#include <avr/io.h>
#include <avr/interrupt.h>

// Define pin numbers
#define POT_PIN 2    // Analog input pin for potentiometer
#define PWM_PIN 1    // PWM output pin

void setup() {
  // Set PWM pin as output
  pinMode(PWM_PIN, OUTPUT);
  
  // Enable ADC and set prescaler to 64 (125kHz)
  ADCSRA |= (1 << ADEN) | (1 << ADPS2) | (1 << ADPS1);
  
  // Set ADC reference voltage to AVCC
  ADMUX |= (1 << REFS0);
  
  // Enable global interrupts
  sei();
  
  // Start ADC conversion
  ADCSRA |= (1 << ADSC);
}

void loop() {
  // No need for anything in the loop, the PWM value is updated by interrupts
}

// ADC conversion complete interrupt
ISR(ADC_vect) {
  // Read ADC value
  uint16_t adcValue = ADC;
  
  // Map ADC value (0-1023) to PWM range (0-255)
  uint8_t pwmValue = map(adcValue, 0, 1023, 0, 255);
  
  // Set PWM duty cycle
  analogWrite(PWM_PIN, pwmValue);
  
  // Start next ADC conversion
  ADCSRA |= (1 << ADSC);
}