2D-Game - Ignoring collision in one direction of the ground

Hello guys, anyone have any idea how to ignore the collision only in one direction. For example, my character is under the ground and need to jump through it to climb up, without crush the head in the plataform, like the classic 2D plataformer games. Also I wanting to make it ignore the collision when pressing "down+jump" and fall through this plataform.

Thanks

 

This might help.
http://forum.unity3d.com/threads/125283-Jump-through-platforms

I might consider something as simple as haveing two colliders, one above nd one below the platform. If bottom entered, you can pass thru floor, if top entered you can not pass thru floor.

 

Oh nice, I used your idea plus one that I read in the topic that you showed. Thank you

 

great.

:]

 

Looks like we need here PlatformEffector2D, check the
Blackthornprod tutorial