Two Wire Interface): A4 or SDA pin and A5 or SCL pin. Support TWI communication
using the Wire library.
 AREF (Analog Reference): Reference voltage for the analog inputs.

59. 49
Figure 5.15: Arduino Uno Board Pin Diagram
5.1.7. WIRELESS TRANSCEIVER
When time and RF engineering experience is of abundance, a designer may opt to use RF integrated
circuits (chips or chipsets) to save on RF component costs. Using chips/chipsets, the designer actually
develops the hardware and software workings of the product.
While the individual chips/chipsets offer functionality the designer must dictate how those chips will
work in concert with the software the designer will develop. This task is not for the faint of heart, as
completed designs must also pass rigid regulatory testing for deployment in the various regions of the
world. The regulatory approval process alone can become months or years of a cycle of rejection,
followed by a reworking of the product and continued by rejection and reworking until the product is
approved.
Wireless transceiver (transmitter / receiver) modules offer a faster time-to-market alternative to
chips/chipsets that allow designers at all levels of RF experience to integrate a completed wireless

60. 50
system into their products. Many modules are manufactured as a drop-in solution where designers
create a compatible pin-out on their processor board and supply serial data to the appropriate pins.
Modules offering the easiest integration allow the designer to send raw UART data into the module
and expect that same data out on the receiving end of the wireless link.
Wireless transceiver modules allowing the quickest time-to-market are also FCC and other regulatory
agency approved. That means jurisdictions accepting FCC approval allow designers using FCC
approved modules to bypass further testing for their wireless products.
Figure 5.16: Wireless Transceiver
As an example, Digi has a line of wireless transceiver modules that meet many of the performance and
ease of use suggestions discussed. Their modules are all drop-in RS-232 / RS-422 / RS-485 solutions
that are FCC and other agency approved for use throughout the world. Integrating these wireless data
communication solutions is as simple as sending serial data from a microcontroller or communication
port, while the Digi module handles all of the complexities of spread spectrum transmission and
reception. Of particular note is their ability to communicate at short or long range while consuming
low power and maintaining high levels of interference rejection over transparent peer-to-peer, point-
to-point, and point-to-multipoint and multi-drop networks.
The Digi 9XStream 900 MHz Wireless OEM Module is a frequency-hopping spread spectrum
transceiver that uses a simple UART interface to communicate with the host system. It has transmission
power output of 140 mW and operates at long ranges (up to ¼ mile in urban environments and up to
20 miles in line-of-sight conditions) due to its excellent receiver sensitivity of –110 dBm. Additionally,
the 9XStream uses proprietary filtering technology to provide interference immunity, including 70 dB
of cell phone and pager rejection (10 million times attenuation). Providing OEMs with a robust, reliable
wireless method to transmit serial data.

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5.1.8. CAPACITORS
Figure 5.17: Capacitor
It is an electronic component whose function is to accumulate charges and then release it. To understand
the concept of capacitance, consider a pair of metal plates which all are placed near to each other
without touching. If a battery is connected to these plates the positive pole to one and the negative pole
to the other, electrons from the battery will be attracted from the plate connected to the positive terminal
of the battery. If the battery is then disconnected, one plate will be left with an excess of electrons, the
other with a shortage, and a potential or voltage difference will exists between them. These plates will
be acting as capacitors.
Capacitors are of two types:
1. Fixed type like ceramic, polyester, electrolytic capacitors-these names refer to the material they
are made of aluminium foil.
2. Variable type like gang condenser in radio or trimmer. In fixed type capacitors, it has two leads
and its value is written over its body and variable type has three leads. Unit of measurement of
a capacitor is farad denoted by the symbol F. It is a very big unit of capacitance. Small unit
capacitor are Pico-farad denoted by pf (Ipf=1/1000, 000,000,000 f) Above all, in case of
electrolytic capacitors, its two terminal are marked as (-) and (+) so check it while using
capacitors in the circuit in right direction. Mistake can destroy the capacitor or entire circuit in
operational.
5.1.9 DIODE
Figure 5.18: Diode
The simplest semiconductor device is made up of a sandwich of P-type semiconducting material, with
contacts provided to connect the p-and n-type layers to an external circuit. This is a junction Diode. If

