Build the instrument
Design, build, and characterize a research-grade EEG amplifier.
In Phase 1 you used an amplifier. Here you build the whole signal chain around the same chip that sits inside research systems, and then you measure what it actually does. The difference between "I made an EEG" and "I characterized an EEG" is the difference between a hobbyist and an engineer.
Phase 1 was about a memory. Phase 2 is about a number. By the end of it you will be able to say what your instrument’s noise floor is, how much hum it rejects, and where its bandwidth ends, and you will have measured those things rather than read them off a datasheet.
There are two routes to the same place. Building the ADS1299 board from a KiCad schematic through JLCPCB assembly to working firmware teaches the most and takes a semester of evenings. Buying an OpenBCI Ganglion and reverse-engineering it while you use it gets you to decoding a month sooner. Either way, the phantom head and the characterization report are not optional. They are the phase.
What attaches here
The theory in this phase is the theory of instruments: instrumentation amplifiers, the electrode-electrolyte interface, analog-to-digital conversion, noise, electrical safety, digital filtering, artifact removal, and spatial referencing. Every one of these explainers opens with something you will have just seen on your bench.
Projects
Choose one. Do a second if hooked.Project A: The ADS1299 board
Eight channels of 24-bit EEG around the chip inside most research and consumer systems. Schematic in KiCad, fabricated and assembled by JLCPCB, firmware on an ESP32, streaming into BrainFlow. A semester of evenings, and the whole signal chain becomes yours.
ProjectProject 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, and nearly as educational.
ProjectProject C: Make your own electrodes
Silver/silver-chloride by chloriding a silver wire, dry electrodes from conductive silicone or printed pins, and an active electrode with a buffer on it. Then measure the impedance of each versus frequency and find out why gel exists.
ProjectProject D: The phantom head
Saline gelatin with buried wire dipoles driven at known amplitudes. Now you can measure your amplifier's noise floor, crosstalk, and rejection instead of guessing. The difference between 'I made an EEG' and 'I characterized an EEG.'
ProjectProject E: The eight-channel EMG armband
Eight electrodes around the forearm, a classifier, and hand gestures recognized from muscle activity. The wristband idea, and the most dependable 'control something with your nervous system' demo there is.
ProjectProject F: The software pipeline
From a raw file to cleaned epochs to a topographic map, in MNE-Python, on public data. Build the pipeline before you have your own data so you can trust it when you do.
Explainers
Theory that attaches to what you just built. Read after doing.Instrumentation amplifiers, properly
What is inside the chip you have been trusting. Three op-amps, four matched resistors, and the numbers that decide whether the board records brain or room.
ExplainerThe electrode-electrolyte interface
What happens where metal meets salty skin. Half-cell potentials, why silver chloride is stable, why impedance depends on frequency, and why gel takes half an hour and dry electrodes are a compromise.
ExplainerAnalog to digital
Sampling, aliasing, quantization, and why the ADS1299 gets 24 bits out of a one-bit decision made very fast. The four ideas you need to read any converter's datasheet.
ExplainerNoise, and where the microvolt goes
Thermal, 1/f, amplifier, and electrode noise, added up for a real EEG channel. Why the electrode dominates, why the breadboard was so bad, and how to read a noise floor.
ExplainerElectrical safety, with the numbers
What IEC 60601 actually limits, why a battery satisfies it and a wall supply must be designed for it, how isolation works, and what the 390 kΩ resistor is doing.
ExplainerDigital filters, and what they do to time
FIR versus IIR, Butterworth and its cousins, phase distortion, zero-phase filtering, and the ordering mistakes that quietly wreck analyses.
ExplainerArtifact removal, three ways
Prevent, reject, or model. Regression against EOG, independent component analysis, and artifact subspace reconstruction, with the rule for when each is honest.
ExplainerSpatial filters and montages
There is no neutral spot on the head. Referential, bipolar, average reference, Laplacian, and why the same recording looks different under each.
Skills
Hand skills and software skills picked up along the way.KiCad to JLCPCB
Schematic, layout, and a fabricated, assembled board for the price of a textbook. The workflow, the layout rules that matter for microvolt signals, and the mistakes that cost a reorder.
SkillFirmware and SPI for a biopotential chip
Reading a register, reading a frame on data-ready, unpacking 24-bit two's complement, and shipping samples to a computer without losing any. The four things every acquisition firmware does.
SkillLab Streaming Layer and PsychoPy
How every BCI lab synchronizes a recording with the stimuli that caused it. Streams, timestamps, markers, and a stimulus program with millisecond timing, in an afternoon.
SkillThe characterization report
One page that says what your instrument does, with numbers, methods, and a plot per number. The document that turns a project into an instrument and a student into an engineer.
Ready for Phase 3 when
Checks save on this deviceWhat an interviewer would ask
If you can answer these, you are done here- Why does the ADS1299 use a delta-sigma converter, and what does 24 bits buy you when the signal is 50 microvolts in a 4.5 volt range?
- Two electrodes have impedances of 5 and 50 kilohms. Your amplifier's CMRR is 110 dB. What limits your hum rejection now?
- What is the leakage current limit for a patient-connected device, roughly, and how does a battery satisfy it?
- You filtered your epochs after cutting them. What went wrong?