July 2015 – Page 2 – Killer Robotics

As a software developer I believe it is critical to build reusable code when possible. All software engineers have their toolbox of previously written code that they reuse when the need arises. Keeping this in mind I have built a Class Library, that I continually extend, that contains all the reusable functions that I use across multiple projects. I call this my Core.dll and include it in all the projects I work on.

The project contains multiple classes for a variety of functions, anything from string manipulation to file generation. I will be sharing little code bits from this Core library in the Bite Size C# posts.

Today we will look at my StringExtensions class, which falls in my Core.Extensions namespace.

using System;

namespace Core.Extension
{
    public static class StringExtensions
    {
        public static bool Contains(this string source, string toCheck, StringComparison comp)
        {      
            return source.IndexOf(toCheck, comp) >= 0;
        }

        public static string GetLast(this string source, int tailLength)
        {
            return tailLength >= source.Length ? source : source.Substring(source.Length - tailLength);
        }
    }
}

The Class contains 2 methods:

A Contains function that is similar to the built-in string.Contains method except that it takes a StringComparison parameter so that case sensitivity, culture and sort rules can be configured.

A GetLast method that passes back the requested last bit of a string (for example last 4 characters of a string.)

When this class is included in a project the following operations can be performed:

 private static void Main(string[] args)
        {
            string testString = "This is a test string";
            bool test = testString.Contains("STRING", StringComparison.InvariantCultureIgnoreCase);
                //This will return true as ignore case is set


            string resultString = -testString.GetLast(6);
                //This will return "string", the last 6 characters in the string
        }

This class acts as an extension class to the predefined C# string class, so its methods appear in the class method list exactly like the built-in string method do (such as string.Equals or string.Trim).

Today we will take a detailed look at my Roaming Robot.

Part List:

Sparkfun Magician Chassis (this includes 2 DC motors)
1 x Capacitors 100uF
4 x Resistors 220 Ohm
1 x Micro Servo
Seeed Ultrasonic Sensor
Sharp IR Sensor
2 x Long Arm Trigger Switches
1 x LED (ultra bright white)
1 x Photo-resistor
1 x Arduino Uno R3
1 x Pololu Dual MC33926 Motor Driver Shield

Power supply:

1 x 9V Battery (used to power the 2 DC motors through the motor shield)
4 x AA Batteries in a battery holder (used to power Arduino and PCB\Breadboard)

The Pololu Dual MC33926 Motor Driver Shield plugs into the Arduino female headers and all connectors shown in below diagrams actually plug into the Motor shield and not directly into the Arduino as shown.

The first diagram shows the wiring for the LED, photo-resistor, trigger switches, and the servo:

The two switches shown are actually the 2 long arm trigger switches.

The circuit shown above is very straightforward. However note the capacitor across the servo power terminals. This is to prevent a voltage drop in the circuit caused by the servo starting to move, which draws more current to start moving than when it is already moving.

The below diagram shows how the Seeed Ultrasonic and Sharp IR sensors are wired:

So the Arduino is wired as follows (through the motor driver female headers):

Analog Pins:

A0 – this pin is used by the MC33926 Motor shield
A1 – this pin is used by the MC33926 Motor shield
A2 – Servo
A3
A4 – IR Sensor
A5 – Photo-resistor

Digital Pins:

0
1
2
3 – LED
4 – this pin is used by the MC33926 Motor shield
5 – Ultrasonic Sensor
6 – Right Trigger Switch
7 – this pin is used by the MC33926 Motor shield
8 – this pin is used by the MC33926 Motor shield
9 – this pin is used by the MC33926 Motor shield
10 – this pin is used by the MC33926 Motor shield
11 – Left Trigger Switch
12 – this pin is used by the MC33926 Motor shield
13

The Arduino VDD (5V) and GND pins are used to power the PCB\Breadboard.

The Servo acts as the robots’ neck, it can turn the Ultrasonic Sensor in various directions. The Ultrasonic Sensor is used to detect obstructions, which the robot will then avoid, for obstructions too low for the Ultrasonic Sensor to detect the trigger switches will be pressed and the object can then be avoided. The Photo-resistor is used to detect light level and if it is deemed too dark the LED will turn on. The IR sensor is used to detect drops, so that the robot does not fall down a vertical drop, such as a step.

The two DC motors of the Magician Chassis are connected to the Motor shield, the left motor to the two most left screw terminals on the shield and the right motor to the two most right screw terminals on the shield. The 2 middle screw terminals on the shield are used to power the motors; the 9V battery should be connected to them. (Just note that if one or both of the robots’ motors move in the opposite direction than expected, this can be rectified by switching the 2 motor wires around between the screw terminals they are connected to on the motor shield.)

