1. IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE)
e-ISSN: 2278-1676 Volume 4, Issue 4 (Jan. - Feb. 2013), PP 30-37
www.iosrjournals.org
Solar Energy Based Optimal Battery Charging Mechanism in
Robotic Vehicle by Using Smart Host Microcontroller
S.Menakambal1, A.Satheesh2
1
PG Scholar, 2Professor
1
M.E (Embedded System Technologies)
1,2
Department of EEE, Nandha Engineering College, Erode
Abstract: The PENTRON robotic platform-an autonomous unmanned exploration vehicle specialized in
recognition. The robotic vehicle having pack of two rechargeable batteries each performing charging and
discharging operation independently. The two pack of battery charging system can be controlled by means of
tracked single tiltable solar PV panels for improving PENTRON’s power regardless of its mobility. The design
concept of robotic vehicle is based on a PIC16F877 microcontroller and the efficient wireless camera,
temperature sensor, humidity sensor, light sensor, voltage sensors are attached in the robotic vehicle. The Zig-
Bee wireless technology provides adequate information about the environmental conditions in nearby PC. The
aim of this paper is to reduce the weight of the robotic vehicle by means of reducing the usage of
microcontrollers and to increase the power of the robotic vehicle by the help of solar PV Panels. On the other
hand, the switching time taken by two pack of batteries can be reduced.
Keywords: Wireless camera, Li–Po battery, mechatronic system, photovoltaic (PV), robotic vehicle, solar
tracker, Sensors, Zig-Bee transceiver, PIC Microcontroller
I. Introduction
SOLAR power systems in autonomous robotic vehicles have been often used for some years. A real
example is the VANTER robotic platform uses huge number of microcontrollers and 3 solar PV Panels. This in
turn improves weight of the vehicle and power consumption [1]. The main drawback behind existing system is
that the robotic vehicle having four-wheel-drive (4WD) and the individual control of each wheel allow different
types of movement; including Ackerman configuration, the crabbing maneuver or the rotation with inner inertial
centre. The DC motor is fixed in all the four wheels, each wheel consumes 12V supply and 60mA from the
battery. This leads to huge power consumption. Solar tracker prototypes built in mobile robots have proven that
orientation of PV systems leads to increased energy efficiency relative to systems with fixed solar panels (20–
50% per collector)[2]. In Proposed model, the PENTRON robotic exploration vehicle aims to improve various
aspects of the aforementioned rovers with scientific and academic purposes. The rover was developed to be
guided and has 2 wheels coupled to a plane chassis that can rotate independently. The 2-wheel-drive (2WD) is
placed at one end and the tracking ball is placed at the other end for the movement of robotic vehicle. The two
wheels in PENTRON are sustained by means of independent passive suspension of double aluminium fork to
absorb terrain vibrations shown in (see Fig.1).
Each wheel consists of two motors, one for rotation and another for driving. The forward movement is produced
by means of dc motors (12 V and 60 mA) that provides 120r/min with a torque of 8.87 kg/cm. On the other
hand, the rotation motor provides a speed of 152r/min. The reduction huge microcontroller to single
microcontroller and four wheels to two wheels in the proposed model improves the rover capacity and reduces
power consumption. The robotic vehicle having single tiltable Solar PV Panels it can be controlled by means of
solar tracked panels. The robotic system programming is divided into three main code levels and its hardware
was designed with a hierarchical control structure based on modular microcontrollers. The top level program,
carried out in LabVIEW it is executed in a remote PC and offers a Zig-Bee technology to monitor and control
the whole robotic vehicle. The second code level, programmed in C language, runs autonomously on a master
PIC16F877 microcontroller aboard PENTRON.
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2. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
Fig 1: PENTRON: A solar-powered robotic vehicle
II. Proposed System
The PENTRON rover series has a single solar panel system coupled to an assisted suspension
mechanism. This prevents the manipulator arm mounted on the middle of the rover to minimize solar panel-
generated power and allows it to dust solar panel surface.
2.1 Robot terminal unit
The PIC16F877 microcontroller which monitors PENTRON power consumption and decisions in a
complete autonomous way. The microcontroller performs two main functions: 1) detecting environmental light
level and controlling the solar tracking system to obtain the highest power; and 2) interpreting operation data
from batteries and solar panels to control the working mode of the charger accordingly (see Fig. 2).
Fig 2: Block diagram of PENTRON
The robotic vehicle generally uses four different kinds of sensors: They are Temperature sensors, voltage
sensors,Light sensors and Humidity sensors. The sensors that used in a robotic vehicle observes the remote
environmental conditions and the observed data can be measured and simulated by the help of MP LAB
software in nearby PC. The thermistor is the temperature sensitive resistor which is used to measure body
temperature. The thermistor resistor is varied as per the temperature. The varying resistance level is converted
into corresponding voltage signal which is given to ADC through amplifier. The ADC is nothing but analog to
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3. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
digital converter which converts the input analog signal to corresponding digital signal. The converted digital
signal is given to microcontroller. The LM 324 thermistor consist of four independent high gains internal
frequency compensated operational amplifier which were designed specifically to operate from a single power
supply over a wide voltage range. The voltage sensors are generally used for observing the voltage level of the
Li-Po batteries placed inside the robotic vehicle. A photo resistor or LDR is an electronic component whose
resistance decreases with increasing incident light intensity. The light sensors generally observes the intensity of
light that coming from sun. The light sensors attached in the robotic vehicle predicts the environmental light
intensity and sends it to microcontroller. The robotic vehicle uses humidity sensors for observing the moisture
content of the atmosphere. The wireless camera fixed infront of the robotic vehicle captures the image of the
environment and the captured image can be monitored in our nearby PC through Zig-Bee wireless technology
(see Fig.3).
