The notebook, and the build log
How to write things down so that a plot from March still means something in November, and how a notebook entry becomes a build log on this site.
You are skimming: the title, the first figure, and the short version. Switch to Read in the header for the full page, or Deep to open every deep dive.
The notebook is the one habit on this site that I would keep if I had to drop everything else. Not because anyone will grade it. Because in six weeks you will not remember which gain resistor you used, and in six months you will not remember why the noise floor dropped between Tuesday and Thursday, and the plot you saved will have no axes on it.
What goes in
Every session, before you touch anything: the date, what you intend to do, and what you expect to see. That last line is the important one. Writing down the prediction is what turns fiddling into an experiment.
During the session: what you actually did, with part numbers and values. “Gain resistor 500 Ω, so gain ≈ 100.” “Electrodes at O1 and left earlobe, Ten20, DRL on forehead.” The exact command you ran. A sketch of the wiring, photographed and taped in if it was on paper.
After: what you saw, with numbers and units. “60 Hz peak about 2 V pp at the output before the DRL, about 200 mV after.” What went wrong. What you will do next time. A plot, with labelled axes and a title, saved to a folder named by date.
Paper or digital
Either, as long as it is one place. Paper is faster at the bench and impossible to lose to a corrupted drive. A plain-text file or a notes app is searchable. I use paper at the bench and copy the essential lines into a text file at the end of the day. Photograph the paper pages; a phone photo of a page of wiring notes has saved me more than once.
Whatever you choose, never use a tool that requires a subscription to read your own notes later.
From notebook to build log
A build log is a notebook entry cleaned up for another person. It has a fixed shape on this site, and the shape is the point: what I set out to do, what I actually did, what went wrong, what I measured, what I would change, what surprised me. There is a template and an example.
The build logs are the portfolio. A resume says “built an EEG amplifier.” A build log shows the plot, the noise number, the mistake, and the judgment that came out of it. Recruiters and professors read the second kind of thing, and almost no student produces it.
Two rules for plots
Every plot has axes with units and a title that says what it is and when it was taken. Every plot that matters gets the raw data saved next to it, as CSV, so it can be re-plotted. “Look at this trace I saved as a screenshot” is a sentence that ends careers in labs.
A minimum viable entry
If you are tired and want to skip it, write four lines:
2026-09-14 single-channel EEG, breadboard v2
did: moved DRL from forehead to right earlobe
saw: blink artifact dropped from ~200 µV to ~120 µV; alpha unchanged
next: solder itThat is enough. Four lines a session for four years is a record almost nobody has.