OpenMuscle FlexGrid is a modular 60-sensor pressure-sensing platform designed for advanced forearm-based gesture tracking and biomechanical research.
This device is part of the OpenMuscle ecosystem and represents a leap forward from the original 12-sensor OM12 prototype by introducing high-density, flex-rigid PCBs and better sensor modularity.
📌 For documentation, firmware, and assembly guidance, visit the OpenMuscle Hub.
V4 (in development, 2026-06). Ready for fab. Adds an on-device microSD card socket for local data logging, a discrete RGB status LED on three PWM channels, and a reoriented slimmer board profile that hugs the forearm. Carries forward the V3 power and interconnect architecture, but with the FFC tail width corrected from 11.1 mm to 10.5 mm per the Wurth 687120183722 datasheet, the ADC matrix-row caps reduced from 2.2 uF to 100 pF (resolves V3's 22 ms RC bleed in silicon rather than via post-fab cap removal), all resistors normalized to 0603, and several footprint cleanups. Manufacturing strategy: single-side SMT at JLCPCB for an initial batch of 10 units, plus hand-soldering of bottom-side parts and through-hole connectors at home. Not yet ordered, not yet brought up. Full status and pre-fab checklist in the V4 README.
V3 (stable, 2026-05-13). First revision to use a 20-pin ZIF FFC connector for the flex-to-rigid interconnect (Wurth 687120183722). Two boards populated and tested end-to-end. Sensor matrix delivers clean single-cell press detection across all 60 sensors with ~22% carryover decaying to noise floor within 3 columns. V3 is the first FlexGrid generation usable as a real ML training data source. Firmware: FlexGridV3-Firmware v0.1.7.
→ For V4 hardware files, see KiCad/OM-FlexGrid V4/ and the V4 README. For V3 see KiCad/OM-FlexGrid V3/ and the V3 README. The MicroPython firmware that runs on V3 (and will be ported to V4) lives at FlexGridV3-Firmware.
| Revision | Status | Notes |
|---|---|---|
| V4 | 🟡 In development | microSD + RGB LED + slimmer reorient; 10.5 mm FFC tail; 100 pF ADC caps; not yet fabbed |
| V3 | 🟢 Validated | 20-pin FFC interconnect, integrated stiffened FFC tail, ~140 Hz raw scan |
| V2 | 🟢 Tested | FFC connector exploration, fabric harness testing |
| V1 | 🟢 Tested | First production revision |
| V0 | 🟢 Tested | Original prototype |
→ Full cross-version comparison: KiCad/REVISIONS.md. Manufacturing process used across revisions: docs/JLCPCB_WORKFLOW.md.
FlexGrid uses a flexible pressure sensor matrix with rigid breakout interfaces to detect volumetric muscle contractions in real time. It supports:
- 🧠 Biomechanical signal analysis
- 🦾 Prosthetics and exosuit research
- 🎛️ Machine learning data pipelines
Design files are organized by board type and version:
📂 KiCad/ — all design files, organized by revision.
| Revision | Path | Description |
|---|---|---|
| V4 (in dev) | KiCad/OM-FlexGrid V4/ |
microSD socket, RGB status LED, slimmer reorient, 10.5 mm FFC tail, 100 pF ADC caps. See V4 README. |
| V3 (stable) | KiCad/OM-FlexGrid V3/ |
Validated. 20-pin ZIF FFC interconnect. See V3 README. |
| V2 | KiCad/OM-FlexGrid V2/ |
Tested. FFC exploration + fabric harness. See V2 README. |
| V1 | KiCad/OM-FlexGrid V1/ |
First production revision. |
| V0 | KiCad/OM-FlexGrid V0/ |
Original prototype. |
Each revision folder contains both the flex (OM-FlexGrid-Flex/) and rigid (OM-FlexGrid-Rigid-PCB/) board projects, plus their gerber bundles.
BOMs live next to their KiCad project for each revision:
- V4 Rigid (JLCPCB-ready):
KiCad/OM-FlexGrid V4/OM-FlexGrid-Rigid-PCB/jlcpcb/production_files/BOM-OM-FlexGrid-Rigid-PCB.csv(LCSC part numbers, machine-readable, generated by the JLCPCB KiCad plugin). The hand-soldered parts list (microSD socket, FFC connector, battery JST, pin headers, plus single-side-strategy BOT-side SMT) is documented prose-style in the V4 README. - V3 Rigid:
KiCad/OM-FlexGrid V3/OM-FlexGrid-Rigid-PCB/OM-FlexGrid-Rigid-PCB.csv(KiCad export). - Flex (V3 and V4): no electronic-component BOM. The flex tail integrates the FFC connector pads directly; the only off-board parts are the Velostat sheet and the mating Wurth 687120183722 connector populated on the rigid board.
Older revision BOMs are kept under BOM/ for history.
Instructions for soldering, testing, and integrating the FlexGrid with ESP32-S3 firmware are in development. For now, please refer to the OpenMuscle Hub and follow updates on YouTube Open Muscle or TURFPTAx Youtube.
We welcome improvements to sensor design, firmware, or real-world testing. Please fork the repo and submit pull requests!
Open Muscle is an open-source prosthetic sensor initiative designed for accessibility, innovation, and community collaboration.