A battery charger for an electronic device receives current limited power from an external power source, such as a Universal Serial Bus power interface. The printer includes at least one smart material sensor enclosed in the printer enclosure that monitors for the presence of a contaminant above a selected threshold. The second panel includes a second plate facing the first plate via a discharge space, a plurality of first barrier ribs provided on the second plate, and a dent part opened to a side of the first plate. Where a plurality of the second signal output portions is included, the second signals are sampled in succession. Each electrode has a rod portion and a base end portion.