Brainwave entrainment is the idea of using audio visual stimuli to produce a specific state of mind, and target specific "brainwave bands". I have no idea how much of that is bullshit, but I have found such devices entertaining and relaxing when I've used them, typically at tourist destinations.
However, while the hardware is extremely simple, setups from vendors like MindPlace can cost several hundred dollars, which is excessive, and also the hardware usually looks glossy and consumerized. Yuck.
I therefore decided to cobble some together out of parts I already own.
Components
1×
Basic Goggles
A set of basic goggles, ideally with circular lenses that can be removed. I used these: https://www.amazon.com/dp/B072V7ZYF2
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M5StickC PLUS
A microcontroller to drive the system. https://shop.m5stack.com/products/m5stickc-plus-esp32-pico-mini-iot-development-kit
2×
Hexagonal LED grid
The light source for stimulating the optic nerve: https://shop.m5stack.com/products/hex-rgb-led-board-sk6812
1×
A stereo DAC
A small board to used to drive wired headphones: https://www.amazon.com/HiLetgo-Lossless-Digital-Converter-Raspberry/dp/B07Q9K5MT8
1×
Micro USB adapter
a USB adapter to power the setup. It doesn't have to be micro, or even USB, just some connector you can put on the final board that will give you ground and 5V output. I used these: https://www.amazon.com/dp/B099N2Q2CC
I built a similar device that also uses binaural beats and a sleep mask with leds. What frequencies do you use?