     Serial.println(x);
   }
 
-  if (( x < 1024 ) && (x != OLD_x )) {
+  if (( 1 < x < 1024 ) && ( x != OLD_x )) {
     float calcVoltage = x * (5.0 / 1024.0);
-    dustDensity = 0.17 * calcVoltage - 0.1;
-    OLD_x = x ;
+    if ( (0.17 * calcVoltage - 0.1) > 0 ) {
+       dustDensity = 0.17 * calcVoltage - 0.1;
+       OLD_x = x ;
+    }
     // //    0 ~ 0.5
   }
 

  lcd.setCursor(0, 2);
  lcd.write(2);

  lcd.setCursor(0, 3);
  lcd.write(3);

  lcd.setCursor(8, 2);
  lcd.write(6);


  H  = -1000 ;
  T1 = -1000 ;

    lcd.print(H, 1);   
  }

}


void displaydustDensity()
{
