| 摘要 |
PROBLEM TO BE SOLVED: To surely detect a tap unit with simple circuit constitution by changing time until a next single signal is generated in accordance with delay time, until the single signal is acquired by the tap unit, is sent and is demodulated by a receiver. SOLUTION: When a switch 11 of a single signal generator 10 is temporarily turned on, a single signal is generated from a loudspeaker 2 as sound and is inputted to the input terminal (b) of a delay time detector 4. A single acoustic signal is transmitted by a tap unit 8, is received/demodulated by a reception antenna 5 and a reception/demodulation circuit 1 and is inputted to the input terminal (a) of the delay time detector 4. Delay time data is transmitted to a timing generator 9. The timing generator 9 generates the next single signal in the single signal generator 10, after time which is 99 times as much as delay time passes. When the loudspeaker 2 is moved and a distance 1 becomes short, delay time also becomes short, and time until the next single signal is generated also becomes short.
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