I couldn’t produce a faithful schematic PDF: the available PDF export covers PCB layers only, and the schematic-rendering fallback loses symbol detail. No PDF was created, and your design is unchanged.
I’ll make a cosmetic-only readability pass using the ten requested blocks, left-to-right signal flow and inter-block net labels. I’ll compare the complete netlist, parts and values before and after, and won’t touch PCB layout.
Thought for 1 min 53 sec
10 hrs ago
Thought for 7 sec
1/3 Capture baseline component/value inventory and complete netlist invariants
Capture baseline component/value inventory and complete netlist invariants
Arrange ten schematic blocks and clean cosmetic wiring/labels without electrical changes
Compare before/after netlist and visually check readability; stop without PCB layout
Thought for 42 sec
Awaiting 1 task
"Schematic Readability Pass" completed.
Thought for 59 sec
flux
10 hrs ago
The readability pass is blocked: my available controls do not support schematic canvas placement, frames, or graphical wire/net-label editing, so I made no changes.
Before: 328 components / 188 nets.
After inspection: 328 components / 188 nets.
Parts, values and connectivity remain untouched; no PCB layout started.
I cannot claim the rearrangement or a full before/after netlist comparison was completed. This limitation needs Contact Support.
Accepted decisions and partial hardware — 2026-10-12
Overrides proposal/unresolved statements below: user ACCEPTED10MΩ||1nF, connector-entry ESD, noEthernetshield earthbypass, and±30VDC/±8kVcontact/±15kVair as validationtargetsNOTratings. ProgrammingALWAYSsensorDISCONNECTED; USBremovedBEFOREsensorreconnection, shakeroffaloneinsufficient. NoUSBisolatorrequiredforagreedworkflow; neverliftUSBgroundwhileretainingD+/D−. Earlier nextquestion is resolved; do notaskagain.
Implemented R49VR68000001005JAC00=10MΩ||C68DE1E3RA102MJ4BH01F=1nF betweendistinctCHASSIS/GND; TP23CHASSIS,TP22return. Mechanicalcase/endpanelbond andmounting/connectorinsulation notlayoutcertified. X3boardharnesssensorreturnGND; noBNCpanelpartplaced. EntryTVS/protectedAFEboundary remainsBLOCKEDbydatasheetextraction, notimplemented; optionalchassisclampunattempted. Floatingrearshutdownpairunchanged/separate, freshnetreadbacknoGND/CHASSISbridge. RCnotperfectDCisolation,cannotguaranteenoearthloop,notESDqualification. See iepe-input-design-notes forpartlimits/evidence/benchchecklist. Noassembledvoltage/ESDratingclaim.
Status and scope
2026-10-12: architecture proposal and confirmed requirements, not an implemented or qualified circuit. No schematic, PCB or enclosure changes are made by this document. The present schematic remains a draft; previous power and shutdown validation gates still apply.
Confirmed user requirements
Support IEPE accelerometers with signal return connected through the sensor housing to a grounded shaker, as well as isolated-housing sensors compatible with the electrical input envelope.
Fixed 4 mA excitation in revision 1, no software current adjustment. Provide an accessible current-setting resistor and rework space so a later resistor swap can change current; any increase requires power, cable-drive, thermal and sensor-rating revalidation.
Maximum sensor cable length 30 m. Broad IEPE coax compatibility, limited by a tested total cable-capacitance envelope rather than a claim that every cable or sensor works. Numerical capacitance limit remains to be established against 2 kHz, voltage swing and sensor current consumption.
During measurement, sensor return must be the only intended low-impedance galvanic connection from local electronics to external ground. Use an isolated-output DC adapter without a DC earth bond, transformer-isolated Ethernet, and the existing isolated shutdown output.
Metal enclosure must not be intentionally bonded directly to building earth or local signal ground. USB is only for programming with shaker off; whether the sensor can be unplugged during programming is the next user decision.
