ESP8266 un useable pins - Project Guidance - Arduino Forum
Amazon.com: D1 Mini ESP8266 ESP-12 ESP-12F CH340G V2 USB WeMos WiFi Development Board NodeMCU Lua IOT Board 3.3V with Pins (D1 Mini CH340) : Electronics
Send Data From Arduino to NodeMCU and NodeMCU to Arduino... - Hackster.io