The Turbidity sensor detects water quality by measuring the level of turbidity. This sensor module is composed of an Infrared emitting diode and a matched photo transistor mounted in a plastic shell closure.

Infrared light is used to measure the turbidity level, it is able to detect suspended particles in water by measuring the light transmittance and scattering rate which changes with the amount of total suspended solids in water, the more turbid the water is, the less light will passed through. At the detector (photo transistor) end, the amount of light received will be converted into the corresponding current. If there is more light passing through, the corresponding current will be larger; if there is less light passing through, the corresponding current will be smaller. Therefore the turbidity of water can be defined by measuring the corresponding output current of the photo transistor.