In the design of mobile electronics, power is one of the most difficult restrictions to overcome; and current trends indicate this will continue to be an issue in the future. Consumer electronic equipments are becoming small, portable devices that provide users with a wide range of functionality, from communication to music playing. The battery technology and the power consumption of the device limit the size, weight and autonomous lifetime. One promising alternative to batteries is to use parasitic energy dissipated in the movement of the wearer of device to power it. In this paper we designed a system included a rotary arm extending down from the sole, which ultimately drove the small electrical generator through a stepped-up gearbox. A one- way clutch mechanism was used to transmit torque to the gearbox. This allowed for additional spin following the initial impact of a step, also preventing lockup due to rotary inertia in the gears. The entire generator system was designed to fit in the heel of a standard running shoe, with the rotary arm compressing once during each heel strike.