P08456: Underwater Light

Detail Design

Table of Contents

Area Specific Pages

The final light unit and thruster housing designs are documented on the following pages.
Mechanical Design Information Page
Electrical Design Information Page
Software Design Information Page

Light Design Overview

The light unit designed is a modular housing, containing 4 printed circuit boards that control the power and function of 6 LEDs. 3 of which are white, 3 of which can be an additional color, green LEDs have been used in this design.

Housing Brief

The housing has been made from 6061 aluminum, which has a good combination of strength characteristics, corrosion resistance, low cost, and is readily available. The main consideration in choosing a housing material that will be subjected to sea water is it's corrosion resistance and if place on the galvanic index. The aluminum will come into contact with stainless steel fasteners and mounting hardware, therefore will be susceptible to dissimilar metal corrosion. When two metals come into contact in an electrolytic solution (such as salt water) one metal acts and an anode, the other a a cathode. The anode will corrode, while the cathode will be unharmed. The further apart any two given metals are from each other in the galvanic index predicts the severity of the corrosion. The lower numbered metal of the two will act as the anode. This is the principle behind sacrificial zinc anodes that are used on boats; because the zinc has a very low galvanic rating, it will corrode faster than any other metal on the boat. It must therefore be replaced regularly, but as its name implies is meant to be sacrificed to extend the life of all other components.
Exploded view of Light unit with Type-II black anodized housing. Note board sandwich has not been separated.

Exploded view of Light unit with Type-II black anodized housing. Note board sandwich has not been separated.

Electrical PCB Brief

Within the housing are 4 pcbs that control the functionality of the light unit.

Power Baord

The power board receives the raw 24 v power from the batteries. It then provided a filtered 24 v signal, and a 5 volt output for the on board electronics. All electronics that require an additional power supply have been selected because they can share a 5 v signal.

Micro-controller Board

The micro-controller board is the second board from the waterproof connector. It receives an RS 485 signal from the computer (either ROV CPU or laptop) telling it how to control the light. Both the micro-controller board and power board are shared with the thruster design.

LED Driver Board

The LED Driver board is the third in the stack that is mounted to the inside of the bullet housing. On it is the LED Driver, which receives a PWM signal from the micro-controller. The LED Driver also provides the LEDs with their excitation voltage, and controls the dimming by limiting the current drawn by the LEDs.

LED Board

The LED bard is separately mounted to the lens cap (also called LED Housing). This is because the LED board will generate the most heat, and should provide this heat energy with the most direct part to the outside of the housing. By mounting the LED board separately the heat generated does not have to migrate through the standoffs and other boards before escaping into the atmosphere, either water or air. Besides the LEDs, there is also a temperature sensor on the LED board to monitor the board temp. If the temperature on the board gets too high, one of two things can happen. One option is that a red flag arises on the GUI, and it is up to the operator to dim the lights to reduce the heat generation. The second possibility is that the micro-controller automatically responds to this temp. warning a reduces the intensity of the LEDs.

Control System Brief

The light and thruster units are controlled using a single GUI. The computer sends a USB signal to the USB converter board, which switches it to an RS485 signal. The benefit of using RS485 is that many units can re run individually from the same line by way of selective packet management. Each light/thruster only responds to a signal with its specific ID. The RS485 signal is received by the unit, where the microcontroller processes it into a PWM (pulse width modulation) signal that goes to the LED Driver of motor Driver. The PWM signal changes the intensity of the light or power of the motor by varying the signal's frequency; higher frequency=more light output. The LED Driver then sends the correct forward voltage to the LEDs and limits the current, thus limiting the light output.

Light Architecture system view

Light Architecture system view

Standard Components

See Bill of Materials

Customer Assembly

The replaceable components of the LED light unit are:
Glass Lens
O-rings (2)
Mounting Hardware
Board-mounted LEDs

These three components have been made accessible with minimal disassembly of the light unit. It is suggested that any replacement of parts besides mounting components is handled by the manufacturer. Replacement LED boards should be made available to customers while the burnt out LED board is being sent in for repairs. The repaired boards could again be sold as refurbished components at a reduced price.

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