In the past year or so cellphone jamming has become an increasingly more popular subject. Everyone has been plagued by obnoxious cellphone users in malls, buses, school, work, movie theaters, and in spite of being highly illegal, cellphone jammers are popping up in more and more places.

Green Bay Professional Packet Radio has a great writeup on how it works and even a how-to for building your own

How Stuff Works has a great article explaining the technology behind jamming in simple, non-techie terms.

Lady Ada’s project the Wave Bubble takes it to the next step by making an open source, wide band, self tuning, portable version of the jammer.

For those of you looking to try it out a budget, Instructables has some good ideas too.

Afroman’s digital capacitor writeup is mostly theory, but it has some good applications and looks like it could be pretty useful for future projects

“By manipulating the input/output states on a microcontroller, you can effectively switch capacitors in and out of circuit, as long as the circuit requires one end of the capacitor to be connected to ground when it is in use. When you set a PIC’s tristate buffer bit to be 1, it makes the pin an input and makes it high impedance as if it is an open circuit. When you set a PIC’s tristate buffer bit to be 0 and set the data bit to 0, it makes the pin an effective ground. With this system you can adjust capacitance to whatever you want, with range being dictated by your choice of capacitors and the resolution being dictated by the number of microcontroller pins you have available. This system is suitable for a large number of low power circuits. Here are some crappy pictures explaining it:”

If you’ve ever tried to couple a cheap mp3 player with good headphones, you know much of a pain it can be. This is a walk-through of how to build your own.

“Chu Moy designed a very popular headphone amplifier that’s easy to build, and it can be built small enough to fit in a pocket, power supply and all. It’s powerful enough to drive very inefficient headphones to thunderous volumes from even weak sources, and it sounds excellent considering that you can build a bare-bones CMoy amp for just US$20, and a pretty nice amp for under $50. Considering that the cheapest of the worthy commercial amps is $100 and most of them are in the $200+ range, this is a very worthwhile cost difference.”