The Phone App
Although you could use any battery powered USB (or
other) source to power your tDCS, why not use a battery
most of us have handy with us all the time: our
smartphones! I’ve written a quick free phone app that can
be used to time a session, display electrode placements in
3D, and even power a tDCS device directly from your
phone. Getting power from your phone’s data port can be
useful for many low power electronic projects as well.
The easiest method of getting power from your phone
is to use an On The Go (OTG) cable as in Figure 11. This
is available for both iPhone and Android. By plugging an
OTG cable into your phone, you not only get USB
functionality, but can also power low current devices like
our tDCS circuit (or anything else) directly.
Keep in mind, not all phones are compatible with
OTG. However, you can download a free OTG checker
for your phone from any app store to make sure it’s
If your phone is not OTG compatible, you can still
power a tDCS circuit very easily from a “power bank” cell
phone recharger or any battery powered device with a
USB port. Power bank devices are available from Amazon
and elsewhere for less than $5. I’ll make the phone app
available for anyone who would like it on a special web
page for Nuts & Volts readers at noonco.com/tdcsnv.
There are some very spectacular in-depth manuals
regarding electrode placement available on the Internet.
So, I’ll just cover the topic very briefly here. I’ll also make
links to these manuals available later in the article.
In short, electrode positions are found using the
International 10/20 system. The numbers ‘ 10’ and ‘ 20’
simply refer to the fact that the distances between
adjacent electrodes are either 10% or 20% of the total
front-back or right-left distance of the skull.
Measurement is made from the nasion which is the
point between the forehead and nose, and
the inion which is the lowest point of the
skull from the back of the head.
Figure 12 shows the distribution of
possible positions from that basic
So, if in your research, an electrode is
said to be placed at F3, this measurement
and chart will give you an excellent
Though I’m sure precision placement is
ideal, because electrode coverage areas are
large, most people I have spoken to have
simply used 3D models already set up to
show relative placement. Figure 13 shows
three typical placements. I feel these three
■ FIGURE 12.
■ FIGURE 11.
■ FIGURE 13.
28 July 2017