1. College of William and Mary
Final Project: PHYS 351
ARDUINO BASED IR LED TRACKER
Authors: Dara Kharabi and Jacob McCormick
November 3, 2016

2. 1 Abstract
One of the applications of robotics most present in the public consciousness is that of the
“personal companion,” a robot that acts to serve the needs of its human owners. One of
the fundamental abilities of such a companion robot is that of following its owner around.
Navigating the real world presents a difficult, often non-ideal problem space. Following a
target is a desirable behavior goal because it allows a robot to circumvent many of these dif-
ficulties by following another entity (like a human owner) that already possesses the facilities
necessary for navigation.
To this end, we have designed and implemented a robot capable of detecting, tracking,
and following a pulse-width-modulated infrared signal. Our design uses an array of eight
inexpensive IR receiver sensors to collect data. This data is then processed with an Arduino
Uno microcontroller and used to govern its motion (mediated by two wheels on continuous
rotation servomotors). Our design is highly tolerant to EM noise/interference and can track a
low-power IR LED from up to 14 meters away. With a more powerful IR beacon and suitable
directional lensing apparatus, the system’s tracking range could be increased tenfold or more.
Originally, we planned for the robot to be able to hold and transport loads upward of
50kg, allowing it to assist in household chores and even manned transportation. However,
time and budget constraints led us to design our robot around easily available low-torque
servomotors, constraining these use cases. We do not predict that any additional software-
side challenges will arise from increasing the scale of the robot. In other words, our robot’s
IR tracking system may be used as-is to allow robots that transport supplies or people to
follow human guides in both indoor and outdoor settings.
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3. 2 Executive Summary
For this project, the robot was built around an Arduino Uno microcontroller. The Arduino
Uno board has inputs from an array of 8 sensors located on the upper platform of the 3D
printed chassis. We used a Makerbot Replicator 3D printer to print our chassis to ensure
proper fit of the components and overall durability of the robot. The Arduino is powered
by a battery pack and sends signal to the servos, which drive the wheels. The goal of this
project was to create a robot capable of following an infrared LED light over a relatively
large range with reasonable precision.
Much of the challenge associated with this project was incurred in engineering the physical
aspects of the system. The path of information for the robot remained quite linear. First,
a signal is received by one or more of the sensors on the sensor array. The data collected
by the sensors is then sent to the Arduino Uno microcontroller to be processed. Once the
Arduino Uno has decided the proper course of action, the Arduino sends signals to the Servo
motors to drive the wheels.
The other portion of the project consists of an Arduino that pulses an IR LED at a
frequency that is detectable by the 8 sensor array on the robot. This is the IR LED that the
robot tracks. By moving the LED to specific places, you can then cause the robot to go to
that place. For now, there is just one LED that pulses. However, we can add more LED as
well as code to control which LED is flashing in the future.
Overall, this project was a success because the robot was capable of tracking and moving
toward a pulsing LED. However, there is room for improvement in a variety of ways which
will be discussed later in the report.
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4. 3 Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pg. 4
2. System Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pg.s 5-8
(a) Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pg. 5
(b) Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pg. 6
3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pg. 9
4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pg. 11
5. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pg.s 12-17
(a) Arduino Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pg. 12
(b) Component Pictures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Pg. 16
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5. 4 Introduction
In the modern age, many tasks that were once the responsibility of humans have been
offloaded to machinery. Whether it be by means of a washing machine, dishwater, vacuum
cleaner, etc we can see the value of implementing robotics in every day life. By using robots
to assist people in carrying out their everyday tasks, we can improve our quality of life as
well as improve the efficiency with which we perform these tasks.
One behavior that shows promise as a building block for these helpful machines is fol-
lowing. A robot that follows a target has no need for complicated navigational intelligence
of its own, and can be used in a wide range of beneficial applications.
A robot could follow an individual around their house, carrying useful items such as
laundry or tools in an unobtrusive and hands-free manner. a similar supplies-carrier robot,
fitted with a heavy duty chassis, could assist hikers and infantrymen. Robots that follow a
beam or other hand-held beacon can be used as an alternative to RC robots for situations
where an remote-controlled rover is necessary, such as clearing mines and exploring hazardous
environments.
In this report, we outline the design, construction, and performance of a simple following
robot that identifies an infrared signal and drives toward its source. A guidance system like
the one we built can be used to enable the above range of following robot applications.
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6. 5 System Design
5.1 Hardware
The hardware component of this project is what a majority our time was devoted to.
Though the software aspect certain had its challenges, most of the improvement seen between
the early prototype and finished product came as a result of changes regarding the hardware
used for the robot. There are six main components of interest for our robot. These include
the Arduino Uno board, servos, battery pack, sensor array, 3D printed chassis, and IR
transmitter; each of which will be discussed in some level of detail.
