The D1 R2 is a mini wifi board based on ESP-8266EX.

11 digital input/output pins, all pins have interrupt/pwm/I2C/one-wire supported(except D0)

1 analog input(3.3V max input)

A Micro USB connection

A power jack, 9-24V power input.

Compatible with Arduino

Compatible with nodemcu

 

Programming:

The D1 R2 has a micro USB for auto programming.

Also you can programming it using OTA

 

Warnings:

All IO is work at 3.3V.