62. 52
the positive terminal of the battery is connected to the p-type material (cathode) and the negative
terminal to the N-type material (Anode), a large current will flow. This is called forward current or
forward biased.
If the connections are reversed, a very little current will flow. This is because under this condition, the
p-type material will accept the electrons from the negative terminal of the battery and the N-type
material will give up its free electrons to the battery, resulting in the state of electrical equilibrium since
the N-type material has no more electrons. Thus there will be a small current to flow and the diode is
called Reverse biased.
Thus the Diode allows direct current to pass only in one direction while blocking it in the other
direction. Power diodes are used in concerting AC into DC. In this, current will flow freely during the
first half cycle (forward biased) and practically not at all during the other half cycle (reverse biased).
This makes the diode an effective rectifier, which convert ac into pulsating dc.
1. ZENER DIODE:-
A zener diode is specially designed junction diode, which can operate continuously without being
damaged in the region of reverse break down voltage. One of the most important applications of zener
diode is the design of constant voltage power supply. The zener diode is joined in reverse bias to d.c.
through a resistance R of suitable value.
2. PHOTO DIODE:-
A photo diode is a junction diode made from photo- sensitive semiconductor or material. In such a
diode, there is a provision to allow the light of suitable frequency to fall on the p-n junction. It is reverse
biased, but the voltage applied is less than the break down voltage. As the intensity of incident light is
increased, current goes on increasing till it becomes maximum. The maximum current is called
saturation current.
3. LIGHT EMITTING DIODE (LED):-
When a junction diode is forward biased, energy is released at the junction diode is forward biased,
energy is released at the junction due to recombination of electrons and holes. In case of silicon and
germanium diodes, the energy released is in infrared region. In the junction diode made of gallium
arsenate or indium phosphide, the energy is released in visible region. Such a junction diode is called
a light emitting diode or LED.

63. 53
5.1.10. RESISTOR
Figure 5.19: Resistor
Resistance is the opposition of a material to the current. It is measured in Ohms. All conductors
represent a certain amount of resistance, since no conductor is 100% efficient. To control the electron
flow (current) in a predictable manner, we use resistors. Electronic circuits use calibrated lumped
resistance to control the flow of current. Broadly speaking, resistor can be divided into two groups viz.
fixed & adjustable (variable) resistors. In fixed resistors, the value is fixed & cannot be varied. In
variable resistors, the resistance value can be varied by an adjuster knob. It can be divided into (a)
Carbon composition (b) Wire wound (c) Special type. The most common type of resistors used in our
projects is carbon type. The resistance value is normally indicated by colour bands. Each resistance has
four colours, one of the band on either side will be gold or silver, this is called fourth band and indicates
the tolerance, others three band will give the value of resistance (see table). For example if a resistor
has the following marking on it say red, violet, gold. Comparing these coloured rings with the colour
code, its value is 27000 ohms or 27 kilo ohms and its tolerance is ±5%. Resistor comes in various sizes

64. 54
(Power rating). The bigger, the size, the more power rating of 1/4 watts. The four colour rings on its
body tells us the value of resistor and tolerance value as given below.
TABLE 5.3: The Resistor Value and Tolerance Value.
The first
rings give the
first digit.
The second
ring gives
the second
digit. The
third ring
indicates the number of zeroes to be placed after the digits. The fourth ring gives tolerance (gold ±5%,
silver ± 10%, No colour ± 20%).
In variable resistors, we have the dial type of resistance boxes. There is a knob with a metal pointer.
This presses over brass pieces placed along a circle with some space b/w each of them. Resistance coils
of different values are connected b/w the gaps. When the knob is rotated, the pointer also moves over
the brass pieces. If a gap is skipped over, its resistance is included in the circuit. If two gaps are skipped
over, the resistances of both together are included in the circuit and so on.
Colour 1st
band 2nd
band 3rd
band Multiplier Tolerance
Black 0 0 0 1
Brown 1 1 1 10 ±1% F
Red 2 2 2 100 ±2% G
Orange 3 3 3 1K
Yellow 4 4 4 10K
Green 5 5 5 100K ±0.5% D
Blue 6 6 6 1M ±0.25% C
Violet 7 7 7 10M ±0.1% B
Grey 8 8 8 ±0.05% A
White 9 9 9
Gold 0.1 ±5% J
Silver 0.01 ±10% K
Plain ±20% M

