Curved Circuit Art: Make A Double Helix LED Lantern

Step 2 How It Works

The lantern is designed to run off 12 volts, but can be easily converted to portable battery power. As is, It powers sets of four LEDs in series. A dropping resistor in series with the LEDs keeps the current through each led at 20ma or less. You can use any standard LEDs you want. But you will have to adjust the dropping resistor for every four LEDs as they vary in resistance depending on the color and size of the led. You can use any number of four LEDs wired in parallel as long as the total current does not exceed the carrying capacity of your power cord wires. For this project I chose four sets of four LEDs.

I chose to use PLCC2 surface mount LEDs to maintain the flat profile of the curved circuit board and because they are the easiest surface mount LEDs to solder that put out a bright light. I originally used four white LEDs which required a 68 ohm dropping resistor. Then I decided I wanted a bluer light and changed it to three whites and one blue. The extra resistance of the blue led meant that I didn't need any resistors to keep the current low so I put in some 1 ohm resistors mainly to show where the dropping resistors need to go in the circuit.

Battery Power
To convert to battery power you can install a nine volt battery in the base and remove one Led from each set so that only three LEDs are in series. The three white LEDs in series that I tested, ran at 14 ma without a dropping resistor at nine volts. With four sets of three LEDs in series, the total current is only about 56 ma.