Month: May 2011
Seizuredome light construction photos
The Seizuredome light is an icosahedron made out of aluminum. Each face is 5.5 inches on a side, so the whole thing ends up being about the size of a soccer ball. Each face has three 1″ aluminum spikes sticking out of it, so that when it is not hanging, it does not rest on any of the LEDs.
The light started life as a sheet of aluminum, 24″ on a side. I plotted the net of the icosahedron by constructing a bunch of equilateral triangles with a compass and straightedge. Geometry class is only useless if you’re not planning to make anything interesting in your life.
After that was all plotted out, I cut it out with tin snips and cut arcs out of the corners with a nibbler. The arcs will make the finished shape have a hole at each vertex. Those holes are where I will run the wires for the LEDs, but they also let me more or less ignore the thickness of the material, which would otherwise possibly make the corners look bad.
Then I drilled holes in all the pieces. The holes in the faces are for LED and spike mounting. The ones in the tabs are for rivets that hold the shapes together.
I bent the flat shapes in an improvised metal brake to get them 3-D, and then riveted them together to hold the shape.
The finished shape seems to fit together pretty well.
I added more holes for sheet metal screws. I also added a flat plastic platform inside, so that the electronics have something to rest on, and screwed the spikes to the outside. The spikes are intended to be ornaments for punk clothing, but they mount with screws, so you can stick them on anything you can drill a hole in.
The electronics are also mostly together. I just have to finish up the code, and then mount the control circuit inside, the LEDs outside, and add a power switch.
Mixing software for Linux
As part of my portable sound system, I need something to play. I’m not a DJ, so I’m not going to make mixes on the fly, because I’ll just trainwreck and embarrass myself. Instead, I’m going to carefully tweak and fiddle with mixes at home. That does mean I won’t be able to do the proper DJ thing and have a gradual build, respond to the crowd, etc. Admittedly, some DJs don’t do that either, but I digress…
I also don’t own any records, and only a few CDs. All of my music is MP3s, so I’m going to be making the mix out of MP3s. I’m a Linux user. I have been for 8 years or so. My laptop runs Linux, everything in my house runs Linux, so I’m going to do my mixing on Linux.
Audacity is actively developed, already installed on my machine, and certainly capable of mixing multiple tracks and recording to disk. I know this because I’ve used it before to make a mix of bird sounds, vocals, and machines for a prop that some friends wanted. It supports shifting tempo and pitch, editing MP3s, and adding all sorts of filters and effects.
Mixx also appears to be actively developed, but also looks like it is for live performance. I’m not playing live, so it may be a case of having a great tool for a job that I’m not doing. TerminatorX is also explicitly realtime, and so is not really the tool I’m looking for.
BPMDJ has a lot of sophisticated analysis options (because most club DJs care deeply about Harr wavelet analysis), automixing. On top of that, it appears to be under active development, which is more than I can say about a bunch of Linux mixing tools.
DJPlay looks to be about 4 years old, but may be useful. If nothing else, I can use the BPM counter to figure out the BPM of some of my music and use that as a rough guide for what might mix well. The interface looks like it was designed for live performance, but interacting with controls that mimic physical controls by using a mouse is kind of a recipe for UI disaster.
GDAM is even older, having no new news for the last 8 years. It does, however, support recording mixes to disk. It is intended for live performance, which is not what I’m doing.
Once I’ve installed and played with a few of these mixers, I’ll update this entry with my impressions.
Neural Net book
For a book on a kind of dry subject, this book has an oddly humorous tone:
“It is also interesting to rotate a frog and notices that his eyes try to maintain their orientation up to some maximum angle at which time the frog will close his eyes, giving up the attempt at computing the appropriate adjustment of the visual input. Try not to let anyone see you doing these experiments”
“If a hole is punched in the visual cortex, V1, the only apparent deficit is a hole in the field of view… There are anecdotal records of people receiving damage to this part of the cortex. They report seeing President Bush’s thousand points of light.”
“At a recent neural network conference, Minsky tried to clear up the misconception that he was the devil.”
That last one is because Minsky wrote a proof that single-layer perceptrons can’t do the XOR operation, and funding for neural networks dried up for years. This made him unpopular with the people who had been getting that funding.
