Attiny85_PWM

//------------------------------------------------------------------------------
// ATTINY85 Fast PWM
//
//------------------------------------------------------------------------------
//
// PWM a transistor to control a motor
//
//------------------------------------------------------------------------------

#include <avr/io.h>

// Global Variables
uint32_t previousMillis = 0;
uint16_t interval = 100;
uint16_t potVal = 0;
uint16_t duty = 0;

//------------------------------------------------------------------------------
// SET UP SET UP SET UP SET UP SET UP SET UP SET UP SET UP SET UP SET UP
//------------------------------------------------------------------------------
void setup() {

  DDRB = 0b00010000;  // Leave A1 as input, set PB4 as output
  PORTB = 0b00000000;

//  PORTB = 0b00010000;  // Set PB4 HIGH
//  delay(500);
//  PORTB = 0b00000000;

  TCCR1 = TCCR1 & 0b11111001 | 0x01;  // Adjust Timer1 Prescaler

}

//------------------------------------------------------------------------------
// LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP LOOP
//------------------------------------------------------------------------------
void loop() {

  if (millis() - previousMillis >= interval) {

    previousMillis = millis();

    potVal = analogRead(A1);
    duty = map(potVal, 0, 1023, 0, 255);
    analogWrite(4, duty);

  }

}

// -----------------------------------------------------------------------------