Transcranial Brain Stimulation (tACS) creating Visual Phosphenes

I did some research on transcranial alternating current stimulation today after hearing about experiments [1] in which visual Phosphenes (colorful shapes) can be induced with (non invasive, low-current) electrical stimulation of the visual cortex. Phosphenes are stimuli like those perceived when light pressure is applied to closed eyes.
This sounds interesting to me as a potentially useful machine-input interface for private and clearly perceivable information and the experiment itself is a very hands-on exploration of the mind (or the visual sensory apparatus [2]) and the effects might be recreationally interesting in themselves.

When searching for devices for transcranial electric stimulation, most DIY efforts seem to focus on tDCS (direct current) and seem to my gut feeling to be rather pseudoscientific or at least focus on not very measurable effects, but I might be wrong and would like to hear possible experiences.

At the moment I'm trying to get a technical understanding of how exactly tACS works and is defined in this case.
I would like to propose the following as a first step into building an electronic experimentation toolkit:

  • battery powered stimulator
  • multiple current-limiting safeguards
  • ±2-3mA power use
  • no mains or USB connection for safety reasons
  • adjustable frequceny in a range of around 5-30Hz (findings are strongest phopshenes in the 10-20Hz range)
  • triangle or sine wave oscillation (triangle waves are usually easier produced)
  • two sponge-electrodes

Some more general work on tACS and established safety guidelines can be found in [3] and [4].
Looking for DIY tACS devices, I have found some schematics with very little documentation and much more in the way of tDCS, where it seems to be common to simply use a LM334 or similar adjustable current source.
There are multiple designs for tACs stimulators from and related instructables [5], [6].
These designs and the commentary is quite sophisticated and above my level of thorough understanding of discrete electronics at the moment, but the designs are quite convincing.
The first design [5] is very complex and some flaws are documented. As I mentioned above I would focus on a battery powered and fixed-function implementation. From [6] it seems like it would be quite easy to use a simple Op-Amp oscillator as the control signal for the voltage-controlled current source instead of the photoresistor and LCD system.

With this design I am mainly confused about what seems to me as unusually high and potentially dangerous voltages on the power supply (±60V ?!). Maybe this is a requirement due to losses in the circuit, a simple estimate of 2mA * 10kOhm (mentioned head-resistance) yiels a 20V draw, so this would be equivalent to about a 10-15% effectiveness plus safeties.

I'd be happy to hear any opinions on the topic, experiences with brain stimulation and especially more qualified evaluations on the schematics than I can currently offer.

[1]: Frequency-Dependent Electrical Stimulation of the Visual Cortex,
[2]: Transcranial electrical stimulation over visual cortex evokes phosphenes with a retinal origin,!po=7.60870
[3]: Transcranial alternating current stimulation (tACS),
[4]: Establishing safety limits for transcranial direct current stimulation,
[5]: DIY USB tACS,
[6]: LDR-controlled Simple tACS,

btw, is all rich text gone? Neither BBCode nor Markdown seem to work for me.

EDIT: the lab notes from also mention Phosphenes using tDCS. I also just realized there is an updated arduino-controlled instructable as well (
I still think that a simpler version is a necessary starting point at least for my own attempts but it seems that in 2017 the creator of the designs hasn't fried their brain yet.


  • I've used TDCS before but haven't messed around with it for a while now. While the effects could be a lot of placebo, I still feel that it did work. The phosphene light flashes were definitely real though. I only saw the flash of light when the power was first turned on and when it was turned off so AC probably would cause a much more noticeable flash. I think the flash could be eliminated by adding a capacitor to the circuit so there wasn't an instant on/off but I liked the flash and used it as a sign that the device was working. I would often turn the device on and off part way through the session just to make sure the electrodes were still conducting right.

    The sponge electrodes I used would sting or burn as they dried out so using the device for long periods (like while sleeping) was not possible. A gel electrolyte instead of a salt/baking soda mixture might have taken longer to dry out. The longest I used the TDCS at one time was 45 minutes and it was almost making me sick. 5 or 10 minutes was enough to get the stimulating effect I was looking for but it COULD have been at least partially placebo. I thought about having someone else try the device but didn't want to experiment on a brain that wasn't my own.

    I don't remember the names of the electrode positions I used but + side was over my left eye towards the temple and the - side was either above my right eye or on my right upper arm. I tried reversing the polarity and didn't like the effects. I tried other positions but didn't find any that gave as noticeably positive results for me. The phosphene flashes were only visible if at least one electrode was close to an eye.

    When the device didn't seem to be giving me the effects I was used to, it was caused by the battery getting low and the effects returned when I replaced the battery with a new one.

    I thought about ways to use the light flashes for an information input but never did any more than thinking. The electrodes would need to be able to be worn for long periods.

  • edited October 2017

    I also regularly use tDCS. There was a period of time when I try to use the montage that will reduce my sleeping time (based on this paper: Once I had the cathode on too far back of my head and as a result I started seeing grey lines in my vision that overlaps on everything that lasted for 1 hours or so (ie, I accidentally put the cathodes on my occipital cortex instead of the parietal lobes), so that's certainly not a placebo and tDCS does do something to the brain. It's exactly what it is doing (and also, electrode placement will differ a bit in between people: shape of the skull will change how much of the electric field penetrates, and different people will have a bit different brains - I found that I need to swap my electrodes around probably because I am a left hander).

    Also, I actually have more doubts about AC than DC: the only way that I can think of how transcranial brain stimulation can work is either that the electric fields causing a change in the ions around the neurons and thus stimulating / inhibiting their firing (skin is too much of an insulator for the electric current to actually get deep into the brain). This takes time and the constant changing in current direction in AC makes it less likely for the neurons to be stimulated / inhibited.

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