PC – BASED OSCILLOSCOPE USING MSP430
by
Joemmer T. Antonio
A Design Report Submitted to the School of Electrical Engineering,
Electronics Engineering, and Computer Engineering in Partial
Fulfillment of the Requirements for the Degree
Bachelor of Science in Computer Engineering
Mapua Institute of Technology
August 2011
Approval Sheet
Mapua Institute of Technology
School of EECE
This is to certify that we have supervised the preparation of and read the design
report prepared by Joemmer T. Antonio entitled PC-Based Oscilloscope
using MSP430 and that the said report has been submitted for final
examination by the Oral Examination Committee.
___________________
Wei-Chih Hu, Ph.D.
Design Adviser
As members of the Oral Examination Committee, we certify that we have
examined this design report, presented before the committee on September 5,
2011, and hereby recommended that it be accepted in partial fulfilment of the
requirements for the degree in Bachelor of Science in Computer
Engineering.
____________________
Engr. Dionis Padilla
Panel Member
_____________________
Panel Member
________________________
Engr. Noel Linsangan
Chairman
This design report is hereby approved and accepted by the School of Electrical
Engineering, Electronics Engineering, and Computer Engineering in partial
fulfilment of the requirements for the degree in Bachelor of Science in
Computer Engineering.
________________________
Felicito Caluyo, Ph.D.
Dean, School of EECE
ii
TABLE OF CONTENTS
TITLE PAGE…………………………………………………………………………………………………i
APPROVAL SHEET……………………………………………………………………………………….ii
TABLE OF CONTENTS………………………………………………………………………………….iii
LIST OF TABLES…………………………………………………………………………………………iv
LIST OF FIGURES…………………………………………………………………………….…….……v
ABSTRACT………………………………………………………………………………….………..…...vi
Chapter 1: DESIGN BACKGROUND AND INTRODUCTION………………………………..1
Background…………………………………………………………………...……….1
Statement of the Problem……………………………….………………….…...2
Objectives of the Design………………………….………………………….……3
Significance and Impact of the Design……………………………….………4
Scope and Delimitation………………………….…………………………………5
Definition of Terms………………………………………………………………….6
Chapter 2: REVIEW OF RELATED DESIGN LITERATURE AND STUDIES...............9
Chapter 3: DESIGN PROCEDURES..................................................................15
Chapter 4: TESTING, PRESENTATION, AND INTERPRETATION OF DATA..........33
Chapter 5: CONCLUSION AND RECOMMENDATION.........................................38
Conclusion...............................................................................38
Recommendation.....................................................................39
REFERENCES….………………………………………………………………….……………………..40
APPENDIX………………………………………………………………………….……………………..41
Appendix A: Pictures of the Design……..…………………………………………….42
Appendix B: Program Listing…………………………………………………………….43
iii
LIST OF TABLES
Table 3.1: Voltage Division Circuit Data………..……………………………………………..22
Table 3.2: Voltage Off-Set Circuit Data………………………………………………………..23
Table 3.3: Voltage Division Circuit Connections and Registers………………………..30
Table 3.4: Voltage Off-Set Circuit Connections and Registers….……………………..31
LIST OF FIGURES
Figure 3.1: Block Diagram of the PC-Based Oscilloscope using MSP430.…………15
Figure 3.2: Analog Front-End Circuit Input and Output Representation.…………19
Figure 3.3: Voltage Divider Formula…………………………………………………………..21
Figure 3.4: Voltage Off-Set Circuit Formula……………………………………………….…23
Figure 3.5: Voltage Off-Set Circuit Diagram………………………………………………….24
Figure 3.6: Analog Front-End Circuit Schematic Diagram……………………………….25
Figure 3.7: MSP430 Input and Output Representation…………………………………..27
Figure 3.8: PC Program Screenshot………………………..…………………………………..31
Figure 3.9: Data Transfer Flowchart of PC Program….…………………………………..32
Figure 4.1: Sinusoidal Wave Input, 10 Vpp at 10 Hz………………………………….....34
Figure 4.2: Sinusoidal Wave Input, 10 Vpp at 100 Hz………………………………......35
Figure 4.1: Sinusoidal Wave Input, 10 Vpp at 250 Hz………………..………………....36
Figure 4.1: Sinusoidal Wave Input, 10 Vpp at 500 Hz……………………….……….....36
Figure 4.1: Sinusoidal Wave Input, 10 Vpp at 1 KHz………………………………….....37
iv
ABSTRACT
An oscilloscope is an essential electronic measuring tool used for
experimenting and data analysis on projects that involve visual representation of
digital signals. The project, entitled „PC-based Oscilloscope using MSP430‟, is an
adaptation of a digital oscilloscope using the combination of a personal computer
and MSP430. It is developed to be able to provide a low-cost device that
performs basic oscilloscope functions such as drawing the electrical signal in a
voltage-against-time graph and digitally control the signal which would be very
beneficial for small scale hobbyist, enthusiasts and students alike.
The prototype is able to perform similar oscilloscope function using
MSP430‟s analog-to-digital conversion capability. It is digitally controlled and
display using a PC. It allows the user to observe electrical signals by displaying a
graph of voltage against time on the PC. The input signal can be digitally
controlled through a program in the PC.
Keywords: Oscilloscope, PC, MSP430.
v
Chapter 1
DESIGN BACKGROUND AND INTRODUCTION
This chapter discusses an overview of the design.
This includes the
purpose, objective, significance and scope of the design. Some technical terms
that were used for the documentation were discussed at the end of this chapter.
Background
An Oscilloscope is a test/measuring instrument that is capable of
displaying electrical signals by plotting them in a 2D plane using voltage-againsttime graph. It is one of the most essential digital devices that engineers,
researchers and electronic enthusiast need in analyzing, testing and developing
electronic devices. However, though an oscilloscope is a very useful and
important tool, it is very expensive especially for small scale prototype
developers such as students. And some full scale oscilloscopes that are available
on the market have functions that small scale prototype makers like students
don‟t need most of the time.
