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CHAPTER-1

INTRODUCTION

1.1: EMBEDDED SYSTEMSAn embedded system is a computer system designed to perform one or a few

dedicated functions often with real-time computing constraints. It is embedded as part

of a complete device often including hardware and mechanical parts. By contrast, a

general-purpose computer, such as a personal computer (PC), is designed to be

flexible and to meet a wide range of end-user needs. Embedded systems control

many devices in common use today.

Embedded systems are controlled by one or more main processing cores that

are typically either microcontrollers or digital signal processors (DSP). The key

characteristic, however, is being dedicated to handle a particular task, which may

require very powerful processors. For example, air traffic control systems may

usefully be viewed as embedded, even though they involve mainframe computers

and dedicated regional and national networks between airports and radar sites. (Each

radarprobably includes one or more embedded systems of its own.)

Since the embedded system is dedicated to specific tasks, design engineers

can optimize it to reduce the size and cost of the product and increase the reliability

and performance. Some embedded systems are mass-produced, benefiting from

economies of scale. Physically embedded systems range from portable devices such

as digital watches and MP3 players, to large stationary installations like traffic lights,

factory controllers, or the systems controlling nuclear power plants. Complexity varies

from low, with a single microcontroller chip, to very high with multiple units,

peripherals and networks mounted inside a large chassis or enclosure.

In general, "embedded system" is not a strictly definable term, as mostsystems have some element of extensibility or programmability. For example,

handheld computers share some elements with embedded systems such as the

operating systems and microprocessors which power them, but they allow different

applications to be loaded and peripherals to be connected. Moreover, even systems

which don't expose programmability as a primary feature generally need to support


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software updates. On a continuum from "general purpose" to "embedded", large

application systems will have subcomponents at most points even if the system as a

whole is "designed to perform one or a few dedicated functions", and is thus

appropriate to call "embedded".

1.2: NEED FOR EMBEDDED SYSTEMS

The uses of embedded systems are virtually limitless, because every day new

products are introduced to the market that utilizes embedded computers in novel

ways. In recent years, hardware such as microprocessors, microcontrollers, and

FPGA chips have become much cheaper. So when implementing a new form of

control, it's wiser to just buy the generic chip and write your own custom software for

it. Producing a custom-made chip to handle a particular task or set of tasks costs far

more time and money.

Many embedded computers even come with extensive libraries, so that "writing

your own software" becomes a very trivial task indeed. From an implementation

viewpoint, there is a major difference between a computer and an embedded system.

Embedded systems are often required to provide Real-Time response. The main

elements that make embedded systems unique are its reliability and ease in

debugging.

1.2.1: Debugging

Embedded debugging may be performed at different levels, depending on the

facilities available. From simplest to most sophisticate they can be roughly grouped

into the following areas

Interactive resident debugging, using the simple shell provided by the

embedded operating system (e.g. Forth and Basic)

External debugging using logging or serial port output to trace operation using

either a monitor in flash or using a debug server like the Remedy Debugger

which even works for heterogeneous multi core systems.

An in-circuit debugger (ICD), a hardware device that connects to the

microprocessor via a JTAG or Nexus interface. This allows the operation of the


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microprocessor to be controlled externally, but is typically restricted to specific

debugging capabilities in the processor.

An in-circuit emulator replaces the microprocessor with a simulated equivalent,

providing full control over all aspects of the microprocessor.

A complete emulator provides a simulation of all aspects of the hardware,

allowing all of it to be controlled and modified and allowing debugging on a

normal PC.

Unless restricted to external debugging, the programmer can typically load and

run software through the tools, view the code running in the processor, and

start or stop its operation. The view of the code may be as assembly code or

source-code.

Because an embedded system is often composed of a wide variety of

elements, the debugging strategy may vary. For instance, debugging a software(and

microprocessor) centric embedded system is different from debugging an embedded

system where most of the processing is performed by peripherals (DSP, FPGA, co-

processor). An increasing number of embedded systems today use more than one

single processor core. A common problem with multi-core development is the proper

synchronization of software execution. In such a case, the embedded system design

may wish to check the data traffic on the busses between the processor cores, whichrequires very low-level debugging, at signal/bus level, with a logic analyzer, for

instance.

1.2.2: Reliability

Embedded systems often reside in machines that are expected to run

continuously for years without errors and in some cases recover by themselves if an

error occurs. Therefore the software is usually developed and tested more carefully

than that for personal computers, and unreliable mechanical moving parts such as

disk drives, switches or buttons are avoided.

Specific reliability issues may include


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The system cannot safely be shut down for repair, or it is too inaccessible to

repair. Examples include space systems, undersea cables, navigational

beacons, bore-hole systems, and automobiles.

The system must be kept running for safety reasons. "Limp modes" are less

tolerable. Often backups are selected by an operator. Examples include

aircraft navigation, reactor control systems, safety-critical chemical factory

controls, train signals, engines on single-engine aircraft.

The system will lose large amounts of money when shut down: Telephone

switches, factory controls, bridge and elevator controls, funds transfer and

market making, automated sales and service.

A variety of techniques are used, sometimes in combination, to recover from

errorsboth software bugs such as memory leaks, and also soft errors in the

hardware:

Watchdog timer that resets the computer unless the software periodically

notifies the watchdog

Subsystems with redundant spares that can be switched over to software "limp

modes that provide partial function.

Designing with a Trusted Computing Base (TCB) architecture ensures a highlysecure & reliable system environment.

An Embedded Hypervisor is able to provide secure encapsulation for any

subsystem component, so that a compromised software component cannot

interfere with other subsystems, or privileged-level system software. This

encapsulation keeps faults from propagating from one subsystem to another,

improving reliability. This may also allow a subsystem to be automatically shut

down and restarted on fault detection.

