int currentValue;
int desiredValue;

void setup() {

 pinMode(6, OUTPUT);

 Serial.begin(9600);
 Serial.println("BEGIN");
 Serial.println();

}

void loop() {

 desiredValue = map(analogRead(A3), 0, 1023, 0, 255);

 if (currentValue < desiredValue) {
 analogWrite(6, currentValue);
 currentValue ++;
 }
 else {
 analogWrite(6, desiredValue);
 currentValue = desiredValue;
 }
 
 Serial.println(currentValue);
}