Switching graphic cards on the Thinkpad T400

I just realised that a lot has changed since I looked for support of Hybrid Graphics under Ubuntu/Debian a few years ago. Now, there is a project for switching between the integrated and discrete graphic card called vgaswitcheroo!

In the BIOS settings you have to select "Switchable Graphics" and the computer will boot up with the internal graphics card (in my case Intel 4500) turned on.
With one simple command, you can then switch to the discrete graphics (ATI Radeon HD 3400). The only expense at the moment is, that you have to log out and in again to restart the x-server.

To switch to the discrete graphic card open the Terminal and type:

sudo echo DDIS > /sys/kernel/debug/vgaswitcheroo/switch

Then log out and in again. You can then check your running graphics card under "Details" in the "System Settings" (running Gnome 3.2 or higher).

To switch to the internal graphics type:

sudo echo DIGD > /sys/kernel/debug/vgaswitcheroo/switch

Thanks for this awesome tool!
Source: https://help.ubuntu.com/community/HybridGraphics

Do you want to automate things?

I created a shell script, which detects the running graphics card and asks you whether to switch or not!
Download it, make it executable and run it as superuser! I commented every piece of code to make it readable for you.
Download: https://github.com/j-4/scripts/blob/master/switch_graphics.sh

Have fun!