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A high accuracy sensor module for hydroponic culture system was developed. The module measures water level, temperature, and nutrient concentration values by using a single device equipped with a low-cost ribbon cable and electrodes. The module has two oscillators and the water level and the concentration value are converted into frequencies of the oscillator signals. After the conversion mechanism and adjustment scheme are explained, the high accuracy of the sensor module is demonstrated.
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Nishimura et al. (2016) studied this question.