NodeMCU pinout : In ESP8266 firmware on Arduino IDE pin numbers are defined as follows: NodeMCU Function Pin No on Arduino IDE Alias Name D0 GPIO16 16 D0 D1 GPIO5 5 D1 D2 GPIO4 4 D2 D3 GPIO0 0 D3 D4 GPIO2 2 D4 D5 GPIO14 14 D5 D6 GPIO12 12 D6 D7 GPIO13 13 D7 D8 GPIO15 15 D8 A0 ADC0 A0 analog_ip Tx GPIO1 1 D9 Rx GPIO3 3 D10 Pin Functions Pin numbers in the Arduino IDE correspond directly to the ESP8266 GPIO pin numbers.