An Arduino hack I did at Hack Duke 2013. I used the Arduino to count the shots in a magazine-fed Nerf gun to display on a 7 segment display. I originally intended to use a single 7 segment display but all the displays I brought were common anode and I only had driver ICs for common cathode. Fortunately I was able to find a 4×1 7 segment to use and got it working! 24+ hours well spent!