TDCS Thinking Cap




Introduction: TDCS Thinking Cap

tDCS is an abbreviation for Transcranial Direct Current Stimulation which is a form of neurostimulation which uses constant, low current delivered directly to the brain area of interest via electrodes. It was originally developed to help patients with brain injuries such as strokes but has shown great success on tests with healthy adults. It has been utilized to enhance language and mathematical ability, attention span, problem solving, memory, and coordination.

This is done by positioning electrodes on the head and body then passing a carefully regulated current through the electrodes. 20 minutes is the usual recommended time limit. I can't stress how important it is to research for your own safety. Placing the electrodes in the wrong place could have an unwanted effect but I have never seen anything more than inconvenience and forgetfulness. This stopped immediately when the power was removed. I personally experience a metallic taste in my mouth but this is common.

This set of instructions was designed to be accessible to people of all skill levels and will hopefully encourage more people to try tDCS without breaking the bank. Each step has a single picture and a simple instruction so completing the project is a matter of following each step to the letter. This guide does not have instructions for electrode placement which is a field all its own and the tDCS Placements does a better job than I could.


This was designed to be built during a workshop where all tools have been provided and a minimal cost and traditional soldering skills were not needed. For example, the directions show that I used nail clippers to cut and strip wire but if you have a wire stripper go ahead and use it. A lighter is used to melt ordinary solder however traditional soldering skills can easily be applied.

I've taken a picture of most of the tools used in this project and they cost less than $20. The cost goes under $10 if you build your own helping hands or already own a set.

  • Safety glasses
  • Nail clippers*
  • Emery board**
  • Hot glue gun
  • Tweezers
  • Small phillips screwdriver
  • Lighter***
  • Ruler
  • Helping Hands (not pictured)
  • Millammeter, often selectable on a multimeter

* A wire stripper may be used instead

** A rasp or sandpaper may be used instead

*** A soldering iron may be used for some of the steps where a lighter is used


The materials for this project should be obtainable from a hardware store or even a hobby store.

  • Solder
  • Hot glue stick
  • 9V Battery


The parts for this project are minimal. Great effort was taken to find inexpensive shipping and suppliers with readily available parts so that this project can be reassembled for many years.

  1. Mouser parts****
  2. Solder
  3. Hot glue stick
  4. 9V Battery
  5. 3.5mm plug electrode wires with 2mm pin connectors
  6. Electrodes with 2mm pin connectors

***Mouser makes it very simple to order a set, or multiples, of parts for this project. 1, click the link, click "Order Project." You now have the necessary parts in your shopping cart.

Step 1: Safety Glasses

Put on your safety glasses.

Step 2: Glue Gun

Plug in the hot glue gun

Step 3: Glue Stick

Insert a glue stick as far as it will go through the back hole of the hot glue gun.

Step 4: Battery Case

Remove the cover from the battery case which came in the Mouser order.

Step 5: Red Wire

The the RED wire into the battery enclosure or pull it from the inside with tweezers.

Step 6: Cut the Red Wire

Cut the red wires to 1" (25mm) measuring from the attached side.

Step 7: Strip Wire

Strip 1/4" (5mm) from the RED wire.

Step 8: Cut Component Leads

Cut the leads on the diode so each side has a 1/4" (5mm) wire.

Step 9: Helping Hands

Adjust the helping hands so the clamps are 1" (25mm) apart.

Step 10: Clamp Wire

Clamp the stripped RED wire into the Helping Hands.

Step 11: Clamp Diode

Clamp the diode so the lead opposite the BLACK band overlaps the stripped RED wire.

Step 12: Cut Solder

Cut a 3/4" (20mm) piece of solder.

Step 13: Wrap Solder

Wrap solder around touching leads.

It may be easier to curl the solder into a small helix and put the wires into the solder helix.

Step 14: Position Helping Hands

Position the Helping Hands unit so the solder wrapped parts hang over the edge of the table.

Step 15: Add Heat

Ignite the lighter a few inches (centimeters) below the solder wrap.

Step 16: Raise Lighter

Raise the lighter until it is 1/2" (12mm) below the solder.