Immunity Aware Programming.


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1.3: EXPLANATION OF EMBEDDED SYSTEMS

1.3.1: Software Architecture

There are several different types of software architecture in common use.

Simple Control Loo p

In this design, the software simply has a loop. The loop calls subroutines, each

of which manages a part of the hardware or software.

Interrupt Control led System

Some embedded systems are predominantly interrupt controlled. This means

that tasks performed by the system are triggered by different kinds of events. An

interrupt could be generated for example by a timer in a predefined frequency, or by a

serial port controller receiving a byte. These kinds of systems are used if event

handlers need low latency and the event handlers are short and simple.

Usually these kinds of systems run a simple task in a main loop also, but this

task is not very sensitive to unexpected delays. Sometimes the interrupt handler will

add longer tasks to a queue structure. Later, after the interrupt handler has finished,

these tasks are executed by the main loop. This method brings the system close to a

multitasking kernel with discrete processes.

Cooperat ive Mult i tasking

A non-preemptive multitasking system is very similar to the simple control loop

scheme, except that the loop is hidden in an API. The programmer defines a series of

tasks, and each task gets its own environment to run in. When a task is idle, it calls

an idle routine, usually called pause, wait, yield, nop (stands for no operation),

etc. The advantages and disadvantages are very similar to the control loop, except

that adding new software is easier, by simply writing a new task, or adding to the

queue-interpreter.

Primi t ive Mult i tasking

In this type of system, a low-level piece of code switches between tasks or

threads based on a timer (connected to an interrupt). This is the level at which the


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system is generally considered to have an "operating system" kernel. Depending on

how much functionality is required, it introduces more or less of the complexities of

managing multiple tasks running conceptually in parallel.

As any code can potentially damage the data of another task (except in larger

systems using an MMU) programs must be carefully designed and tested, and access

to shared data must be controlled by some synchronization strategy, such as

message queues, semaphores or a non-blocking synchronization scheme.

Because of these complexities, it is common for organizations to buy a real-

time operating system, allowing the application programmers to concentrate on

device functionality rather than operating system services, at least for large systems;

smaller systems often cannot afford the overhead associated with a generic real time

system, due to limitations regarding memory size, performance, and/or battery life.

Microkernels and Exokernels

A microkernel is a logical step up from a real-time OS. The usual arrangement

is that the operating system kernel allocates memory and switches the CPU to

different threads of execution. User mode processes implement major functions such

as file systems, network interfaces, etc.

In general, microkernels succeed when the task switching and intertask

communication is fast, and fail when they are slow. Exokernels communicate

efficiently by normal subroutine calls. The hardware and all the software in the system

are available to, and extensible by application programmers.

Based on performance, functionality, requirement the embedded systems are

divided into three categories

1.3.2: Stand Alone Embedded System

These systems takes the input in the form of electrical signals from

transducers or commands from human beings such as pressing of a button etc..,

process them and produces desired output. This entire process of taking input,

processing it and giving output is done in standalone mode. Such embedded systems

comes under stand alone embedded systems

Example: microwave oven, air conditioner etc...


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1.3.3: Real-time embedded systems

Embedded systems which are used to perform a specific task or operation in a

specific time period those systems are called as real-time embedded systems. There

are two types of real-time embedded systems

.

Hard Real-t ime embedded s ystems

These embedded systems follow an absolute dead line time period i.e.., if the

tasking is not done in a particular time period then there is a cause of damage to the

entire equipment.

Soft Real Time embedded s ystems

These embedded systems follow a relative dead line time period i.e.., if the

task is not done in a particular time that will not cause damage to the equipment.

Consider a TV remote control system, if the remote control takes a few

milliseconds delay it will not cause damage either to the TV or to the remote control.

These systems which will not cause damage when they are not operated at

considerable time period those systems comes under soft real-time embedded

systems.

1.4: INTRODUCTION TO OSCILLOSCOPES

An oscilloscope is a type of electronic test instrument that allows signal

voltages to be viewed, usually as a two-dimensional graph of one or more electrical

potential differences (vertical(Y) axis) plotted as a function of time or of some other

voltage (horizontal(x) axis). Although an oscilloscope displays voltage on its vertical

axis, any other quantity that can be converted to a voltage can be displayed as well.

In most instances, oscilloscopes show events that repeat with either no change or

change slowly. The oscilloscope is one of the most versatile and widely-used

electronic instruments.


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Figure 1: Traditional Oscilloscope

Oscilloscopes are commonly used when it is desired to observe the exact

wave shape of an electrical signal. In addition to the amplitude of the signal, anoscilloscope can show distortion and measure frequency, time between two events

(such as pulse width or pulse rise time), and relative timing of two related signals.

Some modern digital oscilloscopes can analyze and display the spectrum of a

repetitive event

The digital oscilloscope attempts to achieve the same functionality as a

traditional oscilloscope, using a PIC microcontroller for data acquisition (including

appropriate analogue circuitry) which transfers the data to the PC (via USB). A

Microsoft Windows based software application will then display the waveform as it

would appear on a traditional CRT oscilloscope. This software application will have

additional features not present on a traditional oscilloscope (e.g. printing / saving

waveforms) with greater flexibly as additional features can be added as their

developed without the need for new hardware. Additional function is added in the

circuitry such as MULTIMETER MODE which enables the PC-scope to measure the

circuit parameters like capacitance, resistance, current and voltage of the required

component.

