Build a Human Enhancement Device (Basic TDCS Supply)

This Instructable got cited by a reputable source (pdf link)! Citation #10 in the paper "New tools for neuroenhancement – what about neuroethics?"(html link) Croat Med J. 2016 Aug; 57(4): 392–394. doi: 10.3325/cmj.2016.57.392 ------- Some concern about the ethics of this sort of activity, warnings about changes in personality and hormones as a result of use of tDCS. So I added some warnings.

Site for different tDCS placements and effects.

View this project in the context of my life and intent on my own site here if you wish.

Edit: If you want hardware to do tACS and tRNS in addition to tDCS, I've built some of that too.

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 insanity and/or seizures and/or dismemberment and/or immolation and/or 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 you can 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

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
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]
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.

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. There are other options, though, and sponge electrodes are less likely to cause electrode burns.

Original suggestion at the initial time of writing, the cheapest, but can only be used over hairless skin and may be more likely to cause skin irritation and minor damage:
W1: electrode leads (such as these TENS leads)

A search for "TENS electrode leads" will find the appropriate type

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

Search for "TENS gel electrodes", I recommend 2" x 2" square gel electrodes

New suggestion 1: sponge electrodes that are compatible with 2mm pin connectors instead of gel electrodes. That's an ebay link, though, posted 2016-10-24, and it may not remain live / I can't find any other sellers with 2mm compatible sponge electrodes at the moment.

New suggestion 2: Banana plugs instead of TENS electrodes leads and Amrex sponge electrodes. Those sponge electrodes are $20 each, though, instead of $10 for a pair like new suggestion 1.

New suggestion 3: The guy in the comments who built this, ElChevere, used spoons and kitchen sponges for electrodes, which I wholeheartedly approve of since it's probably the cheapest / most efficient way to get sponge electrodes with commonly available parts :)

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.

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57 Discussions


1 year ago

Is possible to put an optical coupler to pulse the output?

I would drive the optical coupler with a square wave DDS generator app that I have working on Android.

1 reply

Reply 1 year ago

As long as the optocoupler is rated for 36V (really, you want one rated for >45V for safety), you can put an optocoupler in series with R2, the resistor driving the three-diode chain, and it will turn the output on and off. Alternatively, if you can only find low-voltage optocouplers, you can put one in parallel with the three-diode chain; in that configuration, turning on the optocoupler will turn _off_ the output. The voltage across those three diodes controls the output current.


1 year ago

This is my first "real" electronics project.

I had to redo part of it because I misread the transistor pinout, but I think it's good now. My solder bridges between the components are kind of ugly though.

The output is 2.01 mA.

Can somebody confirm that when you test the output voltage with a multimeter it should read 36v?

Can I put a potentiometer right before one of the electrodes to dial the amperage down?

1 reply

The circuit should measure 36V open-circuit (if you just hook a
voltmeter across the output). That's the circuit sensing the high
resistance of the voltmeter and raising its output voltage to maximum in
a vain attempt to put 2.0mA through the voltmeter.

To contol the output current with a potentiometer, the potentiometer would go across the three diodes, with the wiper
connected to the base of the transistor! Just putting the potentiometer
in series with the output will not smoothly decrease the output current,
because the circuit senses the output resistance and compensates for


Question 1 year ago on Step 3

I'd like to be able to dial the amperage down. I think a potentiometer would need to go somewhere, but where? Right before one of the electrode leads?

2 answers

The potentiometer would go across the three diodes, with the wiper connected to the base of the transistor! Just putting the potentiometer in series with the output will not smoothly decrease the output current, because the circuit senses the output resistance and compensates for it.


Answer 1 year ago

Caveat experimenter: I am an outright novice a circuitry!

But to answer your question, yes. It seems as though you could reduce the amperage by placing a potentiometer before an electrode lead. See attached screenshot of a schematic of this instructable author's circuit modified with a 10k ohm potentiometer connected as you described, (the (A) is just an amperemeter as if it were measuring between two electrode leads).

Sweep-to-sweep the potentiometer seems to bring it from -0.5mA to 2.06mA Here's the simulation to see for yourself:


TCDS with potentiometer.png

3 years ago

Great tutorial. I have successfully built the device but was just wondering which of the electrodes is the cathode and which is the anode?

6 replies

Reply 2 years ago

My instructor long time ago told us to use the mnemonic KNAP or CNAP to remember which is what: Katode (Cathode) Negative Anode Positive.


Reply 2 years ago

Anode means negative, cathode means positive in a voltaic cell.


Reply 2 years ago

However, in an electrolytic cell, the anode is taken to be positive while the cathode is now negative


Reply 2 years ago

Oh okay, thanks. So for this E1 would be the cathode and E2 the anode then?


3 years ago

Also found this circuit to be temperature instable. The following circuit fixes this instability.

tDCS with good temperature stability.png
1 reply

Thank you for the feedback; the circuit will drift somewhat with
temperature mostly due to the Vf of the three diodes; I have designed a
revised circuit (with low battery indication, and only one additional
part) using an integrated voltage reference ZR40402F50TA.

The integrated regulator will be more temperature stable, though the NPN
series-pass transistor will still see its VBE fall a bit as temperature
rises, which will cause output current to rise slightly.

Don't trust your simulator for those output current values, breadboard the
circuit! I've built about 50 copies of that circuit and they've all
measured between 1.97mA and 2.02mA with the parts I've got on hand.
Current drifts downwards by about 20uA within the 10 minutes after
turning on, though due to the diodes warming up and losing Vf.

Also, for some reason your simulator seems to think LEDs need more current to visibly glow than they require in real life.


3 years ago

Ah, I forgot to mention that in the simulation I can customize components such as transistors.

Note: Resistors values can vary for you depending on what components you are using.


3 years ago

I changed also values of R5 and R6 to make the output almost perfectly 2mA. Later in the afternoon I'm going to build this circuit, I wish it will work as in the simulator.


3 years ago

I'm testing the circuit in a simulator and it's actually outputting 2.2mA. Is this current considered unsafe?

I changed the value of R1 because the LED in the simulation was not turning on, 1.8K resistor is fine to turn on a red LED.

tDCS (2).png

3 years ago

I am going to modify mine to take 3 23A batteries. And also will put a small pot in line with the 560 and 100 ohm resisters so I can adjust the amps down.