This document explains the design process and methods of a pH sensor and data logger. It shows how taking advantage of the unique spectral properties of a polymeric membrane, a circuit can be conceived to measure the acidity of a solution within a specific pH range. It also goes through the testing of said circuit and its embedding into an already built CO2 monitoring device, as well as a basic programming code to make it work properly. The project focuses on finding out whether this pH monitoring technique can be used as a cheaper alternative to classic methods, making use of already existing tools and the artificially synthetized membrane. It eventually proves as a high potential instrument for pH sensing, with large scope for improvement at an inexpensive cost, thus making it highly useful for unmanned environmental monitoring processes.