Felix over at lowpowerlab.com has been tirelessly creating and documenting an excellent Arduino Home Automation solution. Hack a Day covers it here:http://hackaday.com/2014/03/21/open-source-switchmote-promises-easy-home-automation/Check it out, it's wireless!
Here is a project you can do with your old tablets:


They even link to my in-wall tablet at the end of the post (shameless self promotion).
Thank you to Hackaday.com (one of my favorite websites) for covering my HP Touchpad project.  Link below:

Perfect wall-mounted tablet integration