Hardware Design Concepts and Principles

This page explains the overall design thinking behind the main control board from the perspectives of design goals, hardware layers, key electrical parameters, protection, and control strategy.

Design Goals

Safety: 24V DC power with fuse and TVS protection.
Reliability: fan and heater channels use MOSFETs to support high current and PWM control.
Usability: modular connectors, misplug prevention, and maintenance-friendly.
Expandable: I2C sensors, encoder, and screen interfaces are replaceable.

System Architecture Overview

Main Control: ESP32-S3-WROOM-1-N8 (BOM: U3)
Monitoring: AHT10/AHT20 (I2C), NTC (ADC), INA226 (I2C)
Actuation: heater plate MOSFET, exhaust fan DC/PWM, heater fan, LED strip, and buzzer
Interaction: 3.5-inch resistive touchscreen and EC11 rotary encoder

Power and Protection

Power Path

24V DC input (XT60)
Fuse and TVS protection
Multi-rail regulation for the MCU and peripherals

Key Protection Devices (BOM References)

F1: 15A / 32V one-time fuse (main power protection)
F2: 1A / 12V resettable fuse (low-voltage branch protection)
D3: SMF24A TVS (secondary surge/ESD protection)

Sensor Principles

NTC Temperature Sampling

ADC 12-bit (0–4095)
Reference voltage 3.3V
Pull-up resistor 10kΩ
NTC Beta value 3950, R0=10kΩ@25°C
Temperature conversion uses the Steinhart-Hart equation

INA226 Current/Voltage

Reads bus voltage and current via I2C
Used for current limiting, over-current protection, and display

AHT10/AHT20 Temperature & Humidity

I2C digital sensor
Used for chamber temperature and humidity display

The heater power MOSFETs use a gate driver IC to provide higher gate drive current. This allows faster switching, reducing switching losses and heat, improving efficiency. It also reduces the load on MCU GPIOs and improves overall stability and reliability.

Dual PID Coordination

The system runs a “chamber temperature PID” and a “heater plate temperature PID”. The final output takes the minimum value to keep safety priority:

Chamber temperature PID targets the required chamber temperature
Heater plate PID limits heater plate over-temperature
Minimum output prevents overheating due to chamber temperature demand

Over-Current Soft Reduction

When current exceeds the configured limit, the system reduces PWM output instead of cutting off instantly to avoid temperature overshoot.

Connector and Interface Design

The board uses multiple connector types (MX1.25, PH2.0, ZH1.5, XH2.54) to:

Prevent misplugging and damage
Match current and mechanical strength requirements
Improve reliability in assembly and maintenance

For connector locations and wiring, see:

Key Component List (Excerpt)

ESP32-S3-WROOM-1-N8 (main controller)
INA226AIDGSR (voltage/current monitor)
XL4015E1 (buck converter)
AMS1117-3.3 (3.3V LDO)
MPT045N08S / DOZ100N03 (power MOSFET)
EC11 rotary encoder

Notes

The main power and heater circuits carry high current. Pads and wiring must meet current requirements.
Do not short both 12V/24V selection pads.
MOSFETs and DC-DC modules must be installed with heatsinks.