Software that runs on an ESP8266 (with nodeMCU firmware) which blinks in the presence of open WiFi networks
You may want to first install Lua if you want to test the code Linux:
curl -R -O http://www.lua.org/ftp/lua-5.3.1.tar.gz
tar zxf lua-5.3.1.tar.gz
cd lua-5.3.1
make linux test
MacOSx :
$ brew install lua
Then you will likely want to install a loader to upload your Lua scripts to the ESP8266 through a USB-to-serial connection. (see Talking to your ESP8266)
WARNING: The ESP8266 operates at 3.3v and will not be happy if you use 5v (Arduino and other FTDI boards often operate at 5v)
This project was inspired by a project by @kstevica: https://medium.com/@kstevica/how-to-build-an-open-wifi-finder-using-esp8266-and-two-coin-batteries-9c31eb6f9859 Another (more advanced) open WiFi detector which is in the same vein: http://benlo.com/esp8266/esp8266Projects.html#hotspotfinder
Lua is a light-weight high-level programming language designed for embedded environments. You can find a quick introduction about general Lua syntax here: http://esp8266.co.uk/tutorials/lua-basics/
One important feature of Lua is its Timer API:
You can use up to 7 timers (index=0-6) which can each execute a function
a) once after a timeout of xxx ms (0)
b)repeating the function with an interval of xxx ms (1)
tmr.alarm(index, ms, type, callback)
tmr.alarm([0-6], [0-100000], (0|1), function_to_execute)
http://esp8266.co.uk/tutorials/introduction-to-the-timer-api/
On MacOsX use $ ls /dev/tty.* to find the serial port
Debugging tool for serial ports : http://freeware.the-meiers.org/
You can download one of these tools to help you talk with your ESP8266 e.g. to read output, send commands line by line, upload files, format, flash firmware, etc.)