Specifications

97
wireless chip. After considering readings from the sensors, the web server, and
LCD user interface; the Main Control Unit must come to a decision as to what
course of action to take.
The Main Control Unit then controls the appropriate components of the HVAC
system such as the compressors, air handlers, and dehumidifiers. The Main
Control Unit is designed and programmed to use the least energy possible while
satisfying the conditions set by the user. The Main Control Unit is responsible for
updating the LCD controller with current conditions as well as connecting to the
internet to update the web server with current interior and exterior conditions
associated with the building. Figure 49 shows a basic outline of the user case
processes that happens in the main control system of the Efficient HVAC Control
and Feedback System that we have designed.
User
Power Relays
Adjust Comfort
Settings
Adjust Venting
System
Adjust Settings
Adjust Power
Settings
«extends»
«extends»
Get Sensor Readings
Process HVAC
Control
«uses»
«uses»
Main Control System
Wireless Sensor
Humidifier
AC1
AC2
Venting
Figure 49 - Outline of the User - Case Processes for the Main Control Unit
Our secondary microcontroller incorporates three serial communication
peripherals such as an SPI, I
2
C, and UART modules. The secondary
microcontroller primary task is to take in the data from the SHT21 sensor.
Another component of the secondary microcontroller is the remote battery to
power it. We decided on using the alkaline (AA) battery because compared to
most other batteries it had significant battery life, capacity (in mA/h), and low -
self discharge rate. Also to store the battery we are going to use some type of
box that is weather-proof so that it won‟t short circuit the power connection from
the battery to the secondary microcontroller. The secondary microcontroller uses
a C compiler with a 16 – bit wide data path, and 512 bytes of RAM data memory.
It also incorporates 18 I/O pins that are designed to be programmed to work with
the SHT 21 sensor and the Zigbee RF transceiver. Lastly, it also has Analog to
Digital Converters that are intended to transfer input analog voltages into a digital
number that are directly proportional to the input voltage or current. In Figure 50