Micro-current electrical stimulation device

Discussion in 'The Completed Projects Collection' started by wayneh, Aug 15, 2016.

  1. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Introduction
    This is a project to build a micro-current electrical stimulation device. These are also called tDCS devices and are similar to MENS devices. They are not much like the common TENS devices which use much higher voltage pulses.

    I have posted about this project before here. Since then I've built a couple of these devices for friends and they've been very pleased. So I thought I should update the circuit and post the complete information here.

    A tDCS device provides a constant current from zero to 600µA applied the the earlobes of the user. That alone can produce a therapeutic effect, but it's more effective if
    1) the current is pulsed at ~0.5Hz,
    2) reverses direction (this is an AC device), and
    3) the pulse timing varies "randomly".​

    The changing frequency feels somewhat random and prevents a "burn in" in the patient. It's more effective than a steady beat. This is a probably a small refinement, but I wanted to include it.

    I based my project off this device, described in patents US2010145410, US2010047834A1 and others. I also added TENS capability in my first unit since most of the circuitry was already in place to easily add this capability. I have since removed the TENS circuit. It's a completely different treatment and there is no reason that someone using tDCS will necessarily care about using TENS. And, you can buy very elaborate and nice TENS units for ~$30. No need to build your own.

    Circuit Overview
    The strategy for my circuit was to use a dual timer 556, with the first timer slowly changing the voltage on the second timer's control pin to change the timing. The clock pulses from the second timer go to a 4017 counter to create the proper waveform. Finally, the waveform drives a dual op-amp configured to provide a sort of H-bridge. An adjustable constant-current is applied to the output earclips.

    Schematic and Description
    Screen Shot 2016-08-15 at 11.06.05 AM.png

    The voltage on the timing capacitor C5 of the first timer U2 feeds an op-amp voltage follower U6, and then the voltage is amplified by a 2nd op-amp U7 to make a ~30-second triangle wave from rail-to-rail. It's a crude triangle, since it's really just the middle of the timing capacitor's RC curve . This is applied to the control pin of the second timer U1, which would otherwise be running at ~0.5Hz. Pulling the control pin high and low changes the frequency over a ~4-fold range from 0.25Hz to 2hz. (It also changes the duty cycle, but that's not an issue in this circuit.)

    The 2nd timer's output is fed to a 4017 counter U3 and the "0" and "2" outputs are compared. This provides a way to alternately remove and reverse the direction of current flow. Using the "2" pin against the "0" pin as outputs allows the current to reverse direction with a dead space in between when the "1" pin is hot and the 0 and 2 are both at ground. The pulse on the 3 lights an indicator LED and the counter resets on 4.

    Output from the counter controls the state of a dual op-amp controlled-current circuit. The circuit works with an LM358 for U4 and U5, but the simulation looks better using a TLV2721. The LM358 can't get as close to the ground rail, and the simulation shows the "dead space" intervals as reduced-current shoulders. But the current never goes to zero as it does (in simulation) with the TLV2721. Again, I built two successful units using the LM358. I've switched to the TLV2721 for later builds.

    The current intensity into the load R8 is adjusted using a dual gang pot, since there are essentially two channels, plus and minus. R10 and R11 in the simulation are actually each a 3KΩ fixed resistor and a 10K variable resistor in the pot. The minimum of 3K results in an output intensity of ~0µA. At the maximum of 13K total, the output reaches 800µA, a little higher than the target of 600µA but still quite safe.

    Screen Shot 2016-08-15 at 11.23.25 AM.png

    Parts List
    Following is a recent Mouser order for most of the required parts
    Screen Shot 2016-08-15 at 11.27.46 AM.png
    Screen Shot 2016-08-15 at 11.28.13 AM.png

    I had a few parts, like the LED, on hand already and so there may be a few parts missing from the order. Let me know if you find one missing and I'll add it.

    Here is where I ordered some cheap ear clips on e-bay http://www.ebay.com/itm/331870106853
    I've also ordered from Lhasa Ohms in the past:
    Ear clips: http://www.lhasaoms.com/Ear-Clip-Electrodes.html
    Wire leads: http://www.lhasaoms.com/Lead-Wires-with-3-5-mm-Jack.html

    Build
    I use these 4x6 cm prototyping boards to build the circuit on. Standard fiberglass with 0.1" hole spacing. It's a little tight on the 4x6. Use a 5x7 if you want extra space.

    My circuit design is done is drawing software. I use Intaglio. I can supply the original Intaglio file to anyone that asks but I have not attached it here because I suspect there are few other users of that software here. Instead I'll post the various layers.
    The board:
    Screen Shot 2016-08-15 at 11.45.40 AM.png

    The board plus solder traces
    Screen Shot 2016-08-15 at 11.46.03 AM.png

    Plus components
    Screen Shot 2016-08-15 at 11.46.24 AM.png
    Plus wiring
    Screen Shot 2016-08-15 at 11.46.54 AM.png

    Detail of the output and adjustment pot
    Screen Shot 2016-08-15 at 11.47.14 AM.png

    The backside solder traces, viewed from the back
    Screen Shot 2016-08-15 at 11.53.32 AM.png

    See the project linked in the introduction for a photo of my first complete build. I'll be making more of these soon and will post more detailed photos.
     
