Specifications

32
Battery
Secondary
Microcontroller
SHT21
Temperature and
Relative Humidity
Sensor
PIC24F04KA201
Secondary
Microcontroller
MRF24J40MB
ZigBee Wireless
Transceiver
SPI Interface I
2
C Interface
Ground
Power
Figure 9 Secondary Microcontroller Interfacing
2.4 Relays
Heating, Cooling, and Air Circulation is accomplished with the help of relays that
act as switches to turn on and off these systems. The relays are triggered by
digital logic as a result of readings from temperature and humidity sensors. In all
of the relays that we have encountered in our research the one that would be
best be suited for our design is a normally closed switching electronic relay. In
the HVAC control we will use relays to activate the output to the heating, air
conditioning and air circulation in response to changes in inside and outside air
temperature depending on the settings selected by the user via the LCD touch
screen display.
The main control unit will allow the user to set a specified temperature and
humidity comfort setting. The NC (normally - closed) relay will be closed and
activate the specific circuit, or opened to deactivate the circuit in order for the
temperature and humidity to be achieved. The tolerance and range of the
temperature and humidity sensors will have a direct affect on the output of the
relays and the activation or deactivation of each of the three systems.