P10010: Motion Tracking Sensor
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Wireless Communication Research

Wireless Communications methods for tranfering data from MCU to PC


In order to find the most appropriate method of wireless comm, a few constraints need to be taken
into account:


RF Power
The transmitter power needs to be minimal in order for the system to be power efficient.


Range
Since the device will be used indoors (supposedly in a room), it should be short range, which also helps in power efficiency.


Frequency and Data rate will also have to be taken into account at some point, after more information
is gathered about the project requirements and constraints.


I consulted Dr. Kwasinsky (CE faculty), and he advised two protocols: Bluetooth and ZigBee, which are
IEEE 802.14.2 and 802.14.4 standards respectively.


Moreover, we leaned towards bluetooth, as it is already implemented on most computers or off-the shelf dongles. We'd need an additional module supporting ZigBee, attached to the PC if we were to use the ZigBee standard.



The trick is to decide which interface should be used. Some MCUs have USB interfaces, and some have
serial. There is the UART (Universal asynchronous receiver/transmitter) interface, which can be found
on many MCUs like the TI MSP430 (very power efficient MCU).


For serial interfaces, there bluetooth adapters like the these: http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=42972
http://www.sparkfun.com/commerce/product_info.php?products_id=8550


For USB interfaces there are a few PIC MCUs (PIC18F2455 PIC18F2550 PIC18F4455 PIC18F4550):
please refer to PIC.pdf


The problem with USB interfaces is that MCUs only implement the slave side of the USB, so the
device cannot start a communication. In order to work around this, the interface needs to be converted to USB host.
One way to do this is using Maxim's MAX3421E USB peripheral/host controller,
and then using a bluetooth dongle to provide the communication.


Assuming the MCU controls the comm link, this last method seems much less viable in terms of cost, implementation difficulty
and time constraints, unless we think of switching the slave/master relation, so that instead of the MCU controling the communication,
the application in the PC would
request that data be sent at a certain intervals (refresh rate), thus making it the master.
The Maxim controller would then no longer be needed, simply the USB interface, which can be prebuilt in
the MCU.