Mostly the same as last month, but I’ve switched my music player to MOC. I also used MPD a bit, but I like this one better.
Recently, there have been a few posts on LaserPointerForums with regards to a curious little experiment. A laser is focused as close to the aperture as possible and is pointed straight up at the ceiling. Then, a piece of very soft black plastic or felt marker tip is burned. With some luck, a small particle will burn off, and then seem to float in mid-air. In fact, it looks something like this:
The marker is pointing roughly to the particle in question. It is not smoke and this fact can be verified because you can actually move the laser around gently and the particle will follow it! I made a brief write-up in one post on why this works, but I decided to play around a bit and get some better quality pictures and a few videos.
Here’s the essence of why this phenomenon occurs. A principle called wave-particle duality states that light (but not only light) can be represented as both a wave and a particle; that is, it can have both wavelike and particlelike characteristics. When you observe Airy disks and other diffraction patterns, you are observing wavelike phenomena; the light behaves just as if you were to take a tank of water and perform the same experiments. However, light can also behave like a particle–the term for a particle of light being a photon. Particles have an energy and momentum associated with them and it was shown that photons do indeed have this property. For more information on wave-particle duality, I recommend the HyperPhysics slides on the subject.
Because photons have an associated energy and momentum, they can impart a force onto other objects. This is exactly what is occurring in the picture above! The particle is experiencing a set of force vectors from the laser light which cause it to find an equilibrium position very close to the waist of the beam. Here is an interesting explanation of this phenomenon, known as optical trapping. To borrow a diagram from Wikipedia’s excellent optical tweezers article:
When a particle moves out of its equilibrium position, a restoring force will push it back just above the waist.
To illustrate further, I’ve taken a video (720p 
) and a few pictures:
Edit: It seems as though my video has made it to Reddit and LiveLeak:
http://www.reddit.com/r/science/comments/auh5b/optical_trapping/
A black squirrel lives somewhere in our yard and stops by the bird feeder in the mornings for a meal. Wikipedia has a nice article on these curious creatures. This was also a good way to test the 18x optical zoom of my camera. Unfortunately, by the time I was able to make the necessary adjustments to the camera to improve the contrast, he ran off.
Almost everyone who uses the command line extensively knows about GNU screen. It is a clever utility that allows you to manage your workflow in many ways. When you start a screen session, you will be presented with a virtual terminal where you can do your work. You can launch multiple terminals in a single session and quickly switch between them and even copy and paste between them as well.
I have used screen for a while, but it’s a little too intensive for my needs. Its layout is not very sane by default, but it can be configured extensively. So, when I heard about tmux, an alternative to screen popularly used in OpenBSD systems, and its reputation for being a more elegant solution.
One unfortunate bug with tmux is its failure to render transparent backgrounds in 256-color environments. Apparently this issue is due to the inability to “erase” backgrounds. Fortunately, the latest CVS revision fixes this problem, so I’ve been able to switch entirely from screen to tmux.
Here is my tmux config. I haven’t worked on keybindings yet (I’d like to make them more vim-like). Here are some screenshots from my laptop:
Last Thursday, the (in)famous SparkFun held a rather strange event: “Free Day“. Their goal was to give away $100,000 worth of free items (at $100 max per household) in order to celebrate the move to bigger site hosting. What a cute idea! I mean, all you need to do is be one of the first (roughly) 1000 customers and you only have to pay shipping!
I more or less expected the following to happen: thousands of users would try putting their order through and the whole thing would be over in a matter of minutes. I imagined that I’d be too slow to get to order something, but I decided to try anyways. Sure, there would be some site slowdown, but I didn’t expect everything to CRASH AND BURN.
Sadly, the site did crash and burn, several times, in fact. Most of the time, I couldn’t even open an SSL connection. After about an hour of trying I managed to get to the last page where there was a big button that said “Submit your Order for Free Day” but when I pressed it, I lost the SSL connection or got a blank page. So, after another 44 minutes of trying, all $100k was given away and I ended up with nothing. Apparently, the rumor that I had heard about SparkFun moving to a server cluster (which would have been able to expand to serve the load as needed) was entirely wrong. They were trying to do this on like three servers.
At any rate, I was a little sad that I didn’t get anything, but I never expected to in the first place.
