LowCost Visible Light Communication VLC Using LEDs By

Low-Cost Visible Light Communication (VLC) Using LED’s By: Liam Mc. Kenna, Supervisor: Dr Chao Wang Introduction System Description The project sought to demonstrate a VLC system in simplex form that includes text message communication between adjacent PC’s and audio signal transfer from an auxiliary output device (with encoded audio) to a receiver, to output the audio via a loudspeaker. The system was designed with an appreciation for future VLC implementation and project budget, this considered; Component size, suitability for Optical Wireless Communication (OWC) and cost. The text system was designed such that a micro-controller would act to encode the required message into ASCII binary code using software and modulate a digital output using the OOK modulation scheme. 0 1 1 1 0 0 Results 1 0 1 1 0 0 VLC Concept Text System Diagram This output would then be passed to an LED driver circuit in order to operate a high-powered pc-LED. The light is then projected over freespace and received via a PIN photodiode which produces a small photocurrent that is then amplified and passed through a filter circuit. A second micro-controller then interprets the modulation voltage output and represent these as a digital input, which can then be converted to its ASCII equivalent using software. OWC has the disadvantage of being susceptible to increased noise in the receiver from other ambient light sources which limits the communication range and accuracy of received data. • Therefore an additional aim for the project was to deter ambient lighting interference by implementing appropriate filtering techniques. • An additional objective was to demonstrate flicker-free communication by ensuring the modulation frequency was above a calculated Critical Flicker Frequency (CFF) threshold. Manchester Encoded Flicker and Receivable Message Test Frequency of Bit Rate (bs-1) Data Rate (bs-1) Modulation (Hz) Aim’s and Objectives Modulating light sources with simple techniques such as On Off Keying (OOK), produces visible flicker, which can be a health hazard. Using a High-Pass Filter (HPF) with a cut-off frequency of 100 Hz mitigated UK ambient lighting noise and increased the communication distance. Visible flicker was approximately zero when employing the Manchester line encoding technique (to deter long periods of consecutive bits) and OOK modulation scheme above the calculated CFF of 200 Hz. Audio System Diagram The audio system was designed such that audio encoded data, that can be outputted analogously via a common auxiliary port, would be used to modulate a high powered LED, based on the encoded level of the output. Transmitted over free-space, a PIN photodiode interprets the modulation, which produces a photocurrent that is passed through a current to voltage pre-amplifier and an audio amplifier to drive a low -impedance loudspeaker. Visible Flicker Error-Free Message Received? 175 87 Medium-Low Yes 200 100 Low Yes 225 112 Low-None No 250 125 Low-None No 275 137 None No Press Release Energy efficient low-cost LED’s are not only highly controllable with regard to modulation, but are now a ubiquitous indoor lighting source. As indoor data usage is set to surge with increased data use and devices (including Io. T’s), this leads to the question, why not use the existing infrastructure as a dual purpose device, to provide simultaneous ambient lighting and a communication medium?