Download Project-SW

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Contents
1.0
ABSTRACT (MB) .......................................................................................7
2.0
STATEMENT OF NEED (MB) ..................................................................7
3.0
OBJECTIVE (MB) ......................................................................................8
4.0
RESEARCH SURVEY (MB) ......................................................................8
5.0
MARKETING REQUIREMENTS (MB) ..................................................10
6.0
OBJECTIVE TREE (MB) .........................................................................11
7.0
DESIGN SPECIFICATION (MB) ............................................................11
8.0
CALCULATIONS (MB, DP) ....................................................................14
9.0
DESIGN SPECIFICATIONS (MB, DP) ...................................................15
9.1
Mechanical Design...............................................................................15
9.2
Material Design ....................................................................................15
9.3
Control Design .....................................................................................16
9.4
Electrical Design ..................................................................................16
9.5
Computing Requirements ....................................................................17
9.6
Economic and Ergonomic Design .......................................................18
10.0 ACCEPTED TECHNICAL DESIGN........................................................19
10.1
Hardware Theory of Operation (SW) ..................................................19
10.2
Level I – Hardware (DP)......................................................................20
10.3
Level II – Hardware (DP) ....................................................................23
10.4
Schematics (DP)...................................................................................30
10.5
PCB Artwork .......................................................................................42
10.6
Probe ....................................................................................................44
10.7
Weather Station ....................................................................................51
10.8
Home CPU ...........................................................................................53
10.9
Complete Lawn Probe..........................................................................54
10.10 Testing Procedures ...............................................................................55
10.11 Software (DP,MB,TM) ........................................................................60
10.12 Functionality – Home PC Interative Software (TM) ...........................75
10.13 Software Events ...................................................................................81
10.14 Timer Events ........................................................................................83
10.15 Conversion Functions ..........................................................................84
10.16 xBee Coding.........................................................................................85
10.17 File Structure For Code ........................................................................89
11.0 OPERATION, MAINTENANCE, AND REPAIR INSTRUCTIONS
(DP,TM) .....................................................................................................91
12.0 FINANCIAL BUDGET (DP) ....................................................................97
13.0 GANTT CHARTS (DP) ..........................................................................100
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List of figures
Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30
Figure 31
Figure 32
Figure 33
Figure 34
Figure 35
Figure 36
Figure 37
Figure 38
Figure 39
Figure 40
Figure 41
Figure 42
Figure 43
Figure 44
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Super Sprinkler Objective Tree.................................................... 11
Level I Hardware ......................................................................... 21
Level II Hardware – Lawn Probe ................................................ 23
Level II Hardware – Weather Station.......................................... 26
Level II Hardware – Central Hub ................................................ 28
Level II Hardware – Control ....................................................... 29
Schematic – Probe Charging Circuit ........................................... 30
Schematic – Probe DC/DC Converter ......................................... 32
Schematic – Probe PIC ................................................................ 34
Schematic – Probe XBee ........................................................... 35
Schematic – Weather Station Power Supply .............................. 37
Schematic – Weather Station Temperature Amplifier ............... 38
Schematic – Weather Station Pressure Amplifier...................... 39
Schematic – Weather Station XBee ........................................... 39
Schematic – Central Hub Power Supply.................................... 40
Schematic – Central Hub XBee and Driving Circuit ................. 41
PCB Layout................................................................................ 42
Populated PCB ........................................................................... 43
Flat Model .................................................................................. 44
Charging Circuit ........................................................................ 45
Probe Battery ............................................................................. 46
DC/DC Converter Subsystem ................................................... 47
Lawn Probe xBee Subsystem .................................................... 47
PIC16 Subsystem ...................................................................... 48
Complete Central Hub System, Flat Model .............................. 49
Central Hub Subsystem ............................................................. 50
Driving Circuit Subsystem ........................................................ 50
Complete Weather Station, Flat Model ..................................... 51
Weather Sensor and Temperature Sensor Amplifier Subsystem
52
Pressure Sensor Amplification and Filtering Subsystem .......... 52
Complete Home CPU System.................................................... 53
Complete Lawn Probe ............................................................... 54
Moisture Sensor Graph ............................................................. 56
Pressure Test Results................................................................. 57
Temperature Sensor Test........................................................... 58
Central Hub Information ........................................................... 60
Lawn Probe Information ........................................................... 63
Main Function Flowchart .......................................................... 67
Timer 2 Interrupt Flowchart ...................................................... 68
Pin Change Interrupt ................................................................. 69
Timer 1 Interrupt Flowchart ...................................................... 70
Timer 0 Interrupt Flowchart ...................................................... 71
Probe Shutdown, Not Charging ................................................ 72
Probe Shutdown, Not Charging ................................................ 73
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Figure 45
Figure 46
Figure 47
Figure 48
Figure 49
Figure 50
Figure 51
Figure 52
Figure 53
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Probe Not Shutdown and Charging........................................... 73
Probe Shutdown and Charging.................................................. 74
Battery Charged ........................................................................ 74
Probe in Wake Up State ............................................................ 75
Watering decision flow chart. ................................................... 76
Weather tests flow chart. ........................................................... 77
Rain prediction flow chart. ........................................................ 78
Manual turn on flow chart. ........................................................ 80
Manual turn off flow chart. ....................................................... 80
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List of tables
Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Table 10 Table 11 Table 12 Table 13 Table 14 Table 15 Table 16 Table 17 Table 18 Table 19 Table 20 Table 21 Table 22 Table 23 Table 24 Table 25 Table 26 Table 27 Table 28 -
Engineering Requirements and Justification ................................... 12
Power Calculations ......................................................................... 15
Level I Hardware FR Tables ........................................................... 22
Level II Hardware FR Tables – Lawn Probe .................................. 24
Level II Hardware FR Tables – Weather Station ............................ 27
Level II Hardware FR Tables – Central Hub .................................. 28
Level II Hardware FR Tables – Central Hub .................................. 29
Schematic FR Tables – Probe Charging Circuit ............................. 31
Schematic FR Tables – Probe DC/DC Converter ........................... 32
Schematic FR Tables – Probe PIC ................................................ 34
Schematic FR Tables – Probe XBee .............................................. 36
Schematic FR Tables – Weather Station Power Supply ............... 37
Graphics Table 1 ........................................................................... 61
Graphics Table 2 ........................................................................... 61
Barometric Pressure Graphics ....................................................... 62
Connections Graphics.................................................................... 64
PIC Pin Layout .............................................................................. 66
Encoding packet structure. ............................................................ 85
Decoding echo response packet structure. .................................... 87
Remote ADC packet structure. ..................................................... 88
Frame ID list used ......................................................................... 89
GUI File Structure ........................................................................ 90
Initial Budget ................................................................................ 97
Current and Final Budget.............................................................. 98
Donated Parts ................................................................................ 99
Design ......................................................................................... 100
Implementation ........................................................................... 101
Revised Implementation ............................................................. 102
List of appendices
Appendix – Data Sheets, PIC Code, GUI Code (DP,TM) .................................. 103
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1.0
ABSTRACT (MB)
A lawn sprinkler controller was designed and built. The system is comprised of
the moisture probe, the central hub, weather station, and the home CPU. The moisture
probe monitors soil moisture content of a specified area of lawn, or zone, and wirelessly
transmits data to the home computer station. The central hub is responsible for activating
the sprinkler valves for each respective watering zone. The home computer station
interprets the collected environmental data, and the embedded logic determines which
lawn zones need watered. The system is initially configured to monitor four lawn zones,
but the system is expandable to eight zones.
Key Features:
2.0

Soil moisture, temperature, and barometric pressure sensors

Solar recharging capability of wireless moisture probes

Rechargeable nickel metal hydride (NiMH) batteries in each moisture probe

Point to point minimum communication range of 132 feet for system components

Graphical User Interface for user adjustment
STATEMENT OF NEED (MB)
In-ground lawn sprinklers are a common piece of equipment for many modern
homes. A lawn sprinkler provides a home-owner with a constant source of water to keep
their lawn green and healthy. There is, however, a drawback to the common lawn
sprinkler system. At a specified time, the sprinkler will dispense water across the entire
lawn, regardless of the ground‟s moisture content or the current state of the weather. A
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new sprinkler design capable of monitoring current environmental conditions and ground
moisture solves reduces the chances of unnecessary or excessive watering.
3.0
OBJECTIVE (MB)
The objective is to create a soil moisture and weather monitoring system that is
easily implemented into the existing sprinkler hardware. The system will utilize weather
data from sensors and compare that with soil moisture levels via sensors in the ground.
Individual sprinkler zones will be activated based on this information.
4.0
RESEARCH SURVEY (MB)
Proper irrigation is critical to maintaining a healthy landscape, and it is a
surprisingly complex process because many factors must be accounted for to ensure a
proper watering schedule. One of the first factors to be considered is when to water.
Many cities nationwide prohibit excess water usage during peak demand hours.
Furthermore, it is not beneficial to water during the afternoon as water is wasted through
evaporation and scalding the lawn is more likely to occur. Fungus is likely to grow if
watering routinely occurs during excessively cool and damp hours of the day.
It is also advantageous for a user to include weather as a factor when constructing
a watering schedule.
Water, and ultimately money, is wasted if current weather
conditions are not taken into account. Temperature and barometric pressure are two of
the most important factors to consider for proper watering.
The temperature can
negatively affect watering if too high or too low. As previously stated, watering during
periods of extreme temperature can compromise the health of a lawn. The barometric
pressure must be monitored to detect changes in the weather. The highest atmospheric
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pressure ever recorded is 1,094 mbar (15.87 psi), and the lowest atmospheric pressure
ever recorded is 870 mbar (12.62 psi) [5]. Higher pressure correlates with fair weather
and low pressure correlates with precipitation. For this reason, monitoring the drop in
barometric pressure will alert system when precipitation may be approaching. In this
case, an intelligent system could increase the frequency of soil moisture readings to
ensure watering does not occur during a rainstorm.
Another factor to be considered is how long to water the landscape. Overwatering
causes runoff, which contributes to a significant amount of water wasted over time as
well as damage to the overall appearance of the lawn. However, the watering period
must be long enough to ensure that the water penetrates the surface and reaches the roots
within the soil. Short watering periods may contribute to a shallow root system, which
are more vulnerable to disease and pests capable of compromising the lawn‟s overall
health.
These factors have influenced the creation of intelligent watering systems. While
manually operated watering systems allow for physical control over the watering
schedule, technological advancements allow for more complex, autonomous systems.
One of the more basic systems that are implemented today is a timer on the
master valve. The user can set the time that the valve is opened and closed. This allows
for hands off operation every day. Many companies have taken the automated irrigation
system a step further. Companies such as Cyber Rain [2], Hydro Earth [3] and Rain Bird
[4] offer intelligent systems that water based on weather forecast data downloaded via the
internet, and allow for independent control of each sprinkler head. This market also
includes peripherals that can be integrated within systems to monitor soil moisture,
barometric pressure, and temperature. However, many of these systems require existing
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landscape to be physically altered in order to install the system underground. A need
exists for a wireless control system that minimizes alterations to the existing landscape.
5.0
MARKETING REQUIREMENTS (MB)
The following list is the set of the marketing requirements around which this project
will be based. These are the foundation of the project, from which our engineering and
design specifications stem.
1. The system shall be easy to use.
2. The device shall be durable.
3. The system shall not significantly disturb the existing lawn.
4. The system shall be capable of operating during a long period of time.
5. The system shall provide accurate measurement of soil moisture.
6. The system shall provide accurate measurements of current weather conditions
(barometric pressure and temperature).
7. The system shall be priced competitively.
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6.0
OBJECTIVE TREE (MB)
The objective tree seen in Figure 1 specifies facets of the design to be considered. A
hierarchy of important features is listed for each facet. These aspects are as follows: Easy
to Use, Durability, Unobtrusive Installation, Long Term Operation, Soil Moisture
Accuracy, and Weather Condition.
Figure 1 - Super Sprinkler Objective Tree
7.0
DESIGN SPECIFICATION (MB)
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Table 1 displays the engineering requirements and their justification.
The
engineering requirements are linked directly to the marketing requirements for clarity.
The accepted design shall meet all of the requirements and constraints.
Table 1 Marketing
Requirements
1, 2, 3
2
1, 4
4
4
5, 6
5
5
Engineering Requirements and Justification
Engineering
Justification
Requirements
The dimensions of the The probe must be unobtrusive
prototype
moisture and cause minimal damage to the
probe shall not exceed 2 existing landscape.
