A simple optical audio signal transmitting system using Maximum Length Sequence

In the previous paper, we reported a communication method of audio signal using LED or laser diode. However the interference occurs easily in the receiver side when multiple transmitters exist. In this paper, we propose a new modulation technique which does not produce interference. In this method, the random number signal is generated using Maximum Length Sequence (MLS) by a microcomputer. An audio signal and random number are compared. If the audio signal is larger than the random number, a square wave of AM broadcasting modulates a optical source. If the audio signal is smaller than the random number, the optical source is turned on and off alternately. We change the period of the random number signal and examine the characteristic and the effectiveness of this method by some experiments.