int i = 0;                      //int for analog value
                        bool up = true;                 //bool as switch
                        
                        void setup() {
                            pinMode(A3, OUTPUT);        //speaker pin as output
                        }
                        
                        void loop() {
                            if(up){                     
                            i++;                        //raise the value
                            }else{
                            i--;                        //lower the value
                            }
                            if(i >= 255){
                            up = false;                 //flip switch if value is too high
                            }
                            if(i <=0){
                            up = true;                  //flip switch if value is too low
                            }
                            analogWrite(A3, i);         //write value to speaker pin
                        }