ENGINEERING NOTES
Notes from the bench.
Longer-form writing on the engineering problems that actually come up — obsolescence, firmware ports, board bring-up, and the rest.
- Membrane switch overlay design checklist What to settle before a membrane switch overlay goes to a fabricator: tail exit, venting, domes, material, shielding and enclosure fit, with reasons. Oct 20, 2026
- I2C bus stuck low after a reset Why an I2C sensor holds SDA low after the MCU resets, how the nine-clock bus clear works, and the board and firmware changes that prevent a hang. Oct 19, 2026
- Why a crystal oscillator won't start or runs off frequency How to pick load capacitors, check startup margin and layout for an MCU crystal, so the board boots every time and the clock stays on frequency. Oct 18, 2026
- Where to put ESD protection on a USB or connector port Where the TVS diode goes next to the connector, how to ground it with short stitched vias, and what to keep out of the path so a static zap at the connector… Oct 16, 2026
- Setting a lead-free reflow profile from the paste datasheet How to turn a solder paste datasheet into an oven profile, where to put thermocouples, and which defect points at which part of the curve. Oct 15, 2026
- First power-up of a new prototype board, step by step A bring-up order that finds shorts, bad rails and dead debug links before they cost you a board: what to check on a current-limited bench supply, in what… Oct 14, 2026
- Writing the software for a production test fixture What a functional test script should do on a small production run: program, verify, measure, log, and fail loudly. Existing open-source tools to build on. Oct 13, 2026
- What test points and programming pads a board needs Which signals to bring out for programming, debug and production test, so a board can be flashed and checked on a fixture without a respin. Oct 12, 2026
- Checking KiCad fabrication files before you send them A pre-release check for KiCad Gerbers, drill files, BOM and placement data, so the fab or assembler doesn't email back with questions or build the wrong board. Oct 11, 2026
- BLE module or chip-down for a new product How to decide between a certified Bluetooth LE module and a bare SoC: what each choice does to certification, antenna work, supply and schedule. Oct 10, 2026
- Finding why a device resets in the field How to read the reset-cause register, capture a fault record before reboot, and tell a power problem from a firmware bug on STM32, ESP32 and nRF52. Oct 6, 2026
- When SMT parts that sat open need baking before reflow How to tell whether an opened reel or tray of moisture-sensitive parts is still safe to reflow, why popcorning happens, and what a bake resets. Oct 4, 2026
- When a PCB needs conformal coating How to decide if a board needs coating, which chemistry to pick, and what coating does to test, rework and the layout you hand the assembler. Oct 3, 2026
- Moving a legacy Altium or Eagle design into KiCad What KiCad's importers convert, what they silently drop, the checks that prove the new files match the old board, and what to export before a license dies. Oct 2, 2026
- When a chip revision changes but the part number doesn't How to read a die-revision PCN, find the silicon revision in firmware and on the package, and decide what to requalify before new parts ship. Oct 1, 2026
- Provisioning serial numbers on the line Where per-unit serials, keys and debug locks go on STM32, nRF52 and ESP32, what is irreversible, and how to plan the programming step. Sep 30, 2026
- Checking a chip's longevity before designing How to read ST, NXP, TI, Microchip and Nordic longevity programs, what each one actually promises, and the checks to run before a part goes on the schematic. Sep 29, 2026
- Adding a lithium cell to a product The charger, protection and gauge a lithium-powered product needs on the board, what to ask the cell supplier for, and what to test before it ships. Sep 28, 2026
- PCB layout mistakes that show up at assembly Fiducials, courtyards, polarity marks, panels and placement files: the layout details an SMT line trips on, and how to check each one before you send the job. Sep 27, 2026
- Bare-metal or RTOS on a small MCU How to decide when a superloop is enough, what an RTOS actually costs in RAM and debugging effort, and the checks to run before you commit to one. Sep 23, 2026
- Firmware updates with recovery and rollback Plan firmware updates around recovery: image validation, rollback, application confirmation, compatible data, and failure tests on shipped hardware. Sep 23, 2026
- Second-sourcing the SPI flash on a board A practical review of SPI NOR flash substitutions: check the package, boot path, driver behavior, programming tools, and qualification evidence. Sep 23, 2026
- What to send for a PCB assembly quote Prepare a clear PCB assembly quote package: fabrication data, a parts list, placement files, drawings, quantities, and revision checks before upload. Sep 23, 2026
- Browser-based firmware flashing, no installer Check whether Web Serial or WebUSB can replace your firmware installer, which browsers support the workflow, and what drivers and recovery paths remain. Sep 22, 2026
- Substituting a ceramic cap on long lead time The checks that decide whether a backordered ceramic capacitor can be swapped: DC bias, dielectric, voltage rating, ESR, height and board flex. Sep 21, 2026
- Why sleep current beats the datasheet The usual causes of sleep current far above the datasheet figure: debug probes, pins, pull-ups, regulators, sensors, and a bench method to find them. Sep 20, 2026
- BLE provisioning for a device with no screen How to get Wi-Fi credentials onto a screenless BLE device: what pairing really protects, per-device secrets, phone quirks, and failure paths to design. Sep 19, 2026
- Reverse engineering a board with no schematic What it actually takes to turn a bare circuit board into a working schematic and BOM, and when the process is worth starting. Sep 18, 2026
- When a KiCad autorouter is worth using What FreeRouting and newer GPU autorouters actually handle well in KiCad, where manual routing still wins, and the checks to run before trusting either. Sep 17, 2026
- Designing a pogo-pin test fixture that lasts Pin choice, tip style, pitch, and alignment decisions that determine whether a bed-of-nails fixture gives repeatable results or wears out fast. Sep 16, 2026
- USB-C Power Delivery for a non-phone product How to add USB-C PD input to a product that needs more than 5 volts: controller choices, negotiation gotchas, and where a bare bit-banged sink breaks. Sep 15, 2026
- Cyber Resilience Act firmware architecture The EU's first CRA deadline landed this month. What it actually requires from firmware, and why retrofitting it later costs more than designing for it now. Sep 14, 2026
- When your microcontroller goes end-of-life What an MCU EOL or NRND notice actually means, the four ways to respond, and how to qualify a replacement without a firmware rewrite going sideways. Sep 11, 2026
ENGINEERING NOTES
One note a week on PCB design, firmware and getting hardware built. No sales email.
Double opt-in. Unsubscribe in one click.