Proposed ground domains and mechanical treatment
LOCAL_GND is the electronics reference and joins sensor BNC return at the defined input return point. Do not insert a large resistor into this signal-return conductor. Insulate the sensor BNC shell from the panel so the case is not a second direct return path.
CHASSIS is the electrically continuous metal enclosure/end-panel structure, separate from LOCAL_GND, with insulated PCB supports and no unintended connector-nut or mounting-screw ground bonds. Avoid grounded rack mounting or incidental contact with grounded metal where practicable.
Prototype proposal: one intentional chassis-to-local network, approximately 10 MΩ in parallel with 1 nF, placed at the connector/protection boundary, not beside precision ADC/reference circuitry. Use appropriately pulse-/voltage-rated resistor construction and a safety-/pulse-rated capacitor; exact parts, mechanical connection and parasitic paths require selection and EMC testing before population. This is a starting engineering value, not a verified EMC solution.
The resistor bleeds accumulated case charge toward sensor return when connected; the capacitor couples fast common-mode transients. With ideal 10 MΩ and 1 nF, the isolated RC time constant is 10 ms. At 30 V DC across it, resistor current is 3 µA. If a 30 V rms 60 Hz difference is imposed, the capacitor branch carries approximately 11.3 µA rms. These are calculations for the proposed network, not total system leakage; adapter and other parasitic capacitances add to the result.
This network limits low-frequency loop current; it does not create perfect galvanic isolation between case and local ground, and capacitance deliberately conducts high-frequency current. It cannot guarantee that no loop exists if the enclosure touches earth. No safety-earth fault current may be routed through it.
FLOAT_VIBRUNNER_TERMINAL8 and FLOAT_VIBRUNNER_DIGITAL_GROUND remain an entirely separate contact domain. Do not connect the output BNC shell, its TVS, connector shields or protection to CHASSIS or LOCAL_GND. The proposed chassis RC is NOT across the PhotoMOS isolation barrier.
External interfaces and hidden ground paths
Table
Interface
Proposed requirement
Qualification needed
DC adapter
Isolated-output, no deliberate secondary earth bond; preferably suitable Class II adapter meeting the existing 12 V / ≥1.5 A procurement requirement
Verify exact adapter insulation, output-earth resistance and leakage/coupling capacitance; 'two-wire DC output' alone is not proof
DC connector
Return and metal hardware insulated from CHASSIS unless explicitly assigned to that domain without a local-ground bond
Exact locking inlet/mate and panel stack still unresolved
Ethernet
Compatible transformer-isolated MagJack; default operating cable is unshielded twisted pair, and no conductive cable-shield-to-box/local-ground path
Check actual jack magnetics, cable-side termination/Bob Smith capacitor and all shield tabs. Magnetics do not isolate an RJ45 shield. A shielded plug must not accidentally earth the floating case through a conductive jack shell; insulate that shell from case/local ground or use a nonconductive/unshielded connector construction
Shutdown output
Existing isolated contact; output shell insulated from case and every local circuit
Assembly isolation and local-to-controller working-voltage limits remain unqualified
USB/debug/instruments
Ordinary USB ground and ground-referenced debug/scope equipment add an external ground path even when USB VBUS is not used
Disconnect sensor before nonisolated USB programming, or add verified USB signal-and-ground isolation if sensor must stay attached. Do not remove USB ground while retaining direct D+/D− wiring
Ground-difference voltage: proposed target, not a present rating
Present verified ground-difference tolerance: not established. No continuous voltage rating can be claimed for the assembled product from its relay hipot rating, unselected Ethernet magnetics, unselected adapter or an RC value.
The input is not a separately isolated or differential ground-offset receiver: sensor return is directly LOCAL_GND. Therefore it does not accept, for example, ±30 V between the sensor return and the box's local electronics ground; those points are intentionally joined. Cable return resistance/inductance can still produce error, which this connection does not reject perfectly.
