Title: Wireless soil moisture meter network
Abstract: A wireless soil moisture meter network includes a central display unit and a plurality of remote sensor units. Each sensor unit uses a probe to measure moisture content in soil, and uses a wireless transmitter to transmit the measurement through a wireless channel to the central display unit. The central display unit receives and displays the measurement in a format selectable by a user. The user may add to or remove from the network a sensor unit using a user interface of the central display unit.
Patent Number: 6,975,236 Issued on 12/13/2005 to Staples
| Inventors:
|
Staples; Peter Ethan (Hermosa Beach, CA)
|
| Assignee:
|
Blue Clover Design, LLC (Los Angeles, CA)
|
| Appl. No.:
|
347771 |
| Filed:
|
January 19, 2003 |
| Current U.S. Class: |
340/602; 340/870.01; 73/1.73 |
| Intern'l Class: |
G08B 021/00 |
| Field of Search: |
340/602-604,584,618,620,539.16,870.06,870.01,612,539.17,870.11,870.16,870.17
73/73,131,173
|
References Cited [Referenced By]
U.S. Patent Documents
| 3224676 | Dec., 1965 | Rauchwerger.
| |
| 3732435 | May., 1973 | Strandberg, Jr. et al.
| |
| 4069716 | Jan., 1978 | Vanasco et al.
| |
| 4396149 | Aug., 1983 | Hirsch.
| |
| 4531087 | Jul., 1985 | Larson.
| |
| 4588943 | May., 1986 | Hirth.
| |
| 4892113 | Jan., 1990 | Fattahi.
| |
| 5031358 | Jul., 1991 | Sussman.
| |
| 5117359 | May., 1992 | Eccles.
| |
| 5179347 | Jan., 1993 | Hawkins.
| |
| 5621669 | Apr., 1997 | Bjornsson.
| |
| 6292096 | Sep., 2001 | Munch et al.
| |
| 6340892 | Jan., 2002 | Rynhart et al.
| |
| 6343255 | Jan., 2002 | Peek et al.
| |
| 2001/0045892 | Nov., 2001 | Thomas et al.
| |
Primary Examiner: Hofsass; Jeffery
Assistant Examiner: Blount; Eric
Attorney, Agent or Firm: Schox; Jeffrey
Claims
1. A method of establishing a wireless soil moisture meter network, the method comprising:
(a) using a portable central display unit to assign a wireless channel number
to a remote sensor;
(b) upon the activation of a synch mode, placing the central display unit in
a wait state until a predefined bit sequence is received; and
(c) enabling the sensor to send the predefined bit sequence and a unique identifier
of the sensor to the central display unit.
2. The method of claim 1 further comprising repeating the steps of (a), (b),
and (c) to add additional remote sensors to the network.
3. The method of claim 1 further comprising storing the identifier at the central
display unit for the assigned channel number.
4. The method of claim 1, wherein the central display unit is set to an ALL mode
before the wireless channel number is assigned.
5. The method of claim 1, wherein the wireless channel number is assigned using
a channel button of the central display unit.
6. The method of claim 1, wherein the predefined bit sequence and the unique
identifier are sent when a synch button is activated at the remote sensor.
7. A method for establishing a network between a central display unit and an
environmental sensor, comprising the steps of:
(a) selecting a channel for the sensor;
(b) activating a "wait" mode on the display unit;
(c) transmitting a sensor identifier from the sensor to the display unit; and
(d) storing the sensor identifier and corresponding channel in a memory device
of the display unit.
8. The method of claim 7 wherein step (a) further includes: activating an "add
channel" mode on the display unit.
9. A method for establishing a network between a central display unit, a first
environmental sensor, and a second environmental sensor, comprising the steps of:
(a) activating a "wait" state for the display unit and transmitting a predefined
sequence and a first sensor ID from the first sensor to the display unit;
(b) upon receiving the predefined sequence and the first sensor ID, recording
the presence of the first sensor in a memory device;
(c) activating a "wait" state for the display unit and transmitting the predefined
sequence and a second sensor ID from the second sensor to the display unit; and
(d) upon receiving the predefined sequence and the second sensor ID, recording
the presence of the second sensor in the memory device.
10. The method of claim 9, wherein step (a) and step (c) further include: activating
the "wait" state for the display unit upon the activation of an "add channel" mode
on the display unit.
11. The method of claim 10, wherein step (a) further includes: allowing selection
of a first channel for the first sensor, end wherein step (c) further includes:
allowing selection of a second channel for the second sensor.
