tinydaq a microcontroller based daq device vikent woon universiti

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tinydaq a microcontroller based daq device vikent woon universiti
i
TINYDAQ A MICROCONTROLLER BASED DAQ DEVICE
VIKENT WOON
UNIVERSITI TEKNOLOGI MALAYSIA
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I declare that this thesis entitled “ title of the thesis “ is the result of my own
research except as cited in the references. The thesis has not been accepted
for any degree and is not concurrently submitted in candidature of any
other degree.
Signature : ....................................................
Name : ....................................................
Date : ....................................................
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ACKNOWLEDGEMENT
In the process of carrying out this project, commencing from the title deciding
until the completion of project, I was in contact with many people such as academicians,
postgraduate researchers and lab assistants.
They have rendered their assistant in
various aspects and contributed towards my understanding and thoughts. In particular, I
wish to grab this opportunity to express my sincere appreciation to my project supervisor,
PROF DR SHAMSUDIN HJ MOHD AMIN for his advice, guidance and
encouragement that have led to the success of this project.
I am also indebted to University Technology Malaysia for providing me the
facilities to carry out my project. Librarians at UTM also deserve special thanks for
their assistance in the process of my project information obtaining.
My fellow friends should also be recognized for their continual support and
encouragement. My sincere appreciation also extends to my entire course mate and
others who have provided assistance at various occasions. Their views and tips are
useful indeed. Unfortunately, it is not possible to list all of them in this limited space. I
am grateful to all my family members.
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ABSTRACT
DAQ (Data Acquisition) is simply the process of bringing a real-world signal,
such as voltage, into the computer, for processing, analysis, storage or other data
manipulation. A Physical phenomenon represents the real-world signal you are trying to
measure. In order to optimize the characteristics of a system in terms of performance,
handling capacity and cost, the relevant subsystem can be combined together. Analog
data is generally acquired and transformed into the digital form for the purpose of
processing, transmission and display. Rapid advances in Personal Computer (PC)
hardware and software technologies have resulted in easy and efficient adoption of PCs
in various precise measurement and complex control applications. A PC based
measurement or control application requires conversion of real world analog signal into
digital format and transfer of digitized data into the PC. A data acquisition system that
performs conversion of analog signal to digital data and the digital data to analog signal
is interfaced to a pc to implement the functions of a measurement and control
instrumentation applications.
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ABSTRAK
DAQ (data acquisition) adalah suatu proses untuk mengambil isyarat daripada luar
dunia seperti isyarat voltan dan simpan ke komputer untuk proses, analisis, penyimpanan
data dan pengawal data. Fizikal fenomena adalah salah satu isyarat dari luar dunia.
Untuk optimise ciri-ciri sistem DAQ dalam segi prestasi, kapasity pengendalian dan kos ,
semua sistem yang berkenaan boleh digabung bersama untuk mencapai tujuan tersebut.
Isyarat Analog dikendali dan ditukar ke Isyarat Digital untuk tujuan proses,
penghantaran, dan memaparan. Kemajuan pesat dalam Komputer Peribadi (PC)
perkakasan dan perisian teknologi telah menyebabkan penggunaan mudah dan berkesan
dalam pelbagai ukuran yang tepat dan aplikasi kawalan kompleks. Satu ukuran atau
kawalan aplikasi berasaskan PC memerlukan penukaran sebenar isyarat analog dunia ke
dalam format digital dan pemindahan data digital ke PC. Satu sistem perolehan data
yang melaksanakan penukaran isyarat analog kepada data digital dan data digital kepada
isyarat analog adalah diantaramukakan kepada pc untuk melaksanakan fungsi-fungsi
pengukuran dan aplikasi peralatan kawalan.
vi
TABLE OF CONTENT
CHAPTER
1
2
TITLE
DECLARATION
ii
ACKNOWLEDGEMENTS
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENTS
vi
LIST OF TABLES
vii
LIST OF FIGURES
x
LIST OF APPENDICES
xi
INTRODUCTION
1.1
Background
1
1.2
Objectives
2
1.3
Project Scope
3
1.4
Problem Statement
4
LITERATURE REVIEW
2.1
3
PAGE
Researchers’ Project
5
2.1.1 DAQ by AT89C52
6
2.1.2 FPGA Based DAQ
7
METHODOLOGY
3.1
Hardware Design
8
vii
3.1.1 Microcontroller unit
3.1.1.1 RCM3010 features
10
DAC chip
11
3.1.3 ADC chip
12
3.2
Circuit Design
13
3.3
Software design
3.1.2
4
5
9
3.3.1 Programming on controller
14
3.3.2 Software for programming
15
3.3.3 Programming for DAC
16
3.3.4
Programming for ADC
18
3.3.5
Serial peripheral interfaces
22
3.3.6 Programs Implementation
22
3.3.7 Programs Algorithms
23
3.3.8 Explanation of Main Programs
29
3.3.9 Explanation of Execute instruction Programs
33
3.3.9.1 DAC Output
33
3.3.9.2 ADC Input
35
3.3.9.3 ADC and DAC Calibration
37
3.3.9.4 Digital I/O
38
DISSCUSION
4.1
Introduction
39
4.2
4.3
Experiments on Analog Input Range
Comparison of Output DAC voltage
40
45
4.4
Accuracy of ADC Input Signal
46
CONCLUSION AND RECOMMENDATION
5.1
Conclusion
48
5.2
Problems
49
5.3
Recommendations
51
viii
WORK SCHEDULE
52
REFERENCES
53
APPENDICES
54
ix
LIST OF TABLE
TABLE
TITLE
PAGE
3.1
RCM3010 Features
9
4.1
Experimental Results for Vin Range -10V to 10V
39
4.2
Experimental Results for Vin Range -20V to 20V
40
4.3
Experimental Results of Output Voltage DAC comparison
42
4.4
Accuracy of Single Ended Unipolar Mode
44
4.5
Accuracy of Single Ended Bipolar Mode
44
4.6
Accuracy of Differential Mode
45
x
LIST OF FIGURE
FIGURE
TITLE
PAGE
2.1
Data Acquisition System by AT89C524.1
5
2.2
FPGA Based Data Acquisition System
6
3.1
3.2
Process Design of TINYDAQ
RCM3010 Pin Diagram
7
9
3.3
3.4
3.5
TLV5630
TLV5630 Block Diagram
ADS7870 Pin Diagram
10
11
11
3.6
ADS7870 Block Diagram
12
3.7
Circuit Design of TINYDAQ
13
3.8
RCM3010 Rabbit Core
14
3.9
