March 12, 2018
The above is an ESP8266 module mounted on a "NodeMCU" board, which is how I use them in most (but not all) cases.
Many people think of it as a Wifi "add-on" for other projects, which I think is a big mistake. It can certainly be that, but is absolutely useful as a self contained microcontroller with or without Wifi.
I used to have an extensive set of notes on working with the ESP8266, but they were lost when the machine holding my website had a disk crash. I hope to redo them someday in a better form if I ever stop playing with ARM processors and go back to finish up some of my ESP8266 projects.
If you start wanting to run things from a battery, you will want to ditch the USB to serial chip and LED's and just run a bare module. You will need to give it 3.3 volts somehow, and you will need an independent USB to serial converter for debuggin and to load software. Go buy some ESP-12E modules on AliExpress. They typically sell for about $1.70.
You will wait for 2-3 weeks when ordering via AliExpress direct from China. I order in batches of 10 and am delighted that I can get 10 of these things for less than a miserable AVR controller board.