This program listens to knocks (like a ping pong ball on a table) and sends signals to a mini web server hosted on a WEMOS D1 MINI (ESP8266) board through a websocket.

Watch the demo video here.

Websockets are really useful to get live updates without refreshing the page.
On the front-end I used 10 lines of AJAX/Javascript stored in play.h to listen to the websocket and display this kind of page

You can open the webpage by going to this address once the program is running on the board: http://IP.ADRESS.OF.THE.ESP8266:80 with a desktop or a smartphone on the same wifi as the one you need to configure in the .ino file.

knockio.ino is the programm intented to be loaded in a WEMOS MINI D1 or a compatible ESP8266 board.
For info you can add a program to this type of card with the Arduino IDE.
I used this awesome library for websockets .

Questions/problems/improvements ?

Please open a github issue :) Thanks !