Abstract:
A large number of irrigation system devices connected to a common two-wire cable can be powered and individually controlled from a central location by transmitting over the cable DC pulses of alternating polarity. Control information is conveyed by transmitting a command pulse train consisting of a series of pulses, separated by short no-power intervals, whose polarities indicate logic ones or zeros. Following a command pulse train, a selected watering station decoder acknowledges receipt of instructions by drawing current during a predetermined pulse of an alternating-polarity power pulse cycle, while a sensor decoder returns binary data by drawing current during one or the other of the alternating-polarity pulses of a series of power pulse cycles.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application Ser. No. 60/574,899 filed May 26, 2004 entitled Two-Wire Power And Communications For Irrigation Systems which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to the combined powering, control and monitoring of sprinklers or other components of an irrigation system over a single set of two wires. More particularly, the apparatus of this invention transmits a square wave pulse train from a central location to remote components by alternating the polarity of the two wires with respect to each other. The pulses provide operating power to the components and at the same time can form a code which selects and operates a desired component. Operation of the component is monitored at the central location by sensing momentary current changes in the wires. 
       BACKGROUND OF THE INVENTION 
       [0003]    Large commercial irrigation systems such as those used on golf courses or croplands use sprinklers, sensors or other components which are normally powered from 24 V AC power lines that can be several miles long and can serve many hundreds of components. Various schemes have been proposed for powering and controlling the components of such a system with just two wires. For example, U.S. Pat. No. 3,521,130 to Davis et al., U.S. Pat. No. 3,723,827 to Griswold et al., and U.S. Pat. No. 4,241,375 to Ruggles disclose systems in which sprinklers along a cable are turned on in sequence by momentarily interrupting the power or transmitting an advance signal from time to time. 
         [0004]    A problem with this approach is that it does not allow the operator to freely turn on or off any selected sprinkler or set of sprinklers at different times. This problem is usually resolved by providing separate controllers in the field to operate groups of sprinklers in accordance with a program stored in them, or transmitted to them by radio or other means. Alternatively, it has been proposed, as for example in U.S. Pat. No. 3,578,245 to Brock, to operate individual sprinkler sets from a central location by superimposing a frequency-modulated signal or DC pulses onto the 24 V AC power line. All of these approaches are expensive, and the latter may cause electrolysis problems that can damage the system in the long run. 
         [0005]    Finally, a system with hundreds of sprinklers stretched out over miles using conventional electric water valves requires expensive heavy wiring to accommodate the hold-open current drawn by a large number of valves that may be watering simultaneously. 
         [0006]    It is therefore desirable to provide an irrigation system in which individual components connected to a two-wire cable can be turned on and off (or, in the case of a sensor component, read) from a central location at minimal cost, with a minimal expenditure of electrical power, and without causing any significant electrolysis problems in the system. It is also desirable to have the ability in such a system to monitor the successful execution of the on-off command, or to return data to the central location, without additional apparatus. 
       OBJECTS AND SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a way to both power and control a large number of devices connected to a two-wire cable by energizing the cable with a square wave consisting of power pulses of alternating polarity. When a device operation is desired, the system transmits a command pulse train consisting of a series of pulses separated by short no-power intervals. The polarity of each pulse in that series indicates whether it is a 1 or a 0 in a binary device identification and/or action code. The DC power of one or the other polarity available on the cable during each power or command pulse powers the decoder circuitry of each device and powers the desired operation of the device. The presence of power on the cable allows the selected device to signal receipt of the instruction by drawing a burst of current during the first pulse following the end of a command train. Electrolysis problems are minimized by the fact that statistically, the number of pulses of one polarity is about equal to the number of pulses of the opposite polarity. 
         [0008]    If the command is an interrogation of a sensor such as a flow, temperature, soil moisture or rain sensor, the sensor transmits data to the central location by drawing current during one of the pulses of each set of alternating-polarity pulses following the command train. Current draw during a pulse of a first polarity signifies a “1”, while current draw during a pulse of the other polarity signifies a “0”. The absence of any current draw following any command indicates a system or component failure and can be used to trigger an alarm. 
