Retrotechtacular: Shedding Light On Holograms

March 11, 2014 by Kristina Panos 10 Comments

This week’s Retrotechtacular is a 1972 introduction to holography produced by the fine folks at Encyclopædia Britannica. It details quite admirably what holograms are and how they’re made.

Holograms are quite different from photographs, though both are recorded on film. Holography is based on the additive effects of waves: two crests of equal amplitude create a larger crest, while a crest and a trough of equal amplitude cancel each other out, causing an interference effect. The video demonstrates the concept nicely with water ripples and explains that the same effect happens with sound waves and light waves.

Lasers are the key to the intense and spectrally pure light required for holography. Incandescent light consists of too many wavelengths to be effectively split into two identical light wave sources. To create a hologram, a laser is split with an optical device into two beams. One beam is focused directly on the object being recorded and is called the object beam. The second beam is directed away from the scene through a series of mirrors and shone directly onto a film emulsion.

The film records the interference between the waves of the two beams. It appears to be blank after development, but upon close inspection reveals stripes of light and dark. When the exposed film is placed in the path of only the reference beam, the interference patterns recorded on the film split the beam back into two, recreating the scene. With the aid of a screen for projection, the hologram can be seen showing the original object in 2D. Another big difference between photographs and holograms is that even a small portion of a hologram can reproduce the entire scene, but a piece of a photograph is just that.

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Welcome To Droning On

March 10, 2014 by Adam Fabio 15 Comments

droning-on-logo

Tesla_boat1 Welcome to Droning On, Hackaday’s new column covering all things unmanned. In this column we will primarily focus on aerial vehicles, both fixed and rotary wing. Expect to see traditional R/C, as well as First Person View (FPV) models, computer controlled autopilot systems, as well as anything new that shows up on our radar.

First, a little bit of history. The earliest radio control vehicle in history was designed by a man known well to Hackaday, Nikola Tesla. Tesla presented a radio controlled boat at an electrical exhibition in New York in 1898. Tesla called the system “Teleautomaton” and said the craft utilized a borrowed mind. In addition to cruising around a man made pond, the boat could solve equations by blinking lights atop two of its masts. Tesla would encourage viewers to call out math equations, then flash the lights from the boat’s control panel.

For many years R/C as well as its cousins Free Flight and control line were hobbies occupied solely by hackers. One needed to have metal machining skills to build engine parts, draftsman skills to read plans, and carpentry skills to build airframes. Radios were built from tubes. Control, if it may be called such, was all or nothing – so-called “bang-bang” systems. Much like their model railroad compatriots, R/C plane modelers built with the parts they had on hand. Several early DIY R/C planes were controlled by rotary telephone dials. Dial 1 to pull up, 2 to turn left, etc. Control surfaces were moved by rubber powered escapements rather than the servos we’ve come to know and love. Aerodynamics also came into play. With such rudimentary control systems, planes were designed to be inherently stable. Thankfully there were numerous proven air frame designs available from the free flight arena. Slow flight, high dihedral, and docile stall behavior were the rule of the day. Early R/C planes could be thought of as free flight vehicles with occasional suggestions via radio control. Click past the break to find out more about drone history, and to read about the recent FAA judgement.

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Hackaday Links: March 9, 2014

March 9, 2014 by Brian Benchoff 4 Comments

Thinking about starting a CNC machine, 3D printer, or laser cutter project? Misumi has you covered. They’re offering up $150 worth of free stuff with a coupon code. [CharlieX] is putting together a BuildLog laser cutter, a whole bunch of people on reddit are building 3D printers, and I have most of the rods for an i3 build. Just use the promotion code First150 on your order. Actually, read the terms and conditions, but rest assured – this is legit.

A few months ago, we saw this Enigma cypher machine that combines the classic late-30s aesthetic of the original with modern hardware – including a few 16-segment displays. Now there’s a Kickstarter for the Open Source Enigma replica, and it looks like it’s going to end up being pretty popular. Here’s the site with all the deets. Check out that QWERTZ keyboard.

[Jason] has a love of LEGO and a terrible keyboard. Combine the two and he came up with a functional LEGO keyboard. The electronics are, sadly, an old PS/2 membrane keyboard, but the mechanicals are a work of art – all the keys are mounted on a grid of Technic parts that can be positioned over each of the membrane buttons.

Want a really cool look for your next enclosure? How about LED pipes? They’re those clear plastic bits that direct the light from LEDs around corners and can make any enclosure looks like a Star Trek set piece. You can cut these things with a laser cutter like the Alima team did with their indoor air quality meter. Looks pretty cool.

Ask Hackaday: Wiping Your Bum With An Arduino?

March 9, 2014 by Brian Benchoff 83 Comments

Over or under? Standing or sitting? Truly, toilet paper has been the focus of the most irreconcilable arguments ever. The folks on the Arduino Stack Exchange have a far more important question: how do you trigger an alarm when your TP supply is low?

