In one general aspect, various embodiments are directed to a surgical instrument that can supply mechanical energy and electrical energy to an end effector of the surgical instrument. The surgical instrument may be operated in a first operating mode in which a transducer of the surgical instrument produces mechanical energy, or vibrations, that are transmitted to the end effector and a second operating mode in which electrical energy, or current, can flow through the end effector to perform electrosurgery. In another general aspect, the surgical instrument may comprise a clamp, or jaw, which can be moved into a closed position to hold tissue against a waveguide, or blade, of the end effector. In the second operating mode of the surgical instrument, current can flow from a power source, through the waveguide, and return to the power source through a path comprising the jaw.In one general aspect, various embodiments are directed to an ultrasonic surgical instrument that comprises a handpiece housing that operably supports an electrical contact assembly therein that is in electrical communication with a signal source. An acoustic assembly is supported within the handpiece housing in rotatable contact with the electrical contact assembly. In various embodiments, the signal source produces at least one of an ultrasonic signal and a radio frequency signal.In one general aspect, various embodiments are directed to a surgical instrument that can supply mechanical energy and electrical energy to an end effector of the surgical instrument. The surgical instrument comprises an ultrasonic generator module coupled to an ultrasonic drive system, which comprises an ultrasonic transducer coupled to a waveguide and an end effector coupled to the waveguide. The ultrasonic drive system is configured to resonate mechanically at a resonant frequency to generate a first ultrasonic drive signal. An electronic circuit is coupled to the ultrasonic generator module to monitor an electrical c
