AD8232 EMG — ESP32-C5 WROOM + OTA

Safety

Note

Use OTA for normal firmware updates whenever possible. Avoid connecting the EMG setup directly to a PC over USB while it is attached to the body, because ground faults, wiring mistakes, or accidental shorts can create an unnecessary safety risk. Use USB only for the initial flash and prefer battery-powered operation during measurements.

Modular multi-channel surface EMG using one or more AD8232 modules and an ESP32-C5 WROOM. Channel count, pin assignment and labels are defined in a single table in firmware/emg_ota/config.h — add a row to add a channel; the API and GUI pick up the new layout automatically. Data streams over WiFi to a Python GUI. The ESP32-C5 WROOM runs on a USB powerbank; flashing is done wirelessly via OTA after the first USB flash.

See also: Roadmap · Single-Channel EMG Guide · Multi-Channel EMG Guide · Changelog · API Reference · License

Wiring — 2× AD8232 → ESP32-C5 WROOM

Each AD8232 module connects to 3V3, GND, SDN (tied high) and three GPIOs. The current two-channel configuration for the ESP32-C5 WROOM:

AD8232 (CH0 — FCR, flexor)       ESP32-C5 WROOM
─────────────────────────────    ──────────────────────────────────────
3.3V    ──────────────────────── 3.3V       (shared rail)
GND     ──────────────────────── GND        (shared rail)
OUTPUT  ──────────────────────── GPIO 4     (ADC1_CH4 — EMG signal CH0)
LO+     ──────────────────────── GPIO 6     (lead-off detect +, CH0)
LO-     ──────────────────────── GPIO 7     (lead-off detect −, CH0)
SDN     ──────────────────────── 3.3V       (always on)

AD8232 (CH1 — ED, extensor)      ESP32-C5 WROOM
─────────────────────────────    ──────────────────────────────────────
3.3V    ──────────────────────── 3.3V       (shared rail)
GND     ──────────────────────── GND        (shared rail)
OUTPUT  ──────────────────────── GPIO 5     (ADC1_CH5 — EMG signal CH1)
LO+     ──────────────────────── GPIO 8     (lead-off detect +, CH1)
LO-     ──────────────────────── GPIO 10    (lead-off detect −, CH1)
SDN     ──────────────────────── 3.3V       (always on)

GPIO 0–3 avoided for ADC output: GPIO 0 carries a BOOT pull-down on most dev boards which corrupts readings. GPIO 9 avoided for LO pins: it is the BOOT/strapping pin with an internal pull-up that causes permanent LEAD_OFF.

ESP32-C5 ADC constraint: only ADC1 pins (GPIO 0–6) work while WiFi is active. Never wire AD8232 OUTPUT to any other GPIO. LO+ / LO- are digital inputs and accept any free GPIO.

Adding or removing modules

Edit firmware/emg_ota/config.h. One row = one module. Update NUM_CHANNELS to match. Re-flash. The API and GUI discover the new layout automatically.

#define NUM_CHANNELS 2   // ← change this number

static const ChannelPins CHANNELS[NUM_CHANNELS] = {
    {  4,  6,  7, "FCR" },   // CH0 — forearm flexor   (palm-up,   near elbow)
    {  5,  8, 10, "ED"  },   // CH1 — forearm extensor (palm-down, near elbow)
 // {  2, 11, 12, "FCU" },   // CH2 — ulnar flexor              (uncomment to add)
 // {  3, 13, 14, "BRD" },   // CH3 — brachioradialis / radials (uncomment to add)
};

Full ADC1 pin reference (ESP32-C5)

Channel	GPIO	Use
ADC1_CH0	GPIO 0	avoid — BOOT pull-down on dev boards
ADC1_CH1	GPIO 1	avoid — strapping pin on some boards
ADC1_CH2	GPIO 2	CH2 OUTPUT (future)
ADC1_CH3	GPIO 3	CH3 OUTPUT (future)
ADC1_CH4	GPIO 4	CH0 OUTPUT
ADC1_CH5	GPIO 5	CH1 OUTPUT
ADC1_CH6	GPIO 6	digital only here (LO+ CH0)

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Electrode Placement (forearm, surface EMG)

Each AD8232 module has three leads: YELLOW (LA+), RED (RA−), GREEN (RL ref). Clean skin with alcohol before attaching. The two active electrodes must be aligned along the local muscle fiber direction, 2–3 cm apart.

