CODE :-  

int A=3;

int B=5;

int C=9;

int D=10;

int Speed=100;

String Command;

void setup() {

  // put your setup code here, to run once:

pinMode(A,OUTPUT);

pinMode(B,OUTPUT);

pinMode(C,OUTPUT);

pinMode(D,OUTPUT);

Serial.begin(9600);

}


void loop() {

  // put your main code here, to run repeatedly:


while (Serial.available()==0) {

  

}

Command=Serial.readString();

Serial.println(Command);

if (Command=="forward") {

 analogWrite(A,Speed);

analogWrite(B,LOW);

analogWrite(C,LOW);

analogWrite(D,Speed);

}

if (Command=="stop") {

 analogWrite(A,LOW);

analogWrite(B,LOW);

analogWrite(C,LOW);

analogWrite(D,LOW);

}

if (Command=="backward") {

 analogWrite(A,LOW);

analogWrite(B,Speed);

analogWrite(C,Speed);

digitalWrite(D,LOW);

}

if (Command=="right") {

 analogWrite(A,LOW);

analogWrite(B,LOW);

analogWrite(C,LOW);

analogWrite(D,Speed);

}

if (Command=="left") {

 analogWrite(A,Speed);

analogWrite(B,LOW);

analogWrite(C,LOW);

analogWrite(D,LOW);

}

}