Dimming Control for Visible Light in a Wireless Identification System Using Manchester Code

A wireless identification system was developed in which visible light was simultaneously used for illumination and for transmitting an interrogating signal from a reader to a transponder. We used the Manchester code to modulate the visible light to ensure flicker-free lighting, and the duty factor of the Manchester code was utilized for dimming control. The average optical power of the light emitting diode (LED) array in the reader, and the solar cell current in the transponder, increased when the duty factor of the Manchester code was increased. In experiments, the capture range of the identification system was about 2.3 m when the duty factor was 90%. This configuration can be useful in an automatic vehicle identification system for security checks or fare calculation, using an LED lamp installed at toll gates or parking places.