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Credits: Jie Qi
Year: 2012
video: http://youtu.be/hlZOExfOXIA
Photos: http://www.flickr.com/photos/jieq/sets/72157634587082013/
Materials: Copper tape, conductive fabric tape, solder, 1206 surface mount LEDs in red, yellow, pink, blue and white, magnets for battery holder
Techniques: Soldering to components, copper tape and conductive fabric tape. Copper tape folding to make switches. Magnets and a folded flap were used to construct the battery holder
Dimensions: 12cm x 8.5cm

The LED color graph demonstrates the varying voltage drops of different colors of LEDs, and how this voltage difference can be used to automatically turn multiple sets of LEDs on and off with only a single switch.
LEDs with similar voltage drops, such as red (1.9V) and yellow (2.0V) can be turned on simultaneously in parallel with a single battery. However, if you try to turn on a higher voltage color in parallel with a lower voltage one, like blue (3.2V) with red (1.9V), only the lower voltage color will light up. This is because without a protective resistor in the circuit, the battery voltage actually drops to the lower color LED voltage. As a result, the battery voltage becomes too low to fully light the higher voltage color LED. The resulting effect is that when LEDs of certain color combinations are connected in parallel, one color of light automatically dims when you turn on the other light of lower voltage. Thus, you can turn on/off two sets of lights with only one switch.
This circuit is made using paper circuit techniques. Copper tape and solder were used to make electrical connections and switches. The battery holder is made from magnets (which cling to the battery) and conductive fabric tape to withstand repeated folding.”

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