Abstract:
This invention describes a drip irrigation system wherein drippers are provided with valves, and wherein these valves are independently and remotely controlled. This invention also describes a drip irrigation system wherein drippers are controlled via a communication network, to turn individual drippers ON or OFF as required.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of drip irrigation, and more specifically it addresses the possibility of controlling of individual elements of the irrigation system via a data communication network.  
         BACKGROUND OF THE INVENTION  
         [0002]    Irrigation systems have been used for generations as the means to allow agricultural utilization of land where natural precipitation is not sufficient. The most ancient method known, employed the flooding of fields. To allow better control and more efficient use of irrigation water, irrigation using canals and trenches replaced field flooding. To allow even better control and water usage efficiency, pipes and sprinklers are used to deliver irrigation water just to the places where irrigation is required. Yet even with sprinklers, unnecessary waste of water can not be avoided. Sprinklers irrigate an area, not just the plants that need to be irrigated. With sprinkler irrigation systems, a large amount of water is still lost due to evaporation, runoff, and the scattering of water droplets by wind.  
           [0003]    Drip irrigation systems seem to provide the ultimate method of water conservation. In drip irrigation systems, as in sprinkler systems, pipes are used to deliver the water, but in a drip irrigation system, small emitters also known as drippers are used instead of sprinklers. In a sprinkler based irrigation system, sprinklers are placed in locations that will allow an even distribution of irrigation water over an area. Sprinklers are designed such that water squirted out of the sprinklers will ultimately fall evenly on a large area of coverage assigned to the sprinkler. In contrast in drip irrigation systems only a very small area around a dripper is irrigated. Drippers are placed immediately next to plants, which they irrigate, and thus ultimately irrigate only the roots of the plants to which they are assigned. To place the emitter at the desired locations drip irrigation pipes are made of flexible plastic material, and are not laid in the field in straight lines, as it is customary with sprinkler pipeline irrigation systems. Instead drip irrigation pipeline are meandered between the plants, such that the drippers are located in close proximity to the plants to be irrigated. In low-grade drip irrigation systems, drippers are installed on the outside of the pipeline, next to every plant, or wherever else it is desirable. In professional drip irrigation systems, a dripper is a sophisticated flow control structure placed inside the irrigation pipes with only tiny orifices in the skin of the pipe through which water is squirted out of the pipe. The flow control mechanism typically includes a special narrow and long labyrinth through which water must pass to get to the orifice. As the water passes through the labyrinth, friction with the labyrinth walls causes the water pressure to drop, and as a result water arriving at the orifice are at a low and constant pressure, resulting in an even and measured emission of water from the orifice. During the manufacturing (by extrusion) of the high-grade drip irrigation pipe, the elaborate flow control mechanisms are inserted inside the water delivery pipe, at fixed intervals, and orifices are drilled in the skin of the water-delivering pipe in locations where control mechanisms are placed inside the pipe. In drip irrigation pipelines water is emitted out of the orifices in a slow but constant rate of flow, and is absorbed in the soil in the immediate proximity of the drippers. Thus, water is only delivered where it is necessary, without runoffs, evaporation, and scattering.  
           [0004]    Despite all their benefits, drip irrigation systems still suffer from several undesirable problems. In the present drip irrigation systems, all the drippers along the pipe receive water simultaneously, and are expected to deliver the same amount of water everywhere along the pipe, regardless to variations of the specific need at any point along the pipe. The “one flow rate everywhere method”, requires that all the plants along the irrigation system pipe, be homogeneous in type, specie, and size, without room for diversity. Also as the water delivering pipes become long, and with many drippers along the line, a pressure gradient develops along the pipe with a significant pressure difference between the near and far ends of the pipe. As a result, the amount of water delivered by the drippers, drops with the drop in water pressure in the pipe, and water delivery rate becomes uneven. Many improvements in existing drip irrigation emitters are aimed at dealing with equalizing the water delivery rate in long pipelines despite the water pressure drop along the line.  
         DESCRIPTION OF THE PRIOR ART  
         [0005]    Typical prior art drippers follow the basic diagram shown in FIG. 1. The differences between various dripper designs are typically limited to methods of reducing the water pressure between the water delivery pipe, and the orifice, methods of controlling the flow rates, and methods for avoiding clogging of the water passages and the orifices. A prior art drip irrigation system is shown in FIG. 2, wherein a plurality of drippers are installed along pipelines, and wherein a plurality of dripping pipelines are combined to form the irrigation system, and further wherein the flow of water in each dripping pipeline is controlled by a shutoff valve.  
