2014 Fifth International Conference on Intelligent Systems, Modelling and Simulation
Building of A Low-Cost Wireless Battery Analyzer
Boon-Huat Wilson Tan
Chee-Chiang Derrick Tiew
SIM University, School of Science & Technology,
Singapore
e-mail: wilsontan002@unisim.edu.sg
SIM University, School of Science & Technology,
Singapore
e-mail: derricktiew001@unisim.edu.sg
Abstract—This paper presents the design methodology,
implementation and testing of a low cost wireless battery
analyzer. The initial goal of this project is to build a battery
analyzer to enable the remote monitoring of a 24V backup
battery installed in a submarine. The implemented battery
analyzer is microcontroller-based, incorporates features to
sense and monitor the battery voltage level, discharge current
and the surrounding ambient temperature. Each of the sensing
signals is converted and stored as 10 bits stream. The data
values are reported to the crew via the screen of a laptop/PC
over a Bluetooth wireless communication link. Alarm will be
triggered whenever the battery voltage level, current and/or
ambient temperature fall out of preset allowable limits.
x
Keywords-battery analyzer; current sensor; temperature
sensor; wireless; bluetooth technology; serial port
x
x
x
x
x
I.
INTRODUCTION
The 24V backup battery system is one of the most
important systems onboard a submarine as it continues to
provide the required load (electrical supply for equipment)
for sustained silent operations and fighting capability when
the main 24V supply is not operative. Hence, when the 24V
backup battery is activated, it is critical for the submarine
crew to monitor the health and capacity of the batteries so as
to ensure the submarine continues her mission without any
restriction and limitation.
The original idea of designing a wireless battery analyzer
is to assist the submarine crew to monitor the 24V back up
battery. Due to the space constraint on board the submarine,
it is a challenge to monitor the battery status in such a
constraint space where the battery was installed. Hence, a
wireless battery analyzer will definitely be useful for the
crew to monitor the battery performance in the event when
the 24V back up battery system is activated.
II.
x
Bluetooth Module: To communicate and provide
wireless link between microcontroller and PC for
displaying real time readings.
Microcontroller: To record the voltage, current and
temperature readings from the battery sensors and
converts the data to obtain the real time battery’s
parameters to be displayed. When the limitation of
the battery system is reached, it will send a signal to
alert the users.
PC Display: To display battery’s parameters for
monitoring purposes.
Buzzer: Alert the users when the battery limitation
has reached.
LEDs: To indicate the status of the analyzer and the
battery.
GUI: Using ASP.NET (Visual Studio) to
graphically display the readings of the battery
analyzer.
5V power supply: To supply 5V to the
microcontroller.
HARDWARE DEVICES
A. System Architecture
The system architecture of the wireless battery analyzer
using Bluetooth technology is illustrated in Fig. 1. The
system is made up of the following components:
x
24V DC battery: 24V backup battery system to be
monitored.
x
Battery Sensors: To record the voltage, current and
temperature of the 24V backup battery system in the
submarine and send the readings to the
microcontroller.
2166-0662/14 $31.00 © 2014 IEEE
DOI 10.1109/ISMS.2014.140
Figure 1. System architecture of the wireless battery analyzer
765
B. Bill of Materials
Table I lists the hardware devices used in constructing
the wireless battery analyzer. The total purchase cost falls
below USD $70 for the components, and well within the
budget allocated to this project.
TABLE I. BILL OF MATERIALS FOR THE CONSTRUCTION OF THE
WIRELESS BATTERY ANALYZER
Figure 3. ACS712 current sensor and its pin-out
The analog signal from the current sensor is transmitted
to the microcontroller and this signal is then converted to
digital values by the ADC module in the microcontroller.
This digital value will be used to compare with the preset
value and determine whether a high current has been
detected.
E. Temperature Monitoring Circuit
There is a need to monitor the ambient temperature of the
battery as the rise of temperature would speed up the
discharging rate of the battery, and drain the battery at a
faster pace [3]. Hence, the battery’s ambient temperature
needs to be monitored closely, and appropriate action is
required to bring down the temperature once it exceeds
certain pre-determined unacceptable level.
LM35 temperature sensor was selected for this project.
The LM35 series are precision integrated-circuit temperature
sensors, with an output voltage linearly proportional to the
temperature (in °C). The scale factor for LM35 is 10.0
mV/°C with 0.5°C accuracy (at +25°C), and temperature
measuring range from −55°C to +150°C [4]. Fig. 4 shows
the pin out of LM35DZ while Fig. 5 shows the connection of
its output to AN0 (analog channel input) of PIC18F4520
microcontroller.
