Abstract:
A environmental sensor network having at least two environmental sensor units and a central display unit. Each sensor unit includes a sensor adapted to measure a condition and a transmitter adapted to operate in an “activation” mode in which the transmitter transmits a predefined sequence and a sensor ID and a “data” mode in which the transmitter transmits data based on the measurement. The central display unit includes a receiver adapted to receive a transmission from the two environmental sensors, a memory device, and a processor adapted to selectively operate in an “add” mode in which the processor records the presence of an environment sensor unit in the memory device upon the receipt of the predefined sequence and the sensor ID, and a “display” mode in which the processor outputs information based on the measurement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of prior application Ser. No. 10/347771, filed 19 Jan. 2003, which is incorporated in its entirety by this reference. 
     
    
     BACKGROUND  
       [0002]     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.  
         [0003]     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.  
         [0004]     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.  
       SUMMARY  
       [0005]     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.  
         [0006]     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.  
         [0007]     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.  
         [0008]     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&#39;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.  
         [0009]     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.  
         [0010]     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.  
         [0011]     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  
       [0012]      FIG. 1  shows an example of a wireless soil moisture meter network;  
         [0013]      FIG. 2  shows a remote sensor unit (RSU) in the network;  
         [0014]      FIG. 3  shows a central display unit (CDU) in the network;  
         [0015]      FIG. 4  illustrates a process of the CDU for reading the measurements from the RSUs;  
         [0016]      FIG. 5  shows a Liquid Crystal Display (LCD) and a user interface of the CDU; and  
         [0017]      FIG. 6  shows a process of the CDU for adding a channel to the network. 
     
    
     DETAILED DESCRIPTION  
       [0018]      FIG. 1  shows a wireless soil moisture meter network lo 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.  
         [0019]      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.  
         [0020]     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.  
         [0021]     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  14  causes changes in the gypsum&#39;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.  
         [0022]     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 .  
         [0023]     In an alternative embodiment, the probe  116  may include two metallic rods or plates 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.  
         [0024]     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 .  
         [0025]     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 .  
         [0026]     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&#39;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 .  
         [0027]     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.  
         [0028]     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 lo. 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&#39;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 .  
         [0029]      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.  
         [0030]      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 ).  
         [0031]     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.  
         [0032]     The user may view the moisture measurements on the LCD screen  18 . In the example shown in  FIG. 5 , at the top of the screen  18  is a label 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 (add 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  18  is a message line  54  that helps the user understand the various modes of the CDU  15 .  
         [0033]     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.  
         [0034]     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.  
         [0035]     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.  
         [0036]     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 ).        
 
         [0042]     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.        
 
         [0046]     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”.  
         [0047]     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.  
         [0048]     Accordingly, other embodiments are within the scope of the following claims.