Fall 2007

Total Price: Probably Too Much

It's been a while since I've been up to any good with the Tiny26, but I decided to integrate it into my latest project. I can't entirely remember at which point I decided to begin this project, but I seem to have remembered seeing an article online at Hardocp.com mentioning a niffty lamp which used an RGB power LED. I did some research at mouser.com and digikey.com with respect to the latest LED technology. To my suprise, it was possible to buy very bright LEDs, thanks in large part to recent research which aims to have LEDs replace incandescent bulbs. Further searching for LED parts led me to some pretty cool looking heatsinks, at which point I began spending money.

The design is based around a new LED offering from a company called Lamina Ceramic, who seemed to have been able to dramatically increase the brightness through an innovative new ceramic-based backing. Learn more here. It is designed to be driven at 350mA, with a maximum operating current of 700mA. To be extra safe with my hard-earned money, I decided to drive it at tad under 350mA. From what I can gather, LEDs, especially hi-power ones, are very sensative to current, rather than voltage. With this in mind, I set about to find a design for a simple constant-current driver. After finding many complicated and expensive circuits, I found this one, which is very simple.

I built 3 individual constant-current drive circuits, using a 1.5Ohm - 1W resistor for R2, R4, and R6. These resistors determine the current to maintain, which in this design is around 333mA. The MOSFET power transistors need heatsinks - probably ones larger than what I used. I also used a Lamina Ceramic heatsink for the LED. I'm sure there are cheaper sollutions for cooling the LED, but none look this cool. All of the other details of the driver design are from the Instructables.com article.

Most other people who have done a project like this and documented it on the web used a PIC microcontroller. I have no experience with this device, so I used Atmel's Tiny26L instead. I have one output pin per LED, so theoretically if I invested time in a quality program, I could use software PWM to generate 16 million colors. However at this time I have already lost enough of my eyesight staring at the colors to begin more complex programming.

The program I use to control the colors is a simple while loop with delays, which makes 7 colors through turning on and off the individual red, green, or blue LEDs. I intend to reduce the frequency of color change to about 5 minute intervals.

Finally, to make my project more usefull, more appealing, and less dangerous for the eyes, I have placed it into an IKEA sourced lamp (idea from here).

Schematic:

Click Here for Full Size Schematic

Click Here for Current Code

The Final Product, Outside of the Lamp:

All of the Parts :

Testing the Diodes for the First Time :

LED On Outside of Lamp :

All of the Presently Working Colors (Red, Lt. Blue, Purple, Green, Blue, Yellow, White):

Click to See a Video of the Dazzling Colors ~347KB

-Requires Windows Media Player