For demo video click here: https://www.youtube.com/watch?v=oXAM9RpDKxk

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

Features:
Based on the ESP-8266EX.
Arduino Compatible, you can use it on Arduino IDE.
NodeMcu Compatible
All IO pins are 3.3V
11 Digital I/O pins
1 Analog Input pin
OTA -- Wireless Upload(Program)
On board switching power supply -- Max 24V input, 5V 1A output