Document Type

Restricted Campus Only

Publication Date

4-30-2013

Abstract

SCUBA divers, both recreational and professional, need an effective way to communicate underwater, but there are drawbacks to all of the existing methods. Hand signals can easily be misinterpreted, and devices that use ultrasonic waves can disturb the underwater environment. This project explores using visible light as the signal canier instead of ultrasonic waves because it minimally disturbs the environment with a single beam of light instead of bouncing ultrasonic waves throughout the water. It also has virtually no harmful effects on the environment, and most divers already cany a light with them during a dive.

The prototype costs $464.46 to build, less expensive than current underwater communication systems, and consists of a transmitter unit, a receiver unit, a set of bone conduction headphones, and a microphone. These parts are all waterproof except for the microphone, which will be enclosed in the diver's full-face mask. The device uses an analog transmission scheme where the intensity of an array of four light-emitting diodes (LEDs) in the transmitter directly conesponds to the voice that the microphone captures. The photodiode in the receiver then picks up these changes in intensity, and the headphones play back the speaker's voice. The receiver is powered by a single 9 V battery, while the transmitter is powered by two 9 V batteries: one for the printed circuit board (PCB) and one for the microphone.

Since it is difficult to observe the circuit on a PCB with standard lab equipment due to its size, several signal tests are conducted with breadboard prototypes. According to the power consumption tests, if both the transmitter and receiver are powered by a single 9 V battery, the estimated battery life would be 2 hours and 43 minutes, which meets the 1 hour goal stated in the project charter. The project charter also states that the signal-to-noise ratio (SNR) of the headphone output must be at least 14 dB and operate at least 4 m apart. Depending on the lighting conditions, the SNR ratio varies considerably. The test results clearly show that the design cannot function at a distance of 4 m no matter what the lighting conditions. With respect to noise expected in an outdoor, underwater environment, the design achieves at least 14 dB up to a distance of around 0.61 m (2 ft) depending on the lighting conditions.

The frequency response shows that the circuit passes frequencies between 25 Hz and 7 kHz, which encompasses the entire range of human voice and rejects most of the other frequencies within human hearing. Since the design is only intended to transmit human voice, any frequencies outside of human speech are not necessary.

Outdoor and environmental testing with the breadboard prototype also shows that the design works in non-laboratory settings. The design works outside, provided the photodiode is not in direct sunlight. The sunlight's DC current saturates the photodiode, rendering it incapable of detecting changes in LED intensity. To ensure clarity of the system alone, soundproof rooms with clear doors are also used in tests to isolate the listener from the speaker. These qualitative tests indicate that the system transmits voice clearly on its own. As expected, water attenuates the signal more than air, and greater distances produce greater differences in attenuation.

The design described in this report can be improved in several ways. The design has not been properly tested on the PCB, and the transmitter and receiver should be condensed into a single unit powered by a single battery. More LEDs should also be used to improve SNR at a farther distance. All of the devices should also be waterproofed for common SCUBA diving depths. However, this design serves as a successful proof of concept for an underwater visible light communication system for SCUBA divers.

Comments

Dr. Joshua Schwartz, Advisor

ENGR-4382

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