Feature references for pins used:

• 1 x i2c input for display or sensors - pins A4(SDA), A5(SCL)
• 1 x Serial output for display or blutooth module (Nextion TFT HMI) - pins RX3, TX3
• 3 x Solid State Relay pins (5v & 12v-Selectable pads & GND switched via transistors) - pins 2. 3. 4
• 1 x 12v PWM fan connection - pin 5(TX1/PWM)
• 1 x Sense amplifier IC for a K-type thermocouple. - pins 12(DIN), 10(!CS), T-, T+, 13(LED/IC pin5)