           [0006]    Technologies such as Micro-machined Electro Mechanical Systems (MEMS), and magnetic latches, used in embodiments of electronically controlled valves described in this invention, have been demonstrated in prior art.  
         SUMMARY OF THE INVENTION  
         [0007]    This invention describes a solution for problems associated with drip irrigation systems, in a way that allows precise control over the delivery of water at any individual water delivery point in the entire system. The primary and foremost reason for the deployment of drip irrigation system is to deliver irrigation water in the most efficient and conservative way. For this purpose it is desirable to be able to control the amount of water delivered at any distinct point in the area covered by the irrigation system.  
           [0008]    According to this invention, each dripper is fitted with an electrically controlled water valve that can enable or stop the flow of water out of the said dripper. Also according to this invention, the valve of each and every dripper can be individually controlled, remotely, via an electronic communication network.  
           [0009]    An electronic valve to control the water flow in an individual dripper must comply with certain requirements. It must be small in size, such as to fit inside emitter flow control mechanisms, which in turn are installed inside the water delivery pipe, without obstructing the flow of water in the pipe. It must be very reliable to guarantee millions of ON/OFF operations without failure. It must be maintenance free. It must operate with, and consume very little power. It must not be clogged by water regularly used in agriculture, and it must be controlled via a communication network.  
           [0010]    The electronic valve to be used in an electronically controlled dripper, and comply with the requirement set forth above, may be produced using Micro-machined Electro-Mechanical System (MEMS) methods. Micro stepper motors, racks and gears have already been demonstrated, on a single semiconductor chip, using MEMS technology, and a valve based on a sliding bolt, or a flexing level, motivated by a micro stepper motor, a gear and a pinion, Piezo-electric force, are examples of possible embodiments. Alternative embodiments may be based on a sliding bolt activated by an electro-magnetic field, and held in place by a magnetic latch, wherein a short electrical current impulse switches the valve ON or OFF. A hydraulic mechanism controlled by means described above, and assisted by the static pressure of the water in the pipe is also conceivable as device to be used for a controlled valve.  
           [0011]    A communication network to control the drip irrigation system must be able to connect to each and every dripper in the system, address each dripper individually, and control its operation. Power must also be delivered to every dripper to operate the emitter valve and an associate controller. In an embodiment described by this invention, a special network can be used both as communication media, and as a power delivery conduit to all the drippers in the system. For system reliability, given the fact that drip irrigation systems are deployed in field where both humans and machines work, the communication and power delivery network may needs to include redundant communication and power delivery paths to allow continuous failure free operation. Ultimately a communication system should have a command and response provision to allow inquiry into the status and condition of a dripper, and even provide information generated by sensors placed outside of the dripper.  
           [0012]    In order to facilitate the communication via the communication network, to receive instructions over the network, to interpret such instructions, and to control the operation of the emitter, each dripper is equipped with an associated electronic controller. The said controller may also detect events of malfunction of the dripper or its valve, and report the status of the dripper back to the system&#39;s master controller.  
           [0013]    Drip irrigation systems are typically deployed such that main feeder lines are connected to the main water source valve, and arms of water delivery pipes fitted with drippers connect as multiple parallel arms to the main feeder lines. To allow for redundancy in both water delivery paths and data communication and power access, the water delivery pipes as well as the communication and power delivery network are each connected to the main feeder lines and to the system controller on both ends of each of the arms. With this redundant connection, a break in the network path in an arm will not prohibit the power delivery to, and the communication with drippers on that arm, as they are still connected through the redundant connection. The communication protocol is designed to allow the redundant connection.  
           [0014]    In an alternative embodiment and method of deployment, each dripper is equipped with a small solar cell to power the dripper&#39;s valve and controller. Such solar sells are typically seen on pocket calculators and other small appliances, and can provide just enough electrical power to the emitter valve, the controller, and the means for communication with the controller. A two-way radio communication device attached to the dripper&#39;s controller allows the establishment of a UHF wireless communication network between the dripper and the system controller. Such a network will enable the system controller to directly control each individual dripper in the drip irrigation system. Other embodiments including the use of optical fibers as means to facilitate power delivery and a communication network are also conceivable. In such cases, the optical fiber provides a conduit to pipe high intensity light to every dripper. In every dripper, a photocell replaces the solar cell described above, as the means to convert light into electrical power.  