Digital oscilloscopes have two main advantages over traditional analogue

scopes


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1. The ability to observe slow and very slow signals as a solid presentation on

the screen. Slow moving signals in the 10-100 Hz range are difficult to see

and measure on a normal analogue oscilloscope due to the flicker of the trace

and the short persistence of the spot on the screen.

2. The ability to hold or retain a signal in memory for long periods.

The PIC microcontroller has a built-in ADC (8, 10 or 12 bits) which has a voltage

range of 0 to 5V. This voltage range is not ideal as most oscilloscopes have a much

wider voltage range including negative voltages (e.g. -100 to 100V); hence an

analogue circuit is requiredto reduce the voltage positive signals so they fall between

2.5 and 5V and voltage negative signals between 0 and 2.5V (i.e. bipolar). The built-in

ADC on the PIC is slow and will limit the maximum sampling frequency; hence an

external Flash ADC with direct memory access will be required to produce a high-

performance digital storage oscilloscope (e.g. AD9070 10Bit, 100MSPS ADC)


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CHAPTER-2

AIM AND SCOPE OF PROJECT

2.1:AIM OF THE PROJECTThe main aim of the PC based is to improve the features of the oscilloscope. The

circuit comprises of micro controller which has a USB 2.0-compliant transceiver and a

CPU running up to 12MIPS.

The digital oscilloscope attempts to achieve the same functionality as a traditional

oscilloscope, using a PIC microcontroller for data acquisition (including appropriate

analogue circuitry) which transfers the data to the PC (via USB). A Microsoft Windows

based software application will then display the waveform as it would appear on a

traditional CRT oscilloscope. This software application will have additional features

not present on a traditional oscilloscope (e.g. printing / saving waveforms) with

greater flexibly as additional features can be added as their developed without the

need for new hardware.

2.2: SCOPE OF THE PROJECT:

Additional function is added in the circuitry such as MULTIMETER MODE

which enables the PC-scope to measure the circuit parameters like capacitance,

resistance, current and voltage of the required component.The major advantage of

this two-channel PC based oscilloscope is to drive the analogue-to-digital converters

and an analogue input to a PIC micro controller.The major advantage of this two-

channel PC based oscilloscope is to drive the analogue-to-digital converters and an

analogue input to a PIC micro controller.


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Figure 3:A typical axial resistor

The electrical functionality of a resistor is specified by its resistance: common

commercial resistors are manufactured over a range of more than nine orders of

magnitude. When specifying that resistance in an electronic design, the required

precision of the resistance may require attention to the manufacturing tolerance of the

chosen resistor, according to its specific application. The temperature coefficient of

the resistance may also be of concern in some precision applications. Practical

resistors are also specified as having a maximum power rating which must exceed

the anticipated power dissipation of that resistor in a particular circuit that is mainly

concerned in power electronics applications.

3.1.2: Variable Resistors-Presets

These are miniature versions of the standard variable resistor. They are designed

to be mounted directly onto the circuit board and adjusted only when the circuit is

built. For example: to set the frequency of an alarm tone. A small screwdriver or

similar tool is required to adjust presets.

Presets are much cheaper than standard variable resistors so they are sometimes

used in projects where a standard variable resistor would normally be used. Multi-turn

presets are used where very precise adjustments must be made. The screw must be

turned many times (10+) to move the slider from one end of the track to the other,

giving very fine control.

Figure 4: Preset Symbol


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3.2: CAPACITORS

A capacitor (formerly known as condenser) is a passive two-terminal electrical

component used to store energy in an electric field. The forms of practical capacitors

vary widely, but all contain at least two electrical conductors separated by a dielectric

(insulator).

C

Figure 5: Capacitor symbol

Mainly used capacitors here are

1. Ceramic capacitor

2. Polyester capacitor

3. Electrolytic capacitor

3.2.1: Ceramic Capacitors

In electronics, a ceramic capacitor is a capacitor constructed of alternating layers of

metal and ceramic, with the ceramic material acting as the dielectric. The temperature

coefficient depends on whether the dielectric is Class 1 or Class 2.A ceramic

capacitor is a two-terminal non-polar device. The classical ceramic capacitor is the

"disc capacitor". This device pre-dates the transistor and was used extensively in

vacuum-tube equipment. A ceramic capacitor (especially the class 2) often has high

dissipation factor, high frequency coefficient of dissipation.

Figure 6:Ceramic capacitors


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3.2.2:Polyester Capacitors

Polyester capacitors use a polyester dielectric and they are ideally suited to

decoupling or bypass applications. In polyester capacitor has dielectric strength of

150% less than of 5 sec, and it has high quality and stable operating voltages.

Figure 7:Polyester capacitors

3.2.3:Electrolytic Capacitors

An electrolytic capacitor is a type of capacitor that uses an electrolyte, an ionic

conducting liquid, as one of its plates, to achieve a larger capacitance per unit volume

than other types. They are often referred to in electronics usage simply as

"electrolytics". They are used in relatively high-current and low-frequency electrical

circuits, particularly in power supply filters, where they store charge needed to

moderate output voltage and current fluctuations in rectifier output. They are also

widely used as coupling capacitors in circuits where AC should be conducted but DC

should not.

Figure 8:Electrolytic capacitors

3.3 USB 2.0

Universal Serial Bus (USB) is an industry standard developed in the mid-1990s

that defines the cables, connectors and communications protocol used in a bus for


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connection, communication and power supply between computers and electronic

devices.

USB was designed to standardize the connection of computer peripheralssuch

as keyboards, pointing devices, digital cameras, printers, portable media players, disk

drives and network adapters to personal computers, both to communicate and to

supply electric power. It has become commonplace on other devices, such as smart

phones, PDAs and video game consoles.USB has effectively replaced a variety of

earlier interfaces, such as serial and parallel ports, as well as separatepower

chargersfor portable devices.

