The USB cable on my RetroPad is cumbersome in the car. So, I got rid of the wire! I bought a cheapy Targus wireless keypad and popped it open along with an original NES controller I had.
I cut out the controller IC and cable. I trimmed the PCB and glued a AAA battery holder in. I'll be replacing the keypad's original AA battery with a NiMH AAA.
Here's the tricky part. The NES controller uses 8 inputs and one ground for it's switch state input. The keypad uses a 4x5 matrix decoder. So I split the ground trace on the control pad into 2 parts (you can see this cut in the second image below) and gave each ground to a column on the keypad. Then I jumpered pairs of buttons on the control pad and connected each pair to one of four rows on the keypad, effectively giving me / 8 2 0 for A B Sel Start and * 9 3 . for Up Rt Lf Dn.
That's it! I connected the battery, moved a few components around to allow the back to close and we have a working wireless joypad from an original NES controller. Now I just map the keys the joypad generates in our emulator to the proper buttons and I'm playing Dr. Mario in the car.
There are a couple issues. First, this is a cheap RF keypad. It has an effective range of 3-4 ft, but fine for the car or desk. Also, this keypad doesn't like it when you use more than one key at once. So, when playing Super Mario Brothers, while running and you jump, you stop going forward. I think both of these issues can be resolved up upgrading to a more expensive keypad. Cost: $27 (not including the controller) Time: 2 hours
I did this some time ago when I first started working full time at the company I currently work for. Reaching over to the KVM box for the servers or using the key sequence to change the input was a hassle. So I took the faceplate off this Belkin Omniview KVM. I took out the PCB which the display LEDs and input switch button were on and opened up the keyboard I was using. I found a nice spot above the arrow pad where the PCB could fit and cut out the pattern. I'm pretty sure I used hot glue to secure everything. I used a piece of CAT5 to make an extension for the harness that connected the display to the KVM itself. It's made switching displays 3x easier.