float t = 0;
float f = 100; //frecuencia
float p = 1/f; //periodo
unsigned long oldMicros = 0;
unsigned long nowMicros = 0;
 
const byte PRESCALER2 = 0b001;
 
void setup() {
  Serial.begin(115200);
  //ajusta la frec. salida PWM pin 3
  TCCR2B = (TCCR2B & 0b11111000) | PRESCALER2;
  pinMode(3, OUTPUT);
}
 
double dt = 0;
double tf = 0;
double signal = 0;
 
void loop() {
  nowMicros = micros();
  dt = double(nowMicros - oldMicros)/1000000;
   
  t += dt;
  tf = t*f;
  //Distintas señales a elegir
  //signal = tf; //dientes de sierra
  //signal = (sin(tf*2*PI)+1)/2 ; //seno  
 //signal = sin(tf*PI); //seno positiva
 signal = (sin(tf*2*PI) > 0) ? 1: 0; //cuadrada
  //signal = (sin(tf*2*PI) >= 0) ? 2*tf: 2-(2*tf); //triangular
   
  byte value = byte(255 * signal);
  analog(value);
 
  oldMicros = nowMicros;
   
  //cuando alcanza un periodo se reinicia
  if(t >= p){ 
    t = 0;
  }
}
 
//compensa el desajuste de la salida analogica
void analog(byte value){
  value += (255 - value) >> 4; 
  analogWrite(3, value); 
  Serial.print(value);
  
}