The project, entitled „PC-based Oscilloscope using MSP430‟, is an
adaptation of a digital oscilloscope using the combination of a personal computer
and MSP430. It is developed to be able to provide a low-cost device that
performs basic oscilloscope functions such as drawing the electrical signal in a
voltage-against-time graph and digitally controlling the signal. These functions
that the PC-based Oscilloscope has are those functions that most common
1
prototype maker needs. It performs real-time and is composed of three major
parts, the Analog front-end circuit, the MSP430 and the PC.
The prototype is able to perform similar oscilloscope function using the
combination of MSP430‟s analog-to-digital conversion capability, the Analog
Front-End Circuit‟s ability to control the input voltage and the PC‟s capability to
visually display the output graph. It is digitally controlled and displayed using a
PC. It allows the user to observe electrical signals by displaying a graph of
voltage against time on the PC. The system is digitally controlled through the PC
and is capable of adjusting incoming analog signal to achieve the desired visual
output.
Statement of the Problem
An oscilloscope is an essential tool for electronic prototyping, research and
data gathering. The majority of the oscilloscopes in the market are highly
expensive and provides a very wide range of capability that most of the small
scale prototype developer and students don‟t need anymore. Full-scale industry
quality oscilloscope ranges from $1,500 to $3,000, a price that would be very
unwise to spend if you would not be using its full capabilities.
Undergraduate students of Dr.Hu, professor of the bio-signal processing
laboratory where the internship of the designer was done, are in need of a
simple personal signal analyser/oscilloscope that they could use for their class
2
whenever their professor asks them to analyze and test prototypes they make in
their class at their own home.
There is also a need for a logic signal analyzer/oscilloscope that students,
developers and enthusiast can easily build on their own and be used for their
school works and data gathering. It is not economically wise for students to
purchase their own personal oscilloscope to suffice their need for a simple signal
analyzer.
Objective of the Design
The main objective of the design is to be able to design and develop a
practical, digitally-controlled, PC-based oscilloscope that performs the basic
capability of a regular oscilloscope. By stating „practical‟, it should be able to
provide the basic function of an oscilloscope which is to display the visual
representation of an analog signal through the PC and be able to digitally-control
the signal for adjustment, specifically through voltage division and voltage offset. Full-scale industry quality oscilloscope ranges from $1,500 to $3,000
(www.testequipmentdepot.com), a price that would be very unwise to spend if
you would not be using its full capabilities.
This design should be able to supply the need of Dr.Hu‟s undergraduate
students for a simple logic signal analyser/oscilloscope that they could personally
use and could be built on their own. The cost of the design should also be lower
3
than the market price of full scale oscilloscope otherwise it would not be
beneficial for students.
Significance and Impact of the Design
The project will enable students, hobbyists and electronic enthusiasts to
have their very own logic analyser/oscilloscope at a very low cost compared to
the actual oscilloscope. It will enable them to see and analyse electrical signals
using their personal computer. This shall provide people their own personal
oscilloscopes that they could use at a fraction of the market cost of an
oscilloscope. It shall also encourage more students and enthusiast to engage
more in digital design and electronic prototyping with having their own personal
oscilloscope. Small scale researches will also be able to perform various
researches that need the use of an oscilloscope for data gathering.
The design would allow small-scale electronics enthusiasts to be able to
test electrical signals that are generated by their prototype without the expense
of a full scale oscilloscope which is very expensive. Since it is part of the design
objective to develop an oscilloscope where students, engineers, hobbyists and
electronics enthusiasts can build on their own, it would create an inviting
environment for those who are interested in the field of electronic prototyping to
involve themselves to this field of engineering and science.
4
Scope and Delimitation
Scopes:
1. The prototype is able to accept external analog input signal up to 20
Vpp.
2. It can plot any kind of waveform as long as it is within the boundary of
20 Vpp.
3. It is capable of adjusting the input signal through voltage division by
the factors 20, 16, 10 and 6.
4. It is capable of off-setting the signal by .25 V, .50 V, .75 V and 1 V.
5. It displays the output waveform in the PC using a C++ based program
written using Borland C++ Builder version 6.
6. It saves the incoming digital data from the MSP430 to a text file.
Delimitations:
1. It is not capable of providing frequency measurement.
2. Does not provide industry quality precision.
3. Limited to only four options for voltage division and four options for
voltage offset.
4. Can only accommodate one input signal at a time.
5. Can only handle a maximum of 20 Vpp at 1000 Hz.
5
Definition of Terms:
1. Oscilloscope - An electronic instrument that produces an instantaneous trace
on the screen of a cathode-ray tube corresponding to oscillations of voltage
and current.
2. PC (Personal Computer) - A computer built around a microprocessor for use
by an individual. Personal computers have their own operating systems,
software, and peripherals, and can generally be linked to networks.
3. MSP430 - A mixed-signal microcontroller family from Texas Instruments. Built
around a 16-bit CPU, the MSP430 is designed for low cost, and specifically,
low power consumption embedded applications. The architecture dates from
the 1990s and is reminiscent of the DEC PDP-11.
4. Analog – Expressed by means of one or more physical properties that can
express any value along a continuous scale. For example, the position of the
hands of a clock is an analog representation of time
5. Digital - Expressed in discrete numerical form, especially for use by a
computer or other electronic device
6. Microcontroller - (sometimes abbreviated µC, uC or MCU) A small computer
on a single integrated circuit containing a processor core, memory, and
programmable input/output peripherals. Microcontrollers are designed for
embedded applications, in contrast to the microprocessors used in personal
computers or other general purpose applications.
6
7. Multiplexer - A device that interleaves several activities; a switching device.
(computing, telecommunications) A device that combines several input
signals into a single output signal.
