Arduino code

12V Adapter (+) ──> Inline 5A Fuse ──> CS707025Z (NC @ 70°C) ──> PCB( +12V)
12V Adapter (–) ─────────────────────────────────> PCB (GND)

Heater Channel (MOSFET IRLB8721)
Q1 Gate ──> D10 via 100 Ω series resistor (RgH) + 100 kΩ pull-down (RpH) Gate→Source
Q1 Drain ──> HEAT−
Q1 Source ──> GND plane (common)

Fan Channel (MOSFET P36NF06L)
Q2 Gate ──> D11 via 100 Ω series resistor (RgF) + 100 kΩ pull-down (RpF) Gate→Source
Q2 Drain ──> FAN−
Q2 Source ──> GND plane (common)

Mini Step Down Module
HW-613 VOUT+ ──> 5V+
HW-613 VOUT− ──> GND
HW-613 VIN+ ──> 12V+
HW-613 VIN− ──> GND

Arduino Uno
GND ──> GND plane
5V ──> 5V bus

DHT22 Sensor (Air Temp)
DHT22 VCC ──> 5V
DHT22 GND ──> GND
DHT22 DATA ──> Arduino D6

Quad Alphanumeric Display (Adafruit 0.54″ I²C)
SDA → Arduino A4
SCL → Arduino A5
VCC → 5V
GND → GND

Rotary Encoder
Encoder A → Arduino D2
Encoder B → Arduino D3
Encoder GND → GND

The original incubator design came from this instruction.