C. Voltage Monitoring Circuit
As the monitoring battery is 24V, there is a need to step
down the battery voltage level to ~3V before feeding it to the
PIC18F4520 microcontroller for analog to digital conversion
(ADC). Fig. 2 shows the voltage monitoring circuit
comprises a voltage divider.
Figure 2. Voltage monitoring using voltage divider
The analog signal from the battery voltage is transmitted
to the microcontroller and this signal is then converted to 10bit binary stream by the ADC module in the microcontroller.
This digital value will be used to compare with the preset
value to determine whether a low voltage has been detected.
The maximum input voltage at AN4 is 3.13V which is
safe for the microcontroller. The equation for the voltage
divider is shown below.
Vout (to AN4 ADC) = R2 / (R1+R2) * 24V
= (1.5 / 11.5) * 24V
= 3.13V
The resolution of the sensing voltage Vout is given by
3.13V / (210 - 1) = 3.06 mV.
Figure 4. Temperature sensor LM35DZ pin-out
D. Current Sensing Circuit
The battery efficiency decreases as the average discharge
current from the battery increases [1]. There is a need to
closely the monitor and limit the discharge current from the
battery in order to prolong the battery lifetime.
Module type ACS712 current sensor was selected for
monitoring the discharge current from the battery. The
ACS712 current sensor provides economical and precise AC
and DC current sensing and also allows easy
implementation. It consists of a precise, low-offset and linear
Hall sensor circuit [2]. Fig. 3 shows the ACS712 current
sensor and its pin-out.
Figure 5. Integration of temperature sensor LM35DZ with micro-controller
PIC18F4520
F. Bluetooth Module
This prototype uses Roving Networks RN-42-SM
Bluetooth module to implement the wireless communication
link. Roving Networks is the subsidiary company of
Microchip. Hence, the compatibility between the Bluetooth
module and PIC microcontroller is assured. It requires only
a simple connection as shown in Fig. 6.
766
graphical user interface (GUI) for displaying the values of
sensed signals using Microsoft Visio Studio IDE.
A. Microcontroller Programming
After sensing the battery voltage level, current and the
ambient temperature, those analog signals need to be
converted to binary numbers for digital control and display
purpose. The analog to digital conversion (ADC) were
carried out via PIC18F4520 microcontroller. The codes
were written in C language. The software integrated
platform MPLAB IDE provided by Microchip was used to
write the program codes, test and debug the PIC18F4520
microcontroller. PICkit3 was then used to program the
prototype [7]. Once the integration and testing of the
hardware and software were successful, the program codes
were permanently transferred and stored in the
microcontroller.
The PIC18F4520 microcontroller pins were assigned to
respective usage prior to the software programming. Table
II shows the configuration of PIC18F4520 ports for the
wireless battery analyzer.
Figure 6. Connection diagram of Roving Networks RN-42-SM Bluetooth
module
The Bluetooth module uses the Serial Port Profile (SPP)
to communicate with the microcontroller via a virtual serial
(COM) port [5]. It acts as a wireless connection between the
microcontroller and the laptop for data transmission. The
serial output function of the microcontroller and the
Bluetooth module configurations have to be matched before
data can be transmitted.
G. Microcontroller
PIC18F4520 microcontroller was selected for the
implementation of this prototype. It is a 40 pin 8-bit
processor with 5 set of I/O ports and an built-in Analog to
Digital Converter (ADC) which features high resolution and
quick conversion of analog signals [6]. The 13 channels of
analog inputs for the ADC of PIC18F4520 are more than
sufficient the wireless battery analyzer. Fig. 7 shows the pin
out of the 40-pin PDIP PIC18F4520.
Pin
2
7
8
13
14
25
26
33
34
35
39
40
TABLE II. CONFIGURATION OF PIC18F4520 PORTS
Port
Usage
AN0
Temperature sensor
AN4
Voltage sensor
AN5
Current sensor
RA6
Oscillator
RA7
Oscillator
RC6
Bluetooth
RC7
Bluetooth
RB0
Green LED
RB1
Red LED
RB2
Buzzer
RB6
PICkit3
RB7
PICkit3
Fig. 8 illustrates the microcontroller’s ADC process for
the voltage monitoring circuit. The same flow chart also
applies to other sensing signals, i.e. for sensing current and
temperature.
