Publication

Abstract : Low-power optical communication is an attractive substitute for radio frequency (RF) links in RF-sensitive areas and energy-constrained environments. Power consumption by the transmitting light-emitting diodes (LED) is a hurdle in achieving low-power operation. Retroreflective modulators modulate the incident light and send the same light back, eliminating the need for a transmitting LED. In this work, a low-cost, low-power retroreflective optical sensor node with a liquid crystal 9 (LC) shutter placed in front of a prismatic retroreflective tape is designed and experimentally characterized. A custom-designed microcontroller board based on the ATmega328 is developed, which achieves an 81% reduction in current consumption compared with standard Arduino Uno boards by eliminating nonessential peripherals. Through changing distances and angular misalignments, reliable optical data transmission is demonstrated experimentally. Open eyes are seen in eye-diagram analysis at the half-angle of 30 deg up to 1.1 m and at 40 deg up to 0.7 m. Code division multiple access chips were demodulated successfully up to ±30 deg at 1.1 m, which equals a 60 deg field-of-view when no carrier modulation is used. The dominance of diffused and retroreflected light in the total received light was also analyzed. The entire system, including the shutter and the controller, costs INR 900 (∼USD 10), demonstrating a scalable, energy-efficient solution for low-data-rate optical communication in embedded sensing applications.