I've lost track of all the little things I've done, but off the top of my head,
1. My Guitar Hero controller cord shorted, so I cut off the end, wired it to an RJ-45 port, creating a little pigtail, and wired up another RJ-45 port inside the guitar so I could use a detachable ethernet cable as the cord. I did a pretty good job with the hole I had to make in the guitar for the port; if fits quite snug, it's flush with the guitar, and I did it before I had my Dremel!
Figure that one out!
2. A friend of mine had a faulty GBA charger cable, so I told her I'd take it home with me and take a look at it. The PSU was blown; there was nothing I could do with what I had. So, I cut off the end and soldered it to a spare USB cable. Instant GBA USB charger! It worked great, even though it was only outputting 5V when the charger was rated for 5.2V. Next time I went to her apartment, I plugged it into her Playstation 2's USB port and started charging her GBA from it.
She was pretty impressed and grateful for that.
3. I have a pair of walkie talkies, and one of the unit's battery was faulty. So I wired it up to a spare AC/DC wall wart... One unit usually stays in the house anyway, and it's nice not to have to worry about the battery dieing.
4. I built an RCA (composite video and stereo audio) splitter/S-video to composite video converter with some salvaged jacks from a broken A/V switch. I also built a second one (splitter only) with jacks from a satellite receiver. These have been SO useful to me!
5. I built myself a 2 port SNES controller to parallel port converter a long time ago, which I have since added 2 more ports to for 4-player Bomberman. This is the best thing I have ever built, because I never stop using it for emulation. (Never stopped getting good reactions about it from the anime club either... we'd use the interface to emulate SNES games on the projectors at the college when we had an ADA (all day anime, where we also play games in a secondary room)... that was always fun.
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6. Even longer ago, I made a null-modem cable that I pseudo-networked my two computers with so I could share my internet connection. That was really satisfying because it was the first time we were ever able to use the internet with two computers at once.
The computers were on opposite ends of the house, so I literally had that cable running clear across the middle of the living room floor, DUCT-TAPED to the floor!
It was slow as dirt, too. After all, it was internet over a serial port.
I can't remember what baud rate I was able to run it at, but it wasn't terribly high.
7. This one was just a couple weeks ago... My third party GC controller had a very strange problem: It started "holding" left on the d-pad whenever it was plugged in. I opened it up, and found that the pad was fine; it WASN'T a mechanical problem. So, I began looking for shorts. I tested the contacts with my multimeter: No continuity.
I plugged it in and turned on my GC, and tested again... continuity. This is very odd. Clearly, the IC is pulling the input down to ground. I still don't know why. But I tried pulling it back up (shorting it to V+) and it actually stopped pressing left, but shortly after, my 'cube turned itself off.
Lucky this was a safety measure, and it booted right back up. I tried soldering a pull-up resistor to it instead; didn't work. It was a 1k resistor, I think. So, I tried a 5k: It worked.
That's right; pulling the button up to V+ with a 5k pull-up resistor actually fixed the problem, and the button is now 100% functional. Get that.
