| 摘要 |
PROBLEM TO BE SOLVED: To measure temperature of a coil with a simple configuration in an acoustic signal converter which converts an electric signal into an acoustic signal by energizing the coil.SOLUTION: An audio signal output from a sound source circuit 14 flows into a coil 16 in a transducer for vibrating a sound board, and an acoustic signal is generated by vibration of the sound board. A prescribed direct current voltage from a constant voltage source circuit 21 is superposed on the audio signal by an adder circuit 23 to flow into the coil 16. A current flowing in the coil 16 is detected by a resistor 25 for current detection, and only a direct current voltage component of a voltage signal at both ends of the resistor 25 is extracted by a low-pass filter circuit 26 and is supplied to a microcomputer 40 by an A/D conversion circuit 27. The microcomputer 40 calculates a value of resistance and temperature of the coil 16 with the use of the direct current voltage component and the prescribed direct current voltage value. |
