EPD 3D G6 — Orthomate

Battery-powered adaptive orthopedic insole controller. Redistributes plantar pressure in real-time using three micro linear stepper actuators driven by force sensor feedback. Includes a BLE companion Android app for live monitoring.

Hardware at a glance

Component	Detail
MCU	ESP32-C6 SuperMini
Stepper drivers	3× TMC2209 (STEP/DIR mode, ENN hardwired LOW on PCB)
Actuators	3× micro linear bipolar stepper
Pressure sensors	4× FSR (R1 1kΩ + C 100nF RC filter per channel, R2 10kΩ pull-down)
Display	0.91" OLED (SSD1306, I2C)
Charger	TP4056 Type-C
Boost converter	XL6009 → 5 V system rail
Battery	1S LiPo 2000–3000 mAh
User input	1× momentary mode button
BLE	NimBLE-Arduino 2.5.0 — advertises as EPD3DG6

Repository structure

orthomate/
├── Electronics Reference.txt   # Hardware design spec (v6.0)
├── BOM.txt                     # Bill of materials
├── firmware/
│   ├── main/                   # Full operational firmware (PlatformIO)
│   │   ├── platformio.ini
│   │   └── src/main.cpp
│   ├── ARDUINO IDE APP TEST/   # Minimal Arduino IDE sketch for BLE app testing
│   │   └── sketch_apr14a/sketch_apr14a.ino
│   ├── stepper_test/           # Single-axis stepper back-and-forth smoke test
│   ├── homing_test/            # Blind homing: retract to min, extend to 12 mm
│   ├── button_test/            # Button + OLED input test
│   └── oled_test/              # OLED display test
├── android_app/                # Kotlin/Compose BLE companion app
│   ├── app/src/main/java/com/epd3dg6/bleapp/MainActivity.kt
│   └── app/src/main/AndroidManifest.xml
├── kicad pcb/                  # KiCad schematic + layout files
├── drill files/                # Gerber drill files (latest PCB)
└── docs/
    ├── FIRMWARE_MAIN.md        # Detailed firmware walkthrough
    ├── FLASH_GUIDE.md          # PlatformIO build & upload instructions
    ├── ANDROID_APP_GUIDE.md    # Android app build & sideload instructions
    └── TMC2209_CURRENT_TUNING.md

Firmware — operational logic

The main firmware (firmware/main/) implements a full fitting cycle driven by one button:

DISCONNECTED ──[plug in]──► CONNECTED ──[btn]──► MEASURING
                                                      │ (auto)
                                                  MEASURED ──[btn]──► ACTUATING
                                                                           │ (auto)
                                                                         DONE ──[unplug]──► DISCONNECTED
                                                                         (insole retains shape)

On next plug-in with actuators extended:  DISCONNECTED ──► HOMING ──► CONNECTED

Mode	Behaviour
CONNECTED	Idle; shows battery %, BLE status on OLED
MEASURING	Reads all 4 FSR channels, 7-sample median filter, computes relative load fractions
ACTUATING	Drives each actuator inversely proportional to region load — lowest load = largest extension
DONE	Holds position; unplug to use insole as-is
HOMING	Auto-triggered on reconnect when actuators are extended; retracts all to home

Extension formula: $ext_i \propto (1 - r_i)$ where $r_i = F_i / \sum F$

BLE — Android companion app

The ESP32 advertises a GATT service and notifies a JSON payload at ~4 Hz:

{"fsr1": 42, "fsr2": 18, "fsr3": 75, "mode": "MEASURING", "batt": 67}

BLE field	Value
Device name	EPD3DG6
Service UUID	4fa0c560-78a3-11ee-b962-0242ac120002
Characteristic UUID	4fa0c561-78a3-11ee-b962-0242ac120002 (NOTIFY + READ)
Notify rate	~4 Hz (every 250 ms)
MTU	185 bytes

The Android app (android_app/) displays real-time FSR forces as animated colour circles, current mode, battery %, and BLE status. See docs/ANDROID_APP_GUIDE.md for build and install instructions.

GPIO assignment (ESP32-C6 SuperMini, Hardware Ref v6.0)

GPIO	Function
0	FSR1 METATARSAL (ADC, 11 dB attenuation)
1	FSR2 ARCH (ADC, 11 dB attenuation)
2	FSR3 CALCANEUS (ADC, 11 dB attenuation)
3	FSR4 AUX (ADC, 11 dB attenuation)
4	MODE_BUTTON (INPUT_PULLUP) — boot-safe
5	VBAT_SENSE (ADC1 ch5, 11 dB attenuation, 1:2 divider)
6	OLED SCL (I2C)
7	OLED SDA (I2C)
14	ACT2_DIR
15	CONN_DETECT (INPUT_PULLDOWN)
16	ACT3_STEP
17	ACT3_DIR
18	ACT2_STEP
19	ACT1_DIR
20	ACT1_STEP

Quick start

• Flash firmware: docs/FLASH_GUIDE.md
• Install Android app: docs/ANDROID_APP_GUIDE.md
• Firmware internals: docs/FIRMWARE_MAIN.md

Design rules

• Charging and actuator operation are mutually exclusive — never simultaneous.
• Never start all 3 motors simultaneously — stagger motor starts by 75 ms.
• Sample FSRs only when motors are idle; use 7-sample median filtering with 4 ms settling per sample.
• ADC attenuation must be set to 11 dB (ADC_11db) on all analog pins for correct readings at the operating voltage range.
• VBAT < 3.35 V → disable actuators; VBAT < 3.5 V → show low battery warning.
• OLED updates are content-cached — only redraws when text changes (prevents I2C writes during motor current spikes).

License

MIT — see LICENSE