This is one of my favorite ESP8266 microcontroller board, often used for many Wi-Fi IoT devices.
It’s based on ESP-12F chip, and like all ESP8266 it’s a 3.3V logic level board: you can power it thought the 3.3V pin and all the IO pins run at 3.3V.
It includes anyway an internal voltage regulator (RT9013) to step down 5V to 3.3V if you prefer to power the board using the Micro USB port or using the 5V pin.
There are 11 digital IO and only 1 analog input (3.2V max input).
The serial-USB converter is a CH340 chip (Click here if you need Windows driver)
One of the key advantages of this board is the very small size 34.2*25.6 mm.
Another important feature is the low power consumption, about 77 mA in deep sleep.
To enable deep sleep you need to connect D0 (GPIO16) pin to RST pin, or, only in this 3.0 board version, you can also solder the two SLEEP pin on the back of the board.
Take in mind, while deep sleep is enabled you cannot upload new firmware to the board, so solder the pins only once your development is completed.