A VLC receiving devise using audio jacks with a folding noise

In recent years, LEDs (light emitting diode) are in widespread use as a light emitting element with power-saving and faster response speed. In connection with it, VLCs (visible light communications) attracts attention. VLC is a communication method that a light source such as the LED which illuminates space is changed quickly and data is transmitted by changing brightness. The feature is that users can identify the communication range visually. It is expected to use general mobile devices as the receiver, because of the commercial use of communication system. However, the camera mounted on the mobile device cannot use as the VLC receiver because the response is slow. Although how to connect a receiving module can be considered, the mobile device such as a smart phone has few common ports for external connection. Accordingly, it is not easy to use a mobile device as a receiver for VLC. We focus on the audio jacks equipped with many mobile devices and propose constructing VLC system for mobile devices as an input device to solve the above-mentioned problem. It is necessary to consider not only the transmission characteristic of VLC but also audio jacks. As a modulation method, we compose FSK (frequency shift keying) and PWM (pulse width modulation) used for VLC and infrared transmission, respectively. FSK has the feature that transmitted electric power and a throughput are constant. PWM is simple and has the feature which can make the ripple ingredient of output voltage small. Hence, we consider that if both are applied to the visible light communications using audio jacks, FSK excels PWM because there is little error in A-D conversion. In order to show this feature, we measure the energy per bit to noise power spectral density ratio and the bit error rate. The result of our experiment clearly shows that to use audio jacks is applicable to this VLC system. The modulation method finds that it is appropriate to use FSK rather than PWM. The PWM signal that the duty rate is not one to one is affected by the folding noise.