Help with hardware side of automotive circuit driver

Greetings! I'd like to build a board that does two things:

  • Provide ramped (theater-style) dimming of a 12V LED strip (less than 1A total load)
  • Provide ON/OFF control for a pair of 30A cooling fans

On the fan side, I would imagine my output fires a transistor which fires the relay which controls the fan. I know that much, I just don't know what transistor and how to wire it!

The 12V I really have no idea. I imagine there are power transistors that will drive that, but how to breadboard something is a bit beyond me.

The software side I'm fine with. I've built basic atmel and arduino stuff before so I'm not a total noob but would need help once I get past the Radio Shack 150-in-One kit level of stuff!

I have an UNO so of course answers that relate to it are even better!

For the LEDs I would use a logic level MOSFET transistor in the lower amp range controlled by PWM signal from Arduino:

For fans you could use either power MOSFETs or relays, my choice would be 12 volt automotive relays designed for the task, you would still need "helper" transistors to handle the relay's coil current. You would need to know the relay's continuous coil current to select a transistor switch.