Do you know how many devices are on your local network? That is what we where wondering at our hackerspace HackBergen.
Yes, there are available programs and Apps to scan your network, but we can also scan with the Raspberry Pi (RPi) and show the result on a set of 7-segment displays.
These look cool, retro, are cheap and can be seen from a distance for you to have a general idea of how many devices are currently operating on your local network in these IoT times.
This build uses 3 modules of 7-segment common Anode LED displays that are controlled by an Atmega328. We use 3 because normal home LANs are C nets with a maximum of 256 devices and I had 3 of these nice 7-segment displays lying around. :)
The (AVR Atmega) 328 is loaded with the Arduino bootloader on an Arduino Uno 28pin AVR and then programmed with the Arduino 1.0.1 IDE through the Raspberry Pi on board serial port. The software is the firmware that Sparkfun uses on their serial backpack, but we have to modify a couple of lines since they use a 32 pin SMD 328 instead of the normal 28pin DIP version from the UNO.
By using an 328 for this, we do not need more than the serial port's 2 pins to control the display, and all multiplexing and buffering is done by the 328. No need for a program to do the multiplexing of the 7-seg displays and be problematic with irregular timing. We can also use the built in i2c bus to control it if we want to.
Using the serial port makes it very easy to display 7-seg chars on the display, remaining there until we update it again. This is great for piping information from scripts, and we do not need a program running constantly as a daemon.
You could of course buy a single 4 digit display from SparkFun ready-made and connect it to your Linux box or your RPi, losing all the DIY fun. That is totally up to you. :)