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ProjectTwo weeks of eveningsAbout $625 (Ganglion) or $1,249 (Cyton), both often sold outTier 2

Project B: Reverse-engineer a bought board

If you buy an OpenBCI Ganglion or Cyton instead of building, read its schematic, trace the signal chain, read its firmware, and characterize it as if it were yours. Faster to decoding, nearly as educational, and no longer the cheaper path.

AssumesProject B: One channel of youSpineAnalog / mixed-signal hardwareDecoding / signal processing / ML
On this pageTwo weeks of evenings
  1. Which board
  2. Read the schematic like this
  3. Read the firmware like this
  4. Measure it like it is yours
  5. Modify one thing

There is no shame in buying the amplifier. publishes every schematic, every board layout, and every line of , so a bought board can be read like a textbook that happens to work. The deal you make with yourself is this: you will read the whole schematic and be able to explain every part on it, you will find the sample-conversion code in the , and you will measure the board’s and rejection on the head exactly as if you had designed it. Then you will get to Phase 3 a month sooner than the builders.

Which board

OpenBCI: from electrodes to the GUIOpenBCI2:43Open on YouTubeThe official three-minute path from a boxed board to a trace on the screen. Everything after that is you reading the schematic.

The Ganglion has four channels, uses a Microchip MCP3912 converter rather than the , and talks Bluetooth. Its four channels are enough for , , and a two-channel sleep band. The Cyton has eight channels around the , an optional eight-channel daisy board, and a radio link; it is the research-lite standard.

Neither is cheap any more. The Ganglion is 624.99andtheCytonis624.99 and the Cyton is 1,249, and both were sold out when this page was last checked, which is nearly three times and six times what building the eight-channel board costs. Buy one only if a lab, a grant, or a club is paying, or if a used one turns up on eBay, which happens often enough to be worth watching for. If what you want is a commercial board to read rather than a finished instrument, the BioAmp EXG Pill is $34.49 assembled, its schematic is published, and it is a real single-channel front end you can trace end to end; what it does not give you is the converter, the radio, or the , which is most of what the Cyton teaches.

Read the schematic like this

Print it. With a highlighter, trace one channel from the connector to the converter input, and mark every component you pass. For each one write, in the margin, what it is for. A series resistor: input protection and RF filtering. A capacitor to ground: the other half of that . A ferrite: keeping radio out of the analog section. When you reach a component you cannot explain, that is your reading for the evening.

Then do the same for the bias () path, the reference path, the power path from battery to analog rail, and the lines. Four highlighter colours. Photograph the annotated schematic into your notebook.

Read the firmware like this

Find three things. The register initialization: which registers are written at startup and to what values; compare each to the ’s register map. The data-ready handler: how the frame is read and how the 24-bit two’s-complement values are unpacked. The scaling: the line that turns counts into volts, and the constant in it. Compute the constant yourself from the reference voltage, , and bit depth, and check it matches.

If you find a discrepancy, you have found either a bug or a subtlety, and either one is worth a note in the forum.

Measure it like it is yours

The phantom head and the characterization report apply to a bought board unchanged. with inputs shorted. Common-mode rejection with a known hum injected. accuracy and bandwidth with a swept sine. Crosstalk between channels. Compare each to the manufacturer’s stated numbers. Boards usually meet them; the exercise is in knowing how to check.

Modify one thing

Once you can read it, change it. Ideas: replace the stock with ones you made in the electrodes project and compare impedance and noise. Write your own receiver in Python that speaks the board’s serial protocol and publishes to . Add a hardware trigger input for experiment timing. Design a 3D-printed headset that positions the at O1, O2, C3, and C4 repeatably.

Recall
What three things should you find in a board's firmware before trusting its data?
The register initialization values (compared to the datasheet map), the data-ready frame unpacking (24-bit two's complement), and the counts-to-volts scaling constant, which you recompute yourself.
Recall
What is the difference between owning a peripheral and owning an instrument?
An instrument is one whose signal chain you can explain component by component and whose performance you have measured (noise floor, CMRR, bandwidth). A peripheral is one that works and you cannot say why.