PCB Schematic Draft

Corrections from my microscope inventory sheet: (1) U1 is a 6-pin small IC (marking "T18 AU8 2DZ"), not 10-lead — please make the U1 placeholder 6 pins. (2) R6's marking is ambiguous between 103 (10k) and 105 (1M) — keep it annotated as "verify by measurement". (3) There may be an R5 on the silkscreen — add a note, not a part. (4) D1-D3 might be LEDs rather than rectifier diodes — annotate as "confirm diode vs LED". (5) C1-C3 values are unmeasured — annotate. Keep all these as visible open questions on the schematic notes rather than guessing values.

Thought for 10 sec

flux

I’ll apply those corrections: swap U1 to a 6-pin placeholder, adjust the uncertain annotations, and update the schematic notes/open questions without adding R5 as a component.

Worked for 1 min 45 sec

flux

U1 is now a 6-pin placeholder with no assumed pinout. I’m updating the part notes so the uncertainties stay visible instead of encoded as guessed values.

Worked for 4 mins 50 sec

flux

Applied the microscope-inventory corrections: U1 is now a 6-pin placeholder, R6/C1-C3/D1-D3 are annotated as uncertain, and possible R5 is documented as a note only.

Open items:

U1 pins are intentionally floating until trace mapping confirms pinout.
R6, R7, C1-C3, D1-D3 type/polarity, and possible R5 still need measurement/confirmation.
ERC still reports expected unresolved placeholder pins and missing MPNs for generic draft parts.

Updated files: Schematic Capture Notes and Project Specification.

Suggested next steps:

Measure R6/R7 and C1-C3.
Confirm D1-D3 with diode/LED test mode.
Provide U1/U2 continuity maps so I can wire the placeholders correctly.

Clean notes and review

Arrange schematic groups

Create measurement checklist

Add photo map plan

Check BOM placeholders

Files

Schematic

Layout

Preview

Preliminary Safety FMEA — NSS-Bridge-3

Scope

This is a design-stage risk file for a reverse-engineered wearable electrical stimulation PCB. The schematic is incomplete and contains placeholder ICs for U1 and U2. This document must be updated after physical trace mapping and bench measurements.

Prominent Safety Warning

This PCB is an electrical stimulation device intended to drive electrodes on or near the body. Because the output stage, waveform limits, firmware/control behavior, and unknown IC pinouts have not been fully verified, the device must not be used on humans or animals. All testing should use isolated bench equipment and dummy loads until safety limits and single-fault behavior are characterized.

Failure Mode Table

Table

Subsystem	Failure mode	Effect	Severity 1-10	Likelihood 1-10	Detection 1-10	RPN	Mitigation / next action
Output stage	Excessive stimulation current	Pain, burn, nerve/tissue injury	9	4	7	252	Measure current into low/nominal/high dummy loads; define hardware current limiting.
Output waveform	Net DC through electrodes	Skin irritation, electrochemical injury	8	4	7	224	Measure DC offset and charge balance; require blocking/charge balancing if absent.
Boost rail	VSTIM overvoltage	Excessive electrode voltage or component stress	8	4	6	192	Identify U2, confirm feedback divider, measure open-load VSTIM.
Unknown U1/U2	Misidentified pinout/topology	Incorrect schematic, unsafe assumptions	8	6	6	288	Use continuity mapping, IC identification research, and bench probing before layout/manufacture.
Battery	Coin-cell short or reverse insertion	Heating, leakage, failure	6	3	5	90	Add/verify protection and polarity features; inspect original mechanical design.
Brownout	Control IC malfunction at low battery	Unexpected stimulation or stuck output	8	4	7	224	Test depleted battery behavior; verify reset/disable paths.
Electrodes	Open/intermittent contact	High-voltage transients or unexpected pulses	7	5	6	210	Test open-load and intermittent-load conditions; add output clamps if needed.
Lab test setup	Mains-referenced instrument connected while worn	Shock hazard / isolation defeat	10	3	5	150	Never test on body while connected to bench instruments; use isolated/differential measurement.
Materials/contact	Skin-contact material not biocompatible	Irritation/allergy	6	4	6	144	Track electrode plating/material; evaluate ISO 10993 if productized.

Electrical Output Safety Limits to Measure

Maximum output voltage on VSTIM and each electrode pad.
Maximum current into representative electrode loads.
Pulse width, repetition frequency, duty cycle, and waveform shape.
Charge per phase and charge imbalance.
DC leakage/current through electrodes.
Behavior with open electrodes, shorted electrodes, wet/sweaty skin-equivalent loads, and depleted battery.

Test Precautions

Do not test on humans or animals during reverse engineering.
Use dummy loads first, not skin.
Include low, nominal, and high impedance load cases.
Use battery-powered or isolated differential measurement where appropriate.
Avoid mains-referenced instruments connected to the device during any body-contact scenario.
Test power-up, power-down, reset, brownout, battery insertion, and fault states.

Top Risk Priority Actions

Identify U1 and U2, or map every pin electrically.
Confirm the output topology and diode/resistor polarity.
Measure all stimulation parameters on dummy loads.
Define hard safety limits for current, charge, DC offset, and fault behavior.
Only then proceed toward layout/manufacture for anything beyond reverse-engineering documentation.

Scope
Prominent Safety Warning
Failure Mode Table
Electrical Output Safety Limits to Measure
Test Precautions
Top Risk Priority Actions