Notes from the bench
Write-ups on the parts of PCB design that decide whether a board works the first time — layout, power, manufacturing packages, and bring-up.
The Firmware Constraints Behind the Layout
Bulk caps sized for Wi-Fi current spikes, strapping pins left free, and a flashing path you can still reach: layout choices that only make sense if you have read the firmware.
Read the note- SignalsJul 30, 20264 min read
Opto-Isolation and the Gap You Must Not Cross
An optocoupler only isolates if the layout does too: no copper on any layer crossing the barrier, a slot to extend creepage, and an LED resistor sized for worst-case CTR.
Read - Bring-upJul 19, 20264 min read
REV_A Notes: Write Down What You’d Change
The friction you notice during assembly disappears from memory within a week. A REV_A notes file and a CHANGES log keep it, and handing both to a client builds trust rather than doubt.
Read - PowerJul 8, 20265 min read
Protecting the Input: Polyfuse, TVS, and Reverse Polarity
Polyfuse, TVS, and reverse-polarity protection each cover a different failure, and the order matters. How I size and sequence all three on a 24V input.
Read - LayoutJun 27, 20265 min read
Decoupling: Placement Beats Value
Loop inductance, not capacitance, decides what a decoupling cap can do. Why a well-placed 100nF beats a bigger one two millimeters away, and what DC bias really costs you.
Read - ManufacturingJun 15, 20265 min read
BOM Discipline: Part Numbers That Survive Assembly
Every BOM line needs a real MPN and a distributor code, checked for stock and lifecycle before you commit a footprint. The discipline that keeps an assembly job from stalling.
Read - SignalsJun 4, 20265 min read
3.3V Logic, 5V LEDs: Level Shifting Done Right
A 3.3V GPIO sits 200 mV below what a 5V WS2812B needs. Why that passes on the bench and fails in the field, and why a 74AHCT125 — not a FET shifter — is the fix.
Read - Bring-upMay 24, 20265 min read
Bring-Up Order: Smoke, Rails, Buses, Firmware
Unpowered checks, a current-limited first power-up, rails one at a time, then buses, then firmware. The bring-up order that finds a mistake before it costs you the board.
Read - PowerMay 13, 20265 min read
Buck Converter Layout: The Loop That Matters
The hot loop — input cap, high-side switch, return path — is the one thing in a buck layout that has to be physically tiny. How I lay out the 24V to 5V stage on a 2-layer field I/O design.
Read - ManufacturingMay 2, 20265 min read
Footprint Libraries That Don’t Rot
Ship a project a client can still edit in five years: project-local libraries, land patterns verified against the datasheet, and a checklist for third-party footprints.
Read - LayoutApr 21, 20265 min read
Trace Width Is a Thermal Problem
An 8x8 WS2812B matrix pulls close to 4A at full white. A worked IPC-2221 example: how wide that 5V trace must be, why 2 oz copper beats it, and where copper necks down.
Read - PowerApr 10, 20265 min read
USB-C Won’t Enumerate: The 5.1k Story
A Type-C source never turns on VBUS until it sees 5.1k on CC. Why the pull-down goes on both CC1 and CC2, and why one shared resistor fails only with good cables.
Read - ManufacturingMar 30, 20265 min read
Read the Fab Capability Sheet Before You Route
Minimum trace, drill, annular ring, mask dam, silkscreen height: pull them off your fab's sheet into your design rules before you route, not after the gerber review.
Read - SignalsMar 18, 20264 min read
One Pull-Up Pair Per I2C Bus
Four breakouts with 4.7k pull-ups give you a 1175 ohm bus. Here is the math, the 967 ohm floor at 3.3 V, the rise-time ceiling, and how to fix a bus that already has too many.
Read - LayoutMar 7, 20265 min read
Ground Planes: The Return Path Nobody Draws
Return current flows directly under the trace, not wherever it likes. What a slot in the pour really does, and how a 2-layer field I/O design keeps logic ground and field ground apart.
Read - PowerFeb 24, 20265 min read
AP2112K vs AMS1117: Stop Defaulting to the Wrong LDO
The AMS1117 needs 1.1 V of dropout and burns 5 mA doing nothing. The AP2112K-3.3 needs 250 mV and 55 µA. Worked numbers for USB and LiPo boards, plus when to use a buck instead.
Read - ManufacturingFeb 2, 20265 min read
What Actually Ships to the Fab
A fab never opens your board file. Here is every file that actually ships (Gerbers, Excellon, BOM, CPL, docs, DRC proof) and what each machine on the other end does with it.
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