In places where water contains higher concentration of dissolved minerals is considered to be hard ware. It does not affect human health, but teapots, washing machines and dishwashers suffer from calcification. To avoid this problem, there are water softeners used where special salt is used to soften water. Of course this salt also dissolves and needs to be refilled time to time. David always forget to refill the tank because there is no visual indicator of it. So what you don’t see – you don’t care. To avoid future conflicts with his wife, he decided to add visual indicator to water softener.
On front panel he mounted LED bar graph where salt level is displayed. Also he added photocell to detect room light. It simply detect if someone is in the room or passes by by dropping a shadow. Other time bar graph is turned off. This hopefully prolongs life of LEDs and saves a bit of electricity. Another part is measuring salt level. Since salt is hard material, he used Sharp GP2D12 Infrared Distance sensor. It is able to measure distance from salt from 10cm to 80cm.