Who needed to be in college to have that kind of pranking fun?
Sophomore year in high school (circa 1977) my buddies and I were having
all kinds of fun with a book we'd stumbled into in the reference section of the
school library - it had been published in the 40s, and had all kinds
things that teenage boys would love in it. Explosive mixtures, self igniting paper airplanes, NI(3), you name it.
But the librarian gave us grief over the excited talking we'd do in the
reference section when we found the next fun thing to try...
It was annoying.
She annoyed us, so we decided to annoy her.
Between the three of us, we knew just enough about electronics to hack
together a simple little circuit. ( We may have had help from a article
in Popular Electronics, but I'm not sure on that one, it was a long time ago!)
Nothing more than an oscillator, a simple amplifier, a speaker, and a 9V battery.
The catch was the battery didn't directly power the rest of the circuit. Instead we used the
leakage current from a transistor to charge a capacitor. When that
cap charged to the right voltage, which took a few minutes, depending
on the temperature of the room, it would turn on another transistor that
allowed power into the oscillator/amp, and discharge the cap.
What's that noise?
End result was
a roughly 1/2 second "chirp" every couple of minutes. Note that this predates
smoke detectors, but it was like a detector with a low battery. And just as
hard to find, and just as annoying.
Especially since we hid it in her desk, behind the drawers.
And left it there for a month.
They called in exterminators to get rid
of the "cricket" at least twice we know of. IIRC, we estimated that the circuit
could run for 6+ months before the battery was exhausted.
Of course, now ThinkGeek sells an "annoy-a-tron" that is similar in function
but can only run for 2 weeks on it's little lithium battery. I have a few of them.
I use them.
alas no. But I do remember the method - and it's doubtful you can get the materials the way things are these days. Pretty simple - dissolve phosphorus in carbon tetrachloride. when the CCl4 evaporates, it leaves the phosphorus behind. *poof*
A friend of mine hid a noisemaker to annoy management but it was trickier than most, two ways: 1)it only made noise when stimulated by certain outside sounds and 2)it was buried in a piece of office furniture, with only a small aperture for sound to exit.
It ran for about 2-1/2 months before someone figured out how to find it and managed to locate it. The lithium coin cell was still pretty healthy, probably because it only made noise when triggered by outside sounds.
In high school we had a pager / pa system that wold make an annoying beep to which the teacher of the room being beeped would always respond yes or what ever. Each room had a box with two circular opening containing a clock and the speaker for the pager / pa system. I noticed that the beep sounded almost exactly like a 9V buzzer I had at home. I took an LMC555 and wired it for a long delay short duty cycle output so the buzzer sounded like a page about every 5 minutes. My math teacher was a real moron and the inspiration for the prank. Drove guy nuts. Every time he tried to communicate with the buzzer for the entire class. After class I was hanging around waiting for an opportunity to retrieve the device and was busted by the next teacher. He knew me and after hearing the first beep figured out I was probably behind it. He got up on a chair after the math teacher left and retrieved the device. He said I know this is yours and if I find another one in this school you again you will be in big trouble. He knew I hated the math teacher and he did not particularly like him ether. He gave me back the device.
I used the same buzzer in collage on a control systems professor who would always pace back and forth in the front of the classroom and two or three times each class he would catch the pencil sharpener knocking off shaving holder. By the end of the second class I decided he cold probably be trained. So I took a mercury switch the buzzer and 2 batteries to make it really loud. Hi missed it on the firs pass, second pass, the anticipation is killing me. 4th pass he hits it and it makes a racket so loud that he jumps, looses his glasses, drops his chalk and fumbles several times while he straightens the shaving holder causing a few more small beeps. He never hit the shaving holder again. I did not retrieve that system until after dinner.
I had a great time with "drip" circuits! An article I posted about them to sci.electronics in 1988: http://groups.google.com/group/sci.electronics/msg/d71d22473f28ecba?&dmode=source
The magazine I mention was in fact Popular Electronics. I used one of these as retribution against my brother once when he annoyed me. He had a bunkbed with verticals made of large-diameter tubing, with 1/2" holes along the length to attach the bedframes at different heights. I made one of these circuits with cells smaller than 9V batteries so it would fit through one of the holes, and dropped in it. There was no getting it out even after he found it...
I built a similar device when I was in the Navy back in 1969. It was an electronic drip noise maker. I put it in the electronics shop on top of a light fixture. It drove people nuts but it didn't bother me a bit, I knew what it was.
Someone gave me one of these devices recently. It has a photocell that cuts it off when light falls on it, which makes it almost impossible to find. It's somewhere near my workbench - when I find it I'll try and post the schematic.
Blog Doing Math in FPGAs Tom Burke 23 comments For a recent project, I explored doing "real" (that is, non-integer) math on a Spartan 3 FPGA. FPGAs, by their nature, do integer math. That is, there's no floating-point ...