× 3.3 × 1.5 inches.
The moisture probe
Only the soil moisture sensor face
housing shall be
should remain outside of the
resistant to moisture and protective housing; remaining
elements.
hardware must be isolated from
the elements.
The moisture probe shall The XBee module operates at a
be able to operate from a low voltage. A current draw
low voltage source and budget estimate was developed
will draw a maximum of with potential components and
250 mA.
250 mA was an upper limit of
current estimated.
Sleepmode shall be
Power must be conserved because
incorporated into
the supply may be limited with
moisture probe.
the solar recharging circuit.
The barometric pressure
sensor and temperature
sensor will be supplied
by 120 AC.
The barometric pressure
sensor and temperature
sensor
should
be
accurate up to 1% of
their respective range.
Data rate for
communication shall be
9600 bps.
These sensors must be supplied
with a continuous power supply in
order to monitor real time weather
conditions.
Accurate weather data must be
measured to ensure that watering
during rainstorms is avoided.
This is the default set data rate,
and it is ideal for serial
communication.
Communication range These dimensions are based on
must be average yard the tabulated data of an average
size of 93 × 93 square lawn size study.
feet [1].
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1, 5, 6
1, 4
1, 5
7
System shall operate
autonomously and also
offer user ability to alter
weather parameters
(temperature and
barometric pressure
thresholds) and blackout
time periods.
The system GUI shall be
designed for keyboard
and mouse inputs and
allow users to set their
own watering
parameters.
System shall include
three (3) monitoring
zones, with the ability to
expand to eight (8)
zones.
Product cost (excluding
labor) shall not exceed
$400.
The controller must have a
“hands-off” mode that gives
owners the freedom to let the
controller decide watering needs.
However, it must also provide the
user with the ability to adjust the
system operation based on their
restrictions.
The system msut be intuitive to
users, and it must allow user
flexibility ensure an optimal
watering schedule can be
manually created.
Monitoring system should be
capable of adapting to sprinkler
systems of variable size.
This is based on competitive
market analysis and previous
system designs.
Marketing Requirements
1: The system and its components shall be easy to use.
2: The system and its components shall be durable.
3: The system components shall not significantly disturb the existing lawn.
4: The system shall be capable of operating for an extended period of time.
5: The system shall provide quick and accurate measurements of soil moisture.
6: The system shall provide accurate measurements of current weather conditions
(barometric pressure and temperature).
7: System should be priced competitively.
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8.0
CALCULATIONS (MB, DP)
Power consumption was calculated within the soil moisture sensor.
The power
consumption at the central hub and the weather station were neglected as these
components will be continuously supplied with their respective DC or AC supplies. The
Nickel Metal Hydride (NiMH) batteries only have a capacity of 2300mAh.
Table 2 includes power calculations for hardware necessary to complete the
design.
The following should be noted on the power calculations:
1. One minute (60 seconds) was used as the duration for all components except for
the solar cells. This interval was used because the internal components of the
probe are only powered for one minute every four hours.
2. The soil cell power calculation is to be taken as a very rough estimate. As
previously mentioned, the solar cells were mounted at 23.5 degrees. The cells
will not see direct sunlight the entire duration from sunrise to sunset. A time of
six hours was used at the cells maximum voltage and current ratings of 8.4 volts
(series connection of two cells) at 22 milliamps.
3. An example calculation set is shown for the soil sensors (form followed for all
moisture probe components):
Instantaneous Power =
Power =
kWh
mAh
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Table 2 -
Power Calculations
Power Calculations
Part
Part #
VG400
PRO (TX)
Voltage
(V)
3.3
3.3
Current
(mA)
<0.8
270
PRO (RX)
3.3
55
2.0
5.0 × 10-5
2.0
220 × 10-
Voltage Regulator
PIC16F684
(Sleep)
PIC16F684
(Norm Op)
LP2950
917.0 ×
10-3
2.0 × 10-4
3.3
DC/DC Converter
Solar Cells (2x)
LM2954
-
3.3
8.4
Soil Sensor
(mAh)
13.0 × 10-3
4.5
XBee Module
Microcontroller
9.0
Instantaneous
(kWh)
Power (kW)
2.64 × 10-6
4.4 × 10-8
891.0 × 10-6
15.0 ×
10-6
-6
181.5 × 10
3.0 × 10-6
10 × 10-3
4.0 × 10-8
4.0 × 10-3
4.4 × 10-7
4
66.7 × 10-3
13.0 × 10-6
11
22
183 × 10-3
132
36.0 × 10-6
185 × 10-6
7.33 ×
10-9
2.16 ×
10-7
6.0 × 10-7
1.11
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DESIGN SPECIFICATIONS (MB, DP)
The following provides a brief summer summary of the system design including,
but not limited to mechanical design, power, and control design.
9.1
Mechanical Design
9.1.1
Static Design and Structural Consideration
No static considerations needed to be accounted for within this system. The
housing consists of a 3‟‟ by 3‟‟ by 2‟‟ plastic project box. Holes were drilled to
mount the XBee antenna, push button, power led, and soil moisture sensor. Two
solar cells, measuring approximately 3.5‟‟ by 1.5‟‟, were mounted at
approximately a 23° angle atop the project box. These panels were sealed within
plexi-glass to ensure isolation from the weather.
9.2
Material Design
9.2.1
Material Properties
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The moisture sensor itself has a plastic extension that measures the dielectric
constant of the soil. This extension is brittle and with some effort can be broken.
The housing of the moisture probe, as initially stated, consists of a black, opaque,
plastic project box that shields the internal components (PCB, batteries) from the
elements. Holes in the project box were filled with silicone sealant to protect all
internal components.
9.3
Control Design
9.3.1
Control System
The digital control system that exists within the home CPU will make
determinations about current moisture levels and current weather patterns to see if
lawn sprinklers, specifically which zones, should be turned on. The moisture,
temperature, and barometric pressure sensors all output analog information that
must be converted to digital for use by the microcontroller.
9.3.2
Sensors
Three sensors will be implemented in this system. Parameters measured include
soil moisture, barometric pressure, and ambient temperature. The data from these
sensors will be analyzed to determine proper run/soak times for each respective
lawn zone.
9.3.3
Actuators
The existing controller should contain an override mechanism for manual control.
A driving circuit will be responsible for generating a signal which will be capable
of activating each of the respective valves. This circuit is not responsible for
providing power to the valves; it is merely for opening the valves.
9.4
Electrical Design
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9.4.1
Communication Requirements
The system shall communicate wirelessly to each part (probes, central hub,
weather sensing unit, home CPU). The average yard size of 93 ft. by 93 ft. has
been named the range constraint on wireless communication between the
respective modules. The bit rate for wireless communication will be set at 9600
bps. This is the standard rate for XBee wireless modules.
9.4.2
Bandwidth
The bandwidth shall be big enough to hold information for the instance every part
is communicating at once.
Each packet of data from the analog to digital
converter comes in at twenty (20) bytes at each probe, plus twenty (20) bytes
from the weather sensor, as well as a sixteen (16) byte echo response from the
central hub. This comes to [36 + 20n] bytes, where n is the number of probes
used in the system.
9.5
Computing Requirements
9.5.1
Coding
The main executed file on the system shall be coded in C#. The microcontroller
on each probe shall be coded in C++.
9.5.2
Storage
The user PC shall provide enough storage to keep parameters saved and logs of
the system usage.
9.5.3
I/O Lines
There shall be enough I/O lines on the central hub to control each sprinkler zone.
The weather sensing unit shall provide three (3) I/O lines for ADC. The probe
shall provide two (2) I/O lines for ADC.
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9.5.4
Interrupts
The main program shall provide interrupt routines for receiving wireless data to
be processed. The GUI shall provide interrupt routines for each button that is
selected.
9.5.5
Electrical and Electronic Design
Connections and external components for DC/DC converters shall be connected
for maximum efficiency and minimal interference. Amplifiers shall be used on
all sensors to adjust the voltage range to 0V – 3.3V. Low pass filters shall be
used on all power lines to reduce interference. Proper wiring gauges shall be used
to carry rated current.
9.6
Economic and Ergonomic Design
9.6.1
Cycle Life and Reliability
Reliability will be based on the physical condition of the system components.
Physical damage to system will obviously compromise the integrity of system
operation. The rechargeable probe batteries are the only part that would need to
be replaced.
Assuming no damage to the batteries, replacement would be
recommended every two to three years.
9.6.2
Maintainability
This system will be easily maintainable. The lawn unit requires zero maintenance
once it is in the ground.
The system shall be capable of year round operation.
However, wireless probes are easily removed from the ground to protect the
components during the winter season.
9.6.3
Testability
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This system can be tested on request. Once the probe is inserted into the ground,
the weather sensors are supplied power, and the main program executed, the
system is immediately testable.
9.6.4
Human Factors, User Interfaces
The user interface for this system will be placed on a home CPU. It will provide
data on barometric pressure, temperature, and moisture levels as well as current
weather conditions. The GUI will be capable of taking in keyboard and mouse
inputs. This full control is one user intuitive than older, primitive controllers.
9.6.5
Economics
For complete system and one lawn probe, the system will be approximately
$300.00. Each additional probe will be roughly $80.00.
9.6.6
Safety Considerations
No high voltages or currents will be established within this system. Appropriate
insulating material will provide will provide proper grounding isolation of the
probe electronics. The weather sensors and the home computer will be supplied
by standard 120VAC outlets, and the pre-existing grounding techniques will be
more than adequate for the system.
10.0
ACCEPTED TECHNICAL DESIGN
10.1
Hardware Theory of Operation (SW)
The hardware necessary for the sprinkler monitoring system to behave as desired
is as follows. The moisture sensor will be powered by a series of rechargeable batteries,
which will be recharged by way of a solar cell. In addition to moisture data, the system
will also record temperature and pressure data and these three pieces of information will
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be sent to a home computer. At the computer, the system logic will decide if it‟s
necessary to turn on the lawn sprinklers. If watering is necessary, the system will power a
driving circuit that will actuate the lawn sprinklers. The process then repeats at a
designated interval of four hours.
10.2
Level I – Hardware (DP)
The level I diagram gives a generic overview of the complete super sprinkler
system. This begins with the lawn probe. This unit is placed in the soil and has the
ability to relay soil moisture data wirelessly to the control module. The weather station
contains the pressure and temperature sensors. Like the lawn probe, information is sent
wirelessly to the control on current temperature and pressure. The ideal location for the
weather station is in the home garage, to ensure weather readings are as accurate as
possible to outside conditions, without the unit being exposed to the environment. The
central hub receives all watering information from the control unit. This should be
placed next to the existing sprinkler controls as it provides the actuating signal to turn on
specific valves to water the lawn. As for the control block, this is the home computer. It
contains logic to make decisions on watering and when to take in information pertaining
to soil moisture. Along with this logic, a GUI is included to allow for user inputs and
adjustments for the watering decisions.
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Figure 2 - Level I Hardware
Figure 2 shown above provides a graphical representation of the level I system.
To further describe the functionality of these blocks, functional requirements have been
provided for each below Table 3.
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Table 3 -
Level I Hardware FR Tables
Module
Lawn Probe
Inputs
Outputs
Functionality
Sunlight (recharging); Command Signals (from control unit)
Soil Moisture, 0-3VDC
This block‟s sole function is to take soil moisture readings at increments
as determined by the control and the end user. Because it must be a
completely wireless unit, it is powered by a rechargeable battery. This
is where sunlight is required, to keep the batteries at a necessary voltage
level.
Module
Weather Station
Inputs
Outputs
Functionality
Current Weather Conditions (temperature and pressure)
Temperature and Pressure Readings, 0-3.3VDC each
The role of the weather station is to continuously monitor temperature
and pressure conditions. These will be used as determining factors
where watering is concerned. Like the lawn probe this is a completely
wireless unit with the exception of its power source. Because of the
need for continuous monitoring, a 120VAC source will be used to
provide power.
Module
Central Hub
Inputs
Outputs
Functionality
Watering Decision from Control Unit
Current Status of Zones being Watered
The central hub sends the actuating signal to the sprinkler valves.
Similar to the weather station, it needs to be continuously powered;
therefore a constant 120VAC source will be used.
