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.

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.

<p>I built this, I think it is working as needed. Output current is ~1.5mA, output voltage is .65V ... All I had on hand was some small metal electrodes from an EEG kit, I read online should have 2&quot; sponge electrodes though, so I suppose I will find some spoons as ElChevere did. Thank you for sharing! </p>
<p>I succesfully build the device, works like a charm. I tried the more simple one before, just a 9V battery with a resisitor but I experienced flashes, phosphane I think it's called. This one is much better. Then the electrodes weren't good so I made them of teaspoons, = stainless steel. Broke of the handle and drilled holes in them, see picture. Now I'm experimenting with improving my Spanish, 25 min. a day, let's see what happens. And I'm thinking of putting a big capacitor over the diodes to make a soft start, that could be an improvement. But thanks for the diagram, simple and stable, parts easy to find!</p>
<p> .</p>
<p>Hola, amigo. &iquest;Te funcion&oacute;?</p>
<p>I like your electrode setup, it seems better than the one I was originally suggesting, so I've added it to the body of the article!</p>
<p>Glad to be of service! The spoon/sponge electrode setup is exceptional. If you use a 1000uF (1mF) capacitor across the diodes, then the time constant will be 12 seconds, so it will ramp up to 63% in the first 12 seconds and then to 86% after the next 12 seconds, being within 1% of the full output current within about a minute. Note that this capacitor only needs to be rated to withstand about 5 volts, since the diodes will clamp the voltage across it to 2.1V maximum.</p>
<p>That's exactly what I did, a 1000 uF capacitor across the diodes, works like you say.</p>
<p>Great tutorial. I have successfully built the device but was just wondering which of the electrodes is the cathode and which is the anode?</p>
<p>Anode +</p><p>Cathode -</p>
<p>My instructor long time ago told us to use the mnemonic KNAP or CNAP to remember which is what: Katode (Cathode) Negative Anode Positive.</p>
<p>Anode means negative, cathode means positive in a voltaic cell.</p>
<p>However, in an electrolytic cell, the anode is taken to be positive while the cathode is now negative</p>
<p>Oh okay, thanks. So for this E1 would be the cathode and E2 the anode then?</p>
<p>E1 anode, E2 cathode</p>
<p>Also found this circuit to be temperature instable. The following circuit fixes this instability.</p>
<p>Thank you for the feedback; the circuit will drift somewhat with <br>temperature mostly due to the Vf of the three diodes; I have designed a <br>revised circuit (with low battery indication, and only one additional <br>part) using an integrated voltage reference ZR40402F50TA.<br></p><p><a href="https://github.com/quicksilv3rflash/SMD_tDCS" rel="nofollow">https://github.com/quicksilv3rflash/SMD_tDCS</a></p><p>The integrated regulator will be more temperature stable, though the NPN <br>series-pass transistor will still see its VBE fall a bit as temperature <br>rises, which will cause output current to rise slightly.</p><p>Don't trust your simulator for those output current values, breadboard the <br>circuit! I've built about 50 copies of that circuit and they've all <br>measured between 1.97mA and 2.02mA with the parts I've got on hand. <br>Current drifts downwards by about 20uA within the 10 minutes after <br>turning on, though due to the diodes warming up and losing Vf.</p><p>Also, for some reason your simulator seems to think LEDs need more current to visibly glow than they require in real life.</p>
<p>Ah, I forgot to mention that in the simulation I can customize components such as transistors. </p><p>Note: Resistors values can vary for you depending on what components you are using.</p>
<p>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.</p>
<p>I'm testing the circuit in a simulator and it's actually outputting 2.2mA. Is this current considered unsafe?</p><p>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.</p>
<p>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. </p>
<p>I just built this circuit. Have not put it on yet but tested it with a direct short to the output and it read exactly 2ma. I did add a 3ma ammeter I bought from amazon in line with the final output to make sure that I am getting 2ma. I think I may add a variable resistor to the circuit also so I can adjust the out put ma's if needed. </p>
