Xybernaut Head Mounted Display to VGA hax!

I have a Xybernaut Xyberview HMD, which originally connected to a Xybernaut MA-V or MA-IV wearable computer. Xybernaut went out of business after some questionable corporate shenanigans, but while they were around, they made a solid product. Unfortunately, they used a custom, or at least obscure, connector to hook that solid product together.

Thanks to the Wayback Machine, I’ve found the pinouts for the connector, and wired mine up so that it takes a standard VGA input. I also built a power supply for it, because it needs 5V and 15V power. The power supply takes 15V from a laptop power brick and drops part of it to 5V while also providing a 15V pass-through. I used a switching regulator, because otherwise I’d be dropping 10V at unknown current as heat.

I initially had the red and blue lines of the VGA connector crossed, but I think that is because they are crossed in the instructions that I found. My corrected pinout is below. If you happen to actually be equipped to do this hack, please do let me know if I made an error, and your terribly expensive, extremely obscure hardware from the mid ’90s somehow fails to work.

The HMD connector has two rows of pins in a connector that looks a little like a miniature Centronics connector. Assuming the longest edge of the connector is on top, there are 13 pins in the upper row (U1-U13) and 13 pins in the lower row (L1-L13).

Wire colors are described as the color of the wire, the color of the mark on it, and whether the marks are sparse. So Yellow/Red (sparse) means a yellow wire with a red mark on it that is less dense than the wire described as Yellow/Red. You’ll know it when you see it.

Signal Name       Xybernaut  Wire Color             VGA Pin
Red               L4         Pink/Red (sparse)      3
Red ground        L3         Pink/Black (sparse)    6
Green             L2         Yellow/Red (sparse)    2
Green ground      L1         Yellow/Black (sparse)  7
Blue              U14        Gray/Red (sparse)      1
Blue ground       U13        Gray/Black (sparse)    9
H Synch           L6         White/Red (sparse)     13
V Synch           L7         White/Black (sparse)   14
Synch ground      U10        Pink/Black             10
+5V               U1         Gray/Red
+5V               U2         Yellow/Red
+5V               U3         White/Red
+15V              U5         Pink/Red
Digital ground    L13        Yellow/Black           5
Digital ground    L10        Gray/Black
Digital ground    L5         White/Black
Analog ground     U8         White
Headphone out     L12        Pink
Mic in            U7         Yellow
HMD Sense         L8         Gray                   11

I connected the Gray/Black and White/Black wires to the ground of my power supply, the Yellow/Red, Gray/Red, and White/Red wires to 5V, and the Pink/Red wire to 15V. The display powers up, and I can drive it from my laptop using 640×480 resolution at 60Hz.

Unfortunately, none of this hacking changed the fact that wearing an HMD makes you look like a cyborg from space.

Brain Transplants for Toys

I have a bunch of old toy skeletons sitting around. They are not toy versions of the bones of animals, but the frameworks and some of the motors from things like a toy tracked robot, an RC truck, a few toy robot insects, some tiny RC cars, a robot base with continuous-rotation servos, and so forth. All of these things have motors or servos in them. All of them need some form of controller to make them into autonomous robots to do my bidding (or wander around banging into things).

To that end, I’ve developed a little embeddable controller around the ATMega8, ATMega48/88/168, and other pin-compatible microcontrollers. That is the same chip used in the Arduino, so my board will be software-compatible with the Arduino as well.

My controller, which I’m calling ToyBrain, has a pair of 1A (stackable for more current) H-Bridge motor drivers, so it can control up to four motors in one direction, two motors bidirectionally, or one stepper motor. It also provides two headers for servo motors. For inputs, it has four analog or digital inputs and two digital inputs that are connected to interrupt lines, so it can do things like handle bumper switches in an interrupt service routine.

I’ve ordered 10 boards. When they arrive, I’m going to populate them with whatever chips I have around and try to get a few of my old toys running. Assuming everything goes well and I get a polished device together over the winter, this may end up being something I sell at the MIT flea regularly. I’ll hook up a bunch of toys with the same controller, to show off its versatility, and offer the controller as a kit people can buy.

Reactive Inflatables

I’m working on a project to make inflatable sculptures that react to contact. The inflatable shapes are sewn together out of materials like umbrella fabric and ripstop nylon. Those fabrics block air well, and so a shape made of them can be inflated by a fan.

I am planning to have them react to contact by monitoring the speed of the fans that inflate them. If the inflated shape is pushed, the air pressure in it will increase, and escaping air will try to turn the fan backwards. This should show up as a decrease in fan speed, which I can detect with a microcontroller. The fans are computer cooling fans, so they already have speed sensors built into them. The speed sensors were originally intended to allow the computer that the fans cooled to detect fan failure and shut down gracefully.

I have a couple of inflatable shapes together, but I need a beefier 12V benchtop supply to run them. each fan draws 1.1A at 12V. That is a lot more than a normal computer fan, but these are high-volume server cooling fans, so they move a lot more air.

Unresolved imports in Eclipse/Pydev

The Pydev plugin for Eclipse (at least on my system, Ubuntu Linux on a PC) has a hard time with imports, reporting them as unresolved when Python can actually find them.  I find this particularly bothersome when I do projects with OpenCV and Beautiful Soup, as it can’t find either of them and so can’t do code completion.

This thread has the answer. In case that goes away, what you need to do is this:

Go to Project Properties -> Interpreter -> the “Configure an Interpreter not listed” hyperlink

Uncheck and recheck the box next to the interpreter you are already using (probably the default one), or make some other change that doesn’t really change things.

Hit “Apply” and go for a soda while PyDev reindexes things.

Open some file with the bogus unresolved import and make an edit, then save it. Pydev will recheck the imports and stop whinging about the unresolved ones.

As they say on the Heart of Gold, anything you cannot deal with now is your own problem.

HTTP status codes

I was reading up on HTTP status codes, and I got a bad idea. There are a small number of official status codes, like the ubiquitous 404 (file not found), an even smaller number of less-official status codes, like 418 (I am a teapot), and a lot of undefined status codes.

So what happens if a browser gets an undefined status code? What if it gets a malformed code? Writing a simple test for this would be easy. It would just be a web app framework that returns whatever you pass it on the URL as the error code, so www.example.com/errorCodes/200 would get you HTTP OK, while www.example.com/errorCodes/499 would get you the undefined code 499.

I would hope that the browser runs the code past its short list of defined codes, doesn’t recognize it, and shows an error page to the user saying something like “The server returned an invalid error message. It may be misconfigured. Please try back later.”

However, some browsers may mishandle the message, and hand anything that starts off with, say, 2xx to the page renderer, whereupon things might go horribly awry. I hope modern browsers are immune to this sort of shenanigans, but it may be no one has beaten on them in that particular way.

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.

Vindication for geometry teachers

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.

Light parts

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.

Flat shapes

I bent the flat shapes in an improvised metal brake to get them 3-D, and then riveted them together to hold the shape.

Now in 3-D!

The finished shape seems to fit together pretty well.

The general idea

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.

Made of hate

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.

Seizuredome electronics
 

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.

http://audacity.sourceforge.net/Audacity

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.

Until now.