Low cost data transmission system via LED lighting with over 50 Bps speed was a small collaboration project with my friend Tahmid. In this project we tried to implement a communication system with light as medium. LED panels were used as light source and the panel was modulated. The frequency of modulation was chosen such that for naked eye the panel will seem to be constantly on. So communication can be done in parallel with the lights serving their purpose of lighting an area.
The data transfer is done between two nodes: a transmitter and a receiver. For transmission large LED panel light was used, which was driven using mosfet with adequate power handling capability. For transmission the LED panel was modulated using Pulse Width Modulation technique. For bit 1 a duty cycle and for bit 0 a different duty cycle was used and in both the case the frequency remained same. To make the LED panel more useful the LED panel was kept on the whole time, so for data transmission the waveform used was slightly aberrant. The wave started with initially being low and then going high . To speed up the data transmission the panel was modulated for one complete cycle only. And on the receiving side PIN photodiode was used in reverse biased stage. The current was allowed to flow through a resistor which allowed for a voltage drop to be measured. The PIN diode used in the project was BPW34. The BPW34 is a very high speed and highly sensitive PIN photodiode in a small flat plastic package. Its top view construction makes it ideal as a low cost replacement of TO-5 devices in a lot of applications. Because of its water-clear epoxy the device is sensitive to visible and infrared radiation. The large active area gives the photo detector a high sensitivity at a wide viewing angle. This is ideal as a receiver because it has a rise time and a fall time of 100 ns each which is good enough for detecting high frequency light pulses making it a perfect candidate to be used as a receiver.