Abstract:
A circuit arrangement having a master microcontroller operably connected to a sensor for detecting a parameter. A power communications line is connected between the power source, master microcontroller, and sensor, wherein the power communications line carries power to the sensor as well as communication signals between the sensor and the master microcontroller. An embodiment of an automotive ultrasonic sensor system for object detection is disclosed, where the master microcontroller is connected to a number of external ultrasonic sensors via the circuit arrangement. The circuit arrangement is also advantageous in enabling a separate wire harnesses to be configured for the external ultrasonic sensors that operates at logic power levels (e.g., 5V) rather than the vehicular accessory drive voltage (typically 12V) present in the vehicular wire harness that interfaces the master microcontroller with other controllers in the vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation-in-part of PCT International Application No. PCT/CA2008/001862 filed 23 Oct. 2008, which claims the benefit of U.S. Provisional Patent Application No. 61/000,091 filed on Oct. 23, 2007. This application also claims the benefit of U.S. Provisional Patent Application No. 61/161,478, filed 19 Mar. 2009, the contents of which are incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates generally to the field of sensor control circuits, and more particularly to automotive ultrasonic-based object detection sensor systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Sensor circuits have been utilized in automotive applications for providing a measure of data for a given parameter that is being monitored. For example, sensors are used in engine components for the purpose of determining the position of various valves or actuators during normal operation. Additionally, sensors have also been incorporated to measure environmental factors such as temperature, light, and objects external to the vehicle. Most sensor circuitry utilizes at least three wires for communicating between the sensor, microcontroller, and power source. For example, two wires will be used for supplying power to the microcontroller and sensor unit. A third and/or possibly fourth wire is used for communicating with the sensor unit. Reducing the number of wires and connections is desirable from the stand point of saving manufacturing time, equipment, as well as reducing the possibility of equipment failure by virtue of the fact that a lesser number of wires are being used. Thus, it is desirable to develop sensor circuits that need fewer than 3 wires between the microcontroller and the sensor. 
         [0004]    While it desirable to reduce the manufactured cost of any automotive sensor system by reducing the number of components to achieve the same function, such as by reducing wire count, there are impediments to doing so. For example, the need exists to continue to interface with other pre-existing devices, components or circuitry in the vehicle. The invention seeks to ameliorate such issues. 
       SUMMARY OF THE INVENTION 
       [0005]    One aspect of the invention is directed to a circuit arrangement having a master microcontroller operably connected to a sensor for detecting a parameter. The microcontroller is connected to the power source by a microcontroller power line. A power communications line is connected between the power source, the master microcontroller, and the sensor. The power communications line carries power to the sensor as well as digital communication signals between the master microcontroller and the sensor. 
         [0006]    The digital values communicated between the master microcontroller and sensor are preferably delineated by selective arrangement of the on and off flow of power over the power communications line. 
         [0007]    The circuit arrangement of claim  1 , further comprising a diode ( 26 ) and a capacitor ( 24 ) operably connected between said power communications line and a power supply input of said sensor ( 16 ) for continued supply of power to said sensor when no power flows over said power communications line. 
         [0008]    The circuit arrangement preferably includes a low impedance line connected between the power source and the power communications line, and a high impedance line connected between the power source and the power communications line, where the high impedance line has a greater resistivity than the low impedance line. An impedance switch is disposed in the low impedance line and is controlled by the master microcontroller to control the flow of power through the low impedance line. 
         [0009]    The power communications line is preferably connected to a data input of the sensor and to a ground signal via a first switch controlled by an output of the master microcontroller, thereby enabling the master microcontroller to communicate data signals to the sensor. Likewise, the power communications line is also preferably connected to an input of the master microcontroller and the ground signal via a second switch controlled by an output of the sensor, thereby enabling the sensor to communicate data signals to the master microcontroller. 
         [0010]    The master microcontroller preferably controls the impedance switch to disconnect the power supply from the low impedance line when a communications signal or a portion thereof is transmitted over the power communications line. 
         [0011]    In preferred embodiments, a bit of the digital communications signal has a logic value of 0 or 1. When the communication signal value is 1, a pulse at the power source voltage level is transmitted across the power communications line for a first predetermined time period and when said communications signal value is 0, a pulse at the power source voltage level is transmitted through the power communications line for a second predetermined time period. Each bit is preferably transmitted within a predetermined time window greater than the first or second predetermined pulse periods. 
