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.

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.

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.

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.

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.