NOTAS DE INGENIERÍA
Notas desde el banco de trabajo.
Textos más largos sobre los problemas de ingeniería que realmente aparecen — obsolescencia, portabilidad de firmware, bring-up de placas, y más.
Por ahora, estos artículos se publican solo en inglés.
- Linux board or microcontroller for a new product How to decide between a Linux compute module and a microcontroller: the tests on power, storage, updates and supply that settle it before layout starts. Nov 8, 2026
- Why an ESP32-P4 MIPI DSI display stays black A bring-up order for an ESP32-P4 MIPI DSI panel: DPHY power, timing, init sequence, touch, and the v3.2 silicon change that affects old boards. Nov 7, 2026
- How many parts to buy on a last-time buy A way to size a last-time buy from build plan, scrap, spares and shelf life, plus the deadline traps in a discontinuance notice that change the number. Nov 6, 2026
- How to pick an I2C pull-up resistor value Work out the smallest and largest I2C pull-up from supply, sink current, rise time and bus capacitance, then pick a value and check it on a scope. Nov 5, 2026
- Why a GT911 touch controller doesn't respond over I2C Fix a GT911 touch panel that never answers: the INT address strap, reset sequence, status-register clearing and the schematic checks that prevent it. Nov 4, 2026
- Why KiCad DRC says USB-C pads A4 and B9 are shorted Why a stock USB-C footprint trips DRC on stacked VBUS and GND pads, and the four ways to fix the symbol and footprint pair so ERC and DRC both pass. Nov 4, 2026
- Why an ESP32-S3 RGB display shifts or flickers with LVGL What starves an ESP32-S3 RGB panel of PSRAM bandwidth, how bounce buffers and LVGL render modes differ, and the checks that separate flicker from tearing. Nov 2, 2026
- Why an NTC thermistor reads wrong on a microcontroller Why a thermistor on an ADC pin drifts, jumps or reads high: divider placement, the curve math, self-heating and leads. Checks to run before you blame the chip. Nov 1, 2026
- Logging to an SD card without corrupting it on power loss How to log to an SD card without corrupting it when power drops: when to sync FAT, where littlefs fits, and the hold-up hardware that matters. Oct 31, 2026
- Will a PCB antenna still work inside a metal enclosure? Why a metal case detunes a PCB antenna, the three ways out (window, external antenna, or plastic section), and what to test before you cut tooling. Oct 30, 2026
- Ordering PCBs before a tariff exclusion expires What the Section 301 exclusion deadline means for small bare-board orders, what to confirm with your broker, and what not to rush in the design. Oct 29, 2026
- Why a microcontroller ADC reading is noisy or wrong Find out whether a noisy or offset ADC reading comes from source impedance, sample time, reference, layout or firmware, with a check order for each. Oct 28, 2026
- Preparing for the CRA 24-hour vulnerability reporting duty What triggers a CRA report, the 24-hour, 72-hour and final deadlines, and the firmware and process pieces a small hardware maker needs in place first. Oct 27, 2026
- Choosing a display interface for a touchscreen product SPI, 8080 parallel or RGB for a product display: what each costs in pins, RAM and memory bandwidth, and how to pick before the layout is frozen. Oct 26, 2026
- Why an IMU reads wrong once it's in the enclosure Mounting stress, aliasing, clipping and offset calibration: the four reasons an IMU that worked on the bench misbehaves in a product, and the checks. Oct 25, 2026
- Why a humidity sensor reads wrong inside an enclosure Why humidity and temperature sensors read off once the case is closed, and the placement, venting, duty-cycle and test checks that fix it before tooling. Oct 24, 2026
- Why a load cell reading drifts with an HX711 Why load cell readings creep or jump with an HX711, and the wiring, reference, filtering and calibration checks that separate real drift from noise. Oct 24, 2026
- Why a PT100 or PT1000 reading is wrong by a degree or two How lead wires, a drifting excitation current and the reference resistor throw off an RTD reading, and the front-end checks that fix each one. Oct 24, 2026
- Why a thermocouple reading is off by a few degrees Where cold-junction error comes from on a thermocouple input, how to place the sensor and connector, and what to check before you trust the reading. Oct 24, 2026
- Why an e-paper display ghosts after partial refresh Why e-paper ghosts after repeated partial refreshes, what the vendor docs say to do about it, and the firmware rules that keep the panel readable and healthy. Oct 24, 2026
- Why a current monitor reads wrong at 1 mA Why an INA226-class shunt monitor misreads small currents, how to size the shunt, and when to switch ranges or measure sleep current another way. Oct 23, 2026
- Swapping an out-of-stock part without missing a pin A checklist for replacing a sold-out IC on a finished board: pinout, quiescent current, output capacitors, land pattern and what to test before you rebuild. Oct 16, 2026
- Why a boost converter fails when the Wi-Fi radio starts Why a battery ESP32 design browns out or kills its boost converter at Wi-Fi transmit, and the inductor, capacitor and layout checks that find it. Oct 16, 2026
- Reverse polarity protection for a DC power input Series diode, P-channel MOSFET or ideal-diode controller: what each costs the board, and the datasheet checks that stop a wrong plug from killing it. Oct 15, 2026
- Debugger can't connect to a new board over SWD A short checklist for 'no target found' on a custom ARM board: power, wiring, reset, sleeping firmware and locked chips, plus what to put on the PCB. Oct 14, 2026
- 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 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
- 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 11, 2026
- Why a USB-C board works on USB-A but not C-to-C Why a board powers from a USB-A to C cable but dies on C-to-C, plus the CC resistor, receptacle and bench checks that find the cause before respinning. 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
- 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 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
- 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 6, 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 4, 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
- 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 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
- 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. 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
NOTAS DE INGENIERÍA
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