sketch

int led = 10;
float frequency = 100;
float timeDelay;


void setup(){
  Serial.begin(9600);
  pinMode(led, OUTPUT);


}

void loop(){
  frequency = Serial.read();
  int frequency;
  map(frequency, 1, 100, 100, 1000);
  Frequency(frequency);
  timeDelay = ((1 / frequency) * 500)*1000;
}
void Frequency(float frequency){
  digitalWrite(led, HIGH);
  delayMicroseconds((int) timeDelay);
  digitalWrite(led, LOW);
  delayMicroseconds((int) timeDelay);



 }