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Photovore
(November 2011)
Allen J. Bell, Stephen R. Taylor, and William E. Abell, ELEC5530, Group 12
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Abstract—This paper describes the theory, design, and
assembly of an autonomous robot. Its purpose is to detect and
move toward the greatest light source.
IV. HARDWARE
The goal of this assembly is to create an autonomous light
seeking robot. With the aid of photo cells on each of the
robot’s faces, the robot will be able to detect the direction with
the greatest light source. Under these parameters the robot
will be able to operate under a wide array of environmental
lighting.
The greatest obstacle in this project was to take a digital
output from the microcontroller and use it as a mechanical
switch to allow voltage to form across the DC motors. Our
solution was to use a MOSFET "switch". With a 10k ohm
resistor from gate to ground, a voltage can be held from an
input signal such as the digital output from our
microcontroller. The dc motor can then be attached to the
drain of the MOSFET in parallel with a flyback diode. Lastly
a 57 ohm resistor is placed in series to keep the voltage across
the motor at the desired of 3 volts.
II. THEORY OF OPERATION
V. SOFTWARE
I.
INTRODUCTION
The photo cells act as a variable resistor whose resistance is
dependent on the amount of light incident on its "face". Under
dark conditions the resistance reaches 1M Ohms but falls to
approximately 10k Ohms under light conditions. By adding a
10k Ohm resistor in series the voltage can be read using an
analog input on an Arduino Development Board. Because the
photo cell acts as a variable resistor the voltage across the 10k
Ohm resistor becomes a function of the amount of light
incident on the area.
This robot has four cell circuits, one on each side. The
robot then reads the voltage values across the 10k Ohm
resistor. The microprocessor then performs an analog to
digital conversions and saves each value to memory. Once
data has been taken the program can then compare and
perform tasks under these conditions.
III. SCHEMATIC
One of the most critical aspects to this design is the analog
to digital conversion. The choice of an Arduino was made
with this concept in mind. The Arduino software and
programming language makes analog to digital conversions
simple. The board is able to take a voltage value from 0 to 5
volts and map it as a value in the range of 0 to 1023.
The Arduino software is based on C/C++ language and
provides new users a common ground on which to begin.
Much like C/C++ control structures can be created and used
such as 'if' loops. After the microcontroller obtains analog
values from each photo cell circuit, the variables containing
each digital conversion are compared via 'if' statements within
a method that constantly loops.
Because we wanted our robot to always move forward, the
'if' statements' conditions were always made with respect to
the northern photo cell's value. These means there had to be
four conditions for the greatest light source location: north,
south, east, or west. The analog reading with the lowest value
indicates the greatest light source.
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If the northern value is greatest, both motors should
be allowed to rotate.
If the southern value is greatest, the right motor is
allowed to rotate while the left motor is not until the
northern photocell becomes the highest value.
If the eastern value is greatest, the right motor is
allowed to rotate while the left motor is not until the
northern photocell becomes the highest value.
If the western value is greatest, the left motor is
allowed to rotate while the right motor is not until the
northern photo cell becomes the highest value.
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VI. OBSERVATIONS
Originally one 9 volt battery was applied to a +5 volt
regulator and used to power the Arduino board. The amount of
current needed to power two dc motors was too much under a
previous design. The amount of current from the regulator
would suffice for one motor so as an adjustment a second
power supply and regulator were added.
REFERENCES
[1]
[2]
[3]
Roland Siegwart, Illah R. Nourbakhsh, and Davide Scaramuzza,
Introduction to Autonomous Mobile Robots(Book Style). Cambridge,
Massachusetts: The MIT Press, 2004, pp.77-82.
Richard C. Jaeger and Travis N. Blalock, Microelectronic Circuit
Design (Book Style). New York, New York: McGraw Hill, 2008, pp.
275 - 341.
Arduino Language Reference, ANSI Standard 2011. Available:
http://arduino.cc/en/Reference/HomePage