         [0009]    The system of this invention is fail-safe in that a valve actuating capacitor is continuously charged except during the actual actuation of the associated water valve solenoid. If power is lost, the capacitor discharges through the solenoid and puts the valve into the “off’ state. Additionally, the decoders of this invention can be set to predetermined run times by the command pulse train, whereupon they will automatically shut the watering station off upon expiration of the commanded time. 
         [0010]    By using latching solenoids actuated by the discharge of an actuating capacitor, power consumption of the system is minimized, and wiring as small as 14 gauge can successfully be used for cable runs of several miles controlling hundreds of watering stations or other devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]      FIG. 1   a  is a block diagram showing the system of this invention; 
           [0012]      FIG. 1   b  is a block diagram of the motherboard of  FIG. 1   a;    
           [0013]      FIG. 1   c  is a block diagram of a daughterboard of  FIG. 1   b;    
           [0014]      FIG. 2   a  is a time-amplitude diagram showing the voltage on the cable while no commands are being transmitted; 
           [0015]      FIG. 2   b  is a time-amplitude diagram showing the voltage on the cable during the transmission of a command pulse train; 
           [0016]      FIG. 2   c  is a time-amplitude diagram showing the voltage and current on the cable following a water valve solenoid operating command; 
           [0017]      FIG. 2   d  is a time-amplitude diagram showing the voltage and current on the cable following a sensor interrogation command; 
           [0018]      FIG. 3   a  is a block diagram of a watering station decoder; 
           [0019]      FIG. 3   b  is a partial circuit diagram of the watering station decoder of  FIG. 3   a;    
           [0020]      FIG. 3   c  is a partial circuit diagram showing the generation of a current burst; and 
           [0021]      FIG. 4  is a block diagram of a sensor decoder. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      FIG. 1   a  provides a general overview of the system  10  of this invention. An RS232 or other communication system  12  transmits action commands from a PC or other control unit  14  to a gateway  16 , and receives acknowledgments or other device information from the gateway  16  for conveyance to the control unit  14 . The gateway  16 , which in the preferred embodiment contains a motherboard  17  and a pair of daughterboards  19   a  and  19   b , receives power from a power source  18 . As explained in more detail in connection with  FIGS. 1   b  and  1   c  below, the function of the daughterboards  19   a ,  b  is to selectively apply, in the preferred embodiment, the following potentials to the wires A and B of their respective cables  20 : 1) +40 VDC on A with respect to B; 2) +40 VDC on B with respect to A; or 3) an equal potential on both A and B. The daughterboards  19   a ,  b  are also equipped to detect current drawn by the decoders of the system, and to report that information to the control unit  14  through the motherboard  17 . Device decoders such as watering station decoders  22  and sensor decoders  24  are connected in parallel to the wires A and B, and are arranged to operate the system components (e.g. water valves  26  or sensors  28 ) connected to them. 
         [0023]    As best seen in  FIG. 1   b , the motherboard  17  is powered from a line transformer  30  that steps the commercial AC voltage down to 28 VAC. Following surge protection at  21  in the preferred embodiment, this is applied to a bridge rectifier  32  which converts the 
         [0024]    AC voltage to +40 VDC. This voltage is transmitted to the daughterboards  19   a  and  19   b  of  FIG. 1   c  through connector  23 . The output of bridge rectifier  32  is also applied to an operational amplifier  25  which provides incoming voltage information to the microprocessor  27 . In addition, the output of bridge rectifier  32  is applied to three sets of voltage regulators  29   a - c  and isolation circuits  31   a - c  which provide isolated 5 VDC power to the microprocessor  27 , the daughterboards  19   a ,  b , and the two-way isolation circuitry  33 , respectively. 
         [0025]    The microprocessor  27  receives information from the control unit  14  through RS232 connector  35  as well as through an external pump pressure sensor  37  and an external rain sensor  39  ( FIG. 1   a ). Its outputs include a pump start signal  41  that controls the irrigation system&#39;s water pumps  43 , and a control signal  45  that operates the microprocessors  47  of the daughterboards  19   a  and  19   b  through the connector  23 . The microprocessor  27  may also provide appropriate outputs to operate LED indicators  49  to convey status information such as Watering In Progress, PC Connection Live, Power On, Transmitting Data, Receiving Data, Pump Pressure Normal, Rain Sensed, and Pump On. A communication line (Tx) connects the microprocessor  47  ( FIG. 1   c ) to the RS232 connector  35  through connector  23  and two-way isolation circuitry  33  for the transmission of commands and response data as described below. 