The USB 2.0 specification was released in April 2000 and was ratified by

the USB Implementers Forum (USB-IF) at the end of 2001. Hewlett-Packard,

Intel, Lucent Technologies(now Alcatel-Lucent), NEC and Philips jointly led the

initiative to develop a higher data transfer rate, with the resulting specification

achieving 480 Mbit/s, a fortyfold increase over the original USB 1.1 specification.USB

2.0 a popular version of USB developed to improve on the performance and reliability

of older versions of the standard called USB 1.0 and USB 1.1 (together often referred

to asUSB 1.x) USB 2.0 is also known as USB Hi-Speed.

Figure 9: USB Plug

The B-style connector is designed for use on USB peripheral devices. The B-

style interface is squarish in shape, and has slightly beveled corners on the top ends

of the connector. Like the A connector, it uses the friction of the connector body to

stay in place. The B-socket is an "upstream" connector that is only used on peripheral

devices.
http://en.wikipedia.org/wiki/File:USB-Connector-Standard.jpg


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Internally it consists of an oscillator which generatesThe required signals are

generated and given to the oscilloscope for the measurement purpose. The below

figure shows the basic function generator

4.3: PROBES

These are used for the connection purpose, between function generator and

oscilloscope kit.

Figure14: connecting probe

4.4 MICROCONTROLLERS

Figure 15: Microcontrollers

4.4.1: Introduction to Microcontrollers

Circumstances that user find ourselves in today in the field of microcontrollers

had their beginnings in the development of technology of integrated circuits. This

development has made it possible to store hundreds of thousands of transistors into

one chip. That was a prerequisite for production of microprocessors, and the first


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computers were made by adding external peripherals such as memory, input-output

lines, timers and other. Further increasing of the volume of the package resulted in

creation of integrated circuits. These integrated circuits contained both processor and

peripherals. That is how the first chip containing a microcomputer, or what would later

be known as a microcontroller came about.

Microprocessors and microcontrollers are widely used in embedded systems

products. Microcontroller is a programmable device. A microcontroller has a CPU in

addition to a fixed amount of RAM, ROM, I/O ports and a timer embedded all on a

single chip. The fixed amount of on-chip ROM, RAM and number of I/O ports in

microcontrollers makes them ideal for many applications in which cost and space are

critical.

The microcontroller used in this project is PIC16F877A. The PIC families of

microcontrollers are developed by Microchip Technology Inc. Currently they are some

of the most popular microcontrollers, selling over 120 million devices each year.

There are basically four families of PIC microcontrollers:

PIC12CXXX 12/14-bit program word

PIC 16C5X 12-bit program word

PIC16CXXX and PIC16FXXX 14-bit program word

PIC17CXXX and PIC18CXXX 16-bit program word

4.4.2:Description

4.4.2.1:Introdu ction to PIC Microc on trol lers

PIC stands for Peripheral Interface Controller given by Microchip Technology

to identify its single-chip microcontrollers. These devices have been very successful

in 8-bit microcontrollers. The main reason is that Microchip Technology has

continuously upgraded the device architecture and added needed peripherals to the

microcontroller to suit customers' requirements. The development tools such as

assembler and simulator are freely available on the internet at www.microchip.com.

Low - end PIC Architectures


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Microchip PIC microcontrollers are available in various types. When PIC

microcontroller MCU was first available from General Instruments in early 1980's, the

microcontroller consisted of a simple processor executing 12-bit wide instructions with

basic I/O functions. These devices are known as low-end architectures. They have

limited program memory and are meant for applications requiring simple interface

functions and small program & data memories. Some of the low-end device numbers

are 12C5XX, 16C5X and 16C505.

Mid-range PIC Architectures

Mid-range PIC architectures are built by upgrading low-end architectures with

more number of peripherals, more number of registers and more data/program

memory. Some are: 16C6X,16C7X and 16F87X.

Program memory type is indicated by an alphabet.

C = EPROM, F = Flash, RC = Mask ROM

4.4.2.2: Popular i ty of the PIC microco ntrol lers is du e to the fo l lowing factors

1. Speed: Harvard Architecture, RISC architecture, 1 instruction cycle = 4 clock

cycles.

2. Instruction set simplicity: The instruction set consists of just 35 instructions (as

opposed to 111 instructions for 8051).

3. Power-on-reset and brown-out reset: Brown-out-reset means when the power

supply goes below a specified voltage (say 4V), it causes PIC to reset; hence

malfunction is avoided. A watch dog timer (user programmable) resets the

processor if the software/program ever malfunctions and deviates from its

normal operation.

4. PIC microcontroller has four optional clock sources.

Low power crystal

Mid-range crystal

High range crystal

RC oscillator (low cost).

5. Programmable timers and on-chip ADC.


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6. Up to 12 independent interrupt sources.

7. EPROM/OTP/ROM/Flash memory option.

8. I/O port expansion capability

.

4.4.3: CPU Architecture

The CPU uses Harvard architecture with separate Program and Variable (data)

memory interface. This facilitates instruction fetch and the operation on

data/accessing of variables simultaneously.The Architecture of PIC microcontroller is

shown below:

program Register

8 bits

Data

14 bits 13 bit 8 bits 14 bit

Figure 16: Architecture of PIC microcontroller

4.4.4: MicrocontrollerPIC18F2550

4.4.4.1: A Br ief Histo ry o f PIC18F2550

The original PIC was built to be used with General Instruments' new 16-bit

CPU, the CP1600. While generally a good CPU, the CP1600 had poor I/O

performance, and the 8-bit PIC was developed in 1975 to improve performance of the

overall system by offloading I/O tasks from the CPU. The PIC used simple microcode

stored in ROM to perform its tasks, and although the term was not used at the time, itshares some common features with RISC designs.

