Abstract: The present disclosure relates to a sensor assembly (100) for sensing the turbidity of a cleaning medium in a cleaning appliance (190), comprising: a printed circuit board (122) having a substantially planar top surface and a substantially planar bottom surface; a light emitter (112) operably mounted to said printed circuit board (122), configured to emit an electromagnetic signal in a first direction substantially perpendicular to and away from said planar top surface; a light receiver (114) operably mounted to said printed circuit board (122) spaced apart from said light emitter (112) along said substantially planar top surface, configured to receive said electromagnetic signal from a second direction substantially perpendicular to and towards said planar top surface of said printed circuit board (122); and a light guide (150), operably coupleable between said light emitter (112) and said light receiver (114), defining a signal path (116) extending from said light emitter (112) to said light receiver (114)