         [0026]      FIG. 1   c  shows the details of one of the two identical daughterboards  19   a  and  19   b  of  FIG. 1   a . The +40 VDC line of the connector  23  is applied through the current sensor  38  to a Four-transistor H bridge  50  which is switched by microprocessor  47 , through an isolation circuit  51 , into the three possible output states of A-positive-with-respect-to-B, B-positive-with-respect-to-A, and A-and-B-at-same-potential. These are the states required by the protocol described below. A status LED  48  may be provided to monitor the operation of the microprocessor  47 . The wires A and B are preferably connected to the decoder cable  20  through a surge protector  57 . 
         [0027]    The sensing of current by the current sensor  38  is conveyed to the microprocessor  47  through an isolation circuit  55 . A current pulse is detected when the current (in either direction) sensed by current sensor  38  rises through a predetermined threshold. The microprocessor  47  interprets this and conveys the appropriate information to the control unit  14  ( FIG. 1   a ) via the Tx line and the RS232 connector  35 . 
         [0028]    A preferred protocol for the operation of the system of this invention is illustrated in  FIGS. 2   a - d . Normally, the daughterboards  19   a ,  b  impress a square wave  53  alternating between +40 V (A positive with respect to B) and −40 V (B positive with respect to A) across their respective outputs A and B at a 60 Hz rate. This provides a square-wave power supply ( FIG. 2   a ) to all the decoders  26 ,  28  along the cable  20 . As pointed out below, the decoders  26 ,  28  can use power of either polarity. Because the time of the circuit at one polarity is equal to its time at the other polarity, no electrolysis problem is generated. 
         [0029]    If it is now desired to actuate a specific sprinkler or sensor, the command pulse train  52  shown in  FIG. 2   b  is transmitted. The command train begins with a no-power segment  54  in which the wires A and B are both grounded for 1/120 second. This is followed, in the preferred embodiment, by eight pulses  56  separated by similar no-power segments or delimiters  54 . The pulses  56  may be either +40 V (signifying a “1”) or −40 V (signifying a “0”). Taken together, the pulses  56  define the desired runtime (in minutes) of the device now to be selected. 
         [0030]    The next twenty pulses  58 , again separated by no-power delimiters  54 , define the address of the desired device  26  or  28 . Next, the nature of the desired command is specified by the four pulses  60 . The command pulse train  52  illustrated in  FIG. 2   b  may, for example, convey the command “Turn Station 3 of decoder 2873 on for 25 minutes”. Upon completion of the command pulse train, the microprocessor  46  of  FIG. 1   b  returns control of the wires A and B to the power relays  40 ,  42 . The output of gateway  16  thus resumes the square-wave format of  FIG. 2   a.    
         [0031]    If a selected decoder  26  has received and understood the command (see  FIG. 2   c ), it momentarily draws a high current burst  62  during the +40 V portion of the first square wave  64  following the command pulse train. This is detected by the current sensor  38  of gateway  16  and constitutes an acknowledgement that the decoder has received its instruction. If no current is detected during the first square wave  64 , a control failure is indicated, and the microprocessor  46  may transmit an alarm to the control device  14 . 
         [0032]    If the addressed device was a sensor decoder  28  (see  FIG. 2   d ), the chosen decoder responds with current bursts  66  during the eight (in the preferred embodiment) square waves  68  following the command train. In each of these square waves, a current burst  70  during the +40 V portion transmits a “1” to the gateway  16 , while a current burst  70  during the −40 V portion transmits a “0”. As in the case of a station decoder  26 , the lack of any current burst during a square wave  68  indicates a system failure and may trigger an alarm. 
         [0033]    An examination of  FIGS. 2   a - d  will show that in the preferred embodiment, a complete command and response cycle requires a little more than one second. Consequently, the described system can execute about fifty commands per minute. 
         [0034]      FIG. 3   a  illustrates a station decoder  22  used in the system of this invention. The power and communication signals from the gateway of  FIG. 1   b  appearing on wires A and B are applied to a bridge rectifier  72  that rectifies the incoming signals and conditions them to be interpreted by the microprocessor  74 . A power capacitor  76  is continually charged by the rectified power and communication signals in order to provide operating power to the microprocessor  74  through the no-power intervals  54  ( FIG. 2   b ), and long enough to perform an orderly shutdown in the event of a power failure. 
