Color Sensor From An RGB LED And A Photocell

August 29, 2017 by Dan Maloney 27 Comments

When you need to quantify the color of an object, you’ve got quite a few options. You can throw a Raspberry Pi camera and OpenCV at the problem and approach it through software, or you can buy an off-the-shelf RGB sensor and wire it up to an Arduino. Or you can go back to basics and build this reflective RGB sensor from an LED and a photocell.

The principle behind [TechMartian]’s approach is simplicity itself: shine different colored lights on an object and measure how much light it reflects. If you know the red, green, and blue components of the light that correspond to maximum reflectance, then you know the color of the object. Their sensor uses a four-lead RGB LED, but we suppose a Neopixel could be used as well. The photosensor is a simple cadmium sulfide cell, which measures the intensity of light bouncing back from an object as an Arduino drives the LED through all possible colors with PWM signals. The sensor needs to be white balanced before use but seems to give sensible results in the video below. One imagines that a microcontroller-free design would be possible too, with 555s sweeping the PWN signals and op-amps taking care of detection.

And what’s the natural endpoint for a good RGB sensor? A candy sorter, or course, of which we have many examples, from the sleek and polished to the slightly more hackish.

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Boredom + Lasers = Projector!

August 29, 2017 by James Hobson 7 Comments

[Krazer], a post-doctoral researcher at MIT, loves him some lasers. When out of boredom one afternoon he hatched an idea for a laser projector, it grew until a few years later he wound up with this RGB laser for a projector — Mark IV no less.

In addition to 3D-printing the parts, the major innovation with this version is the ability to re-align the lasers as needed; tweaking the vertical alignment is controlled by a screw on the laser mounts while the horizontal alignment is done the same way on the mirror mounts. This simplifies the design and reduces the possibility of part failure or warping over time. An additional aluminium base epoxied to the projector aims to keep the whole from deforming and adds stability. With the help of a mirror for the final alignment — sometimes you must use what you have— the projector is ready to put on a show.

True to the spirit of the art [Krazer] used all open source software for this iteration, and sharing his designs means you can build your own for around $200. As always with lasers take extra precautions to protect your eyes! This 200mW setup is no joke, but that doesn’t mean fun and games are out of the question.

Rushing The Design And Construction Of LED Centerpieces

August 11, 2017 by Donald Papp 7 Comments

‘Dragon Flame’ RGB LED table centerpieces, by [Alex Lao]

Sometimes the most important thing is getting something done.

[Alex Lao] was recently in such a situation. His sister was getting married and he designed, built, and delivered twenty RGB LED table centerpieces in a rush. There were no prototypes made, and when the parts arrived all twenty were built all at once over a single weekend. These table centerpieces are illuminated by RGB LEDs and battery-powered, but have an option to be powered by a wall adapter.

[Alex] helpfully shared some tips on reducing the production risks and helping ensure results in such a limited time frame. His advice boils down to this: reduce the unknowns. For Alex this meant re-using code and components from a previous project — even if they were not optimal — so that known-good schematic and footprint libraries could be used for the design.

From one perspective, the PIC32 microcontroller inside each lamp is overkill for an LED centerpiece. From another perspective, it was in fact the perfect part to use because it was the fastest way for [Alex] to get the devices working with no surprises.

For an added perspective on needing to get production right the first time on a much larger scale, be sure to check out getting an installation made up of 25,000 PCBs right the first time.

A Hypnotizing Interactive Art Piece For Visualizing Color Theory

August 8, 2017 by Cameron Coward 4 Comments

Digital color theory can be a tricky concept to wrap one’s mind around – particularly if you don’t have experience with digital art. The RGB color model is about as straightforward as digital color mixing gets: you simply set the intensity of red, green, and blue individually. The result is the mixing of the three colors, based on their individual intensity and the combined wavelength of all three. However, this still isn’t nearly as intuitive as mixing paint together like you did in elementary school.

To make RGB color theory more tangible, [Tore Knudsen and Justin Daneman] set out to build a system for mixing digital colors in a way that reflects physical paint mixing. Their creation uses three water-filled containers (one each for red, green, and blue) to adjust the color on the screen. The intensity of each color is increased by pouring more water into the corresponding container, and decreased by removing water with a syringe.

