DIY Arduino calorimeter: Converting commercial thermally insulated coffee-cups into precision isobaric calorimeters

We present the design, construction, and validation of a low-cost digital calorimeter intended for teaching thermochemistry in chemistry, engineering, and life sciences curricula. The device repurposes a commercial 380 mL thermal container with integrated magnetic stirring, transforming it into a closed and well-insulated constant-pressure system suitable for calorimetric experiments. Temperature monitoring is achieved with a waterproof Dallas DS18B20 digital sensor interfaced to an Arduino UNO board, allowing adjustable resolution and automated data acquisition. Open source software provides real time graphical visualization, CSV export, and optional Windows executables for straightforward deployment. Compared to traditional educational calorimeters based on manual thermometry, this device offers improved reproducibility, elimination of reading errors, and enhanced student engagement through live data analysis. In contrast to professional-grade commercial calorimeters (US $15,000-100,000) and basic educational kits (US $50-500 without digital monitoring), our Arduino-based system (∼US $30 in components) provides an accessible middle ground that democratizes laboratory experimentation. Validation experiments, including neutralization and dissolution reactions, confirm reliable thermometric response, stable equilibrium detection, and enthalpy values consistent with literature. This open-hardware calorimeter not only broadens access to thermochemistry education but also serves as a platform for interdisciplinary training in electronics, programming, and laboratory automation, fostering early exposure to modern research practices.