The fuzzy logic controller of a washing machine basically uses two types of input variables. One is concerned with the degree of dirt on the clothes and the second one is concerned with the type of dirt on the clothes
A single optical sensor is used to obtain both these inputs. The level of dirt is determined by the clearness of the water which is used to wash the clothes. On the other hand, the kind of dirt is determined by the time it takes to reach the point of saturation
In other words, if the clothes are very dirty, the transparency of the water will be very low. If they are greasy, the duration of time it will take the change in the transparency of water to reach close to zero will be longer