In 1985, General Instruments spun off their microelectronics division and the

new ownership cancelled almost everything which by this time was mostly out-of-

date. The PIC, however, was upgraded with internal EPROM to produce a

programmable channel controller and today a huge variety of PICs are available with

Program

memoryCPU

Special

purposeregisters

+

Data

memory


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various on-board peripherals (serial communication modules, UARTs, motor control

kernels, etc.) and program memory from 256 words to 64k words and more (a "word"

is one assembly language instruction, varying from 12, 14 or 16 bits depending on the

specific PIC micro family).

PIC and PIC micro are registered trademarks of Microchip Technology. It is

generally thought that PIC stands for Peripheral Interface Controller, although

General Instruments' original acronym for the initial PIC1640 and PIC1650 devices

was "Programmable Interface Controller". The acronym was quickly replaced with

"Programmable Intelligent Computer".

4.4.4.2: Introdu ctio n

PIC is a family of Harvard architecture microcontrollers made by Microchip

Technology, derived from the PIC1640 originally developed by General Instrument's

Microelectronics Division. The name PIC initially referred to "Peripheral Interface

Controller".

PICs are popular with both industrial developers and hobbyists alike due to

their low cost, wide availability, large user base, extensive collection of application

notes, availability of low cost or free development tools, and serial programming (and

re-programming with flash memory) capability. Microchip announced on February

2008 the shipment of its six billionth PIC processor. The 18F2550 is a microcontroller

for more demanding applications having lots of program memory (16k) and RAM (2k)

and a full USB interface- V2.0 Compliant (Low Speed (1.5 Mb/s) and Full Speed (12

Mb/s).

4.4.4.3:Features

10-bit, up to 13-channels Analog-to-Digital Converter module (A/D) with

programmable acquisition time

Two-Speed Oscillator Start-up Flexible Oscillator Structure

Wide operating voltage range (2.0V to 5.5V

8 x 8 Single-Cycle Hardware Multiplier

High-current sink/source 25 mA/25 mA


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Dual oscillator options allow microcontroller and USB module to run at different

clock speeds.

Power-on Reset (POR), Power-up Timer (PWRT) and Oscillator Start-up Timer

(OST).

Watchdog Timer (WDT)

In-Circuit Serial Programming TM (ICSPTM) via two pins.

Full Speed USB 2.0 (12Mbit/s) interface

1K byte Dual Port RAM + 1K byte GP RAM.

16 Endpoints (IN/OUT)

Consists of internal Pull Up resistors (D+/D-).

Pin-to-pin compatible with PIC16C7X5


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4.4.4.4: PIN Descr ipt ion

Figure 17: PIN Diagram of PIC18F2550


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Table 1: Pin Description of PIC18F2550

Pin

name

Digital

I/O

Analog

inputOther

Pin on

ChipMicrochip name

0 Yes NoI2C I/O - SPI

SDI21 RB0/AN12/INT0/FLT0/SDI/SDA

1 Yes NoI2C SCL -

SPI SCK22 RB1/AN10/INT1/SCK/SCL

2 Yes No - 23 RB2/AN8/INT2/VMO

3 Yes No - 24 RB3/AN9/CCP2/VPO

4 Yes No - 25 RB4/AN11/KBI0

5 Yes - - 26 RB5/KBI1/PGM

6 Yes - - 27 RB6/KBI2/PGC

7 Yes - - 28 RB7/KBI3/PGD

8 Yes - Serial Tx 17 RC6/TX/CK

9 Yes -Serial Rx -

SPI SDO18 RC7/RX/DT/SDO

10 Yes - - 11 RC0/T1OSO/T13CK

11 Yes - PWM 12 RC1/T1OSI/CCP2/UOE

12 Yes - PWM 13 RC2/CCP1

13 Yes Yes - 2 RA0/AN0

14 Yes Yes - 3 RA1/AN1

15 Yes Yes - 4 RA2/AN2/VREF-/CVREF


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16 Yes Yes - 5 RA3/AN3/VREF+

17 Yes Yes - 7 RA5/AN4/SS/HLVDIN/C2OU

RunOutput

only - Run 6 RA4/T0CKI/C1OUT/RCV

USB+ - - USB 16 RC5/D+/VP

USB- - - USB 15 RC4/D-/VM

Vusb - - USB 14 VUSB

Reset - - Reset switch 1 MCLR/VPP/RE3

Vdd

(5V)- - - 20 Vdd

Vss

(GND)- - - 8 Vss

Vss

(GND)- - - 19 Vss

OSC1 - - Quartz 9 OSC1/CLKI

OSC2 - - Quartz 10 OSC2/CLKO/RA6

VSS, VDD: Supply voltages.

I/O Port

Depending on the device selected and featuresenabled, there are up to five

ports available. Some pinsof the I/O ports are multiplexed with an alternatefunction

from the peripheral features on the device. Ingeneral, when a peripheral is enabled,

that pin may notbe used as a general purpose I/O pin.Each port has three registers

for its operation. Theseregisters are

TRIS register (data direction register)


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PORT register (reads the levels on the pins of thedevice)

LAT register (output latch)

The Data Latch register (LATA) is useful for readmodify-write operations on the value

driven by the I/Opins.