Clock Cycles for Fetching Instruction Code
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3.10
Clock Modes for RCM3010
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3.11
Instruction Bytes
17
3.12
Timing Diagram for an 8-Bit Read Operation
19
3.13
Output Codes versus Input Voltage
19
3.14
Serial Peripheral Interfaces
20
3.15
Main Program Algorithms
22
3.16
Execution Instruction Algorithms Part 1
23
3.17
Execution Instruction Algorithms Part 2
24
3.18
LABVIEW User Interfaces Algorithms
25
3.19
Connection test using Hercules
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3.20
LABVIEW User Interfaces
26
xi
3.21
SPI Initialization code
27
3.22
TCP/IP Connection Initialization code
27
3.23
Digital I/O Initialization programming code
28
3.24
Clock Initialization programming code
28
3.25
EEPROM save Structure
29
3.26
TCP listen programming code
29
3.27
TCP read programming code
30
3.28
DAC main function programming code
31
3.29
ADC calibration programming code
32
3.30
ADC output type programming code
33
3.31
ADC fetch instruction programming code
33
3.32
DAC and ADC calibration data structure
34
3.33
DAC and ADC calibration equation
34
3.34
Configure digital output programming code
35
3.35
Configure digital input programming code
35
4.1
Circuitry Design of Signal Conditioning
37
4.2
Linear Graph with Vadc =0-5V and Vin =±10V
38
4.3
Graphs on Single Ended Unipolar
45
4.4
Graphs on Single Ended Bipolar
46
4.5
Graphs on Differential Input
46
xii
LIST OF SYMBOLS
DAQ
-
Data Acquisition
SPI
-
Serial Peripheral Interfaces
I/O
-
Input or Output
ADC
-
Analog to Digital Converter
DAC
-
Digital to Analog Converter
V
-
Voltage
R
-
Resistor
Vadc
-
Input Voltage Signal of Analog to Digital Chip
Vref
-
Reference Voltage
Vdac
-
Output Voltage Signal of Digital to Analog Chip
Vin
-
Input Voltage
MOSI
-
Master Out Slave In
MISO
-
Master in Slave Out
SCLK
-
Clock Frequency
FS
-
Chip Select
TCP
-
Transmission Control Protocol
IP
-
Internet Protocol
RCM
-
Rabbit Core Module
USB
-
Universal Serial Bus
PC
-
Personal Computer
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LIST OF APPENDICES
APPENDIX
TITLE
PAGE
A
Parts ADC Programming Code
54
B
Schematic Design of ADC
57
C
PCB Design of TINYDAQ
58
D
Casing design of TINYDAQ
60
E
LABVIEW design of TINYDAQ User Interfaces
61
F
Structure of TINYDAQ
62
1
CHAPTER 1
INTRODUCTION
1.1
Background
Data acquisition is process of converting the samples signal into digital form to
analyze. With the advance of the technology nowadays, many types of high capabilities
data acquisition devices have been developed to corporate with others highly advanced
devices. Data acquisition (DAQ) systems basically change the input analog signal to
output the digital signal for processing the collected data. Data acquisition has a wide
range of application which include military use, heavy and light industry, and security
and surveillance technology.
In the recent past, Data acquisition system has been greatly use in manufacturing
company. Data acquisition system work with the system it’s attach with to perform
several function. In addition, data acquisition system also contain digital input and
output to help control the electric devices it’s attached in order to smoothed the progress
of controlling the devices. Data acquisition hardware usually comes with a PC which
using to display the result of collected data. It usually has a build in serial port
connection, USB connection or Ethernet port connection to interface with PC. In my
case, I will use the Ethernet port which has already built in to interact with PC and the
data acquisition devices. The data acquisition hardware named TINYDAQ will use
RCM3010 rabbit core as the motherboard to be programed as a DAQ devices
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incorporate with external circuit. TINYDAQ will be designed in small structure yet
with lot of configurable digital Input and output and analog input and output.
TINYDAQ capable of convert analog signal into digital signal and also configure
digital input and output. TINYDAQ use Ethernet port to interface with PC. PC will
transfer instruction to TINYDAQ and also display converted result signals.
1.2
Objectives
This project aimed to enhance the data acquisition capabilities. There are 3 main
objectives to achieve in this project:
1. Reduce the size, cost and weight of TINYDAQ.
2. Friendly User interface using LABVIEW
3. Build TINYDAQ in small size yet many digital I/O port which enough to
operate in huge electric devices.
1.3
Project Scopes
TINYDAQ aimed to be able to perform following function:
1. Able to perform ANALOG TO DIGITAL CONVERTER (ADC)
2. Communicate between TINYDAQ and PC
3. Able to configure digital input and output.
4. Able to calibrate ADC.
5. Able to save the calibration data for ADC.
6. Able process unipolar, bipolar and differential analog signals.
7. Able to manipulate the software based gain to perform ADC in wide range of
analog signals.
3
1.4
Problem Statement
Traditional DAQ hardware needs PC for interfacing, fetching instruction and
reading measured data. There have been many type of DAQ hardware build in small
structure but contrary it has limited digital I/O port which is insufficient for some huge
electric equipment.
The Traditional DAQ hardware is expensive and the connector which uses to
communicate with PC is not stable. Most of previous DAQ hardware uses USB
connection for PC interaction yet the PC sometimes has difficulties in detecting the
connected DAQ device.
This result in the user will has a hard time to fetch the instruction to DAQ
hardware or reading the measured data from PC.
4
CHAPTER 2
LITERATURE REVIEW
There are many similar and relevant project can be found throughout the internet
and library. There will be some explanation about the relevant information about data
acquisition hardware and it’s functionality in this discussion.
Data acquisition system is the data collected on-site processing, transmission,
storage, display and other operations. Data acquisition system's main function is the
analog signals into digital signals, and analysis, processing, storage and display. Many
companies large and small multi-national development of data acquisition products and
cards and the like, which makes digital information to provide a great convenience.
