Friday, March 28. 2008
Of all the 500 series modular scopes made by Tektronix, the 547 is one of the most desirable due to its 50 MHz bandwidth and innovative dual timebases. When released, this machine was way-hot high tech, crammed with a mix of vacuum tubes and discrete semiconductors, and worth as much as a new car. I got mine through a friend who found it at a church rummage sale and paid $10 for it, complete with cart, some extra modules, and manuals for everything. Any problems? Well sure - the thing's been in service for 40 years, knocked about by at least two private companies (judging by the calibration stickers) and its original owner, the United States Navy. A short list:
- The dust filter that covered the fan was missing, because the bolts that kept the bezel on were sheared off - though the bezel came with the scope in the drawer of the cart, at least.
- The original power inlet was cracked, and missing its ground pin, which is more than a little dangerous.
- The fuse holder was chewed up and unable to retain the fuse and cap, which was missing entirely.
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Categories:
Inventions
Friday, March 7. 2008
Our New Year's Eve fireworks shows are something to see—or so I gather from the reactions of the crowd. I don't really know, to tell the truth. Running around with a blowtorch lighting fuses doesn't give you a chance to watch the show for yourself and see what everyone's ooh-ing and aah-ing about. So for the last couple of years, my friends and I have been working our way towards the holy grail of backyard pyro—complete, automated computer control of the fireworks show. We started out the usual way, with a variety of electrical ignitors hard-wired into a "nail board" or a console of switches; I'll have to write a more complete history of these attempts sometime, more for my dear readers' laughs than for their technical edification. This year, however, we rolled out the first version of something completely different—a 12-channel, serial-controlled, microcontroller-driven, battery-powered, pyro ignition device!
On to the engineering, then: the microcontroller is an Atmel AVR, a 90S8515 running at 8 MHz to be exact (obsolete chip, sure, but I had one lying around—the next version uses an ATMega16 instead). This accepts RS-232 serial via the MAX-232 driver, interprets the byte it receives and fires the appropriate squib by pulling the gate of a NMOS high. The MOSFETs are STI P16NF06L's in TO-220 packages, good for 16 amps of drain current each; this high-current capability is built in to accommodate some types of very low resistance squibs that need a lot of current to fire.
As a temporary kludge for New Year's (I ran out of time as usual), I packaged the board and a 12V Sealed Lead-Acid battery in a tupperware tub. Since this was sited close to my mortar rack, which might spit out flaming bits onto the plastic box, I protected the top with a folded piece of sheet aluminum.
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Categories:
Out and About
Monday, February 4. 2008
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Sunday, January 27. 2008
Friday night the boys and I spent some hours immersed in a weird mix of high-octane drag racing and electrical engineering geekery—the Florida Electric Auto Association took over a "run-what-you-brung" drag racing event as part of their Battery Beach Burnout weekend. The venue was one Countyline Dragway, an 1/8 mile strip of pavement in the middle of the woods in northwest Dade county. One of the competitors brought this homebrew 240 volt electric bike, with 20 batteries driving a shifter kart tire hard enough for a smoky burnout - in the picture I'm holding the brake down to keep the bike from moving as he tensions his drive chain, which unfortunately broke on his first run of the night.
The following picture is of a Porche 912 with an improbable modification: two DC motors inline and hanging out of the back like a rocket engine. This car set the Countyline Dragway electric record at 67 miles per hour at the 1/8 mile.
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Artworks
Monday, January 21. 2008
I made some Mjolnir (that would be the hammer of Thor for those who don't speak pagan-geek :) ) pendants for viking party costumes. It was also an opportunity to try my hand at sculpting and moldmaking, bringing me one step closer to living the life of a mythbuster—that is, a mythbuster without his own television show. I based the design on this one (found on google images); for the price, I probably should have just bought that one instead, but that's not really in the creative spirit of this whole New Year's Eve theme party thing.
