// the setup function runs once when you press reset or power the board

int led=7;
int brightness = 0;
float frequency = 0.5;//Hz
int i=0;
const float pi = 3.141593;
float rad_step=20;

void setup() {
  
  // initialize digital pin "led" as an output.
  pinMode(led, OUTPUT);
  
}

// the loop function runs over and over again forever
void loop() {
  
  analogWrite(led, brightness);   // turn the LED on (HIGH is the voltage level)
  
  // change the brightness sinusoidally for next time through the loop:
  brightness=int(127*sin(i*2*pi/rad_step)+127);//frequency/(2*pi)*

  i=i+1;
  
  delay(1000/frequency/rad_step);                       

}