int motorPin = 7;

byte speed=0;
byte speedup=1;


unsigned long currentMillis = 0;

unsigned long motor_prev_millis = 0;
unsigned long motor_period = 30; 




void motor_speed () {
  if(currentMillis - motor_prev_millis >=motor_period){
    motor_prev_millis=currentMillis;
    analogWrite(motorPin,speed);
    speed += speedup;

}
 
}


void setup() {
  
  pinMode(motorPin, OUTPUT);

  Serial.begin(9600);
}

void loop() {
  currentMillis=millis();
  motor_speed();
Serial.println(speed);
}