Specifications

105Environmental Automation
Transmit power, antenna gains and
losses, transmission medium losses,
receiver sensitivity, noise, interference
sources, and other environmental
factors can all have an eect. Errors in
the data can be detected and corrected
using cyclic redundancy checking (CRC)
or more sophisticated algorithms, or
a retransmission can be requested.
Repeaters can be used to extend the
length of the link. Maxim has some
of the most sensitive receivers on the
market providing extended link range.
The third problem is data security. A
variety of methods can be implemented
to protect data from unauthorized
acquisition. Data encryption is the
most applicable to this discussion,
but other measures exist, such as
CDMA and spread spectrum, but
for simple ISM band radios using
ASK, FSK, or OOK modulation, data
encryption is the common method
of securing the data. This is applied in
the microprocessor in the system. The
MAXQ1004 microcontroller incorporates
AES encryption and a random-number
generator to enable master/slave
challenge-response authentication
so data will not be transmitted until
a valid link is found. Once found, the
data will be encrypted, making it
unintelligible without knowing the key.
ISMRF (Industrial, Scientific,
and Medical RF) Radios for
Environmental Automation
ISMRF consists of low-power (5mA
to 20mA, 3V) radios that work in
unlicensed radio bands from 300MHz
to 950MHz. They have been used in
applications that require low duty cycle
(0.1% to 10%) and low burst data rates
(1kbps to 30kbps), such as remote
car keys, garage door openers, home
security, home lighting, window shade/
curtain control, and TV remotes.
Many of the scenarios listed in this
chapter can be served by these simple
radio links. Depending on the needs
and complexity, these links can be
one-way (transmitter at one end and
receiver at the other) or two-way
(transceivers at both ends). The Maxim
parts in these radios comprise, at
the very least, an ISMRF radio IC and
often a MAXQ
®
microprocessor.
The gures above illustrate two areas
of environmental automation where
these radios could be used: building
security and HVAC. One conguration
contains a one-way radio link and the
other contains a two-way radio link.
Other Wireless Environmental
Automation Applications
• Two-way building security. Intrusion
sensor turns on its transmitter due to
an alarm condition. Security controller
interrogates intrusion sensor and
checks for response indicating proper
operation and battery health.
• One-way HVAC. (1) Transmitter on
thermostat, receiver in heater or AC,
replaces control wire. (2) Transmitter
on heater, receiver in thermostat.
Change thermostat setting at random
times in a remote or closed area
without sending someone inside.
• Storage facilities environmental
control. Remote control center
for outside storage area monitors
temperature, humidity, air circulation,
and light level, and sends commands
to control systems to adjust each to
maintain a particular environment.
• Hothouses for growing vegetables
in the winter. Remote control center
for outside growing area monitors air
temperature, humidity, soil wetness,
and soil pH, and sends commands
to control systems to adjust each
to maintain optimum growing
conditions.
Specific Maxim IC Grouping
• One-way:
◦ MAX7044 ASK Tx, MAX7036 ASK Rx,
MAXQ610 microprocessors
◦ MAX7057 ASK/FSK Tx,
MAX1471 ASK/FSK Rx,
MAXQ610 microprocessors
• Two-way:
◦ MAX7032 ASK/FSK TRX,
MAXQ1004 microprocessors
ZONE
CONTROL
PANEL
ZONE
CONTROL
PANEL
WALL UNIT
KEYPAD
BUILDING SECURITY INTRUSION ALARM SYSTEM
WALL UNIT
RX
OPEN/SHUT
SENSOR
WIRELESS
TX
GLASS BREAK
SENSOR
WIRELESS
TX
OCCUPANCY
SENSOR
WIRELESS
TX
TEMPERATURE
AND
CLIMATE CONTROL
WIRELESS
TRX
BUILDING HVAC, ENERGY MANAGEMENT
THERMOMETER/
THERMOSTAT
WIRELESS
TRX
THERMOMETER/
THERMOSTAT
WIRELESS
TRX
One-way building security. Intrusion sensors (open/shut, glass break, motion, or IR) turn on the transmitter only when an alarm
condition occurs. With one-way communication there is no way to check the status of the sensors or the transmitter remotely.
Two-way HVAC. Thermostat turns heater/AC on and off wirelessly via commands transmitted from the thermostat to the HVAC
controller. The HVAC control center changes the thermostat setting on a nonperiodic basis via communication in the opposite direction.