ESP32 Heater Controller

R

roboticsnerd

Okay. I had to move R4 and J7. Sorry if that messes anything up.
Also. There are still issues. RT6 is only connected on one side. C23. RT4 C25. C14. Countless others are only wired up on one size.
Also, ESP32 devkits have a capacitor? Or resistor? That is wired in so you can flash firmware without the S1 and S2 buttons. And I'm not sure if the buttons are necessary, so I'm happy to save money if we can safely nix them.

flux

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.

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:
  1. Visually inspect the routed PCB.
  2. Add/verify GND pours and antenna keepout.
  3. Run full manufacturing DRC before export.
  4. 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
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Schematic

Layout

3D View

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

HazardSourceCurrent MitigationGap / Additional Mitigation
Overtemperature in passive enclosureFour 1 W heaters plus electronics, no heatsinkingFirmware temperature monitoring, power budget, conservative MOSFET loadingValidate worst-case enclosure thermal rise; define accessible-surface limit
Heater stuck onMOSFET drain-source short, firmware hang, GPIO faultGate pulldowns, firmware safe boot, NTC monitoringAdd/require independent cutoff: thermal fuse/PTC heater, hardware watchdog, load switch, or comparator cutoff
Wrong USB-PD voltageSTUSB4500 default/high PDO or NVM errorDesign intent is 5 V-onlyProgram/verify 5 V-only NVM before PD use; consider hardware gating of VBUS path
USB source overloadDumb 5 V source with insufficient currentMP5036 eFuse current limit around 2 AFirmware power policy must derate heaters until source capability is known
Heater cable/connector shortOff-board wiring damage or installation faultMP5036 board-level eFuseConsider per-channel protection/current limiting; test connector fault cases
NTC failureOpen/short/drift or thermal lag from off-board heaterSix NTC dividers, firmware plausibility checksPCB-mounted NTCs are not sole safety control for off-board heaters; test lag and fault cases
ESP32 crash/resetFirmware defect, brownout, watchdogSafe firmware default offAdd watchdog/latch-off policy and verify gates during reset/bootloader
RF/EMI malfunctionHeater PWM, buck converter, USB cableGate resistors, ESD protectionEMC test with heater leads and enclosure; add filtering if needed
User burn/contact riskWarm enclosure or heater-adjacent areasTarget <38 C heater-control conditionDefine 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

DesignatorPartMPNSafety RoleNotes
U4eFuse/current limiterMP5036AGJ-ZInput current limiting/protectionR1 = 1.1 kΩ sets ~2 A class limit
D1TVSSMF5.0AVBUS surge/transient clampNot protection against negotiated 15/20 V PD
U5USB ESDUSBLC6-2SC6USB D+/D- ESD protectionVerify final vendor/ratings
U2USB-PD sinkSTUSB4500QTRSource negotiationMust be programmed/verified 5 V-only
Q1-Q4Low-side MOSFETsSI2302Heater switchingVerify final vendor RDS(on) at 3.3 V and thermal margin
RT1-RT6NTC sensorsBOM currently shows ABNTC-0603-103J-3950F-T while symbol name references NCU18XH103F6SRBTemperature sensingResolve final NTC curve/MPN before firmware calibration
J2-J5Heater terminal blocks691137710002Off-board heater connectionVerify 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
  1. Decide whether to add independent hardware heater cutoff or require heaters with integrated thermal cutoff/PTC behavior.
  2. Define the controlled temperature point and safety shutdown thresholds precisely.
  3. Resolve STUSB4500 5 V-only gating/programming risk before PD-source testing.
  4. 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