Sometimes the cunning plan for a cool project doesn't end up the way you'd expect...
The cunning plan for this project was to create a small box that sat on a shelf in a house and which monitored WiFi, and/or Ethernet for cyber attacks, monitored MAC addresses looking for unusual values, and other neat tricks to keep the network safe.
The Arduino Yun (https://www.arduino.cc/en/Main/Arduino_BoardYun) seemed like an excellent candidate for this. It contains a Linux capable MIPS risk processor, that isn't the more popular ARM, and isn't an Intel processor ... making it less likely (but not impossible) to fall victim to attack. (I suspect that sentence is now out of date!). And it also contains an Arduino.
There is a very neat Arduino code library to communicate between the two processors, and it's possible to edit code both on the MIPS processor and the Arduino AVR to make the board do cool things.
In the design for the project a 2x16 backlit LCD panel with switches was used, and mounted in a box. ... now there are certain times in a project when, knowing that eventually neat looking grommets and 3D printed switch covers (which on this project have sadly fallen off) will hide many sins, that 'drilling a hole' in the case is much easier by just just pushing the soldering iron through it...!
To ensure a reasonable time powered up, 6 AA batteries were used along with a 7805 converter to generate 5V for the Yun.
To support multiple functions, the buttons and the LCD display were used to create a nested menu of functions, such as scanning and displaying WiFi network names and information, and monitoring WiFi or Ethernet networks.
Now for the (few) problems ... though the Arduino Yun is a fantastic board, it takes (after some experimentation) around 70 seconds to boot Linux. This isn't a big deal once the project is finished, but during testing, this is a loooooong time. it's also quite complex to programme if you want to add special calls or features, requiring some knowledge of Linux concepts. The other problem was entirely my fault ... always make sure the ground from the USB connection to Yun is connected to the ground for the battery driving the Yun ... or, after a short while, the USB to the Yun won't work any more, and it's not possible to upload new code. oops.
The box was still able to boot and run the code that was last installed which included several cool functions, including the scanner, and some other cyber protection features.
.... but sadly, that was then end of this potentially awesome project.