An Arduino is used to detect the water levels, and controls what the user sees on the screen. In one mode, the user can experiment with how the color levels affect the way a picture looks. The game mode is even more interesting, with the goal being to mix colors to match a randomly chosen color that is displayed on the screen.

The practical applications for this project may be somewhat limited, but as an interactive art piece it’s hypnotizing. And, it may just help you with understanding RGB colors for your next project.

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Edge-lit Pendants Show Two Layers Are Better Than One

July 28, 2017 by Donald Papp 7 Comments

Engraved acrylic lights up nicely with LED lighting. Simply engrave clear acrylic with a laser engraver, then edge-light the acrylic and watch the engraving light up. This badge made by [Solarbotics] shows how they used this principle when creating some pendants for an event that performed particularly well in the dark.

The pendants they created have two engraved acrylic panels each, and that’s about it. Two LEDs and a CR2032 battery nestle into pre-cut holes, and the engraved sides are placed face-to-face, so the outer surfaces of the pendant are smooth. By using some color-cycling RGB LEDs on one panel and blue LEDs on the other panel, the effect is that of an edge-lit outer design with a central element that slowly changes color separately from the rest of the pendant.

The design stacks the LED leads and coin cells in such a way that a simple wrap of tape not only secures things physically, but also takes care of making a good electrical connection. No soldering or connectors of any kind required. [Solarbotics] found that CR2032 cells would last anywhere between a couple of days to a week, depending on the supplier.

This design is great for using a minimum of materials, but if that’s not a priority it’s possible to go much further with the concept. Multiple layers of edge-lit acrylic were used to make numeric 0-9 display modules as well as a full-color image.

A Wordsearch Twist On The Word Clock

March 16, 2017 by Donald Papp No comments

We love seeing new takes on existing ideas, and [Danny] certainly took the word clock concept in an unusual direction with his Wordsearch Clock. Instead of lighting up words to spell out the time, [Danny] decided to embrace the fact that the apparent jumble of letters on the clock face resembles a word search puzzle.

In a word search puzzle, words can be found spelled forward or backward with letters lined up horizontally, diagonally, or vertically. All that matters is that the correct letters are in a line and sequentially adjacent to one another. [Danny]’s clock lights up the correct letters and words one after the other, just as if it were solving a word search puzzle for words that just happen to tell the correct time. You can see it in action in the video, embedded below.

[Danny] went the extra mile in the planning phase. After using a word search puzzle generator tool to assist in designing the layout, he wrote a Processing sketch to simulate the clock’s operation. Visually simulating the clock allowed him to make tweaks to the layout, identify edge cases to address, and gain insight into the whole process. If you’re interested in making your own, there is a GitHub repository for the project.

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Light Pipes And LEDs Team Up For A Modern Take On The Nixie Tube

December 22, 2016 by Dan Maloney 35 Comments

There’s no doubting the popularity of Nixie tubes these days. They lend a retro flair to modern builds and pop up in everything from clocks to weather stations. But they’re not without their problems — the high voltage, the limited tube life, and the fact that you can have them in any color you want as long as it’s orange. Seems like it might be time for a modern spin on the Nixie that uses LEDs and light pipes. Meet Nixie Pipes.

Inspired by an incandescent light-pipe alphanumeric display from a 1970s telephone exchange, [John Whittington]’s design captures the depth and look of a Nixie by using laminated acrylic sheets. Each layer is laser etched with dots in the shape of a character or icon, and when lit from below by a WS2812B LED, the dots pick up the light and display the character in any color. [John]’s modular design allows one master and an arbitrary number of slaves, so large displays can simply be plugged together. [John] is selling a limited run of the Nixie Pipes online, but he’s also open-sourced the project so you can build your own modules.

We really like the modularity and flexibility of Nixie Pipes, and the look is pretty nice too. Chances are good that it won’t appeal to the hardcore Nixie aficionado, though, in which case building your own Nixies might be a good project to tackle.

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