# Building the HUB-ee Buggy

## This Tutorial is Retired!

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Contributors: Nick Poole

## Basic Object Avoidance

The HUB-ee Buggy is almost ready to go, but right now it doesn't have any way of avoiding obstacles. We need to tell it what to do when it encounters a wall or other large object. There are a lot of really clever ways to do this, and you can make the code as complicated as you want. In this case, though, we'll keep it basic. The HUB-ee Buggy will keep an eye out for obstacles and turn around when it gets too close to one. This will be achieved by reversing one of the wheels for a few milliseconds.

Plug the Redboard into your computer, and load up this Arduino code:

``````language:c

// Define the pins to make the code more readable

// Our Sharp IR sensor is connected to A4
#define sharpIR A4

// Our left HUB-ee is connected to D6, D7 and D8
#define leftPWM 6
#define leftIN1 7
#define leftIN2 8

// Our right HUB-ee is connected to D9, D10 and D11
#define rightPWM 9
#define rightIN1 10
#define rightIN2 11

// This is the threshold for how close an object will
// be allowed to get before the HUB-ee Buggy changes
// its direction of travel. You may need to adjust it.
int tooClose = 200;

// This stores the value read from the Sharp IR sensor
int irVal = 0;

void setup() {

// Set the infrared sensor as an input. This isn't
// strictly necessary because the ADC is an input
// by default but it's good practice.
pinMode(sharpIR, INPUT);

// Set all of the outputs accordingly
pinMode(leftPWM, OUTPUT);
pinMode(leftIN1, OUTPUT);
pinMode(leftIN2, OUTPUT);

pinMode(rightPWM, OUTPUT);
pinMode(rightIN1, OUTPUT);
pinMode(rightIN2, OUTPUT);

}

void loop() {

// Read the initial value of A4 (or whatever sharpIR is defined as):

// The Buggy will execute the code inside the 'while' brackets
// as long as the IR sensor input isn't higher than the
// 'tooClose' value

// This original statement compared the pin number (0) to 'tooClose,'
// always returning true. This causes the buggy to spin in circles
// while(sharpIR<tooClose){
// -------------------------------------------------------------------
// Instead, we should compare the value read from A4 to 'tooClose.'
// Also, the Sharp IR module specified in the bill of materials
// reads higher as the distance closes, so we should be watching for
// when the value on A4 is greater than, not less than, 'tooClose.'
// This works:
while(irVal > tooClose) {

// The wheel direction pins are set according to the
// HUB-ee datasheet and the speed output is set to
// 200, pretty quick.
digitalWrite(leftIN1, HIGH);
digitalWrite(leftIN2, LOW);
analogWrite(leftPWM, 200);

// The wheel direction pins are set opposite on
// the right wheel because it needs to turn the
// same direction as the left and its mirrored.
digitalWrite(rightIN1, LOW);
digitalWrite(rightIN2, HIGH);
analogWrite(rightPWM, 200);

// IMPORTANT:
// It is crucially important that you do not change the direction
// of the HUB-ee wheels too rapidly. I learned this \$55 lesson
// the hard way.
// Let's put in a delay, otherwise we're reading from
// A4 as fast as this while loop can execute
delay(100);

// Read the value of the Sharp IR sensor

}

// When the IR sensor detects a close object, the code
// outside the brackets above will execute. In this
// case, we're reversing one of the wheels to make
// the Buggy turn. We'll run it this way for half a
// second (500 milliseconds) before returning to
// normal mode.
digitalWrite(leftIN1, LOW);
digitalWrite(leftIN2, HIGH);
delay(500);
}
``````

Note: It's best to give the wheels a small delay before switching directions. Doing so too quickly may result in damaging the wheels.

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