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Wiring Diagram

This page explains how to connect components around ESP32. First, a general pinout map, then connection of each node and rules for power section layout.

Check your board pinout first

The pin numbers below are examples. Different ESP32-C3 and ESP32-S3 boards have different numbering and pin layouts. Before assembly, verify the pinout of your specific board. Not all pins can be used freely: some are occupied by boot, flash, or USB.

Pinout Map (Example)

Node Line ESP32 Pin (example)
SHT31 SDA GPIO8
SHT31 SCL GPIO9
Thermistor ADC signal GPIO2
Heater (switch) control GPIO4
Fan (switch/PWM) control GPIO5

Sensor power is 3.3V and GND from the board. The power section is powered separately.

SHT31 over I2C

SHT31 connects with four wires:

  1. Sensor VCC — to board 3.3V.
  2. Sensor GND — to board GND.
  3. Sensor SDA — to SDA pin (example: GPIO8).
  4. Sensor SCL — to SCL pin (example: GPIO9).

I2C lines are short. If the sensor is far from the board, keep the wires as short as possible and twisted together. Most SHT31 modules have pull-up resistors already on the module board.

SHT31 Address

SHT31 typically has address 0x44 (sometimes 0x45). If the sensor does not respond, check the address and SDA/SCL lines.

Thermistor on ADC

The thermistor is connected in a voltage divider with a pull-up resistor:

  1. One thermistor pin — to 3.3V.
  2. The other thermistor pin — to the junction point with the 4.7 kΩ resistor and the ADC pin (example: GPIO2).
  3. The other end of the 4.7 kΩ resistor — to GND.

The controller measures the voltage at the midpoint of the divider and calculates the thermistor resistance from it, then the temperature. The thermistor type is set in the firmware (see Heating Control).

Details on thermistor verification and assembly — Checking Thermistor.

Heater and Fan via Switch

ESP32 does not control the load directly, but through a switch. Which switch depends on the version from System Bill of Materials.

Version A (24V/12V) — MOSFET Module

  1. The module signal input (PWM/SIG) — to the ESP32 control pin (example: GPIO4 for heater, GPIO5 for fan).
  2. Module GND — to common GND with ESP32.
  3. Module power input and load — to the 24V power supply.

Common Ground

The controller GND and the power supply GND must be connected together. Without a common ground, the control signal has no reference level, and the switch works unpredictably.

Fan connection with control is detailed in Connecting Fan. Switch logic — MOSFET Module.

Version B (220V) — SSR/Relay

Before assembly of the mains section

All connections to the mains must be made with the device completely de-energized. The case with the mains section must have protective grounding and a fuse. Use mains wires of sufficient cross-section and secure them in the terminals reliably.

SSR has two sides. Control — a low-voltage input controlled by the controller. Power — terminals through which the mains voltage of the load passes. The sides are isolated from each other by an optocoupler inside the SSR, so the network can be controlled with a weak 3.3V signal.

  1. The control input is usually marked DC+ and DC- (sometimes + and -) and is rated for 3–32V DC. Connect DC+ to the ESP32 control pin (example: GPIO4), and DC- to the controller GND. The 3.3V voltage from the ESP32 pin is sufficient to open the SSR.
  2. The power pins (often marked as mains/AC and load/LOAD) are inserted in the break of one of the heater mains wires — just like a switch in the wire.
  3. The fan is switched with a separate SSR or relay in the same way.

Why SSR needs a heatsink

When the SSR switches, it heats up slightly, and the higher the load current, the greater the heating. Therefore, the SSR is screwed to a heatsink (a metal plate for heat dissipation), and the SSR is chosen with a current margin — notably higher than the load current. What margin and heatsink you need for your current — Solid-State Relay (SSR).

Layout: Signal and Power Sections

  • Keep signal wires (sensors, control) separate from power wires.
  • Do not run thermistor and I2C wires along power wires of the heater — this is a source of noise.
  • In version B, physically separate the mains and low-voltage zones inside the case.
  • Bring all low-voltage grounds to a single point.

Fan noise and poor grounding are a common cause of "floating" readings and reboots. See Wiring Mistakes.

Checklist Before Powering On

  • Sensor power is 3.3V, not 5V.
  • Thermistor and voltage divider resistor are assembled correctly, ADC pin at the midpoint.
  • Common ground between controller and power supply.
  • In version B — case grounding, fuse, reliable terminals, insulation.
  • No short circuits between power and ground (check with multimeter).

Multimeter checking — Multimeter.

What's Next

Hardware assembly is complete. Move to Firmware Start on Core: create a project and bring the device to Online status on the portal.