Module
Control
Inputs
Outputs
Functionality
All Weather and Soil Moisture Data
Watering Decision; Commands to Lawn Probe
The control unit is the brains of the whole system. It contains the logic
to determine whether or not to water and, specifically, which areas to
water. The user can also set certain parameters, such as how long to
water and weather restrictions, and the control unit will send these
commands accordingly to the lawn probes.
The level I description gives a broad overview of the super sprinkler system. In
the level II system each of the blocks from level I are broken down into more detail.
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10.3
Level II – Hardware
(DP)
Lawn Probe
A deeper look into the Lawn Probe can be seen in figure 3. Starting at the solar
cell; sunlight is used to charge the battery. The charging circuit contains components to
regulate this charging. The battery is a 6V NiMH pack and is used to power the whole
probe. The PIC, XBee, and Moisture Sensor all run off 3.3V, therefore a switching
DC/DC converter is used for its higher efficiency compared to a linear regulator. The
moisture sensor is physically connected to the XBee, which relays the moisture readings
to the control. The PIC is the control center of the probe. It turns the charging circuit
and DC/DC converter on and off, and has the ability to put the probe in sleep mode when
not taking readings. The PIC can also shut down the probe all together if the battery can
no longer provide sufficient power.
Figure 3 - Level II Hardware – Lawn Probe
23
A more detailed description of each block in figure 3 is shown in their respective
functional requirements below in Table 4.
Table 4 -
Level II Hardware FR Tables – Lawn Probe
Module
Solar Cell
Inputs
Outputs
Functionality
Sunlight
8.4 VDC at 22mA (nominal)
The solar cells will provide recharging power to the battery. This will
help to ensure the lawn probe can remain a standalone unit.
Module
Charging Circuit
Inputs
Outputs
Functionality
Solar Power, 8.4VDC; Charge Signal (from PIC)
Charge Power (approx 7.5VDC); Solar Voltage Level (to PIC)
The charging circuit utilizes BJT‟s to turn on and off the charge power
to the batteries. It also has a diode to prevent the solar cells from
draining the battery when not charging. The current level of voltage
provided by the solar cells is sent to the PIC to ensure the power is
sufficient to charge the battery pack.
Module
Battery
Inputs
Outputs
Functionality
Charge Power (approx 7.5VDC); DC/DC Shutdown Signal (from PIC)
6VDC (to PIC); 6VDC (to DC/DC); DC/DC Shutdown Signal (from
PIC)
The battery pack provides 6VDC to the PIC and to the DC/DC
converter. It also relays the shutdown signal from the PIC to the DC/DC
converter. Lastly, the charge power coming from the charging circuit is
used to charge the battery pack.
Module
DC/DC
Inputs
Outputs
Functionality
6VDC (from battery); DC/DC Shutdown Signal
3.3VDC
The purpose of the DC/DC converter is to provide a stepped down
voltage of 3.3VDC to the XBee and the Moisture Sensor. This
converter has a shutdown feature that will be utilized in the event that
the probe needs to completely shutdown.
Module
PIC
Inputs
6VDC (power source from battery); Solar Voltage Level; Transmit
Signal (from XBee)
Charge Signal; DC/DC Shutdown; Various Signals to XBee
The PIC acts as the control unit for the Lawn Probe. It has the ability to
turn the charging on and off, and the DC/DC converter on and off. It
also sends signals to the XBee unit. These include a “wake-up” signal,
the current battery voltage signal, and a reference voltage of 3.3VDC.
The wake-up will be used to turn on the XBee unit when a moisture
reading should be taken. The current battery voltage will be transmitted
by the XBee back to the control module for reference by the user.
Outputs
Functionality
24
Finally, Vref is the reference voltage used by both the PIC and the XBee
module.
Module
XBee
Inputs
3.3VDC (power from DC/DC); Wake-up Signal (from PIC); Vref
(from PIC); Battery Voltage (from PIC); Soil Moisture Level 0-3VDC
3.3VDC (power for moisture sensor); Transmit Signal (to PIC);
The XBee is the communication transceiver for the lawn probe. It will
take in data on soil moisture, as well as various diagnostics information
about the probe itself and relay it to the control unit. When it is done
transmitting, it sends a signal to the PIC, and in turn the PIC puts the
XBee to sleep to conserve power.
Outputs
Functionality
Module
Moisture Sensor
Inputs
Outputs
Functionality
3.3VDC (power from XBee module)
0-3VDC Moisture Level Signal
The moisture sensor measures the dielectric constant of the surrounding
soil to determine the soil‟s moisture content, as one of the parameters
that change the dielectric constant is water content. This level is scaled
as a 0-3VDC output and this voltage is sent to the XBee to be
transmitted to the control unit.
Weather Station
Figure 4 displays a detailed look into the weather station block from figure 2.
There is a power supply block that takes in 120VAC and separates this into 3.3, +5 and 5VDC depending on the component‟s need. Both the pressure and temperature sensors
have wide output range. To make the ranges of the sensor outputs appropriate to the
Super Sprinkler system, signal amplifier circuits are used. These are then sent to the
control unit.
25
Figure 4 - Level II Hardware – Weather Station
26
The tables (Table 5) that follow go into greater detail about each block in the
figure above.
Table 5 -
Level II Hardware FR Tables – Weather Station
Module
Power Supply
Inputs
Outputs
Functionality
120 VAC (house supply)
3.3VDC; +5VDC; -5VDC
The Power Supply has a DC/DC converter and a voltage regulator to
provide the three voltages needed. The 3.3VDC level is used for the
Pressure Sensor and the XBee. The +5VDC is used for the Temperature
Sensor. The ±5VDC is used to power the Amplifier circuits.
Module
Temperature Sensor, LM335
Inputs
Outputs
Functionality
+5VDC (power)
0-3.3VDC
The Temperature Sensor measures the ambient temperature of the area
around the sensor itself. While the overall range of the sensor is greater,
for this application the range has been restricted to 0º to 120ºF.
Module
Pressure Sensor, SDX30A2
Inputs
Outputs
Functionality
3.3VDC (power)
0-3.3VDC
The Pressure Sensor measures the absolute pressure of the area
surrounding the sensor itself. Like the Temperature Sensor, the Pressure
sensor output has been restricted to an approximate range of 14-17 psi,
corresponding to a 0-3.3VDC voltage output.
Module
Temperature Amplifier
Inputs
Outputs
Functionality
0-3.3VDC (temperature reading); ±5VDC (op-amp power rails)
0-3.3VDC
While the input and output voltages are the same, the point of this
amplifier is to offset and remove a portion of the range on both the high
and low end range of the sensor. This will allow for greater accuracy
between the temperatures of 0º to 120ºF.
Module
Pressure Amplifier
Inputs
Outputs
Functionality
89-92mVDC (pressure reading); ±5VDC (op-amp power rails)
0-3.3VDC
The purpose of this amplifier is to restrict the range of pressure
measured to between 14 and 17 psi. It also amplifies the voltage to the
0-3.3VDC range to be transmitted by the XBee. This amplifier will
ensure an enhanced accuracy of the sensor output.
Module
XBee
Inputs
3.3VDC (power); Two 0-3.3VDC Signals (temperature and pressure
data)
Wireless Data Stream to Control Unit
The XBee unit in the Weather station transmits the data received from
Outputs
Functionality
27
the temperature and pressure sensors to the control.
Central Hub
Figure 5 - Level II Hardware – Central Hub
The Level II diagram for the Central hub is shown above in figure 5. The Power
Supply provides a constant 3.3VDC source to the XBee module. It is connected to the
house‟s 120VAC supply. The XBee in the central hub acts as receiver for watering
decisions from the control. It also provides the driving signal for the sprinkler valves in
different zones. The tables (Table 6) below go into greater detail about the two portions
of the Central Hub.
Table 6 -
Level II Hardware FR Tables – Central Hub
Module
Power Supply
Inputs
Outputs
Functionality
120VAC (house supply)
3.3VDC
The sole purpose of the Power Supply is to provide a constant 3.3VDC
power source to the XBee unit. This is accomplished by using a wall
wart AC/DC converter that is then stepped down using a voltage
regulator to obtain the necessary 3.3VDC.
Module
XBee
Inputs
Outputs
Functionality
3.3VDC (power); Watering Decisions
Current Status of Zones being Watered
This XBee is directly connected to the home‟s existing sprinkler system
and provides the actuating signal for the water valves.
28
Control
Figure 6 - Level II Hardware – Control
Figure 6 displays the Level II hardware diagram for the Control unit. This
module receives all information regarding sensor data as well as probe vitals. All the
logic for decision making is contained in the home CPU. This also houses the graphical
user interface which allows the user to change parameters regarding watering decisions.
The following tables (Table 7) provide more detail about the functionality of the XBee
and home CPU.
Table 7 -
Level II Hardware FR Tables – Central Hub
Module
XBee
Inputs
All Sensor Data; Probe Vitals; Watering Decision (from home CPU);
Commands for Lawn Probe (from home CPU)
All Sensor Data (to home CPU); Probe Vitals (to home CPU);
Watering Decision (to central hub); Commands for lawn probe
The XBee in the control unit takes all the outside information including
lawn probe vitals and all sensor data. This is then sent to the home CPU
via the USB connection.
Outputs
Functionality
Module
Home CPU
Inputs
Outputs
Functionality
All Sensor Data; Probe Vitals
Watering Decision; Commands for Lawn Probe
The home CPU contains all the decision making logic and the GUI for
the user to set personal parameters for how they want the system to
operate. The end user is also able to see lawn probe vitals including
current charge status and the most recent moisture reading.
29
10.4
Schematics (DP)
This section could be considered as the Level III portion as it will provide a
deeper look into many of the modules introduced in the Level II diagrams. Functional
Requirement tables will also be included for each component in the schematic.
Charging Circuit
Referring back to figure 3, the charging circuit manages the power coming from
the solar cells and provides a charge to the battery pack. There is a transistor switch used
to turn the charging on and off based on the current battery charge. There is also a
protection Schottky diode to prevent the solar cells from draining the battery when not
charging.
Vsolar
U1
TIP32
D1
R9
Vbatt
STPS10L25
1k
R1
2.7k
U2
R2
PIC16F684 (PIN 6)
2N2222
2.7k
0
Figure 7 - Schematic – Probe Charging Circuit
Below, the tables (Table 8) take a deeper look into each component in figure 7.
30
Table 8 -
Schematic FR Tables – Probe Charging Circuit
Designation
U1
Part
Functionality
TIP32, PNP BJT
This transistor carries the charge signal from the solar cell and delivers it
to the battery pack. It is turned on when the base is drawn to ground by
the U2 transistor being turned on. This was chosen for its higher current
carrying capabilities.
Designation
D1
Part
Functionality
Schottky diode
D1 prevents the solar cell from draining the battery when not charging.
It was selected to be a Schottky diode for the low forward voltage drop
of 0.46V at 10 Amps. Because this application involves much lower
current, a significantly lower voltage drop is present.
Designation
R9
Part
Functionality
1kΩ resistor
This resistor is used as a current limiter. In the event that the circuit
would have a voltage source with much higher charging current
capability, this resistor would restrict the current flow to prevent
damaging the system.
Designation
R1
Part
Functionality
2.7kΩ resistor
This resistor restricts current at the base of the transistor U1. Its sole
purpose is to save power in the system.
Designation
U2
Part
Functionality
2N2222, NPN BJT
This transistor is turned on by the signal from the PIC. It connects the
base of U1 to ground and in turn activates U1 as a switch to allow
charging.
Designation
R2
Part
Functionality
2.7kΩ resistor
Like R1, this resistor limits the current in the base branch of U2 in an
effort to conserve overall power consumption.
31
The DC/DC converter is next. This is comprised of the LM2594 switching
regulator. This part provides an ON/OFF feature being utilized by the PIC to cut power
and put the lawn probe to sleep when necessary. As before, each of the components in
figure 8 is described in detail in the tables (Table 9) below.
D2
0
L1
1N5817
Vo
100uH
Vbatt
LM2594
C2
120u
C1
68u
DC/DC
0
0
0
R11
Vbatt
1k
U3
243
A0
15
B0
3
A
4
1
5
B3
12
B2
13
B1
1
2
R3
PIC16F684 (PIN 8)
2N2222
2.2k
0
Figure 8 - Schematic – Probe DC/DC Converter
Table 9 -
Schematic FR Tables – Probe DC/DC Converter
Designation
DC/DC
Part
Functionality
DC/DC switcher, LM2594
This device provides the necessary switching for the DC/DC converter.
