TL;DR
Project Patchouli is an open-source effort to build electromagnetic resonance (EMR) drawing tablet hardware, with designs, firmware and documentation published by the maintainers. The project includes a coil array, RF front end built from commercial components, and DSP algorithms, and reports compatibility with many commercial styluses.
What happened
Project Patchouli launched in January 2024 to create an open-source implementation of EMR pen-tablet hardware and accompanying technical documentation. The project package covers physical hardware elements — including a coil array and an RF front end assembled from broadly available components — plus digital signal processing code and descriptions of pen protocols from several vendor lines. A small-scale prototype was tested in March 2024, and the documentation was later published on Read the Docs in January 2025. The maintainers publish source materials on a GitLab repository and have released project documentation under Creative Commons Attribution 4.0; hardware designs use the CERN-OHL-S license while program code is generally under GPLv3. The project identifies Yukidama as project lead, is sponsored by the NLnet Foundation NGI Zero Core Fund, and remains under active development.
Why it matters
- Open access to EMR hardware designs could lower barriers for custom input device research and hobbyist projects.
- Detailed documentation of mechanisms, circuitry and signal processing can help developers and researchers better understand proprietary tablet technologies.
- Compatibility with many commercial pens may reduce dependency on single-vendor ecosystems for experimental hardware builds.
- License choices (CC BY 4.0, CERN-OHL-S, GPLv3) clarify reuse conditions for documentation, hardware and software respectively.
Key facts
- Project start date: January 2024.
- First small-scale hardware prototype tested: March 2024.
- Documentation hosted on Read the Docs: January 2025.
- Project lead listed as: Yukidama.
- Source materials and code are published on a GitLab repository.
- Documentation and most project resources licensed under Creative Commons Attribution 4.0.
- Hardware designs released under the CERN Open Hardware License (CERN-OHL-S).
- Program code is generally licensed under the GNU General Public License v3 (GPLv3).
- Project sponsored by the NLnet Foundation NGI Zero Core Fund.
- Project provides a contact email (prj.patchouli@gmail.com) and a public Discord server for community engagement.
What to watch next
- Roadmap for full-scale hardware and broader prototype testing — not confirmed in the source
- Plans for expanded compatibility testing across more pen models and vendors — not confirmed in the source
- Release timeline for production-ready schematics, kits or reference boards — not confirmed in the source
Quick glossary
- Electromagnetic resonance (EMR): A technology used in pen-input tablets where an electromagnetic field generated by a coil grid interacts with a passive or active stylus to determine position and inputs.
- Coil array: An organized set of coils laid out beneath a tablet surface that generates and senses electromagnetic fields used to locate a pen and read its signals.
- RF front end: The radio-frequency circuitry that transmits and receives signals between the coil array and processing electronics.
- Digital signal processing (DSP): Algorithms and techniques used to analyze, filter and interpret raw signals from hardware into usable position and input data.
- CERN-OHL-S: A reciprocal open hardware license variant from CERN used to govern reuse and distribution of hardware designs.
Reader FAQ
Where is the project hosted?
Project assets and code are published on a GitLab repository.
Is the hardware compatible with commercial pens?
The project reports compatibility with most commercial pens from different vendors.
Who leads the project and how can I contact them?
The project lead is listed as Yukidama; contact options include prj.patchouli@gmail.com and a public Discord server.
What licenses apply to the project materials?
Documentation is CC BY 4.0, hardware designs under CERN-OHL-S, and program code generally under GPLv3.
Is the project production-ready?
Not confirmed in the source.
Project Patchouli Open-Source EMR Pen Tablet Hardware Implementation and Documentation Patchouli is an open-source electro-magnetic drawing tablet hardware implementation, including a coil array, an RF front end built using commercially…
Sources
- Project Patchouli: Open-source electromagnetic drawing tablet hardware
- Project Patchouli
- Yukidamayaki / Patchouli
- Patchouli: Open-Source EMR Drawing Tablet
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