About multi-level LEDs driving in visible light communication

In museums exhibits and works are presented in a variety of ways to visitors. There is a method using a visible light communications which superimposes information to a spotlight illuminating the exhibits. The visible light communication transmits and receives signal by blinking of the light. In addition, the spotlight has been using the LED as the element. LED is suitable for visible light communication because it can blink very fast. In this paper, we focus on the duct rail that the spotlight is connected. Usually a duct rail is used for power supply of the spotlight. And we can use the duct rail not as the power supply but control of LEDs. In this method, when multi-spotlights are connected to certain duct rail, all of them are connected in parallel. So they have the same flash pattern, and can only send the same information. Here we pay attention to a negative voltage. By using a negative voltage on the control line, we can control two kinds of spotlight. We propose a method for distributing two kinds of information from the duct rail using both a positive voltage and a negative voltage. But when signals output both a positive voltage and a negative voltage at the same time, they are added and their voltage becomes 0. Here we use the carrier which is consisted of a lot of fast square waves. In addition, when signal is consisted of only a negative voltage, we should use a carrier to output a 0V and -5V in turn. We use the diode to extract the voltage of the positive and negative. Instead of using a lot of electric parts, we have to set the only diode on the circuit board. In this proposed method, the LEDs on the duct rail have different flash patterns according to each voltage and they can send different information.