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A dial type of resistance box contains many dials depending upon the range, which it has to cover. If a
resistance box has to read up to 10,000, it will have three dials each having ten gaps i.e. ten resistance
coils each of resistance 10. The third dial will have ten resistances each of 100.The dial type of
resistance boxes is better because the contact resistance in this case is small & constant.
5.1.11. CRYSTAL OSCILLATOR
Figure 5.20: Crystal Oscillator
A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a
vibrating crystal of material to create an electrical signal with a precise frequency. This frequency is
commonly used to keep track of time, as in quartz wristwatches, to provide a stable clock
signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers.
The most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits
incorporating them became known as crystal oscillators, but other piezoelectric materials including
polycrystalline ceramics are used in similar circuits.
Quartz crystals are manufactured for frequencies from a few tens of kilohertz to hundreds of megahertz.
More than two billion crystals are manufactured annually. Most are used for consumer devices such
as wristwatches, clocks, radios, computers, and cell phones. Quartz crystals are also found inside test
and measurement equipment, such as counters, signal generators, and oscilloscopes.
Function
Crystal is a circuit element commonly used in the clock, full name is called the crystal oscillator, crystal
oscillator in the microcontroller the role of the system is very large, is a combination of MCU's internal
circuitry, resulting in the need microcontroller clock frequency, single-chip implementation of all
directives are built on this basis, the crystal clock frequency to provide higher speed and that the sooner
SCM.

66. 56
Crystal with a can into electrical energy and mechanical energy between the crystal in the resonant
mode of operation in order to provide stable and accurate single frequency oscillation. In normal
working conditions, the ordinary crystal oscillator frequency absolute accuracy of up to 50 millionths.
High-level precision. Some crystal by the applied voltage can also be adjusted within a certain range
of frequencies, known as voltage-controlled oscillator (VCO).
Crystal's role is to provide the basic system clock signal. Usually a system share a single crystal, easy
to synchronize the various parts. Some of the fundamental frequency communication systems and RF
using a different crystal and electronic means to adjust the frequency to keep pace.
Crystal is usually used in conjunction with the phase-locked loop circuit to provide the required system
clock frequency. If different sub-systems need a different clock signal frequencies can be used with the
same crystal connected to a different phase-locked loop to provide.
Here I will introduce the specific role of crystal, as well as the principle of crystal commonly used in
Figure 1a, three-terminal type capacitor (Colpitts) to exchange the equivalent oscillation circuit; the
actual exchange of crystal equivalent circuit shown in Figure 1b, which Cv is used to adjust the
oscillation frequency, tends to be used with different varactor reverse bias voltage to achieve, which is
the role of voltage-controlled mechanism; the crystal equivalent circuit instead of crystals shown in
Figure 1c. Where Co, C1, L1, RR is the crystal equivalent circuit.
5.1.12. LM7805
Figure 5.21: LM7805
A regulated power supply is very much essential for several electronic devices due to the semiconductor
material employed in them have a fixed rate of current as well as voltage. The device may get damaged
if there is any deviation from the fixed rate. The AC power supply gets converted into constant DC by

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this circuit. By the help of a voltage regulator DC, unregulated output will be fixed to a constant voltage.
The circuit is made up of linear voltage regulator 7805 along with capacitors and resistors with bridge
rectifier made up from diodes. From giving an unchanging voltage supply to building confident that
output reaches uninterrupted to the appliance, the diodes along with capacitors handle elevated efficient
signal conveyed.
5.1.12.1 DESCRIPTION
As we have previously talked about that regulated power supply is a device that mechanized on DC
voltages and also it can uphold its output accurately at a fixed voltage all the time although if there is
a significant alteration in the DC input voltage. ICs regulator is mainly used in the circuit to maintain
the exact voltage which is followed by the power supply. A regulator is mainly employed with the
capacitor connected in parallel to the input terminal and the output terminal of the IC regulator. For the
checking of gigantic alterations in the input as well as in the output filter, capacitors are used. While
the bypass capacitors are used to check the small period spikes on the input and output level. Bypass
capacitors are mainly of small values that are used to bypass the small period pulses straight into the
Earth. As we have made the whole circuit till now to be operated on the 5V DC supply, so we have to
use an IC regulator for 5V DC. And the most generally used IC regulators get into the market for 5V
DC regulation use is 7805. The output generated from the unregulated DC output is susceptible to the
fluctuations of the input signal. IC voltage regulator is connected with bridge rectifier in series in these
project so to steady the DC output against the variations in the input DC voltage.