Coupled with the inductor and capacitor, this converts the battery input
to 3.3VDC used by the lawn probe.
Designation
D2
Part
Functionality
Diode, 1N5817
This diode is an integral portion of a DC/DC buck converter. At
moments when the switching is in the “open” state, this diode will
conduct and allow current to flow, completing the source-load circuit.
When the switching is in the closed state this diode will block current.
Designation
L1
Part
Functionality
Inductor, 100mH
L1 is another necessary component in the DC/DC buck converter. It
stores energy when the switch is closed and releases it to the load when
the switch is open. The properties of an inductor ensure that the current
output will not drop to zero since current cannot change in an inductor
instantaneously.
32
Designation
C2
Part
Functionality
Filtering capacitor, 120μF
This capacitor is used to filter out any noise at the output generated by
either the switching of the DC/DC converter, or any other outside noise
that could be present. This will help guarantee a clean DC source of
3.3V.
Designation
C1
Part
Functionality
Filtering capacitor, 68μF
The C1 capacitor filters out noise at the input side of the DC/DC
switcher.
Designation
R11
Part
Functionality
Resistor, 1kΩ
This resistor connects the ON/OFF pin (pin 5) of the DC/DC converter
to Vbatt. When pin 5 is connected to battery terminal voltage, it will
turn the DC/DC converter off. Normal operation will have the U3
transistor in the ON state, enabling the DC/DC converter.
Designation
U3
Part
Functionality
2N2222, NPN BJT
For the DC/DC converter to remain ON, pin 5 must be at ground
potential. The PIC will enable this BJT to remain in the on state as long
as necessary while taking soil moisture measurements and transmitting
data. The benefit is being able to turn U3 off when it is desired to
disable the DC/DC converter.
Designation
R3
Part
Functionality
Resistor, 2.2kΩ
This resistor limits the current in the base of the U3 transistor to
conserve power, while still ensuring enough current is available to turn
on U3 when needed.
The PIC module, seen in figure 3, is the control unit of the lawn probe. It is
programmed to put the probe in sleep mode, or wake it up, when necessary. It also
determines when to charge the battery, and can shut the probe down completely if the
battery voltage dips too low. Below in figure 9 is a more detailed representation of this
portion of the lawn probe.
33
OUT
GND
IN
Vref
Vbatt
1
2
3
SW1 1
C3
0
1u
Xbee (PIN 19)
R4
Xbee (PIN 11)
Vbatt
4.7k
R5
3.3k
R2
Xbee (PIN 9)
1
2
3
4
5
6
7
0
a
b
c
d
g
fe
jih
q
trs
PIC16F684
14
13
12
11
10
9
8
0
2
0
R10
0
10k
R7
R3
Vsolar
10k
R8
3.3k
0
Figure 9 - Schematic – Probe PIC
Each component seen above is described in more detail in the tables (Table 10)
that follow.
Table 10 - Schematic FR Tables – Probe PIC
Designation
Vref
Part
Functionality
3.3VDC Voltage Regulator
Vref utilizes power directly from the battery and regulates it down to
3.3VDC for use by the PIC. The PIC cannot use the DC/DC converter
as a power source because one of the PIC‟s responsibilities is to
shutdown the DC/DC converter. Vref provides a constant source of
power for as long as there is charge in the battery.
Designation
PIC16F684
Part
Functionality
PIC Module
The PIC is programmed to be the control center of the lawn probe. It
has the ability to enable or disable charging, shutdown the DC/DC
converter, and wake up the XBee module when it‟s necessary to take a
moisture reading.
Designation
SW1
Part
Functionality
Momentary Push Button Switch (normally open)
This switch is mounted on the outside of the lawn probe and is used to
manually wake up the probe in the even the user wants to take an
unscheduled moisture reading. The switch is connected to pin 11 of the
PIC and when engaged, will supply a 3.3VDC signal to the PIC.
Designation
C3
Part
Functionality
Capacitor, 1μF
This capacitor filters out unwanted noise to provide a clean 3.3VDC
signal for the PIC.
Designation
R10
Part
Resistor, 10kΩ
34
Functionality
This resistor is for the manual wake up feature of the Lawn Probe.
When SW1 is engaged, the PIC will see 3.3V across R10 to signify the
probe to wake up and take a measurement.
Designation
R7, R8
Part
Functionality
Resistors, 10kΩ and 3.3kΩ respectively
These resistors create a voltage divider. The values were chosen such
that the voltage seen by pin 10 of the PIC would never be greater than
3.3VDC. This scaled solar voltage is used to ensure enough voltage is
available from the solar cells to charge the battery.
Designation
R4, R5
Part
Functionality
Resistors, 4.7kΩ and 3.3kΩ respectively
These resistors create a voltage divider. The values were chosen such
that the voltage seen by pin 3 of the PIC would never be greater than
3.3VDC. This scaled battery voltage is used to ensure enough voltage is
available from the battery to operate the probe.
The final component in the lawn probe to be further detailed is the XBee module.
This is the wireless transceiver which sends and receives information from the control
unit.
Vo
LED1 R6
Vo
330
PIC16F684 (PIN 7)
1
2
3
4
5
6
7
8
9
10
0
20
19
18
17
16
15
14
13
12
11
a
b
c
d
g
k
o
fe
jih
m
q
ls
n
trp
Moisture Sensor
Battery Voltage Div ider
Vref
PIC16F684 (PIN 2)
XBee Pro
Figure 10 -
35
Schematic – Probe XBee
The following tables (Table 11) delve deeper into the functionality of each
component in figure 10.
Table 11 - Schematic FR Tables – Probe XBee
Designation
XBee Pro
Part
Functionality
XBee Pro Transceiver
The XBee is the communication center for the lawn probe. Any signals
that need to be sent or received are passed through here. These include
data on soil moisture, and probe vitals such as current battery charge.
Designation
LED1
Part
Functionality
LED
This LED indicates when the XBee unit is on. It is position such that
when PIN 9 on the XBee drops to a low state, indicating the XBee is
ON, the LED will illuminate.
Designation
R6
Part
Functionality
Resistor, 330Ω
R6 limits the current flowing into PIN 9 to ensure it does not exceed the
maximum allowable by the XBee.
Referring to figure 4, the following schematics represent each block for the
weather station. While the pressure and temperature sensors have already been described
in detail, they are still included in proceeding circuits.
The first of these is the power supply. This unit provides the necessary 3.3VDC,
+5VDC, and -5VDC to the weather station‟s circuits. Each component in the power
supply is described by the functional requirements that follow in Table 12.
36
5.5V Wall Wart
1
2
3
IN
GND
OUT
R12
SDX30A2 (PIN 5)
LP2950
5.5V Wall Wart
IN
GND
OUT
R16
0
C4
4.7u
1
2
3
0
0
LF33CV
4.7u
4.7u
C6
3
4
5
+Vin
-Vin
-Vout
GND
+Vout
VASD1-S5-D5-SIP
0
Op-Amp (+) Power
Op-Amp (-) Power
Xbee (PIN 1)
C5
Figure 11 -
R24
1
2
Schematic – Weather Station Power Supply
Table 12 - Schematic FR Tables – Weather Station Power
Supply
Designation
LF33CV
Part
Functionality
Fixed Output Voltage Regulator
This regulator provides a constant 3.3VDC supply to the XBee module
for the weather station.
Designation
LP2950
Part
Functionality
Precise Fixed Output Voltage Regulator
The LP2950 supplies a constant 5VDC source to the rest of the weather
station. A more precise regulator was required to achieve the exact
offsets needed for the sensor amplifiers.
Designation
VASD1-S5-D5-SIP
Part
Functionality
±5V DC/DC Converter
This DC/DC converter provides the ±5V to power the op-amps.
Designation
C4, C5, C6
Part
Functionality
4.7μF Capacitor
These filter the outputs of the DC/DC converter and the precision
voltage regulator.
Figures 12 and 13 represent the two amplifier cirucits used in the weather station.
The first of these defines the range for measure of the temperature sensor.
Stage one is meant to buffer the output from the sensor itself. While the LM335
temperature sensor has a range of -40º to 212º F, for greater accuracy, this has been
37
restricted to 0º - 120º F. This is done using the second stage op-amp. To restrict the
maximum temperature to 120º F, the final stage op-amp is used to scale the value of the
max temperature to 3.3VDC.
R16
LP2950 (PIN3)
20k
ADJ
Vin
GND
LM335
1
2
3
R15
10k
0
1
1
R12
2k
U4
+
-
uA741
1
OUT
R13
2
OUT
2
U5
10k
+
R17
uA741
-
U6
uA741
+
Temperature Output
OUT
2
-
22k
LP2950 (PIN3)
R14
20k
R18
5.1k
0
0
Figure 12 - Schematic – Weather Station Temperature Amplifier
The amplification of the pressure sensor required more op-amps to yield a precise,
properly scaled measurement.
The pressure sensor measures the absolute pressure
referred to an internal vacuum. This measurement is taken as the voltage across a bridge
circuit. For more details see attached datasheet on the SDX30A2. The differential
voltage is then buffered through two separate op-amps and the difference is amplified by
a factor of 100. This is done using op-amps U7-U9. Once this raw pressure reading is
amplified to a more usable value, the full range output of the sensor, being 0-30 psi, is
scaled between realistic pressures normal to the environment. This is done by first
offsetting the output to the lowest pressure, and then amplifying that signal to make the
maximum output of 3.3VDC to be the highest pressure of the determined range.
38
1
2
3
SDX30A2
6
5
4
-Out
NC1
GND
+Vs
+OUT NC2
LP2950 (PIN3)
LP2950 (PIN3)
0
1
R24
15k
U7
R19
+
R21
OUT
2
-
1k
U9
1
1
100k
-
uA741
R23
OUT
1
+
R20
R26
5.1k
1
OUT
2
1k
15k
-
33k
R27
4.7k
0
Figure 13 -
Pressure Output
uA741
R28
R22
100k
uA741
+
OUT
2
uA741
0
+
U11
+
uA741
OUT
2
U10
5.1k
2
U8
-
R25
0
Schematic – Weather Station Pressure Amplifier
The derivation of each stage found in both amplifier circuits can be found in the
testing procedures for each sensor. These were omitted here to focus on the functionality
of the amplifiers themselves.
The final portion of the Weather Station is the XBee module. Like the other
XBee‟s, this one transmits all data to the control. It‟s only two inputs are the amplified
temperature and pressure readings. As for pins 18, 17 and 11, these are LEDs to indicate
temperature being too hot, too cold, and a pressure reading low enough to predict rain is
on the way, respectively.
LF33CV (PIN3)
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
a
b
c
d
g
k
o
fe
jih
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n
trp
Temperature Output
Pressure Output
R29
LED2
330
R30
LED3
330
R31
LED4
0
0
0
0
330
XBee Pro
Figure 14 -
Schematic – Weather Station XBee
39
For the central hub, this consists of a power supply, XBee module, and a set of
driving circuits. The power supply uses the LF33CV constant output voltage regulator.
This will provide power to the XBee and the base current for the driving circuit.
5.5V Wall Wart
1
2
3
IN
GND
OUT
0
Xbee (PIN 1)
LF33CV
Figure 15 -
Schematic – Central Hub Power Supply
The XBee for the central hub takes in commands from control unit based on
watering. This XBee is connected to four driving circuits to represent four different
watering zones. These driving circuits can be configured in different ways depending on
existing circuit hardware. In this example they are used to complete the DC circuit, by
providing ground through a transistor operating in the switching region. Essentially,
5VDC is applied to the coil of a relay on the existing sprinkler system, while the ground
is connected through transistors U12 through U15 for zones 1-4 respectively. When the
zone in question is to be actuated, the switch will be turned on by the XBee, completing
the circuit and enabling the relay, turning on the sprinklers for that zone. Indicator LEDs
are also included for each zone to show when the zone is watering.
40
+
Sprinkler Switch Ground (Zone 1)
U12
R32
D3
2.7k
R39
2N2222
LED5
0
330
Sprinkler Switch Ground (Zone 2)
0
LF33CV
U13
R33
1
2
3
4
5
6
7
8
9
10
2.7k
20
19
18
17
16
15
14
13
12
11
a
cb
d
kg
o
fe
jih
m
lsq
n
trp
R38
LED6
0
R37
LED7
0
0
330
Sprinkler Switch Ground (Zone 3)
330
U14
R34
2.7k
0
D4
2N2222
D5
2N2222
XBee Pro
0
R36
LED8
0
330
Sprinkler Switch Ground (Zone 4)
U15
R35
2.7k
D6
2N2222
0
Figure 16 -
Schematic – Central Hub XBee and Driving Circuit
41
10.5
PCB Artwork
Shown below in figure 17 is the schematic for the printed circuit board (PCB) that
was used for the lawn probe. The program that was used to develop the PCB was a
freeware program by the name of PCB123, which is developed by Sunstone.
