I will show you how can you make a Wall Fallowing Car With PID.

Step 1: PARTS

Here is a list of parts that i used to make this project:

Arduino UNO
4*DC Motor and Whell
2*HC-SR04 Ultrasonic Sensor
L298 Motor Driver
2* Breadboard
On/Off Switch
Jumper Wires

Step 2: SCHEMA

I use adaptor and LM2596 voltaj regulator instead of battaries because i couldn't afford it.Don't wory about wire which you will see in the video.

Step 3: CODE

The code has explanations of code functions. You will easly understand it. If you have a problem , you can contact me.

//SATDELIASLAN //
const int ln1=9;                  //define L298 motor pins
const int ln2=8;
const int ln3=6;
const int ln4=7;
const int enA=10;                 //define L298 enable pins
const int enB=5;                  //!enable pins have to connect with arduino's PWM pins!
const int trigpin=A3;             //define left HC-SR04 pins
const int echopin=A4;
const int trigpin2=A1;            //define front HC-SR04 pins
const int echopin2=A2;
int distance1;                    //define distance and time
int time1;
int distance2;
int time2;
int redLed=4;                    //define leds
int greenLed=2;
void setup() {
  pinMode(ln1,OUTPUT);            //all motor pins output
  pinMode(ln2,OUTPUT);
  pinMode(ln3,OUTPUT);
  pinMode(ln4,OUTPUT);
  
  pinMode(enA,OUTPUT);
  pinMode(enB,OUTPUT);
  pinMode(trigpin,OUTPUT);       //trigpin is output because it sends sound wave
  pinMode(echopin, INPUT);       //echopin is ınput because it receives sound wave 
  pinMode(trigpin2,OUTPUT);
  pinMode(echopin2,INPUT);
  pinMode(redLed,OUTPUT);
  pinMode(greenLed,OUTPUT);
  Serial.begin(9600);
}
void loop() {
  //FOR MEASURE THE DISTANCE
  digitalWrite(trigpin,LOW);      //first, we start trigpin low 
  delay(45);
  digitalWrite(trigpin,HIGH);     //second, we open trigpin and send sound made
  delay(45);
  digitalWrite(trigpin,LOW);      //then, we close again for other loop
  time1 = pulseIn(echopin,HIGH);  //then, we open echopin and receive sound made and
                                  //we measure the time with pulseIn() function.
  distance1 = time1/(2*29.1);     ////finally, we measure the distance between wall and the robot 
  digitalWrite(trigpin2,LOW);
  delay(45);
  digitalWrite(trigpin2,HIGH);
  delay(45);
  digitalWrite(trigpin2,LOW);
  time2 = pulseIn(echopin2,HIGH);
  distance2 = time2/(2*29.1);
    //FOR LEDs
   int baseDistant=17;
   
   if(distance1 >= (baseDistant-1) && distance1 <= (baseDistant + 1) ){
     digitalWrite(redLed,HIGH);digitalWrite(greenLed,LOW);
   }
   else if(distance1>(baseDistant + 1)){
     digitalWrite(greenLed,HIGH); digitalWrite(redLed,LOW);
   }
   else{
     digitalWrite(redLed,LOW);digitalWrite(greenLed,LOW);
   }
   //FOR PID
float error;
float lastError=0;
float integral=0;
float motorSpeed;
float rightMotorSpeed;
float leftMotorSpeed;
float rightBaseSpeed = 90;      
float leftBaseSpeed  = 100;
float kp = 6.5;  //kp,ki,kd values should be chance for better result
float ki = 2.4;
float kd = 1;
  
  error = distance1 - baseDistant; 
  integral +=error; 
  motorSpeed = (kp*error) + (kd*(error - lastError)) + (ki*integral);
  lastError = error;
    rightMotorSpeed =rightBaseSpeed + motorSpeed/2;
    leftMotorSpeed  =leftBaseSpeed  - motorSpeed/2;
    //to avoid high speed
    if(rightMotorSpeed > 150){
      rightMotorSpeed = 150;
    }
    if(rightMotorSpeed <0){
      rightMotorSpeed =0;
    }
    if(leftMotorSpeed > 150){
      leftMotorSpeed = 150;
    }
    if(leftMotorSpeed < 0 ){
      leftMotorSpeed = 0;
    }
    
    digitalWrite(ln1,HIGH);
    digitalWrite(ln2,LOW);
    analogWrite(enA,rightMotorSpeed);
    digitalWrite(ln3,HIGH);
    digitalWrite(ln4,LOW);
    analogWrite(enB,leftMotorSpeed);
     
    if(distance2 < 20){     //if front distance smaller than 20cm 
       //TURN RIGHT 
      digitalWrite(ln1,LOW);
      digitalWrite(ln2,HIGH);
      analogWrite(enA,250);
      digitalWrite(ln3,HIGH);
      digitalWrite(ln4,LOW);
      analogWrite(enB,250);
    }
}