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.

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.

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.

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.