design and development of a tablet based real time wireless data logger ieee 2012 embedded android

8/11/2019 Design and Development of a Tablet Based Real Time Wireless Data Logger IEEE 2012 Embedded Android

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Design and Development of a Tablet Based Real

Time Wireless Data Logger

Zhan Wei Siew, Chen How Wong, Shee Eng Tan, Hou Pin Yoong, Kenneth Tze Kin Teo

Modelling, Simulation & Computing Laboratory, Material & Mineral Research UnitSchool of Engineering and Information Technology

Universiti Malaysia Sabah

Kota Kinabalu, [email protected], [email protected]

Abstract —To date, data loggers are getting more implementation

in business and home applications compare with several years

ago. Data loggers can be customized according to the application

requirement based on the available resources in the market.

Thus, this creates a cost effective solution for the end user. In this

paper, a wireless data logger with remote control capability via

PC and tablet is introduced. The proposed wireless data logger is

developed using microcontroller with analog-to-digital converter

(ADC). The design of the portable wireless data logger is compact

and light to increase the mobility and usability. Sampled data

with time stamp from real time clock (RTC) module will be

stored into SD memory card which is attached to controller

board. Wireless data logger can directly transmit the data to end

user if the device is in the communication coverage or stored the

data into memory card if it is out of range. Graphic user

interface (GUI) developed using Visual Basic and Android

application. These applications can communicate with wireless

data logger through wireless XBee module and Bluetooth

module. End user can change the data logger settings such as,

data sampling frequency, date and time remotely.

Keywords—wireless communication; data logger;microcontroller; Android

I. I NTRODUCTION

Electronic devices that have the capability to record datafrom sensors in specific location over time are referred as dataloggers. Typically, data logger is equipped withmicroprocessor, memory, and sensor for data collection.Mobility is one of the advantages of data logger since the sizeof the microprocessor, memory, and sensor is small.

The design of the data logger can be made based on theneeds of specific environment or application type. Many of thegeneral purpose data loggers are machines with fixed

parameters. However, there are some with re-programmablecapability.

One of the most important advantages of using data loggeris the capability to collect data automatically over a long

period. Measurement results can be collected without humansupervision just by deployment and activating the data loggeron the intended location. This does not only reduce the humanresources in data recording, but also provide an accurate

picture of the environmental conditions during the monitoring period.

For most of the scientific research works, monitoring andcollecting data of the phenomenon for a given period is veryimportant to draw conclusion from analyzing the data. For thecase that requires monitoring done in a large spaceenvironment such as in agriculture, [1]-[3] and weather station[4], [5], multiple of wireless data loggers are required to cover

all the area. It forms a wireless sensor network problem. Manyresearches such as in [6]-[8] focus on prolonging the networklife time since it is battery powered. To extend the operationtimes, technology such as mechanical generators,thermoelectric generators, and solar cells are use to harvestenergy from the surrounding.

Continuous development of the emerging technology ondata logger has brought the creation of new innovation andapplications. By using the available resource in the market suchas personal computer and tablet [9], it is possible to customizedata logger according to their application requirements.

The content of this paper is organized as follows. In thenext Section, the design of the wireless data logger is

explained. The hardware development of data logger andmobile portable data logger is described in Section III. Afterthe development of the hardware, software development will

be carried out in Section IV. The software developmentincludes the development of the source code for data loggerand monitoring software. Section V presents the future workand the conclusion of this paper.

II. THE DESIGN

Wireless data logger provides decision making, real timedata logging, data storage and wireless data transmissioncapability. In this Section, two data logging methods will bedemonstrated. The first method is PC based data logging as

shows in Fig. 1. The developed data logger has an ability todirectly transmit the sensed data to PC-end use for real timemonitoring. This method is very suitable for data logging inexperimental and plant monitoring. The PC is always located ata place with electric supply, shelter and internet access. Thedata logging method can be enhanced by adding internet accessto the PC and short message service (SMS) via Global Systemfor Mobile (GSM) modem.

Fig. 2 shows the alternative way of data logging in this paper. Sometimes, the data logger may be located at the placewhere it is far away from PC. Therefore, to retrieve the

2012 IEEE Global High Tech Congress on Electronics

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information, the user has to physically retrieve from the datalogger. Introduction of a mobile portable data logger providesan alternative way to collect the data from data logger. Portabledata logger can download data from data logger when thedevice is in the data logger communication coverage. Inaddition, the use of Tablet with the mobile portable data logger

provides data logger a user control panel interface. Which, theuser can remotely access into the data logger as how the PC

does. This method can be enhanced by utilizing the built-inhardware such as global positioning unit (GPS) to retrievelocation information, for example to retrieve the data loggercoordinate.

