As featured on Hacked Gadgets and Hack a Day.
    How to add a rapid fire button to your Game Boy Advance, so you don't have to keep taping that darn "B" button.

!!WARNING!! I'm not liable for any damage caused by following this tutorial, continue at your own risk!

Parts list:
    (1)Dual two input nand gate IC (I used a triple three input NAND gate IC because it was what I had on hand)
    (1)2n2222 NPN transistor
    (1)0.1uF ceramic capacitor
    (1)Mini momentary on switch from a computer mouse, or similar
    (1)1M ohm resistor (the value of this resistor can be mucked around a bit)
    Some thin wire
Tools list:
    Soldering iron
    Solder
    Screwdriver to take apart your GBA (if you don't have a tri-wing screwdriver handy, a small flat blade will do)
    Dremel
    Small phillips head screwdriver

    Start out by taking apart your GBA by removing the screws on the back cover and the screw under the battery cover. Then remove the phillips head screws that attach the circuit board to the case. Flip the circuit board over carefully so you do not damage the ribbon cable that connects the board to the LCD. Then solder two wires, one to a pad labeled TP1, and the other to the metal part supporting the button. The metal part is ground. TP1 is close to the R button.

Now take those wires and solder up the circuit based on this schematic

GND should be connected to the wire that you soldered to the metal bit, and the pin on the transistor labeled TP1 should be connected to the wire you soldered to the TP1 pad. Like so:

Here is a close up of the IC:

Now you need to hook up power and ground to the NAND gate IC. To do this solder two wires to the battery contacts labeled + and -.

Take the other end of the - wire and solder it to the negative lead of the NAND gate IC. Now you need to decide where you want to put your rapid fire button, I put mine in a dremeled out accessory attachment point. Here is a couple pictures of where I put mine:

Solder the other end of the + wire to a lead of the momentary switch, and then solder the other lead of the momentary switch to the positive lead of your NAND gate IC. Now you're done! Congratulations on your new rapid fire button!

How does it work?
    The two NAND gates create a square wave which switches the base of the transistor high and low, which in turn disconnects and connects TP1 to ground really fast, resulting in the detection of many button presses. Normally when you press the "B" button it just shorts TP1 to ground once, resulting in one button press being detected.