           [0015]    Ability to control the water flow in each individual dripper, regardless of the operation of other drippers on the line, allows for the outmost utilization of the dripper pipeline, and to avoid needless waste of water. In the system described by this invention, the amount of water delivered by a dripper is controlled by the length of time at which the dripper&#39;s valve is turned ON. Each dripper is uniquely identified by an address or code, and may be turned ON for a desired duration. Each dripper may be individually turned ON and OFF using the direct control of communication system, or as an additional option, each dripper may be programmed, in the field, to turn ON at specified times for a certain lengths of time. Broadcast type commands may simultaneously address all, or any group of drippers, set to be controlled consequently. Sensors attached to the communication system and installed in the field can provide information on soil humidity at different locations and different depths, and thus further modify the dripper&#39;s control programs to allow the ultimate efficiency in water usage. 
       
    
    
     A BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The theory of operation of this invention, its objectives, and advantages, along with its distinction from prior art, will be best understood from the study of the following description taken along with the accompanying drawings in which:  
         [0017]    [0017]FIG. 1, Shows the construction of prior art drippers.  
         [0018]    [0018]FIG. 2, Show a typical deployment of a prior art drip irrigation system.  
         [0019]    [0019]FIG. 3, Shows an embodiment for a valve based on MEMS technology, to be integrated into a programmable dripper.  
         [0020]    [0020]FIG. 4, Shows an embodiment of an electrically controlled valve based on a magnetic latch.  
         [0021]    [0021]FIG. 5, Shows a typical deployment of a field programmable drip irrigation system in accordance with this invention,  
         [0022]    [0022]FIG. 6, Shows an embodiment of a field programmable dripper.  
         [0023]    [0023]FIG. 7, Shows an embodiment of a drip irrigation system utilizing wireless communication, and solar power.  
         [0024]    [0024]FIG. 8, Shows an embodiment of a dripper assembly to be used in the wireless drip irrigation system.  
         [0025]    [0025]FIG. 9, Shows an embodiment of a communication interface for wired drip irrigation systems.  
         [0026]    [0026]FIG. 10, Shows an embodiment for a communication interface for wireless drip irrigation systems.  
         [0027]    [0027]FIG. 11, Shows an embodiment of the irrigation system master controller for wired system deployment.  
         [0028]    [0028]FIG. 12, Shows an embodiment of the irrigation system master controller for wireless system deployment.  
         [0029]    [0029]FIG. 13, Shows an example of a communication protocol in wired drip irrigation systems.  
         [0030]    [0030]FIG. 14, Shows an example of a communication protocol in wired drip irrigation systems, where a response is expected.  
         [0031]    [0031]FIG. 15, Shows an example of a communication protocol in wireless drip irrigation systems.  
         [0032]    [0032]FIG. 16, Shows an example of a communication protocol in wireless drip irrigation systems, where a response is expected. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration of specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail, to enable those of ordinary skill in the art, to make and use the invention. It is to be understood that structural, logical or procedural changes may be made to the specific embodiments disclosed without departing from the spirit and scope of the present invention.  
         [0034]    To allow sufficient water supply to all the drippers on very long dripping lines, either the pipe must be large in diameter, or the pressure in the pipe must be high. Since a large diameter pipe is undesirable, drip irrigation systems are typically based on high water pressure in the dripping pipes. A hole in the skin of a highly pressurized water pipe causes a high-pressure jet of water to be squirted out of the hole. The amount of water coming out of the hole is uncontrolled and depends both on the water pressure inside the pipe, and the diameter of the hole. To eliminate the possibility of such water jets, a controlling device is required between the highly pressurized water in the inner part of the pipe, and the orifice on the skin of the pipe. The pressure reduction is achieved by allowing the water to flow through very long and narrow passages, in which friction slows down the velocity of the water current, and thus reduces the pressure as the water flows through these passages. The design of such pressure reduction devices is prior art, and is not a subject dealt with in this invention.  
         [0035]    The pressure controlling mechanisms in prior art are not designed to allow intentional blockage of the water flow to the orifice.  
