Many efforts have been made over the last decade to provide useful simulation tools allowing designers to estimate the power needs of an embedded system. Most of these tools are based on an event driven technique. This way of modeling embedded systems leads to inaccuracies in power estimation. This is especially the case for wireless sensors networks where nodes are running for a long time without changing their activity state, but still consume energy from battery. In this article, we present a new power estimation technique using a fixed-frequency sampling. This technique allows users to improve the accuracy of the power consumption modeling under the OMNeT++ simulator.