    Last edited: Aug 15, 2016
  2. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Here is the LTspice simulation file. It requires the CD4000 library and the model of the TLV272 op-amp to be called as included files.
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    Hi wayneh:
    Please make a direct link or copy the end product to this thread, it may easy to see it, thank you.
     
  4. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    I'm finally getting around to building this. In fact I'm doing 4 at once. I've never done that before, and I'm impressed how much more efficient it is to do them together. I'd guess it takes only 1.5X the time to make 4X as many. Most of your time is spent setting up, picking the parts, and verifying their placement. Oh, and ordering the parts. Doing multiple boards at once adds very little effort.

    Anyway, here is the work in progress. First I place the IC's. They help as landmarks for placing other parts.
    IMG_3063.png

    Here are the boards with all components added. Everything not shown will be mounted to the enclosure and not on the PCB. I think the decoupling capacitors are the only additions not shown in the schematics.
    IMG_3070.png

    The final step is the wiring and the traces on the back. I may not get to that for a while!
     
  5. bfrd6969

    New Member

    Nov 27, 2016
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    What are decoupling capacitors. Do I need them for this build, or are they pictured on the pcb board pictures. Do you have a complete parts list if not. I'm very interested in building this as I have recently tried my friends purchased model and it really helped me with my pain and addiction. Thank you for all you have done as this is the most comprehensive information I have found and your efforts are greatly appreciated.
     
  6. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Decoupling capacitors (the 3 yellow capacitors shown) help reduce incoming and outgoing noise at each IC. 555 timers (my 556 is two of them) are notorious for making quite a bit of noise on the power supply when they switch. I use o.1µF ceramics for this duty. Labeled "104", for ten plus 4 zeroes = 100,000 pF = 100 nF = 0.1µF

    There's an article here somewhere about decoupling capacitors but the search function seems out of order at the moment.

    My order to Mouser above is nearly the entire parts list. Sorry there's not something better. Just go through the schematic to identify the few parts that weren't on that list. An LED and a few resistors I think (probably the resistors that aren't blue in the photos, old ones I had on hand). Maybe I had the caps on hand also. If you aren't set up for soldering, you'll need solder, an iron, some 22 gauge connection wires and a wirestripper. C'mon back for advice on all that if you need to.

    Just curious: What commercial product did you try. Alpha Stim? I was very skeptical of this whole thing until a friend tried it and was profoundly effected, in a good way.
     
    Last edited: Nov 29, 2016
  7. bfrd6969

    New Member

    Nov 27, 2016
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    I tried the bt plus from alteredstates.co a company out of nz. It has 1.5 hz 5 hz 10 hz 78.3 hz and 100hz and was adjustable from 50 to 600 micro amps. My friend had purchased it for about $180 usd. I bored it for a night and it changed something for the better in me and I decided I need to find out how to build one of theses for my self. Is the frequency adjustable on your design if not how would I do that if possible. I do have soldering equipment I've never done any pcb projects just work on hvac equipment and houses so this is new to me. I have ordered the pcbs and ear clips and am going to be making a parts order TN
     
  8. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    The first design of this I made, I included a frequency control and also TENS capability. With usage it became clear that neither is really useful. TENS units are cheap and have lots of features, and address a completely different need. There was really no need to adjust the cranial frequency of this device because no one can be sure what setting to use. It works fine at a fixed (but varying) frequency.
     
  9. bfrd6969

    New Member

    Nov 27, 2016
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    that makes sense do you know the frequency range it would span through.
    Is the decoupling capacitor marked 105 am I able to use a 104 interchangeable? Aldo is that a symbol for an adjustable pot on the adjustable out put and near the power supply and are they the same ?
     
  10. bfrd6969

    New Member

    Nov 27, 2016
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    Sorry for the redundancy i see you stated the frequency range and the 10k ohm dual gang pots thank you again im making an order on mauser as i write this.
     
  11. wayneh

    Thread Starter Expert

    Sep 9, 2010
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    Yes, I used all 104 ceramics in these builds. I might have used a 105 if I had one and that's why I drew that in, to remind myself to take a look. I didn't have any. I'm sure it'll be fine.
     
  12. bfrd6969

    New Member

    Nov 27, 2016
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    I'm having a hard time finding the decoupling capacitors as well as the 4.7 and the 47 mfd caps on Mauser what voltage rating are yours and which type if I can't find there I do have a radio shack near me I could see if they had them.
     
  13. wayneh

    Thread Starter Expert

    Sep 9, 2010
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  14. bfrd6969

    New Member

    Nov 27, 2016
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    Excellent I was able to get an order of all the parts, my pcb's just arrived and all of the components from mauser will be here Monday it looks like i cant wait :D. I am confused as to what exactly ~4-fold range from 0.25Hz to 2hz means is 2Hz the max operating frequency, also do you by chance also have a plan for me to make your first design that i could select the frequency manually up to 100 Hz or what ever the max Hz range could be i am really interested interested different frequency's that correspond with different things like learning and lucid dreaming. Im not sure how to interpret your first diagram of your variable build but if you could make a pictogram like in this build id be willing to pay you for your time, i know i can buy one but id much rather build one. maybe with the tlv 2721 and the n556 timer Thank you anyway;)
     
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