Beacon Locating Robot – Powered by Arduino and IR Transceiver by Christopher Hazlett
After I built my first Arduino-based robot, I wanted to graduate to a little more advanced behavior, and I had it my mind to make a robot that would find a home base via an IR Beacon. Plus I saw that Pololu had the perfect parts for the job, the IR Beacon Transceiver pair. My wife was gracious enough to get me some IR distance sensors, a servo and the transceivers for my birthday in August. If she keeps supporting my hobbies like this, she'll have more robots than she can handle. As always, I'll start with the parts.
The Parts
I, of course, re-used parts from my last robot, but I'll include the links here as well. My robots are nothing if not a source of parts for the next robot.
- Arduino (1 @ $30.00 from Adafruit.com) - I actually got the Arduino Starter kit from Adafruit.com which also came with the 9V battery holder you see in the pictures and videos below.
- Arduino Motor Shield (1 @ $19.50 from Adafruit.com) - I used the motor shield again in this project because I only needed access to the six analog pins for the sensors on the Arduino and it's just so darn easy to use.
- RP5 Tracked Chassis (1 @ 49.95 from Pololu.com) - This chassis has proven to be very versatile and big enough to support a wide array of sensors.
- IR Beacon Transceiver Pair (1 @ 49.95 from Pololu.com) - Fantastic kit from Pololu.com (my favorite store for all things robotic. This acts as the core of the robot's sensors.
- Sharp GP2Y0A02YK0F Analog Distance Sensor 20-150cm (1 @ 13.95 from Pololu.com) - Pretty much your standard IR distance sensor from Sharp.
- GWS PICO Sub-Micro Servo (1 @ 15.95 from Pololu.com) - Great little servo. There's not much more to it than that.
- Pololu RP5 Expansion Plate RRC07A (Narrow) Solid Black (1 @ 6.95 from Pololu.com) - Pololu.com just recently started offering this gem and makes changing and building a robot on the RP5 chassis a little more like geek nirvana than it was before.
- Pololu RP5 Expansion Plate RRC07B (Wide) Solid Black (1 @ 11.95 from Pololu.com) - The bottom plate on the robot.
- Aluminium Standoffs (2 @ 1.95 from Pololu.com) - Little posts...nothing more, nothing less.
- Tamiya 70164 Universal Metal Joint Parts (2 @ 3.90 from Pololu.com) - These are great construction pieces to have lying around. I didn't actually use both kits, but I have two and I know I used scews and nuts from both.
I also used various crimped and un-crimped wires lying around that I use regularly, but that's a separate post.
The Robot
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It's a pretty simple concept, place a home base somewhere and then have the robot find said home base from it's current location and make it's way there. When I first started thinking about how to execute this project, I thought it was going to be much more complicated to institute the seeking behavior I was looking for. The IR transceivers from Pololu.com were much better than I thought they'd be and had a lot of power. As you can see in the video below, the beacons are powerful enough to work around corners, so I never ended up putting a seeking algorithm in place. The beacon took care of that for me. All I had to do was make sure it avoided walls on its way to the home base. To accomplish that, I put the servo and Sharp distance sensor on the front and performed a sweep with the sensor and read the values from analog input 0. That's the bare bones of the robot.
The Home Base

For the home base, I took one of the transceivers and raised it to the height of the robot's head. This ended up being unnecessary. The robot would find the beacon if it was at any level. The home base didn't have to do anything, so I just powered it up and let it run.
The Code
There are a couple of gotchas when writing the code. Because the IR transceivers are always reading, I had to do a comparison of each reading to determine which of the directional sensors was the highest. You can't just read the input as an on or off. The second and harder portion of the code (and actually the most fun) was determining which direction to make the robot move. At first, I just let the robot move after determining which direction was currently being read from the beacon. In practice, this seems completely fine, but you'll see in the videos that the beacon itself changes directions quite frequently. This made the robot indecisive. To combat this problem, I figure out the Mode of the readings. Essentially, I took the last ten readings and counted what the most prevalent direction was. This smoothed out the robot's behavior and it behaved as expected.