The ESP12-E NodeMCU Kit is one of the most used ESP8266 development boards. It features 4MB of flash memory, access to 11 GPIO pins, and one analog-to-digital converter (ADC) pin with 10 bit resolution. The board has a built-in level shifter and you can power up the module using the mini USB socket or the Vin pin.
Uploading code to the board is as easy as uploading code to the Arduino, there’s no need for an FTDI programmer, as it comes with a usb-to-serial converter built-in.
Re: Difference between Wifi shield R3 and Wifi module esp8266
Programming is easy since the whole Arduino library can be used and there are a lot of additional libraries out there in the internet.
The board itself is really small so existing devices can be upgraded with WiFi abilities in a lot of ways without any change at the outline or case.
In sleeping mode (if useable) the power consumption is very small so batteries can be used. With WiFi this could be a problem since the transmitter needs some current.
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