Pulse width modulated visible light communication using digital micro-mirror device projector for voice information guidance system

Visible light communication (VLC) is producing many useful and unique applications using the light emitting diode lights as transmitters. In the VLC, there are two major receiver types; a photodiode detector and an image sensor. The photodiode is simple and has high response time but is limited to a short distance communication. On the other hands, the image sensor has high spatial resolution, but its low frame rate and heavy image processing task are obstacles to realize a high speed and spatial-modulated VLC. In our previous works, as one of the solutions, we experimentally showed that a digital micro-mirror device (DMD) projector as a transmitter could be used as a fine-grained VLC position detection illumination system with millimeter accuracy using the receiver with Raspberry Pi to demodulate the signals. In this paper, we propose the pulse width modulated VLC (PWM-VLC) using the DMD projector for the voice information guidance system to realize the VLC without a microcomputer, and report its fundamental experiments. Our proposed system uses very simple receiver consisting of analog electric circuits driven by dry batteries for amplification and digital-to-analog conversion, so it does not need a complicated signal processing process with the microcomputer. The experiments showed that the system can transmit four different waves which are sine, square, triangular and sawtooth waves to each different direction at the same time using the PWM-VLC technique. In the future, if a higher-speed DMD projector is available, it will allow users to receive the voice information guidance depending on their position precisely using the simple receiver and the DMD projector.