         [0036]    Referring primarily to FIG. 6, which shows the field programmable dripper  100  in accordance with this invention. Unlike prior art drippers shown in FIG. 1, wherein water passes from the inside of the water delivery pipe through the pressure reducing control section to the emitter orifice on the pipe&#39;s skin, in the dripper  100  shown in FIG. 6, an electrically controlled valve  84  is added between the pressure reducer  80  and the orifice  30 , as show in FIGS. 6, and  8 . An electronic controller  88 , and a communication network interface  92 , and  94 , are also added to enable the remote or local control of the valve  84 . With the valve  84  and the controller  88 , the amount of water emitted through the orifice  30  depend mainly on the length of time the valve  84  is open, and to a much lesser degree to the water pressure at the output of the pressure reducer  80 .  
         [0037]    This invention goes beyond the addition of the valve in the dripper, and encompasses the entire irrigation system. With the advent of a controlled valve  84  in a dripper, a controller  88 , and a communication network  92  in place, a system to control each individual dripper is put in place. Thus, according to this invention, each dripper  100 ,  110 , becomes a smart dripper, comprising control and communication facilities. To utilize the control and communication capabilities of the smart drippers  100 ,  110 , a control and communication network is required. Although there are multiple ways to implement the desired drip irrigation system with its communication and control network, only two embodiments are discussed in this invention, in order to demonstrate how this invention can be reduced to practice. Two possible embodiments of drip irrigation system deployments, utilizing valve-controlled drippers are shown in FIGS. 5, and  7  respectively. The drip irrigation system deployment shown in FIG. 5, depicts an embodiment of a system  1  with a control and communication system as well as operational power applied via electrical conductors.  
         [0038]    The embodiment shown in FIG. 7, depicts a similar drip irrigation system  2  wherein a wireless control and communication network is used.  
         [0039]    In the deployment shown in FIG. 5, the dripper local electronic controller  88  communicates with the system&#39;s master control  200  via the communication network  400 ,  410 . Through the communication network  400 , 410 , the electronic controller  88  receives messages sent by the master controller  200 , responds to received commands, activate specific irrigation programs, controls the operation of the valve  84 , and reports the status of the dripper  100  back to the master controller  200 . Upon receiving a specific control signal, the valve  84  is opened to allow the flow of water to the orifice, and upon a different control signal, the valve  84  closes, and stems the flow of water.  
         [0040]    Two embodiments for the valve  84  are shown in FIGS. 3, and  4  respectively. FIG. 3, shows an embodiment of a valve  84  based on the Micro-machined Electro Mechanical System (MEMS) technology. Here the valve  84  is based on a sliding bolt  50 . Part of the bolt  50  is machined as a rack  62 . The bolt  50  is held in place by the braces  54 , which allow the bolt  50  a lateral movement from right to left and from left to right. A micro stepper motor  66  has a gear  58  on its spindle. The gear  66  in turn is engaged with the rack  62 . When the motor  66  turn counter clockwise, it causes the bolt  50  to move left, and block the orifice  30 . When the motor  66  turn clockwise, the bolt  50  moves to the right unblocking the orifice  30  and allowing the flow of water through the orifice  30 .  
         [0041]    [0041]FIG. 4, shows an alternative embodiment of an electrically controlled valve  84 . In this embodiment, a permanent magnet shuttle  10  is mounted on a non-magnetic bolt  18 , which can move laterally from right to left and from left to right inside the armature  14 , which is made of a ferromagnetic material. An electrical wire  22  is wound on the armature  14 . When an electrical current is conducted through the electrical winding  22 , it causes the armature  14  to become magnetized, wherein the polarity of the resulting magnetic flux depends on the direction of electrical current flow in the electrical winding  22 . Thus an impulse of electrical current through the electrical wire winding  22 , in one direction, causes the armature  14  to become temporarily magnetized, causing the permanent magnet shuttle  10  to be expelled from one side of the armature  14 , and to be attracted by the opposite side of the armature  14 , forcing the shuttle  10  to slide, along with the bolt  18 , from one side to the opposite side of the armature  14 . When the electrical current impulse has ended, the magnetic flux through the armature  14 , caused by the current flow through the windings  22  is terminated. However, the shuttle  10 , being a permanent magnet, is still attracted the ferromagnetic armature  14 , and thus does not move. An impulse of electrical current, flowing in an opposite direction, causes a magnetic flux in the opposing direction through the armature  14 , causing the shuttle  10  to be expelled from the side of the armature  14  where it is in rest, and to be attracted to the opposite side of the armature  14 . This causes the shuttle to slide back to its initial position. A sliding gate  26  is attached to one end of the bolt  18 . When the shuttle  10  and the bolt  18  move to the left, the gate  26  blocks the flow of water through the orifice  30 . When the shuttle  10  and the bolt  18  move to the right, the gate  26  slide to the right as well, unblocking the orifice  30 , and allowing the flow of water through the orifice  30 .  