8. USB - Universal Serial Bus Type of serial bus that allows peripheral devices
(disks, modems, printers, digitizers, data gloves, etc.) to be easily connected
to a computer. A “plug-and-play” interface, it allows a device to be added
without an adapter card and without rebooting the computer (the latter is
known as hot-plugging). The USB standard, developed by several major
computer and telecommunications companies, supports data-transfer speeds
up to 12 megabits per second, multiple data streams, and up to 127
peripherals.
9. Operational Amplifier - Amplifier whose output voltage is proportional to the
negative of its input voltage and that boosts the amplitude of an input signal
many times, i.e., has a very high gain. It is usually connected so that part of
the output is fed back to the input. Operational amplifiers were originally
developed to be used in synthesizing mathematical operations in analog
computers, hence their name. Because of recent advances in semiconductor
technology, they have become available as integrated circuits. They are
widely used when a closely controlled amount of gain or some form of signal
processing is necessary in an electronic system.
7
Chapter 2
REVIEW OF RELATED DESIGN LITERATURES AND STUDIES
This chapter includes the compiled research works and studies that are
related to the design. The contents of this chapter are used as reference for the
development of the design. The designer used the following related articles,
research works and inventions as a reference which will aid in having an in-depth
understanding about the design that the designer is working on.
In the application report entitled, “Implementing IrDA with the MSP430”,
by Melisa Nunez-Arzuaga and Andreas Dannenberg, it shows the capability of the
MSP430 to provide a demonstration application for Windows-based PCs. In this
report, an application was written on C programming language and shows an
IrDA connection between a PC and the MSP430 IrDA stack by using standard
Windows API calls only.
The hardware design for this application focuses on the interfacing of the
MSP430F149, the MSP430FG4619, and the MSP430F2274 with the SHARP
GP2W0110YPSF IrDA transceiver device. Other MSP430 family members can be
used as well, depending on the requirements of the end application. The SHARP
GP2W0110YPSF was selected because it follows all ISO specifications stipulated
for IrDA V1.0. The fact that this part can be used at a 3.0-V level is a benefit
when interfacing with the MSP430, because no external circuitry is necessary to
adapt the voltage levels. It also needs only three signals for interfacing with the
8
microcontroller: transmit, receive, and shutdown. This leaves most of the MCU
pins free for other purposes.
This report also states the usage of an external circuit connected to the
MSP430 which validates the capability of the microcontroller to interact with
other circuitry connected to it.
The PC demonstration application supplied with this application report is
provided as both C source code and as an executable single-file Win32 command
line application. It has been decided to develop the software as a command line
application to make it both easy to understand and also compatible with all
common Windows-based C development systems such as Microsoft Visual C++
or Borland C++.
The demonstration software requires at least Windows 2000 or Windows
XP operating system and a properly installed infrared port. This IR port can
either be integrated (such as those found in notebook computers) or provided by
an external Windows-supported IrDA adaptor (for example, the Actisys ACTIR220L+). The current Windows operating systems come with a built-in IrDA
stack that implements various IrDA communication modes, such as the 9-wire
IrCOMM mode. This mode can easily interface with external devices like PDAs,
cell-phones, and the presented MSP430 IrDA stack. Microsoft decided to expose
the IrDA stack through the Windows sockets library rather than by providing
virtual COM ports. If virtual COM ports need to be used, then additional thirdparty driver software such as IrCOMM2k is required. However, the more elegant
9
approach is to perform IrDA communication by using the standard Windows
built-in driver model as shown in this demonstration application.
Murugavel Raju wrote the application report classified under mixed signal
processing entitled “Ultrasonic Distance Measurement with the MSP430”. This
application report describes a distance-measuring system based on ultrasonic
sound utilizing the MSP430F413 ultralow-power microcontroller. The system
transmits a burst of ultrasonic sound waves towards the subject and then
receives the corresponding echo. The MSP430 integrated analog comparator
Comparator_A is used to detect the arrival of the echo to the system. The time
taken for the ultrasonic burst to travel the distance from the system to the
subject and back to the system is accurately measured by the MSP430. Assuming
the speed of sound in air at room temperature to be 1100 ft/s, the MSP430
computes the distance between the system and the subject and displays it using
a two-digit static LCD driven by its integrated LCD driver. The distance is
displayed in inches with an accuracy of ±1 inch. The minimum distance that this
system can measure is eight inches and is limited by the transmitter‟s transducer
settling-time. The maximum distance that can be measured is 99 inches. The
amplitude of the echo depends on the reflecting material, shape, and size.
Sound-absorbing targets such as carpets and reflecting surfaces less than two
square feet in area reflect poorly. The maximum measurable range is lower for
such subjects. If the amplitude of the echo received by the system is so low that
10
it is not detectable by the Comparator_A, the system goes out of range. This is
indicated by displaying the error message E.
The devices used to transmit and receive the ultrasonic sound waves in
this application are 40-kHz ceramic ultrasonic transducers. The MSP430 drives
the transmitter transducer with a 12-cycle burst of 40-kHz square-wave signal
derived from the crystal oscillator, and the receiver transducer receives the echo.
The Timer_A in the MSP430 is configured to count the 40-kHz crystal frequency
such that the time measurement resolution is 25 μs, which is more than
adequate for this application. The measurement time base is very stable as it is
derived from a quartz-crystal oscillator. The echo received by the receiver
transducer is amplified by an operational amplifier and the amplified output is fed
to the Comparator_A input. The Comparator_A senses the presence of the echo
signal at its input and triggers a capture of Timer_A count value to capture
compare register CCR1. The capture is done exactly at the instant the echo
arrives at the system. The captured count is the measure of the time taken for
the ultrasonic burst to travel the distance from the system to the subject and
back to the system. The distance in inches from the system to the subject is
computed by the MSP430 using this measured time and displayed on a two-digit
static LCD. Immediately after updating the display, the MSP430 goes to LPM3
sleep mode to save power. The Basic Timer1 is programmed to interrupt the
MSP430 every 205 milliseconds. The interrupt signal from the Basic Timer1
wakes up the MSP430 to repeat the measurement cycle and update the display.
