Stop Tennis Feuds with This Pocket Scoreboard

Tennis is infamous for its bizarre and mysterious scoring rules — likely an intentional strategy by posh tennis clubs to keep out the riffraff. I mean, love, 15, 30, 40, and deuce? What even is that? Those enigmatic rules inevitably lead to arguments and fist fights between novice tennis players, which is a real problem for the aforementioned tennis clubs. To avoid befuddlement among new players and to keep those clubs from becoming war zones, 0xBERNDOG created this pocket scoreboard that does all the hard work of tracking points.

Conceptually, this is pretty easy to understand. It is just a small device with buttons and a screen that tennis players can interact with to keep track of the score in a match. After several weeks of studying tennis rules, most makers could build a device with those features in an afternoon with an Arduino. But 0xBERNDOG gave himself some additional feature requirements that made it a much, much more challenging endeavor.

The requirement with the biggest impact was a long battery life on a small battery — an extremely long battery life on a very small battery. That battery is a small coin cell (exact type unspecified) and 0xBERNDOG says it can last a whopping 20 years when the device is in idle mode (device on, but screen off). That’s because it draws less than a microamp in that state. Even with the screen on 24/7, the battery would last about 200 days.

To make that possible, 0xBERNDOG put a lot of effort into optimizing power efficiency. The device runs an STM32L4 ultra-low-power microcontroller and the screen is a Sharp memory LCD from Adafruit (0xBERNDOG says it is a Toshiba, but we’re pretty sure he meant Sharp). Those displays bridge the gap between e-ink and standard LCDs, offering fast refresh rates and very low power usage. The components go on a custom PCB that fits in a custom 3D-printed enclosure that looks quite nice.

Even with all of that, 0xBERNDOG had to do a lot of work with the firmware to make the device sip power so frugally. He built that firmware using FreeRTOS with a HAL (Hardware Abstraction Layer), which let him keep the microcontroller in something like a deep sleep until an event (like a button press or screen update) requires attention.

Now we just need to cross our fingers and hope 0xBERNDOG builds a similar device to avoid bloodshed on the pickleball courts.