Wireless sensor networks could be widely used in a large variety of applications such as smart cities, structural health monitoring. However, their large scale deployment is limited by the lifetime of the nodes. A joint optimization of both hardware and software is a promising solution to decrease the overall consumption. To achieve such an optimization, it is necessary to finely understand the consumption of each components of the node in conjunction with the software (state of the node). An experimental platform has been designed to monitor the energy consumption, and is used to better model this consumption. A focus is done on the interest of saving data on SD cards before sending via the radio.