The Arduino Uno board can be considered the brain of the robot. It looks at the data
collected by the sensory pieces on the robot, ie. the sensor array, and makes decisions based
on the data. The Arduino Uno microcontroller also receives power from the battery pack.
The Arduino then regulates this input voltage and supplies a constant 5 Volts to the servo
motors, as well as all of the sensors on the sensor array. The Arduino receives input from 8
input pins; one pin for each IR sensor. The Arduino only outputs two signals; one to each
of the servos to govern their speeds and directions of motion.
The servos that we use for the robot are continuous rotation servo motors. Continuous
rotation simply means that they are not constrained to a 180 or 360 degree range of motion.
This allows the servos to spin the wheels continuously in one direction or the other. The
servos use a 5 Volt signal for their power and accepts a dynamic voltage value that it
interprets as a correspond rotation velocity and direction.
The battery pack supplies a constant 9 Volts to the Arduino Uno microcontroller and
acts as the primary power supply for the robot. The battery pack creates this 9 Volts using
6 1.5 Volt batteries and allows the robot to function without being tethered to a wall outlet,
or other static power source.
The sensor array is comprised of eight infrared sensors TSOP38238 that send data to the
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7. Arduino Uno board. The sensor array is placed slightly above the other components on the
robot, so that each sensor has a clear line of sight. This ensures that the sensor is able to
see whatever infrared light is present. This helps to narrow down the potential causes for a
malfunction of the robot in detecting the infrared signal.
The 3D printed chassis acts to provide structural support for the robot, as well as a
secure fit for all of the components of the robot. The sensor array sits on a raised platform
that is integrated into the chassis. There is a hole for the sensor wires to exit out of. There
is a depression for each of the components that ensures that no components accidentally fall
off of the robot, compromising the function of the robot.
Finally, the IR transmitter is actually independent of the robot itself. The IR transmitter
is composed of another Arduino Uno board powered by a small 9V battery pack. There is
a small circuit that powers an infrared LED, which is given in figure () in the appendix.
The Arduino Uno microcontroller is used to pulse the infrared LED at around 38 kHz, a
frequency that can be detected by the infrared sensors on the robot.
5.2 Software
The software component of this project comprises two programs written in the Arduino
IDE: the code that runs the remote, and the control script for the robot.
The remote’s code is relatively simple: we use the external TimerOne library to generate
a 5V, 38kHz square wave that we then feed into our IR LED assembly. We have to use
TimerOne to generate the square wave, as Arduino’s standard loop function doesn’t iterate
quickly enough to generate the kind of wave we need.
The code that controls the robot works by doing some basic trigonometry to the input
from the 8 IR sensors mounted on the robot to compute an X and a Y coordinate. These
coordinates represent the components of a vector that, ideally, points toward the IR trans-
mitter. The program then runs this information through a bunch of conditional statements
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8. to determine how to direct the robot:
• If the vector points behind the robot, it will turn in place in order to face the trans-
mitter.
• If the vector points in front of the robot, but at an angle, it will move forward while
also turning to face the transmitter head-on.
• If the vector points directly ahead of the robot, it will simply move forward.
Moreover, a number of fail-safes are built in:
• If no IR transmitter is detected, the robot will turn in place, scanning for a IR signal
source.
• If a transmitter is detected, but the signal’s direction is unclear, the robot will move
in a circle in order to establish a clearer signal.
Finally, the code contains functions to linearly interpolate the speed of the two servos.
This is important for three reasons. First, interpolating the control signal sent to the servo
protects it from sudden changes in speed or direction, lengthening the life of the servo. Sec-
ond, interpolation prevents the robot from jerking uncontrollably if it has to turn suddenly,
increasing its turning accuracy. Finally, interpolation has a smoothing effect on the servo
motion: noise in the IR sensor data that would otherwise cause the robot to turn back and
forth in subsequent iterations and reduce accuracy instead cancels out, having a minimal
effect on the robot’s motion.
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9. Figure 1: The control script sums the directional information obtained from each sensor,
yielding a vector that ought to point toward the remote.
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10. 6 Results
The completed robot was tested in a number of different environments. When put a long
hallway with the transmitter pointed directly at it, the robot identified and tracked the signal
from up to 14 meters away. The IR sensors we used for this project have a very large field
of view. While this is undesirable when navigating very close to the signal source, it does
allow the robot to track a signal source inclined above or below it. This means our robot
can handle tracking signals through modest hills and valleys. Using a 38kHz square wave
as our signal, we found no noticeable interference arising from incandescent or fluorescent
light fixtures, ambient radio noise, or even an LCD projector remote control pointed at the
robot. In the event that we had experienced interference issues, these issues could have
been resolved by transmitting and searching for a message conveyed via PWM with a 38kHz
carrier wave.