11
In the application report written by Lutz Bierl entitled “MSP430 Universal
Synchronous Asynchronous Receive/Transmit Communication Interface”, it gives
a short overview for the use of the MSP430 universal synchronous, asynchronous
receive/transmit communication interface (USART) as an RS232 interface, also
called a serial-controller interface (SCI). Tested software examples, with and
without the use of the interrupt capability, are given for the transmission and the
reception of UART (universal asynchronous receive/transmit) signals. Full duplex
mode is used for all examples running in active mode and low power mode 3
(LPM3).
On the software simulation side, George P. Banky, a professor from
Faculty of Engineering and Industrial Sciences, Swinburne University of
Technology, Melbourne, Australia, wrote a paper entitled “Using circuit simulator
software in the study of electronic circuit behaviour”. His paper reports on a pilot
research project that investigated the use of a digital circuit simulation software,
EasySim, in the study of digital electronics in the first year of an undergraduate
engineering course. The ultimate aim of this research, completed in 2005, will be
to investigate the student experience with such software and its effect on one of
their study outcomes (that is their exam results). Students were encouraged to
use the tool during their normal learning activities. Those who used the software
found it to be helpful. Statistical analysis of exam results for the pilot group
indicated a strong relationship between the exam marks obtained and the time
spent using the software.
12
In his summary, he stated that even though the sample size of this pilot
study was small and probably biased, in that only interested students responded
to the survey, there is enough strong trending to suggest that within the small
group of students those who used the software tool perceived a benefit to their
study of digital electronics concepts. Also there was a strong trending between
the times spent using EasySim and the exam results for the students who
responded to the survey. Further for the whole subject group of students those
who did well in the digital electronics exam question also did well in the rest of
the exam paper. Since this relationship was also found for the responding group,
it may be concluded that in answering the exam questions there is no benefit to
the students who used the software simulator as a study aid.
There is enough evidence to support further investigation by repeating
this research in 2005, ideally using a more comprehensive simulation software
tool, probably Electronic Workbench , with a larger participating group of
students who will be using the software for a longer period of time (about 14
weeks) and more often (for assignments and laboratory preliminary submissions
as well as for private study) in order to try to establish any statistical significance
in the observed trends.
13
Chapter 3
DESIGN PROCEDURES
This chapter discusses the procedures that were followed in the
development of the experiment. This includes the Block Diagram, the
Experiment‟s Flowchart and the discussion on how the Experiment was
developed.
Design’s General Block Diagram
Analog
Front-End
Circuit
MSP430
PC
Figure 3.1 Block Diagram of the PC-Based Oscilloscope using MSP430
Figure 3.1 shows the basic block diagram of the design process. The
project is composed of a three-part design process, the Analog Front-End Circuit,
MSP430 and the Windows-PC Software. Each design stage is essential to the
next because each stage requires the output from the adjacent stage to act as
its input to be able to perform its function. The relationship of the three stages is
show in Figure 3.1.
14
Each block represents a specific design process unique to the others,
which will all be separately discussed later. Individual design block requires a
different approach to the others and entails a different design approach.
The first design block, named as “Analog Front-End Circuit”, is a circuit
that is designed to act as the analog signal receiver of the circuit. This part
involves pure hardware designing of circuit that is capable of limiting and
adjusting the incoming analog signal that would be safe and usable for the next
stage of the design, which is in the MSP430. This stage involves a combination of
multiplexing the signal to which direction or path in needs to go to be able to
perform the necessary adjustment the user intends to do. Each of these paths
corresponds to a specific voltage division factor and voltage off-set.
The second design block involves the designing of a program that shall be
embedded in the MSP430 microcontroller. This program shall be able to perform
various functions such as conversion of analog input to digital output,
transmission of the digitized data to the PC through the USB and synchronization
of the two. In this part, a program called „IAR Embedded Workbench‟ was used
to write and to load the designed program to the MSP430. Pin configurations of
registers and its purpose were one of the most critical parts of this design block.
This design block plays the most important role in the whole design as it acts as
the mediator for the two other design blocks. Both of the two design blocks (The
Analog Front-End Circuit and the PC) is connected to this block and is constantly
communicating to the two said blocks in a synchronous manner. The timing and
15
speed of transfer of data towards the PC is programmed and configured in this
part of the design. Improper synchronization shall result into a distorted output
waveform in the latter part of the project, which is in the displaying of the
waveform done in the last part of the design. The MSP430 is placed on its builtin circuitry readily available in the laboratory. It is interfaced using a Serial-toUSB connection, which also comes along in the package of the said
microcontroller. The program that was embedded in MSP430 is written in C
programming language.
The third design block involves the use of a personal computer using
Windows operating system. This part of the design involves the output medium
for the prototype. Using a previously designed program that enables the
computer to capture and plot data that was received from the MSP430, the
prototype is capable of displaying the output signal that was produced from the
circuit by means of the window-type computer program that was part of this
phase. One of the key factors in this part of the design is the assigning of values
that needs to be passed through USB connection towards the MSP430 that shall
act as the trigger on how much will the voltage division and the voltage offsetting should be done. For prototype purposes, voltage division and voltage offset options was limited to four choices only. Each choice was represented by a
button in the program which triggers the program to send a byte towards the
transmit part of the USB unto the MSP430, which uses that byte as a signal on to
16
which path should the signal flow. Further design process shall be discussed
later.
Part 1: Analog Front-End Circuit
The first step in the whole design process is the designing of the analog
circuit that will be able to reduce and adjust the input signal to its desired state.