Rave in a Briefcase
As part of preparations for a local party, I am building a sound system to fit in a small suitcase and run on 12V DC. The system consists of a small DJ mixing deck and a car audio amplifier. Powering the car amp is easy, as it was designed to take 12V DC power. Powering the mixing deck is not so easy.
Mixers are audio gear, so they tend to have audio signals that are AC, and have components above and below 0V. As a result, they have double-ended power supplies. For the mixer I have, there is an 18V AC power brick, which gets rectified, filtered, and put through a +15V regulator and a -15v regulator. 15, being higher than 12, is an inconvenient number of volts to get out of a 12V battery. Since it’s double-ended, I really need a voltage spread of 30V, with a 0V rail in the middle.
The simple, stupid way to do this is to power the rig with two 12V batteries and two 6V batteries. Across each set of one 6V and one 12V, I would have 18V, and if each of the pairs of batteries shared a common ground, that would be my 0V rail. Unfortunately, I’d also have to manage charging, connecting, and monitoring charge on all of those batteries, not to mention carrying them to wherever I was using the audio. Lead-acid batteries are heavy. Since this is inelegant, heavy, and requires lots of fiddling, I’m going to call it “Plan C” and only do it if everything else fails.
Another simple solution is to use a 12V DC to 120V AC inverter. That takes up a lot of space, and isn’t all that efficient, but it means I don’t have to build a replacement power supply for the amplifier. I have all the parts for it, and it requires less hauling and fiddling than Plan C, but it is still inefficient, so this is “Plan B”.
Since the AC wall wart is rated for 300mA, I have an upper bound on what the mixer can draw. That means I can start looking into DC/DC converters. Vicor makes a 12V to 15V converter, but it costs $99 dollars and I would need two of them. Since I don’t need a lot of current, I can probably make a pair of step-up converters that have a 15-18V output. This site has a simple schematic, and more importantly, the equation for the output voltage, given the current and frequency of a switching circuit in the converter. The control IC takes care of monitoring the output voltage and varying the frequency, but I may be able to use a simpler circuit and change the frequency by splitting off part of the output voltage and feeding it back to the RC timer circuit.The whole circuit would be small, and probably more efficient than using an inverter and the power supply of the mixer.
What is going on
I started this blog to keep a sort of running list of what projects I have going on and my progress on each of them. Instead of doing that, I’ve been working on the projects and ignoring the blog.
My main project right now is the Seizuredome. The “dome” part is an icosahedron made out of electrical conduit. Five of the faces of the icosahedron are left off, and it rests on the ground on that side, forming a sort of dome. I used the construction techniques from Desert Domes to build the frame, but the process is essentially flattening the ends of the pieces of pipe and drilling holes in them so they can be held together with bolts. There is a picture of the completed dome frame in a previous post. That frame will be covered with mylar “space blankets” to provide a reflective surface.
The “seizure” part of the dome is a little more complicated. If you close your eyes and look at a bright light, you can still sort-of see the light, as a red glow through your eyelids. If that light pulses in the 5-20Hz range, you would expect to see the blinking through your eyelids. Instead, most people end up seeing colorful patterns, like swirling fractals, tye-die designs, spiderwebs, and such. What happens is that the blinking signal is close enough to the patterns of electrical activity in the brain that it can drive the dominant frequencies of neural activity to synchronize with it, resulting in hallucinations and mildly altered states of consciousness. You can buy goggles with blinking lights in them, or make your own devices, which will allow one person to do this. I’m building a photic driver for multiple users.
The Seizuredome will have a bright red strobing light in its center. This light is made of 20 1-watt red LEDs mounted on the surface of an aluminum icosahedron. Each LED is driven by a constant-current driver, which is controlled by a TLC5940 LED driver chip. The TLC5940 chips are controlled by an Arduino. Power for the whole thing is supplied by a LM7805 supply with a beefy pass transistor. That light will be hung inside the reflective dome, illuminating the inside. Since the light is suspended inside a reflective dome, there will probably be no place inside the dome that isn’t strobing red, so users inside the dome will be able to see the psychedelic show by entering the dome and closing their eyes.
That still doesn’t really answer why I called it the Seizuredome, though. I turns out that some people are photosensitive epileptics, but don’t know it. Strobing lights of the frequencies most likely to cause seizures by interfering with neural electrical activity are rare, and don’t usually last long enough to trigger seizures. As a result, it’s possible for someone to grow up without ever seeing a blinking light that is intense enough for a long enough time to cause a seizure.