Figure 17 -
PCB Layout
Shown below in figure 18 is a picture of a populated PCB, based off of the design
that can be seen above in figure 17. The PCB was designed in such a way that the several
subsystems for the lawn probe are grouped in close vicinity of one another.
42
Figure 18 -
Populated PCB
It is worth noting that there were two changes that had to be made to the original
PCB design, both of which were simple fixes. The first difference is obvious and that is
that R9 has been jumpered and no physical resistor is placed here. This is due to the fact
that the original design was done using breadboards and Agilent power supplies as
opposed to actual batteries and sunlight. The Agilent supplies provide a great amount of
consistent current so the R9 resistor was necessary to pull that current down slightly. The
difference is that in the real world, the batteries don‟t generate nearly as high of a current
so the inclusion of that resistor brought the current down to an unacceptable level, so it
was not included. Additionally there should have been a jumper between the pin 11 of the
PIC16 and R10. This jumper connects the push-button and allows the probe XBee to be
woken up by the manual push-button.
43
10.6
Probe
Figure 19 is the complete flat model for the entire probe circuit shown in figure
18. For demonstration purposes, the flat model of the probe has been split apart into each
individual subsystem for convenience and understanding.
Figure 19 - Flat Model
Figure 19 showed an overview of the entire probe circuit. With this information in
hand, the probe circuit subsystems will now be looked at individually so that they can be
related back to previously presented information. The first of those systems can be seen
below in Figure 20, the charging circuit.
44
Figure 20 -
Charging Circuit
The purpose of the charging circuit is to ensure that the probe batteries remain
charged at an appropriate level, and do not get over charged. The connections shown in
Figure 20 correlate exactly with what is shown in figure 3 of the Level II Hardware
diagram. The input on the top of the charging circuit will be connected to the solar cells,
with the bottom connection going off to the PIC16. The PIC16 will monitor the battery
levels and determine whether or not it is necessary to charge the batteries. The charging
circuit outputs to the battery, (right-most connection) and allows the battery to charge
when necessary.
The battery system itself can be found below in figure 21. The function of the
battery is to power all of the various systems in the probe.
45
Figure 21 -
Probe Battery
The top input to this board is for the physical connection of the battery packs. The
connector on the left goes to the charging circuit, which will dictate when the batteries
are allowed to charge. The bottom connector feeds back to the PIC16 so that the battery‟s
energy levels can be monitored at all times. The connector on the right connects to the
DC/DC converter so that the voltage may be stepped down for use by the xBee. This
relationship was also portrayed above in figure 3 of the Level II Hardware diagrams.
Now that the battery subsystem has been covered, the batteries are used to power the
DC/DC converter, which is shown below in figure 22.
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Figure 22 -
DC/DC Converter Subsystem
For as complicated as the DC/DC converter looks, its only purpose is to take the
voltage provided by the battery and step it down to 3.3VDC so that it can be used by the
XBee. The XBee system can be seen below in Figure 23. The XBee is the device that
allows for wireless communication between the lawn probe and the home CPU system,
which will be discussed shortly.
Figure 23 -
Lawn Probe xBee Subsystem
The xBee only has one output, which is to the PIC16. This is because when the
lawn probe isn‟t taking moisture readings, the xBee will be turned off to conserve power.
47
For demonstration purposes the xBee is also connected to a switch and a potentiometer. It
is worth noting that in the actual physical system, these two components will not be
present. The switch allows for the users to alternate between taking actual physical
readings from a moisture sensor, which would be connected to the bottom right hand pin,
and between a user manipulated potentiometer. The switch and potentiometer will also
not be found above in Figure 2 of the Level II Hardware diagrams, it is merely an
addition that assists in demonstration and testing. The final probe subsystem can be found
below in Figure 24 and that is the PIC16 microcontroller. The PIC16 allows the system to
control the battery voltage, as well as when the xBee transmits moisture readings from
the moisture sensor itself.
Figure 24 -
PIC16 Subsystem
The PIC16 has been discussed at length aside from one small device, which is the
push-button wake-up. As the super sprinkler system is designed, it will take moisture
readings at user-defined intervals throughout the day. The purpose of the push-button is
to provide an override to these user defined parameters. The user would simply press this
48
button, and the xBee would wake up and transmit current moisture levels back to the
home CPU.
Central Hub
The central hub is a middle communication zone between the home CPU and the
sprinkler driving circuit. The central hub‟s main purpose is to send the actuating signal to
the sprinkler solenoids in the event that watering is necessary. The flat model for the
central hub can be seen below in Figure 25.
Figure 25 -
Complete Central Hub System, Flat Model
As was seen in Figure 4 of the Level II Hardware diagrams, this system aligns
exactly with what was described there. The central hub xBee is powered by a dedicated
120VAC line that is obtained from the home. The central hub xBee is constantly running
so that it will always be available to send an actuating signal in the event that it is
necessary to water the lawn. The central hub itself is shown below in Figure 26.
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Figure 26 -
Central Hub Subsystem
For the purpose of our demonstration, there were 4 zones that contained moisture
probes. These four zones were monitored by the 4 LED lights shown in Figure 26. In the
actual physical system, these lights would not be present. The last part of the central hub
system is the driving circuit, which is shown below in Figure 27.
Figure 27 -
Driving Circuit Subsystem
The driving circuit behaves as expected. Its purpose is to send out an actuating signal to
the existing sprinkler system in the event that it is necessary to water. It is hard-wired to
the central hub xBee in order to receive this information.
50
10.7
Weather Station
A major feature of the super sprinkler system is that it has the capability to predict
the weather based on two constantly running sensors, one of which measures temperature
and the other measures barometric pressure. The complete weather station can be seen
below in Figure 28.
Figure 28 -
Complete Weather Station, Flat Model
The weather station shown above was modeled after the exact same systems that appear
in Figure 3 of the Level II Hardware diagrams shown above. Both the temperature and
pressure sensors are sent to an amplifier so that their values can be amplified and
recorded. This is due to the fact that we are monitoring a very small range of
temperatures and pressures and in order for the changes in those values to be measured,
they must be amplified so that their changes are more pronounced.
The board shown below in Figure 29 contains the pressure and temperature
sensors, as well as the weather station xBee and the temperature sensor amplifier.
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Figure 29 -
Weather Sensor and Temperature Sensor Amplifier
Subsystem
Similar to the lawn probe board shown above in Figure &, the weather sensor
board also has input pins for switches and potentiometers. Similar to the above system,
these are included to assist in the demonstration of the system but would not be included
in the final product. The switches and potentiometers are included so that it is possible to
alternate between the actual sensor readings and user manipulated values. The board
shown below in Figure 30 is the last remaining component and it is simply the
amplification and filtering system used for the pressure sensor.
Figure 30 -
Pressure Sensor Amplification and Filtering Subsystem
52
It is worth noting that a finished super sprinkler product will not have the weather
station setup as shown above. The same systems will be present, but they will be placed
into a more compact system and housed in such a way that protects the electronics from
the elements. This system is displayed as such due to the fact that the system must be
demonstrated and this style of presentation allows for clear representations of the weather
station as a whole.
10.8
Home CPU
The final system, which also happens to be the one that contains all of the system
logic, is located at the home CPU. The entirety of this system consists of an xBee
connected to a computer by way of a USB cable. A potential configuration for this
system can be found below in Figure 31.
Figure 31 -
Complete Home CPU System
53
The system as a whole does not include a personal computer, as that must be
provided by the user. The software provided with the system is loaded onto the home
computer and this system contains all of the logic that is used to make decisions about
whether or not it is necessary to turn on the sprinklers. If watering is necessary, the home
CPU xBee relays this information back to the central hub xBee to actuate the lawn
sprinklers. This process repeats at a designated interval.
10.9
Complete Lawn Probe
Shown below in Figure 32 is a photo of a complete probe circuit, which
corresponds to the flat model that was shown above in Figure 19.
Figure 32 -
Complete Lawn Probe
The manual wake up button can be seen on the right side of the probe. The
antenna on the left side of the case was included so that the probe would be useful for
54
very long distances. The solar cells used to charge the batteries are placed on the top of
the case and are angled in such a way as to provide optimum charging capabilities. The
moisture sensor then sticks out of the bottom of the case so that it may be easily inserted
into the ground for use.
10.10
Testing Procedures
There were three sensors that were used to accomplish all of the challenged
presented by this project. These three sensors, including their testing and calibration
methods are discussed below.
Moisture Sensor
The first sensor used in this system is the moisture sensor. The moisture sensor can be
found out in the lawn probe and its purpose is to measure the moisture content of the
surrounding soil so that this information can be relayed to the home CPU for analysis.
This sensor used was the Vegetronix VG400 series. In order to properly test the device
the sensor was placed into a 12”x14” tub with 5” of dirt inside. Water was then added at
regular intervals and the voltage measured by the sensor was recorded. Figure 33 is a
graph of the the result of this test.
55
Figure 33 -
Moisture Sensor Graph
As can be seen, the sensor behaves in a linear fashion until a certain point is
reached, at which point the sensor saturates and the output voltage doesn‟t change
regardless of how much water is added to the system. The output voltage for the moisture
sensor is from 0-3VDC. The reason why the sensor capped itself around 2.1VDC is
because of the container that was used in the experiment. The version of moisture sensor
that is used is one that operates at a low frequency. Since the operating frequency of the
moisture sensor is so low it causes the size of the container to impact the sensor‟s output
voltage. In order to achieve a maximum output voltage from the sensor the volume of the
container must be large, such as a lawn. Also it is worth mentioning that as water was
added to the soil, the output voltage changes nearly linearly as the amount of water
increases. At a certain point, this linear relationship starts to break down and this is also a
result of the version of sensor that was used. This also occurs because of the low
operating frequency of the moisture sensor. These two shortcomings both result from the
56
fact that the sensor has a low operating frequency, and in spite of these shortcomings this
sensor was used because the low operating frequency means that the power needed to
operate this sensor is extremely low. This was advantageous to this design because of the
fact that power management was essential for long term sustained operation and this low
operating frequency version of the moisture sensor provided that capability.
10.10.1
Pressure Sensor
The next sensor that needed to be tested was the pressure sensor. The pressure sensor that
was used was the Honeywell SDX30A2. The pressure sensor is a main component of the
weather station. Its purpose is to measure the barometric pressure levels outdoors to assist
in making judgments about whether or not it is going to rain. In order to test the pressure
sensor an air compressor was used. The air compressor was pressurized to a certain psi
and then the nozzle was hooked onto the pressure sensor. At this point the air in the
compressor was released and the pressure sensor‟s output voltage was measured. Figure
34 shows the results of this test.
Figure 34 -
57
Pressure Test Results
The pressure that is being applied in the graph above is applied on top of the already
existing pressure in the room. This test was repeated five separate times to check the
consistency of the sensor. As can be seen from the graph above, the pressure sensor
behaves in a linear fashion throughout the entire operating range. This implies that the
sensor will function properly through normal conditions.
10.10.2
Temperature Sensor
The final sensor that needed to be tested was the temperature sensor. The temperature
sensor that is used is the LM335. The temperature sensor is the other main component for
the weather station. The purpose of the temperature sensor is to measure the outdoor
temperature to assist in making judgments about whether or not it is going to rain. In
order to test the temperature sensor, it was placed outside and allowed to settle at the
surrounding temperature. From here, the sensor‟s output voltage was measured and the
corresponding temperature to that voltage was recorded. This measured temperature was
then compared with the actual outside temperature. Figure 35 displays the results of this
test.
Figure 35 -
Temperature Sensor Test
58
This test was repeated once daily over a period of 10 days. As can be seen from the graph
above, the temperature sensor that was used behaves in a linear fashion. The data sheet
for this particular sensor claimed that the sensor responds at a rate of 10mV/K and this
behavior was confirmed by testing. The only issue with the temperature sensor was that is
measured roughly 4ºF less than the measured temperature. This was due to inaccuracies
in the sensor which were known and specified in the data sheet.