The MSP430 microcontroller is only capable of accepting input within the range
of 0 to +3.0 volts. Besides the said limit, the MSP430 clips the signal off up to
the said boundaries. To enable the project to be able to accept signal from +3.1
volts up to 20 volts, it requires an analog circuit that will adjust the incoming
signal before it enters the MSP430. This requires the circuit needs to be able to
perform voltage division and to off-set the signal up to the required range of 0 to
+3 volts. A visual diagram that represents the ideal output of this circuit is shown
in Figure 3.2.
17
Figure 3.2: Analog Front-End Circuit Input/Output Representation
For prototyping purposes, the design was initially made to perform voltage
division and voltage off-set with four options for both. Voltage Division can be
done by factors of 20, 16, 10 and 6. Voltage off-set can be done by .25 v, .50 v,
.75 v and 1 v. Choosing between these options can be done through the
software that was developed on the stage-3 of the design, the Window-Type
Program on the PC.
The first design issue is on how the signal will be controlled under said
voltage division and voltage off-set condition. In order to do so, an analog
multiplexer/demultiplexer shall be used in order properly control where the signal
should flow. This said multiplexer should also be able to be fully controllable by a
digital signal that will be generated by the MSP430 that was triggered due to a
control button in the window-type program. It has also been part of
18
consideration in this part of the design is the availability of the multiplexer that is
capable
of
providing
the
needed
functions.
The
use
of
the
Analog
Multiplexer/Demultiplexer (74HC4067) is fit for the requirement of the task it
needs to fulfill. It has 15 readily available input/output ports and one common
input/output. It is also controlled by 5-bit signal that can be generated through
the MSP430. With the use of 74HC4067, it enables the circuit to be digitally
controlled by the MSP430 through its four Select pins and one Enable pin. These
pins (S0, S1, S2, S3, and E) receive logic signals that are generated by MSP430
through selection done in the PC. An Op-Amp (L234) was used to be able to
implement voltage off-setting.
The design requirement requires two set of input adjustment that needs
to be done to the input signal, voltage division and voltage off-set. The first 4067
is used for selection on how much will the input signal be divided. Four channels
were used to correspond for the division factors of 20, 16, 10 and 6. The second
4067 is used for selection on how much the reduced signal will be off-sat. Four
channels were also used to correspond for the .25 v, .50 v, .75 volt and 1 volt
off-set. Channel 8, 10, 11 and 12 were both used for the two 4067‟s
corresponding to each of the division factor and the corresponding voltage offset.
The first stage of the analog front-end circuit deals with the voltage
division of the incoming input signal. Voltage division is necessary to be able to
properly display the proper waveform of the input signal. The MSP430 can only
19
accept signal from 0 volt to +3 volts. The voltage division part of the design aims
to reduce incoming signal to 1 Vpp, which is suitable for output display.
Conventional voltage divider circuits were used in this part of the design. The
74HC4067 is capable of acting as either a multiplexer or a demultiplexer, the
input signal was connected to the pin 1 of the IC, which was labelled as common
input/output port. This part of the design requires an input coming from the
MSP430 in the form of 4-bit data select and 1-bit enable. The input signal is
generated in the MSP430 as digital signal which were connected to the pins 10,
11, 13 and 14 for the channel select and to pin 15 for the enable pin.
Figure 3.3: Voltage Divider Circuit
Since the prototype requires four voltage division factors, specifically 20,
16, 10 and 6, each of these factors corresponds to a channel that should provide
20
an output of 1 Vpp per channel. As expected, each channel should correspond to
the amount of Vpp as input to be able to arise with at least 1 Vpp so the MSP430
can accept it. Computation for the values of each resistor is shown in table 3.1.
Voltage Division Circuit
Channel Division Factor
Vin
R1(Ohms) R2 (Ohms) Expected Vout
I8
By 20
20 Vpp
19k
1k
1 Vpp
I10
By 16
16 Vpp
15k
1k
1 Vpp
I12
By 10
10 Vpp
9k
1k
1 Vpp
I14
By 6
6 Vpp
5k
1k
1 Vpp
Table 3.1: Voltage Division Circuit Values Table
After the voltage division has been done, shown in figure 3.2, the
expected output will pass below the 0 V boundary. This will produce clipping the
voltage divided input signal again as the MSP430 can only accept incoming signal
ranging from 0 volt to +3 volts. In order to remedy this problem, a digitally
controllable voltage offsetting circuit was implemented. Using an op-amp voltage
offset circuit, shown in figure 3.4, the designed was able to positively offset the
signal by .25 volt, .50 volt, .75 volt and 1 volt. This was done by series of
calculations using the formula shown in figure 3.4.
21
Figure 3.4: Voltage Off-Set Formula
Using the formula shown in figure 3.4, specific values had been acquired,
which is show in table 3.2 below.
Voltage Off-Set Circuit
Channel Offset Factor Gain
R1 (Ohms) Expected Vout
I8
.25 Volt
1
1k
1 Vpp
I10
.50 Volt
1
1k
1 Vpp
I12
.75 Volt
1
1k
1 Vpp
I14
1 Volt
1
1k
1 Vpp
Table 3.2: Voltage Off-Set Circuit Values Table
The input voltage coming from the voltage division circuit is referred to as
V1, while the V2 was acquired from a controlled DC source generated from the
MSP430. Like what was done in the first multiplexer, channel was also selected
by means of the digital signal coming from MSP430 towards the analog front-end
circuit to act as a selector. Once the channel was selected, the selected DC signal
22
along with the output of the voltage divided signal passes through an op-amp to
perform the offsetting of the signal, as shown in figure 3.5.
Figure 3.5: Voltage Off-Set Circuit Diagram
The final output signal that was generated through the analog front-end
circuit was connected to the MSP430 as its primary input signal that will be
processed. The final circuit design is shown in figure 3.6.
