Well, it's not as easy for foreigners as it should be..

The Catalans obviously don't want foreigners to vote so it appears they are making it as difficult as posible.

To vote you previously need to register your intention to vote.

You need to provide:

1. ID (Passport/NIE)
   
2. Document from the Ajuntament confirming you have been registered (empadronado) for the required time (one year for EU residents, three years for non-EU residents)
   
3. Request to vote - document can be downloaded here:
   http://www20.gencat.cat/docs/consulta/Documents/Arxius/VR1.pdf
   

This must all be presented to the 'comissió de seguiment' in your area and the time limit is between 1st and 8th October!

As of this moment I have no idea where this is for us in this area but I will post more as soon as I find out.

http://www.9nconsulta2014.cat/qui-te-dret-votar.html
http://www.9nconsulta2014.cat/regles-especifiques.html#bloc3