Here are the pics & wiring diagram from 'goflow' for tDCS, just in case their website disappears  :  )

Obviously we cannot use their plastic parts, but the circuit board can be housed in any suitable object. Velcro is good for holding components in place. We aim to build our own so that clearer step-by-step instructions can be portrayed. If anyone wants to have a go, send us pics of the assembly procedure and we'll put them up for students.

(from original site)

We designed the GoFlow β1 to be the simplest, safest, easiest to build, transcranial direct-current stimulation (tDCS) device possible This tDCS kit can be assembled and configured in half an hour. This is the first ever standardized tDCS kit, and we are incredibly excited to share it with you all. Our design does everything possible to allow for safe consistent experimenting with tDCS. The kit is crazy easy to assemble, no soldering or burnt fingers required! The kit is not yet released, but we have shared our schematic so you can build your own.