Finishing the LEDs

After spending many hours designing a various different heat-sinks for the LEDs, we settled on putting the LEDs on the outside of the acrylic dome to minimize the reflection and interference with our cameras. Space has also been another huge issue for our LED setup. To minimize the space used by these LEDs, we have decided to put them into a 12mm pipe (10mm ID) attached to a 10mm rod.

The LEDs will be glued onto a copper strip and then onto a 10mm aluminum rod. This unit will then slide into the larger 12mm rod. The lens will be glued into the end of the pipe and the wires will come our via slots in the aluminum piping.

After routing out the aluminum pieces (shown below) we glued the LEDs to the copper strips, soldered on the power and ground wires, and covered the wire leads in order to ensure that electrical jumping did not occur. We then attached the copper to a 10mm rod and were done building the heat-sinks!

In order to have the lights on outside of the water and at variable brightnesses in the water we are using pulse width modulation (PWM) to control them. By wiring the LEDs to our 12v power supply on the sub and then using a MOSFET (metal-oxide-semiconductor field-effect transistor) we were able to translate the variable pulses to variable brightness on the LED.  The MOSFET can be attached by sending DATA to the gate pin, attaching the GROUND of your LED to the drain pin, and finally attaching the GROUND of your power source to the source pin.

After wiring up the MOSFET you can easily control is using the RPi.GPIO library on your Raspberry Pi. Read this post to get a handle on the basic concepts of PWM control. By simply sending varied duty cycles to the gate pin, you will get a variable brightness LED. Below is a small clip of the LED pulsing using the MOSFET and RPi.GPIO:

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