In this paper a literature study is carried out to show there is still a tangible gap in terms of what can be achieved from scavenging energy. Indeed, in the framework of energetically autonomous microsystems, we review different existing methods of producing a sufficient amount of energy (at micro Watt level) that eventually need to be stored in a secondary source of power such as a battery or super-capacitor, since an enduring that is a sustainable system must be ensured. In order to minimise the gap mentioned above, the proposed solution that is an energy harvester to focus our own investigations on is described: it is based on a piezoelectric structure using bridge/road vibrations to supply LEDs (electro luminescent diodes with a typical power requirement of a few mW) that can be utilised for traffic regulation lights for example.