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
The chip needs 3.3V at supply and all input pins. 5V are _forbidden_.
So TTL/RS232 convertors or some kinds of USB/serial convertors are not useable (in fact these devices can be used but one have to convert the levels … an additional board has to be used).
Pre-resistors for LEDs have to be changed and for example solid state relays or opto-couplers are difficult to be used since a LED _always_ needs a pre-resistor (due to their characteristics) and since these devices often needs at least 3V the difference is very low to use a resistor (SSR or opto-couplers are with LEDs at the input). That can be a problem for controlling high-current or main-source devices.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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