The Rainbow Apparatus

Author: marciot, published on 2015-07-04

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Colors collide in this fabulous device. Was it made by aliens? Is it a mechanism for sending kaleidoscopic messages to motley colored extraterrestrials?

Build one and you’ll find out!

Video of thing in action:

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This project involves soldering, small-parts, electrical components and an extremely bright LED. You assume all risks and liabilities should you wish to undertake it.

Print it:

The lamp consists of several parts that snap together. You will need one base, three pillars, a top ring, and a cover.

I have also included an EXPERIMENTAL projection disc. The Rainbow Apparatus arose from the idea that you could paint a picture using light rather than pigments. My original concept called for projection discs that could be loaded on the platform of the Rainbow Apparatus. This idea proved far too ambitious for my 3D printer and my attempt at a color logo led to a jumbled mess. I do not recommend you print the projection disc unless you have access to a very high accuracy printer.

Light it up:

I used three 20mm high-power LED stars for my build. I chose red, green and royal blue LEDs because these are primary additive colors. When their lights mix you can get four additional colors (cyan, yellow, magenta and white)

A pack of ten LEDs of each color costs less than $5 on eBay. The LEDs are rated at up to 3W. I strung all LEDs together in series and am driving them at about 9V.

Be careful not to look directly at the LED. It is extremely bright and could damage your eyes.

Power it:

A string of LEDs in series will begin running at about 8V-9V, so you will need a suitable power supply. I used a bench-top adjustable power supply for testing, but in my final build I used a recycled 12V wall wart combined with a adjustable micro DC-DC step-down converter from e-bay. The particular one I used was listed as “10pcs Mini DC-DC Converter Step Down Module Adjustable Output 1-17V for RC PLANE” and sold by axeprice. It was small enough to fit in the base of the lamp, but you could also mount a larger module outside of the lamp. The converter has an adjustable output voltage, so you can tune the brightness of the LEDs and balance it against heat output.

Choosing the correct voltage:

Because in my build I did not use resistors, picking the correct voltage for the LEDs is very critical. The LED string will begin conducting at a certain voltage, but beyond that, the current will increase very sharply. The sweet spot is only a few tenths of a volt beyond the initial conduction point. I recommend using a bench-top power supply with a variable voltage knob and an integrated ammeter to determine the voltage that causes enough current to run through the LED without overheating (about 0.4A for a 3W LED). Once you have determined the correct voltage, re-check it using a multimeter and write it down. You will use this voltage to tune the DC-to-DC converter during assembly.

Assemble it:

Assembly consists of soldering the various parts together. Be very careful about the polarity of the components. The following build sequence worked for me:

  • Cut the plug off your AC wall wart and separate the two wires.
  • Solder the wires to the input pads of your DC-to-DC converter (In+ and In-). Use a multimeter to determine which wire is positive and which is negative if you cannot tell. Polarity is very important.
  • Plug in the AC wall wart and using the multimeter adjust the voltage on your DC-to-DC converter to the value you determined above. If you do not have a multimeter, set it to 7V to start — this will keep you from blowing out your LED when you first power it up.
  • Position the LEDs on the base and determine the length of wire you will need to wire them up.
  • Solder the three LEDs in series. A set of set of bench top helping hands is very good for this task. Be careful of the polarity, the + of one LED needs to be soldered to the – of the next.
  • At the beginning and end of the LED chain, solder two longer lengths of wire, preferably of two different colors, so you can keep track of which is positive and which is negative.
  • Glue down the LEDs to the wells on the base and feed the terminal wires down one of the vertical shafts.
  • Flip over the base. Solder the other end of the wires to the output terminals of the DC-to-DC converter. Mind the polarity — if you get it reversed, the LED will not light.
  • Position the DC-to-DC converter to the recess and secure with glue or electrical tape.

Tune it:

Once you first plug it in, run your lamp without the cover and monitor it to make sure the LEDs are not getting too hot. Let it run a couple minutes and checking regularly to make sure that it is not getting too hot to the touch. If it is, dial back the voltage on the DC-to-DC converter.

You want the LEDs to run warm, but not hot enough to melt the plastic or cause a fire hazard. Do not run the lamp unattended until you have monitored it for several hours to make sure heat is not a problem.

Customize it:

This design is fully customizable. Be sure to check it out in the Makerbot customizer!

License: GNU – GPL

Tags: art, customizer, education, kaleidoscope, lamp, LED, LightItUp, physics, rainbow, science