Today, the PC can automatically process and analyze data; there are many alternative
methods to collect data. The choice of which depends on many factors, including task
complexity, the required speed and accuracy, you want evidence of information and so
on. Whether simple or complex, the appropriate data acquisition system can run and
play its role. (Hai Feng Zhou February, 2012)
5
2.1
Researcher’s Project
2.1.1
Data Acquisition System by AT89C52
Figure 2.1
Data Acquisition System by AT89C52
The design using AT89C52 microcontroller as the core of the data acquisition
system control, data acquisition system is divided into modules, A / D converter module,
system control module, keyboard module, display module and other parts. Multi-channel
system can capture the data stream, after treatment on the LED display. The data
acquisition card, AT89C52 microcontroller as the core component with a data
acquisition, object control, display, keyboard and many other more complex features a
complete automation system. Use RS-232 serial communication to communicate with
the microcontroller.(Hai Feng Zhou February, 2012)
6
2.1.2
FPGA Based Data Acquisition System
Figure 2.2
FPGA Based Data Acquisition System
Aiming at a storage system of high-speed data acquisition, it is designed with 6
channel, 16-bit AD converter chip AD7656 and a programmable logic device
EP2S90F102. The K9W8G08U1M chip made in SAMSUNG is selected as storage unit,
and FPGA controls the needed logic for FLASH and AD converter. At the end of data
acquisition, the stored data can be transmitted to the host through the USB2.0 interface.
(Ning, Guo et al. 2012)
7
CHAPTER 3
METHODOLOGY AND APPROACHES
Generally, building data acquisition system required knowledge from various
aspect, discipline and studies, thus a systematic approach is crucial in the development
process. In this chapter, I will explain and descript the methodology and guidelines in
designing data acquisition system which is able to perform analog to digital conversion,
communication with PC and configurable digital I/O ports. There will be 5 major parts
in developing data acquisition system.
HARDWARE DESIGN
CIRCUIT DESIGN
SOFTWARE DESIGN
INTERGRATION OF
HARDWARE AND
SOFTWARE
TESTING AND
CALIBRATION
FIGURE 3.1
Process Design of TINYDAQ
8
Choosing the right hardware and parts for data acquisition system is very
important. After research have been done, the suitable hardware and parts are chosen
and circuit will be design to connect the whole system together in order to make the
system work as one. Hardware design and software design will be separated at the
beginning and integrated after both design have been completed. Testing and
experiment will be conducted to ensure the prototype function properly.
3.1
Hardware Design
3.1.1
Microcontroller Unit
RCM3010 RABBITCORE will be chosen to act as core for my data acquisition
system. RCM3010 RABBITCORE is selected based on several advantages over others
controller:
1. Has internal Flash memory and Static RAM which are huge in capacity.
2. Low power consumption
3. Small structure
4. Low cost embedded microprocessor module
5. Sufficient digital I/O ports and 6 serial ports
6. Support Ethernet port connection
9
FIGURE 3.2
RCM3010 Pin Diagram
3.1.1.1 RCM3010 Features
TABLE 3.1: RCM3010 Features
MICROPROCESSOR
EMI REDUCTION
ETHERNET PORT
FLASH MEMORY
SRAM
GENERAL-PURPOSE I/O
TIMERS
PULSE WIDTH
MODULATORS
INPUT CAPTURE
SERIAL PORTS
SERIAL RATE
REAL TIME CLOCK
POWER
RABBIT 3000 at 30 MHz
SPETRUM SPREASER FOR REDUCE EMI(RADIATED EMMISIONS
10 BASE-T INTERFACE
256K
128K
52 parallel digital I/O
TEN 8 -BIT TIMERS
10-BIT-FREE -RUNNING COUNTER AND FOUR PUSE-WIDTH
REGISTERS
2-CHANNEL INPUT CAPTURE
6 shared high speed, CMOS compatible ports
MAXIMUM ASYCHRONOUS BAUD RATE = CLCK/8
YES
3.3V
10
3.1.2
DAC Chip
FIGURE 3.3 TLV5630
In order for my data acquisition system able to perform analog-to-digital
conversion, DAC chip is necessary to include in my hardware design. TLV5630 is
chosen for DAC chip because it features eight voltage output DACs in one package.
It is compatible with SPI SERIAL PORTS which I will use it to interact
TLV5630 with RCM3010 to fetch and execute instruction. TLV5630 is monotonic over
temperature and has low power consumption which only consumed 48 mW at 3V. The
reference voltage for the DAC chip can be either internal or external. The internal
voltage can supply up to 2V and if 2V is insufficient, external voltage can be added to
increase the reference voltage at my desire level.
Pin LDAC able to simultaneously update all the output voltage. The data format
for programming is in 16 bit serial string. 4 bits for the address of the selected output
voltage port and the remaining 12 bits are for data bits which are the amount of output
voltage.
11
FIGURE 3.4 TLV5630 Block Diagram
3.1.3
ADC Chip
FIGURE 3.5
ADS7870 Pin Diagram
ADS7870 is the ADC chip I chosen for data acquisition. The reason for using
ADS7870 over other ADC chip because of it’s a complete low power data acquisition in
a single chip. Additional, it’s also features programmable gain amplifier which provide
high impedance output, noise reduction and accurate gain. It can be programs to adjust
any desire gain from 1, 2, 4,5,8,10,16 and 20V. It also consists of programmable inputs
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which are 4 differential inputs and 8 single ended inputs. Serial interface allow me to
programs ADS7870 from RCM3010 through SPI.
The programming instruction code for ADS7870 is 8 bits code consisting two kind
of mode which direct mode and register mode. Direct mode allow user to direct convert
the selected input into digital signal while register mode allow user to read or write the
register of ADS7870 for further modification.
FIGURE 3.6 ADS7870 Block Diagram
13
3.2
Circuit Design
TLV5630
POWER SUPPLY
RCM3010 RABBIT
CORE
PC
ADS7870
FIGURE 3.7 Circuit Design of TINYDAQ
As above figure, the circuit has been designed after all the consideration has been
made. DAC and ADC chip will use SPI connection to interact with Rabbit Core to fetch
instruction. The whole system is then connected to PC through Ethernet port to send
instruction code and observed measure data. Since RCM3010 does not have power
supply in it, hence extra power supply circuit is added to power up the circuit.
14
3.3
Software Design
3.3.1 Programming on Controller
FIGURE 3.8 RCM3010 Rabbit Core
RCM3010 is the core for data acquisition systems. In order to control TLV5630
and ADS7870, the SPI ports in RCM3010 are used. SPI will perform MISO and MOSI
during transferring instruction code. The SPI ports in RCM3010 cannot directly use, it
should have to initialize before using. A lot of consideration should be made during
programming RCM3010, SPI require CLCK and CHIP ENABLE to execute but CLCK
for RCM3010 consist of 4 types of mode while TLV5630 and ADS7870 will only
receive the instruction in the correct CLCK mode. The following shows the function of
RCM3010 I/O ports in operating the data acquisition systems.
