---

    int potPin = 2;    // select the input pin for the potentiometer
    int ledPin = 11;  // note onlly 5,6, 9,10,11 are PWM
    int wait = 0;      // variable to store the value coming from the sensor


    void setup() {
  //  Serial.begin(9600);
      pinMode(ledPin, OUTPUT);  // declare the ledPin as an OUTPUT
    }

    void loop() {
      wait = analogRead(potPin) - 28; // read the value from the sensor
      if(wait > 950){
        digitalWrite(ledPin, LOW);
      }else{
        digitalWrite(ledPin, HIGH); // turn the ledPin on
        delayMicroseconds(1023 - wait); // stop the program for some time
        digitalWrite(ledPin, LOW); // turn the ledPin off
        delayMicroseconds( wait); // stop the program for some time
      }
  //  Serial.println( wait );
    }

---

---

/*
Timer/Counter2 PWM mode = 3
Counting sequence : WGM21& WGM20 in TCCR2

Compare Output mode , Fast PWM mode.
COM21 = 1; COM20 = 0 ( non-inverting mode )

TCNT2 inc or dec
OCR2 compare with Timer/Counter
when TCNT2 == OCR2
PWM output == OC2 ( PD2 ???), will go low until counter reach MAX.
Clock source == CS22:0

Frequency = Fclk/( N.256)
== 16 x 2^20 /( 8 * 256)
== 2^24 / ( 2^3 * 3^8 )
== 2^13 == 8K cycles
*/
#include <avr/io.h>
#include <avr/interrupt.h>

int OCR2APin = 11;
int analogpin = 0;
int dutyCycle = 0;

#define bit_on(BYTE, BIT)  BYTE |= 1 << BIT;

void setup() {
  pinMode ( analogpin, INPUT);
  pinMode ( OCR2APin, OUTPUT);
  // set dutycycle == 50
  OCR2A = 128 ;

  // SET PRESCALE == 8 page 119 ( 16M / 8/ 256) == 7812 ( frequency  )
  TCCR2B &= 0xF0 ; // preserve 4 msb bits
  TCCR2B |= _BV(CS21) ;  //prescale = 8
 
  // SET MODE 3 ( waveform Generation, fast pwm ) page 117
  bit_on ( TCCR2A, WGM21) ;
  bit_on ( TCCR2A, WGM20) ;
 
  // SET COMPARE OUTPUT, FAST PWM MODE ( PAGE 118)
  // CLEAR OC2 ON COMPARE MATCH, non-inverting mode
  bit_on( TCCR2A, COM2A1); 
 
  // TIMER/COUNTER INTERRUPT MASK REGISTER (TIMSK)
  // SET OUTPUT COMPARE MATCH
  bit_on ( TIMSK2, OCIE2A) ;

  // START FAST PWM MODE
  bit_on( SREG, SREG_I);
}

void loop() {
;
}

ISR( TIMER2_COMPA_vect) {
  int analog = analogRead( analogpin)/4;
  OCR2A = analog ;
}

---