Abstract: A piezoelectric speaker according to one aspect of the present disclosure includes: a plurality of piezoelectric elements; a plurality of diaphragms vibrated by expansion/contraction of the plurality of piezoelectric elements, the plurality of diaphragms each having a rectangular principal surface; and a cover that has a box shape and is arranged to cover one surface of the principal surface of each of the diaphragms, the cover being arranged so that an air chamber is formed between the cover and the one surface of the principal surface of each of the diaphragms, in which the lengths of the long sides of the principal surfaces of the plurality of diaphragms are different from one another, and the cover includes an opening formed on one of surfaces of the cover perpendicular to the principal surface of each of the diaphragms.

Abstract: A secondary battery charging system includes a secondary battery charging device and a power generation device that generates a charging current. The secondary battery charging device controls the charging a secondary battery, which has a protection timer that counts a first elapsed time from a start of charging. The secondary battery charging device includes a charging switch that controls a supply of the charging current, a time management timer portion that counts a second elapsed time starting from a point at which the charging switch becomes conductive and performs a charging stop determination and that counts a third elapsed time starting from a point at which the charging switch is cut off and performs a charging start determination, and a charging control portion that causes the charging switch to be conductive or cut off based on results of the charging stop determination and the charging start determination.

Abstract: A secondary battery charging system includes a secondary battery charging device and a power generation device that generates a charging current. The secondary battery charging device controls the charging a secondary battery, which has a protection timer that counts a first elapsed time from a start of charging. The secondary battery charging device includes a charging switch that controls a supply of the charging current, a time management timer portion that counts a second elapsed time starting from a point at which the charging switch becomes conductive and performs a charging stop determination and that counts a third elapsed time starting from a point at which the charging switch is cut off and performs a charging start determination, and a charging control portion that causes the charging switch to be conductive or cut off based on results of the charging stop determination and the charging start determination.

Abstract: The tuning device also includes an input unit for inputting a sound of an instrument to be tuned or a musical sound signal, a conversion information storing portion in which a plurality of pieces of information on filters for tuning are stored, a control unit for extracting the piece of information on an arbitrary one of the filters from the conversion information storing portion, and a conversion unit for converting a signal of the input unit into a signal of an arbitrary frequency band in response to a signal from the control unit. Owing to this structure, even if ambient noise has mixed with a sound of the instrument to be tuned, the sound is filtered into a signal component of a target scale or a target pitch name. By extracting a pitch from this signal component, the number of erroneous tuning operations can be reduced.

Abstract: The tuning device also includes an input unit for inputting a sound of an instrument to be tuned or a musical sound signal, a conversion information storing portion in which a plurality of pieces of information on filters for tuning are stored, a control unit for extracting the piece of information on an arbitrary one of the filters from the conversion information storing portion, and a conversion unit for converting a signal of the input unit into a signal of an arbitrary frequency band in response to a signal from the control unit. Owing to this structure, even if ambient noise has mixed with a sound of the instrument to be tuned, the sound is filtered into a signal component of a target scale or a target pitch name. By extracting a pitch from this signal component, the number of erroneous tuning operations can be reduced.

Abstract: A tuning apparatus comprises a piezoelectric element provided on a tuner case, and a mounting member which enable the tuning apparatus to be mounted on a musical instrument to be tuned. The piezoelectric element converts vibration provided by the musical instrument through the tuner case into an electric signal, and outputs the electric signal to a pitch calculation circuit. The tuning apparatus prevents the detection error due to a harmonic component having a larger amplitude than that of fundamental wave component by making the resonance frequency of the tuner case lower than the frequency of the lowest note of the musical instrument to be tuned.