PortA

PortA is an 8-bit wide, bidirectional port. The correspondingdata direction

register is TRISA. Setting aTRISA bit (= 1) will make the corresponding PortA pinan

input. Clearing a TRISA bit (= 0) willmake the corresponding PortA pin an.Reading

the PortA register reads the status of thepins; writing to it will write to the port latch.

PortB

PortB is an 8-bit wide, bidirectional port. The correspondingdata direction

register is TRISB. Setting aTRISB bit (= 1) will make the corresponding PortBpin an

input. Clearing a TRISB bit (= 0) will make the corresponding PortB pin an output.

Each of the PortB pins has a weak internal pull-up. Asingle control bit can turn on all

the pull-ups.

PortC

PortC is a 7-bit wide, bidirectional port. The correspondingdata direction

register is TRISC. Setting aTRISC bit (= 1) will make the corresponding PortCpin an

input. Clearing a TRISC bit (= 0) will make the corresponding PortC pin an output.

PortC is primarily multiplexed with serial communicationmodules, including the

EUSART, MSSP moduleand the USB module. Except for RC4 andRC5, PortC uses

Schmitt Trigger input buffers.

PortE

PortE is a 4-bit wide port.Three pins (RE0/AN5/CK1SPP,

RE1/AN6/CK2SPPand RE2/AN7/OESPP) are individually configurable asinputs or

outputs. These pins have Schmitt Trigger input buffers. When selected as an analog

input, thesepins will read as 0s.


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Memories

There are three types of memory in PIC18F2550 enhancedmicrocontroller

devices:

Program Memory

Data RAM

Data EEPROM

As Harvard architecture devices, the data and programmemories use separate

busses; this allows for concurrentaccess of the two memory spaces. The

dataEEPROM, for practical purposes, can be regarded asa peripheral device, since it

is addressed and accessedthrough a set of control registers.

4.5 MCP6S91

4.5.1 Desc riptio n

The Microchip Technology Inc. MCP6S91/2/3 isanalog Programmable Gain

Amplifiers (PGAs). Theycan be configured for gains from +1 V/V to +32 V/V andthe

input multiplexer can select one of up to two channelsthrough a SPI port. The serial

interface can alsoput the PGA into shutdown to conserve power. These PGAs are

optimized for high-speed, low offset voltageand single-supply operation with rail-to-rail

input andoutput capability. These specifications support singlesupplyapplications

needing flexible performance ormultiple inputs.The one-channel MCP6S91 and the

two-channelMCP6S92 are available in 8-pin PDIP, SOIC and MSOPpackages. The

two-channel MCP6S93 is available in a10-pin MSOP package. All parts are fully

specified from-40C to +125C.


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4.5.2: PIN Configuration of MCP6S91

Figure 17: Top view of MCP6S91

Table 2: PIN Description of MCP6S91

PIN Name Function

VOUT Analog output

CH0,CH1 Analog inputs

VREF External reference pin

VSS Negative power supply

CS Chip select

SI Serial data input

SO Serial data output

SCK Clock input

VDD Positive power supply

4.5.3:Features

Multiplexed Inputs: 1 or 2 channels.

8 Gain Selections:

o +1, +2, +4, +5, +8, +10, +16 or +32 V/V

Serial Peripheral Interface (SPI).

Rail-to-Rail Input and Output.

Low Gain Error: 1% (max).

1 8

2 MCP6S91 7

3 6

4 5VSS

VDDVOUT

VREF

CH0

CS

SCK

SI


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Offset Mismatch Between Channels: 0 V.

High Bandwidth: 1 to 18 MHz (typ).

Low Noise: 10 nV/Hz @ 10 kHz (typ).

Low Supply Current: 1.0 mA (typ).

Single Supply: 2.5V to 5.5V.

Extended Temperature Range: -40C to +125C.

4.5.4: Applications

A/D Converter Driver.

Multiplexed Analog Applications.

Data Acquisition.

Industrial Instrumentation.

Test Equipment.

Medical Instrumentation.

4.6: LF353

4.6.1: Description

This IC has two operational amplifiers.

Op-Amp A is used as Voltage Shifting Amplifier.

Op-Amp B is used as Voltage Followers.

TheLF353isaJFETinputoperationalamplifierwith an

internallycompensatedinputoffsetvoltage.TheJFETinput

deviceprovideswidebandwidth,lowinputbiascurrents and offsetcurrents.

4.6.2: PIN CONFIGURATION OF LF353

Figure 19: Top view of LF353

1 8

2 LF353 7

3 6

4 5

OUT1

OUT2

VCC

VEE

IN1 (+)

IN1 (-)

IN2 (-)

IN2 (+)


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Figure 20: 8-pin DIP

Table 3: Absolute maximum ratings

PARAMETER SYMBOL VALUE UNIT

Power supply voltage Vcc 18 V

Differential input voltage VI(diff) 30 V

Input voltage range VI 15 V

Output short circuit duration - Continuous -

Power dissipation Pd 500 mW

Operating temperature range Topr 0 to +70 C

4.6.3:Features

Internally trimmed offset voltage: 10mV

Low input bias current: 50pA

Wide gain bandwidth: 4MHz

High slew rate: 13V/s

High Input impedance: 1012

4.6.4:Applications

High speed integrators.

Digital to analog converters.

Sample and hold circuits.


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4.7:ICL7660

4.7.1:Description

The MAX1044 and ICL7660 is monolithic, CMOS switched-capacitor voltage

converters that invert, double, divide, or multiply a positive input voltage. They arepin

compatible with the industry-standard ICL7660 andLTC1044. Operation is guaranteed

from 1.5V to 10V withno external diode over the full temperature range. Theydeliver

10mA with a 0.5V output drop. The MAX1044 has a BOOST pin that raises the

oscillator frequencyabove the audio band and reduces external capacitorsize

requirements. The MAX1044/ICL7660combines low quiescent currentand high

efficiency. Oscillator control circuitry and four power MOSFET switches are included

on-chip.