A. Graphic User Interface

As shown in Fig. 1 and Fig. 2, user can view real-time datafrom the data logger through a PC or Tablet. In Windows basedPC, monitoring software is developed by using express versionof Visual Basic (VB). VB is a third-generation event-driven

programming language from Microsoft. The design of VB is to provide users with easy to learn and use environment. Thelayout of the monitoring software interprets important

information form data logger such as real-time graph of thesensed data from each channel with a basic data logger control panel. The details of the software development will be carriedout in Section V.

Today, two types of mobile operating systems are gainingrapid attention from the markets, and it has occupied almost85% of the mobile devices sold. They are Android fromGoogle and iOS from Apple. In this paper, Android fromGoogle is selected as development platform for Tablet.Google’s Android is open-source, which allows developersaccess to OS source code. Through this advantage, it providessuperior customization over others OS. Therefore, developerscan develop better software by utilizing system resources. In

Section V, we will discuss about the framework of themonitoring software.

Figure 1. Data logging method (PC).

Figure 2. Data logging method (Tablet).

B. Real-Time Monitoring

Basic data logger is equipped with the external memory

storage to log real-time data with date and time stamped. Butthe external memory has to be removed for data analysis after a period of sensing time. Wireless data logger provides moreadvantage over cable type data loggers, which it can providereal-time information to the user without the long, expensiveand inflexible cable. But the use of wireless transmission maynot guarantee the accuracy of the data logger information. Ahybrid between wireless communication and external storage

provide intelligence solution to the problem, it ensures the datawill not be lost in case of communication failure. Fig. 3 showsthe hybrid of information delivery method.

As shown in Fig. 3, designed data logger has a choice tostore the data into external storage module or directly transmitthe data through wireless communication module. The use ofwireless communication only will be active when the receiveris in the communication coverage. Otherwise the data will bestored into external storage to prepare for next reliable dataretrieval. If the receiver is back into communication coverage,the data stored in the external storage will be transmitted to thereceiver beginning from the last sent data.

Figure 3. Hybrid of information delivery method.

Processing Unit

External Storage

Module

Wireless

Communication

Module

Data Logger

Mobile Portable

Data Logger

Smartphone-End User

Data Logger

PC-EndUser


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C. Remote Access Control

In practice, the data logger is located at the place where physical accessing to the data logger for software upgrade,calibration and adjustments is time consuming and impractical.Therefore, in this project the designed data logger includesremote access control capability. The terms remote accesscontrol means user can wirelessly access into data logger tochange the control settings. The operation of the designed

wireless data logger consists of two modes, these are activemode and command mode. In the active mode, it includes theoperations such as data transmission state and sensing state.While in command mode, user has the authentication to changethe data logger settings.

If the wireless data logger is in communication coverage,users can remotely access by using Tablet or PC. For example,user can change the data sampling rate in the logger bytransmitting a specific command and desired sampling intervaltime. The modifiable data logger settings include date and time,data sampling rate, channel activation and also data logger

basic operation. Each command will be sending into datalogger through a pre-designed format, the reason is to avoid

data collision. The details of each command will be describedin Section V.

III. HARDWARE DEVELOPMENT

In this Section, hardware development of wireless datalogger will be demonstrated. The demonstration is split intotwo parts, first is the main controller board and followed by thecommunication modules. Fig. 4 shows the controller diagramof both data logger and mobile portable data logger. Thecontroller consist of 4 basic modules, these are microcontrollerunit, wireless communication module, external data storagemodule and real-time clock module. For ease of development,all the modules are attached to the main microcontroller unit

module.

Fig. 5 shows the prototype of data logger with tunable potentiometers which acts as sensors. Fig. 6 shows the mobile portable data logger with two types of wireless modulesattached in the prototype. The use of different type of wirelessmodules is to convert data sending from data logger via XBeeto the user Tablet via Bluetooth. In this stage, both prototypescan be power up from single 9 V batteries or USB power.

Figure 4. Controller diagram.

Figure 5. Prototype of data logger.