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Figure 5.22: Voltage output from the LM7805
5.1.13. LM358
Figure 5.23: LM358 Op-Amp
The LM358 consist of two independent, high gain, internally frequency compensated operational
amplifiers which were designed specifically to operate from a single power supply over a wide range
of voltage. Operation from split power supplies is also possible and the low power supply current drain
is independent of the magnitude of the power supply voltage. Application areas include transducer
amplifier, DC gain blocks and all the conventional OP-AMP circuits which now can be easily
implemented in single power supply systems.
5.1.13.1. FEATURES
a. Internally Frequency Compensated for Unity Gain
b. Large DC Voltage Gain: 100dB
c. Wide Power Supply Range: LM358 3V~32V (or ±1.5V~ 16V)
d. Input Common Mode Voltage Range Includes Ground
e. Large Output Voltage Swing: 0V DC to Vcc -1.5V DC
f. Power Drain Suitable for Battery Operation.

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Figure 5.24: Internal Block Diagram of Op-amp.
5.1.14. ACCESSORIES
5.1.14.1. ADAPTER
The ac-dc adapter is a commodity. So, they impose their own stringent specifications and de-rating
guidelines while requiring low costs. The key performance criteria for adapters are Power density,
Safety, Low case temperature Also, it’s designed to cope with universal mains voltage: 220𝑉𝐴𝐶, 60 Hz.
Input: 220𝑉𝐴𝐶 , 50/60 Hz Output: 5𝑉𝐷𝐶 ±2% at 1.0 A continuous (5W); constant voltage/constant
current.
5.1.14.2. CONNECTOR
Figure 5.25: Connector wire.
A short electrical wire with a solid tip at each end (or sometimes without them, simply "tinned"),
which is normally used to interconnect the components in circuits. They are used to transfer
electrical signals from anywhere on the circuit to the input/output pins of a microcontroller.

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Connectors are fitted by inserting their "end connectors" into the slots provided in the circuit that
beneath its surface has a few sets of parallel plates that connect the slots in groups of rows or columns
depending on the area. The "end connectors" are inserted into the circuits, without soldering, in the
particular slots that need to be connected in the specific prototype.
5.1.14.3 SWITCH
An electrical switch is any device used to interrupt the flow of electrons in a circuit. Switches are
essentially binary devices: they are either completely on (“closed”) or completely off (“open”).
There are many different types of switches, and we will explore some of these types in this chapter.
Though it may seem strange to cover this elementary electrical topic at such a late stage in this book
series, I do so because the chapters that follow explore an older realm of digital technology based
on mechanical switch contacts rather than solid-state gate circuits, and a thorough understanding of
switch types is necessary for the undertaking. Learning the function of switch-based circuits at the
same time that you learn about solid-state logic gates makes both topics easier to grasp, and sets the
stage for an enhanced learning experience in Boolean algebra, the mathematics behind digital logic
circuits. The simplest type of switch is one where two electrical conductors are brought in contact
with each other by the motion of an actuating mechanism. Other switches are more complex,
containing electronic circuits able to turn on or off depending on some physical stimulus (such as
light or magnetic field) sensed. In any case, the final output of any switch will be (at least) a pair of
wire-connection terminals that will either be connected together by the switch’s internal contact
mechanism (“closed”), or not connected together (“open”).Any switch designed to be operated by a
person is generally called a hand switch, and they are manufactured in several varieties:
1. TOGGLE SWITCH
Figure 5.26: Toggle switch.
Toggle switches are actuated by a lever angled in one of two or more positions. The common light
switch used in household wiring is an example of a toggle switch. Most toggle switches will come
to rest in any of their lever positions, while others have an internal spring mechanism returning the

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lever to a certain normal position, allowing for what is called “momentary” operation.
2. PUSHBUTTON SWITCH
Figure 5.27: Pushbutton switch.
Pushbutton switches are two-position devices actuated with a button that is pressed and released.
Most pushbutton switches have an internal spring mechanism returning the button to its “out,” or
“unpressed,” position, for momentary operation. Some pushbutton switches will latch alternately on
or off with every push of the button. Other pushbutton switches will stay in their “in,” or “pressed,”
position until the button is pulled back out. This last type of pushbutton switches usually have a
mushroom-shaped button for easy push-pull action.
3. SELECTOR SWITCH
Figure 5.28: Selector Switch.
Selector switches are actuated with a rotary knob or lever of some sort to select one of two or more
positions. Like the toggle switch, selector switches can either rest in any of their positions or contain
spring-return mechanisms for momentary operation.
4. JOYSTICK SWITCH
Figure 5.29: Joystick switch.
A joystick switch is actuated by a lever free to move in more than one axis of motion. One or more
of several switch contact mechanisms are actuated depending on which way the lever is pushed, and
sometimes by how far it is pushed. The circle-and-dot notation on the switch symbol represents the