conversion of distance detected by sensor to a count value

have a hc sr04 sensor coupled with arduino..the sensor detects distance(analog value)..now how to convert into a digital value or a count so that it can drive a vibration motor!!?

not quite sure how far you are, but you just need a loop of reading the value and then map it to 0 to 255. write the value(0 -255) to the PWM pin:

//send a trigger signal
  digitalWrite(trig, HIGH);
  delayMicroseconds(10);
  digitalWrite(trig, LOW);
  //receive the trigger signal echo, and calculate cm to the object
  dist= pulseIn(echo, HIGH);
  dist= dist/58; //converts raw to cm, valueSensor/74/2 = inches

VibVal = map(dist, 0 80,0,255);

analogWrite(PWMpin, VibVal);

it also depends on how you are driving the vibrator.