int ledpin=13,sensorpin=0,minDuration=500,maxDuration=1000;
void setup() {
  pinMode(ledpin, OUTPUT);
}
void loop() {
int rate=analogRead(sensorpin);
rate =map(rate,200,800,minDuration,maxDuration);
digitalWrite(ledpin, HIGH);
delay(rate);
digitalWrite(ledpin, LOW);
delay(rate);
}