Who doesn't like a project with LEDs! We certainly do! For this one, we needed to invent a solution for tracking ball hits on the net and producing visual feedback, so the players could train. Basically, blink the LEDs to show where you hit and how precisely. We made a set of Bluetooth devices with new InvenSense (now TDK) specialized ICM-20601 IMUs which just came out and featured really fast reaction time and accuracy - specifically for sports applications. Really liked those IMUs, too, but they're hard to get now, maybe because of the TDK acquisition they had to cut some of the IMU series.
Anyway, we made a really thick PCB and used four bright 3518 LEDs - which drained the battery fast, but we only needed to blink them, so it was ok. Also we had some ideas on how to charge a set of devices (from 4 to 12 of them at once) and how to attach them to the net.