P11011: Modular Motion Tracking Knee Flexion Unit V1
/public/

Interface Control Document

Interface Control Document


Interface between Base unit and sensors must be a single, standardized digital bus protocol. The following options have been considered:
I2C, SPI, RS232, and USB.

The considerations include:

Needs:


The ending choice is USB. This is because USB has a speed capability (400Mhz) that is sure to satisfy our current needs and any future scalable needs to come. Usb also has a very simple and standardized connector type. Usb cables are readily available in any configuration and come fully shielded to protect the signal as it travels across the cable. The expected baseboard for the base unit (Beagleboard) already has Usb 2.0 installed, so there is no hardware design needed on that end. Also, the IMU projected has a usb interface as well. There will be some hw design needed for the knee flexion sensor, but it is simple enough for our time/resource constraints. Usb also has a very low power consumption due to its differential pair signal path. With a differential pair, noise is cancelled out between the two conductors, allowing a clear signal to pass with minimal power required to drown out noise.


The other interfaces listed above were also investigated.


I2C:


SPI


RS232