PORT A2 is used for CHIP ENABLE for TLV5630
PORT A3 is used for CHIP ENABLE for ADS7870
PORT F0 is act as CLCK for both TLV5630 and ADS7870
PORT C0 used to fetch the instruction code for both TLV5630 and ADS7870
PORT C1 used to read the measured data from data acquisition.
PORT D4 used to update all the DAC voltage on the output of TLV5630
The rest of the port will programmed as configurable digital I/O ports.
15
3.3.2
Software for Programming
For RCM3010, it has its own programming software which named Dynamic C.
It integrated development system used for writing programming. It also designed only
for Rabbit base microprocessor. In single software, it able for editing, compiling, linking,
loading and debugging. Dynamic C is easy to use since many are common with C
language and additional feature for Dynamic C is it’s contain library made for Rabbit
processor and also other useful source code. Dynamic C use PRINTF command for
debugging and observe the result of programs. It also provides sufficient debugging
tools to ease the process of programs debugging. Dynamic C use USB programming
cable to connect to RCM3010 to burn the programs.
3.3.3
Programming on Digital to Analog Converter
FIGURE 3.9 Clock Cycles for Fetching Instruction Code
From the clock cycles, the chips receive the instruction code every failing edge
of SCLK while FS is at low condition. TLV5630 will only able to receive the
instruction code from the require clock mode. If I do not provide the correct clock mode
from the RCM3010, the chips will not functioning.
16
FIGURE 3.10 Clock Modes for RCM3010
From the 4 types of clock mode that RCM3010 can provide. I have to set clock
mode to 10 in order for TLV5630 can operate correctly. The pin connected to TLV5630
should be initializing or otherwise it will not be functioning.
Since I using Port C0 and Port C1 for SPI connection, I have to initialize SPI
serial port D. Port A2 which use as CLCK will program to toggle between 1 and 0 while
same goes to Port D4 which will update all the output simultaneously at low condition.
Since I am using internal reference voltage, I can program to get the reference
voltage between 1.024 V and 2.048 V which are built in the chip. To set the internal
reference voltage, I have to write bit 1 and bit 2 into register address 0x1001.
The Instruction code is 16 bits which the most significant 4 bits are address and
the rest are the instruction code. The address of output voltage is 0000 until 0111. The
remaining 12 bits is the input digital signal for converting to analog signal. The input
range for digital signal is from 0x000 until 0xFFF. The output voltage for each of the
input can be obtained using the following formula.
17
3.3.4
Programming on Analog to Digital Converter
FIGURE 3.11 Instruction Bytes
There are two types of instruction mode for ADS7870, which are direct mode
and register mode, both mode execute different kind of function. ADS7870 serial
interfaces operate base on 8- bit instruction bytes. The mode of the instruction byte
determines by the most significant bit which is D7. If bit D7 = 1, it is in direct mode and
if bit D7 = 0, it is in register mode. In direct mode, it is the conversion command. D6 to
D4 is for programmable gain amplifier while D3 to D0 is the address channel for
conversion and also configure for single ended of differential mode. In register mode,
D6 is selected for read or write operation, D5 choose whether the read or write data is in
16 bit word or 8 bit word. D4 to D0 is the address register required for read or write
operation.
Registers 0 and 1, the A/D Output Data registers, contain the least significant and
most significant bits of the A/D conversion result (ADC0 through ADC13). Register 0
also has three fixed zeros (D3, D2, and D1), and a bit to indicate if the internal voltage
limits of the PGA have been over ranged (OVR). This is a read only register. Write an
8-bit word to register 0 and the ADS7870 resets.
Register 2, the PGA Valid register, contains information that describes the nature
of the problem in the event that the allowable input voltage to the PGA has been
exceeded.
18
Register 3, the A/D Control register, has two test bits (best left set to zero), a bit
to convert the output format to straight binary (BIN), an unused bit set to zero, two bits
to configure an automatic read back mode of the A/D results (RBM1, RBM0), and two
bits that program the frequency divider for the CCLK (CDF1, CDF0).
Register 4, the Gain/Mux register, contains the input channel selection
information (M0 through M3) and the programmable gain amplifier gain set bits (G0
through G2).
Register 5, the Digital I/O State register, contains the state of each of the digital
I/O pins (I/O3 through I/O0). In addition, registers 4 and 5 contain a convert/busy bit
(CNV/BSY) that can be used to start a conversion via a write instruction or sense when
the converter is busy with a read instruction.
Register 6, the Digital I/O Control register, contains the information that
determines whether each of the four digital I/O pins is to be an input or an output
function (OE3 through OE0). This sets the mode of each I/O pin.
Register 7, the Ref/Oscillator Control register, controls whether the internal
oscillator used for the conversion clock is on or off (OSCE), whether the internal voltage
reference and buffer are on or off (REFE, BUFE), and whether the reference provides
2.5 V, 2.048 V, or 1.15 V.
Register 24, the Serial Interface Control register, controls whether data is
presented MSB or LSB first (LSB bit), whether the serial interface is configured for 2wire or 3-wire operation (2W/3W bit), and determines proper timing control for 8051type microprocessor interfaces (8051 bit).
Register 31, the ID register, is read only.
19
FIGURE 3.12 Timing Diagram for an 8-Bit Read Operation
The above diagram shows the example of 8 bit read operation. The instruction
code receives by the ADC chip at rising edge. The instruction code can ether reach at
rising edge or failing edge depend on the pin 10 (RISE/FAIL). If pin 10 set to 0 , the
code will reach at failing edge while pin 10 set to 1, the code will read at rising edge.
Upon completion of the read operation, the ADS7870 is ready to receive the next
instruction byte. Read operations reflect the state of the ADS7870 on the first active
edge of SCLK of the data byte transferred.
The 12-bit A/D converter in the ADS7870 is a successive approximation type.
The output of the converter is2s complement format and can be read through the serial
interface MSB first or LSB first.
Figure 3.13 Output Codes versus Input Voltage
20
3.3.5
Serial Peripheral Interfaces
Figure 3.14
Serial Peripheral Interfaces
As I have been mention before, the communication between microcontroller and
the ADC and DAC chip is based on master and slave relationship. The microcontroller
act as Master and the chip act as Slave. It is a synchronous communication at which
sending and receive data is in the same time with the correct clock mode. To allow such
communication, some initialization has to be called before it can be used.
