A Transparent 7-Segment Display

January 9, 2014 by Marsh 40 Comments

Though [Connor] labels it as a work in progress, we’re pretty impressed with how polished his transparent 7-segment display looks. It’s also deceptively simple.

The build uses a stack of seven different acrylic panes, one in front of the other, each with a different segment engraved onto its face. The assembly of panes sits on a small mount which is placed over seven rows of LEDs, with 5 LEDs per row. [Connor] left an air gap between each of the seven individual acrylic panes to clearly distinguish which was lit and to match the separation of the LED rows. To display a number, he simply illuminates the appropriate LED rows, which scatter light across the engraved part without spilling over into another pane.

You can find a brief overview and some schematics on [Connor’s] website, and stick around for the video demonstration below. We’ve featured [Connor’s] work before; if you missed his LCD data transfer hack you should check it out!

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A Blindingly Bright Larson Scanner

January 8, 2014 by Marsh 31 Comments

craylarsonscanner

This hulking monument to illumination is [DJJules’s] 6-foot-long Ultimate Larson Scanner. If you’re scratching your head in confusion, the Larson Scanner is the ever-popular scrolling LEDs seen on KITT (the car) from Knight Rider and on Cylons in Battlestar Galactica (1978), named after the creator of the series.

[DJJules’s] iteration consists of sixteen 10W LEDs, each mounted on a heat sink which bolt on to a 6′ long piece of angle aluminum sourced from a local hardware store. He used a basic MOSFET constant current driver for each LED, attaching the MOSFETS to the heat sink with 4-40 screws. Each LED module then connects to a TLC5940 LED driver breakout board from Sparkfun, which plugs into an Arduino Pro Mini.

Check out the Instructables page for the source code and other important details, including safely powering the build (the LEDs can draw around 1A each), then grab your sunglasses and stick around for a quick video below.

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Controlling Cheap, Awesome Christmas Lights

January 7, 2014 by Brian Benchoff 13 Comments

LEDs

[James] was wandering around Walgreens after Christmas and found something very interesting – RGB LED Christmas lights that were individually addressable. At $6.50 for a strand of 15 lights, he just had to buy a few and figure out the control protocol. After all, who can turn down a big, cheap, controllable RGB LED strip?

The packaging for these lights – apparently manufactured by BriteStar – includes a ‘try me’ button that cycles through different light patterns. This button is what initially tipped [James] off to the fact the lights on this strand could be individually controllable. Opening up one of the lights, he found exactly what he wanted: an epoxy blob, two wires for power, and three wires for the signaling.

After checking out this light with a scope and logic analyzer, [James] realized there was a very, very simple protocol going on. Essentially, the entire string functioned as a gigantic shift register, taking the values for one light and pushing it down the string. In looking at the protocol, [James] also discovered] these lights support 16 levels of brightness. Yep, RGB LED Christmas Lights with PWM for under $7. Can’t beat that.

[James] wrote an Arduino library to control these strings and put it up on Github. While your local Walgreens has probably already hidden these lights away in the back of the store, it might be worth asking around to see if they have any left.

Green Light LEGO, Red Light Stop

January 6, 2014 by Kristina Panos 7 Comments

Master LEGO craftsman [Baron von Brunk] had the same childhood passions as a lot of us—LEGO (obviously), Transformers, and Nintendo. But he also harbored a passion for traffic lights and road signs. His latest offering, a fully functional LEGO traffic light, is some pretty fantastic plastic. You might recall that we featured [Baron von Brunk]’s LEGO mosaic lamps a few weeks ago. This project is that one on steroids.

The body is made of 1700+ LEGO and Technic pieces. [Baron von Brunk] was kind enough to provide his LDD file, though he says it should be considered a rough guide to construction. The red, yellow, and green 1×1 areas are each lit with a 48-SMD LED floodlight bulb. Colored lights are available, but he used the solid white variety for greater luminescence. The lights are driven by a traffic light controller typically used for model railroads.

[Baron von Brunk] ended up lining the inside with black 1x1s and metallic reflective duct tape to keep the light from leaking out of the masonry. He used some Technic bricks on the rear door to form hinges, and Technic pins to hold the LED lamps.