The first step: I melted down some old bits of candle wax and cast them into a puck shape, from which I carved the original pattern using one of my very favorite tools, the X-Acto knife.
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Inventions
Wednesday, January 9. 2008
One of the new elements in this New Year's Eve fireworks show was this 16-shot mortar rack, designed to accommodate the "festival ball" type of readily available mortar shell. The tubes are HDPE with a 1.875 inch bore, available from Skylighter at $27.25 for a group of six. HDPE is really the best material for this application - do NOT use PVC, as it will shatter into dangerous shrapnel if the shell fails to clear the tube and detonates inside. Certain types of cardboard launch tube, available from pyro suppliers, might be acceptable but I have no experience with this so you take your own risk if you choose to use it. The Skylighter HDPE tubes have a wooden plug at the bottom—I drove stainless steel wood screws into this plug from the base of the rack to secure the tubes.
The rack itself I constructed from various bits of hardware store lumber. Since this rack is deployed outside, in potentially wet environments, I painted it with several coats of Kilz primer, then glossy black exterior latex (glossy to make cleaning off any powder, soot, or dirt easier). I also mounted two carrying handles on either end.
During the New Year's show, this rack was loaded with a mix of Black Cat "Gold Class" spherical shells and their "Fort Knox" cylindrical shells. One row of eight was electronically detonated using my computer-controlled firing board (of which more anon), while the other side was lit with a blow torch, like most of the fireworks that night.
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Artworks
Sunday, January 6. 2008
New Year's Eve 2007 was the latest in what has become a Martinson tradition: a themed costume party. The theme this year? Vikings! As always, this party involved a great deal of creative work beforehand in making the costumes, props, fireworks show, and all the rest of what our guests have come to expect out of a not-so-typical New Year's Eve. I can't publicly thank everyone responsible for these preparations, but you know who you are, and I know what you did. Thank you all. This post (and the ones to follow), however, is more for the benefit of those who weren't at the party, but are interested in some of the projects completed for it. First, my viking shield:
This is probably the only costume item that bears any similarity at all to actual viking kit, or at least measures up to a reasonable re-enactor's standard. Yes, it is plywood (11/32") rather than joined planks, and the fanciful dragon motif (taken from a shield on display at the Norway pavilion in EPCOT center) was probably never seen in actual dark age combat, but other than that, it's not bad. The plywood blank I cut out with a jigsaw. The steel boss was made by an armourer named Mad Matt (it's the "satin-finished" round boss available on his site) - a solid, economical choice I'm very happy with. I also applied an edge-banding of 3" wide rawhide strips (soak a large rawhide dogbone till it unravels, apply when moist and flexible) nailed over the edge with blued carpet tacks. The grip in the back picture is just a bit of hardware-store mild steel bar, drilled and riveted through to the boss.
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Categories:
Administration
Friday, November 30. 2007
I've been getting a few complaints about various sites not being accessible by Comcast users and discovered that quite a lot of domains are inexplicably not resolved by their DNS servers. Here is an extremely partial list, generated purely at random:
These are all popular blogs, and none of them work on Comcast's DNS. So I switched to OpenDNS, a free public dns service. You can sign up for an account, which gives you access to some features like porn-filtering and statistics on DNS usage. You don't have to have an account, however, you can just go ahead and start using the servers: 208.67.222.222 and 208.67.220.220.
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Categories:
Exploits
Wednesday, October 24. 2007
Believe it or not, being a member of junk-mailing lists, in particular those targeted at consumers of high-end "lifestyle" products, can be good. Being a close friend or relative of a person on those lists can be even better. This second approach has gotten me past the door of a surprising number of product launches, luxury car test drives, and top-shelf whisky tastings, usually in the company of my cousin Torm, whose tastes are somewhat better funded than my own and whose addresses are in somewhat wider circulation. But it was this October that Torm, my friend Jay Wilson, and I headed south to the Homestead Speedway to participate in the ultimate free-of-charge luxury-goods marketing event: the Audi Driving Experience. Click on the link to read more and be prepared to accept that all Audi requires from you is a driver's license and the flimsiest pretense of being richer than you actually are to stuff your head into a helmet and set you loose on a racetrack piloting several hundred thousand dollars worth of powerful machinery.