Fig 3: Architecture of Robot terminal unit
2.2 System terminal unit
Zig-Bee is a low-cost, low-power, wireless mesh network standard. The low cost allows the technology
to be widely deployed in wireless control and monitoring applications. The wired serial communication is used
to transfer the data between microcontroller and PC through Zig-Bee communication. PC side is the transmitter
end and Microcontroller is the receiving end. To Interface the micro controller to PC we need level converter
which current TTL compatible voltage level to RS232 voltage level using wireless Zig-Bee. The PC is used to
drive the robot. The robot side captures the image and captured picture is displayed in the PC.
Fig 4: Architecture of System Terminal Unit
The commands send from the PC side is recieved by the Microcontroller as a signals and activates the Driver
Circuit. Driver Circuit consists of Transistor which acts as switch to turn ON and turn OFF the relay. The relay
output is given to motors which are attached in the robot. To drive the robot in the forward direction
corresponding information is transmitted from PC side and received in robot side using Zig-Bee transceiver (see
Fig .4)
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4. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
Fig 5: Mechanical design of the solar tracking system of PENTRON: (a) upper solar panel, (b) mobile
solar panels,(c) aluminium chassis,(d) methacrylate chassis,(e)methacrylate support,(f)pan and tilt
unit,(g)pitch servometer, and(h)yaw servomotor.
Fig. 5. shows the mechanical solar tracking system. This comprises(a) a fixed solar panel mounted horizontally
on PENTRON and (b) Single panels with symmetrical movements. The mechanical structure is mounted on (c)
an aluminium chassis on which the electronics were mounted. On top of this platform (d) a methacrylate panel
with (e) two side supports has been assembled. The solar panel are mounted on (f) pan and tilt units formed
DYS0213MGs metal gear servos. Each pair of digital servomotors allow soft rotations with an amplitude of180◦
in (g) azimuth and (h) elevation, so that the solar panel can be oriented toward any part of the space.
2.3 Li-Po batteries switching operation
The switching system consists of two MAX1538EVKIT selectors with break-before-make operation
logic. Their function is connecting electrically the charge and discharge paths between the batteries, the charger
module, and the load system (see Fig.6) that is, selector 1 is inserted between the charger and the dual-battery
pack. Its function is routing the current from the PV panels to the input of the charger and, from there, to the
battery selected in each moment. Selector 2 is used to connect the selected battery to the load system. Therefore,
the dynamic connections of the electric circuit are carried out according to the PIC16F877-defined logical
operation mode. This is based on the voltage thresholds programmed into the control algorithm. Now, these two
pack of Li-Po batteries performs their charging and discharging operation independently. In the first row,
selector 1 was programmed to charge battery 1 while selector 2 is preset to discharge battery 2. Charge current
obtained from the PV panels is routed to the charger through selector 1 and, from the charger, to the selected
battery. Likewise, the discharge current of battery 2 is routed to the load system through selector 2. The main
advantage of the dual selector system is that it allows hot swapping of separated power supplies. In addition, in
case both batteries were fully discharged, a working mode was programmed in selector 1 to supply the load
system directly from the PV panels.
TABLE I. Logical operation mode of the battery selectors
C= Closed, O= Open, X= Not Connected
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5. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
Fig 6: Overall connection diagram for batteries selectors.
III. Experiment Results
3.1 Measuring parameters
The three parameters like (Temperature, humidity, Battery voltage) are predicted by the sensors
attached in the robotic vehicle and also plot graph depends on parameters. Parameter value received from
microcontroller kit through RS232 port (serial communication) in 9600 baud rate, parity bit is none and data bit
is 8. Proteus7.2 simulation software is used to run and simulate the total process. The software code is written in
MP LAB software with high tech c compiler. The embedded C language is used for program compilation and it
is converted into hex file.
3.1.1 Input Parameter Measuring
Fig 7: Input Parameter Measuring
3.1.2 Waveform of Input Parameters
Fig 8: Characteristics of Temperature
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6. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
Fig 9: Characteristics of Humidity
Fig 10: Characteristics of Battery Voltage
3.1.3 Rotating Direction
The rotating direction of robotic vehicle depends upon the key press from PC (LabVIEW software)
and also we can send the command from pc to microcontroller through RS232 port Key.
TABLE II. Working Principle of Robot Rotating Direction
Key Press Command send LED
from PC to UC Glowing
Forward F 1010
Reverse R 0101
Left L 0110
Right G 1001
Stop S 0000
If the robotic vehicle needs to move in the forward direction corresponding information is transmitted from PC
to microcontroller in the form of signals using Zig-Bee transceiver. In Receiver section, the microcontroller
drives the robot in forward direction as per the appropriate command given by PC. Likewise, the robotic vehicle
can be moved in reverse, left and right direction. The direction of the robotic vehicle can be indicated by LED.
Fig 11: Robot rotating direction
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7. Solar Energy Based Optimal Battery Charging Mechanism in Robotic Vehicle by Using Smart Host Microcontroller
Fig 12: Characteristics of the charge voltage measured in the cells battery
Fig 13: Characteristics of the discharge voltage measured in the cells battery
IV. Conclusion
SOLAR power systems in autonomous robotic vehicles have been often used for some years. In real
example most of the supplied energy is generated by a reduced size photovoltaic (PV) panel. It includes the
construction of a robotic vehicle which we designed is to move robot in forward and reverse with right and left
turns using dual battery. The robot controlling is done with the help of microcontroller which brings the robot on
movement. The proposal includes that the monitoring actions of rover are simulated using LabVIEW software.
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