Figure 6. Prototype of mobile portable data logger.

A. Main Controller Board

In the main controller board, the designed board consists ofa microcontroller development board, a RTC module and anexternal data storage module. The main controller board

provides data logger a controllable platform, the ability toconvert sensor analog signal into digital signal, externalmemory for data storage and real-time clock.

a) Programmable Microcontroller Board: The

microcontroller is selected as it provides developer an easy tolearn and use platform. It contains everything needed to start a

simple project. In this prototype, two microcontrollers are used

for both data logger with sensor and mobile portable data

logger. Both microcontroller boards are equipped with a

16MHz crystal oscillator and have up to a total of 54

input/output pins and 16 analog inputs. The miniature size androbust build makes the boards durable and flexible for design.

b) Real Time Clock (RTC): Is a trickle-charge

timekeeping chip that counts seconds, minutes, hours, date of

the month, day of the week and year (with leap year) until

2099. It is not a good pratice to count time using software

counting in the microcontroller. It is hard to ascertain the time

taken to execute an instruction due to the clock speed may not

be accurate as shown in data sheet. The software has to alwaysactive so it keeps the life time counting. Therefore, the use of

external RTC chip is very important to imaintain the accuracy

Bluetooth

XBee

XBeeSensor

(potentiometers)

Microcontroller

Unit

Wireless

Communication Module

External Data

Storage Module

Real-Time

Clock Module


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of the real-time and provides convenience to the software

development. Fig. 7 shows the RTC operating circuit used in

this paper. The interfaing only requires 3-wire interface. TheRTC module is attached with 3 V cell which is connected to

VCC1. Secondary power supply guranteed the clock is still

running even though there is no power supply to the main

controller board. The use of RTC module provides accurate

time for the main controller board and also to the sense data.

c)

External Data Storage (SD card): Is an external data

storage that uses to store the sensed data. Since the

development board has limited non-volatile memory storage,

therefore the design include external memory storage to record

large number of data. These prototypes use 2 Gb SD card as

external memory for data storage. To access into the SD card, a

voltage converter circuit has been developed. It convert 5 V

from microcontroller board to 3.3 V use in SD card and vice

versa.

B. Communication Modules

In this project, two types of communication modules have

been used. These are XBee wireless module and Bluetoothmodule. Fig. 8 shows the wireless modules that used in datalogger project. Both modules share similar features such ascommunication protocol, operating voltage and they providedata logger a way to communicate wirelessly.

Figure 7. RTC operating circuit.

Figure 8. Wireless modules.

a) XBee Wireless Module: Is the wireless

communication module that used for communicating between

data logger to PC and also to the mobile portable data logger.The transmission of the XBee module is around 30 m for

indoor and 100 m for outdoor. The operating voltage of XBee

is 3.3 V, therefore volatge converter circuit has been developed

so it can be accessed by main controller. To access into XBee

module, UART protocol have been used. The baud rate is set to

9600 and with no parity bit. Since it only use thecommunication function of XBee, only 4 wires have to connect

to XBee module. The description of these 4 pins is shows in

Table I.

b) Bluetooth Module: Is the wireless communicationmodule that use in communication between mobile portable

data logger to Tablet. The transmission range of the module is

around 20 m- 30 m which is far enough for the design.

Bluetooth BEE wireless module adapts XBee design, which the

pinout is compatible with XBee. The operating voltage is same

as XBee, voltage converter circuit have been developed so it

can be access by main controller board. The communication

protocol use in Bluetooth BEE is also the same as XBee,therefore it use the same connection as XBee.

IV. HARDWARE DEVELOPMENT

After the development of the hardware, simple source codeis loaded into the prototypes for hardware verification. Theverification scope includes functionality of the development

boards, RTC chip and SD card. Simple communication testinghas been carried out, there are communication between twoXBee modules, the linkage and data transmission betweenTablet and development board through Bluetooth BEE. In thisSection, software development will be further discussed. Itincludes the framework of the developed software for maincontroller board (data logger and mobile portable data logger)and monitoring software (PC and Tablet).

A.

Data Logger Functionality

The data logger is designed to avoid data disruption as theintegrity and reliability must be preserved. Fig. 9 shows the

basic framework of the data logger. The framework includesthe operations of analog-to-digital converter (ADC), datatransmission and also data storage into external memory.

