Specifications

98
shown below, illustrates the block diagram of the secondary microcontroller
which contains the peripheral connection with the different components.
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 50 - Secondary Microcontroller Interfacing
In designing the Efficient HVAC Feedback and Control System there are two
types of relays that are involved with the main control unit. The 24 V AC Control
Relays and the 220/240 V AC Power Relays. Control relays are switches that
can be turned on or off when a decision is made. For the main control unit, when
the control relays are switched on and the decision to turn their specific
component on has been made. The output of each control relay is 24 V AC.
Next is the 220/240 V AC Power Relays which are located outside at the
compressor and at the inside air handler. When the power relay is turned to the
on - position, the 220/240 V AC is connection to the compressor or the air
handler. It will run until the main control unit decides when it is time to stop and
the relay in return is turned back to the off - position. The power relays will be
used for the air conditioners (1 ton, 2 ton and 3 ton) as well as the ventilation and
the dehumidifier. Figure 51 shows the typical HVAC relay setup that will be
utilized.