Designs of a free-space white-LED mass-storage transceiver for SD-card file transfer
Two visible-light mass-storage prototypes have been constructed. They enable file transfers between the SD (Secure Digital) memory card and the PC via white-LED light. The entire system consists of a pair of identical white-LED transceivers: one is connected to the PC, whereas the other is connected to the SD-card subcircuit. File transfer operation is able to execute at 19200 bps. Prototype 1 is based on pulse-position modulation (PPM), while Prototype 2 is based on pulse-width modulation (PWM). It was found that the PPM design consumes less power and is more stable. Full-speed (12 Mbps) USB 2.0 VLC transceiver designs for slave and host devices are also included.