Pico W 6DOF BLE Sensor

This project implements a 6 Degrees of Freedom (6DOF) sensor application on a Raspberry Pi Pico W, exposing sensor data (accelerometer, magnetometer, orientation, and on-board temperature) via Bluetooth Low Energy (BLE).

The primary sensor used is the LSM303DLM, which provides 3-axis acceleration and 3-axis magnetic field data. This data is processed to calculate pitch, roll, and heading (both raw and tilt-compensated).

Features

• Reads 3-axis accelerometer and 3-axis magnetometer data from an LSM303DLM sensor.
• Calculates orientation:
  • Pitch
  • Roll
  • Heading (uncompensated/raw)
  • Heading (tilt-compensated)
• Applies a moving average filter to sensor readings for smoother output.
• Reads the Pico W's on-board temperature sensor.
• Exposes sensor data via BLE GATT services:
  • Device Name
  • Temperature (Environmental Sensing Service)
  • Custom service for Orientation data (Pitch, Roll, Headings) and Sample Rate.
• Allows configuration of the sensor data sample rate via BLE.
• Provides notifications for sensor data updates.
• Toggles the on-board LED as a heartbeat indicator.
• Uses I2C for communication with the LSM303DLM sensor.

Hardware Requirements

• Raspberry Pi Pico W
• LSM303DLM sensor module (or compatible)
• Connecting wires

Software & Libraries

• Pico SDK
• BTstack library for Bluetooth Low Energy functionality
• CYW43 wireless driver

BLE GATT Profile

The BLE services and characteristics are defined in 6dof_sensor.gatt. Key characteristics include:

• GAP Service:
  • Device Name: picow_sense (Read)
• Environmental Sensing Service (ORG_BLUETOOTH_SERVICE_ENVIRONMENTAL_SENSING):
  • Temperature (ORG_BLUETOOTH_CHARACTERISTIC_TEMPERATURE): Read, Notify, Indicate, Dynamic
• Custom Orientation Service (UUID: 19B10010-E8F2-537E-4F6C-D104768A1214):
  • Sample Rate (UUID: 19B10012-...): Read, Write Without Response, Dynamic (uint16_t, Hz)
  • Orientation Pitch (UUID: 19B10013-...): Read, Notify, Dynamic (float32, degrees)
  • Orientation Roll (UUID: 19B10014-...): Read, Notify, Dynamic (float32, degrees)
  • Heading Raw (UUID: 19B10015-...): Read, Notify, Dynamic (float32, degrees)
  • Heading Compensated (UUID: 19B10016-...): Read, Notify, Dynamic (float32, degrees)

User descriptions and format descriptors are provided for clarity.

Setup & Building

1. Clone the repository (or set up your project).
2. Ensure Pico SDK and BTstack are correctly set up in your development environment.
3. Connect the LSM303DLM sensor:
   • SDA to Pico GPIO16 (I2C0 SDA)
   • SCL to Pico GPIO17 (I2C0 SCL)
   • VCC to 3.3V
   • GND to GND
4. Build the project: The 6dof_sensor.gatt file is automatically converted to 6dof_sensor.h during the compilation process (typically found in build/generated/...). Follow the standard Pico SDK build procedure (e.g., using cmake and make).

   mkdir build
   cd build
   cmake ..
   make

5. Flash the .uf2 file to your Pico W.

Usage

1. Power on the Pico W. The on-board LED should start toggling.
2. Use a BLE scanning application (e.g., nRF Connect, LightBlue) on your phone or computer.
3. Scan for BLE devices and connect to "picow_sense".
4. Once connected, you can:
   • Read the current temperature, pitch, roll, and heading values.
   • Subscribe to notifications for these characteristics to receive updates automatically.
   • Read the current sample rate.
   • Write a new sample rate (as a uint16_t value representing Hz) to the Sample Rate characteristic.

Pinout

• I2C0:
  • SDA: GPIO16
  • SCL: GPIO17
• LED:
  • On-board LED (controlled via CYW43)

Code Structure

• main.c: Main application logic, sensor reading, BLE handling, and calculations.
• 6dof_sensor.gatt: Defines the BLE GATT profile.
• lsm303_sensor/: Contains the driver for the LSM303DLM sensor.
• server_common.c/server_common.h: Common BLE server helper functions (assumed).

Constants and Configuration

Key parameters are defined at the top of main.c:

• I2C_PORT, I2C_SDA, I2C_SCL: I2C configuration.
• HEARTBEAT_PERIOD_MS: Interval for BLE updates and LED toggle checks.
• SENSOR_READ_FREQUENCY_HZ: Target frequency for reading the LSM303 sensor.
• MOVING_AVG_SIZE: Size of the window for the moving average filter.
• TEMP_UPDATE_INTERVAL_MS: How often the on-board temperature is read and potentially notified.
• LED_TOGGLE_INTERVAL_MS: How often the LED state is toggled.

License

This project is based on the Raspberry Pi (Trading) Ltd. temp_sensor example code and includes modifications. SPDX-License-Identifier: BSD-3-Clause applies.

Further modifications/tweaks by C Gerrish (Gerrikoio) (c) May 2025.

Acknowledgements

• Raspberry Pi (Trading) Ltd. for the original temp_sensor example.
• Google Code Assist for assistance in generating parts of the LSM303 sensor integration, formulating the orientation data, and in modifying the code for BLE event handling.

---