JP2865627B

An apparatus for accurately transmitting and receiving acoustic waves indoors is provided. The apparatus contains a microphone, a speaker, a processing circuit, a first amplifier, a second amplifier, and a power control circuit. The microphone converts an input acoustic wave into an electric signal, and the speaker generates an output acoustic wave based on input data. The processing circuit processes the electric signal to produce processed data and outputs the input data to drive the speaker. The first amplifier receives a power signal and detects if a starting signal is contained in the electric signal output from the speaker. Then, the amplifier outputs a first detection signal when the starting signal is detected and outputs the power signal when the first detection signal is output. The second amplifier receives the power signal from the first amplifier and detects if a non-starting signal is contained in the electric signal when the starting signal is detected. The amplifier outputs a second detection signal when the non-starting signal is detected. The power control circuit supplies the power signal to the processing circuit when the first and second detection signals have a predetermined relationship. Furthermore, methods for accurately detecting data contained in the input acoustic wave are also provided.