It is worth mentioning that the temperature sensor is designed such that it can have an
output voltage of 2.3 to 3.7VDC for its full temperature range. For the super sprinkler
system, this output range has been offset and scaled so that the output voltage will vary
from 0 to 3.3VDC. This was accomplished by passing the temperature sensor output
through an initial amplifier so that the signal is boosted and becomes more readable. The
low end of the temperature range is then taken and converted into a voltage using the
equation shown above in the Temperature Sensor Output Voltage vs. Temperature
graph. This voltage will now become the offset that makes the low end temperature
equal to 0VDC. This becomes the next amplifier stage for the offset. The next stage is
first created by repeating the process with the high end temperature. From here, the
difference between the high end temperature and low end temperature voltages is
recorded and then 3.3 is divided by this difference. This becomes the value for the final
gain stage amplifier. This circuit can be found above in Figure *** in the Level III
Hardware diagrams.
This process is repeated in an identical fashion for the pressure sensor. The circuit for
this amplifier and offset is found above in Figure ### of the Level III Hardware
diagrams.
59
10.11
Software (DP,MB,TM)
10.11.1
GUI
The structure of the GUI is too complex to be explained with flow diagrams;
therefore event states will be used accompanied by appropriate figures.
The GUI
displays information from the central hub, weather station, lawn probes, and the control
XBee.
It also allows the end user to modify parameters such as watering time,
temperature limits, and the desired moisture level of the lawn. Though the system is
designed to run on auto with limited user interaction, there is a manual feature included
should one desire to control each zone at will. Figure 36 below is an example of what a
typical GUI would look like for a Super Sprinkler system with four zones.
Figure 36 -
Central Hub Information
The central hub portion of the GUI displays the current status of each zone
configured for the system.
The maximum number of zones is eight; however this
particular example consists of four. For each zone, different graphics are used to notify
60
the user of various states the zones may be in. Two graphics are included for each zone.
The left most is that of the watering condition, the right is the connection status. These
are described in detail in the following two tables, Tables 13 and 14.
Table 13 - Graphics Table 1
Graphic
State of Zone
Zone is not setup. This means the zone in question does not exist.
Not connected. Zone has not taken a reading since the application (GUI)
was last started.
Auto disabled. This occurs when the control is not automatic. In other
words, this zone is set to be manually turned on and off.
Sleep mode. Probe in the zone is in sleep mode, previous readings have
been taken since application was last started
Reading. Lawn probe is currently taking a moisture reading.
Timeout. At each time a moisture reading is taken, four are actually taken
and averaged. While this normally takes approximately 30 seconds, the
PIC in each probe will time out in two minutes. When this occurs, this
image is displayed.
Table 14 - Graphics Table 2
Graphic
State of Zone
Not watering. Zone is not currently watering
Manual watering. Zone is being manually watered by user.
Try to water. The actuating signal was sent to the driving circuit but
watering is not occurring.
Auto watering. Zone is set up for automatic watering and the zone in
question is currently watering
Force stop. User has manually forced the zone to cease watering.
Watering still on. Zone is still watering even after the specified watering
time has elapsed. This can occur when the application is shut down during
a watering session.
Weather Station Information
The weather information displayed by the GUI is a combination of graphics and
numerical data. The real time temperature is displayed at all times in ˚F, whereas the
pressure will be displayed as a “graphical range.” Both pressure and temperature have
accompanying graphics. Because pressure is used to help predict stormy weather the
61
measurement will be compared to four ranges of barometric pressure. The levels are
sunny, fair, rainy, and stormy. These figures are shown below in table 15.
Graphic
Table 15 - Barometric Pressure Graphics
State
Sunny. Pressure is in the top 75% of the range.
Fair. Pressure is between 50 and 74% of the range.
Rainy. Pressure is between 25 and 49% of the range.
Stormy. Pressure is between 0 and 24% of the range.
Weather restrictions disabled. The user has selected to not incorporate
weather information in the watering decision.
Under temperature. Temperature is below the user specified limit.
Over temperature. Temperature is above the user specified limit.
Figure 37 below shows one of the two graphics for temperature. In this case the
temperature has dropped below the minimum threshold. Thus the under temperature
graphic appears.
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Figure 37 -
Lawn Probe Information
The probe information section of the GUI shows the user details about each probe in
operation. A selector menu allows toggling between the different probes. The GUI will
display:

The description of the probe in question (defined by user)

When the specific zone was last watered

When the last soil moisture reading was taken

The soil moisture content, in percent, from the most recent reading

The battery voltage level of the probe from the most recent reading
Each of the three information sections, central hub, weather, and probe also has a
connection display to show signal strength or loss of connection.
At the very bottom of the GUI application, the connection between the control XBee and
the home CPU is depicted using the following images shown in Table 16.
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Table 16 - Connections Graphics
Graphic
State
Connected. XBee is connected to CPU via USB cable.
Not connected. XBee is not connected to CPU.
The type of control and weather restrictions is also shown at the bottom of the
interface. The control can either be automatic, meaning the logic will decide on watering
decisions based on soil moisture, temperature and pressure, or manual, meaning the user
decides directly when to water. The weather restrictions can also be enabled or disabled.
When enabled, the system will again utilize the logic based on all three parameters, soil
moisture, temperature, and pressure. When disabled, the decision to water will be solely
based on soil moisture.
The GUI has several drop-down menus to adjust settings and define user
parameters.
The first is system settings.
To get to the system settings, select
Settings>System Settings, in the upper left corner.
The system settings allows the
assignment of the default serial port, the central hub wireless address, network PAN ID,
the pause between central hub network pings, and the weather and probe voltage
reference values. These settings should generally not be adjusted by the average user.
The user can also select which probes to be manually controlled, and which are
controlled by the logic of the system. This can be done by selecting Settings>Probe
Configuration>Online>Zone #. When selected a check mark will appear next to the zone
in the drop down menu, and the watering decision for that zone will be based on the
sensor logic. When un-selected, the watering for that zone can only be actuated by user
control through the GUI.
To define the settings for each zone individually, select Settings>Probe
Configuration>Settings>Zone #. This will allow the user to specify a description of the
64
probe, the moisture threshold, as a percentage, the zone watering runtime, and the
individual wireless address of the XBee in the probe.
To toggle the weather restrictions on or off, select Settings>Weather>Restrictions.
When the restrictions are enabled, a checkmark will appear next to the word restrictions.
Likewise, when no checkmark is present, the watering decision will be based on soil
moisture only.
The user can also adjust maximum and minimum temperature settings. The
minimum setting is the lowest temperature at which the zones can be watered. The
maximum is just the opposite; the logic will not allow watering above this maximum
temperature. To access these settings select Settings>Weather>Settings. The user can
also specify the weather XBee‟s wireless address in this setting box.
In the Settings drop down menu, the “Home Base” submenu is used to specify the
port that is connected to the control XBee module. The GUI will search the computer‟s
hardware to find the available COM ports and list them here.
The Control menu allows the user to switch between automatic control and
manual control. It also has sub menus to manually turn on and off different zones. Any
zone can be manually turned off whether automatic control is selected or not. However,
to manually turn on a zone, the automatic control must not be selected.
Lastly, the System menu has selections to close, debug, disconnect, and reload
app. The close option closes the application. The debug selection was used for testing
purposes and troubleshooting by the programmer. When disconnect is selected, the
connection between the CPU and the control XBee is severed. Finally, reload app
reinitializes the program, the same effect as closing it down and re-opening.
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10.11.2
Lawn Probe Embedded Software (MB)
The PIC16F684 is the chosen microcontroller for probe battery management and
probe sleep mode. This is done through the management of four interrupts.
The pin layouts can be seen in Table 17 below. Pins 4, 9, and 13 remain unused.
Table 17 - PIC Pin Layout
Pin
I/O
Function
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Vdd
RA5
RA4 (AN3)
RA3
RC5
RC4
RC3
RC2
RC1
RC0 (AN4)
RA2
Vref (RA1)
RA0
Vss
Power: main power (battery input)
Input: xBee done xmitting
Input: Battery voltage ADC input
*unused
Output: Debug (TMR0 interupt signal)
Output: Charge signal (enable/disable charge)
Output: Wakeup signal for xBee module
Output: Battery voltage shutdown
*unused
Input: Charging source ADC input
Input: Manual wakeup (external wakeup button)
Power: Reference voltage (RA0) {3.3V reference diode)
*unused
Power: Ground
The probe sits idle in a low power sleep mode in four hour intervals. The probe will
remain unless one of the following two actions occur:
1. The four hour sleep cycle is completed and the microcontroller automatically
wakes up the XBee, which is denoted as the Timer 2 Interrupt.
2. The manual push button is activated to wake the probe up, which is denoted as the
Pin Change Interrupt.
Concerning the Timer 2 Interrupt, every four hours the microcontroller will check to
ensure the batteries have been recharged to a high enough voltage to provide power to the
probe circuit. When this voltage has been concerned, the XBee is awoken through setting
RC3 low. The flow charts for the main function and the Timer 2 Interrupt can be seen in
figures 38 and 39, respectively.
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Figure 38 -
Main Function Flowchart
67
Figure 39 -
Timer 2 Interrupt Flowchart
Concerning the Pin Change Interrupt, when the manual push button is engaged the
microcontroller will first check to ensure the batteries have been recharged to a high
enough voltage to provide power to the probe circuit. When this voltage has been
confirmed, the XBee awakes through pin RC3 being pulled low. The flowchart can be
seen in figure 40.
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Figure 40 -
Pin Change Interrupt
When the probe circuit is turned on through Pin RC3, the microcontroller begins the
Timer 1 interrupt. This interrupt is responsible for monitoring data transmission through
the XBee through a transmission timeout counter. A time interval of 90 seconds has been
specified for data transmission. If the XBee completes transmission pin RA5 will be set
high, and the microcontroller will wait one sentence and turn off the probe circuit by
setting pin RC3 high. Waiting allows the XBee to reset to its original state. If the XBee
fails to complete transmission within the allotted time the microcontroller will put the
probe back into sleep mode, and the timeout counter will be turned off. The Timer 1
Interrupt flowchart can be seen in figure 41.
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Figure 41 -
Timer 1 Interrupt Flowchart
One final interrupt, Timer 0, has also been implemented to monitor the battery
voltage and manage recharging. The battery voltage and so voltage are respectively
assigned to the analog to digital converters on channels three and four, and both are
initialized to zero. The voltage tests are synced to the clock through the debug pin RC5.
This syncs state changes to occur on every other clock cycle. Figure 42 displays the
Timer 0 Interrupt flowchart.
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Figure 42 -
Timer 0 Interrupt Flowchart
A function designated checkCharge is responsible for managing the recharging
function of the probe. If the battery voltage is less than 7.15 volts (constant defined in
the header file), the voltage across the solar cells is compared to the battery voltage.
Charging begins if the solar cell voltage is greater than the battery voltage. When the
battery voltage reaches 7.6 volts (also defined in the header file), charging is stopped.
When charging is stopped, the voltage will drop from 7.6 volts. Setting the charging
71
voltage to 7.15 provides a hysteresis which prevents the probe from getting stuck in a
constant charging state.
A function called checkShutdown is responsible for disengaging the DC/DC
converter if the battery drops below 5.95 volts. This low threshold also governs whether
or not the probe will energize when the four hour interval has ended or the manual push
button has been engaged. The flowcharts for checkCharge and checkShutdown can be
seen in Figure 41, the Timer 0 Interrupt Flowchart.
The following five figures are simulation waveforms that visually explain the
previously explained operation of the microcontroller. The following waveforms are
defined as such: D0 – Interrupt Clock; D1 - !Shutdown; D2 – Charge; D3 – Sleep. Figure
43 shows that the battery voltage is less than 5.95 volts, and the probe is shut down and
not charging.
Figure 43 -
Probe Shutdown, Not Charging
72
Figure 44 shows that the probe is not shutdown, but is also not charging. This case
represents a scenario in which the battery is within the 7.3 to 7.6 volt range where
charging does not occur.
Figure 44 -
Probe Shutdown, Not Charging
Figure 45 shows the scenario in which the probe is shutdown and charging. In this
case, the battery voltage is below 5.95 volts, and the solar cell voltage is greater than the
battery voltage.
