Wednesday, February 17, 2010

Super LED

Well might parts have all come in get the RGB led working

Parts so far
  • 10 watt RGB LED (ebay)
  • 3x LED Drivers, one for each color (
  • Wire (sparkfun)
  • 3x 10k Rheostats (sparkfun)
  • Heatsink (savaged from spare parts bin)
  • TIM, thermal interface material (spare parts)
  • 12v powersupply (using spare atx pc power supply)
  • Arduino Mega
  • Character LCD 2x16
LED's are finicky things, they like constant current power instead of the typical constant voltage power. They also need an exact amount of current (amps), too much and you will burnout the LED. With normal led's, you limit the amps by using resisters but doing that with these high power leds is horribly inefficient. That's where the LED driver comes in. It uses a special chip to convert the power into something the led will like with great efficiency (up to 98%).

Sureelectronics had the cheapest led driver I could find for high power leds($4each) but they were out of stock the 350ma ones I needed, but they had plenty of the higher capacity 700ma ones. I looked at the spec sheet and found the only difference was the 700ma one had two addtional resisters on it that I could easily remove. The chip on driver determines what the output amperage by reading what the resistance is between to of its pins.

So the first thing i did was remove the two resisters to change the output amperage to 350ma. A little work with my soldering iron and they were off. Next, I soldered the drivers into the adapter boards that have the nice screw terminals.

Next I soldered leads to the LED which I then used to connect the LED to the drivers. Then drivers I the wired together to the 12volt powersupply. The white wire takes 5v PWM from the arduino to control the brightness of the led.

I mounted the LED on a heatsink to exhaust the heat it generates. The led needs to be in perfect contact with the heatsink so I put some TIM on the bottom of the led to fill any gaps between it and the heatsink. Then I tacked the led down with a bunch of Hot glue.

I got the rest of the arduino wired up with three rheostats, one for each color-, red, green, and blue athing them to the analog inputs 0-2.

A little debugging to get the get values right (the lcd is perfect for this)

and voila! I can turn the knobs to create any color I want! The LED is blindingly bright so until I have time to fabricate a shade for it, a rolled up piece of trace paper works.

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