Current Limiting Diode Use And Tutorial

January 6, 2014 by Todd Harrison 20 Comments

Not that this happens often, but what do you do when faced with a repair where you don’t know the power source but you do know you have to drive LED backlighting? When faced with this dilemma [Eric Wasatonic’s] solution was to design for ambiguity. In this interesting hack repair [Eric] needed to restore backlighting for an old car stereo LCD display. First he guaranteed he was working with a DC power source by inserting a small full-wave bridge rectifier. Then knowing he needed 4 mA to power each LED for backlighting he used some 1978 vintage current limiting diodes designed to pass 2mA each regardless of voltage source, within limits of course.

Sure this is a simple hack repair but worthy of being included in anyone’s bag of tricks. Like most hacks there is always knowledge to be gained. [Eric] shares a second video where he uses a curve tracer and some datasheets to understand how these old parts actually tick. These old 1N5305 current limiting diode regulators are simply constructed from a JFET with an internal feedback resistor to its gate which maintains a fixed current output. To demonstrate the simplicity of such a component, [Eric] constructs a current limiting circuit using a JFET and feedback potentiometer then confirms the functionality on a curve tracer. His fabricated simulation circuit worked perfectly.

There was a little money to be made with this repair which is always an added bonus, and the recipient never reported back with any problems so the fix is assumed successful. You can watch the two videos linked after the break, plus it would be interesting to hear your thoughts on what could have been done differently given the same circumstances.

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[Fran]’s LEDs, Nixies, And VFDs.

January 4, 2014 by Brian Benchoff 21 Comments

With a love of blinky and glowey things, [Fran] has collected a lot of electronic display devices over the years. Now she’s doing a few teardowns and tutorials on some of her (and our) favorite parts: LEDs and VFD and Nixie tubes

Perhaps it’s unsurprising that someone with hardware from a Saturn V flight computer also has a whole lot of vintage components, but we’re just surprised at how complete [Fran]’s collection is. She has one of the very first commercial LEDs ever made. It’s a very tiny red LED made by Monsanto (yes, that company) packaged in a very odd lead-and-cup package.

Also in her LED collection is a strange Western Electric part that’s green, but not the green you expect from an LED. This LED is more of an emerald color – not this color, but more like the green you get with a CMYK process. It would be really cool to see one of these put in a package with red, green, and blue LED, and could have some interesting applications considering the color space of an RGB LED.

Apart from her LEDs, [Fran] also has a huge collection of VFD and Nixie tubes. Despite the beliefs of eBay sellers, these two technologies are not the same: VFDs are true vacuum tubes with a phosphorescent coating and work something like a CRT turned inside out. Nixies, on the other hand, are filled with a gas (usually neon) that turns to plasma when current flows through one of the digits. [Fran] has a ton of VFDs and Nixies – mostly military surplus – and sent a few over to [Dave Jones] for him to fool around with.

It’s all very cool stuff and a great lead-in to what we hear [Fran] will be looking at next: electroluminescent displays found in the Apollo Guidance Computer.

Videos below.

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Controlling Ten Thousand RGB LEDs

January 2, 2014 by Brian Benchoff 51 Comments

RGB LEDs are awesome – especially the new, fancy ones with the WS2812 RGB LED driver. These LEDs can be individually controlled to display red, green, and blue, but interfacing them with a microcontroller or computer presents a problem: microcontrollers generally don’t have a whole lot of RAM to store an image, and devices with enough memory to do something really cool with these LEDs don’t have a real-time operating system or the ability to do the very precise timing these LEDs require. [Sprite_tm] thought about this problem and came up with a great solution for controlling a whole lot of these WS2812 LEDs.

[Sprite] figured there was one device on the current lot of ARM/Linux boards that provides the extremely precise timing required to drive a large array of WS2812 LEDs: the video interface. Even though the video interface on these boards is digital, it’s possible to turn the 16-bit LCD interface on an oLinuXino Nano into something that simply spits out digital values very fast with a consistent timing. Just what a huge array of RGB pixels needs.

Using a Linux board to drive RGB pixels using the video output meant [Sprite_tm] needed video output. He’s running the latest Linux kernel, so he didn’t have the drivers to enable the video hardware. Not a problem for [Sprite], as he can just add a few files to define the 16-bit LCD interface and add the proper display mode.

[Sprite_tm] already taken an oscilloscope to his board while simulating 16 strips of 600 LEDs, and was able to get a frame rate of 30 fps. That’s nearly 10,000 LEDs controlled by a single €22/$30USD board.

Now the only obstacle for building a huge LED display is actually buying the RGB LED strips. A little back-of-the-envelope math tells us a 640×480 display would be about $50,000 in LEDs alone. Anyone know where we can get these LED strips cheap?

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