Retrotechtacular: Lighting the Way for Talkie Pictures with Optical Sound Recording

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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Halloween Links: October 30th, 2013

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Happy Halloween from everyone at Hackaday! To help you enjoy the holiday here are a few festive links:

[Mike Kohn] whipped up a set of motion tracking eyeballs to make his decor extra creepy.

There’s not much to this jet-pack costume but the results are pretty amusing.

The eyes on [Tim Butler's] skeleton prop don’t follow you around the room, but they do use a PIR sensor to light up the skull.

Speaking of skulls, [Tom] is using some real skulls as decorations. He also added lights where the eyeballs should be, but he is using a photoresistor and comparator to turn on some LEDs.

[Clark] built a Mecha Robot Warrior costume for his son. With all of those LED strips we think he’ll be pretty safe when crossing the street!

And finally, [Jesse] added a lot to his prop in order to produce a Sinister Joker. That’s Joker-as-in-cards and not as in Batman. It’s got an IR distance sensor as a trigger, with a motor to move the wrist, lights for the eyes, and a sound shield to give it a disturbing voice.

Light Controller Goes Overboard for Halloween

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Yep, we said it. This Halloween decoration goes way overboard… and we love it! Not only does [Shelby Merrick] put on an incredible sound and light show for the neighborhood, but he keeps us happy by posting all the details for the lighting controller he designed. He calls the creation FloodBrain as it’s switching a set of flood lights to achieve the effects seen above. But for the full experience you’ll want to watch the demo videos below as well.

He needed a way to switch twelve RGB flood lights which pull 10 Watts. His controller was designed to communicate with them via RS485, with an AVR Xmega8E5 controlling the system. We like it that he included some images of the manufacturing process, using a stencil for solder paste before placing components for reflow.

The floodlights themselves are also an interesting hack. To get what he wanted at the best price he picked up 10W white LED flood lights for about eight bucks a piece, then swapped out the LED itself for an RGB version (same wattage) using the same heat sink and case.

More often that not we see this type of system controlling Christmas lights. [Shelby] mentions that he did get help from Christmas light controller forum We also think he should have no problem repurposing the controller for that type of application.

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Fail of the Week: 27 Face Jack-o’-Lantern

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Sheer luck brings a Halloween themed project for this Fail of the Week post. [Stryker] wrote in to the tips line to share a link to what is an extremely awesome hack. He carved four three different faces on the sides of his pumpkin, then sliced the eyes, nose, and mouth into different sections. Couple this with an internal skeleton made of wood and PVC and he’s got himself a nice hack which lets trick-or-treaters spin the sections to select one of up to 27 different faces.

The sections do spin rather well and the finished project looks fantastic. So what is it that failed? We’ll cover that after the break.

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A Killer Arcade Cabinet for Halloween

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It’s already pretty cool that [Clay] co-owns an Arcade, but he’s really impressed us with his custom-made Splatterhouse cabinet built to get his patrons in the Halloween spirit! A Namco brawler title from 1988, Splatterhouse came in an unadorned and otherwise forgettable cabinet. [Clay] salvaged an old Williams Defender, coating the sides with a cocktail of drywall compound, sand, and paint to achieve a stone texture. He then carved up some pink insulation foam into a tattered “wooden” frame and used it as a monitor bezel. For accents, he fashioned strips of latex to resemble torn flesh and placed them among the boards. The control panel is yet another work of art: [Clay] 3D printed a life-size human femur for the game’s joystick, and converted the buttons to look like eyeballs.

[Clay] decided to go beyond the stunning cosmetics, though, and tapped into the game’s CPU with a custom daughterboard that detects different in-game events and state changes such as player health. An ATMega165 uses four PWM outputs connected to a number of LEDs inside the cabinet and around the monitor bezel to react to the different events. If a player takes damage, red lights flash around the monitor. Inserting a coin or dying in the game causes a different set of LEDs behind the marquee to go nuts.

Check out his detailed project page for more information and see a video overview below. If building a full-scale arcade machine is out of your budget, you can always make a tiny one.

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Class Up your Haunted House with a Disney Mansion Prop

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Die-hard Disney fan [Brandon Etto] must have one of the coolest houses in the block around this time of year, especially now that he’s built his own Master Gracey changing portrait. If you’re unfamiliar with the Disney Haunted Mansion attraction, there are a few different versions at theme parks around the world; the Orlando one features a portrait above the fireplace that miraculously ages into skeletal form.

[Brandon's] recreation uses a Raspi loaded with a Video Looper SD image that cycles through a clip of the aging man image. He fabricated a box to hold a 19″ LCD monitor and mounted an inexpensive IKEA frame to the front. The magic is hidden with window film applied to turn the frame’s glass into a two-way mirror: a technique [Brandon] borrowed from this Halloween Instructable.

For a step-by-step tutorial, you’ll want to head over to [Brandon's] writeup on MAKE, but stick around for a quick video demonstration after the break and check out another Haunted Mansion hack: the Singing Heads.

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Fire Breathing Jack-O-Lantern of Death

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[Rick] is at it again, this week he has conjured up an even more dangerous Halloween hack. Thankfully [Rick] has included a warning of just how dangerous this hack can be, especially if children are around. Don’t do this hack unless you know what you’re doing and you can do it safely.

For [Rick]’s number four hack of the month he gives us the Fire Breathing Jack-O-Lantern of death! This isn’t a new idea but it is a very unique and simple implementation. We always love seeing the ingenuity of hackers to repurpose existing commercial products. In this case, [Rick] uses an automated air freshener which dispenses a flammable spray for the pumpkins breath if you dare get too close, but not so close as to get burned. The trigger distance is controlled by an Arduino and a Parallax Ping))) sensor so as to fire only when people are farther than 3 feet but closer than 5 feet. You can get a copy of the Arduino sketch from his blog posting.

A small candle is used to ignite the flammable spray, which shoots out 5 to 10 inches from the pumpkin’s mouth when triggered by the ultrasonic sensor. It couldn’t be simpler. The most challenging part was getting the large air freshener dispenser in the pumpkin with the flames coming out the mouth. A little extra whacking at the pumpkin fixed the fit, but planning for a larger pumpkin would be advised.

Theoretically the Arduino shouldn’t trigger and throw flames if people are too close, but when kids are running around they may come right into the target area unexpectedly. If this hack is used in the right place it would make for a great Halloween display item and could be used safely.

After the break you can watch [Rick’s] flame breathing Jack-o-Lantern build tutorial.

[Read more...]

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