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Debouncing with Time and State
2026-02-22
Button debouncing is one of the smallest problems in embedded systems and one of the most frequently mishandled. That combination makes it a perfect teaching case. Engineers know contacts bounce, yet many designs still rely on ad-hoc delays or lucky timing. These solutions pass demos and fail in real operation. A robust approach treats debouncing as a tiny state machine with explicit time policy.
Mechanical bounce is not mysterious. On transition, contacts physically oscillate before settling. During that interval, GPIO sampling can see multiple edges. If firmware interprets every edge as intent, one press becomes many events. The correct objective is not “filter noise” in the abstract; it is to infer a human action from unstable electrical evidence with defined latency and false-trigger bounds. ... continue
Ground Is a Design Interface
2026-02-22
Many circuit failures are not caused by “bad signals.” They are caused by bad assumptions about ground. Designers often treat ground as a neutral reference that exists automatically once a symbol is placed. In reality, ground is a physical network with resistance, inductance, and shared current paths. If we ignore that, measurements lie, interfaces become unstable, and debugging turns into superstition.
The mental shift is simple but profound: ground is not the absence of design. Ground is part of the design interface. Every subsystem communicates through it, injects noise into it, and depends on its stability. Once you frame ground this way, layout and topology decisions stop feeling cosmetic and start feeling architectural. ... continue
Debugging Noisy Power Rails
2026-02-22
Noisy power rails cause some of the most frustrating hardware bugs because the symptoms look random while the root cause is often deterministic. A board that “usually works” at room temperature can fail after five minutes under load, pass again after reboot, and mislead you into chasing firmware ghosts for days.
A useful mindset shift is this: unstable power is not a side issue. It is a primary signal path. If voltage integrity is poor, every digital subsystem becomes statistically unreliable, and software symptoms are just the final expression. ... continue
Why Constraints Matter
2026-02-10
Give a programmer unlimited resources and they’ll build a mess. Give them 640 KB and they’ll build something elegant.
Constraints force creativity. The demoscene proved that artistic expression thrives under extreme limitations. The same principle applies to web design: this site uses no JavaScript, and the CSS-only approach has led to solutions I would never have considered otherwise. ... continue
Restoring an AT 286
2026-02-01
I found a Commodore PC 30-III (286 @ 12 MHz) at a flea market. The power supply was dead, the CMOS battery had leaked, and the hard drive made sounds like a coffee grinder.
After recapping the PSU, neutralizing the battery acid with vinegar, and replacing the MFM drive with a XTIDE + CF card adapter, the machine booted into DOS 3.31. The CGA output on a period-correct monitor is a shade of green that no modern display can reproduce. ... continue