Specifications

20
microcontroller to ensure we develop the main microcontroller to operate to their
exact specifications. The performance of the main microcontroller is truly a
“make or break” aspect of the Efficient HVAC Control and Feedback System that
we are developing. The section below describes the research conducted to find
the most appropriate microcontroller for the given set of requirements. The
following are some topics that need to be addressed:
Microcontroller Compatibility with Other Components:
The main microcontroller must interface with a ZigBee wireless chip, an 802.11b
wireless chip, a Sensirion SHT21 temperature and relative humidity sensor and
an Evervision LCD display. Both the ZigBee and the 802.11b chip come from the
www.microchipdirect.com website. Since two of the four devices required to
interface with the main microcontroller were sold by Microchip, we decided to
start our search there.
Footprint and size of microcontroller constraints and
mounting style:
All of our components will be placed on printed circuit boards and since pricing
for printed circuit boards is dependent on the size, our design will be as space
efficient as possible. In order to keep the PCB as small as possible, we will
choose the smallest part available that meets our criteria. We plan on surface
mounting as many of the components as possible, so when it is an option we will
always pick the product that is made to be surface mounted. We have chosen to
go with as many surface mount products as possible because they are generally
smaller than their through hole counterparts and are more cost effective. The
main microcontroller will be small and only account for a small percentage of the
overall layout of the main control unit printed circuit board design.
Analog to digital and digital to analog converters:
When exploring microcontroller options, we have found that most
microcontrollers have at least one internal analog to digital converter. We may
need to make use of a converter when sending wireless information within our
system, or when communicating with the router that will connect the system to
the internet. Therefore, at this point we are only considering microcontrollers that
have at least one analog to digital converter onboard.
Input / Output Ports:
Input / Output ports are how the microcontroller will interface to the other
components of the system. For our project, the main microcontroller must
communicate with a temperature and relative humidity sensor (2 I/O ports), a
ZigBee wireless chip (4 I/O ports), an 802.11b wireless chip (4 I/O ports), and to
the LCD display (3 I/O ports). This comes to a total need of 13 I/O ports for the