**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.

**Signing Up**

## Step 1: Circuit Principle of Operation

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] ) ) .

## Step 2: Practical assembly

This is the schematic of a working 2mA current supply that may be used for tDCS. It is based on the transistor regulator described in the previous step. Parts were added to allow on/off functionality, on state indication, and redundant safety measures.

---PARTS LIST---

B1: 4 9V battery clips, series configuration (add 9V batteries to provide power)

S1: SPST switch

D1: indicator LED

D2-D4: 1n400x (I used 1n4003)

T1: TIP31C (or TIP29C)

R1,R2: 12 kohm 250mW

R3,R4: 2.2 kohm 250mW

R5: 560 ohm 250mW

R6:100 ohm 250mW

Wires and gel electrodes are easiest to find sold for TENS devices, but will allow tDCS, though only in areas that are hairless.

W1: electrode leads (such as these TENS leads)

http://www.amazon.com/s/ref=nb_sb_noss_1?url=searc...

E1,E2: gel electrode pads (also sold for TENS units)

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=TENS+electrodes&rh=i%3Aaps%2Ck%3ATENS+electrodes

Perfboard is best for assembling this circuit permanently.

Hot-melt glue is useful for gluing wires in place to prevent strain.

## Step 3: Testing and quality verification

Once your device is constructed, you should test it before adhering it to your head and torso and activating it. Check the short-circuit output current with an ammeter. The value should be 2 mA +/- 10%.

Have fun. Try to get better.

Look into piracetam but remember that it seems to work best when taken with supplemental choline.

Good luck.

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

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.

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?

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

Buy a commercially produced one ...

Do you have a recomendation?

Good plan. Unintentional electroconvulsive therapy is no fun :)

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

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

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

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.

ffs, 4 9v batteries?

Another version using one 9v:

http://brmlab.cz/_media/project/brain_hacking/tdcs.jpg?w=800