const int pwm = 2 ; //initializing pin 2 as pwm
const int in_1 = 8 ;
const int in_2 = 9 ;
char myCol[20];
void setup() {
   Serial.begin (115200);
   pinMode(pwm,OUTPUT) ; //we have to set PWM pin as output
   pinMode(in_1,OUTPUT) ; //Logic pins are also set as output
   pinMode(in_2,OUTPUT) ;
}
void loop() {
  int lf = 10;
  if (Serial.available() > 0) {
  Serial.readBytesUntil(lf, myCol, 1);
    if(strcmp(myCol,"o") == 0){
        digitalWrite(in_1,HIGH) ;
        digitalWrite(in_2,LOW) ;
        analogWrite(pwm,255) ;
    }
    else if(strcmp(myCol,"a") == 0){
        digitalWrite(in_1,LOW) ;
        digitalWrite(in_2,HIGH) ;
    }
    else if(strcmp(myCol,"b") == 0)
    {
      digitalWrite(in_1,LOW) ;
      digitalWrite(in_2,LOW) ;
    }
  }
}