An electricity generator including a first converter suitable for converting a variation of an energy to be harvested into a corresponding excess of electrical charges. The generator includes a circuit for collecting the excess of electrical charges, the circuit has a first controllable mechanical switch, and a control device for the first switch designed to control the switching of the switch to its closed position when the excess of electrical charges exceeds a first predetermined threshold. The switch is a magnetic switch and the control device comprises a variable magnetic field source which controls the switching of the first switch to its closed position only at the time when the excess of electrical charges exceeds the first predetermined threshold.