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Inventions
Saturday, September 1. 2007
Brandon Moore and I have made it into local glossy Boca Raton Magazine with our desalination project. Many thanks to Kevin Kaminski for the article; many thanks also to the photographer, whose name escapes me, for taking on the thankless task of making two scruffy geeks look good. If you live in Dade, Broward, or Palm Beach county, go and buy a million copies, on newsstands September 1.
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Friday, August 31. 2007
So far I'm relatively satisfied with my new Mediatemple DV hosting service. I have, however, discovered a problem with the Mediatemple configuration of Awstats, the logfile-analyzing web statistics package I use. Awstats can't find its images because the path is broken in the standard Mediatemple installation - browser and country icons are missing, and the bar graphs are empty:
Here's how to fix it.
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Inventions
Sunday, August 12. 2007
One of my recent google searches about pipe-crawling robots brought up this link, which appears to be a translation into Polish of some of the documents I wrote about my senior engineering project. It includes pictures from both the pipe crawler web page and the final report we submited to our professors. I should thank ... er ... somebody, though I'm not exactly sure who. They appear to be a lab or research institute of some kind. Well, thanks for the translation anyway!
I'd also like to take a few words here to insist that my friends Sheraz Wasi and Mark Miller be credited as co-authors of the Pipe Crawler work. It seems like my name is the only one that gets attached to it anymore, because I wrote and hosted the web page about it, and that's not fair; both of them toiled away in the robot lab from morning to midnight just as I did. By the way, this is not a criticism of my new Polish friends—many web sites and email correspondents get the impression that I was the only author simply because the page happens to be hosted at www.eikimartinson.com, and this seems like a good opportunity to set the record straight.
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Administration
Saturday, June 23. 2007
As of yesterday this site is now hosted at Media Temple on my own "Dedicated Virtual" server. It's not exactly a true dedicated server, but it appears as such to me - I get a root login and the ability to reboot the "machine". I get statistics based on Apache logs (something my old service, csoft.net, did not provide for shared hosting). I'm a good deal more insulated from all the other users than I would be on a shared service, which is good for application performance, reliability, database security, etc. But best of all, regular users of this site will notice load times have shortened by a factor of 5!
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Inventions
Wednesday, May 30. 2007
I would like to bring to the attention of my readers an impressive
technological advance made by one David Worden, lately graduated
from the University of Wisconsin with a well-deserved degree in
Electrical Engineering. Mr. Worden enlivened his graduation ceremony
with a light
show built into his mortarboard: 64 LEDs driven by a
microcontroller programmed to produce a variety of animated
effects. Let me be the first to congratulate Mr. Worden on his
splendid achievement in Mad Science—but as a Mad Scientist myself,
let me also remind the young upstart that he was not the first to have
this idea!
In the long-past days of my miss-spent youth
(err … 2004), I also graduated with a degree in Electrical
Engineering, and sported a light-show hat of my own at the ceremony. The mortarboard had
four diagonal lines of 8 white LEDs each, controlled by a central PIC
microcontroller; all five circuit boards were painted black and
atttached to the top of the hat with velcro. Though I must admit,
Mr. Worden's design is rather more complex, with twice as many LEDs as
mine and a fully-concealed circuit.
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Inventions
Sunday, April 15. 2007
As a small project for my Inventive Thinking class, I worked on a simulation of creatures avoiding each other or performing tasks like crossing a street or forming a swarm. The creatures navigate by choosing simple actions (like turning right or left) based on the "Looming" principle of obstacle avoidance studied by my thesis advisor, among others. The simulation runs in your web browser (Firefox or recent IE have been tested, but probably others as well). You can view it (fun to watch) and play with the parameters to your heart's content at this link: Looming Simulation
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