12. The method of claim 11, wherein step (b) further includes: recording the
presence of the first sensor and the corresponding first channel selection in the
memory device, and wherein step (d) further includes: recording the presence of
the second sensor and the corresponding second channel selection in the memory device.
13. A wireless network comprising:
a first environmental sensor unit including a sensor adapted to measure an environmental
condition, a transmitter adapted to transmit a data stream through a wireless channel,
and a button adapted to cause the transmitter to transmit a predefined sequence
and a first sensor ID upon activation;
a second environmental sensor unit including a sensor adapted to measure an environmental
condition, a transmitter adapted to transmit a data stream through a wireless channel,
and a button adapted to cause the transmitter to transmit the predefined sequence
and a second sensor ID upon activation; and
a central display unit including a receiver adapted to receive a data stream
through a wireless channel, a memory device, and a processor having an "add channel"
mode in which the processor is adapted to record the presence of the first environment
sensor unit in the memory device upon the receipt of the predefined sequence and
the first sensor ID and further adapted to record the presence of the second environment
sensor unit in the memory device upon the receipt of the predefined sequence and
the second sensor ID.
14. The wireless network of claim 13, wherein the sensors of the first environmental
sensor unit and the second environment sensor unit are adapted to measure soil
moisture levels.
15. The wireless network of claim 13, wherein the first environmental sensor
unit and the second environmental sensor unit further include a controller adapted
to cause the sensor to measure an environmental condition and to cause the transmitter
to transmit the measurement.
16. The wireless network of claim 15, wherein the central display unit further
includes a screen, and wherein the processor also has a "display" mode in which
the processor is further adapted to display the measurement of a sensor on the screen.
17. The wireless network of claim 13, wherein the processor is further adapted
to enter a "wait" state while in the "add channel" mode.
Description
BACKGROUND
Moisture meters exist today in various forms. There are complex moisture
meters used by agriculture and gardening professionals as part of a larger weather
monitoring or irrigation system. In the case of weather monitoring systems, they
generally are used to record soil moisture along with a collection of other weather
related data to detect trends to aid in making decisions affecting crop yield.
Moisture meters are sometimes part of largescale irrigation systems used with golf
courses or other large properties for the purpose of water management. These large
systems are sometimes moveable, but still too large and expensive to be suitable
for household use.
Handheld moisture meters, which are suitable for household use, exist as
well, however, these are standalone devices without the ability to be networked
to a common display unit. This limits their functionality since the user must be
in the same physical location as the soil to be measured. Moreover, if there are
multiple locations, with different soil types or different watering patterns, the
user must go to each location to take the moisture reading.
Most recreational gardeners employ an "appearance and feel" technique to determine
if their plants require watering. In other words, they visually examine the soil
and feel it to see whether or not it is damp. This technique is used because is
it simple and does not require special equipment. The disadvantages are that it
is time-consuming and requires specialized knowledge in order to obtain an accurate
reading. It is also difficult to estimate the moisture level at soil substantially
below the surface.
The invention consists of portable handheld sensors wirelessly networked to a
common display unit. This makes it possible for the user to observe the moisture
level of the soil in multiple locations from a single conveniently positioned display unit.
The goal is to keep the soil moisture below the saturation level and above the
permanent wilting point. This window is referred to as the management allowed depletion
(MAD) zone. Saturated soil lacks the necessary oxygen and dry soil causes plant
stress. Soil kept within the MAD zone, however, is a good environment for healthy plants.
SUMMARY
In one aspect, the invention relates to a wireless soil moisture meter network.
The wireless network includes a plurality of handheld sensor units and a portable
central display unit. Each of the handheld sensor units includes a sensing probe
to measure moisture content in soil, and a wireless transmitter to transmit the
measurement through a wireless channel. The portable central display unit receives
and displays the measurement from the sensor units.
Embodiments of the above aspect of the invention may include one or more
of the following features. The sensing probe includes a tube filled with a porous
material, e.g., gypsum. Each of the sensor units also includes a synch button which,
when pressed, enables the transmitter to send a bit sequence indicating the presence
of the sensor unit. Each of the sensor units may also include a temperature sensor
to measure soil temperature.
The central display unit may include a channel selector. The central display
unit may also include a mode selector, which may be used to select a first, second,
third, fourth, fifth, or sixth mode. The first mode toggles between display of
a single sensor unit's measurement and simultaneous display of measurements from
multiple sensor units. The second mode toggles between a numerical value and a
non-numerical descriptor describing a moisture level. The third mode permits a
sensor unit to be added to the wireless network. The fourth mode permits a sensor
unit to be deleted from the wireless network. The fifth mode causes all of the
sensor units to be deleted from the wireless network. The sixth mode causes an
alarm to sound when the measured moisture content is below a predetermined threshold.