3.3.6
Programs Implementation
I used dynamic C software to burn the program code into the microcontroller. It
is C++ language which very common and easy to understand. The program burned is
used to control the whole system of DAQ device allowing the users to take control of the
DAQ device. LAVIEW is used to build user interface for easy exploitation of the
functionality of DAQ device without the need to understand the low level language.
3.3.7
Programs Algorithms
Microcontroller is the function of computing and control for the whole DAQ
device. It used to taking instruction from the User Interface from PC and interpret the
command and pass it to the system to do the job. As an example, from the user interface,
21
users choose to read the signal from the Analog input. The instruction is sent to
microcontroller via Ethernet cable. Microcontroller receive the instruction and sent
required code to analog to digital chip which enable it to read the signal from the input
and sent the data to PC for display.
In order to for the flow of the system to be smooth, an algorithm has to been
designed which enable the DAQ device act according and response faster. The
algorithm explains how the systems allowing the microcontroller take control of all the
functionality of data acquisition. There are lots of consideration to be made in the
algorithm, different designs are made and improved to make sure there are not even a
slightly mistake could be made.
Moreover, the User Interface is also a part of the system but different category
since it used LABVIEW to develop. So another algorithm will be build which is
specialized for User Interface. It explains the flow of the User Interfaces, showing how
it is works and how it is used to send the instruction to the DAQ device.
22
START
INITIALIZATION
Initialize SPI
Initialize clock mode
Initialize Port
Initialize IP address
Initialize calibration data
Waiting For
Instruction code
from User
Interface
NO
YES
Checking if the
instruction is
valid
NO
YES
Execute the instruction
Figure 3.15
Main Program Algorithms
23
Figure 3.16
Execution Instruction Algorithms Part 1
24
ADC INPUT
Check instruction type
ADC CALIBRARION
Execution instruction
ADC input
Execution instruction
ADC calibration
Set GAINCODE
SET INPUT CHANNEL
Load value 1
Load value2
Load Voltage 1
Load Voltage 2
Save calibration
Check ADC MODE
UNIPOLAR
BIPOLAR
Run on singe ended
unipolar mode
DIFF
Run on singe ended
bipolar mode
Run on differential
mode
Check value type
VOLT
RAW
Display rawdata
Display voltage
Return
Figure 3.17
Execution Instruction Algorithms Part 2
25
START
Established connection
Waiting user input
DAC OUTPUT
ADC INPUT
DIGITAL INPUT
DIGITAL
OUTPUT
CALIBRATION
Set type
Set type
Set PORT
Set PORT
Set RAW VALUE
Set BIT
Set BIT
Set VOLTAGE
VALUE
Set port
Set value
Set mode
Set port
Set STATE
Send instruction code
Figure 3.18
LABVIEW User Interfaces Algorithms
26
Figure 3.19
Figure 3.20
Connection test using Hercules
LABVIEW User Interfaces
27
3.3.8
Explanation of Main Programs
The flow chart shown describes how the main program works. It basically waits
for the user to send the instruction from the user interface. The initialization part is the
most important part of program to make the whole thing works.
Figure 3.21
SPI Initialization code
The program above used to initialize serial peripheral interfaces allowing
microcontroller to use the SPI connection to control the ADC and DAC chip for
manipulating the functionality of data acquisition system. There are some SPI
connections available in the microcontroller, since I initialize SPI serial D; I have to use
PORT C BIT 0 and PORT C BIT 1 for the connection.
Figure 3.22
TCP/IP Connection Initialization code
28
The above program code is used to initialize the TCP connection using Ethernet
port from PC to DAQ device. Without the initialize part at above program code the
connection would not be able to establish since the PC does not know the IP address of
the DAQ device thus no connection is being setup.
Figure 3.23
Digital I/O Initialization programming code
In order set digital output or digital input for DAQ device, the initialization
above is coded, and every time I turn on the DAQ device, it will automatically load the
previous state of the digital I/O. As an example the saved memory loaded an output
state from PORT A of the microcontroller, hence the programming code above will set
PORT A to digital output.
Figure 3.24
Clock Initialization programming code
A SPI connection require a clock to send and receive data, the clock have to be in
the correct form, or else the data will not be able to receive by the ADC and DAC chip
since the clock between the Master and Slave is difference. So to set the correct clock
for the microcontroller that is compatible to the DAC and ADC chip, I have to write
PORT E BIT 5 and BIT 4 to STATE 1 and STATE 0 respectively.
29
Figure 3.25
EEPROM save Structure
To able the DAQ device load the calibration data every time it is turn on, I have
to create a way which can save the data along with other information and can be extract
without any difficulty. The easiest way is construct a structure, with the above structure;
I can load any data I want accordingly. As for the calibration data, I save it in the
variable name “ calibdata”. Under the variable, it is a structure too, containing the
calibration data both for ADC chip and DAC chip.
Once the initialization part finish, the main programming is ready to receive
instruction from user via the User Interface. The TCP connection is always listening,
waiting for the user instruction.
Figure 3.26
TCP listen programming code
The code above used to call the connection program, and once the socket is
establish, the connection will be complete and proceed to read bytes which allowing the
device to read the instruction from PC via TCP connection.
30
Figure 3.27
TCP read programming code
The DAQ device read the instruction from the buffer in the STATE_READ
programs code shown above. The instruction is then will be processed and checked
whether the instruction received is valid and executable. Once the instructions have
been confirm, it will be proceed to execute instruction program. The main program will
keep looping itself, letting user to take control all the time.
3.3.9 Explanation of Execution Programs
According to the flow chart of execute instruction program algorithms, the
function of the DAQ device consist of 6 parts which are : configure digital input,
configure digital output , set DAC output, set DAC calibration data, set ADC input, set
DAC calibration data.
31
3.3.9.1 DAC Output
Figure 3.28
DAC main function programming code
The above is showing how the programming code manipulates the DAC chip to
output a desire voltage value. This is the main code for setting the voltage output from
DAC chip, the main program will call the function to execute the instruction which
involving DAC output. If the value type is voltage value, it will undergo calibration
before send to the DAC chip, the calibration data is load from “gstFlashData” as shown
as above programming code. If the value type is raw data, it will send directly to DAC
chip. It is used to collect the calibration data from the DAC chip by comparing the raw
data with the output voltage.
