2 layers260 × 55 mm
OM-60-Flex
Open-Muscle/OpenMuscle-FlexGrid
60-sensor wearable with flexible PCB and pressure matrix
62 parts19CERN-OHL-S-2.0
4 layers33 × 65.5 mm
OM FlexGrid Rigid PCB
Open-Muscle/OpenMuscle-FlexGrid1960-sensor wearable with flexible PCB and pressure matrix
- Size
- 33 × 65.5 mm
- Copper layers
- 4
- Thickness
- 1.6 mm
- Parts
- 65
- Nets
- 89
- Pads
- 298
- Tracks, vias
- 899, 110
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 10.0 (file 20260206)
- Created
- 19 May 2025
- Updated
- 4 Nov 2026
Overview
OM FlexGrid Rigid PCB is an open-source printed circuit board by Open-Muscle, from the Open-Muscle/OpenMuscle-FlexGrid repository on GitHub, published under the CERN-OHL-S-2.0 licence. It is a 4-layer board of 33 × 65.5 mm with 65 parts on 89 nets, routed with 899 tracks and 110 vias.
It is built around the ESP32-S3-WROOM-1-N16R8, CD74HC4067M and ICM-42688-P, with the TPS7A03DQN, USBLC6-2SC6 and BAT54C among its other parts. Its parts include 21 resistors, 11 capacitors, 8 connectors, 6 ICs and 5 diodes. It belongs with the sensors and measurement and wearables boards and the ESP32 boards of this library.
Main components
6
ESP32-S3-WROOM-1-N16R8
SMD,25.5x18mm-103.5dBm -40℃~+65℃ 2.4GHz 20.5dBm 355mA 3V~3.6V 95mA ESP32-S3R8 On-board PCB Antenna UART、SPI、I2C、GPIO、I2S、USB SMD,25.5x18mm WiFi Modules ROHSEspressif SystemsWiFi Modules
CD74HC4067M
SOIC-24-300mil-55℃~+125℃ 16 160Ω 16:1 22ns 2V~6V 345ns 365ns 89MHz Bidirectional analog channel、Glitch-free switching SOIC-24-300mil Analog Switches, Multiplexers ROHSTexas InstrumentsAnalog Switches, Multiplexers
ICM-42688-P
LGA-14(2.5x3)-40℃~+85℃ 1.71V~3.6V 16bit 2KB 7.5uA IMU (accelerometer + gyroscope) SPI、I2C X,Y,Z X,Y,Z ±16g ±2000dps Motion Event Detection, Synchronization, Timestamp Support LGA-14(2.5x3) Accelerometers ROHSTDK InvenSenseAccelerometersTPS7A03DQN
UncategorisedTexas Instruments
USBLC6-2SC6
SOT-23-60.35pF、0.8pF 100nA 150W@8/20us 15V 2 5V 6A@8/20us 6V ESD SOT-23-6 ESD and Surge Protection (TVS/ESD) ROHSUMWESD And Surge Protection (TVS/ESD)
BAT54C
SOT-231 Pair Common Cathode 200mA 2uA@25V 30V 600mA 800mV@100mA SOT-23 Schottky Diodes ROHSNexperiaSchottky Diodes
README
README.md🧠 OpenMuscle-FlexGrid
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.
🚀 Current revisions
V4 (current, validated). Fabricated at JLCPCB in June 2026 (10-unit batch, single-side SMT), brought up 2026-06-23 and in use since. Two V4 bands were assembled, flashed with FlexGridV4-Firmware v4.0.1 and shipped as the first OpenMuscle starter kit in October 2026. V4 is the best-performing FlexGrid revision to date and the one to build. It 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. It carries forward the V3 power and interconnect architecture, 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 plus hand-soldering of bottom-side parts and through-hole connectors. The design files are now at board revision V4-2 (2026-11-03): USB presence sensing for the firmware, vias moved out of the SMD pads, USB data lines re-routed as a pair. V4-2 has not been fabricated yet, and its BOM, placement and Gerber files are still the June 2026 as-ordered set. Full status, bring-up findings and the fab checklist are in the V4 README.
V3 (previous, validated 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. Firmware: V4 bands run FlexGridV4-Firmware; V3 boards run FlexGridV3-Firmware.
| Revision | Status | Notes |
|---|---|---|
| V4 | 🟢 Validated (current) | microSD + RGB LED + slimmer reorient; 10.5 mm FFC tail; 100 pF ADC caps; fabbed 2026-06, in starter kits since 2026-10; design files at V4-2 (USB sensing, vias out of pads, USB pair; not yet fabbed) |
| V3 | 🟢 Validated (previous) | 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.
🧬 Overview
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
📁 Hardware Design Files
Design files are organized by board type and version:
🔌 KiCad Schematics & PCB Layout
📂 KiCad/ — all design files, organized by revision.
| Revision | Path | Description |
|---|---|---|
| V4 (current) | KiCad/OM-FlexGrid V4/ | Validated. microSD socket, RGB status LED, slimmer reorient, 10.5 mm FFC tail, 100 pF ADC caps. See V4 README. |
| V3 (previous) | 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.
📦 Bill of Materials
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). This is the June 2026 as-ordered V4 set; the V4-2 additions (R19, R20, R21) are not in it yet. 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.
