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13 Color LED Rainbow

13 Color LED Rainbow

This circuit uses a set of 13 differently colored LEDs to generate a full color spectrum. The spectrum could be extended on both the IR and UV sides. The circuit board can be mounted on a piece of white hardboard, the white paint reflects the colors nicely.
A brief scan through the Mouser catalog indicates the availability of these IR wavelengths: 940nm 880nm, 875nm, 870nm, 850nm. UV LEDs at 400nm, 395nm and 380nm are also available. There are also many LED colors available with wavelengths between the 13 colors shown, the colors selected were chosen for an evenly spaced color spectrum. An open-collector LED driver circuit could be connected to the negative LED leads for computer control.

The circuit could be used in conjunction with a photo detector for characterizing optical filter curves. Typically, the photo detector output is sent to a logarithmic converter, the log-ratio of the direct light versus the filtered light characterizes the attenuation at a given wavelength.

The circuit was built on a prototype perforated board with printed solder pads. The circuitry is hand-wired on the back side of the board. Care should be taken when soldering to the LEDs, a clip-on heat sink should be used while soldering the leads. Care should be taken to avoid zapping the LEDs on the violet side of the spectrum, they are sensitive to static electricity.

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