Audio-Visual Brain Entrainment Using An Arduino

There are some interesting theories about the ability of low frequency light and sound to alter brain states. I created the Rich Decibels Brainwave Disruptor to investigate some of the theories.

Theory

Electrical activity in the brain is rhythmic. The frequency of this rhythm depends on the state the brain is in: An active, alert state correlates to rhythms in the range of 30-100Hz. As brain activity reduces in frequency, the brain state changes. 8-12Hz is associated with relaxation, 4-7Hz with meditation and below 4Hz indicates deep sleep.

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The concept behind “brainwave entrainment” is the idea that you can induce different brain states by causing brainwave frequencies to fall into step with external stimulus.

Concept

My device generates this external stimulus with binaural beats by creating two tones whose frequencies are separated slightly, along with flashing lights and a pulsating audio filter.

Hardware

The handsome case was designed in Sketchup and laser-cut in my Personal Factory. The text is engraved and then filled with white-out fluid. Under the hood is an Arduino Uno and two interface boards I designed.

Board 1 has “pitch” and “separation” controls connected to the Arduino’s analogue inputs. It also has a pair of low-pass filters (one for each channel), whose intensity is controlled by the “depth” control. The filter cut-off is set by a vactrol whose brightness is set using the Arduino’s PWM outputs.

underside | layout | schematic

Board 2 has six transistor circuits to drive the LEDs in the goggles along with a volume control for the audio.

underside | layout | schematic

Software

There are many ways to generate audio with an Arduino. uC Hobby has a great round-up that goes into some depth about the many different approaches. I personally learn better from real-world examples, so I started out by stealing the code from the Nebulophone and paring it down from there.

In the end, I settled on a “bit-bang” approach: Toggling an output pin High-Low-High-Low at the right frequency to generate rudimentary audio. Here’s the code in its current form if you’d like to have a tinker.

Testing

Astonishingly, it works! At certain frequencies, the flashing lights especially have a really eerie effect by generating crisp geometric hallucinations on the inside of my closed eyelids. Something I hadn’t expected were audio hallucinations. Its as if the brain gets bored listening to two consistent tones wobble on indefinitely and starts to invent harmonies and chord progressions. My sense of time was thrown out the window, too, with 90 minutes passing in what felt like 20.

Health And Safety Warning

This is a potentially dangerous device. In my research I’ve seen claims of between 1-in-4,000 and 1-in-10,000 people suffering seizures from visual stimulus like this. I’ve not seen any evidence of low frequency audio having the same effect, but you should proceed with caution regardless.