🛠 Assembly & Testing
For V4: the build video covers hand-soldering the parts JLCPCB does not populate, BRINGUP.md in the firmware repo covers flashing, and the band reference explains every button and light pattern. Recording, training and inference software lives in OpenMuscle-Software. For the wider picture see the OpenMuscle Hub and the videos on YouTube Open Muscle or TURFPTAx Youtube.
🤝 Contributions
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.
Parts
65| Qty | Value | Footprint | References |
|---|---|---|---|
| 7 | 10k | Resistor_SMD:R_0603_1608Metric | R10, R11, R12, R13, R14, R15, R19 |
| 5 | 100k | Resistor_SMD:R_0603_1608Metric | R7, R8, R9, R20, R21 |
| 5 | SW_Push | OpenMuscleDevKit:EVQP2P02M | BOOT1, MENU1, SELECT1, SW_PWR1, SW_RST1 |
| 4 | 100 pF | Capacitor_SMD:C_0603_1608Metric | C12, C13, C14, C15 |
| 4 | MountingHole_Pad | MountingHole:MountingHole_2.2mm_M2 | H1, H2, H3, H4 |
| 3 | 330 | Resistor_SMD:R_0603_1608Metric | R16, R17, R18 |
| 3 | 5.1K | Resistor_SMD:R_0603_1608Metric | R1, R2, R6 |
| 2 | 2.2 uF | Capacitor_SMD:C_0603_1608Metric | C8, C11 |
| 2 | 4.7uF | Capacitor_SMD:C_0805_2012Metric | C6, C7 |
| 2 | IRLML2060 | Package_TO_SOT_SMD:SOT-23 | Q1, Q3 |
| 1 | 0.1 uF | Capacitor_SMD:C_0603_1608Metric | C10 |
| 1 | 100 nF | Capacitor_SMD:C_0603_1608Metric | C5 |
| 1 | 100 uF | Capacitor_SMD:C_0603_1608Metric | C9 |
| 1 | 150 | Resistor_SMD:R_0603_1608Metric | R5 |
| 1 | 1K | Resistor_SMD:R_0603_1608Metric | R3 |
| 1 | 1N4007 | Diode_SMD:D_SOD-123 | D4 |
| 1 | 1N5819 | Diode_SMD:D_SOD-123 | D1 |
| 1 | 2k | Resistor_SMD:R_0603_1608Metric | R4 |
| 1 | BAT Terminal | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | J2 |
| 1 | BAT54C | Package_TO_SOT_SMD:SOT-23 | D3 |
| 1 | CD74HC4067M | Package_SO:TSSOP-24_4.4x7.8mm_P0.65mm | U1 |
| 1 | CHRG LED | LED_SMD:LED_0805_2012Metric | D2 |
| 1 | Conn_01x02 | Connector_PinHeader_2.00mm:PinHeader_1x02_P2.00mm_Vertical | J5 |
| 1 | Conn_01x02_Pin | Connector_PinSocket_2.00mm:PinSocket_1x02_P2.00mm_Vertical | J7 |
| 1 | Conn_01x03_Pin | Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical | J6 |
| 1 | Conn_01x04 | Connector_PinHeader_2.54mm:PinHeader_1x04_P2.54mm_Vertical | SCRN1 |
| 1 | Conn_01x06_Pin | Connector_PinHeader_1.27mm:PinHeader_2x03_P1.27mm_Vertical | J1 |
| 1 | Conn_01x20 | OpenMuscleDevKit:687120183722-20P-Bottom | J3 |
| 1 | ESP32-S3-WROOM-1-N16R8 | footprints:ESP32-S3-WROOM-1-N16R8 | U2 |
| 1 | ICM-42688-P | Package_LGA:LGA-14_3x2.5mm_P0.5mm_LayoutBorder3x4y | IC1 |
| 1 | LED_RGB | LED_SMD:LED_RGB_PLCC-6 | D5 |
| 1 | LTC4054ES5-4.2 or STC4054GR | Package_TO_SOT_SMD:TSOT-23-5 | U4 |
| 1 | MAX16054 | Package_TO_SOT_SMD:TSOT-23-6 | MAX1 |
| 1 | Micro_SD_Card | footprints:CONN_503398-1892_MOL | J9 |
| 1 | TPS7A03 | Package_TO_SOT_SMD:SOT-23-5 | U3 |
| 1 | USBLC6-2SC6 | Package_TO_SOT_SMD:SOT-23-6 | U5 |
| 1 | USB_C_Receptacle | Connector_USB:USB_C_Receptacle_HRO_TYPE-C-31-M-12 | J4 |
| 1 | VP0610T or BSS84 | Package_TO_SOT_SMD:SOT-23 | Q2 |
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Questions
How big is the OM FlexGrid Rigid PCB PCB?
It measures 33 × 65.5 mm and has 4 copper layers, 1.6 mm thick.
What parts does the OM FlexGrid Rigid PCB use?
65 parts, built around the ESP32-S3-WROOM-1-N16R8, CD74HC4067M, ICM-42688-P and TPS7A03DQN. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the OM FlexGrid Rigid PCB KiCad files?
From the Open-Muscle/OpenMuscle-FlexGrid repository on GitHub, at the commit this page was made from: the board is KiCad/OM-FlexGrid V4/OM-FlexGrid-Rigid-PCB/OM-FlexGrid-Rigid-PCB.kicad_pcb and its schematic KiCad/OM-FlexGrid V0/OM-60-Flex/OM-60-Flex.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the OM FlexGrid Rigid PCB design in my own project?
Its repository publishes it under the CERN-OHL-S-2.0 licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).