         [0042]    The electronic controller  88  is a simple low power electronic controller, having the facilities to communicate via the communication network, and to activate the electrically controlled valve  10 . In the irrigation system, each dripper  100  is assigned a unique identification address, stored permanently inside the controller  88 . The electronic controller uses this address to identify messages and commands sent over the communication network  400 ,  410  by the system&#39;s master controller  200 , and only accept those messages for which it is the addressee. The controller  88  interprets commands it receives, and follows in action after the instructions. Upon command it turns the valve  84  ON or OFF. Upon different commands, the controller  88  stores new operational programs received from the master control  200  via the network  400 ,  410 , or it modifies existing ones. The micro-controller  88  can also run programs autonomously, turn the water flow in the dripper ON and OFF automatically, based on a pre-programmed schedule.  
         [0043]    The control and communication network can be implemented using electrical wires, as depicted in deployment  1 , shown in FIG. 5. In this embodiment, all the drippers  100  are connected through electrical wires into a communication network  400 ,  410  that doubles also as the source of power to all the drippers  100  in the system. In an alternative type of deployment  2 , shown in FIG. 7, the drippers  110  are each completely independent. As the drippers  110  are not connected to electrical wires as means to provide power and a communication conduit, each dripper  110  must generate its own power, and communicate with the system&#39;s master controller  200  via electromagnetic waves, such as radio waves. For that reason, each dripper  110  comprises its own solar power source  380 , and a radio transceiver  94  and an antenna  370 , to communicates with the system&#39;s master controller  200  via a wireless communication network, as shown in FIG. 7.  
         [0044]    The programmable drippers  110  are similar to the drippers  100 , except for their power source and communication interface. The communication interface  92  in the drippers  100  is designed to interface to a communication network via electrical conductors, wherein the communication interface  94  in the drippers  110  is based on a radio transceiver connected to an antenna  370 , which enables a wireless communication network interface. An embodiment of the communication interface  92  is shown in FIG. 9. The communication network  400 ,  410 , is comprised of two electrically conducting wires. A potential voltage difference is normally applied between the two conductors, such that the LINE+  204  is at a potential more positive with respect to the conductor LINE−  208 , which is also the negative reference potential for all the electronic circuits in the dripper  100 . Under these conditions electrical current can flow through the diode  212 , and charge the chargeable battery  216 . The negative side of the battery  216  connects to the negative reference  208 , and the positive side of the battery  216  connects to the positive reference  228 , which becomes the positive supply for all the electronic circuits in the dripper  100 . If the potential between the lines LINE+  204 , and LINE_ 208 , becomes smaller than the potential on the battery  216 , the diode  212  stops conducting, a condition know to the skilled in the arts of electronic circuits as the condition of “reverse bias”, and thus the battery  216  can not discharge through the diode  212 , and the battery  216  remains charged.  
         [0045]    The irrigation system master controller  200  in the system deployment  1 , shown in FIG. 5, is both the source of power for the entire system, and the controller of the system. An embodiment of the controller  200  is shown in FIG. 11. Since the lines of the communication network may be very long and thin, there may be significant voltage differences between different physical locations on the network. For that reason, the data communication over the network is conducted in the form of electrical current flows, and not voltages, as is typically the case in data communication networks. The convention used in this invention considers the presence of current flow as the logic state of “1”, and the absence of electrical current flow is interpreted as the logic state of “0”.  
