int speedPin=5;
int dir1=4;
int dir2=3;
int mSpeed;
int jPin=A0;
int jVal;

void setup() {
  // put your setup code here, to run once:
pinMode(speedPin,OUTPUT);
pinMode(dir1,OUTPUT);
pinMode(dir2,OUTPUT);
pinMode(jPin,INPUT);

Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
jVal=analogRead(jPin);

Serial.println(jVal);
if (jVal<512){
digitalWrite(dir1,LOW);
digitalWrite(dir2,HIGH);
mSpeed=-255./512.*jVal+255.;
analogWrite(speedPin,mSpeed);
}
if(jVal>=512){
digitalWrite(dir1,HIGH);
digitalWrite(dir2,LOW);
mSpeed=(255./512.)*jVal-255.;
analogWrite(speedPin,mSpeed);
}
}