Under Water VLC - Week 2 - Week 6 ( Updating the existing system )

Week 2 - Week 6 ( Updating the existing system )

we divided the entire development process into two categories, the design and implementation of the communication link and the control system and focused on 4 main sections/ components.

Water tank
Transmitter
Receiver
Light Following robot

1. Water Tank

The existing water tanks was used. In the previous phase of the project by last year group, they have come across some refraction effects from the glass surface and it has affected the clearness of the images and the readings. To reduce the effects by refraction from glass surfaces, we covered the inner surface of the tank with black PVC stickers.

Fig 1: Glass tank/ Water channel before modifying

Fig 2: Modified tank with black PVC stickers in inner side of the tank

2. Transmitter

The previous phase of the project had used different colors ( red, blue, green ) of the basic 5mm LEDs. Their transmitter was made of a triangle shaped LED array, as in Figure 3. In our proposing method, we use a 10*10 square shaped LED array as the transmitter.

Fig 3: Previously used transmitter

Fig 4: Modified transmitter used for testing purposes

Fig 5: Modified Transmitter with blue LEDs

The colour of the LED used in the transmitter plays a significant role in deciding the amount of penetration it can make in the water.

For the modified transmitter we used 100 blue ( as blue color has the lowest attenuation in water ) LEDs as a 10*10 square shaped arrangement. Oval-shaped LED type was chosen over flat-top LEDs and power LEDs which are typically used in VLC applications so as to avoid interference due to larger spreading angles and high power consumption in the latter .

LED ( OVLGC0C6B9 ) which has a narrow viewing angle than the normal LEDs. We are used this LED type for the final transmitter. The datasheet is attached.

OVLG_SERIES-45098.pdf

OOK (On Off Keying) modulation is considered one of the easiest and the default modulation choice and also a more practical modulation technique that most suits our purpose. Hence it was chosen to modulate data to be transmitted.

Fig 6: Spatial distribution of LEDs

Fig 7: Transmitter with RaspberryPi

Fig 8 : Transmitter Circuit Diagram

3. Receiver

Rather than using a general web cam for the receiver, we have used a advanced camera considering the frame rate and the image quality. Logitech C920 camera which has a constant frame rate of 30 fps was used as the receiver.