         [0046]    The master controller  200  comprises of a power supply  466 , a master micro-controller  490 , a power switch  458 , a current sensing amplifier  470 , and the transistor  478 . Both the supply of power to all the drippers in the system, and data communication are conducted via the communication network  400 ,  410 . All communications are initiated by the system&#39;s master control  200 . In idle operation, when communication is not conducted, the controller  490  asserts the power switch  458  to the close position, allowing the flow of electrical power to all the drippers  100  in the system  1 . To begin a communication session, the master, the controller  490  asserts the power switch  458  to the open position, disconnecting the power supply  466  from the LINE+  204  in the communication network  400 ,  410 . At this state, the power supply does not force the line  204  to a certain potential with respect to the line  208 . This state is sensed by the communication interfaces  92 , of all the drippers  100 , as the logic state of “ 0 ” , or “idle”. At this state no electrical current is flowing through the communication network  400 ,  410 , line, either into or out of any dripper  100  in the system  1 . When the controller  490  asserts the transistor  478  to the ON state, the transistor  478  places a “short” between the lines  204 , and  208 , causing electrical current to flow in every dripper  100 , from the rechargeable battery  216 , through the resistor  224 , into the line  204 , the transistor  478 , and the line  208 . As a result of this flow of electrical current, a voltage is developing across the resistor  224 , following Ohm&#39;s law V=IR, wherein V is the voltage across the resistor, I is the electrical current, and R is the resistance of the resistor  224 . The voltage developing across the resistor  224 , is sensed by the amplifier  220 , and interpreted as logic condition of “1”. By asserting and de-asserting the transistor  478 , the controller  490  causes electrical currents to flow out of the drippers  100 , when the transistor  478  is asserted ON, and no current flows when the transistor  478  is asserted OFF, thus generating successions of “1”s and “0”s received in all the drippers  100  in the system  1 .  
         [0047]    All communication sessions in the system  1  follow a protocol shown in FIGS. 13, and  14 . A communication session starts with the disconnection of power, which brings about an idle period. Following the idle the transmission commences with the transmission of a succession of “1”s and “0”s in a special pattern which indicates the Beginning Of the Transmission (BOT). The BOT pattern is followed by an address pattern, indicating to which dripper  100  that particular message is intended. Though all the drippers  100  in the system  1  receive the transmission simultaneously, only the dripper  100  to whom the transmission is addressed responds to the transmission, and acts in accordance with the commands that follow. The address is followed by a command that may be trailed by data associated with the command. A single transmission may contain several commands and data segments. At the end of the transmission an End Of Transmission (EOT), code is inserted, followed by an idle period before the resumption of flow of power to the drippers  100 . When a command in the transmission requires a response by the dripper  100  addressed by the command, the communication protocol follows the example in FIG. 14, and allows the designated dripper to respond, at the proper time, by asserting its transistor  244  to the ON or OF states, thus allowing current flows through the resistor  474  in the system&#39;s controller  200 , which is sensed by the amplifier  470 . Data generated by the amplifier  470  is transferred to the micro0controller  490  in the system&#39;s controller  200 . Since only one dripper is addressed in this mode of operation, only that one dripper is responding, avoiding any data collisions on the communication network.  
         [0048]    The sources of power, and the means of communication are different in the wireless drip irrigation system deployment  2 . In this deployment the drippers  110  are used, where each comprises of the pressure reducer  80 , the valve  84 , the micro-controller  88 , the communication interface  94 , the solar cell  380 , and the antenna  370 , the embodiment of which is presented in FIG. 8. In the drippers  110 , the communication interface  94  is used, and its embodiment is shown in FIG. 10. The communication interface  94 , uses the solar cells  380  as the power source to charge the batteries  262 , through the diode  258 . The batteries  262  are required, to guarantee operation at night times. A tiny radio transmitter/receiver (transceiver)  278 , and the antenna  370  are used as the means of communication. Since all the communication sessions are initiated by the system&#39;s master controller  900 , all the drippers  110  have their transceivers  278  in the receive mode, and there are no transmissions. The embodiment of controller  900  for the system  2 , is shown in FIG. 12, and it comprises of the master micro-controller  910 , the power supply  918 , the transmitter  930 , and the antenna  360 . The controller initiates a communication session by broadcasting a radio message, which is received by the radio receives  278  in all the drippers  110 . The message is comprised of data in a format shown in FIG. 15. The message starts with a Start Of Transmission (SOT) code, followed by an address indicating to which dripper  110  the message is intended. There after the message continues with a command, which may be followed by data related to that command. Several commands and data segments may be stringed in a single message. The message ends with an End Of Transmission (EOT) code. If the command transmitted requires a response from the dripper  110  to whom the message was addressed, the controller  900  goes off the air at the end of its message, and waits to receive the response from the dripper  110  as shown in FIG. 16.  
         [0049]    While the invention has been described in detail in connection with preferred embodiments known at the time, it should be readily understood that the invention is not limited to the disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention.