well if u have tried resistors the next best thing i can think of is a potentiometer... but the are kinda big to stuff inside a psp... i mean im sure u can do it considering the fact tht u got 3mm leds in it lol... i typically use 0603 smd leds... but back to ur question... u can pick up a small potentiometer or harvest it from just about any electronic device... i put one on my goggles to be able to adjust the brightness of the leds i put on them worked like a charm... hope this helps