DSpay is my high-school thesis on a digital payment system at school. I studied the existing system and possible alternatives, set requirements for a new system, and conducted research through interviews and surveys. I then designed and implemented a functional prototype with a Node.js + PostgreSQL web server/interface and an ESP8266-based demo payment terminal programmed in C++.
Though this system was never adopted, the thesis did received a grade of 90%. You can download it here (in dutch).