What is it?

BlueSense is a 30x30mm extensible platform for wearable motion sensing, sensor research and IoT applications.

It is designed to be functional out-of-the-box yet extensible. It’s primary purpose is to be an inertial measurement unit for wearable applications based on the Invensense MPU9250 and an AT1284p microcontroller. Yet it is extensible for IoT applications with a number of features making it appealing for this purpose.

Wearable motion sensing

As a wearable platform, BlueSense is a tiny device which can be used to capture body movement and orientation with a 9DoF motion sensor. The data can either be logged on an SD card or streamed over USB or Bluetooth 2. BlueSense could be used to prototype a custom fitness tracker. Its extension ports allow to plug-in additional sensor modalities for research purposes. A display is being developed converting it into a smartwatch.

IoT platform

As an IoT device it’s main appeal is a true hardware off which allows to put the device entirely to sleep (everything is powered down, including voltage regulators), yet wake up at programmed intervals thanks to a real-time clock wakeup. This allows to achieve very long battery life, as the device can wake up at desired times (once an hour, once a day, …) to acquire and send sensor data. The extension ports allow to plug in custom sensor modalities which make this device highly versatile.

Firmware

The application firmware has been designed to be useful for a wide range of applications out of the box. It has been optimised for high-speed motion data logging and streaming (500Hz), and high-speed external ADC acquisition (1+KHz), informed by the need of wearable motion tracking and activity recognition applications.

Other features

Besides USB, Bluetooth 2 and SD card interface with a FAT32 compatible filesystem, BlueSense has a real-time clock, a coulomb counter to measure it’s own battery level and power consumption, true hardware off, and connectors for extensions. This makes the platform also suitable for sensor research, IoT applications, or as an compact alternative to other microcontroller boards.

Hardware specifications

• ATmega1284P core (128KB flash, 16KB RAM)
• LTC3553 battery charger and voltage regulator
• 3V regulated power supply
• MPU9250 9DoF motion sensor, with software attitude and heading reference system
• USB interface for charging, device interaction
• RN41 Bluetooth 2 interface for device interaction
• MicroSD card (SDHC standard)
• DS3232 Real-Time Clock, one of the most accurate RTC on the market (+/-5ppm over the entire temperature range, <0.6ppm at identical temperature)
• LTC2942 Coulomb counter allowing precise measurement of battery charge/discharge and characterisation of real-time current consumption by software
• Extension ports with analog inputs, digital I/O, I2C, SPI, timekeeping, etc.
• True hardware off (<70uW) and programmable wake-up by RTC (e.g. for measurements once a day)

Why did you make it?

BlueSense addresses the needs of sensor research (it's an extensible platform) for wearable applications (it has a form factor smaller than what you would get with an Arduino or Teensy), with high-speed motion sensing (up to 500Hz currently, up to 1KHz in upcoming revision) which is useful for sports application or use in robotic setups.

What makes it special?

• It has high speed motion sensing (raw data and orientation as quaternions) up to 500Hz
• Data logging and data streaming
• High accuracy real-time clock: 5ppm over the entire temperature range from -40°C to +85°C; <0.6ppm at identical temperature
• True hardware off
• Extensible
• Open firmware
• Used in science applications