mrhaineux comments on the Make.com blog…

Seriously, if you’re excited to do this, invent an “electrode hat” that requires little to no skill to apply, and does not require finicky salt water or electrode paste. That is the best possible thing to do, and can be parlayed into a multi-million-dollar business.

Then, if you’re still interested in tDCS, find a doctor to help you get a Soterix. It has a current source, but it also measures the actual resistance and current being used as a safety precaution, provides feedback if things aren’t right, and has a micro controller to do stuff like timing, logging, etc. You could build one for a lot less than the asking price, but it’s much more complicated (and better) than a 9V with a current source chip.

via MAKE | NEWS FROM THE FUTURE – Transcranial direct current stimulation (tDCS) kits.