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

Power and Thermal Budget — ESP32 Heater Controller
Status
Draft budget based on the first schematic implementation.
Implemented Power Architecture
Diagram



  
    
  
  
    
  






















USB-C VBUS node_5V
VBUS TVS + USB ESD
STUSB4500 USB-C PD Sink
MP5036A eFuse / Current Limit
5V_PROTECTED
4x node_5V / node_1W Heaters
AP63203 3.3V Buck
3V3
ESP32-S3 Module
OLED I2C Connector + Encoder + RGB LEDs
6x NTC Divider Sensors
Key Design Caveats
  • The heater rail is a 5 V rail. The STUSB4500 must be configured for a 5 V-only sink profile unless a separate 5 V regulator/power path is added.
  • The design can connect to USB-C PD laptop chargers, but the load must remain within available 5 V source capability.
  • Firmware should derate or disable heaters if USB source capability is insufficient or unknown.
  • The front RGB indicator is implemented as three discrete 0603 LEDs after two RGB LED library parts showed datasheet pin-label conflicts.
5 V Rail Budget

Table

LoadCurrentPowerNotes
Heater 1200 mA1.0 W5 V / 1 W film heater
Heater 2200 mA1.0 W5 V / 1 W film heater
Heater 3200 mA1.0 W5 V / 1 W film heater
Heater 4200 mA1.0 W5 V / 1 W film heater
3.3 V buck input, typical~220 mA~1.1 WAssumes ~300 mA at 3.3 V, 90% buck efficiency
3.3 V buck input, peak~440 mA~2.2 WAssumes ~600 mA at 3.3 V, 90% buck efficiency
STUSB4500 / protection overhead<20 mA<0.1 WConservative placeholder
Total typical active~1.04 A~5.2 WFull heaters + typical electronics
Total peak active~1.26 A~6.3 WFull heaters + peak electronics
Recommended input rating5 V / 2 A10 WGives margin for cable/source variation
3.3 V Rail Budget

Table

LoadTypicalPeakNotes
ESP32-S3-WROOM-1120–250 mAup to ~500 mAWiFi/BLE burst allowance
Display connector budget20–50 mA80 mADepends on selected OLED/display module
6x NTC dividers~1 mA~1 mA10 kΩ / 10 kΩ dividers at 3.3 V
I2C pull-ups / encoder<2 mA<2 mAStatic/dynamic small-signal loads
RGB indicator LEDs2–8 mA~10 mALow-brightness status target
STUSB4500 I2C pullups/logicsmallsmallController itself is VBUS-powered; I2C pullups from 3.3 V
Design budget~300 mA~600 mAAP63203 2 A rating provides strong margin
Protection / Current Limit Sizing
  • eFuse/current-limit IC: MP5036AGJ-Z.
  • Current-limit resistor: R1 = 1.1 kΩ.
  • Datasheet relation: ILIMIT ≈ 2183.5 / R_LIMIT.
  • Expected typical current limit: 2183.5 / 1100 ≈ 1.98 A.
  • This is above the estimated ~1.26 A peak system draw while still protecting against hard shorts and wrong wiring.
Thermal Checks
Heater MOSFETs
  • MOSFET: SI2302, low-side switching.
  • Heater current per channel: 0.2 A.
  • RDS(on) worst-case from datasheet extraction: roughly 59 mΩ max at VGS = 2.5 V.
  • Dissipation per MOSFET: I²R = 0.2² × 0.059 ≈ 2.4 mW.
  • Even with temperature margin, each MOSFET should run essentially cool; no heatsinking is required.
eFuse
  • MP5036A internal FET RDS(on): about 43 mΩ typical.
  • At ~1.26 A peak: P ≈ 1.26² × 0.043 ≈ 68 mW.
  • At 2 A current limit: P ≈ 2² × 0.043 ≈ 172 mW before current limiting/thermal shutdown behavior.
  • Layout should give the IC copper area, but this is reasonable for passive cooling.
3.3 V Buck Regulator
  • AP63203 is used instead of an LDO to avoid avoidable heat.
  • At 600 mA peak 3.3 V load: output power is 3.3 × 0.6 = 1.98 W.
  • At 90% efficiency, loss is about 1.98 × (1/0.90 - 1) ≈ 0.22 W.
  • This is much better than an LDO, which would dissipate (5 - 3.3) × 0.6 ≈ 1.02 W at the same peak load.
NTC Self-Heating
  • Each 10 kΩ / 10 kΩ divider draws about 3.3 / 20kΩ ≈ 165 µA near 25 °C.
  • NTC dissipation near 25 °C is about I²R ≈ 0.27 mW, low enough to avoid meaningful self-heating.
Heater Connectors
  • Würth 691137710002 terminal blocks are rated far above the 0.2 A/channel heater load.
  • This is a deliberate mechanical/reliability margin, not an electrical necessity.
Firmware Safety Requirements Driven by the Budget
  • Default all heater GPIOs off at boot/reset.
  • Refuse heater operation until all six temperature channels pass plausibility checks.
  • Detect NTC open/short conditions.
  • Add temperature rate-of-rise checks.
  • Add maximum-temperature cutoff and latch/fault behavior.
  • Derate heater duty cycle if USB source capability is below the design target.
  • Enable ESP32 brownout detection and watchdog behavior.
Open Thermal / Safety Items
  • Final enclosure airflow and sensor isolation need layout/prototype validation.
  • PCB-mounted heater-adjacent NTCs do not directly measure heater surface temperature; firmware thresholds must be validated empirically.
  • If future UL-style review becomes a near-term goal, consider adding an independent hardware thermal cutoff or external thermal-fuse loop in the heater supply path.

  • Status

  • Implemented Power Architecture

  • Key Design Caveats

  • 5 V Rail Budget

  • 3.3 V Rail Budget

  • Protection / Current Limit Sizing

  • Thermal Checks

  • Heater MOSFETs

  • eFuse

  • 3.3 V Buck Regulator

  • NTC Self-Heating

  • Heater Connectors

  • Firmware Safety Requirements Driven by the Budget

  • Open Thermal / Safety Items