const int voltsInPin = A3;
const int ledPin = 9;

void setup() {
  pinMode(ledPin, OUTPUT);
}
void loop() {
  int rawReading = analogRead(voltsInPin);
  int period = map(rawReading, 0, 1023, 100, 500);
  digitalWrite(ledPin, HIGH);
  delay(period);
  digitalWrite(ledPin, LOW);
  delay(period);
}