In another aspect, the invention relates to a method of establishing a wireless
soil moisture meter network. The method comprises (a) using a portable central
display unit to assign a wireless channel number to a remote sensor; (b) placing
the central display unit in a wait state until a predefined bit sequence is received;
and (c) enabling the sensor to send the predefined bit sequence and a unique identifier
of the sensor to the central display unit.
Embodiments of the above aspect of the invention may include one or more
of the following features. The method may include repeating the steps of (a), (b),
and (c) to add additional remote sensors to the network. The method may also include
storing the identifier at the central display unit for the assigned channel number.
The central display unit may be set to an ADD mode before the wireless channel
number is assigned. The wireless channel number may be assigned using a channel
button of the central display unit. The central display unit enters the wait state
when a synch option is selected at the central display unit. The predefined bit
sequence may be sent when a synch button is activated at the remote sensor.
Embodiments may have one or more of the following advantages. The sensor
units and the central display unit are all portable, making the network quick and
easy to set up. Once established, the network provides a convenient way to monitor
the moisture level of the soil in various locations. The low cost of the network
makes it suitable for household use. It is simple to add more sensors to the network,
so the network can be scaled up to accommodate lawns, gardens, and potted plants
of various sizes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an example of a wireless soil moisture meter network;
FIG. 2 shows a remote sensor unit (RSU) in the network;
FIG. 3 shows a central display unit (CDU) in the network;
FIG. 4 illustrates a process of the CDU for reading the measurements from the RSUs;
FIG. 5 shows a Liquid Crystal Display (LCD) and a user interface of the CDU; and
FIG. 6 shows a process of the CDU for adding a channel to the network.
DETAILED DESCRIPTION
FIG. 1 shows a wireless soil moisture meter network
10 including a plurality
of remote sensor units (RSU)
11 and
12, and a central display unit
(CDU)
15. Each of the RSUs includes a probe
116 or
126 that
is placed in the soil to read the moisture content, a converter unit
118
or
128 to convert the sensor reading into a digital value, and a wireless
transmitter
110 or
120 that sends signals representing the digital
value to the CDU
15. The CDU
15 receives the signals from the plurality
of RSUs
11 and
12 and displays the readings on an LCD screen
18.
The CDU
15 also includes a user interface
16 that allows the user
to select the format of the readings.
FIG. 2 shows an embodiment of the RSU
11. The RSU
11 is handheld
and highly portable so that the RSU can be easily relocated. The RSU
11
is suitable for indoor or outdoor use. The RSU
11 has a plastic casing
21.
The plastic casing
21 of RSUs intended for outdoor use is weatherproof and
includes a rubber seal. The plastic casing
21 prevents water and dust from
interfering with the interior electronics. The RSU
11 has its own power
source, which may be a battery housed inside the plastic casing
21 or a
solar array
28 affixed to the top of the RSU.
The probe
116 of the RSU
11 includes a metal rod
22 enclosed
by a non-corrodible metal tube
23, e.g., stainless steel or aluminum. Inside
the tube
23 is a porous material
24 such as gypsum. Numerous holes
25 are drilled into the tube
23 so that moisture may pass through
the holes between the gypsum
24 and the soil to be measured. The user may
leave the RSU
11 in contact with the soil. However, the user may replace
the RSU
11 approximately every two years since the porous material
24
inside the tube
23 dissolves over time.
The tube
23 is inserted into the soil within the root zone of interest.
Water in the soil naturally moves in and out of the gypsum
24, depending
on the level of soil moisture. The fluctuating moisture level in the gypsum
24
cause changes in the gypsum's electrical characteristics including conductivity.
Higher moisture levels cause an increase in the conductivity. These conductivity
changes are then measured with a voltmeter
26 to produce an analog voltage measurement.
When a measurement is taken, a fixed amount of current is sent through the metal
rod
22. Then the voltage between the rod
22 and the tube
23
is measured with voltmeter
26. This voltage divided by the current represents
the resistance of the gypsum
24. The resistance level indicates the moisture
content in the gypsum
24.
In an alternative embodiment, the probe
116 may include two metallic rods
enclosed by a nonmetallic tube. The rods may take the form of two traces etched
into a circuit board. Operation is similar to the embodiment in FIG. 2 except that
the voltmeter
26 is connected to the two rods to measure the resistance
between them.
