Project report

by Rory Ortlepp

Project aims

Visible light communications (VLC) seeks to make use of the terahertz of bandwidth available within the visible light spectrum to provide faster download speeds as, with the increasing amount of data being downloaded, the radio spectrum is becoming too full to keep up with demand. Since visible light is used this means that the LED lamps used in our homes and office spaces can be turned into data transmitters by modulating the light at high speeds. This fast switching is not noticeable to the human eye and, since the lights are already in use for lighting, the data transmission comes for effectively free in terms of energy use. This project involves creating the hardware and equipment for implementing an intelligent luminaire for use in an office environment. The award will be spend on the components necessary to build the VLC transmitter and receiver.

Results

The project took place in the University’s Rankine building in a lab which is operated by the team’s supervisor, Professor Anthony Kelly. With the funding, we have been able to purchase two Raspberry Pi 4Bs and some electronic components and equipment required for the project. Your funding has been vital in allowing us to proceed with the project and as a result we were able to construct a VLC system.

Our system allows a one Raspberry Pi to communicate data to another using just an LED. We do have to apply some signal processing to make sure the signal can be inputted into the other Raspberry Pi however this form of signal processing is standard in communication systems.

I have attached some photos of the setup and of myself (with the glasses) and my colleague Luca in the lab. We also have two other team members working remotely on the project: Martin and Alexander.

The data we send is modulated in an on/off manner. The LED sends the data to a photoreceiver via a convex lens. The photoreceiver then converts the optical power of the LED light into a voltage. This voltage is then amplified and sent via an inverter to the other Raspberry Pi. This Raspberry Pi can understand the data sent and show the information that is sent.

Specifically, the signal traces you are seeing are as follows:

Blue Signal: The voltage of the transmission signal which drives the LED. This signal is produced by the first Raspberry Pi.
Pink Signal: The output voltage of our photo receiver. This is a measure of how the light from the LED is converted into a voltage signal
Yellow Signal: The output voltage of the amplifier. We need to amplify the pink signal so that it is high enough to be received. You can see that this signal is inverted here, so we need to invert it back to its original form
Green Signal: The output of the inverter. This signal is then inputted into the second Raspberry Pi for receival.

And the data we are sending is the letter “H”.