[user706837] asked the Internet this question in response to his kids never replacing an empty roll. This eliminates the most obvious means of notifying someone of an empty roll – looking at it before you sit down – and brings up a few interesting engineering challenges.

Most of the initial ideas deal with weight or some sort of light sensor that can differentiate between the white TP and the brown roll. A much, much more interesting solution puts a radioactive source in the TP holder’s spring-loaded rod and uses a sensor to detect how much TP is left. A quick back-of-the-wolfram calculation suggests this might be possible, and amazingly, not too dangerous.

We’re turning this one over to you, Hackaday readers. How would you design an empty toilet paper alarm? Bonus points awarded for ingenuity and cat resistance.

Image source, and also one of the longest and most absurd Wikipedia articles ever.

Fail Of The Week: WS2811 Pixel Failure On FLED

March 6, 2014 by Mike Szczys 36 Comments

This Fail of the Week project comes from one of Hackaday’s own. [Ben] took on the FLED data visualization project as a way to make the SupplyFrame decor a lot more fun. He had quite a bit of help soldering the 96 WS2811 pixels into their custom made 6’x4′ enclosure and the results are really awesome. In addition to showing server load and playing games, FLED has become something of a job interview. Sit the prospective employee down at a terminal and give them an hour to code the most interesting visualization they are capable of.

But two weeks ago [Ben] staggered into the office and found the display was dead. Did he try turning it off and back on again? Yes, but to no avail. The power supply wasn’t the issue and there was no option but to pull the display off the wall and crack it open for a look at all those pixels. Since every one of them had 4 solder joints on either side he figured the problem was with a broken connection. But not so. He resorted to a binary search for the offending pixel by cutting the strand in half, and testing each portion. He tracked it down to the pixel whose underside was blackened as you can see above.

[Ben] thinks one of the capacitors inside the sealed enclosure blew, but isn’t certain. Feel free to tell us what you think failed in this component. But the thing we’d really like to know is if there is a more clever way to sniff out the offensive pixel without cutting the connections? Four hours on the floor with this thing (and no knee-pads) and [Ben] has sworn off sourcing pixels from random Chinese suppliers. He might go with pre-assembled strings next time. We chuckle; this is the high-tech equivalent of trying to get old strands of Christmas lights to work.

If you haven’t seen FLED in action, check it out after the break. It amazing how LED intensity and quality diffuser material can make a perfect grid of LEDs seem to dance in waves and color curves.

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Hackaday 68k: Blinking An LED

March 5, 2014 by Brian Benchoff 47 Comments

Time for another update for the Hackaday 68k, the 16-bit retrocomputer developed on Hackaday to show off both our love for vintage hardware and our new project hosting site. There’s still invites to be had, people. Get ’em while they’re hot.

This post is going to cover exactly how complex a simple 68000 system is. The answer is, “not very.” A simple 68k system is at least as simple to design than some other homebrew systems we’ve seen around here. Yes, a 16-bit data bus means there’s more wires going everywhere, but like she said, just because it’s bigger doesn’t mean it’s harder.

There is some progress to report on the construction of the Hackaday 68k. The processor has been verified as working with a blinking LED. It’s the ‘Hello World’ of computer design, and it’s at least as complex as blinking a LED with an Arduino.

You’re gonna want to click that ‘Read more’ link.

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Retrotechtacular: Lighting The Way For Talkie Pictures With Optical Sound Recording

March 4, 2014 by Kristina Panos 14 Comments

This week’s Retrotechtacular is a 1943 Encyclopædia Britannica film focusing on optical sound reproduction for motion pictures. Both the sound and the images are recorded on film, which is only affected by light. Therefore, the sound waves must be converted to changes in light.

This is done the way you might expect: the sound waves hit a microphone and the changes in current are amplified and used to control the intensity of light falling on the film. Three types of soundtracks are described and wonderfully demonstrated at the end of the film.

All three types are made from a series of thin bars of light, and the corresponding current value is represented by changes in either their length or their width. In the Unilateral Variable Area recording, the bars extend from the right side of the sound track. Bilateral Variable Area recorded bars emanate uniformly toward the edges from the center. In Variable Density recording, all of the bars extend from the left to right extremes, but their thickness varies.

Variable Density recording is done with a light valve, which contains a pair of delicate metallic ribbons in a magnetic field that move like shutters when the sound current flows through them. The light coming through to the film is varied by the slot created in the space between the ribbons. The light patterns are changed back to sound through a photoelectric cell, which converts the variations in light back to changing current. These changes are amplified and run through a loudspeaker. Be sure to watch to the end to catch a demonstration of the recording methods, set to what we’re pretty sure is Camille Saint-Saëns’ Danse Macabre.

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