<p>So I tried the new TCDS unit I built. What a strange sensation that was. Very interesting feeling. Looking forward to trying it again and again.</p>
<p>good day, when I was in highschool I bought a disassembled power supply, there is a rotary to be pointed at 3, 4.5, 6, 9 and 12 v, and has a 750 mA.<br>how do I make the current 2 mA?<br>Thanks.</p>
<p>Do NOT--NEVER EVER--attempt to do TDCS with a device plugged into a wall socket. Seriously--NEVER DO THIS.</p><p>If a component fails, you could suffer a horrendous brain injury. Use 9v or 12v (23A) battery powered devices only.</p>
Its too late bro my brother is dead
<p>are you serious? that's horrible! I'm sorry for your loss and very surprised no one responded to your post!?</p>
<p>It's not only when a component fails, there's always a leakage in wall-plugged devices which, under normal conditions, is harmless. But with good conducting electrodes on a body you easily exceed 30 mA, that can kill you. </p>
<p>I'll just assume that if you know what you're doing, this will work (I hope!). </p><p>However, for something I'm connecting to my cranium (brain), I went with a commercial device from TheBrainDriver tDCS. I did A LOT of research and it's a good device at a reasonable price. Get it directly from their site or from Amazon.</p><p>For the amount of time it would take to learn how to build this thing here, I'm already using one.</p><p>Good luck to those wanting to build one themselves. You are brave :)</p>
<p>For curiosity's sake, would something like this be a valid method as well? https://www.youtube.com/watch?v=EXTRKXhvBJU </p>
Is there a way to tune it to 40hz?
<p>it DC current it always 0 HZ . you need an inverter to do that.</p>
<p>You're thinking of tACS</p><p>https://www.instructables.com/id/DIY-tACS-Hardware-for-machine-human-telepathy-expe/</p>
<p>I read an article about this in Wired. It was ver interesting. Have you tried this out on yourself?</p>
<p>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.</p>
<p>the reason your pupils dilated is because you aren't using it properly, if you are using 2mA then you shouldn't use it more than once a week at all, and for no longer than 20-30 seconds, your pupils most likely would dilate like that because, because the brain isn't designed to handle that kind of electrical current, so the repeated surges in electricity would have triggered the systems in your brain that allow the pupils to dialate, or it would have sped up the speed in which the brain processes the chemicals in your brain, either way you're burning through the neurotransmitters in your brain, doing it that much, and you should dial it down to a much lower dose if you want to avoid long term brain damage and/or dying early, you probably will be fine but dial it down before you aren't dude. O.O</p>
<p>The information I've got says 20 minutes is fine at 2mA. Accepted safety limits (the Gottingen protocols) allow &quot;currents of 1 &ndash; 2 mA applied for durations up to 20 minutes&quot;.</p><p>&quot;Establishing Safety Limits for Transcranial Direct Current Stimulation&quot;</p><p>http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2754807/</p>
<p>hi,</p><p>would it be possible to get any more photos of the device up? im beginning my build as we speak. I'd like to to take a closer look at the wiring around your semiconductor/how that section was mounted.</p><p>cheers.</p>
<p>Thank you! I'm so interesting your design.</p><p>Does it work?</p>
<p>I built this but the current across the electric leads is 6.91 mA. ( 345% above the safe reading. )</p>
<p>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.</p>
<p>Come to think of it it looks like *all* the diodes are reversed.</p>
<p>I thought the band marked the cathode of the diodes. The green jumper is the cathode. ( I didn't have a red jumper ).</p>
<p>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.</p>
<p>Hello</p><p>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?</p>
<p>you use 3 diodes in series (this provides a positive bias voltage on the transistor base and allows current to flow)</p>
This is highly useful, but I have no clue how to make it from this tutorial.
<p>Buy a commercially produced one ... </p>
<p>Do you have a recomendation? </p>
I plan to.
<p>Good plan. Unintentional electroconvulsive therapy is no fun :)</p>

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