After more than half a year of work in my spare time, I have built a complete set of hardware and software system for water quality testing. From the selection of silicon photocell sensors and light sources, PCB layout design, 3D design of appearance and structure, 3D printing and mold opening, to the design of software function logic and UI, the data connection between hardware and software, and finally the actual measurement and calculation of various testing items, it is finally almost completed.