Most smart pens hide behind an app. You write something, then you have to pull out your phone to see the result. We thought that defeated the whole purpose.
The Design Philosophy
Nexus Pen's core principle is zero context switching. If you have to put down the pen to interact with AI, you've already lost the moment. The OLED display keeps everything in your line of sight — answers, settings, status — without ever breaking your flow.
Why OLED
We chose a 1.3-inch SH110X OLED display for several reasons:
- True blacks — OLED pixels emit their own light, so black pixels are completely off. On a black pen body, the display blends seamlessly
- Readability — High contrast ratio means text is crisp and readable even in bright environments
- Power efficiency — Only lit pixels consume power. Our mostly-dark UI is extremely battery-friendly
- Thin profile — OLED panels are incredibly thin, which matters when your enclosure is a pen
What Appears on Screen
The display adapts to context. In idle mode, it shows connection status and battery level. During a conversation with Donna, it shows her response as scrolling text. In settings mode, it becomes a full menu system navigated with the pen's three buttons.
We even built a developer mode (accessible through a secret code in settings) that shows system diagnostics and easter eggs for our most curious users.
The Technical Challenge
Driving an OLED display while simultaneously streaming BLE audio and processing button inputs on an ESP32 is a juggling act. The I2C bus that communicates with the display can briefly block the main loop, which would cause audio stuttering if we weren't careful.
Our solution: triple-sized I2S DMA buffers that hold 340ms of audio — more than enough to survive any display update. The audio never skips, even when the screen is refreshing.
The Result
Users consistently tell us the display is their favorite feature. It transforms Nexus Pen from a "pen that connects to an app" into a truly standalone smart device. You can get answers, adjust settings, and interact with Donna without ever touching your phone.
That's the future we're building: intelligence you can hold in your hand.