Figure 7. Pin out diagram of 40-pin PDIP PIC18F4520
H. LEDs
PORTB pins will be used as output by setting TRISB =
0b00000000. Pin 1 to 2 of PORTB pins are used to drive the
LEDs. Logic ‘1’ is set to the designated pins for the LEDs to
light up, e.g. the red LED will light up whenever battery
voltage level drops below 22V or the temperature rises above
40oC.
Start
Starts receiving voltage value
Starts converting voltage value
I. Buzzer
Pin 3 of PORTB is used to activate the buzzer. Logic ‘1’
is set as the output to the pin for buzzer activation. The
buzzer will sound whenever battery voltage level drops
below 22V or the temperature rises above 40oC.
No
Voltage value converted?
Yes
Data store in buffer
III.
SOFTWARE DEVELOPMENT
Transmit data via Bluetooth
For display
This section will discuss the software development
involved in the building of the prototype. The first part will
touch on the C programming on the microcontroller for
analog to digital signal conversion and digital control of
devices. The second part will discuss the development of a
End
Figure 8. Flow chart illustrates the process of analog-to-digital conversion
(ADC) via PIC18F4520 microcontroller
767
Three analog channels (AN0, AN4 & AN5) were
selected for the ADC. Channel 0 (AN0) is used for
temperature sensor, Channel 4 (AN4) is for voltage sensor
while Channel 5 (AN5) is for current sensor. The converted
10-bit binary stream was stored in 2 bytes with long right
justified format.
Fig. 9, 10 & 11 show the C program source code to
perform the analog to digital conversion (ADC) of voltage,
current and temperature sensing signals via PIC18F4520
microcontroller respectively. The ADCON0 register controls
the operation of the A/D module. The ADCON1 configures
the functions of the port pins. The ADCON2 register
configures the A/D clock source, programs acquisition time
and justification [4]. Red LED light will light up and buzzer
will sound whenever battery voltage level drops below 22V
or the ambient temperature rises above 40oC.
Figure 11. C program source code for the analog-to-digital conversion
(ADC) of temperature sensing signal via PIC18F4520 microcontroller
B. Graphical User Interface
A graphical user interface (GUI) was created for the
prototype using Microsoft Visio Studio IDE. The GUI could
be installed on a laptop/PC, and it will be functional as long
as the distance between the wireless battery analyzer and
laptop/PC is within a 20 m range. It will display the values of
sensing voltage, current and temperature as well as status
indication if the battery voltage level has fallen below a
threshold, the current exceeds a certain value, and if the
temperature has risen beyond a set point. In this case, the
battery voltage level will change its indication from
NORMAL to LOW whenever the voltage falls below 22V,
the current’s indication will toggle from NORMAL to HIGH
once it exceeds 5A, and the temperature’s indication will
switch to HIGH from NORMAL once its value crosses over
40oC. Fig. 12 shows the created GUI while Fig. 13 shows the
source codes to create the GUI.
Figure 9. C program source code for the analog-to-digital conversion
(ADC) of voltage sensing signal via PIC18F4520 microcontroller
Figure 10. C program source code for the analog-to-digital conversion
(ADC) of current sensing signal via PIC18F4520 microcontroller
Figure 12. Graphical User Inteface (GUI) created using Microsoft Visio
Studio IDE
768
A. Overall System Circuit Diagram
All the components were integrated and controlled via
PIC18F4520 microcontroller as shown in Fig. 14.
Figure 14. System Integration of Wireless Battery Analyzer
Fig. 15 shows the complete prototype of a wireless
battery analyzer. All hardware devices were soldered
around the PIC18F4520 microcontroller with some its
signals controlled by the microcontroller.
Voltage monitoring circuit
Figure 15. The complete prototype of a wireless battery analyzer
Flow chart as shown in Fig. 16 illustrates the program
progression of the prototype wireless battery analyzer. At the
start of the program when 5V is made available and the
battery supply is connected to the prototype, the prototype
will begins to detect the readings of the battery and sent to
the laptop for display on screen via Bluetooth technology.
The red LED will light up when the detected readings cross
over the pre-determined threshold. The moment the red LED
light up, the buzzer will also sound.
Figure 13. Source codes to create the Graphical User Inteface (GUI)
IV.
