Disclosed is a control panel assembly for a washing machine, which provides an improved structure enabling a knob smoothly to rotate without making noise. The invention can be also used for regenerating activated carbon for air-treating devices in other areas. A negative resist is used to define source and drain electrodes which extend over the insulating layer up to the step formed therein adjacent an edge of the gate electrode. This plate has an aperture that is shaped such that it has at least three surfaces of engagement for the free end portion of the supporting elements which are connected to the inside of the upright edge of the display window.