Here is the code used with the Robot (it is written in C and must be deployed on the Arduino):

#include "DualMC33926MotorShield.h"
#include "Servo.h"

#define IR_PIN A4
#define SERVO_PIN A2
#define PING_PIN 5
#define BUMPER_LEFT_PIN 11
#define BUMPER_RIGHT_PIN 6
#define LDR_PIN A5
#define LED_PIN 3
#define IR_DROP 450 //Distance considered a potential drop
#define MIN_LIGHT 300 //Level of light to turn on LED for light

DualMC33926MotorShield md;
const int M1Speed = 300;
const int M2Speed = 300;
int IRDist = 0;
int bpLeft = 0;
int bpRight = 0;
int LDRValue = 0;
const int dangerThresh = 12;// (in cm) used for obstacle avoidance
int leftDistance, rightDistance; //distances on either side
Servo panMotor; //'neck' servo
long duration; //time it takes to receive PING signal

void setup()
{
pinMode(BUMPER_LEFT_PIN,INPUT);
pinMode(BUMPER_RIGHT_PIN,INPUT);
pinMode(LED_PIN, OUTPUT);
}

void moveStop()
{
md.init();
md.setSpeeds(0,0);
}

void moveForward()
{
md.init();
moveStop();
md.setSpeeds(M1Speed,M2Speed);
delay(250);
}

void turnLeft()
{
md.init();
moveStop();
md.setSpeeds(M1Speed,-M2Speed);
delay(250);
}

void turnRight()
{
md.init();
moveStop();
md.setSpeeds(-M1Speed,M2Speed);
delay(250);
}

void moveBack()
{
md.init();
moveStop();
md.setSpeeds(-M1Speed,-M2Speed);
delay(250);
}

int checkDrop()
{
pinMode(IR_PIN,INPUT);
IRDist = analogRead(IR_PIN);
if(IRDist &lt; IR_DROP)
{
return 1; //Drop present (determined with IR distance sensor)
}
else
{
return 0;
}
}

void lightDarkness()
{
LDRValue = analogRead(LDR_PIN);
if(LDRValue &lt; MIN_LIGHT)
{
digitalWrite(LED_PIN,HIGH); //It is dark, turn on the light
}
else
{
digitalWrite(LED_PIN,LOW);
}
}

int checkLeftBumper()
{
bpLeft = digitalRead(BUMPER_LEFT_PIN);
if(bpLeft == HIGH)
{
//HIT!
return 1;
}
else
{
return 0;
}
}

int checkRightBumper()
{
bpRight = digitalRead(BUMPER_RIGHT_PIN);
if(bpRight == HIGH)
{
//HIT!
return 1;
}
else
{
return 0;
}
}

void compareDistance() {
if (leftDistance&gt;rightDistance) //if left is less obstructed
{
turnLeft();
}
else if (rightDistance&gt;leftDistance) //if right is less obstructed
{
turnRight();
}
else //if they are equally obstructed
{
moveBack();
}
}

long ping()
{
// Send Ping pulse
pinMode(PING_PIN, OUTPUT);
digitalWrite(PING_PIN, LOW);
delayMicroseconds(2);
digitalWrite(PING_PIN, HIGH);
delayMicroseconds(5);
digitalWrite(PING_PIN, LOW);

//Get duration it takes to receive echo of Ping sent
pinMode(PING_PIN, INPUT);
duration = pulseIn(PING_PIN, HIGH);

//Convert duration into distance (cm)
return duration / 29 / 2;
}

void loop()
{
lightDarkness();
if(checkDrop() == 1)
{
moveBack();
compareDistance();
}
else
if(checkLeftBumper() == 1)
{
moveBack();
compareDistance();
}
else if(checkRightBumper() == 1)
{
moveBack();
compareDistance();
}
else
{
moveStop();
int distanceFwd = ping();

if (distanceFwd&gt;dangerThresh) //if path is clear
{
moveForward();
}
else //if path is blocked
{
moveStop();

panMotor.attach(SERVO_PIN);
panMotor.write(20); //look right

delay(250);

rightDistance = ping(); //scan to the right
panMotor.write(160); //look left

delay(600);

leftDistance = ping(); //scan to the left
panMotor.write(90); //look to centre

delay(300);

panMotor.detach();
compareDistance();
}
}
}

Killer Robotics

Adventures in Robotics, Development and Electronics.

Menu

Month: July 2015

Coming Soon!

Bite Size C#

Roaming Robot