INTEGRATION & TESTING
This section will discuss the process steps involved in
integrating the various components of the system, and the
interfacing of software with hardware components. Testing
was carried out to validate the successful integration of the
various hardware devices and the developed source codes.
769
Figure 18. Battery readings appeared in Hyper Terminal
C. Testing of Voltage Monitoring Circuit
For the test, a power supply unit was used to simulate a
24V battery. The voltage readings were obtained from the
voltage monitoring circuit and the value displayed out on
the GUI. Fig. 19 shows the successful testing of the voltage
monitoring circuit.
.
Figure 16. Operational flow chart of Wireless Battery Analyzer
B. Hyper Terminal
A Hyper Terminal session was set up to test the wireless
communication link between the battery analyzer and laptop
/ PC via the Bluetooth module.
This could be done by launching the Bluetooth function
in laptop / PC to connect with the Bluetooth module
incorporated as part of the battery analyzer. A Hyper
Terminal was launched to create a new connection. A COM
port was selected to connect with the Bluetooth module.
Once the COM port has been selected, the correct Baud rate,
Data bits, Parity, Stop bits and Flow Control have to be set as
shown in Fig. 17.
Figure 19. Testing of voltage sensing circuit
D. Testing of Current Sensing Circuit
For the test, a 12 Ω resistor was used as a simulated load
to the prototype. A current of 2A was detected (24V/12Ω =
2A) as shown in Fig. 20 below.
Figure 17. Port setting for Hyper Terminal
After the above settings were done, HyperTerminal was
then ready to communicate with the Bluetooth module. Fig.
18 below shows the battery readings appearing in the
HyperTerminal which indicates a successful set up of the
wireless communication link.
Figure 20. Testing of current sensing circuit
E. Testing of Temperature Monitoring Circuit
Temperature readings were obtained from the LM35
temperature sensor at room temperature 28°C and at 34°C
770
(external heat was introduced by using hands). Fig. 21 shows
the successful testing of the temperature monitoring circuit.
V.
CONCLUSION
A low-cost functional wireless battery analyzer was
successfully built. The process involved in the design and
build of the wireless 24V battery analyzer using Bluetooth
technology was demonstrated in this paper. The analyzer will
be able to sense the lead acid battery’s voltage, current and
ambient temperature, and the microcontroller will process
and send the signals to the laptop/PC via Bluetooth module.
The data will then be displayed on the laptop/PC real time.
With the aid of the wireless battery analyzer for the 24V
backup battery system, submarine crew would be able to
monitor, manage and control the 24 V backup battery system
which is critical for the submarine operation.
ACKNOWLEDGMENT
The authors would like to express gratitude and
appreciation to School of Science & Technology, SIM
University for the provision of budget and support of this
project.
Figure 21. Testing of temperature monitoring circuit
F. Testing of LEDs and Buzzer
The test is to ensure that the LEDs and buzzer are
functioning satisfactory. The green LED will light up when
the power supply is available and there is no fault detected as
shown in Figure 22.
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
Figure 22. The lit-up of Green LED during normal operation with 5 V
power supply
[7]
Once a fault is detected or abnormality occurs, e.g. 0 V
being sensed, the red LED will light up as well as the
activation of the buzzer as shown in Fig. 23.
Figure 23. The lit-up of Red LED and the activation of buzzer when the
battery voltage level drops below 22 V
771
Massoud Pedram and Qing Wu, “Design Considerations for BatteryPowered Electronics,” IEEE 36th Design Automation Conference, pp.
861-866, Jun 1999.
Allegro ACS712 Datasheet, “Fully Integrated, Hall Effect-Based
Linear Current Sensor with 2.1 kVRMS Voltage Isolation and a LowResistance Current Conductor”.
Dariga Meekhun, Vincent Boitier and Jean-Marie Dilhac, “Study of
the ambient temperature effect on the characteristics and the lifetime
of Nickel-Metal Hydride secondary battery,” IEEE Electrical Power
& Energy Conference, 2009.
Texas Instruments LM35 Datasheet, “LM35 Precision Centigrade
Temperature Sensors”.
Roving Networks RN-41-SM / RN-42-SM Datasheet, “Calss 1/Class
2 Bluetooth® Socket Module”.
Microchip PIC18F2420/2520/4420/4520 Datasheet, “28/40/44-Pin
Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt
Technology”.
Microchip PICkitTM 3 Programmer/Debugger User’s Guide.