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 | #include <Servo.h> #include <AFMotor.h> #define TOPSPEED 200 // SERVO SCANNING VARIABLES // Servo myservo; // create servo object to control a servo int servoPosition = 0; // variable to store the servo position const int SERVO_PIN = 10; int floorState = 0; long frontReading = 0; boolean scanIncrement = true; //increase position? byte servoIncrementValue = 6; byte servoDecrementValue = 6; // MOTOR VARIABLES // AF_DCMotor rightMotor(4, MOTOR12_8KHZ); AF_DCMotor leftMotor(3, MOTOR12_8KHZ); // TRANSCEIVER VARIABLES // int notFoundSensitivity = 500; int west = 0; int south = 0; int east = 0; int north = 0; int dir = 0; boolean detected = false; // TRANSCEIVER DIRECTION MODE VARIABLES // const int NUM_READINGS = 10; int directionReadings[NUM_READINGS]; int modeOfDirections = 1; int index = 0; void setup() { Serial.begin(38400); myservo.attach(SERVO_PIN); // attaches the servo on pin 9 to the servo object myservo.write(0); rightMotor.setSpeed(200); leftMotor.setSpeed(200); delay(1500); } void loop() { scan(); move(); } void move() { if(servoPosition >= 0 && servoPosition <= 84 && frontReading > 550){ //Object on the left turnLeft(); }else if((servoPosition >= 85 && servoPosition <= 105) && frontReading > 600){ // Object in Front turnAround(); }else if((servoPosition >= 106 && servoPosition <= 180) && frontReading > 550){ // Object on the Right turnRight(); }else{ moveTowardBeacon(); } } void moveTowardBeacon() { readTransceiverandSetDirection(); if(modeOfDirections == 3 || modeOfDirections == 4){ //South or West turnRight(); } else if(modeOfDirections == 2) { // East turnLeft(); } else if(modeOfDirections == 1){ //North moveForward(); } } void scan() { scanIncrement ? servoPosition+=servoIncrementValue : servoPosition-=servoDecrementValue; //increment or decrement current position if (servoPosition >= 180){ scanIncrement = false; servoPosition = 180; } else if (servoPosition <= 1){ scanIncrement = true; servoPosition = 1; } frontReading = measureFront(); //Serial.print(servoPosition); //Serial.print("|"); //Serial.print(frontReading); //Serial.print(";"); myservo.write(servoPosition); delay(15); } long measureFront() { return analogRead(0); } void moveForward(){ Serial.println("Move Forward"); rightMotor.run(FORWARD); leftMotor.run(FORWARD); } void speedUp(){ for (int i=0; i==TOPSPEED; i++) { rightMotor.setSpeed(i); leftMotor.setSpeed(i); } } void slowToStop(){ for (int i=TOPSPEED; i==0; i--) { rightMotor.setSpeed(i); leftMotor.setSpeed(i); } rightMotor.run(RELEASE); leftMotor.run(RELEASE); } void turnLeft(){ Serial.println("Turn Left"); rightMotor.run(BACKWARD); leftMotor.run(FORWARD); } void turnRight(){ Serial.println("Turn Right"); rightMotor.run(FORWARD); leftMotor.run(BACKWARD); } void stop(){ Serial.println("Stop"); rightMotor.run(RELEASE); leftMotor.run(RELEASE); delay(500); } void turnAround(){ stop(); delay(500); moveBackward(); delay(300); turnLeft(); delay(300); stop(); //runAway = true; } void moveBackward(){ Serial.println("Move Backward"); rightMotor.run(RELEASE); leftMotor.run(RELEASE); rightMotor.run(BACKWARD); leftMotor.run(BACKWARD); } // BEACON LOGIC // void readTransceiverandSetDirection(){ west = analogRead(2); south = analogRead(3); east = analogRead(4); north = analogRead(5); getDirection(); setModeOfDirections(); } boolean foundBeacon(){ if(west < notFoundSensitivity and east < notFoundSensitivity and south < notFoundSensitivity and north < notFoundSensitivity){ return false; }else{ return true; } } void getDirection(){ int minValue = 1200; if(minValue > west){ minValue = west; dir = 4; } if(minValue > south){ minValue = south; dir = 3; } if(minValue > east){ minValue = east; dir = 2; } if(minValue > north){ minValue = north; dir = 1; } addDirectionToReadings(); //Serial.print("W:"); //Serial.print(west); //Serial.print(" | S:"); //Serial.print(south); //Serial.print(" | E:"); //Serial.print(east); //Serial.print(" | N:"); //Serial.println(north); //Serial.println("================================="); //if(dir == 1){ // Serial.println("North"); //}else if(dir == 2){ // Serial.println("East"); //}else if(dir == 3){ // Serial.println("South"); //}else if(dir == 4){ // Serial.println("West"); //} } void addDirectionToReadings(){ directionReadings[index] = dir; index = (index + 1); if (index >= NUM_READINGS) // if we're at the end of the array... index = 0; } // ========================================= // In order to smooth out the directions readings from the // IR transceiver, You have to take the mode (most prevalent number in a collection) // of the directionReadings Array. This allows the program to determine which // direction is being read the most from the device. // Otherwise, the readings make the robot squirrelly. // ======================================== void setModeOfDirections(){ int currentValue = directionReadings[0]; int counter = 1; int maxCounter = 1; int modeValue = modeOfDirections; int directionCounts[4] = {0,0,0,0}; //{North(1), East(2), South(3), West(4)} for (int i = 1; i < NUM_READINGS; ++i){ Serial.print(directionReadings[i]); Serial.print("|"); ++directionCounts[directionReadings[i]-1]; } //Determine mode of directions from count array Serial.println(""); int modeCount[2] = {1,directionCounts[0]}; //This array holds the current maximum count and the direction it points to. for(int i = 0; i < 4; ++i){ //Serial.print(directionCounts[i]); //Serial.print("|"); if(modeCount[1] >= directionCounts[i]){ modeCount[0] = i + 1; // set direction modeCount[1] = directionCounts[i]; //set count } } modeOfDirections = modeCount[0]; Serial.println(""); Serial.print("Direction Mode: "); Serial.println(modeOfDirections); } |
There you have it. Let me know if you have any questions about the code or construction.
- Chris