Step 17: Extinguish Lighter

Remove the flame when the solder has melted.

Step 18: Unclamp Parts

Unclamp the diode and wire.

Step 19: Test Solder

Test the solder joint by tugging. There should be no wobble.

Step 20: Clamp Diode

Clamp diode so unsoldered end is between clamps.

Step 21: Clamp Red Wire

Place tinned end of RED wire in other clamp so it overlaps the unsoldered diode lead.

Step 22: Repeat 12-19

Repeat steps 12-19 to solder the RED wire to the other lead of the diode.

Step 23: Cut Shrink Tube

Cut a 1" (25mm) piece of shrink tube.

Step 24: Apply Shrink Tube

Put shrink tube over RED wire and diode so diode is centered under shrink tube.

Step 25: Clamp Wire

Clamp wire near shrink tube.

Step 26: Position Clamps

Positions clamps and shrink tube over edge of table.

Step 27: Start Lighter

Ignite lighter a few inches (centimeters) below shrink tube.

Step 28: Raise Lighter

Raise lighter while slowly waving back and forth across length of shrink tube.

Step 29: Extinguish Lighter

Release lighter when all portion of tube have shrunk.

Step 30: Rotate Tube

Rotate shrink tube if necessary and repeat steps 25 through 29.

Step 31: Unclamp Wire

Release the wire from the clamp.

Step 32: Fit Diode Inside

Position diode on switch cover inside 9V enclosure.

Step 33: Thread Red Wire

Feed RED wire back out enclosure hole.

Step 34: Glue Diode Down

Put a thin layer of hot glue over and around diode. Use as little as possible because large gobs can gum up the switch or keep the cover from fitting properly.

Step 35: Cool Glue

Allow the glue to cool for 10 seconds or so.

This is the halfway point in the instructions and maybe a good time for a break.

Step 36: Test Switch

Ensure the switch can still operate.

Step 37: Test Cover

Ensure the cover can still close on the 9V enclosure.

Step 38: Cut Shrink Tube

Cut a 3" (75mm) piece of shrink tube.

Step 39: Insert Wires

Put RED and BLACK wires into shrink tube sleeve until the shrink tube is 1/4" (5mm) into the 9V enclosure.

Step 40: Glue in Place

Apply glue inside 9V enclosure to hole wires and shrink tube.

Step 41: Unplug Glue Gun

Unplug the hot glue gun and set it to the side where it cannot be accidentally touched.

Step 42: Optional Step

Use the lighter to shrink the tubing covering the RED and BLACK wires.

Step 43: Trim Wires

Trim the RED and BLACK wires to 1/4" (5mm) beyond shrink tube end.

Step 44: Strip Wires

Strip 1/8" (3mm) of insulation from each wire.

Step 45: Open Phone Socket

Open package with phone socket and select hollow metal piece

Step 46: Put Case on Wire

Put wires thought phone socket cover, unthreaded end first.

Step 47: File Phone Terminal

File backside of longest terminal in phone socket.

Step 48: Place Wire

Put stripped BLACK wire into post hole.

Step 49: Cut Solder

Cut 1/2" (12mm) piece of solder.

Step 50: Wrap Solder

Wrap solder around long post and exposed black wire.

Step 51: Clamp Post

Clamp post and BLACK wire together with RED wire bent away.

Step 52: Position Clamps

Position exposed wire, solder, and long post over edge of table.

Step 53: Repeat 15-19

Repeat steps 15 through 19.

Step 54: File Post

File rounded post with emery board.

Step 55: Bend Terminal

Bend square terminal away. It would also be acceptable to cut it off entirely.

Step 56: Clamp Socket

Clamp the rim of the phone socket.

Step 57: Position Wire

Position RED wire tip over the rounded terminal in the phone socket.

Step 58: Cut Solder

Cut a 1/2" (12mm) piece of solder

Step 59: Wrap Solder

Wrap solder around rounded post.

Step 60: Place Wire

Put RED wire under solder wrap.

Step 61: Position Clamp

Position exposed RED wire and rounded post over edge of table.

Step 62: Repeat 15-19

Repeat steps 15 through 19.

