Ubuntu – the difference between add-apt-repository & apt-add-repository

PPAs in Launchpad are connected to People/Teams, rather than projects. Your best bet is to click on the "Maintainer" for the project ("Cardapio Team" in this case):

From there, follow the link on under "Personal Package Archives" on their profile page. There may be multiple options here, you'll just have to use your best guess based on their names.

The name of the PPA will be on this page:

However, this is not guaranteed to work, as the developers can use any PPA they want for their project. It could be ppa:someunrelatedteam/foobar for all you know. There is no way to know for sure from the Launchpad project.

Alternatively, googling "[project name] PPA" tends to give good results.

It appears this is a known issue/bug, you could try this workaround:

To install PPA's, add them to /etc/apt/sources.list in the form:

Before:

ppa:<user>/<repo>

Add to sources.list:

deb http://ppa.launchpad.net/<user>/<repo>/ubuntu oneiric main

Then sudo apt-get update and download whatever packages you want.