A concentration auto-detecting device for cyanobacteria is developed based on fluorescent characteristic wavelength of phycocyanin. AT89 C52 microcontroller unit（ MCU） is used as the core control device and the concentration detecting device is designed by an unique mechanical structure and optical structure. The fluorescence intensity of phycocyanin is converted into electrical signal by photoelectric sensor under the light source of specific wavelength

and the regression model between cyanobacteria concentration and voltage signal is established. The experimental results show that there is a good linear correlation between the measured voltage and the concentration of cyanobacteria. The device has the characteristics of low cost

simple and convenient

as well as high accuracy.