Changing architecture

A project log for Human Limb Tracking

A system that tracks limb movement of people who have movement disorders to assist in diagnosis and therapy

Jonathan KellyJonathan Kelly 08/13/2016 at 01:100 Comments

Having wires to each sensor introduces problems with the wires getting tangled and in the way when moving, connector integrity, issues with transmission of the I2C signals for sensors attached a long way from the controller, the need to wear a controller on the body and difficulty attaching the sensors.

I want to move this to a wirelss solution.

I have been experimenting with using ATMEL atsamr21 type devices. These devices combine an ARM processor with a low power 2.4GHz wireless module and are being pushed for use in "IOT" type applications.

They have low power consumption, are cheap and small.

The small size of the units means I think I can create a small node with an IMU (Inertial Measurement Unit) , processor and wireless, that would remove the need for the controller device (the current body worn Raspberry PI) and move a lot of the maths processing of the IMU data to the sensor node itself.

This will simplify things a lot.

Currently I have a hacked up system working that uses the MPU9150 IMU sensors, hooked up to various atsamr21 boards (atsamr21-xpro and atsamr21b-mz210pa) to get the code working and see if it is feasible.

I am using the RIOT OS operating system to manage the nodes, it also allows me to access a shell like interface to each node while I am working. I have forked a version of RIOT to allow me to add support for the XPRO and 21b-mz210pa boards plus add some bits I need to make it work.

The processor on each board is calculating quaternions representing the physical orientation of the IMU chip it is connected to and sending that using a 6lowPAN network to a edge router (currently an ATSAMR21ZLL-EK evaluation board) that connects to a PC running a web service allowing browser applications to track the sensors.

The next step is to move to making a small node that houses the processor, IMU and power source that can easily be attached to the body.

I will update the parts list and links to code for my forked RIOT and the nodes themselves on GitHub soon.