One problem we experienced was that the sensors’ wide field of view resulted in a loss of
directionality information when the robot was close to the transmitter. We initially tried to
solve this by designing and 3D printing a cap for the sensor array with blinded sectors for each
sensor. While the cap exhibited moderate success at improving the robot’s accuracy at close
ranges, it also limited the robot’s maximum range. Later, when servo signal interpolation
was added to the robot’s software, accuracy at close ranges improved somewhat. Combining
the blinder cap with software interpolation would provide the best accuracy at close ranges,
and would be ideal for applications where long-range tracking isn’t necessary.
Another problem we experienced had to do with our IR transmitter’s light source re-
flecting off of objects in the environment and triggering sensors not directly in line with the
transmitter. Three measures that lessened the effect of this issue were using the blinder cap,
interpolating the servomotor signal, and wrapping electrical tape around the transmitter
LED to collimate the light. We predict that using a stronger and more tightly directed
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11. signal source would go a long way toward mitigating our reflection problems. As it is, the
robot experiences intermittent difficulty tracking in environments with lots of IR-reflective
objects, but seems to eventually navigate to the signal source.
Navigating spaces was unproblematic, except for infrequent occasions where the robot
would drive itself into a corner or other tight spot. In these cases, the robot was often
incapable of extricating itself. A distance sensor and some extra code could help remedy
this scenario.
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12. 7 Conclusion
After testing the robot, we found that the initial goal of having the robot track and follow
an infrared signal was accomplished. There was some issue that arose when the robot was
place in a small area with reflective surface. However, in an area that does not suffer from
these issues, the infrared sensors on the robot were sensitive to infrared light from up to
14 meters away. Moreover, the robot was able to track toward the infrared light in a near
straight manner, very seldom deviating to the point where it could no longer see the infrared
light. Because of this, whenever the robot detected a light, it was most often the case that
the robot would successfully reach the light. For the times that the robot did not successful
reach the infrared light source, it usually ended up in a corner where the light source couldn’t
reach. One issue that occurred frequently was that the field of view got too large as the robot
got very close to the infrared light source. This was because almost all of the sensors were
seeing the light at the same time. When this occurred, the robot had a hard time determining
which direction it needed to go.
For the future of the project, we plan to add distance sensors to the robot so that it can
track along the wall if it loses the light. This ensures that if the robot gets stuck in a corner,
it can find its way back into the open. We also plan on using a stronger light source as well
as multiple light sources and a way to dictate which light is on. This would allow us to give
the robot new information on the fly. We would be able to place the lights at different places
of interest inside of a space so that the robot is able to travel to these different points of
interest. Finally, we plan on scaling up this project to be able to carry heavier loads, perhaps
even its human owners. Overall, the project was a relative success and we have learned a lot
of essential information for future development of the project.
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13. 8 Appendix
8.1 Arduino Code
Code for the robot:
#include <Servo.h>
// Assign pin numbers for servos
const int pinServoL=13;
const int pinServoR=12;
// Assign pin numbers 8 IR sensors
const int pinN=7;
const int pinNE=10;
const int pinE=9;
const int pinSE=6;
const int pinS=2;
const int pinSW=5;
const int pinW=8;
const int pinNW=3;
// Constants that govern servo speed
const int stoppedSpeed = 92;
const int FSpeed = 180;
const int RSpeed = 1;
// Default step size for servo speed smoothing
const int defaultStepSize = 10;
// These are variables that govern smooth servo motion
// Here, we’re declaring them and setting initial values
int speedL = stoppedSpeed;
int speedR = stoppedSpeed;
int goalSpeedL = stoppedSpeed;
int goalSpeedR = stoppedSpeed;
int stepSize = defaultStepSize;
// Declare the two servo motors as Servo objects
Servo servoL;
Servo servoR;
// Convenience functions:
// - park() will stop the robot
// - scanL() will cause the robot to turn in place anticlockwise,
// and is used to scan for an IR signal
// - scanR() behaves similarly to scanL, but has the robot spinning
// clockwise
void park()
{
setServos(stoppedSpeed, stoppedSpeed);
}
void scanL()
{
setServos(RSpeed, FSpeed);
}
12

14. void scanR()
{
setServos(FSpeed, RSpeed);
}
// All calls to change servo speed are routed through this function,
// providing a convenience point to modify servo motion.
void setServos(int l, int r)
{
goalSpeedL = l;
goalSpeedR = r;
}
void updateServos()
{
// Linearly interpolates between actual and goal speed value,
// leading to smoother movement. Set stepSize to 180 to disable.
int diffL = goalSpeedL-speedL;
int diffR = goalSpeedR-speedR;
if (diffL >= 0) speedL += min(diffL, stepSize); else speedL -= max(diffL, stepSize);
if (diffR >= 0) speedR += min(diffR, stepSize); else speedR -= max(diffR, stepSize);
servoL.write(min(max(abs(180-speedL), 1), 180));
servoR.write(min(max(speedR, 1), 180));
// Below is code to print diagnostic information through serial. It can
// be commented out without negatively affecting the robot’s performance.
