Project Patchouli debuts open-source EMR drawing tablet hardware

Project Patchouli is putting the guts of an electromagnetic resonance (EMR) drawing tablet on the workbench, open-sourcing the hardware stack that powers battery-free styluses. What’s notable here is the target: EMR digitizers have long lived behind NDAs and custom ASICs, making independent innovation and repair tough. An open reference design-schematics, PCB layout, and firmware-gives developers a way to study, reproduce, and tune the sensing path rather than treating it as a black box.

Under the hood, EMR works by scanning a coil matrix, energizing a resonant pen, and measuring induced signals to reconstruct position (and typically pressure) with tight latency budgets. That makes the signal chain-demodulation, filtering, calibration, and USB/input framing-the real battleground. The bigger picture: an open EMR design could lower barriers for niche form factors and embedded integrations (think e‑paper devices or custom panels), reduce vendor lock-in, and invite serious benchmarking of noise, jitter, and throughput across firmware revisions. Worth noting: interoperability hinges on pen frequency/encoding and shielding/layout discipline; coil alignment, per-unit calibration, and HID conformance will determine whether this lands as a plug‑and‑play tablet or a developer board that rewards careful tuning. Either way, exposing the full stack moves pen computing from “proprietary module” to “inspectable system”-a meaningful shift for indie hardware teams and OS/input maintainers alike.