The voltage measured in the probe
116 is applied to an analog to digital
converter (ADC)
27 to produce a digital data stream. The ADC
27 may
be a specialized component, a 555 timer circuit, or a microcontroller with an analog
input. In the case of a 555 timer circuit, the timer circuit generates a stream
of square wave pulses. The duration of each pulse is a function of the voltage
applied to the circuit. The varying duration of the pulses is interpreted in the
RSU
11 or by a microcontroller in the CDU
15.
The RSU
11 generally takes measurements on a relatively infrequent basis
(e.g., every half hour) to conserve power. The frequency of the measurements may
be a fixed frequency or may be set by the user. Each new measurement may be triggered
by either a digital timer or a slowly draining capacitor in the RSU
11.
The RSU
11 may also possess the ability to measure the temperature of
the soil. A thermistor or a solid-state temperature sensor may be embedded in a
plastic tip
20 of the probe
116. In the case of the thermistor, the
voltmeter
26 may be used to measure the thermistor's resistance, which varies
with temperature. This resistance measurement is sent to the ADC
27 where
a digital temperature value is produced. Alternatively, the solid-state temperature
sensor produces a digital temperature value directly. In both cases, the digital
temperature value is combined with the moisture measurement and sent to the transmitter
110 for transmission to the CDU
15.
Before sending the digital data stream to the CDU
15, the wireless
transmitter
110 modulates the carrier frequency with the data stream. The
data stream consists of a header (a sequence of bits preprogrammed in the RSU
11
and CDU
15), a sensor ID code, and a most recent moisture measurement. Since
the transmissions are short in duration relative to the frequency of the measurements,
all of the RSUs
11 and
12 use the same frequency. This is effectively
a time-division multiple access system, but the RSUs
11 and
12 themselves
are not synchronized. The RSUs
11 and
12 simply transmit whenever
a new reading is taken. In the case of a digital timer, a randomizer may be employed
to slightly delay the transmission to reduce the chance of two RSUs repeatedly
transmitting at the same time.
The user may use a synch button
29 on the RSU
11 to override the
normal transmission cycle for the purpose of testing or adding a new RSU to the
network
10. When the synch button
29 is pressed, the transmitter
110 immediately sends a special bit sequence indicating the presence of
the new sensor as well as the sensor's unique ID. For testing, the RSU
11
also takes a moisture measurement upon pressing the synch button
29 and
sends the measurement to the CDU
15.
FIG. 3 shows an embodiment of the CDU
15. The CDU
15 is a separate
unit that receives the measurements from the RSUs
11 and
12 through
an antenna
34 and displays the readings from the RSUs on the LCD screen
18. The CDU
15 is approximately 4"×6"×0.25" and is therefore
very portable. The CDU
15 is powered by a power source
33, which
may be batteries replaceable by the user. When the power is low, a "low battery"
indicator appears on the LCD screen
18. The CDU
15 can also be used
to verify proper installation of the RSUs
11 and
12. Immediately
after adding a RSU to the network
10 and inserting the RSU into the soil,
the user may press the synch button
29 on the RSU and observe the measurement
on the LCD screen
18 to verify proper installation. The CDU
15 also
includes a receiver
31, a microcontroller (MCU)
32, and the user
interface
16. The receiver
31 and MCU
32 may be implemented
on separate integrated circuits.
FIG. 4 illustrates a process
40 of the receiver
31 and the MCU
32 for reading the measurements from the RSUs. The MCU
32 is initially
in a sleep mode. When the receiver
31 detects a known bit sequence (box
41), the receiver wakes up the MCU
32 (box
42). The receiver
31 does not distinguish between the various RSUs, instead the receiver demodulates
the incoming signal and passes the resulting data stream to the MCU
32 (box
43).
The MCU
32 compares the data stream from the receiver
31 against
the IDs of the various RSUs stored in registers inside the MCU
32 (box
44).
When the incoming data stream matches one of the IDs, the pulse pattern that follows
is stored for processing. The pulse stream is compared against a lookup table to
determine the corresponding moisture reading (box
45). The moisture reading
is then stored as the latest value in the register for the channel corresponding
to that RSU (box
46). The values from all the RSUs are stored within the
CDU
15 so that any channel may be examined by the user at any time.
The user may view the moisture measurements on the LDC screen
18. In the
example shown in FIG. 5, at the top of the screen
18 is a label
51
indicating the mode that the CDU
15 is currently in. The CDU
15 may
be set to one of the modes: ALL (display all), NUM (numerical display), ADD (and
a channel), DEL (delete a channel), CLR (clear all channels), and BUZ (activate
the alarm). On the left side of the screen
18 is a channel label
52
indicating the channel to which an RSU is assigned. To the right of the channel
label
52 is the latest measurement
53 from the RSU corresponding
to that particular channel. At the bottom of the screen is a message line
54
that helps the user understand the various modes of the CDU
15.