Figure 45 -
Probe Not Shutdown and Charging
73
Figure 46 displays the scenario when the probe is not shutdown but the batteries are
charging. The battery voltage is at approximately 6 volts. The probe is asleep
Figure 46 -
Probe Shutdown and Charging
Figure 47 shows the battery is charged (D2 shows not charging).
Figure 47 -
Battery Charged
Figure 48 shows the XBee in its woken state. Signal D3 is low, signifying wake up.
74
Figure 48 -
Probe in Wake Up State
10.12
Functionality – Home PC Interative Software (TM)
10.12.1
Watering Decision
A watering decision is made each time a new moisture reading is recorded. This
will happen every four hours (or when wireless probe is manually turned on) per zone.
Figure 49 shows the flow chart for the watering decision. Once a moisture reading is
received and recorded, the reading is compared to the user set threshold for that zone. If
the moisture is below the threshold (the ground is dry), the watering decision continues to
test more conditions. If the reading is above the threshold, the zone will not be watered
and the probe will go back to sleep after three more readings (four total per a wake up).
75
Figure 49 -
Watering decision flow chart.
If testing is continued, the program makes sure that the zone is currently online.
Also, if the zone is online, the system needs to be set to automatic. If either is disabled,
watering will not take place. Next, weather conditions are tested if weather restrictions
are enabled (see below for more information on weather testing). If there are no alerts, or
restrictions are disabled, watering will take place if it has not already started. Once
watering is started, the wireless probe will be informed to go back to sleep and the main
GUI will be updated.
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10.12.2
Weather Test
The weather test is used to prevent watering at un-ideal times. The test is made
up of three checks: over temperature, under temperature, and rain. As previously
mentioned, hot air outside could scorch the grass when watering or the cold air may
promote fungus growth or freeze. These two tests will make sure watering does not
occur during the set temperature thresholds. The thresholds are determined by the user
interface parameters located in the weather settings. The third test determines if it is
raining or about to rain. In this situation, the system will save water and wait for the rain
to moisturize the zone. Figure 50 shows the flow chart of the weather test at the top
level.
Figure 50 77
Weather tests flow chart.
The temperature extreme test is a simple comparison of the current temperature
versus the two thresholds. The rain test is a little more involved in the process. Figure 51
shows the flow chart for the rain prediction. Prediction is done using the recorded
pressure. If the pressure is at the low extreme (29.50”Hg), it will most likely rain. Also,
if the weather is fair (using 30.5”Hg) and has been dropping (at a rate of
0.30”Hg/20minutes) it may rain. To show if it is not likely to rain, pressure will be above
the low extreme (29.50”Hg) or if the pressure has been increasing (at a rate of
0.30”Hg/20minutes) and is above 29.15”Hg. These are just predictions and do not
confirm actual rain.
Figure 51 -
Rain prediction flow chart.
78
If any weather test shows an un-ideal condition, watering will not take place. Due
to predictions being made, they may not always deliver the desired result based on an
uncommon weather pattern. Disabling weather restrictions will skip all these test. The
user will still be informed of the alert, but will not affect the watering choice. Another
system bypass to ignore weather decisions is the last watered timestamp. If the system
has needed water for more than 10 hours (3rd probe wake-up cycle) and has not watered
due to a rain prediction, the prediction will be overthrown and watering will take place.
Alerts are shown in two physical locations. The first is located on the GUI. As
explained previously, the appropriate image and text warning will let the user see an issue
with the weather. On the weather station itself is three LED‟s. Each LED represents an
alert. The red shows an over temperature, the white shows an under temperature, and the
blue shows possible rain.
10.12.3
Manual Control
The GUI allows the user to manually control the sprinkler system. To turn on a
specific zone, the system must be on manual or the zone must be offline. Otherwise, the
zone will not water and the command will be ignored. Once watering has begun, the user
is responsible for turning off the zone. No timer is set for manual control.
Turning off a zone can occur at any time as long as the zone is currently enabled.
This feature allows the user to stop manually started watering, or to override an
automation decision. Figure 52 and Figure 53 shows the flow chart for the two cases.
79
Figure 52 -
Manual turn on flow chart.
Figure 53 -
Manual turn off flow chart.
While in manual control (per zone or whole system), the probe readings are still
updated. No watering decision is made, however. When switching back to auto control,
any manually turned on zones will be shut off.
10.12.4
External Files
80
External files are used to store various amounts of data. These are included in
three text files: settings.txt, parameters.txt, and lastreadings.txt. The files are needed for
the program to run correctly. Files should not be manually changed by the user due to the
sensitivity of their formatting
The „settings.txt‟ file holds all the setting information. When a setting is adjusted
in the GUI, the file is updated. These settings are stored into internal variables in the
program for startup.
The „parameters.txt‟ file holds the different parameters used. These values are
also stored in internal variables to be used in the program at initialization. Any
adjustments to parameters are saved and written into the text file.
The „lastreadings.txt‟ files holds data to initialize reading values at startup and
remember important timestamps. Every ten central hub pins, the current values of all the
readings are saved into the file. This allows the sprinkler program to restart seamlessly in
case of an accidental shutdown. This auto save also occurs every time a new moisture
reading is received. This file also keeps track of the last time each zone was watered.
10.13
Software Events
Once the software starts up, it sits idle until an event occurs. An event will occur
every time the user interacts with the GUI. These events control the functions described
in the GUI. Other events occur internally based on data received from the serial port and
timers within the code.
10.14
Wireless Data Received
81
Wireless data is sent and received through the connected serial port. Data is
coming from a wireless probe, the weather station, or the central hub. By scanning the
incoming wireless packet, the address is used to determine which location the data is
coming from.
When data is received from the wireless probe, the moisture reading and battery
voltage is sent as a 10-bit ADC as well as the connection strength. The program converts
these analog voltages into usable data based on voltage dividers, voltage reference, and
any other scaling involved. Once data is recorded, the program calls for the watering test
as described above. Probe readings are recorded up to four times. After four readings, a
shut down signal is sent to put the probe back to sleep. If the zone is determined to
water, the probe will go to sleep before four readings.
Data is received from the weather stations every three seconds. Each reading
updates the weather portion of the GUI. Temperature and pressure readings are retrieved
from the weather station and converter to their proper units. Weather tests will be done
to determine if any alerts need to be issued. Any found alerts will be displayed on the
GUI and taken into account when a water decision is called for. No watering decision,
however, is made during this event.
The central hub is mainly used as an output station to control the sprinkler driving
circuit. However, it also receives data to check the connectivity to the central hub as well
as the states of the pins. This happens every time the central hub is pinged based on the
timer event described below. The states of the pins are stored in variables internally to
complete error checking tests against the logic state the pin should be in. The central hub
also receives data to confirm that the driving pins are successfully being toggled.
82
10.15
Timer Events
Different timer events run in the background while the program is running. Two
timers are started when the application is ran and continue until the application is closed.
The other is turned on and off when needed.
The central hub timer is essential to the program to keep the user aware of any
issues with the system. The event is a user defined setting that occurs from 60 seconds to
10 minutes. To use less timers, various timestamps are stored and checked during this
event and are analyzed. The first check is for probe connectivity. If the program has not
seen a reading within four hours (sleep cycle for the probe), the probe is then considered
no longer connected to the system. If the probe was in the middle of taking readings and
did not shut off within two minutes (the wireless probe auto sleeps in around 90 seconds
if it was not told to sleep), the probe is considered to have timed out. The ping also
checks on the status of the weather station. If the weather station has not seen a reading
in five minutes, it is considered no longer connected to the system (a reading should be
received every three seconds).
After connectivity between components is determined, the ping calls for the
program to send out various remote commands to check signal strength and the state of
all the outputs on the central hub xBee. Once the states have all been received, they are
compared to their logical value (the state the pin is supposed to be in). If any pin is
enabled when it is supposed to be off, it is then shut off. This check is to safe guard
against an accidental closure of the program during the middle of watering.
The next timer is used for remember settings throughout the open time of the
application. The timer event occurs after every five central hub pings. At this time, a list
of all the current readings, last watering time for each zone, and settings is compiled.
83
This list is then saved in the „lastreadings.txt‟ file to be used the next time the program is
opened.
The last timer event is the sprinkler watering run time. Each zone has its user
defined run time that watering will continue. Once a zone has been automatically turned
on, this timer will start (manual events so not start the timer as previously mentioned).
After the timer is expired, the program will find the zone which expired, and disable
watering until next event is called. After disabling the watering, the timer is shut off.
10.16
Conversion Functions
Different conversions are used to convert analog readings into usable data. Other
conversions are used to convert units between each other. Conversions are also used to
construct wireless packets and decode them. Construction and decoding is described
below.
Moisture readings are taken as percentage. The moisture sensor is on a scale of 03V. From this, the percentage is found by dividing the analog voltage found by 3V. No
other scaling is done for this sensor.
Battery readings are shown in voltage. The analog voltage read is a scaled
version. The actual battery voltage goes through a voltage divider to get a scale of 0-8V.
The actual voltage is found by multiplying the analog voltage by the ratio (2.42424).
Temperature readings are scaled through two stages of operation amplifiers. To
find temperature, the temperature sensor voltage needs to be found by going through the
stages backwards. The analog voltage is divided by the gain stage (4.914) to get the pregain voltage. The previous stage offsets the voltage (-2.424V), so this voltage is added to
the pre-gain voltage. The resulting voltage is the actual voltage at the temperature sensor.
84
The sensor‟s specification in the datasheet state 1 Kelvin / 10mV. Therefore, the voltage
is multiplied by 100 to get Kelvin. Kelvin is finally converted into Fahrenheit.
Pressure is found the same way temperature was found. However, different gains,
offsets, and specifications are used. There is also an extra gain. The pre-gain stage has a
gain of 8.09 and an offset of -1.7V. Finally, the differential voltage is found by dividing
the first gain stage (103.017). From calibration, it was determined 0.825mV / PSI.
Multiplying by 825 then results in PSI. Once PSI is found, it is converted into inches of
mercury (“ Hg).
10.17
xBee Coding
10.17.1
Encoding
There are essential parts of the xBee coding to successfully send a wireless packet
to the network. Table 18 shows the packet structure to send a remote AT command.
Table 18 - Encoding packet structure.
Byte
Meaning
Comments
1
Start delimiter
0x7E
2-3
Packet length
Length of the packet not including bytes 1-3
4
API ID
0x17 for remote AT commands
5
Frame ID
Value used to identify command. See below for list of
used frame IDs located in the echo response.
6-13
64 Bit address
For short address on PAN ID, uses 0x000000FFFE
14-15
Short destination
address
Address of destination probe. Addresses of each system
component are stored internally to be accessed.
16
Apply changes
0x00 will change value, 0x02 will change and apply.
17-18
AT Command
Command being used. Refer to xBee manual for list.
85
Byte
Meaning
Comments
19-n
Parameters
Used for setting the command with the parameter
n+1
Checksum
Checksum to test integrity of packet (see below for
calculation)
10.17.2
Decoding
When receiving a packet, this program receives two types of responses: remote
ADC reading and an acknowledgment response (echo). Echo responses confirm if a
remote AT command was sent of returns a query response. Table 19 shows the packet
structure for an echo response. As data is received through the input, it is stored into a
temporary buffer. Once the packet length is found, data is read into buffer until the end
of the packet is reached. This data in stored as a packet and processed. Data in the
temporary buffer is then shifted over and repeated until no data is left to process. If a
start delimiter is not found, the packet is trashed until 0x7E is received.
86
Table 19 - Decoding echo response packet structure.
Byte
Meaning
Comments
1
Start Delimiter
0x7E
2-3
Packet length
Length of packet being sent not including bytes 1-3
4
API ID
0x97 for remote command response
5
Frame ID
Used to determine which command trigged the response.
(see below for list of frame IDs)
6-13
64-bit Address
Serial number of transmitting xBee
14-15
Short Address
Address stored to determine which xBee is transmitting
16-17
AT Command
Command that was sent
18
Command Response
Status of command. 0x0 = successfully sent. Refer to
manual for other responses.
19-n
Query Response
Only if AT command was used to query
(n+1) or
19 if not
queried
Checksum
Checksum of packet
87
ADC responses are sent differently. Table 20 shows the ADC packet structure. The table
shows one sampled reading of two ADC inputs and a digital sample. Multiple samples
loop through bytes 12-17.
Table 20 - Remote ADC packet structure.