         [0035]    The microprocessor  74  includes three subprocessors: the power manager  78 , the communications manager  80 , and the control manager  82 . The power manager  78  controls the charging of the actuating capacitor  84  whose discharge, under the control of control manager  82 , operates the station (i.e. watering valve) solenoids  86   a - d  in the manner described below in connection with  FIG. 3   b . An A/D converter  88  converts the charge level of the actuating capacitor  84  into a digital signal to allow control manager  82  to monitor the charge level of capacitor  84 . The power manager  78  controls the charging of capacitor  84  from the bridge rectifier  72  through an on/off switch  90  under the guidance of control manager  82 . 
         [0036]    The communications manager  80  interprets any communication signals that appear at the bridge rectifier  72 , enables the bridge rectifier  72  to provide power to the on/off switch  90  if it determines the decoder  22  to have been selected, and informs the control manager  82  of the desired action. The communications manager  80  also controls the current drawn from wires A and B by the bridge rectifier  72  so as to produce the above-mentioned current burst  62  ( FIG. 2   c ) that acknowledges receipt of a command to the gateway  16 . The microprocessor  74  generates the current burst  62  by transmitting a pulse  87  ( FIG. 3   c ) which causes the output of bridge rectifier  72  to be momentarily bridged by a low-impedance resistor  89  through the source-drain circuit of transistor  91 . 
         [0037]    The control manager  82 , pursuant to instructions from the communications manager  80 , operates triac output stages  92   a - d  to actuate the solenoids  86   a - d  and determines whether the solenoids  86   a - d  are to be turned on or off. Its function is shown in more detail in  FIG. 3   b , in which input  100  denotes the operating power from bridge rectifier  72 . Input  102  is the on/off signal from power manager  78 , with transistor  104  being driven by the on/off switch  90 . When switch  90  is on, power from input  100  can flow into the actuating capacitor  84  through transistor  104 . The voltage on capacitor  84  is monitored by the A/D converter  88  connected to output  106 . 
         [0038]    When the solenoid  86   a  is to be actuated, either by a received command or by the expiration of a runtime interval stored in the microprocessor  74  by pulses  56  ( FIG. 2   b ), the control manager  82  causes power manager  78  to turn off switch  90  so as to block transistor  104 , and applies power to input  108 . At the same time, the control manager  82  uses input  110  to switch triac bridge  92   a  to the desired output polarity for turning the water valve  26  on or off. The capacitor  84  now discharges through the transistor  112  and the solenoid  86   a , opening or closing the water valve  26  depending upon the polarity of the output of triac bridge  92   a . The triac bridge  92   a  also provides some degree of surge protection to the solenoid  86   a.    
         [0039]    Following an actuation of the solenoid  86   a , the control manager  82  removes power from input  108  and directs the power manager  78  to turn switch  90  back on to recharge capacitor  84 . The control manager  82  will not execute an actuation command until the charge on capacitor  84  is back to a sufficient level. If a power failure occurs, the power manager, which continuously monitors the presence of power at the bridge rectifier  72 , causes the control manager  82  (which remains powered for a while by the power capacitor  76 ) to immediately go through a closing routine of all the water valves  26  as described above. 
         [0040]      FIG. 4  illustrates a sensor decoder  24  according to the invention. The bridge rectifier  72 , microprocessor  74 , power capacitor  76 , power manager  78  and communications manager  80  serve the same functions as in the station decoder described above in connection with  FIG. 3   a . In the sensor decoder  24 , however, the control monitor  82  of  FIG. 3   a  is replaced by a sensor manager  120 . The sensor manager  120 , when so commanded by the communications manager  80 , causes a sensor read circuit  122  to read and condition the sensor data which is continuously transmitted by the sensor  28  to the interface  124 . The interface  124  preferably contains surge components and, if appropriate, A/D conversion circuitry. 
         [0041]    The data received by the sensor manager  120  is conveyed to the communication manager  80  and is used by it to produce the current bursts  66  ( FIG. 2   d ) that transmits the data to the gateway  16 . 
         [0042]    Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.