A CMOS Algae Growth Period Monitor for Algaculture Applications

In this work, a complementary metal–oxide–semiconductor (CMOS) algae growth period monitor is newly investigated for algaculture applications. The proposed monitor includes an algae sensor and a CMOS converter. The proposed monitor can transform the algae growth period into a duty cycle linearly. Through the duty cycle of the proposed CMOS converter, the algae growth status could be easily and quickly obtained. In addition, in order to be adaptively utilized in different kinds of algae growth environments, the proposed CMOS converter has a wide differential rail-to-rail voltage to the current converter and the adjustment sensitivity circuits. The measured wide-range differential rail-to-rail voltage of the CMOS converter was from −1.5 to 1.5 V, and the range of output duty cycle corresponded from 1.04% to 99.3%. The sensitivities could be varied to 41.21%/V, 32.8%/V, 27.38%/V, and 23.5%/V, respectively. The measured range of algae growth period was 1 to 5.5 days, and the range of output duty cycle was 24.96%–90.19% under different concentrations of algae nutrients (0.6 ‰, 0.8 ‰, and 1 ‰). A 0.49% of the measured maximum linear error was obtained. Lastly, two types of algae (Nannochloropsis sp. and Isochrysis galbana) were experimented. Convinced by the measurements and experiments, the proposed CMOS algae growth period monitor had correct functionalities for algaculture applications.