         [0012]    The sensor is preferably configured for active traffic environment sensing using ultrasound. 
         [0013]    According to another aspect of the invention, a traffic environment sensing arrangement is provided for a vehicle having one or more body panels. The arrangement includes: a power source; a master microcontroller; a microcontroller power line connected between the power source and the master microcontroller; a plurality of ultrasonic sensors mounted in the one or more body panels; a power communications line connected between the power source, the master microcontroller, and each of said plurality of ultrasonic sensors. Each ultrasonic sensor further includes: a communications port and a sensor power line operably connected to the power source, wherein the sensor power line branches off of the power communications line; a capacitor on the sensor power line; and a diode positioned between the capacitor and the sensor power line. 
         [0014]    Another aspect of the invention relates to an ultrasonic object detection sensor system for automotive applications. The system includes a main sensor having, in one enclosure, a master microcontroller functionally connected to a DC/DC voltage regulator, a vehicular communication interface, an internal ultrasonic sensor disposed within the enclosure, and an external sensor interface. The DC/DC regulator has an input receiving a power signal from a vehicular wire harness at a first voltage level and has an output providing a power signal at a different, second voltage level. The DC/DC regulator output is connected to at least the external sensor interface. The system also includes a plurality of ultrasonic sensors that are each disposed external of the enclosure. A wire harness interconnects the external ultrasonic sensors with the main sensor via its external sensor interface, where the wire harness operates at the second voltage level and carries at least one instance of the output power signal. The master microcontroller controls the internal and external ultrasonic sensors to send and receive ultrasonic bursts in order to detect a potential object within the field of view of each ultrasonic sensor. The master microcontroller consolidates data from the internal and external ultrasonic sensors and communicates the existence of an object to another device within the vehicle via the vehicular communication interface. 
         [0015]    The wire harness preferably includes at least one power communication wire for connecting the plurality of external ultrasonic sensors, each power communication wire being connected to the external sensor interface and carrying both power and digital communication signals at the second voltage level between the external ultrasonic sensor and the external sensor interface. 
         [0016]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The foregoing and other aspects of the invention will be more readily appreciated having reference to the drawings, wherein: 
           [0018]      FIG. 1  is a schematic of the two wire sensor circuitry; 
           [0019]      FIG. 2   a  is a graph showing voltage versus time when the logic signal value is 1; 
           [0020]      FIG. 2   b  is a graph showing voltage versus time when the logic signal value is 0; 
           [0021]      FIG. 3  is an example of a logical communications scheme for the circuit arrangement; 
           [0022]      FIG. 4  is a perspective view of the sensor circuit as incorporated in a two wire ultrasonic sensor arrangement; 
           [0023]      FIG. 5  depicts a perspective view of the vehicle having a plurality of ultrasonic sensors connected to the vehicle; 
           [0024]      FIG. 6  is a state diagram showing the state of switches in the two wire sensor circuitry for implementing the communications scheme; 
           [0025]      FIG. 7  is a system block diagram of an ultrasonic traffic environment sensor system according to the prior art; 
           [0026]      FIG. 8  is a system block diagram of a preferred embodiment of an ultrasonic traffic environment sensor system according to the invention; 
           [0027]      FIG. 9  is a functional block diagram of a master sensor employed in the system of  FIGS. 8 ; and 
           [0028]      FIG. 10  is a functional block diagram of a slave sensor employed in the system of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0030]      FIG. 1  is a schematic view of a circuit arrangement  10  having a master microcontroller  12 , a power source  14 , and a sensor  16 . The circuit arrangement  10  in one embodiment of the invention is a two wire digital or active environmental sensor used to sense objects in the external vehicle environment. The sensor  16  can be, but is not limited to a traffic environment sensor, weather sensor and an object sensor. However, the scope of this invention is not limited to environmental sensors or digital technology. The sensor  16  is an ultrasonic type sensor that utilizes sonar or sound waves to detect the presence or absence of an object as well as the distance from the object. One particular embodiment of the invention shown in  FIG. 5  depicts the sensor as being used as an active ultrasonic park assist sensor. However, it is within the scope of this invention for the sensor  16  to be any type of sensor for detecting a given parameter while being able to operate using the two wire technology. Both the sensor  16  and the microcontroller  12  are connected to the power source  14 . The power source  14  in this particular circuit arrangement  10  has a power source level that is a 5 volt direct current power source such as a battery. The use of a 5 volt power source with this circuit arrangement  10  provides a significant advantage over other arrangements that typically use a 12 volt power source. Using a 5 volt power source allows the circuit arrangement to be connectable to the same power source as the vehicle electronic control unit which also uses a 5V power source. However, it is possible to have a different type of power source having a different voltage depending upon the particular needs of an application. For example any types of voltage power source can be used, however, it is contemplated that 6 volts and 12 volt power sources are within the scope of this invention. 
