Hardware
uMyo is a single-channel wearable EMG sensor with a full motion sensor and its own radio. 47 × 22 × 2.5 mm (~6.5 mm thick at the connector), 9 g with dry electrodes. Certified open-source hardware — OSHWA UA000003.
On the board
Section titled “On the board”| Function | Part | Notes |
|---|---|---|
| EMG front-end | AD8293G160 instrumentation amp (with bias compensation) | gain 160, ~500 Hz bandwidth — sets the EMG frequency ceiling; feeds the nRF52’s built-in ADC, no external ADC |
| MCU + radio | nRF52832 BLE SoC | ARM Cortex-M4F; BLE + 2.4 GHz direct radio; 2.45 GHz, 4.91 dBi chip antenna |
| IMU | LSM6DS3TR-C | 16-bit; accel ±2 g (16384 LSB/g) + gyro ±500 dps |
| Magnetometer | QMC5883P | 3-axis |
| Protection | PTC resettable fuse | short-circuit protection |
| Control | tact switch | power on/off + radio-mode cycle |
| Power | 2 × JST-PH 2.0 mm connectors + BAT+/GND pads | battery/charger, or daisy-chain power; solder pads for a direct battery |
| Indicator | RGB LED | muscle-activity level + radio mode |
| Wearable | two bracelet loops | thread the bracelet through; dry electrodes sit against the skin |
Signal
Section titled “Signal”- 1 EMG channel, sampled at ~1150 Hz (8 samples/frame → ~144 frames/s). One 8-sample gap appears every few seconds when the ADC pauses to check the battery — invisible for control, a minor artefact for raw analysis.
- Digital mains-noise filter — 50/60 Hz, auto-detecting, on-device (firmware).
- On-device: a 4-bin FFT and an IMU-fused quaternion (±32000 = ±1.0). What the numbers mean → Signal.
- Design note: the AD8293’s high input bias current is tamed with a filtered PWM bias through a 10 MΩ resistor — the full story is in uMyo history.
Electrodes
Section titled “Electrodes”- Dry metal — the metal button contacts; worn with the bracelet. Reusable, no gel. This is the intended way — the bracelet and the whole device are built around it.
- Wet / gel — snap connectors for disposable gel electrodes. They need soldering or a firm push to hold, and gel signal is cleaner than the real dry-electrode use case — a niche option, not the default.
Power & charging
Section titled “Power & charging”- LiPo (recommended): 3.7 V, JST-PH 2.0 mm 2-pin (mind the black/red order), or solder to the BAT+/GND pads. ~11 mAh draw → a 220 mAh cell ≈ 20 h. One battery can power several uMyos via the JST daisy-chain.
- Charging: USB-C, via a separate LiPo charger PCB — or any TP4056-style LiPo charger. Details, and how to attach/solder a cell → Powering & charging.
Firmware & radio
Section titled “Firmware & radio”- Three radio modes — 🟢 base · 🩷 nRF24 · 🔵 BLE → Connectivity.
- OTA firmware updates → Firmware.