“CHIPSELECT” is one of the elements for SPI connection. It allows the master
to differentiate which slave is turn on at the moment. This helps the Master to control
32
more than one slave without sending the data to the wrong Slave. Since DAC and ADC
chips used the same SPI connection with microcontroller, it is necessary for the Master
to identify the correct chip for the correct data.
“SPIWRITE” is used to send the command to the DAC chip.
3.3.9.2 ADC Input
Figure 3.29
ADC calibration programming code
The programs above is the function to be called when user ask to check the input
signal from the channel input. According the input mode of the ADC, the program will
call the calibration data from its respective address in EEPROM of microcontroller and
used it to make the calibration before send to the ADC chips. Similar to DAC programs,
ADC programs allows users to choose whether the output data is in raw data or voltage
value, the raw data is an output of the ADC without calibration, it is used to collect data.
33
Figure 3.30
ADC output type programming code
This is how the program differentiate the raw data type and voltage type from the
instruction code, if the user choose raw data, result coming from the chips will not go
through calibration and shown in hexadecimal format. If the users choose voltage value
type, it will undergo calibration and display the voltage value.
Figure 3.31
ADC fetch instruction programming code
The difference between DAC and ADC chip are DAC programs only to send SPI
Write as user sent it to output their desire voltage value, there is no digital signal can be
read from the chips. Users can check if the DAC chip is doing its job by check the
voltage coming out from the output pin. While ADC need to read back the data from
ADC chip as users need to display the value of the analog signal measured. To the data
display, I need to use SPI Read command to read back the contents from the register of
the respective input signal.
34
3.3.9.3 ADC and DAC Calibration
Figure 3.32
DAC and ADC calibration data structure
The above code is use to construct a structure unit for both ADC and DAC
calibration. With the help of structure, I can easily save the calibration data together
with other information and extract the calibration data when it is need without disturbing
other information which is saved in the EEPROM of the microcontroller
Figure 3.33
DAC and ADC calibration equation
Both calibration use same equation, in the for calibration data, I require the 2 voltage
value and 2 raw data from the chips. From the result I have collected from the chips, the
35
calibration programs will generate 2 calibration data which are offset and gain. This 2
data will be used to calibrate the outcome from ADC and DAC chips to produce more
accurate output.
3.3.9.4 Digital I/O
Figure 3.34
Configure digital output programming code
The DAQ device can provide digital input and output, the digital input and
output is coming from the microcontroller. Since the digital input and output is from
microcontroller, hence it is a straight away setup, no connection require for
communication between chips to chip. “ioConfigureBit” use to setup the direction of the
PORT BIT, for an example from above, it configure PORT A , BIT i into an output. As
an output, it should has output bit 0 or bit 1, so do I used “ioSetBit” to set it output a
digital output according to the default.
Figure 3.35
Configure digital input programming code
To set a digital input, I just have to change to input in the command of
“ioConfigureBit” as above code. Since it take signal from outside the microcontroller,
so I do not need to set the Bit value but to read from the PORT BIT to check the value of
the input.
36
CHAPTER 4
RESULT AND DISCUSSION
4.1 Introduction
The progress of the project has been able to achieve according to schedule. The
component required has bought with the minimum budget. The schematic design for the
ADC has been done. The design is based on combining the ADC chip, DAC chip and
the microcontroller. In order to able the ADC chips to process negative voltage;
experiment has been conducted using voltage divider with bipolar voltage at the end, I
found that the negative voltage can be converted to positive first before it go into the
ADC input channel. Then, the converted voltage will display in the monitor with
calibrated value.
Extra work has been done on programming part, the programming part supposed
to done in the next semester but since there is some extra time, some part of the
programming has been studied and discussed. The ADC and DAC simple program has
been done to try out if the chip is functioning with the programming code. In addition,
the TCP/IP connection programming has been done in half way for the DAQ device
communication function.
LABVIEW programming also been studied for the User Interface of DAQ device
for fetching instruction code and displayed measured data.
37
4.2
Experiments on Analog Input Range
This experiment is conducted to understand the signal conditioning signal using
voltage divider and from the experiment, I will know the relationship between analog
input range and resistor and reference voltage.
The analog input scale of ADS7870 is between -0.5V to 6.0V, so in order to
allow bipolar signals and signals which are out of scale able to act as an input for
ADS7870, a voltage divider is used. The voltage divider use to scale down the input
voltage to match the input range of ADS7870.
Vadc
Vdac
Vin
R1
Figure 4.1
R2
Circuitry Design of Signal Conditioning
An experiment conducted to test the relation between the elements in the voltage divider.
Through the experiment, resistor R1 and R2 and Bias Voltage can be determined
correspond to the desired range of input voltage and ADS7870.