Well, by now, you’ve probably figured out what happened, so you could probably scroll down to the pictures now. I saw my name on my dorm’s package list and I assumed that my flashlight from DealExtreme had arrived, but when the worker picked up a huge box from the floor, I was a little confused.
Okay, now time for pictures. I ordered a digital soldering station.
I bought a package of seven CREE XP-G LEDs from Cutter Electronics on a single board. At around 2400 lumens total, these LEDs can throw a ton of light.
The LEDs are driven with a buck driver, which is powered by a trimmable 24V PSU that I had lying around. I purchased a heatsink for the board, but the screwholes don’t line up, so I’ll have to drill some new ones. I also bought some integrating optics to help smooth out the light output.
At any rate, I was very impressed with the results. With a little mechanical engineering to dissipate the heat efficiently, this LED assembly will be the perfect projector replacement bulb. The light output is simply stunning; it lit up my whole room very nicely.
Using some crystals generously donated by Kenom, I managed to confirm that the diode I purchased lased at 808nm. This rules out one theory on why I am not getting output from my original crystals. These new crystals were used in a cheap laser pointer, so they are bonded together into one package. As a result, it’s fairly easy to put them in front of a beam and watch the green on the other side. However, my original crystals are unbonded, which leads me to believe that there is an alignment issue. The diode that originally pumped those crystals had a countersunk hole for the mounting screw; the diode I’m currently using does not, so it doesn’t quite align as the original diode did.
Yes, I literally stuck a huge chunk of aluminum on the back of the LM317 because it was overheating and the output current was dropping.
Throughout this past semester, I was continually impressed by the benefits of powernapping. However, unfortunately, I’m one of those people who shut off their alarms and go back to sleep all the time. So, my 20-minute powernaps became full nights’ rests. Normally, I wouldn’t mind that, but it made things very difficult when I had a major assignment due the next day.
So, I present icsy:
http://jwcxz.com/projects/icsy
icsy (I Can’t Sleep Yet) helps to prevent you from falling back asleep after waking you up by asking you some simple math questions to get your mind going again. You can customize all sorts of features including the alarm time, snooze time, number of questions, and audio file or alarm command.
It’s very easy to use. Just invoke icsy -h for instructions.
I bought a Polaroid Polaview 350i projector off of eBay a few weeks ago for about $30–not bad considering that it retailed for a few thousand when it was being made. Of course, projectors that are sold on eBay usually don’t come with bulbs; their owners decided that the price to replace the bulb (at roughly $200-300 a piece) simply was no longer worth it.
I bought the projector originally with two ideas in mind: if it turned out to be totally broken, then I would just salvage the optics in it; there are some pretty cool lenses and cubes in there that are easily worth $30. If I could find a cheap bulb, then I’d just install it and get the projector running immediately.
Well, I couldn’t find a cheap bulb and I didn’t have the heart to tear it apart since it seemed to be in great condition (although it’s missing the remote). So, I decided to try building and installing an LED replacement for the projector lamp. Based on my research, there have been several attempts to do this. However, those that I came across all used standard white LEDs, which have very little light output compared to the original bulbs.
A company named CREE makes high-quality lighting-class LEDs. Their XP-G LED is the most efficient on the market and I intend to use 7 of them on a prebuild board from Cutter Electronics. This will provide just over 2400 lumens, which is a little over the original bulb’s specification (~2200 lumens).
Interfacing the LED bulb with the original electronics will not be easy. The projector uses a HID mercury arc lamp. These lamps require a 5kV pulse to ignite, followed by about 50V to run. If I can kill the initial pulse somehow, then I should be able to use the 50V supply to power a simple buck converter. Also, I need to bypass the lamp checker; the projector won’t start up if it doesn’t think that there’s a bulb in there.
Anyways, here are some pics:
(horrible picture, sorry)
It worries me that little shards of glass fell out of the device. I might have to replace some optics that are difficult to get to.
The big RGB cube is under here. After I got the mainboard off, I realized just how difficult it will be to mess with the internals of this thing.
I’ve also started a page for my ongoing work.
It’s December. That means three more weeks until I have a normal sleep schedule again. Anyways, here’s what my desktop looks like this month. I’ve switched to zsh, which is faster and much more powerful than bash. It also supports all kinds of really advanced autocompletion, which can be helpful when you’re trying to remember the syntax of some command you don’t use very often.
