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Illumination device design

This prototype device uses two super-bright blue LEDs (470nm, 2400mcd) to illuminate cells. It will be used to drive the LOVtap promoter, which is responsive to blue light. The device is controlled by an open-source arduino microcontroller and can be custom-programmed to cycle through various light states for various amounts of time. Source code and schematics for the final device will be posted soon.

Calculating the proper resistor

The LED we used has a forward voltage of typically 3.5V with a max of 4V. The Arduino Duemilanove outputs at 5V. Thus, we used the resistor calculator located [http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng here] to calculate the proper resistors to use:

We only had a limited number of resistor types in stock, so we used a 56 Ohm resistor. The light output was not as bright as we wanted, so we switched to a 37 Ohm resistor. This may stress the LED more than usual, but should be enough resistance that it will not easily burn out.