An electrically stimulated electrode system comprises injection and return electrodes and a power supply for causing electrical current to flow through a subterranean formation. An electronic system for the injection electrode includes: a power harvester extracting electrical power from current flowing in the injection electrode, a control for the injection electrode current, a sensor of the injection electrode and/or formation, or a telemetry for the injection electrode and/or formation, or any combination thereof. A sensor comprises: a pair of spaced apart electrodes, a power conversion device connected to the spaced apart electrodes for providing electrical power, and a processor providing a representation of a current. The electronic system may include: a power harvester, a commandable and/or programmable current control; and a control system for commanding and/or programming the current control, whereby the current flowing in the injection electrodes may be independently controlled and/or sequenced in time.