Batteryless optical wireless audio receiver uses 1-bit ∑Δ-modulated visible light and spherical Si solar cells

Spherical Si solar cells (diameter: 1 mm) with a reflector cup (diameter: 2.2 mm) were used with 1-bit ∑Δ-modulated illumination from white LEDs to provide optical wireless digital-sound transmission. The solar cells have a high directivity with regard to incident light, thus largely eliminating the environmental noise from fluorescent lighting. To verify the effectiveness of our optical, wireless digital sound transmission scheme, we fabricated an experimental system consisting of a transmitter and a receiver. The transmitter contains a battery-operated lamp with 50 white LEDs and a 1-bit ∑Δ modulator that controls the current to the lamp. The receiver consists of a spherical-solar-cell module and an earphone. In the experiment, the transmitter produced a 1-kHz analog signal at an illumination of 70 1x that traveled over a distance of 50 cm. The measured output spectrum of the receiver showed that it recreated a sinusoidal waveform with little distortion. Even under fluorescent lighting with an illumination of 200 1x, the measured spectrum showed that a sinusoidal waveform with a signal-to-peak-noise ratio of 25 dB was obtained.