This article presents a methodology for a faster development of observers. On board real-time high frequency measurements are logged and used as inputs to validate an open-loop observer in an offline simulation. It allows embedded implementation constraints to be taken into account as early as possible in the development process. The proposed method facilitates and speeds up the design procedure compared to on-board validation, which often involves trial and error gain tuning. The suggested approach is illustrated through the design of an observer for mechanical sensorless control of Permanant Magnet Synchronous Moteur (PMSM) using an industrial benchmark. The solution is implemented on a low-cost microcontroller, using Rapid Control Prototyping (RCP) on Matlab/Simulink. The overall strategy and logged data are available online under an open-source license.