26 July 2017
USB output to approximately 11. 5 volts to
overcome skin resistance, and the LM334
will then limit current to between . 5 and 2
mA, depending on the feedback resistor.
If you are making a scrap drawer assembly and don’t
happen to have an LM334, it is important to make certain
that the voltage regulator you use is stable at very small
currents of less than 2 mA. Figure 3 shows the simple
completed perfboard assembly.
Note: For experimentation, it’s possible to replace S1
with a single 100 ohm potentiometer connected to R5 if
you would like infinite adjustment (within the set range)
for your own experimentation.
Last, a simple ammeter can be
connected as shown in series with your
anode to verify your output for testing.
When prototyping my first tDCS, I used the
100 ohm pot mentioned above, and built
the ammeter into the case as in Figure 4.
Figure 5 shows the traditional way electrodes
were made for most of the university and military
studies I’ve seen. A simple piece of copper screen is
attached (often sewn) to a small clean sponge
approximately 1/4” thick. A wire is soldered to the
screen, and attached to your tDCS device.
The actual material a sponge is made from is
largely unimportant, though a higher density is
preferred for best conduction. (A very porous
sponge can lead to some skin irritation due to the
lack of contact.) Figure 6 shows typical sizing of
■ FIGURE 4.
■ FIGURE 6.
■ FIGURE 5.
■ FIGURE 7.