A $7 Usability Improvement for the tDCS-Kit.com Device

I recently reviewed the tDCS-Kit.com devices and found them to be useful but “bare-bones”.  For about $40 you get a current regulated tDCS device that puts out a max of about 2 mA. ( See http://speakwisdom.wordpress.com/2013/11/03/product-review-tdcs-kit-com-tdcs-devices/ ) While I’m not a fan of the USB version, the 9-volt battery version deserves consideration. Being “bare-bones”, the device is a bit harsh on start-up and shutdown and offers no control of the current delivered other than the 2 mA limit.

I constantly receive emails and messages from folks from all over the world complaining that they cannot afford the $250 (or more) the more sophisticated tDCS devices cost. Yet they are desperate for help with depression, chronic pain, etc.  So the price of the tDCS-kit.com device is attractive – it provides a serviceable tDCS device at a very low cost.


(tDCS-Kit.com Device)

With a very simple modification, the tDCS-kit.com device can have current control! That means you can start and end a tDCS session by ramping current  up and down in a comfortable way – and limiting current at a desired level (say 1 or 1.5 mA.)

Here is what you need:
1. 5 k-Ohm linear potentiometer RS part 271-1714 $3.49
1. Project box RS part 270-1801 $3.49
1. Knob from your junk box or other source

You also need the ability (or have a friend) who can do some basic soldering.

Simply put, the potentiometer will be connected ACROSS the anode and cathode lead from the tDCS-kit.com device. It will act as an adjustable alternate pathway for current so that not all of the  2 mA from the tDCS device will pass through your head. Along the way, you may want to replace the “pin” style connectors with alligator clips (my preference) or banana plugs.

Adjustable current for the tDCS-kit device
(Simple diagram of the mod to the the tDCS-Kit.com device.)

Inside Current Control for tDCS-Kit device
(I put the potentiometer in a little project box. Note that I clipped the pin connectors off and soldered the red-striped lead to the center of the potentiometer.  The red anode lead to the electrode also goes there. The black cathode leads are soldered to the bottom terminal of the potentiometer.)

Current control box for tDCS-kit device
(Complete! tDCS-Kit module is at the left. Leads to electrodes appear at the right.)

May I suggest you also spend a little money and buy a digital multi-meter (many for $10 or less.) You will need that to monitor the current level you are using for your tDCS session. The multi-meter is set to read current and is placed in series with the red (anode) lead and connects to that electrode. With the modification shown above, you can vary current up to the max of 2 mA that the device will deliver.

Warning: Disconnect the battery when not using the device as there will always be a load present.

I think you will find this simple modification makes the tDCS-Kit.com device far more versatile and comfortable to use.

As with any DIY tDCS project, you are responsible for your own actions and safety. If you are not sure what you are doing STOP and get help from a professional and/or read, read, read about tDCS.

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20 comments on “A $7 Usability Improvement for the tDCS-Kit.com Device

  1. dear brent
    thanks so much for your giving

    since you praised foc.us instrument and i purchased the instrument, I unfortunately must inform you that they do not care to “support” .until this very day I did not get any response to my help-inquries , although it is already few weeks since I wrote to them.
    as a result I wasted ca. a week thinking the device is activated while it was not….
    (I later found the right way to activate it.of course i do not hold you responsible for that. you do only good things.)
    besides, I cannot tell that I feel anything new in my life after ca 2 weeks of everyday 20 minutes session.
    can u please comment on the average time (days? weeks? months?) after which a stable change usually does show?
    thanks a lot for your input that motivated me to learn about tdcs and to trust the whole issue and to then purchase an instrument

  2. So does the kit actually have a LM334z inside it? Can you do a tear-down of that little case so I can see what is inside and how it is connected? I would like to make my own version without shelling out $40 for it. I have LM334z’s here and lots of resistors, just need to know how to hook it up properly. Plus once created, do I measure it with a load on it to see if it is working? Or just connect to the leads with my Multi-meter?

    • Adding an ammeter would be easy. I’d suggest buying a 3 mA analog meter from Ebay and put it in series with the anode lead of your tDCS device (currently selling for about $6.) It could be built into a nice case if you like.

      Brent

  3. The pictures you have posted don’t really show what you are supposed to do. Can you give step by step instruction as to exactly which wires you are supposed to solder where?

    • If the diagram does not provide the information you need, then you should not build a device yourself. Have an electronics trained friend do it or buy a commercial unit.

      Safety first.

      Brent

    • Does the setup as shown actually work? It seems to me to wire the pot properly you would attach one end of the anode wire to the center post on the pot and then the other end of the anode wire to one of the outer posts to wire it in series – and have is serve as a variable resistor. It, therefore, wouldn’t make sense to attach the cathode to the pot at all. It seems to me that the way it is wired in the picture and the diagram above would bypass the pot entirely. Please help me understand.

      • Yes – it works well. the potentiometer acts as a current shunt. The tDCS device always tries to deliver 2 mA, the shunt divides the current so part goes through the head and part through the shunt – you can vary how much uses either path.

        Brent

  4. I did the modification like you said, but I put a 3ma ebay ammeter inline with the red lead. I can still get 2.1ma out of it with the electrodes shorted to eachother, but I can only get about 1.5ma with the sponges touching eachother, or on my head. Could it be that a 10k pot might get the full current easier?

    • What is the highest current you measure with no pot connected? If it is substantially higher than what you are seeing with the pot connected, then a higher value pot will help as the alternate path for current will have higher resistance.

      Brent

      • Ya, I’ve ordered a 10K, a 20K and a 50K. I disconnected the pot for now, so I’m back to having a straight 2.1ma output till the other pots arrive. I’ll let you know how high I have to go in a couple weeks when they get here :-)

      • I tried the 10K pot today. I only got 1.5 milliamps out of it with the sponges touching. Still waiting on the 20K and the 50K

      • If you are using a 9 volt battery, your skin/skull resistance may be too high for the device to work at higher than 1.5 mA. Actually many researchers (and myself) stick with 1.5 mA (or less) because it works and reduces skin irritation.

        Brent

      • I think I’ve settled on the 50K pot. I don’t know if it needs to be so high because of the ebay ammeter, or if I just have abnormally high skull resistance (thick skulled?),
        I can turn it up to 2milliamps if I really want to, or have a bad sponge connection, but it’s not too touchy to be able to easily turn it down to 1.5 milliamps for better comfort. I’d be interested to hear if other people need to use such high resistance pots in their own devices.

  5. Hi,
    Thanks for your blog. I’m building this for my wife, migraine sufferer with chronic pain. Adding the potentiometer by itself works great.

    The puzzling issue is when I add the ammeter in series the current to the pins disappears, though the ammeter still reads 2mA when turned the pot is turned all the way up. Any clue why this is?

    The ammeter is necessary b/c only a very small turn of the pot’s knob is required to go from 0mA to 2mA, so without the ammeter you’d be in for a jolt.

    I’ll post pictures if this allows.

    Thanks for any help
    Pete

    • Do you have the ammeter in series with one of the electrode leads? If you have it across the leads you are providing a short circuit path so no current will go to the electrodes. The ammeter must be in series with an electrode lead.

      Brent

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