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Microcontroller Setup Guide

Initial Setup

  1. Factory reset the device
  2. Install UF2 bootloader

File Deployment

Copy all files from the microcontroller/ directory to the device, excluding the setup_circuitpython/ folder.

Directory Structure

microcontroller/
├── code.py                 # Main program file
├── ble_json_service.py     # BLE service implementation
├── config.json             # User configuration file
├── default_config.json     # Default configuration file
└── lib/                    # Required libraries
    ├── adafruit_ble/
    ├── adafruit_bus_device/
    ├── adafruit_register/
    ├── adafruit_pixelbuf.mpy
    ├── cedargrove_nau7802.mpy
    └── neopixel.mpy

Operation Guide

Serial Console Output

To monitor the serial output while usb-c connected:

  1. Find the device ID:
ls /dev/tty.*
  1. Connect to the serial console:
screen [device_id]

For more information on using the serial console, see the CircuitPython Advanced Serial Console Guide

LED Status Indicators

The onboard NeoPixel LED indicates the device's current status:

  • Red: Error state or initializing
  • Yellow: Waiting for BLE connection
  • Green: Connected to a BLE device

Sensor Functionality

The device provides two sensor measurements:

  1. Weight Sensor: Uses the NAU7802 load cell amplifier to measure weight. The raw values are averaged over multiple samples (configurable) and scaled according to the configuration.
  2. Voltage Sensor: Reads analog voltage from pin A2, converts it to a percentage based on configured offset and scale factors.

BLE Service

The device advertises a custom BLE service with the following characteristics:

  1. Sensors Characteristic (Read-only)

    • UUID: 528ff74b-fdb8-444c-9c64-3dd5da4135ae
    • Provides real-time sensor data in JSON format: 
      {
  "weight": <value>,
  "voltage": "<percentage>%"
}

  2. Settings Characteristic (Read/Write)

    • UUID: e077bdec-f18b-4944-9e9e-8b3a815162b4
    • Allows reading and updating device settings

Configuration

The device uses a configuration file (config.json) with fallback to default_config.json. Configuration options include:

  • device_name: BLE advertisement name
  • weight_samples: Number of samples to average for weight measurement
  • weight_scale_factor: Scaling factor for weight measurements
  • voltage: Configuration for voltage sensor:
    • offset: Voltage reading offset
    • scale_factor: Voltage scaling factor