Oyu

Open-source wearable EEG hardware
24-bit ADC · instrumentation amp · ESP32-S3 · MIT licensed

оюу · turquoise · a small board that listens

On-head Berger test · OUT0
Eyes open (blue) vs closed (red) · α peak ~10 Hz · ratio 29.66× · PASS

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Why this exists

Most EEG hardware is either closed, expensive, or impossible to modify.

Oyu is the opposite: a real, bench-proven wearable EEG prototype — a TI ADS1220 24-bit ADC and an AD8422 instrumentation amp next to a Seeed XIAO ESP32-S3 in a compact two-board stack.

This is not a toy breadboard. It is a design that was soldered, powered from LiPo, and streamed from the bench — then validated with a classic Berger eyes-open / eyes-closed run (graphs above).

If open brain-computer interfaces matter to you, star this repo.
Stars tell us the community wants more — Gerbers, better docs, and the next open drop.

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Gallery

AFE panel	Main board + AFE	Assembled stack

Left: panelized AFE (AD8422) boards. Center: main carrier with XIAO ESP32-S3 + ADS1220. Right: live stack with electrode harness.

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Architecture

Three PCBs, one ecosystem:

Board	Role	Core parts
NF Mark 3 Main	Carrier, MCU, ADC, power, UI	Seeed XIAO ESP32-S3, ADS1220, LiPo path, LEDs, switches
NF Mark 3 AFE	Analog front-end daughter	AD8422 instrumentation amplifier + passives
NF Mark 3 Expansion	SPI ADC strip (no MCU)	ADS1220 + H8/H9 + U5 breakout

Electrodes  →  AD8422 (IA)  →  ADS1220 (24-bit)  →  ESP32-S3  →  Host (USB serial)

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What you get

Everything you need to understand, rebuild, and iterate:

neurofocus-mark3/
├── schematic/
│   ├── netlist/        # nf-mark3-main / afe / expansion (.tel)
│   ├── gerber/         # fab zips
│   ├── drawings/       # schematic PNGs
│   └── archive/        # original EasyEDA export names
├── assets/pcb/         # PCB layout screenshots
├── hardware/photos/    # Real assembled boards
├── firmware/           # Modular PlatformIO + native unit tests
├── docs/               # Pinout, BOM, fabrication
├── LICENSE
└── README.md

Path	What it is
schematic/netlist/nf-mark3-main.tel	Main carrier netlist (XIAO + ADS1220 + power + UI)
schematic/netlist/nf-mark3-afe.tel	AD8422 AFE daughter
schematic/netlist/nf-mark3-expansion.tel	ADS1220 SPI strip (no MCU)
schematic/gerber/	Gerber packages for all three boards
assets/pcb/	PCB layout screenshots
docs/BOM.md	Parts list
docs/PINOUT.md	XIAO ↔ ADS1220 ↔ OUT0..3
firmware/	Full CLI firmware (b/s/v, presets, tests)

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Pinout (firmware ↔ hardware)

Function	XIAO pin	ADS1220 / board
CS	D7	Chip select
DRDY	D5	Data ready
SCK	D8	SPI clock
MISO	D9	SPI data (ADC → MCU)
MOSI	D10	SPI data (MCU → ADC)
BAT-MEASURE	D0 / A0	Divider (220k / 220k)
OUT0–OUT3	—	ADC AIN0–AIN3 via H8/H9

Full detail: docs/PINOUT.md

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Quick start (firmware)

cd firmware
pio run -t upload
pio device monitor -b 115200

Serial commands (OpenBCI-compatible subset):

Key	Action
b	Begin stream
s	Stop stream
v	Reset ADC config

Samples print as CSV raw counts (4 channels, muxed on the ADS1220).

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Specs

MCU	Seeed XIAO ESP32-S3 (USB-C, Wi-Fi / BLE capable)
ADC	TI ADS1220, 24-bit delta-sigma, SPI
AFE	Analog Devices AD8422 instrumentation amplifier
Channels	Up to 4 single-ended / differential mux paths on ADS1220
Power	USB-C and/or LiPo (JST), onboard switch + battery sense
UI	2× status LEDs, user button
Form	Compact carrier + plug-in AFE strip

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License

MIT — hardware design docs, schematic netlists, photos (as included), and firmware in this repository.

See LICENSE. Use it. Ship it. Improve it. Attribution is appreciated; starring is louder.

Third-party silicon (TI, Analog Devices, Espressif, Seeed) remains under their respective terms. You still need to respect component datasheets and any module certifications.

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What is not in this drop (yet)

Honesty > FOMO:

• Gerber / drill / pick-and-place files are not committed yet. Connectivity is fully specified in the netlists; PCB artwork may be released as a follow-up once cleaned for public fab.
• Advanced firmware (BLE streaming, power management, multi-channel ADS1299-class designs) is outside this open drop.

Want Gerbers next? Star + open an issue titled Gerbers please. If enough people ask, we prioritize the export.

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Contributing

1. Fork and branch from main
2. Keep the tree clean: schematics in schematic/, docs in docs/, no binaries larger than needed
3. Prefer netlists + human-readable docs over mystery EDA project dumps
4. Open a PR with a photo if you fab a board — we will feature community builds

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Star if you want more

  ┌─────────────────────────────────────────────────────────┐
  │  Open EEG should not be a $1k black box.                │
  │                                                         │
  │  Oyu is a stake in the ground.                          │
  │  Star → we ship Gerbers.                                │
  │  Fork → you own the next revision.                      │
  │  Build → show us your brain waves.                      │
  └─────────────────────────────────────────────────────────┘

Built with patience, flux, and too much coffee.

_{MIT · Open hardware · Oyu}