Electrodes and shocks

I'd like to be able to apply little zaps to the skin.
I want to have a micro controller apply a small current to the skin and I'm wondering if anyone has experience designing something like this.  Useful information would be perceptible voltage, useful components and frequency.

My current assumptions are that I will be building a transformer with the primary side attached to the output of my controller and ground.  The secondary side will have its leads attached to the electrodes.  The controller will generate a square waveform.

Currently, pun intended, this is intended for use as an external device as opposed to an implanted one.


  • I once build a microcontroller based EMS. I didn't use a coil, instead i build my own high voltage DC source and a current-driver. If all you are interested is a bit of zapping, the coil thing will work.

    There is no real number on the voltage required, this pretty much depends on the skins resistance and your contact electrode. If you pierce the skin with a needle you can get away with voltages well below 5V. if you put metal on dry skin, you may need 100 or more. The thing is you don't want too much current, or overall energy.

    The inductive voltage spike from the coil can easily reach 400V and more, but you can limit the total energy by adjusting the current in your primary side. The higher the current, the stronger the magnetic field, and that field stores the energy for your 'zap'.
    From my experience, between 80 and 150 pulses per second are a good starting point. You may also want to use a sawtooth like shape instead of rectangular. Slowly ramping up the current, then cutting it off.

    Be sure to add freewheeling diodes to protect your circuits from induced reverse voltages. Also ensure the electrodes have good contact over some area. Those high voltage spikes can create small lightning arcs if no proper contact is given, burning small parts of the skin.

    so much for my almost 6 am recommendations.
  • This is two-fold.  My roommate has a device which straps to her wrist called a ReliefBand© which delivers electrical pulses to relieve feelings of nausea.  Her device is wearing out and I'd like to replace it for her birthday but they're ludicrously expensive for what they are.

    The second part is that I am building a temperature sensing system.  The first version is shown in my profile picture.  That device uses an IR thermometer to read temperatures and a microcontroller translates them to a frequency which I hear through headphones.  The first device works quite well.

    The next version will use an IR thermometer with a narrower field of view so I can sense the temperature of a point far away rather than a broad field of view.  This device will have a variety of other outputs in addition to the frequency.  I'd like one of those outputs to be an electrode.  The second version is also not bare electronics glued to a pair of glasses.  The first version was proof of concept.

    Do I need to be concerned with where on the body this will be placed?  The skin on the bottom of a person's wrist is probably more sensitive than someone's back.  Sensitivity aside, does the resistance of the skin change based on callousness or body location?

    I plan to keep the electrodes close together, maybe a 1/2 gap at the most.  I did not think about making them large so I'm glad you mentioned that, I don't want to scorch anyone's skin.
  • edited February 2014
    I have experience with electrodes and zapping ones-self, from my tDCS experiments.

    I've probably used it 30 times or so, about 20 minutes per session, using 2" square sponge electrodes, building up from 0.5mA to 2mA. The device itself wasn't anything special, a current limiting IC and couple of random components.

    After 20 minutes of use, the skin is red and a little bit irritated, that goes away within an hour.

    The biggest issues I've seen and experienced is with the contact with the skin. If your electrodes are too dry, your saline is too salty in case of sponge electrodes, or when there are issues with the placement the electrodes, you can end up with a smaller area of the skin that gets zapped and that hurts and causes more severe skin irritation, possibly up to burns.
  • What's the simplest method or the cheapest method to get this project rolling?
  • The transformer idea you described at first is about as simple as it gets.
  • Excellent.  I'll keep pursuing that line.
    Have you ever constructed a transformer from scratch?  I'm trying to get something that delivers a noticeable shock before I invest in proper materials and fine tuning.  I've tried wrapping magnet wire around a polished nail and I've tried a safety pin.  Neither seemed effective so I wanted to see if I was barking up the wrong tree with these back-of-the-junk-drawer designs.
    I've never successfully constructed a transformer.  Is there a minimum number of windings I should start with?
  • There's an big amount of theory available on transformers. Simplified it goes something like this:
    You build a magnetic circuit, which can be imagined very much like an electric circuit. Things like iron cores with a large cross section area are good magnetic conductors, smaller cross section area of iron increase resistance, and air-gaps have a very high magnetic resistance. That's like, super simplified.
    So your coils are electric<>magnetic converters, and then you need a good low-magnetic-resistance circuit to the next coil.
    I don't think it's really worth the trouble of building your own transformer. In the end it's just a transformer with worse properties than one you can buy off the shelf for a few cents.
    What's more important is to control the current properly. As the current defines how much energy in stored in the magnetic field (and gets released once you cut off the current).
  • First step is finding the right transformer.  What should I be looking for?  My primary voltage will be 5 volts.  Will the duty cycle of my PWM be enough to limit current or do I need something to instantaneously limit current?
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