Part of Research Notes of Kristof Van Laerhoven. Last update: Tuesday, 25 May 2004 11:00:18 +0100
The 'Spine'
The Spine is a wired approach to a linear distributed network of accelerometers, controlled by a single microcontroller. Twenty acceleration signals are being streamed via the controller to a serial line, so this multi-dimensional data can be stored or processed at fairly high rates at a host PC (often wearable or portable). The origin of the name should become obvious when looking at the two spines in the picture below:
The Spine is a progression of the 30-accelerometer outfit constructed earlier, and uses the same sensor modules. The new PIC microcontroller (an 18F452) is pin-compatible with the previous 16F877, but operates at twice the clock speed (40Mhz) and has more memory. The number of sensors has been reduced to 20 to allow a faster and more reliable throughput of sensor data. The 2D acceleration sensors (ADXL202JE) are placed at approximately 10 centimetre distances from each other, making a total length of the spine around one metre, which should be sufficient to strap to an average arm or leg. Each package requires two 100nF capacitors (one for each axis, to set the bandwidth) and one 68kOhm resistor to set the pulse width:
One of the ADXL202JE sensors provides two acceleration signals (in the X and Y directions) that are scaled to an 8-bit value (i.e., between 0 and 255). These small boards can be taken off in case of sensor failure or for debugging / replacing.
A strong cable connects all power and ground pins, and routes the signal cables to the microcontroller via tiny Molex connectors. At each point where a connector is provided for the sensor boards, the cable has been re-sealed with a glue-gun to make the whole setup as durable as possible. Needless to say that the majority of the production time for a spine goes into the soldering of the cabling. The main unit is able to read all accelerator values at least 50 times per second (so at 50Hz minimally) with ASCII output via the serial port, which should be more than enough for our purposes; higher speeds can be obtained by changing the serial output modus (i.e., in binary) or the individual accelerometers. The main unit is encased in a generic black shell with a 9V battery compartment, again to protect the hardware:
Each Spine runs the IPANTS v1.5 system that can be controlled via the serial port (at 115200 baud, 8b1, no parity); users may choose for either binary or ASCII output, that is either polled for or continuously streamed.
Experiments with Spines. Below are some images of the Spines being worn during some basic activities that we wanted to recognise.
And of course the obligatory plots:
Datasets (in txt format):
Dikaios, Raw data in one chunk
Nicolas, Raw data in one chunk
Dikaios, All static activities
Nicolas, All static activities
Dikaios, Walking
Nicolas, Walking
Nicolas Running
Dikaios, Walking upstairs
Dikaios, Walking downstairs
Last updated by Kristof Van Laerhoven, 25/05/2004 11:00:18 +0100