4.7.2: PIN configuration of ICL7660

Figure21: Top view of ICL7660

Figure22: 8 PIN Dip

The ICL7660 performs supply voltage conversions from positive to negative for

an input range of +1.5V to +10.0V resulting in complementary output voltages of -


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1.5V to -10.0V.Only 2 noncritical external capacitors are needed for the charge pump

and charge reservoir functions. The ICL7660 and ICL7660A can also be connected to

function as voltage doublers and will generate output voltages up to +18.6V with a

+10V input.

The oscillator, when unloaded, oscillates at a nominal frequencyof 10 kHz for an input

supply voltage of 5.0V. This frequencycan be lowered by the addition of an

externalcapacitor to the OSC terminal, or the oscillator may beoverdriven by an

external clock.The LV terminal may be tied to GROUND to bypass theinternal series

regulator and improve low voltage (LV) operation.At medium to high voltages (+3.5V

to +10.0V for theICL7660 and +3.5V to +12.0V for the ICL7660A), the LV pinis left

floating to prevent device latch up.

Table 4: Absolute maximum ratings

Parameter Symbol Value of ICL7660 Unit

Supply voltage V+ 10.5 V

Supply current I+ 500 A

Operating temperature TA -55 to 125 C

Oscillator frequency Fosc 10 KHz

Power efficiency Pef 98 %

4.7.3: Features

Simple conversion of +5v logic supply to 5v supplies.

Typical power efficiency of 98%.

Wide operating voltage range.

Easy to use requires only two external non-critical passive components.

4.7.4:Applications

On board negative supply for dynamic RAMs.

Dataacquisition systems.

Inexpensive negative supplies.

CHAPTER-5


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OPERATION OF THE CIRCUIT

5.1: COMPONENTS USED IN PC BASED OSCILLOSCOPE

Hardware components

Resistors : (1M -2, 82K -2, 33K -2, 220K -2,

150K -2, 1K -2, 4.7K -2)

Capacitors

1. Ceramic : (2.7pF -2, 68nF -4, 150nF -1)

2. Polyester : (0.022F-1)

3. Electrolytic : (10F -1,47F -1)

ICs

1. Voltage converters : ICL7660

2. Dual operational amplifiers : LF353

3. Programmable gain amplifiers : MCP6S91

4. Micro controller : PIC18F2550

Crystal Oscillator : 4MHz

USB : Type-B socket, Cable

5.2: CIRCUIT DIAGRAM


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Theheart ofthis oscilloscope is USB2.0-compliant microcontroller

PIC18F2550 from Microchip.You canalso use PIC18F2445 in place of PIC18F2550.

ThismicrocontrollerhasaUSB2.0-complianttransceiverandaCPUrunning up to 12 MIPS.

MCP6S91 is an analogue programmable gain amplifier that is well suited to

driving analogue to digital convertors (ADCS) and an analogue input to a PIC

microcontroller.

To MCP6S91 programmable gain amplifiers (IC2&IC3) make it possible to choose

the input ranges for each of the two channels, by selecting a gain from 1:1 to 32:1.

And the amplifiers are small, cheap and easy to use. A simple three wire serial

peripheral interface (SPI) allows the PIC to control them through its pins 5, 6, 7.

TheMCP6S91amplifierisdesigned with CMOSinputdevices. It isdesignedtonot

exhibitphaseinversion when the input pins exceed the supply voltages. The

maximumvoltage thatcanbeappliedtotheinputpinis0.3V (VSS) to +0.3V (VDD). Input

voltages that exceed the absolute maximum rating can cause excessive current into or

out of the output pins .current beyond +/-2 mA can cause reliability problems. Applications

that exceed this rating must be externally limited with a resistor to the input pin.

Vref(pin 3), which is ananalogue input,shouldbeatavoltagebetween VSS and VDD. The

voltageatthispin shifts theoutputvoltage. The SPIinterface inputs are chip-select (CS),

serial input (SI) and serial clock (SCK). These areSchmitt-triggered, CMOS logic inputs.

Theonlydisadvantageisthatthese amplifiersacceptonlypositivesignals. Thats

whyvoltage-shifting amplifiersLF353(IC4Aand IC5A) are used, one each for each

channel input.The LF353 isaJFET inputoperational amplifierwith aninternally

compensated inputoffset voltage. The JFET input deviceprovideswidebandwidth,

lowinputbias currentsand offset currents.This voltage-shiftingamplifier resultsinahigh

input impedance and anattenuationfactorof1:4.5. A16V input signal isthen shiftedtothe-

5Vrange when theprogrammed gain is 1:1.

Two halves of the LF353(IC4BandIC5B)are used asvoltagefollowersto provide a

low-impedance shifting voltage (Vref) totheprogrammableamplifiers. This voltage

must beprecisely adjustedwithtwo4.7-kilo- ohm presets to measure precisely 2.5V level

on theinputsofIC2andIC3 whentheinputsignalsare grounded.

Because LF353 op-ampsneedasymmetrical supply voltage, a small DC-DC


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voltageconverter ICL7660 (IC6) is used to feed 5V to LF353. With its small 8-pin DIP

package, it needs onlytwo polarized capacitors. ICL7660 can bereplaced with

aMAX1044. The MAX1044 and ICL7660 are monolithic,CMOS switched-capacitor

voltage converters that invert, double divide or multiply a positive input voltage. These

are pin compatiblewith the industry-standard LTC1044.