         [0031]    The power source  14  is connected to the microcontroller  12  through a microcontroller power line  18 . The sensor  16  receives power through a sensor power line  20  which is connected to a power communications line  22  that is connected to both the power source  14  and the microcontroller  12 . The power communications line  22  transmits both power as well as bit line encoding that is both received by the sensor and sent to the microcontroller  12 . 
         [0032]    The sensor power line  20  has a capacitor  24  disposed on the sensor power line  20  and a diode  26  that separates the capacitor  24  and sensor power line  20  from the power communications line  22 . The diode  26  allows power flow from the power source  14  to the capacitor  24 , but does not allow power to flow in the direction from the capacitor  24  past the diode  26 . The capacitor  24  is configured to supply power to sensor  16  during voltage drops. While this particular embodiment of the invention describes a capacitor  24  being used, it is possible for another suitable energy storage device to be used, such as a battery, switch capacitor or an inductor. 
         [0033]    Connected between the power source  14  and the power communications line  22  is a high impedance line  28 , which is an energy line having a high impedance resistor  30 . A low impedance line  32  having a low impedance resistor is also connected to the power source  14 . The low impedance resistor  34  has a resistivity that is lower than the high impedance resistor  30 . The low impedance line  32  and high impedance line  28  run in parallel. However, the low impedance line  32  has an impedance switch  36  that is controlled by the master microcontroller  12 . When the impedance switch  36  is closed, higher current passes through the power communications line  22  and onto the capacitor  24 . When the impedance switch  36  is open, a lower current will pass through the power communications line  22 . It is during this period of lower current in the power communications line  22  that the line can be used for carrying a communications signal between the master microcontroller  12  and the sensor  16 . 
         [0034]    The master microcontroller  12  has a microcontroller communications line  38  that is connected to the power communications line  22 . The microcontroller communications line  38  is also connected to ground. A master microcontroller output  40  is connected to the microcontroller communications line  38  through a master microcontroller output switch  42 . When the master microcontroller switch  42  is closed, signals are sent from the microcontroller  12  through the master microcontroller output  40  and onto the power communications line  22 . The master microcontroller  12  also has connected to it a master microcontroller input  44  that is also connected to the microcontroller communications line  38  and receives signals from the sensor  16  via the power communications line  22 . 
         [0035]    The sensor  16  has a sensor communications line  46  that is connected to the power communications line  22  and ground. The sensor  16  has a slave sensor input  48  that selectively receives signals from the microcontroller  12  that are outputted through the master microcontroller output  40 . The slave sensor input  48  introduces command signals to the sensor  16  that can cause the sensor to carry out a function such as sending and receiving ultrasonic sound waves. The sensor  16  in carrying out its functions will receive signals that are indicative of its function. For example, an ultrasonic sensor will receive signals that indicate the presence of an object in the path of the sensor  16 . The signals received by the sensor  16  are transmitted to the microcontroller  12  through a slave sensor output  50 . The slave sensor output  50  is controlled by a slave sensor switch  52  that will allow for signals to be transmitted from the slave sensor output  50  when the slave sensor switch  52  is in the closed position. When the slave sensor output switch  52  is in the closed position the sensor communications line  46  will go to ground. 
         [0036]    The operation of the circuit arrangement  10  is controlled by signals generated from the master microcontroller  12 . During initial start up of the sensor  16  the master microcontroller  12  will cause the impedance switch  36  to be closed which allows more power to flow through the power communications line  22  to charge the capacitor  24 . During periods that communications signals are transmitted to the sensor  16  the impedance switch  36  is open in order to impede the power supply and allow the power communications line  22  to carry a communications signal. The communications signals are generated between the master microcontroller  12  and the sensor  16  through the input and output ports connected to the microcontroller communications line  38  and the sensor communications lines  46 . See  FIG. 6 , which provides a state diagram for the state of the impedance switch  36  and master microcontroller output switch  42  (or slave sensor switch  52 ) to transmit a digital low or high bit. However, the sensor  16  can encounter power fluctuation or voltage drops due to communication that can impair or disrupt sensor functions. The invention solves this problem by using the capacitor  24  to supply voltage during the period of power loss or fluctuation. 
