I'd like to use Arduino mini as the control interface for the mods and a middleware to transmit video signal via serial port.

Here's the setup I have in mind:

Inputs are
- a pot connected to analog input (and to LTC1799)
- a tactile switch acting as a button to select which mod to control

You press the button and enter one of the following states (value of each state is controlled by a pot):

- backlight and buttons illumination on/off (basically the leftmost pot position is off the rightmost is on)
- hex inversion on/off
- activate pitch by supplying 5V to LTC
- switch between x1/2 x1 and x2 speed oscillator

Now the last point is a problem. I need a voltage controlled switch activated by voltage. I used NPN transistors in the past to activate power supply to the certain regions of the circuit, but I'm not sure it will work with an oscillators. So any help on that matter will be very appreciated. Thanks!

Oh, and do you have any ideas what else I could with Arduino inside the gameboy? Apart from Arduino boy of course... Cheers!

EDIT:
After some experimenting I discovered:
- Transmitting pixel data to PC via serial port is a nasty bitch (but I'm not sure it completely impossible);
- As I expected transistor is useless for voltage controlled oscillator switch (at least I've learned something);
- Using internal Arduino as a cartridge SRAM reader seems to be feasible (only need as shift register)...