White LED-based visible light ranging and detecting system

• Main Author: Li, Xiang
• Other Authors: Zhong Wende
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: http://hdl.handle.net/10356/68280
• Institution: Nanyang Technological University

In this project, another application of light emitting diodes (LEDs) is explored, which is a ranging and detecting system. This project aims to carry out experimental work on the theory explained below. The theoretical process is as follows: a predetermined sinusoid signal at a fixed frequency is intensity modulated on LED light source. By comparing the detected signal reflected from the object with the original signal, a phase shift can be obtained. The travel distance of the light can then be decided based on the calculation of this phase shift. Applying the theory, I tried to measure the exact distance from the lighting source to the object in front of it. After many experiments and failures, an optimal setting is found that could sense stable phase shifts, as well as reduce the measurement error to a reasonable range. An automation software program is developed using National Instruments’s LabVIEW. The program could automatically obtain the original and received signals, process them, measure the phase shifts, averaging in order to reduce error, and lastly calculate the distance. Factors that affect the measurement accuracy are also analyzed in this report. These include modulated signal’s frequency and amplitude, Oscilloscope’s sampling rate, sample capacity, post signal amplification rate, receiver’s sensitivity, receiver’s detecting area and filter’s bandwidth. These findings could be a solid groundwork for future researches. Accuracy of this system is also explored. If object is placed within a short distance away from receiver, the precision is very good – relative error is as low as 1.58%. Plots showing the relationship between distance and measurement error are also shown in this report.