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Hardware

Source: schematic traced from a real device. Chip identification community-confirmed.

Overview

Component Part Notes
MCU ESP32-C3 (ESP32-C3-MINI-1-H4X) WiFi 2.4GHz, USB-C flashing via CH340K
Heater 300W PTC element Relay-switched (on/off only)
Heater relay MGR-GJ-5-L SSR AC solid-state relay
Fan control BT136-800E TRIAC Phase-angle speed control
Fan driver MOC3021S-TA1 optocoupler TRIAC gate driver
Zero-crossing TLP785 AC optocoupler For TRIAC phase sync
Chamber sensor NTC 100K thermistor → warehouse_temper / cal_warehouse_temp
PTC sensor NTC 100K thermistor Thermal runaway protection only
AC-DC HLK-PM01 110–240V AC → 5V isolated
LDO AS1117-3.3 5V → 3.3V MCU rail
USB-UART CH340K USB Type-C programming interface

Power Supply Chain

AC mains (L/N)
  → F1 fuse (MTST630AL)
  → R1 MOV (10D-11) surge protection
  → EMI filter: CX2-0.1uF/275V X2 cap + PDSQAT1212-303MLB common mode choke
  → HLK-PM01 (isolated AC-DC, 110-240V → 5V)
  → AS1117-3.3 LDO (U5, 5V → 3.3V = MCU-3V3 rail)
  • MCU-3V3 rail powers the ESP32 and logic
  • 5V rail powers relay coil driver and optocoupler
  • L-AC-DC is the live AC line routed to the heater relay and fan TRIAC

ESP32-C3 GPIO Assignments

Net name ESP32 pin Connected to
IO02 6 K3 button (10K pullup via R2)
IO03 7 FAN TRIAC signal
EN 8 RESET button (10K pullup via R4)
TH0 12 NTC thermistor 0 ADC input
TH1 13 NTC thermistor 1 ADC input
IO00 15 K2 button + ZERO crossing
IO04 19 K3-LED
IO05 20 K2-LED
IO06 21 K1-LED
IO07 / ZERO 22 K1 button / ZERO crossing signal
BOOT 23 SW4 (BOOT button, K4)
RLY_MOSFET 26 Relay drive transistor (Q3 base)
TXD0 30 CH340K UART TX
RXD0 31 CH340K UART RX

PTC Heater Control

Relay: MGR-GJ-5-L (solid-state relay, AC output)

  • AC side: L-AC-DC (live AC) → relay → L-OUT → PTC heater connector
  • Control side: 5V coil driven by Q3 (MMS8050-H-TR NPN transistor)
  • Q3 base driven by RLY_MOSFET GPIO via R16 (100Ω) + R18 (10K) pulldown
  • D5: 1N4148 flyback diode

On/off only

The relay either switches full AC power to the PTC element or cuts it. There is no phase-angle or PWM control on the heater. Temperature regulation is achieved by the firmware duty-cycling the relay based on thermistor feedback. The Klipper module does not need to manage this — it only sends work_on: true/false.

Fan Speed Control

TRIAC: BT136-800E (600V, 4A AC switch)

  • Controlled via MOC3021S-TA1 optocoupler TRIAC driver
  • Q2 (MMS8050-H-TP NPN) drives the optocoupler LED
  • FAN GPIO → Q2 base (via R15 10K) → U4 opto → Q1 TRIAC gate
  • Fan AC power goes through Q1 TRIAC

Phase-angle control: R12 snubber network, R14 (220Ω gate resistor) — classic TRIAC phase-angle speed control, firing synchronized to the zero-crossing signal. Fan speed is managed entirely by the firmware; there is no user-settable fan_speed field in the WebSocket API.

Zero-Crossing Detector

TLP785(GB-TP6,F(C)) — AC optocoupler

  • Neutral AC → R30 (100K) → U7 AC side
  • Live AC → R29 (470Ω) → U7 AC side
  • Output: ZERO signal to ESP32 GPIO
  • Used to synchronize TRIAC firing for fan phase-angle speed control

Temperature Sensors

Two identical NTC 100K thermistor input circuits:

TH0 — chamber air temperature

  • Voltage divider: MCU-3V3 → R22 (33K 0.1%) → TH0 node → thermistor → GND
  • Protection: D6 (BAV99 dual Schottky) + R25/R26 (2.37K 1%) series resistors
  • Filter cap C13 (0.1µF)
  • Firmware publishes as warehouse_temper (raw) and cal_warehouse_temp (ADC-calibrated)

TH1 — PTC element temperature (identical circuit)

  • Monitors PTC heater element temperature for thermal runaway protection
  • Firmware publishes as cal_ptc_temp
  • Not used for user-facing temperature targeting

Tip

Use cal_warehouse_temp in preference to warehouse_temper. The firmware applies ADC calibration (adc_cali_raw_to_voltage) to produce the calibrated reading, which is more accurate than the raw ADC value.

Physical Buttons

All three labeled buttons are K6-6140S01 — LED-backlit tactile switches.

Button Net LED net GPIO
SW1 K1 K1-LED IO06 (LED), IO07 (button)
SW2 K2 K2-LED IO05 (LED), IO00 (button)
SW3 K3 K3-LED IO04 (LED), IO02 (button)
SW4 BOOT — BOOT pin (K4 / flash mode)

Buttons do not push WebSocket messages

On v0.0.0, physical button presses do not generate WebSocket messages. The Klipper module cannot rely on push notifications to detect out-of-band state changes from the physical buttons.

USB Programming Interface

CH340K — USB to UART bridge

  • USB Type-C connector (USB_P/USB_N)
  • TXD0/RXD0 → ESP32 UART
  • RST#/DTR# → EMM412R dual transistor → auto-reset/boot circuit

The auto-reset circuit allows esptool to enter bootloader mode automatically without pressing buttons:

esptool.py --chip esp32c3 --port /dev/ttyUSB0 --baud 460800 write-flash 0x0 firmware.bin

On macOS the port will be /dev/cu.usbserial-* or /dev/cu.wchusbserial* (CH340K).

Klipper Integration Insights

  1. warehouse_temper is a real NTC ADC reading — two separate physical sensors, independently wired. Use cal_warehouse_temp (calibrated) where available.

  2. PTC heater is relay-switched (on/off only) — the firmware duty-cycles the relay for temperature regulation. The Klipper module just sends work_on: true/false.

  3. Fan speed is TRIAC phase-angle controlled — firmware manages this entirely. There is no fan_speed write field in the WebSocket API.

  4. Button presses do not push WebSocket messages — the module must poll (or reconnect) to detect out-of-band changes rather than relying on push.

  5. cal_warehouse_temp is the preferred temperature field — it applies ADC calibration correction. Fall back to warehouse_temper if cal_warehouse_temp is absent.