OpenMuscle FlexGrid V4 - Unboxing & Setup

Hand-soldering the OpenMuscle FlexGrid V4: the parts JLCPCB doesn't populate. After the V4 boards came back from JLCPCB with the top-side SMT assembled, there's still a handful of components to add by hand before the band comes alive. In this video I solder the rest: the bottom-side chips, the connectors, and the new microSD socket. FlexGrid is a 60-sensor pressure-myography wearable that reads forearm muscle movement and predicts finger motion with machine learning. Fully open hardware, fully open source. V4 adds onboard microSD storage, an RGB status LED, and a slimmer board. WHAT I HAND-SOLDER IN THIS BUILD U2: ESP32-S3-WROOM-1 module (the controller) U1: CD74HC4067 analog mux (bottom side) microSD socket, SPI mode (Molex 5033981892 / LCSC C428492) Wurth 687120183722 FFC connector (the flex-to-rigid interconnect) USB-C connector (power + data) Through-hole pin headers and JST connectors BUILD IT YOURSELF (all files, open source) FlexGrid V4 hardware (KiCad, BOM, schematic + PCB PDFs, gerbers): https://github.com/Open-Muscle/OpenMu... Full hand-soldered parts list, by reference designator with solder-difficulty notes: https://github.com/Open-Muscle/OpenMu... V4 firmware (MicroPython, ESP32-S3): https://github.com/Open-Muscle/FlexGr... Step-by-step flashing guide: https://github.com/Open-Muscle/FlexGr... All OpenMuscle repos: https://github.com/Open-Muscle Project site: https://openmuscle.org TWO GOTCHAS (documented in the repo for fellow builders) The USBLC6 ESD chip needs a 180-degree rotation on this fab batch (schematic fix already landed for the next order). The as-ordered IMU is a TOKMAS rebrand, not genuine InvenSense; the V4 firmware auto-detects both variants. Full bring-up notes in the V4 README. A 10-board batch landed at about $341 total (~$35/board for the JLCPCB half). Open hardware under CERN-OHL-S 2.0, firmware under MIT. CHAPTERS 0:00 Boards arrive from JLCPCB 0:52 FlexGrid V3 vs V4 1:14 What's left to hand-solder 1:40 Solder paste and placing parts 2:10 The ZIF (FFC) connector 2:45 Reflow and solder-wick cleanup 3:20 USB-C connector 4:12 Back side: ESP32 and multiplexer 6:25 Populating the buttons 7:12 Fixing the ESD chip (rotate 180) 7:33 Mating the flex sensor and first power-on 8:01 Velostat and cloth housing 9:37 Outro #OpenMuscle #OpenHardware #PCB #Soldering #ESP32 #KiCad #JLCPCB #Electronics #DIY #Prosthetics #Wearable #MicroPython