ESP32 Heater Controller

Thought for 11 sec

I’ll re-check the layout after your R4/J7 move, distinguish PCB airwires from actual schematic one-sided wiring, then evaluate whether BOOT/RESET buttons can be removed in favor of ESP32-S3 native USB auto-download behavior.

Worked for 47 mins 2 sec

flux

Done.

Accomplished:

Verified RT6/C25, RT4/C23, C14, and related passives are schematic-connected on both sides; the issue was PCB routing/airwires, not one-sided schematic wiring.
Removed optional S1 BOOT and S2 RESET buttons to save BOM/assembly cost.
Kept the important ESP32 support: R4 GPIO0 pull-up, R3 EN pull-up, and C11 EN reset-delay cap.
Cleaned stale routing from your R4/J7 move and re-routed.
Final checked categories are clean: no airwires, dangling traces, copper overlaps, invalid layers, or relevant ERC errors.

Open items:

If we want best serviceability, add tiny labeled test pads for GPIO0/BOOT and EN/RESET later; they are cheaper than buttons and useful for recovery.

Suggested next steps:

Visually inspect the routed PCB.
Add/verify GND pours and antenna keepout.
Run full manufacturing DRC before export.
Update firmware/bring-up docs to note USB flashing without BOOT/RESET buttons.

Pours, keepout, docs

Add test pads

Verify GND pours

Check antenna keepout

Update docs

Manufacturing review

Files

Schematic

Layout

Preview

Safety Analysis — ESP32 Heater Controller

Status

Draft — schematic-stage.

Applicable Standards / Guidance to Discuss with Lab

UL / IEC 62368-1 for SELV-powered ICT/audio-video style equipment, if applicable
IEC/UL 60730 concepts for automatic controls, if temperature control is central to product safety
Product-specific heater/appliance standards if the final product is legally treated as a heating appliance
USB Type-C / USB-PD specifications if claiming compliance
RoHS / REACH / WEEE for environmental compliance

Hazard Summary

Table

Hazard	Source	Current Mitigation	Gap / Additional Mitigation
Overtemperature in passive enclosure	Four 1 W heaters plus electronics, no heatsinking	Firmware temperature monitoring, power budget, conservative MOSFET loading	Validate worst-case enclosure thermal rise; define accessible-surface limit
Heater stuck on	MOSFET drain-source short, firmware hang, GPIO fault	Gate pulldowns, firmware safe boot, NTC monitoring	Add/require independent cutoff: thermal fuse/PTC heater, hardware watchdog, load switch, or comparator cutoff
Wrong USB-PD voltage	STUSB4500 default/high PDO or NVM error	Design intent is 5 V-only	Program/verify 5 V-only NVM before PD use; consider hardware gating of VBUS path
USB source overload	Dumb 5 V source with insufficient current	MP5036 eFuse current limit around 2 A	Firmware power policy must derate heaters until source capability is known
Heater cable/connector short	Off-board wiring damage or installation fault	MP5036 board-level eFuse	Consider per-channel protection/current limiting; test connector fault cases
NTC failure	Open/short/drift or thermal lag from off-board heater	Six NTC dividers, firmware plausibility checks	PCB-mounted NTCs are not sole safety control for off-board heaters; test lag and fault cases
ESP32 crash/reset	Firmware defect, brownout, watchdog	Safe firmware default off	Add watchdog/latch-off policy and verify gates during reset/bootloader
RF/EMI malfunction	Heater PWM, buck converter, USB cable	Gate resistors, ESD protection	EMC test with heater leads and enclosure; add filtering if needed
User burn/contact risk	Warm enclosure or heater-adjacent areas	Target <38 C heater-control condition	Define whether <38 C refers to heater, PCB sensor, ambient, or user-accessible surface

Isolation / Creepage Analysis

The current design is SELV/5 V USB-powered and has no mains or high-voltage domain on the PCB. Final safety review should still document:

USB source must be certified/SELV.
No hazardous voltage is generated on-board.
Heater terminals are 5 V nominal but can deliver enough current to heat wiring or faults.
Creepage/clearance is not the main safety barrier; thermal and fault-current behavior are the key risks.

Safety-Critical Components

Table

Designator	Part	MPN	Safety Role	Notes
U4	eFuse/current limiter	MP5036AGJ-Z	Input current limiting/protection	R1 = 1.1 kΩ sets ~2 A class limit
D1	TVS	SMF5.0A	VBUS surge/transient clamp	Not protection against negotiated 15/20 V PD
U5	USB ESD	USBLC6-2SC6	USB D+/D- ESD protection	Verify final vendor/ratings
U2	USB-PD sink	STUSB4500QTR	Source negotiation	Must be programmed/verified 5 V-only
Q1-Q4	Low-side MOSFETs	SI2302	Heater switching	Verify final vendor RDS(on) at 3.3 V and thermal margin
RT1-RT6	NTC sensors	BOM currently shows ABNTC-0603-103J-3950F-T while symbol name references NCU18XH103F6SRB	Temperature sensing	Resolve final NTC curve/MPN before firmware calibration
J2-J5	Heater terminal blocks	691137710002	Off-board heater connection	Verify current/temp/flame ratings and wire range

Required Safety Documentation Checklist

Preliminary FMEA
Board bring-up plan with fault tests
Power/thermal budget
Final schematic and PCB layout review
Final BOM with RoHS, lifecycle, and ratings
Enclosure material flame rating
Worst-case thermal test report in enclosure
Abnormal/fault-condition test report
Production test limits for STUSB NVM, rails, NTCs, and heater outputs

Open Items

Decide whether to add independent hardware heater cutoff or require heaters with integrated thermal cutoff/PTC behavior.
Define the controlled temperature point and safety shutdown thresholds precisely.
Resolve STUSB4500 5 V-only gating/programming risk before PD-source testing.
Assign final MPNs to all generic passives and resolve NTC MPN mismatch.

Status
Applicable Standards / Guidance to Discuss with Lab
Hazard Summary
Isolation / Creepage Analysis
Safety-Critical Components
Required Safety Documentation Checklist
Open Items