I ran into a design for a very simple tDCS device via the http://www.diytdcs.com blog. It’s by Keith Spaulding and uses a current regulating diode rather that a current regulating IC. I’ve ordered some CRD’s and will report on building a device in the near future. This is about as simple as a good tDCS device could get! I will add an on/off selector switch and a ramp up/down capacitor to Keith’s idea. I might also use a type 25A 12v battery just to keep things as small as possible. Little need for a meter or other circuit complications! Here is his schematic and a link to his blog… Thank you Keith.
SpeakWisdom 
Hi Brent,
I have been using an LC instead of just the C to ramp up and ramp down. I found an inductor of say 1mH and cap of 10uF gives hundreds of milliseconds of ramp; much larger than you will get with just a cap. thanks, keith