Step 63: Place Bundled Wire

Place bundled wires between crimp points of phone socket.

Step 64: Crimp Socket

Crimp phone socket onto wires.

Step 65: Secure Case

Screw the phone case onto the phone socket to finger tightness.

Step 66: Install Battery

Install the 9V battery.

Step 67: Install Cover

Replace the 9V battery enclosure.

Step 68: Secure Cover

Use the supplied screw and screwdriver to tighten the screw into the cover.

Step 69: Switch On

Flip the 9V switch to the ON position.

Step 70: Test Short Circuit Current

Plug into a mA testing unit or connect the electrode wires and measure the short circuit current. The reading should be less than 2.5mA.

If no current is seen:

  1. check the power switch to make sure it is on.
  2. check the 9V battery has a charge.
  3. verify the meter is working properly.
  4. check the polarity of the diode.

Step 71: Electrolyte Solution

Mix up some warm salt water. Ordinary table salt + ordinary tap water. The salt acts to make the solution more conductive and use warm water so it isn't chilly when it touches your skin.

Most electrodes have a cotton coating which will hold some water. In my case the carbon-rubber electrodes needed a felt sleeve. Do not use a carbon-rubber electrode without a sleeve.

Apply salt water to the electrode until it is saturated.

Make sure the tDCS switch is OFF.

Put the electrode pins into the sockets of the electrodes.

Step 72: Place Electrodes

Here is the most basic placement of tDCS electrodes. Electrode places are also called a montage. More can be found here. The anode (RED) electrode goes on the head 2" (50mm) above the right temple. The cathode (BLACK) electrode goes on the left upper arm.

Turn the tDCS switch to ON.

If there is a strong pinching sensation at the electrode site add more salt water.

You may experience a metallic taste, I do.

You may experience an ability to learn faster, which is the goal. Test yourself with online IQ tests.

Turn the device off after 20 minutes. Do not use for more than 20 minutes in a day or you may experience headaches. Do not sleep with this device on.

Conduct research into this procedure and follow all warnings. This Instructable is about building the device rather than using it. You must perform your own research but there is plenty of source material and people eager to share their findings.

Step 73: About Me

I spend days trying to source parts for this project and that took much MUCH longer than actually assembling it. If you read my blog you will know that this is the second iteration which was built from the exact parts I called out for the Mouser order so that everything would be clear. The first version was more cobbled together but the electrical design is rugged so there are no problems with it.

If this device becomes popular I have some plans for modules which would attach in series to expand the capabilities including a meter, an adjustable current module, and timer, and a switch to cut power if you fall asleep while using this.

As mentioned I run a blog where I talk incessantly about the things I build, including an unabridged version of this projectwith pictures of the first unit as it was being assembled. There are other neat things there like the mA testing box shown in step 70 and an ADJUSTABLE current tDCS unit I slapped together in an Altoids tin.

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    Question 4 years ago on Step 11


    Is it possible to provide me with a little more details regarding the diode used?

    What type is it? Is it a zenner?

    How many volts does it have?

    Im am not sure if its available in my country, what alternative can I use?

    Thanks in advance


    5 years ago

    I think you mixed up two instructables:

    1) A nice guide to making low budget electronic circuits.

    2) Building a simple tDCS device.

    Unfortunately the title suggests it will be #2. But details of tDCS get swamped in the other Instructable. A circuit diagram would have been nice. This is a great article for anyone who doesn't own a soldering iron but a waste of time (I'm not going to read 72 steps, most of no value to me) for those who do. I suggest renaming the article to attract the reader it was written for.


    Reply 5 years ago

    I know exactly where you are coming from. This article was written so that a novice could build a tDCS without many tools. We were planning to do a workshop and I thought it would be easier if the instructions were so explicit that anyone following them closely would be successful. In other words, I had to plan for someone who didn't know what solder was.

    Someone else asked for the schematic in a previous comment so I linked the picture below this paragraph.

    My title, "tDCS Thinking Cap" doesn't guarantee it will be written for someone with your skills and I suspect that when you see the schematic you will say to yourself, "Oh, it's that simple?" Yes, yes it is that simple.

