Handwriting tech - POC in action

Update on the Daptar (educational tablet) project — passive pen detection in action 🔥!

Electromagnetism always felt like magic when I first learned it in school. Seeing it used here for pen input still feels the same.

In my blog post introducing Daptar tablet, I mentioned that handwriting is critical for learning, so we need a solution that makes writing on tablets feel natural. Current options — AES (Apple) and EMR (Wacom, Huion, etc.) — work well but are mostly tied to high-end devices. Sourcing these solutions for a prototype has been a challenge.

That’s why I explored Project Patchouli, an open-source implementation based on expired patents. For Daptar, I adapted the author’s work on a different platform. The demo works (video attached), though the pad is small. A larger, improved version is already in manufacturing.

The project’s author was a huge help in debugging and getting this working — big thanks to them. If you want to learn more, you should definitely join their Discord. I’ve also added a few YouTube videos from others that explain the technology in more detail.

I’m using a Raspberry Pi RP2040 instead of STM32 to drive the panel and detect pen + pressure. This revision will be part of the tablet prototype, alongside an e-ink display (more on that in the next update).

Links -

1. Daptar Tablet Blog Post - https://lnkd.in/ep5nTVDb

2. Project Patchouli Discord - https://lnkd.in/e3WBNyQg

3. Project Patchouli - https://lnkd.in/eJT45JEc

4. Project Patchouli Video - https://lnkd.in/eeUNWqaW

5. Scanlime’s Tablet Prime - https://lnkd.in/euXTeNYK

6. Scanlime’s Tablet Teardown - https://lnkd.in/efFwta-K

P.S. Passive pens are called passive because they work without batteries.