Wednesday, October 13, 2010

Death Ray (automatic smoke ring cannon)

While working on senior project the other day, I decided I wanted to build a death ray. I'm not quite sure why exactly, but it seemed like a spectacular idea. I have built smoke ring launcher things in the past but they were always operated by hitting the back membrane or whatever. This time, I thought it would be cool to use a speaker cone as the back diaphragm instead of the bottom of a garbage can or something.

Lucky for me, back in high school I managed to obtain a couple busted old 15" PA drivers and had built a very rough prototype subwoofer enclosure for it. I was feeling adventurous at the time so I built it with a passive radiator. I built it like crap so it sounded about the same so it was sitting in my basement all alone. The hole where the passive radiator went was quite useful as no holes needed to be cut in the enclosure. I took out the driver and flipped it around to expose the full surface area of the cone to the working side.

With the driver mounted, all that was left was to cut a hole in a piece of cardboard on the front and to get some power to the driver. I started off with a hole the size of a masking tape roll cut centered in a square of cardboard. I generated some waveforms in audacity to feed the driver through an old amp I had laying around. I found that using the top half of a sine wave at a high amplitude worked best. Also, having a reasonable amount of space between pulses helped clean up the smoke rings. I finally settled on using a 40hz wave with spacing between 0.2 and 1 second.

After playing around with that a bit, I cut a final orifice in a piece of 1/2" ply the size of a Minwax can. In all it worked fairly well and shit smoke rings about 12'. It probably would shoot them farther, but it was somewhat windy out and there was a fence in the way. I thing it would be awesome to use propane instead of smoke and shoot flaming rings of fire, but it may not be the smartest thing to do.

Here is a quick video of it in action, it sounds funny, but my little camera just couldn't pick it up properly.

While I had the sub and tone generator out, I decided to test for the brown note. Overall, it didn't do much, but I really felt funny afterward

Monday, October 4, 2010

Worlds Easiest Hack

Last winter, I had a refrigerator die on me, so naturally I tore everything out of it that still worked. This included some relays, a light socket, a heating element, and of course the little switch that turns the light on when the door is open.

About 5 minutes later, it was wired up to the socket that was just obtained with a short chunk of speaker wire. Cool. My roommate Gigawatts and I had some networking stuff in one of our closets with no light so we threw this little device in there with a little bit (really a lot) of hot glue. Here's a quick pic and a short, but awesome video starring Gigawatts' left hand.

Phone Activated Door Hax

This was a quick hack to buzz myself or guests in without using my swipe card or pressing the buzz button on the panel. The Idea was to use the ringing signal on a phone line to trip a relay, therefore opening my door. Ringing phones were not an issue as there are no land line phones connected in the apartment.
After taking some measurements and talking about the project with the phone tech at my school, I figured out what I was going to do. After some research, I determined that phones typically ring in the 90 to 120 VAC range. I measured mine to be around 200, sometimes over 300, Still not a big deal. The other thing though is that there is always 10VDC sitting on the line for when the phone isn't ringing but you're talking etc... To deal with that, I used a pair of non polar capacitors in parallel, as a single .5µf capacitor wasn't passing enough current to trip the relay.

From here, I connected a bridge rectifier chip, which in turn was connected to my 12V relay. I soldered a 47µf 35V cap across the terminals to smooth out the DC. It may not have been necessary, but I had it laying around and I figured at 25Hz I might as well. 

Diagram of the circuit I used