With other interfaces genuinely isolated and USB absent, the entire local circuit follows the sensor return. The meaningful offset specification is then sensor-return/local-domain voltage relative to remote ground across each external isolation boundary, with a separate specification for local-to-enclosure insulation. As a provisional nonhazardous laboratory design target, propose testing −30 to +30 V DC relative to an independent remote-ground reference, across the completed adapter/Ethernet/output/mechanical arrangement. This is NOT demonstrated compatibility, an AC rating, safety isolation or tolerance of faulty protective earthing. It must be reviewed against exact component working-voltage ratings, creepage/clearance and touch/leakage requirements before adoption as a guaranteed rating. AC/EFT/surge/ESD requirements are separate, not extrapolated from 30 V DC.
A direct USB cable while sensor-connected invalidates the floating-offset condition. Shaker off does not necessarily open its earth connection or the sensor's housing-return bond.
Static-discharge proposal for a floating case
Bond enclosure panels together into CHASSIS so a strike initially spreads on the metalwork instead of traversing precision circuitry. Keep both BNC shells electrically insulated as specified.
At the sensor connector, use a short, low-inductance differential protection path from sensor center to its local return, with correctly selected voltage/leakage/capacitance and downstream series/staged clamps. Protection must pass normal IEPE bias, open-circuit excitation and vibration swing; a generic USB-level clamp is unsuitable for this input.
Provide footprints/space for a normally-off pulse-rated chassis-to-local transient clamp near the entry RC if testing shows the RC alone allows excessive internal differential stress. Its stand-off must exceed the chosen continuous chassis offset and its clamp must be coordinated with actual insulation and circuitry. It must not bridge the isolated output contact domain or conduct during ordinary operation. Exact device and population are deferred pending the input/protection design and EMC review.
Place connector protection at the physical entry, with direct return to the appropriate local boundary ground region and tightly coupled/stiched planes; do not steer discharge through the reference/DAC/ADC routing.
ESD does not need a permanent earth wire to affect a floating box. Return current closes through sensor wiring when attached and through distributed capacitance/other isolation-barrier capacitance to the environment; when disconnected the case can retain charge. The bleed only discharges it if the local domain has a return path. 'Floating' does not mean immune, and the capacitor is not an infinite-energy discharge sink.
Prototype EMC target proposed: IEC 61000-4-2 ±8 kV contact / ±15 kV air, not a current claim of compliance. Test case/panels, exposed sensor return and pins as applicable, output-domain BNC, DC/RJ45/USB and indirect discharges with representative 30 m cable configurations, sensor connected/disconnected, grounded/isolated sensor housings and actual floating adapter.
Protection acceptance: no damage, no unintended permission closure; a disturbance that corrupts measurements, resets execution or loses software health must open/latch shutdown according to the final protection contract. Verify contact timing and recovery/rearm behavior. Treat false trips separately from loss of protection; do not claim uninterrupted precision during ESD without testing.
Evidence for the architecture
TI ESD Protection Layout Guide, SLVA680A: connector-first protection, low-inductance return and tightly coupled planes when earth-referenced chassis grounding cannot be used.
TI isolation and ESD/EFT/surge immunity, SLYT725: floating-ground transient loops close through total isolation capacitance; barrier stress and capacitor trade-offs require system-level evaluation.
TI industrial Ethernet EMC guidance, SNLA466A: exposed connector shields and metal-case/return-path treatment matter when direct earth is unavailable. This design's no-second-ground requirement takes precedence over generic shield-to-earth examples.
Ask one question at a time: Can the sensor cable be disconnected before connecting USB for programming? If not, USB isolation becomes a required architecture change and must be selected for the Teensy's programming speed and attach behavior. Do not silently assume that switching off the shaker makes USB safe or loop-free.
No numerical total cable-capacitance limit, complete ground-offset rating, ESD compliance, input-clamp values or chassis-network part selection is certified by this planning document. No schematic/layout mutations were performed.
Entry implementation resumed — 2026-10-12
Accepted decisions and partial hardware — 2026-10-12
Status and scope
Confirmed user requirements
Proposed ground domains and mechanical treatment
External interfaces and hidden ground paths
Ground-difference voltage: proposed target, not a present rating