All the data is transmitted on the D+/D- symmetrical pins using a variable bit rate.

The position of a resistor (R13) on D+ or D- allows you to choose between the full-speed

(12 Mbps) and lowspeed modes (1.5 Mbps). Note that the IC18F2550/2455 devices have

built-in pull-up resistors designed to meet the requirements of low-speed and fullspeed

USB. The UPUEN bit (UCFG=4) enables the internal pull-ups. In this project, R13 is not

used. External pullup may also be used. The VUSB pin may be used to pull up D+ or D-.

The pull-up resistor must be 1.5 kilo-ohms (5%) as required by the USB specification

5.3.1: PIC Software

The program for the microcontrolleris written in C language. MPLAB7.31

along with MPLAB_C18 is usedas the software tool for development. Ifeverything is

fine, plug the oscilloscopewith a USB cable to your PC (runningWindows 98SE or

higher version). ANew hardware detectedUSB2-MiniOscilloscopedialogue box

must immediate appear on the screen. Now you can start the driver

installationprocess.User-interface softwarewritten in Visual Basic 6, called

OscilloPIC,is given torun the set up program from theSetup files. Now by running

the OscilloPIC we can obtain the results.

5.4:EXPERIMENTAL RESULTS

By running the OscilloPIC, the application program looks like asmall digital

oscilloscope as shownin the screenshot below.Various settings for operationsare

given in the following menubars:

1. Inputs: Selects the activechannels.

2. Sampling: Sets time-base andnumber of samples.

3. Trigger: Sets the triggeringCondition.

4. Cursors: Selects horizontal orvertical cursor positions.

5. Num: Shows numericalsampled values, with an exportcommand (text file format).


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6. Config: Configures gain andoffset errors

Calibration is to be done asdescribed below before readingthe output signals

on the monitorscreen by clicking channels calibrationunder Config menu bar.Feed

the input waveforms (say,sine, rectangular, saw tooth, etc)from the source. Click go

button.

The output waveform will bedisplayed on the monitor screen.Channel-1 and

channel-2 outputwaveforms can be differentiated bygreen and red lines,

respectively.By default, the time base is 200 sper division and amplitude is 4Vper

division. You can set these parametersas per your requirements.

Test and calibration

The firststep is to adjust the zero offset error. Connect the two analogue inputs

tothe ground level and tune the two 4.7kilo-ohm presets until pin 2 of bothMCP6S21

is at 2.5V. A more precisetuning can be achieved through OscilloPICsoftware.

Choose the smallestcalibration value at 0.5V for both theinputs.The zero

calibrationcommand tells the PICto start its own internalcompensation for all

calibrations.Dont forget toconnect the inputs to theground while calibrating.The

second parameterto check is the gain error.By clicking the gain calibrationcommand,

itspossible to specify a smallcorrection factor. Thiscan be done after

severalmeasurements. You haveto know the actual levelsand the measured levels

(with the cursors)for the two channels. The gain erroris less than 0.1 per cent. The

numberof samples can be set between 10 and500. The minimum sampl ing rate is5

s for one channel and 10 s for two channels.


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Figure 24: Output waveforms on a PC


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Figure 25: Overview of project kit

5.5:ADVANTAGES

Lighter more portable.

Signals can be stored and processed later.

No need of additional power supply for PCB.

The ability to observe slow and very slow signals as a solid presentation on

the screen.

The PCBO has a very interactive GUI making it more convenient to use than

conventional oscilloscopes.

The circuit is extremely cheap and easy to make.

5.6:DISADVANTAGES

It can effectively process the signals up to 10 KHz.

Limited to serial communication.


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5.7:APPLICATIONS

Monitoring of sound waves, which are difficult to monitor on a traditional

oscilloscope due to the low frequencies involved.

Monitoring of serial communications.

Because of the low cost of the PC based oscilloscope, it is economical for a

school / technical college to have large quantities available for students.

In radar systems.

Medical sector.


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CHAPTER-6

CONCLUSION AND FUTURE SCOPE

6.1:CONCLUSION

The PC based is to improve the features of the oscilloscope. The circuit

comprises of micro controller which has a USB 2.0-compliant transceiver and a CPU

running up to 12MIPS.The oscilloscope uses IC PIC18F2550 from Microchip as the

main controller, which makes the oscilloscope compact as there is no need of

additional power supply for the entire circuit board. Thus we conclude that the

conventional oscilloscope can be replaced with the PC based oscilloscope.

6.2: FUTURE SCOPE

The performance of the oscilloscope can be improved by changing the PIC

and its ADC with a faster model. AD9238 (20 MS/s) is a good choice. This fast,

parallel ADC converter could be used with a powerful DSP PIC. A PIC18Fx455 could

be used for its USB link. This two channel pc based oscilloscope is extended to multi

channel pc based oscilloscope.


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REFERENCES

[1] Basic electronic module

[2] D. Roy Chowdary, Shail B. Jain, Linear Integrated circuits new age

international (p) LTD, 2nd Edition 2003.

[3] S.Salivahanan, Electronics devices and circuits, Tata McGraw-hill

publishing company LTD, NEWDELHI-110008, 2000

REFERENCES ON WEB

[1]www.electronicsforu.com

[2]www.wikipedia.com

[3]www.alldatasheets.com
http://www.electronicsforu.com/http://www.electronicsforu.com/http://www.electronicsforu.com/http://www.wikipedia.com/http://www.wikipedia.com/http://www.wikipedia.com/http://www.alldatasheets.com/http://www.alldatasheets.com/http://www.alldatasheets.com/http://www.alldatasheets.com/http://www.wikipedia.com/http://www.electronicsforu.com/


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