In FIG. 5, the user interface
16 consists of three buttons. One button
is a CHANNEL button
55. Pressing the CHANNEL button
55 allows the
user to cycle through the various channels to observe the reading from the desired
RSU. The second button is a MODE button
56. By pressing this button
56,
the user can cycle through the six modes of the CDU
15. The third button
is a SELECT button
57, which is used to choose options within each of the
CDU modes.
One of the CDU modes is the ALL (display all) mode, which allows the user to
view the moisture measurements on multiple channels simultaneously. In one possible
implementation, nine channels may be displayed on the LCD screen
18 at the
same time. In the event that there are more than nine channels, the measurements
may be shown in groups of nine. The CHANNEL button
55 may be used to cycle
through the various groups. The mode is activated by pressing the MODE button
56
until the word "ALL" is displayed at the top of screen
18. The message line
54 will say "ONE/ALL". When the user presses the SELECT button
57,
all or a group of the active channels are displayed simultaneously and the message
line
54 changes to "ONE/ALL". To return to the single channel format, the
user presses the SELECT button
57 again.
The user may choose between numerical and non-numerical formats of the measurements
displayed on the LCD screen
18. The non-numerical format may include icons
describing moisture levels graphically. For example, the icon can be a glass containing
a variable amount of water. The non-numerical format may include descriptors such
as DRY, DRY+, REG, WET, or WET+. To select a particular display format, the user
presses the MODE button
56 until the word "NUM" is displayed at the top
of the screen
18. The message line
54 then says "WORD/NUM". When
the user presses the SELECT button
57, the measurements are displayed in
numerical form (e.g., a numerical scale from 1 to 10) instead of word form and
the message line
54 changes to "WORD/NUM". To return to the non-numerical
format, the user presses the SELECT button
57 again.
As shown by an example in FIG. 6, the user may add a RSU to the network
10
by following a multi-step add procedure
60:
1. The user presses the mode button
56 until ADD is displayed at the top
of the screen
18 (box
61).
2. The user selects the channel by pressing the channel button until the desired
channel is shown on the left side of the screen
18 (box
62).
3. The message line displays the word "Synch" which prompts the user to press
the SELECT button
57 to initiate a synch process. The CDU
15 is put
into a WAIT state such that it is expecting a predefined bit pattern (indicating
the presence of a new sensor) from a new RSU (box
63).
4. Then the user presses the synch button
29 on the new RSU (box
64).
This causes the new RSU to transmit the predefined bit pattern as well as its unique
ID to the CDU
15 (box
65).
5. The CDU
15 stores the new ID into a register corresponding to the selected
channel. The message line indicates to the user that the new ID has been received
and the sensor was added to the network (box
66).
The user may also delete a channel from the network
10 by following a
multi-step delete procedure:
1. The user presses the MODE button
56 until DEL is displayed at the top
of the screen
18.
2. The user presses the CHANNEL button
55 until the channel to be deleted
is shown on the left side of the screen
18.
3. The user presses the SELECT button
57 to delete the channel shown.
The
message line
54 indicates the channel has been successfully deleted.
Rather than delete each channel individually, the user has the option of deleting
all of the channels at the same time. The mode is activated by pressing the MODE
button
56 until the word "CLR" is displayed at the top of the LCD screen
18. The message line
54 then says "Clear all?". When the user presses
the SELECT button
57, all of the active channels are deleted and the message
line
54 changes to "Done".
The user also has the option to activate an alarm to sound if one of the RSUs
is reporting a low level of soil moisture. The alarm is triggered when the moisture
reading is below a predefined threshold. In some scenarios, this threshold may
be changed by the user. For example, the user may set a different threshold for
different plant types. This mode is activated by pressing the MODE button
56
until the word "BUZ" is displayed at the top of the LCD screen
18. The message
line
54 then says "Alarm ON/OFF". When the user presses the SELECT button
57, the alarm function is activated and the message line
54 changes
to "Alarm ON/OFF". If any of the RSUs reports a "DRY+" measurement for a predefined
extended period, the alarm sounds periodically until a REG, WET, or WET+reading
is reported. A special alarm icon may also appear on the LCD screen
18 to
warn the user of the dry soil condition.
Accordingly, other embodiments are within the scope of the following claims.
*
