Sensor plausibility needs physics
Range checks, rate limits, cross-sensor constraints, stuck values, impossible combinations, and fault detection that knows something about the machine.
ELECTRONICS + EMBEDDED SYSTEMS / ACTIVE DEPARTMENT
FOLLOW THE CURRENT. THEN FOLLOW THE STATE.
Power rails, return paths, electromagnetic coupling, analog measurement, clocks, buses, radios, reset behavior, firmware updates, nonvolatile state, thermal limits, and the hardware-software boundary where “random” failures usually turn out to be deterministic once the right signals are measured.
16 EMBEDDED FIELD GUIDES6 CONNECTED FAILURE DOMAINSOPEN SENSOR / ACTUATOR / PRODUCTION QUEUE
POWER + SIGNAL INTEGRITY
The schematic is only the opening statement.
Rail impedance, return geometry, edge rate, thermal behavior, source transitions, and external cables all become part of the machine once current starts moving through real copper.
001 / POWER INTEGRITY
Brownouts Cause Stranger Failures Than Blackouts
Undervoltage, supervisors, sequencing, interrupted writes, load transients, reset evidence, and partial-power recovery.
Read → 002 / RETURN CURRENTGround Is a Reference, Not a Magic Sink
Shared impedance, ground bounce, mixed-signal layout, decoupling, cable references, and measurement loops.
Read → 003 / EMCEMI Is a Coupling Problem
Conducted, capacitive, inductive, common-mode, and radiated paths plus practical source-path-victim diagnosis.
Read → 008 / THERMAL CONTROLThermal Limits Are Control Inputs
Junction temperature, derating, thermal inertia, sensor placement, throttling, cooling failures, and deliberate capability reduction.
Read → 011 / POWER PATHSBattery Power Paths Deserve Failure Diagrams
Source priority, ideal diodes, charging while operating, inrush, reverse current, USB transitions, and switchover brownouts.
Read →BUS + TIMING SYSTEMS
The wires carry assumptions as well as bits.
I²C, CAN, SPI, and the clocks underneath them fail differently. The common mistake is believing a completed controller transaction proves that the peer, physical layer, and application all agreed.
005 / I²C
I²C Is Simple Until the Wires Are Real
Pull-ups, capacitance, rise time, stuck buses, clock stretching, partial power, level shifting, and bounded recovery.
Read → 006 / CANCAN Is Robust, Not Immortal
Termination, topology, arbitration, error counters, bus-off, common-mode limits, transceiver state, and timing.
Read → 009 / SPISPI Failures Hide in Chip Select and Timing
CPOL/CPHA, chip-select setup/hold, MISO contention, DMA completion, edge rate, transaction framing, and response validation.
Read → 014 / CLOCK TREEClock Failures Masquerade as Protocol Failures
Oscillator startup, PLL lock, tolerance, temperature drift, clock switching, asynchronous boundaries, and inherited peripheral timing.
Read →FIRMWARE + PERSISTENT STATE
Recovery is something the system does, not something reset does for it.
Boot, update, storage, watchdogs, and diagnostics form one survivability problem. A device should fail during update or runtime, recover coherent state, and leave enough evidence to explain what happened.
004 / WATCHDOGS
A Watchdog Is Not a Recovery Plan
Progress monitoring, windowed watchdogs, reset scope, evidence preservation, idempotent startup, and repeated-reset escalation.
Read → 007 / BOOT + UPDATEBootloaders Are Part of the Failure Architecture
Signed images, A/B slots, interrupted updates, provisional boots, rollback, migration, downgrade policy, and recovery channels.
Read → 010 / NONVOLATILE STATEFlash Wear Is a State-Management Problem
Erase granularity, endurance, hot variables, wear leveling, journals, power-fail atomicity, and generation counters.
Read → 012 / DIAGNOSTICSBoot Telemetry Should Survive the Reboot
Reset cause, crash signatures, retained memory, boot attempts, progress markers, watchdog ownership, image state, and clock basis.
Read →MEASUREMENT + RADIO
The number is only as good as the chain that produced it.
Converters and radios are instruments. Resolution, received power, and register outputs only become useful after reference quality, noise, geometry, timing, interference, and application requirements are included.
013 / ANALOG MEASUREMENT
ADC Accuracy Is an Analog System Problem
Reference noise, source impedance, acquisition time, grounding, protection, ENOB, oversampling, calibration, and error budgets.
Read → 015 / RF SYSTEMSRadio Links Fail Before RSSI Reaches Zero
Link budgets, fading, interference, retries, antenna detuning, congestion, latency, energy cost, and deliberate degraded modes.
Read → ROBOTICS / SENSOR FUSIONSensor Fusion Does Not Create Truth
Timing, correlation, bias, covariance, observability, fault detection, and confidence.
Read →TEST + CROSSOVER
Make the machine prove the recovery path exists.
The lab should deliberately create the failure states the architecture claims to survive, then measure detection, containment, degraded capability, evidence, and recovery.
016 / FAULT INJECTION
Fault Injection Should Be a Normal Lab Tool
Power cuts, stuck buses, biased sensors, corrupt storage, cooling loss, network impairment, bad firmware, pass criteria, and reproducible fault campaigns.
Read → ROBOTICS / TIMINGControl Loops Hate Delay
Sampling, transport, estimator age, jitter, filtering, and actuator lag as control constraints.
Read → SOFTWARE / FIRMWAREFirmware Archaeology Starts Before Disassembly
Acquisition, immutable originals, hashing, containers, embedded filesystems, architecture clues, signatures, and safe lab handling.
Read → ENGINEERING / RESILIENCEGraceful Degradation Is an Architecture
Fault detection, isolation, reduced capability, common-mode failure, recovery, and operator visibility.
Read →OPEN QUEUE
Next failures worth turning into reusable knowledge.
Motor current is more than torque
Stall detection, winding resistance, commutation, current control, thermal state, friction, load estimation, and how current becomes both command and diagnostic signal.
Production test should preserve evidence
Serial numbers, firmware versions, calibration records, measured limits, fixtures, test software, failed units, and the difference between pass/fail and useful manufacturing data.
Connectors are electromechanical systems
Contact resistance, fretting, strain relief, ingress, vibration, insertion cycles, intermittent opens, and connectors as one of the least glamorous ways to lose an entire machine.
DEPARTMENT RULE
“Random” is a temporary diagnosis.
Intermittent embedded failures still have state, timing, energy, geometry, and causality. Instrument the rails, preserve reset reasons, timestamp the buses, follow return current, and make the failure leave enough evidence to stop being mysterious.