The design
of this GREENHOUSE CONTROLLER consists of two units, the microcontroller/transmitter
(uC/xmit) and the microcontroller/receiver (uC/recv). The uC/xmit
unit is located in the greenhouse while the uC/recv is located
in the house about 75 feet from the greenhouse. The uC/xmit
units gathers data from temperature sensors and based on this
data operates two vents, heater and a fan. The unit then transmits
the temperature data and the state of the vents, heater and
fan utilizing the license free 433.9MHz band. This information
is also displayed on a 4x20 LCD in the unit. The uC/recv unit
receives and displays the same information on a similar LCD.
This process is repeated every 10 seconds.
The uC/xmit
unit employs three temperature sensors whose outputs are monitored
by the ADC within the AT90S8535 uC. The TOP temperature sensor,
located near the top of the greenhouse, determines the state
of the vents while the BOT temperature sensor, located near
the bottom of the greenhouse, determines the state of the heater.
The state of the fan is dependent on the state of the vents
and the TOP temperature. The uC/xmit unit utilizes potentiometers
so that both the temperature at which the vents open and the
heater turns on are adjustable. The vents open temperature range
is from 69 deg F to 105 deg F. The vents will shut 15 deg F
below the set vents open temperature. The heater on temperature
range is from 24 deg F to 50 deg F and the heater will turn
off 10 deg F above the set heater on temperature. The fan will
turn on 10 deg F above the vents open temperature and turn off
5 deg F above the vents open temperature. Presently the uC/xmit
is powered by a 12 volt battery, which is also monitored by
the uC/xmit unit. The monitored range is from 0 to 18.8 volts.
There is also a temperature sensor, OUT, mounted outside the
greenhouse. Both the battery voltage and OUT temperature is
also transmitted to the uC/recv. The soil moisture in a test
container is monitored as either High or Low. The uCxmit unit
will send an emergency message to the uC/recv if either of the
following occurs and at which time the uC/recv, which utilizes
the AT90S2313 uC, will turn on a buzzer, flash the display and
turn on an LED. This state will persist until the condition
is corrected. During normal reception, the LED only blinks after
valid data is received.
1)
if TOP <= 32deg OR => 110deg
2)
if BOT <= 32deg OR => 99deg
3)
if Battery voltage < 9.1 volts
Both the
uC/xmit and uC/recv units display the same information in the
following format.
TOP=102
VENT76-91=O
BOT=99
M=H FAN=ON
OUT=106
BATT=12.8
HTR=47-57
HEAT=OFFx
The following
is an explanation of the data displayed.
TOP, BOT
and OUT are the respective sensor temperature readings in degrees
Fahrenheit.
VENT76-91=O
indicates that the pot for the vents is set to open the vents
when TOP temperature is =>91 deg F and 15 deg less (76) the
vents will shut, the O indicates that the vents are open.
M=H FAN=ON
indicates High soil moisture in the test container and the fan
is on since the TOP temperature is greater than 10 deg F above
the vents open temperature (91).
The BATT=12.8
indicates that the voltage of battery supplying power to the
uC/xmit unit is 12.8 volts.
HTR=47-57
indicates that the pot for the heater is set to turn on the
heater at 47 deg F and 10 deg greater (57) the heater will turn
off.
HEAT=OFFx
indicates that the heater is off since the BOT temperature (99)
is greater than the heater turn off temperature (57). The "x"
is a number from 0 to 9 that is transmitted and displayed on
the uC/recv display so that it can be determined whether sequential
transmissions are being received.