    When I finished writing this, it took a lot of time, I laughed at myself for breaking it down so far. On the other hand, if you distributed a bag of parts and these instructions ANYONE with capable hands and eyes should be able to build it.

    I am working on a variable-current tDCS with a custom PCB which will probably be more on your level. It will be based on the following link which is not my work but maybe this is more your speed.

    Best of luck with your current and future builds!


    Reply 5 years ago

    You did a great job of making it clear to anyone. If a beginner came to me for advice I would direct them here.


    Reply 5 years ago

    However I would rename it something like "Absolutely simple but completely functional TDCS Thinking Cap." or "Anyone can make this TDCS Thinking Cap." Hopefully that would attract the people that would benefit the most. Especially since that is where you invested most of your effort. Might as well get credit for it.


    Reply 5 years ago

    I have noticed, especially in the mobile app, that long titles get chopped off so people would just see "Absolutely simple but comp..." then they have no idea what the project is about. That's why I put tDCS at the front and explained it a little farther with Thinking Cap. Your title definitely gets the point across but being succinct seemed more important.

    Maybe something like "tDCS Thinking Cap, Beginners Model" would work because the words become less important from beginning to end. Next time I write a title I will keep all this in mind.


    Reply 5 years ago

    Also even though I basically know how to use a soldering iron I'm no electronics wiz. Until I saw the schematic I had no idea there was such a thing as a current limiting diode. I knew about the voltage limiting zener diode. I learned something useful. Versatile these diodes. Thank you.


    6 years ago

    I built this pretty much the same way as you, and the finished device gave a steady 2.2 mA reading on my ammeter. I made electrode pads from a kitchen sponge, backed with some copper foil I had around, and it works great so far. I get a bit of tingling/redness at contact sites.


    Reply 6 years ago

    Congrats on a successful build.
    I love your approach to the electrodes. These instructions were designed like a scavenger hunt to begin with so they're perfect!


    7 years ago

    @24Eng Hi! I wonder if it possible to make this kind tDCS from an iPod? The reason is that I no longer use my iPod: its display is broken, and it is quite obsolete. So I would be really grateful if you could tell me whether it is possible to use an iPod battery as a tDCS batery?


    Reply 7 years ago

    An iPod battery would be lower voltage but it may still work. I've heard of people using 2 nine volts in series for 18 volts. It is EXTREMELY important that you still use a current regulator. The one shown in this project will still work with an iPod battery.
    The biggest problem you will have if you take the battery out of your iPod will be recharging it after use.


    7 years ago

    Is there a way to tune it to 40hz ?


    8 years ago on Introduction

    @24Eng im liking your work by the looks of things you have made this product purely on ohms law (Voltage divider) so wouldnt that mean the current would considerably differ with context of the Load (the head) also when the battery is losing power this would also affect the constant current in doing it role? im not too sure, as i am a novice. is possible you could post your schematic diagrams please.

    Many thanks


    Reply 8 years ago on Introduction

    Thank you for your kind words.

    The circuit is easier than a voltage divider since it only uses one component. That component however is much more expensive than a resistor or silicone diode. The constant current diode actively limits the current passing through. Even if the load changes from a short circuit to a high resistance then back again the current will never exceed the limit.

    You are correct about a voltage divider which could vary greatly depending on the resistance of the subject. A voltage divider would have been much cheaper but far too unreliable.


    8 years ago on Introduction

    The diode is the only thing reducing the voltage? Why does every one else have multiple parts like resistors, transistors, etc?


    Reply 8 years ago

    Good question. Most other devices I've seen use a variable current regulator and supporting components. This variable method is more robust and CHEAPER.

    The advantage to using a single component is the build is simple and small. The downsides are the cost and you are locked into a single setting.


    Reply 8 years ago

    The component in the link is 2mA. Choosing a different model would be hazardous.
    The typical measured current is 2.1mA but this is considered safe and has not hurt me.


    Reply 8 years ago

    Nope. My project is freely available to anyone who wants to build it. I have seen that unit you linked to. I haven't opened one up but I suspect the components are identical.