TABLE I. PIN ASSIGNMENT

Symbol Pin Description

VIN 1 Power Supply 3.3 V

GND 10 Ground

DOUT 2 UART Data Out (To Microcontroller)

DIN 3 UART Data In (From Microcontroller)

X1 X2

VCC2

VCC1

GND

CE

I/O

SCLK

32.768kHz

VCC

3VTo main

board


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Figure 9. Framework of data logger.

In the developed prototype, since few modules are attachedto development board, it is important to monitor each module.Time critical modules, such as wireless module provide instantresponse during the data reception operation. Therefore, it is amust to develop interrupt handle function to avoid data losswhen the program is processing other functions. For example,during ADC operation, the operation can be pause so the

program can handle interrupt operation from UART. The process continues back to ADC operation after it complete theinterrupt operation.

RTC module provide real-time to development board, therefreshing rate to obtain real-time from RTC is every 0.25 sinterval. After completion of each ADC operation, the outputdata will be time stamped via directly retrieve from RTCmodule to acquire accurate time. During the first initializationoperation of data logger, a text file will be created to store thesensed data. Fig. 10 shows data log with timestamp recorded ina text file. The format consists of data number, data loggeridentity (ID), timestamp and data for each channel.

Figure 10. Data log with timestamp.

B. PC – End User Application

VB has been selected as development platform of PCmonitoring software due to its simple to use drag and dropinterface. The development of monitoring software starts withthe communication between data logger and PC. XBee modulewill be connected to PC and recognize by PC as serial port.Simple two ways UART communication between XBee istested using SerialPort class in VB.

Fig. 11 shows the PC monitoring software developed byVB. The layout of the monitoring software consists of COM

port connection block, control panel block, real-timeinformation graph and data log screen. In the COM portconnection block, user can connect to the COM that representsXBee, after the connection is establish which is indicated bythe word ‘Online’. The data logging process is initiated by

pressing the ‘Start’ button in the control panel. The defaultsampling rate is 1 s, user can manually change the samplingrate in the control panel. In the real-time information graph atthe right hand side of the monitoring software, user can selectto view information from each channel.

C.

Android – End User Application

Android has been selected as development platform ofmonitoring software application due to it is open-source andfreely available. The development of monitoring softwareapplication starts with the communication between mobile

portable data logger and Tablet. Communication connection is based on Bluetooth, Tablet built-in Bluetooth and BluetoothBEE.

To provide user a familiar control experience, the design ofAndroid monitoring software is almost same as PC version.Fig. 12 shows the Android application of monitoring softwaredeveloped by Eclipse. The layout of the monitoring softwareconsists of connection block, control panel block, real-timeinformation graph and data log screen. In the connection block,user can connect to the Bluetooth device that represents mobile

portable data logger. Since Bluetooth BEE is used in mobile portable data logger, the default pairing password is ‘1234’.After the connection is established, which it is representing by‘Connected’. The data logging process can be initiated by

pressing the ‘Start Logging’ button in the control panel. Thecontrol panel provide user to change the data logger settings.The developed Android application also utilizes built-in GPSfeatures to retrieve location coordinate.

Figure 11. PC monitoring software.

Start

Initialization of Data Logger

Retrieve Sensors Value (ADC)

Is receiver

request data?

Transmit via

Wireless Module

Store into External Memory

Storage

Yes

No


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Figure 12. Android monitoring software.

V. CONCLUSION AND FUTURE SCOPE

In conclusion, wireless data logger system for real timemonitoring has been successfully developed. The developedmonitoring software in PC or tablet can view and record real-

time information from data logger. In addition, user hasauthentication to access and change the setting via monitoringsoftware. Data logger with external memory storage can storethe sensed data to avoid data lost if the wireless connection islost. At the time when the receiver is back into communicationcoverage, the stored data will be transmitted (download) to thereceiver.

In future, energy consumption of the prototype should beconsidered. It is a need to develop an energy saving data loggerfor a longer sensing period. By replacing prototypingintegrated circuit with ultra low energy integrated circuit.

ACKNOWLEDGMENT

The authors would like to acknowledge the financial

assistance of the Universiti Malaysia Sabah Research GrantSchemes, grant no. SLB0014-TK-1/2011 and scholarshipsupport by Ministry of Higher Education of Malaysia (MoHE)under MyMaster program.

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design and development of a tablet based real time wireless data logger ieee 2012 embedded android

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