38
4.2.1 Procedure
1. Determine the desired range of input voltage and ADS7870.Sketch the linear graph.
Vadc/V
5
-10
Figure 4.2
0
10
Vin/V
Linear Graph with Vadc =0-5V and Vin =±10V
2. Determine the linear equation of the graph. Y= mX+C
3. Derive an equation from the voltage divider.
4. Compare the equation from step 2 and step 3.
(
)
(
……………………(1)
)
………………… (2)
5. From equation 1, Vdac can be determined while the ratio of the resistor can be
obtained from equation 2
39
TABLE 4.1: Experimental Results for Vin Range -10V to 10V
Calculation Result:
Refer to linear graph,
5 = 0.25x + C ……………………(1)
0 = 0.25x + C ……………………(2)
(1) + (2):
5 = 2C, C = 2.5
Y = 0.25x + 2.5
Compare to:
:
Then we can know,
= 0.25
40
=
4R1
= R1 + R2
3R1
= R2
(
)
TABLE 4.2: Experimental Results for Vin Range -20V to 20V
41
Calculation Result:
Refer to linear graph,
5 = 0.125x + C ……………………(1)
0 = 0.125x + C ……………………(2)
(1) + (2):
5 = 2C, C = 2.5
Y = 0.125x + 2.5
Compare to:
:
Then we can know,
= 0.125
=
6R1
= R1 + R2
7R1
= R2
(
)
Vdac = 2.5/0.875
From the result, I can divide into 2 parts: Vin Range -10V to 10V and Vin Range
-20V to 20V. The optimum voltages for Vdac are 3.33V and 2.86V respectively. The
ratio of resistor values are R1: R2 = 1: 3 and 1: 7. After the input voltage pass through
the signal conditioning circuitry, the value of the voltage input is ratio down into the
range of allowable for the ADC chips to work which is between 0V to 5V. As the result
shown, I can manipulate the reference voltage and resistor according to the input range
of analog signal but to design a DAQ device which able to change the mode of the
converter in a single channel input, I have to fix on the value on the resistor and
manipulate the value of reference voltage according to the mode of ADC channel input
42
4.3
Comparison of DAC Output Voltage
This experiment is carried out to show the difference between the actual voltage
value and the calculated voltage value. If the value from actual voltage and calculate
voltage is the same, then it will not necessary to make calibration on DAC chips
This experiment conducted by sending the instrument code to DAC chips to output the
voltage value as the instrument code is in hexadecimal format. Code contains the value
of voltage which I desired for the output. The table below shows the result on the
experiment
TABLE 4.3: Experimental Results of Output Voltage DAC comparison
outpu
t
outA
outB
outC
outD
outE
outF
outG
outH
hex
0x0A0
0
0x150
0
0x220
A
0x390
0
0x4F0
A
0x5FF
F
0x6B0
0
0x770
0
dec
256
0
128
0
522
230
4
385
0
409
5
281
6
179
2
internal Vref= 2.04V
calculation result/
/V
V
internal Vref= 1.04V
calculation result/
/V
V
external Vref=1.76V
calculation result/
/V
V
2.55
2.56
1.28
1.28
2.2
2.16
1.28
1.28
0.64
0.64
1.1
1.08
0.52
0.52
0.26
0.24
0.45
0.48
2.3
2.28
1.15
1.12
1.98
2.76
3.84
3.92
1.92
1.92
3.31
4.28
4.08
4.16
2.04
2.08
3.52
3.66
2.81
3.88
1.4
1.4
2.56
2.56
1.79
1.8
0.91
0.88
1.54
1.6
43
The experiment tested using different kind of reference voltage. There are huge
difference between the actual value and calculated value when I using external voltage,
the rest of result also shown some slightly difference. This kind of error will actually
crucial in data acquisition system. The system require to be accurate, and this is not
accurate enough to compete with other highly commercialize DAQ device. In order to
solve the problem, I have written the calibration program to make the input voltage
exactly the same with the output voltage.
4.4
Accuracy of ADC Input Signal
The accuracy of the ADC input signal is basically base on the calibration data.
So this experiment is used to show the accuracy of the results after calibration. The
experiment conducted at robotic lab and used power supply generator to connect to the
ADC input signal in order to test the range of the ADC input signal and its accuracy.
The program has set the ADC to allow three kinds of mode for data acquisition: single
ended unipolar mode, single ended bipolar mode, and differential input mode.
Single ended unipolar mode has the input range of 0 to 20 volt after signal
conditioning circuit has been added. While single ended bipolar mode has the input
range from -10 volts to +10 volts. Finally for the differential mode has the input range
from -20 volts to +20 volts.
44
TABLE 4.4: Accuracy of Single Ended Unipolar Mode
Actual reading/V
Measured reading/V
0.12
0.01
1.12
1
2.12
2
3.12
3
4.12
4
5.12
4.99
6.12
5.99
7.12
7
12.12
11.98
16.14
15.99
18.14
17.98
20.14
19.98
TABLE 4.5: Accuracy of Single Ended Bipolar Mode
Actual reading/V
Measured reading/V
10.12
9.97
9.12
8.97
8.12
7.98
7.12
6.99
6.12
5.99
5.12
5
4.12
4
3.12
2.99
0.12
0.01
-1.99
-2.09
-2.99
-3.08
-4.99
-5.08
-6.99
-7.09
-9.99
-10.08
45
TABLE 4.6: Accuracy of Differential Mode
Actual reading/V Measured reading/V
20
19.47
19
18.49
18
17.53
17
16.55
15
14.61
10
9.73
8
7.78
6
5.83
4
3.87
2
1.94
0
0.01
-2
-1.95
-4
-3.91
-8
-7.81
-10
-9.75
-12
-11.71
-15
-15.04
SINGLE ENDED UNIPOLAR INPUT
Voltage/V
30
20
Measured reading/V
10
Actual reading/V
0
1 2 3
4
5
6
7
8
9 10 11
12
FIGURE 4.3 Graphs on Single Ended Unipolar
46
SINGLE ENDED BIPOLAR INPUT
VOLTAGE/V
15
10
5
Actual reading/V
0
-5
-10
-15
1 2 3 4 5
6 7 8 9
10 11 12 13
14
Measured reading/V
FIGURE 4.4 Graphs on Single Ended Bipolar
DIFFERENTIAL INPUT
VOLTAGE/V
20
10
0
-10
Actual reading/V
1
3
5
7
9
11
13
15
Measured reading/V
17
-20
FIGURE 4.5 Graphs on Differential Input
47
From the data collected, I put in the tables shown above and convert to graph for
a better analysis. As from the table, for single ended unipolar, there is a slightly different
between the measured data and actual data and it is around measure voltage ±0.20
voltage. For single ended bipolar, the result is almost the same with single ended
unipolar with the error of ±0.18 voltage. For differential mode, the difference is much
steeper than the previous mode with error as high as ±0.40 voltage. This kind error can
be reduced with a little bit effort on calibration data. I have to take more reading from
the raw data of DAC and ADC chips to make a prefect calibration. From the graph, i
can see that all the measured data and actual data line up in parallel which mean the
actual data is directly proportional to the measured data and both data are approximately
the same.
48
CHAPTER 5
CONCLUSION AND RECOMMENDATION
5.1 Conclusion
According to recent development and technology, almost all the industry
machine implemented with data acquisition system. Wide range of application of data
acquisition system is available in industry work such as, research and development,
digital control, analysis and monitoring and so on. With the great potential of data
acquisition device over the market now a day, the customer has demand more from a
data acquisition device instead of having the basic requirement of data acquisition
system such the most critical part is the accuracy of analog input signal. Since the main
function of data acquisition is used to measure analog input signal, hence the accuracy,
repeatability and precision of a data acquisition system must be achieved.
The goal of this project is to build data acquisition device with minimum budget
hence producing a low cost data acquisition device. The demand from industry has
pushed the recent data acquisition device on the market equipped with multiple
functions which is extremely expensive for student to buy for their research. In this
project, I will only code the main function of data acquisition system to reduce cost.
