Instructables

Build a Human Enhancement Device (Basic tDCS Supply)

I was surprised and pleased to learn that human enhancement technologies not only exist, but are within the reach of the basic electronic hobbyist. This instructable is (of course) for educational purposes only and you may be violating local laws by constructing and/or using the device described here. The author of this instructable is not liable for the burns, permanent neurological damage, or other personal injury up to and including death that may result from building and using the device described here.

Transcranial Direct Current Stimulation (tDCS) is a method of external neural modulation that uses a small current run through the brain in order to alter cortical excitability. The details of the mechanism of action and exact enhancements possible are beyond the scope of this article, but start with the wikipedia entry, examine commercially available products, and look at safety data and ethical reviews before deciding if this is something you would like to pursue. Some google scholar searches will turn up interesting things too.

The photo on this page is from this article.
 
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Step 1: Circuit Principle of Operation

Picture of Circuit Principle of Operation
If you don't wish to consider the theoretical basis for the operation of this circuit, skip this step.

The circuit shown is a regulated current sink. You may find it a useful building block in your future projects. It regulates the current through R[L], preventing it from exceeding a set value. This circuit doesn't have active drive capacity, though, and so V[DRIVE] must be large enough to drive the desired current through R[L].

The current through R[L] is equal to I[C].  I[C] is roughly equal to ( V[REF] - (V[BE] of T1) ) / R[LIM] .

To see where this equation originates, begin by noting that the sum of the voltages around the loop formed by V[REF], the base-emitter junction of T1, and R[LIM] must be zero (by Kirchhoff's voltage law):
V[REF] - V[BE] - V[RLIM] = 0
so
V[RLIM] = V[REF] - V[BE] .

The current through R[LIM] (also known as I[E]) is defined by Ohm's law, and we can substitute using the previous equation:
I[E] = V[RLIM] / R[LIM] = (V[REF] - V[BE] ) / R[LIM] .

Ignoring the base current,
I[C] = I[E] ,
so the current through the load resistor is approximately defined by
I[LOAD] = I[C] = (V[REF] - V[BE] ) / R[LIM] .

If you wish to include the effects of the base current of the transistor, you must also factor in the current gain of the transistor, h[FE].
Viewing the transistor as a node, by Kirchhoff's current law,
0 = I[C] + I[B] - I[E]
so
I[B] = I[E] - I[C] .

We know that h[FE] is the factor we can multiply by I[B] to find our I[C]. Thus,
I[B] * h[FE] = I[C] .

Substituting for I[B] from a previous equation,
(I[E] - I[C]) * h[FE] = I[C] .

Solving for I[C],
I[C] = I[E] - (I[E] /(1 + h[FE] ) ) ,
and since I[E] = (V[REF] - V[BE] ) / R[LIM] ,
the exact equation then becomes:

I[C] = ((V[REF] - V[BE] ) / R[LIM] ) - (((V[REF] - V[BE] ) / R[LIM] ) / (1 + h[FE] ) ) .
bryanwheelock2 months ago

I built this but the current across the electric leads is 6.91 mA. ( 345% above the safe reading. )

IMG_0385.JPG
quicksilv3rflash (author)  bryanwheelock1 month ago

What's the voltage with respect to ground at the base of the TIP31C? It should be about 1.9V. Are there any solder bridges shorting out the transistor? From staring at your picture and guessing, it looks like one of the diodes may be reversed leading to +36V instead of +1.9V at the base of the transistor.

Come to think of it it looks like *all* the diodes are reversed.

I thought the band marked the cathode of the diodes. The green jumper is the cathode. ( I didn't have a red jumper ).

The band does mark the cathode of the diodes. What is the voltage at the base of the transistor (vs. ground)? Have you tried re-building the circuit on a breadboard? Also, green is frequently used for cathode/ground. Red's usually used for anode/positive.

Stijnploeg20 days ago

Hello

I have made your tDCS-device for a school project i'm working on, it's pretty cool and it works. But could you maybe explain how the transistor works. I know the diodes take around 0,6V each so that leaves around 1,8V at the base of the transistor. My teacher said that the transistor compares the voltage at the base with the voltage at the emitter and as long as the voltage at the base is higher, current will flow. However, I calculated the voltage, the 2 2.2k resistors take and that is only 6,6V. So that leaves around 30V at the emitter and that is much higher than the 1,8V at the base. Could you please tell me what I did wrong?

aflange2 months ago

you use 3 diodes in series (this provides a positive bias voltage on the transistor base and allows current to flow)

ajensen191 year ago
This is highly useful, but I have no clue how to make it from this tutorial.
quicksilv3rflash (author)  ajensen197 months ago

Buy a commercially produced one ...

Do you have a recomendation?

I plan to.
quicksilv3rflash (author)  ajensen197 months ago

Good plan. Unintentional electroconvulsive therapy is no fun :)

TDCS has been the best thing that I have found while researching brain enhancement.

ateshr1 year ago
for D2, D3, D4; am I to use three diodes or just one?
quicksilv3rflash (author)  ateshr7 months ago

Three. It sets a (roughly) 2.1V reference.

kasualkiller7 months ago

I read an article about this in Wired. It was ver interesting. Have you tried this out on yourself?

quicksilv3rflash (author)  kasualkiller7 months ago

Yes, of course. 20 minutes 3 times a week for a few months. If you do it regularly half your face tastes like metal, and there can be strange side effects. I was taking oxiracetam and huperzine a at the same time as this, and my pupils just started being different sizes... Since then there hasn't been any obvious long term benefit or detriment to me, however.

chello2k91 year ago
Nice warning, I'm slightly terrified
beamrobot1 year ago
nice project.can u please tell me where to place cathode in case of neuronal stimulation and also for anode in case of neuronal inhibition.
cliffreich1 year ago
It's possible to use 1 or more PC USB as energy source?

ffs, 4 9v batteries?
TXTCLA551 year ago
Why are you using 4 9volt batteries? Most circuits for a basic tDCS device require at the most 2.

Another version using one 9v:
http://brmlab.cz/_media/project/brain_hacking/tdcs.jpg?w=800