This is a simple autonomous robot able to detect and avoid obstacles. I use a cheap 4WD robot platform (You can use any of these platforms), an Arduino UNO($18.59 on Amazon), and a cheap HC-SR04 sensor (2 pieces at $2.83 on Amazon).
The robot is programmed to drive forward till an obstacle is detected. Then it turns the sensor left and right. Compare the values returned by the ultrasonic sensor and take a decision.
This is the Arduino code:
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/**
* @file        Arduino UNO Autonomous Robot
* @author      Calin Dragos for intorobotics.com
* @version      V1.0
* @date        13.10.2016
* @description  This is an Arduino sketch for an autonomous robot able to detect and avoid obstacles
*/
#include <AFMotor.h>
#include <Servo.h>
#include <NewPing.h>
Servo myservo;
int ENABLE_A = 6;
int PIN_A1 = 3;
int PIN_A2 = 2;
int ENABLE_B = 11;
int PIN_B1 = 5;
int PIN_B2 = 4;
int SENSOR_DISTANCE;
int LEFT_SENSOR_DISTANCE;
int RIGHT_SENSOR_DISTANCE;
int SNZ_DISTANCE_L;
int SNZ_DISTANCE_R;
int LFT_SNZ_DIS;
int RGT_SNZ_DIS;
#define TRIG_PIN 7
#define ECHO_PIN 8
#define MIN_DISTANCE 40
#define MAX_DISTANCE 200
#define INTERVAL 200
NewPing sonar(TRIG_PIN, ECHO_PIN, MAX_DISTANCE);
 Â
void setup() {
 Â
  Serial.begin(9600);
 Â
  //pin mode for the DC motors
  pinMode (ENABLE_A, OUTPUT);
  pinMode (PIN_A1, OUTPUT);
  pinMode (PIN_A2, OUTPUT);
  pinMode (ENABLE_B, OUTPUT);
  pinMode (PIN_B1, OUTPUT);
  pinMode (PIN_B2, OUTPUT);
  //pin mode for the ultrasonic sensor
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  //for servo motor
  myservo.attach(9);
  //set the ultrasonic sensor to center Â
  sensorCenter();
     Â
  //stop the motors
  stopMotors(); Â
}
void loop() {
   Â
    SENSOR_DISTANCE=sensorDistance();
    Serial.print(“Front sensor distance is: “);
    Serial.println(SENSOR_DISTANCE);
    if(SENSOR_DISTANCE >= MIN_DISTANCE || SENSOR_DISTANCE==0)
      {
      goForward();
      Serial.println(“Go forward”);
        }
      else {
       Â
      //stop the motors
      stopMotors();
      LFT_SNZ_DIS=toTheLeft();
      RGT_SNZ_DIS=toTheRight();
          if(LFT_SNZ_DIS >= MIN_DISTANCE && LFT_SNZ_DIS >= RGT_SNZ_DIS)
          {
            int NEW_SNZ_DIS_LFT;
            //try three times to escape
            for(int i=1;i<=3;i++){
              goLeft();
              Serial.println(“Go left”);
              delay(300);
              //stop the motors
              stopMotors();
              NEW_SNZ_DIS_LFT=sensorDistance();
              if(NEW_SNZ_DIS_LFT >=MIN_DISTANCE)
                  {
                break;
                }
             Â
            }
              sensorCenter();
             Â
          }
            else if(RGT_SNZ_DIS >= MIN_DISTANCE && RGT_SNZ_DIS >= LFT_SNZ_DIS)
            {
            int NEW_SNZ_DIS_RGT;
            //try three times to escape Â
            for(int j=1;j<=3;j++){
              goRight();
              Serial.println(“Go right”);
              delay(300);
              //stop the motors
              stopMotors();
              NEW_SNZ_DIS_RGT=sensorDistance();
              if(NEW_SNZ_DIS_RGT >=MIN_DISTANCE)
                  {
                break;
                }
             Â
            }
              sensorCenter();
          }
        else
            {
              goBackward();
              Serial.println(“Go backward”);
              delay(500);     Â
              //stop the motors
              stopMotors();
              sensorCenter();
            }
      }
}
void stopMotors(){
  analogWrite (ENABLE_A, 0);
  analogWrite (ENABLE_B, 0);
  digitalWrite (PIN_A1, LOW);
  digitalWrite (PIN_A2, LOW);
  digitalWrite (PIN_B1, LOW);
  digitalWrite (PIN_B2, LOW);
  }
int sensorDistance(){
  int distance;
  int uS = sonar.ping();
  distance = uS / US_ROUNDTRIP_CM;
  if(distance !=0){
  return distance;
  delay(300);
    }
  }
void goForward(){
  analogWrite (ENABLE_A, 255);
  digitalWrite (PIN_A1, HIGH);
  digitalWrite (PIN_A2, LOW);
  analogWrite (ENABLE_B, 255);
  digitalWrite (PIN_B1, HIGH);
  digitalWrite (PIN_B2, LOW);
  }
void goBackward(){
  analogWrite (ENABLE_A, 180);
  digitalWrite (PIN_A1, LOW);
  digitalWrite (PIN_A2, HIGH);
  analogWrite (ENABLE_B, 180);
  digitalWrite (PIN_B1, LOW);
  digitalWrite (PIN_B2, HIGH);
  }
void goLeft(){
  analogWrite (ENABLE_A, 180);
  digitalWrite (PIN_A1, HIGH);
  digitalWrite (PIN_A2, LOW);
  analogWrite (ENABLE_B, 180);
  digitalWrite (PIN_B1, LOW);
  digitalWrite (PIN_B2, HIGH);
}
void goRight(){
  analogWrite (ENABLE_A, 180);
  digitalWrite (PIN_A1, LOW);
  digitalWrite (PIN_A2, HIGH);
  analogWrite (ENABLE_B, 180);
  digitalWrite (PIN_B1, HIGH);
  digitalWrite (PIN_B2, LOW);
}
void sensorCenter(){
  myservo.write(90);
  delay(500);
}
void turnSensorLeft(){
  myservo.write(120);
  delay(500);
}
void turnSensorRight(){
  myservo.write(60);
  delay(500);
}
int leftSensorDistance(){
    int LEFT_SENSOR_DISTANCE;
    LEFT_SENSOR_DISTANCE=sensorDistance();
    return LEFT_SENSOR_DISTANCE;
  }
int rightSensorDistance(){
    int RIGHT_SENSOR_DISTANCE;
    RIGHT_SENSOR_DISTANCE=sensorDistance();
    return RIGHT_SENSOR_DISTANCE;
  }
   Â
int toTheLeft(){
    int LEFT_SENSOR_DISTANCE;
    turnSensorLeft();
    LEFT_SENSOR_DISTANCE=leftSensorDistance();
    Serial.print(“Left sensor distance is: “);
    Serial.println(LEFT_SENSOR_DISTANCE);
    return LEFT_SENSOR_DISTANCE;
}Â Â
int toTheRight(){
    int RIGHT_SENSOR_DISTANCE;
    turnSensorRight();
    RIGHT_SENSOR_DISTANCE=rightSensorDistance();
    Serial.print(“Right sensor distance is: “);
    Serial.println(RIGHT_SENSOR_DISTANCE);
    return RIGHT_SENSOR_DISTANCE;
}Â Â
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And this is how the robot navigates autonomously in my kitchen:
