| 摘要 |
PURPOSE:To prevent a wire tapping and to extend the utilizable range of a device by respectively driving a first and a second light sources with a first and a second pulses whose phases are opposite each other and setting a range where both signals are duplicated as a receivable range. CONSTITUTION:The pulses P01 and P02 whose phases are opposite by one hundred and eighty degrees are outputted to output terminals P01 and P02 of a pulse conversion circuit 1 and the respective pulses drive the light sources LD1 and LD2. Now, the range where the transmissible range Z1 by the light source LD1 and the transmissible range Z2 by the light source LD2 are duplicated in an optional position is obtained to be set as the receivable range Z3. In the range Z3 the signals P01 and P02 are made to be superposed, for which a pulse P03 whose frequency is two fold frequency of a carrier can be received. Therefore, the pulse P03 is received by adjusting so as to tune to the frequency of the pulse P03 with the inductance of a reception part and the junction capacity of a light receiving element and demodulated to a voice signal in a decoder to drive a head phone. Thus, since the range Z3 can be optionally set, the prevention of the wire tapping and the use in an exhibition, etc., can be possible. |