23
Figure 3.6: Analog Front-End Circuit Diagram
24
Part 2: MSP430
The second stage of the project involves the programming of MSP430 to
enable it to work as the mediator between the Analog Front-End Circuit (Stage1) and the PC (Stage-3). The design uses a pre-designed MSP430 circuit board
which was assembled and constructed. The pre-designed MSP430 circuit board
also includes a serial-to-USB connector which makes it capable of being
interfaced with a personal computer for embedding and burning purposes.
The MSP430 incorporates a 16-bit RISC CPU, peripherals, and a flexible
clock system that interconnect using a von-Neumann common memory address
bus (MAB) and memory data bus (MDB). Partnering a modern CPU with modular
memory-mapped analog and digital peripherals, the MSP430 offers solutions for
demanding mixed-signal applications. It has embedded emulation capability.
Dedicated embedded emulation logic resides on the device itself and is accessed
via JTAG using no additional system resources. With this capability, unobtrusive
development and debug with full-speed execution, breakpoints, and single-steps
in an application are supported.
The MSP430 needs to act as mediator between the Analog Front-End
Circuit (Stage-1) and the PC (Stage-3). To be able to do so, certain information
in various forms needs to be passed from one stage to the other, as shown in
figure 3.7.
25
Analog Front-End Circuit
INPUT: (From MSP430)
> Logic Select signals for
4067
( For pins S0, S1, S2, S3, E )
MSP430
PC (Window-Type
Program)
INPUT: (From MSP430)
> Digitally Converted
Signal
(Through USB)
-----------------------------------
-----------------------------------
OUTPUT: (To MSP430)
OUTPUT: (To MSP430)
>Adjusted Input
( After passing the Voltage
Divider and Off-Set. )
>Select signal for 4067
( As strings, Through USB )
Figure 3.7: MSP430 Input/Output Diagram
Analyzing these set of requirements, it is very essential to understand the
concepts of digital input/output, UART and ADC functions of the MSP430. Each of
these three components plays a vital role so that the MSP430 can perform its
needed operation. As shown in the diagram above, the MSP430 does most of the
work in this project. It performs the two most important part of the project, The
Analog-to-Digital conversion and the conversion of String Input from PC to logic
signal for MSP430.
MSP430 devices have up to six digital I/O ports implemented, P1 - P6.
Each port has eight I/O pins. Every I/O pin is individually configurable for input
or output direction, and each I/O line can be individually read or written to. Ports
P1 and P2 have interrupt capability. Each Interrupt for the P1 and P2 I/O lines
can be individually enabled and configured to provide an interrupt on a rising
26
edge or falling edge of an input signal. All P1 I/O lines source a single interrupt
vector, and all P2 I/O lines source a different, single interrupt vector.
The ADC12 module supports fast, 12-bit analog-to-digital conversions.
The module implements a 12-bit SAR core, sample select control, reference
generator and a 16-word conversion-and-control buffer. The conversion-andcontrol buffer allows up to 16 independent ADC samples to be converted and
stored without any CPU intervention.
The
universal
synchronous/asynchronous
receive/transmit
(USART)
peripheral interface supports two serial modes with one hardware module. In
asynchronous mode, the USART connects the MSP430 to an external system via
two external pins, URXD and UTXD. UART mode is selected when the SYNC bit is
cleared.
Using the combination of these three elements of the MSP430, the design
would be able to sustain the need of what it needs to perform.
The selection for voltage division and voltage off-set is done in stage3(PC). In this process, the program on the Computer will send a data
(represented as a string) to MSP430 through the USB using its UART function
that will signal the MSP430 to what signals it needs to send to the analog frontend circuit. The signal exchange and equivalents were tabulated below for
clearer representation.
The output signal that is being generated by the front-end circuit
undergoes analog-to-digital conversion through MSP430. The MSP430 is set at
27
Repeat-Single-Channel Mode. It uses MCLK (Master Clock) as its clock source,
and is set to perform continuous conversion automatically as soon as the
previous conversion is done (MSC). However, the built-in ADC clock divider is set
to divide the clock by factor of eight.
The converted signal is then passed to the PC through USB port using its
UART capability. The data were sent as 8-bit data each sequence (CHAR). The
UART is set at 8MHz (MCLK) at 115200 signals per second (Baud Rate). This
process enables the analog electrical signal to be sent to the PC for visual
representation.
The MSP430 Circuit Board was powered by an AC Adapter. It supplies 3.3
V DC for the front-end circuit. A 3.3 V supply for the front-end circuit board was
chosen to compensate for the 3.3 V logic signal that MSP430 outputs as high
logic signal.
The embedded programming was written in C language using IAR
Workbench IDE and was downloaded and burned in the chip through MSP430
USB-Debug Interface (MSP-FET 430UIF).
28
PORT 2
4067
Channels
P 2.0
P 2.1
P 2.2
P 2.3
P 2.4
P2OUT
PC
Input
By 20
I8
0
0
0
0
1
0x10
a
(0x63)
By 16
I10
0
0
1
0
1
0x14
b
(0x64)
By 10
I12
0
0
0
1
1
0x18
By 6
I14
0
0
1
1
1
0x1C
ENABLE
S0
S1
S2
S3
c
(0x65)
d
(0x66)
Table 3.3: Voltage Division Connections and Registers
Table 3.3, entitled Voltage Division Connections and Registers, shows the
connections between the 4067 multiplexer to the MSP430. It also shows the
relationship between the signal that is sent from the computer (PC Input)
towards the MSP430. For example, as the PC sends out signal „a‟ (0x63), the
MSP430 recognizes it as a „By 20 Voltage Division‟ and will be sending the signal
0x10 out through port 2. This event will then trigger the MSP430 to send out
logic signals to its ports 2.0, 2.1, 2.2, 2.3 and 2.4. Ports 2.0, 2.1, 2.2, 2.3 and
2.4 are connected to 4067‟s ENABLE, S0, S1, S2 and S3, respectively.