CH0 — FCR / flexor side (palm up)

Palm facing UP — inner forearm (volar side)

  Elbow                                          Wrist
    │                                              │
────┤███████████████████████████████████████───────┤────
    │                                              │
    │  [YELLOW LA+]    [RED RA-]      [GREEN RL]   │
    │       │               │              │       │
    │   ~5 cm from      ~3 cm toward   wrist bone  │
    │   elbow           wrist          (ulnar       │
    │   (muscle belly)                 styloid)     │

Cable	Pin	Position
YELLOW	LA+	Muscle belly, ~5 cm from elbow, inner forearm
RED	RA−	2–3 cm toward wrist from YELLOW, same line
GREEN	RL	Wrist bone (ulnar styloid) — bony, no muscle

CH1 — ED / extensor side (palm down)

Palm facing DOWN — outer forearm (dorsal side)

  Elbow                                          Wrist
    │                                              │
────┤███████████████████████████████████████───────┤────
    │                                              │
    │  [YELLOW LA+]    [RED RA-]      [GREEN RL]   │
    │       │               │              │       │
    │   ~4 cm from      ~3 cm toward   wrist bone  │
    │   elbow           wrist          (radial      │
    │   (ED belly,                     styloid)     │
    │    outer forearm)                             │

Cable	Pin	Position
YELLOW	LA+	Extensor digitorum belly, ~4 cm from elbow, outer forearm
RED	RA−	2–3 cm toward wrist from YELLOW, same line
GREEN	RL	Wrist bone (radial styloid) — bony, no muscle

The GREEN reference electrode can be shared between both modules if you place it on a neutral bony site (e.g. ulnar styloid). Use a separate wire from a single electrode to both RL inputs. This reduces electrode count from 6 to 5.

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Setup

1. Credentials

cp .env.example .env
# edit .env — fill in WIFI_SSID, WIFI_PASSWORD, OTA_PASSWORD

2. First flash (USB required once)

./flash.sh

Use USB for the first flash only, with the electrodes disconnected from the body.

3. All subsequent flashes (OTA — powerbank only)

./flash.sh

flash.sh auto-detects: ESP32-C5 WROOM reachable via WiFi → OTA, otherwise → USB fallback. OTA is the recommended update path for safety.

Override OTA host:

OTA_HOST=your-esp32.local ./flash.sh

---

Running

# terminal 1 — API server (connects to ESP32-C5 WROOM, exposes REST)
python3 emg_api.py

# terminal 2 — monitor + auto-launch GUI
./monitor.sh

monitor.sh starts the local API automatically on 127.0.0.1:5555 if it is not already running, then launches the GUI.

Or launch GUI standalone (requires API server running):

python3 gui/emg_gui.py

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Calibration (in GUI)

Each channel is calibrated independently.

1. Pick the channel from the CH dropdown
2. Press CALIBRATE
3. Relax that muscle → press START → hold still for 5 s
4. Tense that muscle / make a fist → press START → hold for 5 s
5. Per-channel threshold is set automatically and saved to calibration.json
6. Calibration loads automatically on next start — no need to redo it

Use RESET ALL in the bottom bar to clear every channel's calibration in one go, or POST /channel/{id}/calibration/reset for a single channel.

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Data Stream

The ESP32-C5 WROOM sends a self-describing CSV stream over TCP on port 8888:

#CH:2,FCR,ED         ← header sent on every new connection
2105,42.3,1890,38.1  ← one line per sample tick: rawN,rmsN per channel
2089,38.7,1875,35.2
LEAD_OFF:1           ← per-channel lead-off pulse, 10 Hz while detached

• raw — 12-bit ADC value (0–4095, center ≈ 2048)
• rms — RMS envelope over a 100 ms window (after DC tracker + 20 Hz HP filter)
• header label list comes from CHANNELS[] in config.h

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Project Structure

AD8232-EMG/
├── firmware/
│   └── emg_ota/
│       ├── emg_ota.ino     ESP32-C5 WROOM firmware (WiFi + OTA + EMG sampling)
│       ├── config.h        pin definitions, sampling config
│       └── secrets.h       generated by flash.sh — do not commit
├── gui/
│   └── emg_gui.py          live GUI with built-in calibration wizard
├── emg_api.py              HTTP REST API server (stdlib only, no pip)
├── monitor.sh              terminal monitor + auto-starts local API + GUI
├── flash.sh                compile + OTA/USB upload
├── .env                    WiFi credentials (gitignored)
├── .env.example            credential template
├── calibration.json        saved calibration (gitignored)
├── API.md                  REST API reference for AI agents
└── README.md

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Ports

Service	Port
EMG REST API	5555
ESP32-C5 WROOM TCP stream	8888
ESP32-C5 WROOM OTA	3232

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Contact

arn-c0de@protonmail.com

License

Released under the MIT License.