The energy consumption in Wireless Sensor Networks (WSNs) stills a very interesting challenge in both the industrial and the research field. The IEEE 802.15.4 standard is an excellent result of the collaboration between these both fields in order to well managing the energy consumed in the node by controlling its duty cycle. It presents the most efficient standards for low energy consumption that is why it is considered as the main technology for the Internet of Thing (IoT). Our work consists mainly of validating through an experimental testbed the two methods proposed. The first approach proposed is about computing the energy consumed by the node in its different transmission states with more efficiency. Although, the second approach deals with computing its most convenable duty cycle basing on the remaining energy in the battery of the node which presents a very interesting issue for the energy consumption in wireless communication.