The main elements in this data acquisition device is able perform analog to digital
conversion with three different mode , configuring digital input and output for control
system and finally interfaces with PC for fetching instruction and display measured data.
49
To enable the data acquisition device perform analog to digital conversion with different
mode , digital to analog conversion have to implement along with voltage divider to
convert the input signal into a suitable range of input for the ADC chips to process. For
the first mode, single ended unipolar, the DAC will not output any voltage since the
range of the mode is 0 volts to 20 volts, it only need to pass through the voltage divider
to ratio down into an allowable value. For single ended unipolar and differential mode,
the DAC will output a fixed voltage value to counter the bipolarity voltage signal from
input.
The accuracy of the data acquisition is depend on the calibration data as the noncalibrated output signal is not accurate, from the result shown, I have reduced the error
until ±0.40 voltage and can be even become smaller as I have to do lot more effort on
the calibration parts.
The outcome of the project is achieved and the accuracy of the data acquisition
device depends on the calibration data input from user. As the calibration data is more
accurate, so as accuracy of the data acquisition system takes place.
The schematic design has been design for ADC circuit, and some part of
programming have been done for ADC and DAC chips and also communication part
using TCP/IP connection. All the part from schedule has been carried out successfully.
5.2
Problems
Although I have achieved the project goal but there has some problems have
been encounter during the development of project. The First problems encounter is
actually contrast to one of the project objective which is to build a data acquisition
device in small structure , unfortunately a prototype has be built where the structure is
50
available for debugging. The prototype is built into 3 layers of PCB which widely open
for debugging; hence the data acquisition device is bigger than the expected size.
In additional, the other problems encounter is the wire and circuitry of data
acquisition device. Debugging procedure going on , the wire and circuitry has been
checked, removed, reattached, soldered again and again, hence the connection become
fragile and sometimes making the whole system unable to work as the connection has
been cut off.
Moreover, an accurate DAC and ADC chips not supposed to write a calibration
program for it since the output is already accurate, but I have try out both chips and as
the result, both outputs are not accurate and it is slightly off the original signal. So a
calibration program has to make for an accurate output.
5.3
Recommendations
The data acquisition device developed in this project still has lots more
improvement to implement before it can really go on market. There some
recommendation for the product for future improvement for better performance.
1) Hardware improvement
The device can be built in more compact and smaller structure for portability.
This can be done by changing the entire component into surface mount
component and redesign the circuitry for surface mount component. With the
replacement of surface mount component, the device can be constructing into a
smaller structure giving convenient to customer. Beside than that, the ADC and
DAC chips should be replace with a more accurate replacement, since the current
chips do not give an accurate output. This can be done by searching the
51
information from the net and conduct plenty of experiment for ADC and DAC
chips
2) Software improvement
The user interfaces of the device is not really convenient for some user because
some of the users might need to configure digital input and output or measured
data in the same times, as the current user interface only allow one instruction to
be run at a times.
52
WORK SCHEDULE
Semester 1, Section 2012/13
Semester 2, Section 2012/13
53
REFERENCES
1. Hai Feng Zhou, J. D. D., Yuan Qing Huang (February, 2012). "Design of Data
Acquisition and LED Display System." Advanced Materials Research Automation
Equipment and Systems: 863-866.
2. Ning, Y., Z. Guo, et al. (2012). "Design of Data Acquisition and Storage System
Based on the FPGA." Procedia Engineering 29(0): 2927-2931.
3. Hai Feng Zhou(February, 2002). "Design of Data Acquisition and LED Display
System." Advanced Materials Research Automation Equipment and Systems:
863-866.
4. Hemond, B. D., Wahab, A. A.(2001). MICA: an innovative approach to remote data
acquisition. IEEE Instrumentation & Measurement Magazine, 15(5), 22-27.
5. Mohamad-Ali, B. S., & Maree, A. H. (1999). Low cost medical data acquisition
system using AVR-MCU and PC. Journal Of Theoretical And Applied
Information Technology, 42(2), 217-220.
6. Ning, Y., Z. Guo, et al. (2001). "Design of Data Acquisition and Storage System
Based on the FPGA." Procedia Engineering 29(0): 2927-2931.
7. Wu, Z., Shan, J.F. 2002). “A new real time data acquisition system for low hybrid
current drive system。” Advances in Intelligent Systems and Computing:Pages
299-303
8. http://www.vtiinstruments.com/Data-Acquisition-Signal-Conditioning.aspx
9. http://physweb.bgu.ac.il/COURSES/SignalNoise/data_aquisition_fundamental.pdf
54
Appendix A
PARTS OF ADC PROGRAMMING CODE
55
56
57
Appendix B
SCHEMATIC DESIGN OF ADC
58
Appendix C
PCB DESIGN OF TINY DAQ
59
60
Appendix D
CASING DESIGN OF TINY DAQ
61
Appendix E
LAVIEW DESIGN OF TINY DAQ USER INTERFACE
62
Appendix F
STRUCTURE OF TINY DAQ
63
REFERENCES
1. Hai Feng Zhou, J. D. D., Yuan Qing Huang (February, 2012). "Design of Data
Acquisition and LED Display System." Advanced Materials Research Automation
Equipment and Systems: 863-866.
2. Ning, Y., Z. Guo, et al. (2012). "Design of Data Acquisition and Storage System
Based on the FPGA." Procedia Engineering 29(0): 2927-2931.
3. Hai Feng Zhou(February, 2002). "Design of Data Acquisition and LED Display
System." Advanced Materials Research Automation Equipment and Systems:
863-866.
4. Hemond, B. D., Wahab, A. A.(2001). MICA: an innovative approach to remote data
acquisition. IEEE Instrumentation & Measurement Magazine, 15(5), 22-27.
5. Mohamad-Ali, B. S., & Maree, A. H. (1999). Low cost medical data acquisition
system using AVR-MCU and PC. Journal Of Theoretical And Applied
Information Technology, 42(2), 217-220.
6. Ning, Y., Z. Guo, et al. (2001). "Design of Data Acquisition and Storage System
Based on the FPGA." Procedia Engineering 29(0): 2927-2931.
7. Wu, Z., Shan, J.F. 2002). “A new real time data acquisition system for low hybrid
current drive system。” Advances in Intelligent Systems and Computing:Pages
299-303
8. http://www.vtiinstruments.com/Data-Acquisition-Signal-Conditioning.aspx
9. http://physweb.bgu.ac.il/COURSES/SignalNoise/data_aquisition_fundamental.pdf