Byt
e
Meaning
Comment
1
Start delimiter
0x7E
2-3
Length
Length of packet
4
API ID
0x83 - remote ADC reading
5-6
Short Address
Address of transmitting xBee
7
RSSI
Signal strength of transmission
8
Option byte
Not used
9
Number of samples
Number of samples inside of packet
10-11
Inputs
Gets the enabled inputs
12-13
Digital Inputs
Shows states of digital inputs
14-15
AD0
Shows 10bit ADC conversion on D0
16-17
AD1
Shows 10bit ADC conversion on D1
18
Check Sum
Checksum
Table 21 shows the different frame ID‟s used. The frame ID‟s keep commands
sent by the program in order to determine what function was attempted.
88
Table 21 - Frame ID list used
Frame
ASCII Character
Use
ID
0x43
C
Checking pin state on central hub
0x44
D
Used for sending debugging commands
0x45
E
Central hub echo response (for RSSI)
0x4D
M
Manual turn on / turn off
0x54
T
Toggle pin event (for xBee sleep or weather alert)
0x57
W
Automatic watering
10.18
File Structure For Code
This program uses multiple files to better organize. All these files are included in
the appendix. Table 22 shows the relation of each code file. Only the self created files
are included in this table.
89
Table 22 - GUI File Structure
File
Purpose
Call
Program.cs
Start of the code.
File determines
direction of code.
Monitor.cs
Main GUI.
Initializing all serial
port events, timer
events, and loading
variables
Called from
Program.cs
initialize.cs
Sets root directory
for external files
Called from
Program.cs
stringProcessing.cs
probeConfig.cs
GUI for changing
prope settings
Called from main
GUI
stringProcessing.cs
systemSettings.cs
GUI for changing
system settings
Called from main
GUI
stringProcessing.cs
weatherSettings.cs
GUI for changing
weather settings
Called from main
GUI
stringProcessing.cs
constants.cs
Initializes all needed -variables. Also loads
in values from
external files.
stringProcessing.cs
control.cs
Hold all control
commands for
interpreting wireless
commands, timers,
tests, updating GUI,
and handling events.
--
stringProcessing.cs
constants.cs
stringProcessing.cs
Constructs functions,
holds conversions,
and controls file I/O.
--
--
90
Uses
-
Opens Monitor.cs if not
initializing, otherwise
opens initialize.cs
11.0
OPERATION, MAINTENANCE, AND REPAIR INSTRUCTIONS
(DP,TM)
Warning: Probes should be removed from lawn prior to lawn maintenance (cutting
grass, etc) and during cold/winter months.
Operation:
Setup
Split up lawn into specific zones (average of 4 zones per lawn). Larger lawns
may require more zones.*
Gently place one Lawn Probe near the center of each zone.
o Note: special care should be taken when placing probes into the soil as the
moisture sensor is brittle.**
Attach weather station in a non-environmentally controlled location, such as
garage or screened porch, and connect to wall outlet.
Place Central Hub unit in close proximity to existing sprinkler control box.
Connect power cord to wall outlet.
Connect actuator wires to electronic switches on existing sprinkler controller.
o Note: This may require extensive knowledge of your existing sprinkler
system. The Super Sprinkler System is expandable to as many as eight (8)
zones. If there is only one main valve which operates all sprinkler heads,
only one zone will be able to be used.***
Connect the Control Module to your home PC via the USB cable provided.
Install the user software on your home PC.
Open the Super Sprinkler software and set user defined parameters
91
o Temperature high and low points
o Desired continuous moisture level of soil
o Watering duration
o Note: See GUI section below for more information on the user interface
GUI (Graphical User Interface)
Setting high and low temperature points
o Select Settings>Weather>Settings
o This will open up the weather settings dialog box
92
o Use the sliders to set max and min temperatures
o Click Save to save the changes
Setting desired moisture level of soil and watering duration
o Select Settings>Probe Configuration>Settings>Zone#
o This will open up the zone settings dialog box
93
o Use the sliders to set threshold and water runtime
o Click Save to save the changes
Toggle between automatic control and manual control.
o Select Control
o Ensure that Automatic has a checkmark next to it

This will allow for the weather and soil moisture logic to make
watering decisions without user interaction
94
o When Automatic does not have a checkmark next to it, the user has the
ability to manually turn on sprinkler zones.
To do this select
Control>Turn on zone>Zone#

Note: The manual turn on of the zones is only possible when the
Automatic control is UNCHECKED
o Unlike turning on zones, turning them off using the Control menu can be
done whether Automatic control is checked or not.
Maintenance
System is self sustaining. The Lawn Probes are equipped with solar cells to
ensure the battery can last throughout the watering season. However, because of
the battery type, NiMH, they should be removed from the probes at the end of
each season and fully charged before being put back into service.****
95
For any connection issues, such as loss of connectivity, the system GUI will
display the zone in question, and the error in question. This will help in the
troubleshooting process.
For testing, troubleshooting, or simply for personal desire, the user may, at any
time, press the override button on the side of the probe to command a moisture
reading at that particular time.
Appendix
* Zone sizes are strictly up to the user. Depending on how the previously installed
sprinkler system is set up, there may be several zones already in use. In the event of only
a single, “master valve,” several probes can still be used to keep record of moisture levels
in different areas of the lawn.
** While the moisture sensor probe is made of a durable material, it is possible for this to
snap or break in the event of improper handling or rough insertion into the ground. For
this reason it is highly recommended to take extreme caution when inserting or removing
the probes.
*** When connecting the actuator wires from the Central Hub to the existing sprinkler
system it is highly advisable to contact the system installer or obtain a detailed wiring
diagram of the complete system.
**** Nickel metal hydride (NiMH) batteries have a self discharge disadvantage; that is
even while sitting idle they will begin to lose their charge.
Note: Unfortunately, existing sprinkler systems without an accessible electronic
switch interface are not compatible with the Super Sprinkler system.
96
12.0
FINANCIAL BUDGET (DP)
The budget for this project has changed slightly since the original plan was set.
Some of the components, upon testing, were deemed unfit for the design, and in some
cases new ideas were added to the original concept. Table 23 below is the first budget set
for the project.
Table 23 - Initial Budget
Qty.
2
3
2
2
2
2
2
5
1
2
4
2
2
4
3
3
4
5
5
Part Num.
VG400
WRL-08690
2N2219A
PIC16F684-I/P
LM317T
LM336Z-2.5/NOPB
LF33CV
SDX30A2
LM335Z/NOPB
SolMaxx-Flex-4_2V22mA
A24-HABUF-P5I
XBP24-AUI-001
EVENH15BP4-NH15BP-4-4
PIC16F684-I/P
LM2594N-3.3/NOPB
5800-101-RC
UPW0J680MDD
UPW0J121MDD
Description
Unit
Cost
Moisture Sensor
XBee Communication Module
NPN BJT for Charging Circuit
14 Pin PIC for Charging Circuit
Adjustable Voltage Regulator
Protection Diode
Fixed Output Voltage Regulator
Linear Regulator 3.3V, for Probe Power
Absolute Pressure Sensor
Temperature Sensor
Solar Cell, 4.2V, 22mA
XBee Pro external antenna
XBee Pro Tranceiver
Nimh batteries
14 Pin PIC for Charging Circuit
3.3 V DC/DC converter
100uH inductor for DC/DC converter
input cap for DC/DC converter
output cap for DC/DC converter
Total
Cost
29.95
37.95
59.90
113.85
1.96
0.72
0.96
1.35
3.92
1.44
1.92
2.70
31.66
1.19
2.65
5.00
32.00
11.99
1.96
3.42
1.33
0.34
0.35
Total
31.66
2.38
10.60
10.00
64.00
47.96
5.88
10.26
5.32
1.70
1.75
$398.36
This budget included enough material for testing and implementing two lawn
probes.
Several changes were necessary to meet power and size stipulations.
For
instance, the linear regulator was too inefficient, and was replaced by a switching
regulator. Also, the design was adjusted to accommodate three lawn probes.
Table 24 below is the revised budget for the Super Sprinkler system. Many of the
major components, sensors, communication devices, and the PIC did not change. One
significant addition was that of the NiMH batteries. Originally, a lithium ion battery was
considered, however sufficient voltage was unattainable to meet size and cost needs. The
97
unfortunate downside to these is the self discharge characteristics. This will be overcome
by the solar charging and the low power capabilities of the lawn probes themselves.
Table 24 - Current and Final Budget
Qty.
3
6
3
1
1
4
3
4
3
3
3
3
3
2
1
1
Part Num.
VG400
XBP24-AUI-001
PIC16F684-I/P
SDX30A2
LM335Z/NOPB
SolMaxx-Flex-4_2V22mA
A24-HABUF-P5I
EVENH15BP4-NH15BP-4-4
LM2594N-3.3/NOPB
LP2950ACZ-3.3
STPS10L25
TIP32C
5800-101-RC
LF33CV
LP2950ACZ-5.0
VASD1-S5-D5-SIP
Description
Moisture Sensor
XBee Pro Tranceiver
14 Pin PIC for Charging Circuit
Absolute Pressure Sensor
Temperature Sensor
Solar Cell, 4.2V, 22mA
XBee Pro external antenna
NiMH batteries
3.3 V DC/DC converter
Precision 3.3VDC fixed output voltage regulator
Schottky diode, charging circuit barrier
PNP transistor, charging circuit
100uH inductor for DC/DC converter
Fixed output voltage regulator 3.3VDC
Precision 5VDC fixed output voltage regulator
±5VDC DC/DC converter, op-amp power
Unit
Cost
Total
Cost
29.95
32.00
1.96
31.66
1.19
2.65
5.00
11.99
3.42
1.12
1.61
0.55
1.33
1.35
1.12
5.58
Total
89.85
192.00
5.88
31.66
1.19
10.60
15.00
47.96
10.26
3.36
4.83
1.65
3.99
2.70
1.12
5.58
$427.63
The budget comes in just higher than the $400 allowed for the design. The
majority of this price is taken up by the weather station and central hub portions. As the
number of probes increase, however, the system becomes more cost effective.
Table 25 below is a list of the parts used in the design that were donated by the
university.
98
Table 25 Qty.
1
5
10
3
9
9
8
3
10
6
4
3
8
2
2
1
1
2
3
3
3
3
Part Num.
LM348
UA741
2N2222A
1N5817
LED
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Capacitor
Capacitor
Capacitor
Capacitor
Donated Parts
Description
UA741 op-amp, quad package
Op-amp
NPN transistor, 40V, 0.625W
Schottky diode, DC/DC converter
LEDs (various colors)
330Ω Resistor
1kΩ Resistor
2.2kΩ Resistor
2.7kΩ Resistor
3.3kΩ Resistor
4.7kΩ Resistor
5.1kΩ Resistor
10kΩ Resistor
15kΩ Resistor
20kΩ Resistor
22kΩ Resistor
33kΩ Resistor
100kΩ Resistor
1μF, 50V
4.7μF, 50V
68μF, 6.3V
120μF, 6.3V
99
13.0
GANTT CHARTS
(DP)
Table 26 -
100
Design
Table 27 -
101
Implementation
Table 28 -
Revised Implementation
102
Appendix – Data Sheets, PIC Code, GUI Code (DP,TM)
103
Datasheets
Datasheet
Part
Used In
Ref ID
Diode
Driving Circuit
D3, D4, D5, D6
Quad Op-amp
Weather Station
U7, U8, U9
Single Op-amp
Weather Station
U4, U5, U6, U10,
U11
PIC16F684
Probe
Microcontroller
Lawn Probes
PIC16F684
LP2950-D
Precision 3.3 and
5VDC Regulators
Lawn Probes and
Weather Station
Vref, LP2950
NPN Transistor
Driving Circuit,
Lawn Probes
U2, U3, U12, U13,
U14, U15
Solar Cell, 4.2V @
22mA
Lawn probe
PNP Transistor
Lawn Probe
U1
Schottky Diode
Lawn Probe
D1
Schottky Diode
Lawn Probe
D2
DC/DC Converter
Switcher
Lawn Probe
LM2594
DC Regulator
Central Hub,
Weather Station
LF33CV
1N4001
LM348
UA741
2N2222A
Solar Cell
TIP32C
STPS10L25
1N5817
LM2594
LF33CV
104
SDX30A2
LM335
+- 5VDC DC/DC
Converter
Absolute Pressure
Sensor
Weather Station
SDX30A2
Temperature Sensor
Weather Station
LM335
±5VDC DC/DC
Converter
Weather Station
VASD1-S5-D5-SIP
105