Serial.print("updated servos: L: ");
Serial.print(goalSpeedL);
Serial.print(" R: ");
Serial.println(goalSpeedR);
}
void setup()
{
// Initialize serial (used only for diagnostic information)
Serial.begin(9600);
// Tell Servo.h which pins the servos are connected to
servoL.attach(pinServoL);
servoR.attach(pinServoR);
// Make double-sure the servos start parked.
setServos(stoppedSpeed, stoppedSpeed);
}
int N = 0;
int NE = 0;
int NW = 0;
int Se = 0;
int SW = 0;
int E = 0;
int W = 0;
int S = 0;
int xcoord = 0;
int ycoord = 0;
void loop()
{
13

15. // Read (and invert) IR sensor values (the sensor outputs 0
// upon detecting the remote)
N = abs(digitalRead(pinN) - 1);
NE = abs(digitalRead(pinNE) - 1);
E = abs(digitalRead(pinE) - 1);
NW = abs(digitalRead(pinNW) - 1);
W = abs(digitalRead(pinW) - 1);
Se = abs(digitalRead(pinSE) - 1);
S = abs(digitalRead(pinS) - 1);
SW = abs(digitalRead(pinSW) - 1);
// Compute X and Y components of a vector representing the
// directional information we have this iteration.
// 10 and 7 correspond to 1 and 1/sqrt(2), respectively.
xcoord = 10*(E-W) + 7*(NE+Se-NW-SW);
ycoord = 10*(N-S) + 7*(NE+NW-Se-SW);
// More diagnostic code
Serial.print(N);
Serial.print(NE);
Serial.print(E);
Serial.print(Se);
Serial.print(S);
Serial.print(SW);
Serial.print(W);
Serial.println(NW);
Serial.print(xcoord);
Serial.print(", ");
Serial.println(ycoord);
// If no signal is detected, keep scanning.
if (N+NE+E+Se+S+SW+W+NW == 0) {
scanL();
} else {
// Do Spyyyder loops if signal is unclear
if (xcoord == 0 && ycoord == 0)
{
setServos(FSpeed, 110);
} else if (ycoord <= 0) {
// If the signal is coming from behind the robot, turn in place
// in the appropriate direction so that it faces the remote
if (xcoord < 0) {
scanL();
} else {
scanR();
}
} else {
// If the signal is coming from in front of the robot, move forward
if (xcoord == 0) {
setServos(FSpeed, FSpeed);
// If necessary, turn slightly while moving to correct direction
// turnFactor is determined via a modified version of theta = atan(y/x)
// the constants 50 and 60 were determined empirically based on the
// characteristics of the S4303R servomotors we used.
} else if (xcoord > 0) {
int turnFactor = int(abs(60*atan(float(xcoord)/(float(ycoord)+.01))));
setServos(FSpeed, max(FSpeed - 50 - turnFactor, 10));
} else {
int turnFactor = int(abs(60*atan(float(xcoord)/(float(ycoord)+.01))));
setServos(max(FSpeed - 50 - turnFactor, 10), FSpeed);
14

16. }
}
}
// Step the servo speeds closer to their goal speeds
updateServos();
// Wait a while.
delay(100);
}
Code for the IR transmitter remote:
#include <TimerOne.h>
void setup() {
// Ready pin 9 for output.
pinMode(9, OUTPUT);
// Initialize Timer1, and set a 26.32 us period.
// This translates to a frequencty of around 38kHz.
Timer1.initialize(26.32);
// setup pwm on pin 9 with a 50% duty cycle.
Timer1.pwm(9, 512);
}
void loop() {
// Nothing needs to happen here.
delay(100);
}
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17. 8.2 Component Pictures
Figure 2: IR Transmitter
Figure 3: Robot, top view
Figure 4: Robot, battery compartment
Figure 5: Robot, angle view
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18. Figure 6: Robot, profile view Figure 7: Robot, rear view
Figure 8: Breadboard and Arduino Figure 9: Robot, sensor tower close-up
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