We propose a methodology for participatory prototyping among people with different non-expert skill sets. Our research focuses on simplifying technology through a frugal approach, co-designing open hardware prototypes, and leveraging the outcomes for further research or product development. Results are tangible objects with basic functionalities. Hardware costs are less than 50 Euros. Furthermore, we suggest a perspective to rate the success of prototyping. Our case study employs adapted trans-disciplinary design science research in Berlin and Barcelona, both of which exhibit a focus on data-driven innovation policies and participatory smart city strategies.