29
PORT 1
4067
Channels
P 1.0
P 1.1
P 1.2
P 1.3
P 1.4
P1OUT
PC
Input
By
.25v
I8
0
0
0
0
1
0x10
a
(0x63)
By
.50v
I10
0
0
1
0
1
0x14
b
(0x64)
I12
0
0
0
1
1
0x18
I14
0
0
1
1
1
0x1C
ENABLE
S0
S1
S2
S3
By
.75v
By
1.0v
c
(0x65)
d
(0x66)
Table 3.4: Voltage Off-Set Connections and Registers
Like that of Table 3.3, Table 3.4, entitled Voltage Offset Connections and
Registers, shows the connections between the second 4067 multiplexer to the
MSP430 for its voltage off-Setting function. Like the voltage division part, this
part of the design also uses the same principle and the same logic flow. It shows
the relationship between the signal that is sent from the computer (PC Input)
towards the MSP430. For example, as the PC sends out signal „a‟ (0x63), the
MSP430 recognizes it as a „By 20 Voltage Division‟ and will be sending the signal
0x10 out through port 1. This event will then trigger the MSP430 to send out
logic signals to its ports 1.0, 1.1, 1.2, 1.3 and 1.4. Ports 1.0, 1.1, 1.2, 1.3 and
1.4 are connected to 4067‟s ENABLE, S0, S1, S2 and S3, respectively.
30
PART 3: PC (Window-Type Program)
The third part of the project involves the use of a personal computer as an
input device for voltage division select and voltage off-set select and as an output
device to display and plot the digitized analog input signal.
Using a previously written program for ECG (BCB_ECG_0611_FINAL),
the project used its capability to acquire and plot data that is being sent through
the USB. Initialization in using the program includes the selection of COM port
where the USB is connected, and a built-in filestream system that saves the
digital signals that is being sent in the PC as a text file. Additional function was
added to the said program to enable it to send data to the MSP430 through the
USB. Refer to Table 1 and Table 2 for the respective data that was sent.
The program was programmed using Borland C++ Builder 6.
Figure 3.8: Window-type Program Screenshot
31
Figure 3.9: Data Transfer Flowchart of PC Program
32
Chapter 4
PRESENTATION AND INTERPRETATION OF DATA
This chapter details the data and results from the experiment. The
interpretation and explanation of different data and result are emphasized on
this chapter.
During the design process, each design stage conducted trials and
simulations before the actual construction of the design. Each stage was
separately verified to be able to establish its functionality. For the first part
(Analog Front-End Circuit), simulations and testing were done using NI Multisim
program. For the MSP430 program, simulation and debugging were done using
the program IAR Embedded Workbench.
After simulation and testing were done, the design was put to assembly.
Each design stage was connected to the other as designed. Afterwards, testing
and analysis were done.
During this testing, the design was subjected under a 10 Vpp sinusoidal
wave input at various input frequencies. The input signals show to be at 10 Vpp,
which can be seen in the screenshot that follows. A small discrepancy in terms of
the voltage amplitude can be observed, However, it is acceptable since the
voltage visual waveform is very clear thus enabling it to perform as a logic signal
analyzer.
33
For the initial testing, the design was subjected to a sinusoidal 10 Vpp
input at 10 Hz. The output is shown in figure 4.1. At 8MHz (MCLK) at 115200
signals per second (Baud Rate) The only major concern in displaying the proper
visual output is the frequency of the incoming signal if it can have a proper
timing with the baud rate of the MSP430.
Figure 4.1 : Sinusoidal Wave Input, 10 Vpp at 10 Hz
As the figure 4.1 shows, the design was able to clearly plot and draw the
input signal, which is a 10 Vpp sinusoidal waveform at 10 Hz. Having this result,
the testing and analysis continues for the same input voltage and same
waveform but under different frequency to determine the design‟s capability to
respond to a faster input signal.
34
Several other frequencies were tried to be able to challenge the capability
and the capacity of the 115200
baud rate if it would display the following
frequencies with clarity. At figure 4.2, 4.3, 4.4 and 4.5, frequencies were set at
100 Hz, 250 Hz, 500 Hz and 100 Hz respectively.
Figure 4.2: Sinusoidal Wave Input, 10 Vpp at 100 Hz
Figure 4.2 shows, the design was still able to clearly plot and draw the
input signal, which is a 10 Vpp sinusoidal waveform at 100 Hz. Comparing the
visual representation of the same input waveform with a different frequency, this
shows that the design can better visually represent the input waveform at 100
Hz. Having this result, the testing and analysis continue for the same input
voltage and same waveform again but under different frequency to determine
the design‟s capability to visually represent an input waveform.
35
Figure 4.3: Sinusoidal Wave Input, 10 Vpp at 250 Hz
Figure 4.4: Sinusoidal Wave Input, 10 Vpp at 500 Hz
As the figure 4.3 and figure 4.4 show, the design was still able to clearly
plot and draw the input signal, which is a 10 Vpp sinusoidal waveform at 250 Hz
36
and a 10 Vpp sinusoidal waveform at 500 Hz, respectively. Figure 4.3 shows
clear representation of the input waveform. Figure 4.4, however, can still show
the waveform but it starting to look crowded and difficult to analyze compared to
the previous input signals.
Figure 4.5: Sinusoidal Wave Input, 10 Vpp at 1 KHz
Analyzing these results, it shows that the design is able to clearly
represent waveforms up to 1 KHz. And as the design shows its capability to plot
a full sinusoidal wave, other wave shapes would eventually arrive with the same
result.
37
Chapter 5
CONCLUSION AND RECOMMENDATION
This chapter presents the conclusion of the experiment, as well as the
recommendations
for
future
researches
in
enhancing
the
experiment‟s
capabilities.
CONCLUSION
The design prototype was able to perform visual representation of an
analog electrical input signal by plotting it to a window-type program in
computer. The analog electrical input signal can be digitally adjusted (i.e.,
voltage division and voltage off-set) through the PC program by sending data to
the MSP430 which enables the MSP430 to provide specific logic signals for the
analog front-end circuit. It can properly graph the sent data with clarity up to 1
KHz. The design could also plot and draw other types of waveform as long as it
is bounded by the limit of the microcontroller.
The design procedure in building the prototype is easy and can be done
by everyone who has basic knowledge in electronics and C programming. The
total design cost is very low comparing to today‟s market price of oscilloscopes
and can be easily built by students and enthusiasts.
38
RECOMMENDATION
The prototype shows that the project can still be developed and improved
by implementing and employing other oscilloscope functions such as vertical and
horizontal graph adjustment and measuring capability for frequency and other
variables present in an electrical signal. As for this stage of the design, it can be
used for personal use only and not for projects with a very strict precision need.
It could also be further developed to use more than a single channel of input,
maximizing the free registers of the system.
39
REFERENCES
Harsha Rao (September 2004) , Implementing a Bidirectional Wireless UART
Application With TRF6903 and MSP430
Andreas Dannenberg (October 2006) , MSP430 USB Connectivity Using
TUSB3410
Steve Underwood (2006) , Capacitive Touch Sensing with MSP430
Melisa Nunez-Arzuaga and Andreas Dannenberg (June 2007) ,
Implementing IrDA With The MSP430
Murugavel Raju (October 2001) , Ultrasonic Distance Measurement With the
MSP430
MSP430 IAR Embedded Workbench® IDE User Guide for Texas Instruments
MSP430 Microcontroller Family, © Copyright 1996–2005 IAR Systems.
George P. Banky (2005), Using Circuit Simulator Software In The Study Of
Electronic Circuit Behaviour
40
APPENDICES
41
APPENDIX A. Pictures of the Design
42
APPENDIX B. Program Listing
#include <msp430x14x.h>
#define Num_of_Results 4
static unsigned int results1[Num_of_Results];
static unsigned int results2[Num_of_Results];
char temp;
char voltdiv;
char offset;
void main(void)
{
volatile unsigned int i;
WDTCTL = WDTPW+WDTHOLD;
BCSCTL1 &= ~XT2OFF;
do
{
IFG1 &= ~OFIFG;
for (i = 0xFF; i > 0; i--);
}
while ((IFG1 & OFIFG));
BCSCTL2 |= SELM_2 + SELS;
P5DIR |= BIT4;
P6SEL |= 0x03;
P3SEL |= 0x30;
// Stop watchdog timer
// XT2on
// Clear OSCFault flag
// Time for flag to set
// OSCFault flag still set?
// MCLK = SMCLK = XT2 (safe)
//initialization - adc
// Enable A/D channel inputs
// P3.4,5 = USART0 TXD/RXD
P1DIR |= 0x1F;
P2DIR |= 0x1F;
ADC12CTL0 = ADC12ON+MSC;
// Turn on ADC12, set sampling time
ADC12CTL1 = SHP+CONSEQ_3+ADC12SSEL_2+ADC12DIV_7;
// Use sampling timer, single sequence
ADC12MCTL0 = INCH_0;
// ref+=AVcc, channel = A0
ADC12MCTL1 = INCH_1+EOS;
// ref+=AVcc, channel = A1
ADC12IE = 0x03;
ADC12CTL0 |= ENC;
ADC12CTL0 |= ADC12SC;
// Enable ADC12IFG.3
// Enable conversions
// Start conversion
43
//uart part
ME1 |= UTXE0 + URXE0;
UCTL0 |= CHAR;
UTCTL0 |= SSEL1;
UBR00 = 0x45;
UBR10 = 0x00;
UMCTL0 = 0x00;
UCTL0 &= ~SWRST;
IE1 |= URXIE0;
// Enable USART0 TXD/RXD
// 8-bit character
// UCLK = SMCLK
// 8MHz 115200
// 8MHz 115200
// 8MHz 115200 modulation
// Initialize USART state machine
// Enable USART0 RX interrupt
_EINT();
}
//uart part
while(1)
{
// while (!(IFG1 & UTXIFG0));
// TXBUF0=ADCMEM0;
}
// USART0 TX buffer ready?
#pragma vector=ADC_VECTOR
__interrupt void ADC12ISR (void)
{
static unsigned int index = 0;
P5OUT ^= BIT4;
//results1[index] = ADC12MEM0;
//results2[index] = ADC12MEM1;
//TXBUF0=ADC12MEM0>>4;
//temp1=ADC12MEM1>>4;
while (!(IFG1 & UTXIFG0));
TXBUF0=ADC12MEM0>>4;
(index+1)%Num_of_Results;
}
#pragma vector=UART0RX_VECTOR
__interrupt void usart0_rx (void)
{
while (!(IFG1 & UTXIFG0));
// Move results, IFG is cleared
// Move results, IFG is cleared
// USART0 TX buffer ready?
//index =
// USART0 TX buffer ready?
// while(1)
//{
44
temp = RXBUF0;
// RXBUF0 recieves data.
if(temp==0x61 || temp==0x62 || temp==0x63 || temp==0x64)
{
voltdiv=temp;
}
else if(temp==0x65 || temp==0x66 || temp==0x67 || temp==0x68)
{
offset=temp;
}
if(voltdiv==0x61)
{
P2OUT = 0x10;
}
else if(voltdiv==0x62)
{
P2OUT = 0x14;
}
else if(voltdiv==0x63)
{
P2OUT = 0x18;
}
else if(voltdiv==0x64)
{
P2OUT = 0x1c;
};
if(offset==0x65)
{
P1OUT = 0x10;
}
else if(offset==0x66)
{
P1OUT = 0x14;
}
else if(offset==0x67)
{
P1OUT = 0x18;
}
else if(offset==0x68)
{
45
P1OUT = 0x1c;
};
}
46