         [0037]    Communication can flow from the master microcontroller  12  to the sensor  16 , and vice versa. In the former case, the master microcontroller grounds the power communications line  22 , and in the latter case the sensor grounds the power communications line  22 . In order to avoid collision, the system preferably employs a master/slave communications protocol where the master microcontroller  12  sends a command to the sensor  12  and the sensor sends a reply only in response to the command. After a communication session, the master microcontroller  12  can close the impedance switch  36  to recharge the capacitor  24 , or, the impedance switch  36  can be closed at selected instances during a communication session to quickly recharge the capacitor in the event not enough power flows through the high impedance line. 
         [0038]      FIGS. 2   a  and  2   b  depict two graphs, which both exemplify the data line bit encoding for the circuit arrangement  10 .  FIG. 2   a  depicts the bit encoding when the logic value is set at 1 and  FIG. 2   b  depicts the bit encoding when the logic value is set at 0. The data line bit encoding depicted in  FIGS. 2   a  and  2   b  is distinct from other circuit arrangements for ultrasonic sensors because when the logic value is at 0, there is a pulse of 5 volts for 50 microseconds (in a 150 microsecond bit transmission window) instead of the voltage being 0. When the logic value is 1, there is a pulse of 5 volts for 100 microseconds (in a 150 microsecond bit transmission window). This permits the capacitor to be receiving a voltage charge even when the logic value is at 0 when compared to other system where the voltage value would be 0 when the logic value is 0. It also allows for communications data to be constantly transmitted through the power communications line  22 , even when the logic value is 0. 
         [0039]      FIG. 3  depicts an example of a logical communications scheme signals between the microcontroller  12  and the sensor  16  during various phases of sensor operation. 
         [0040]      FIG. 4  is a perspective view of the sensor circuit as incorporated in a two wire ultrasonic sensor arrangement  100 . An ultrasonic sensor  102  has a power communications line  104  that extends to a circuit box  106  that contains the circuit arrangement  10  shown in  FIG. 1 . The power source connector  108  has two wires extending from the connector into the circuit box  106 . One of the wires provides power to the master microcontroller and the other wire provides power to the circuit arrangement  10  that leads to the power communications line  104 . 
         [0041]      FIG. 5  depicts a vehicle  200  having a plurality of ultrasonic or traffic environment sensors  202  connected to a bumper  204  of the vehicle  200 . In this embodiment, the plurality of ultrasonic sensors  202  are used as proximity sensors for alerting a driver of the vehicle  200  when objects are in the path of the vehicle  200  as the vehicle is backing up. The traffic environment sensors depicted on the vehicle  200  are used primarily for determining the presence or absence of an object in the path of the vehicle  200  while backing up. It is possible for the traffic environment sensors  202  to be used in other areas of the vehicle for providing proximity detection. For example, such sensors can be used for collision avoidance, parking assist, security, and other suitable uses where the detection of objects on the outside environment of the vehicle are desired. 
         [0042]    One particular implementation of an ultrasonic traffic environment sensing system  300  suitable for installation in the rear bumper of a vehicle is shown in system block diagram form in  FIG. 8 . Compared to conventional ultrasonic sensing systems, the system  300  minimizes the functional blocks and the wiring required to add such a system into a vehicle. 
         [0043]    Consider first the topology of a current commercially available ultrasonic sensing system  400  as shown in  FIG. 7 . The conventional system  400  includes a number n of individual ultrasonic sensors  402 , which are controlled by a central electronic control module (ECU)  404 . The n ultrasonic sensors  402  each send and receive ultrasonic bursts in order to detect objects within the field-of-view of the sensor  402 . Each ultrasonic sensor  402  pre-processes the analog data and converts the data into the digital domain. The communication interface to each sensor  402  is a digital interface consisting of low (0) and high (1) voltage signal states. 
         [0044]    The ECU  404  communicates with and controls all the ultrasonic sensors  404 . The ECU  404  processes of the collected raw data and provides the processed data to a vehicle controller  406  in order to drive a human-machine interface (HMI). The ECU  404  requires nine connections for a system  400  with four ultrasonic sensors  402 . Each ultrasonic sensor must be provided with a common 12V DC power line (1 wire), sensor ground (1 wire), an individual communications signal line (4 wires). And the vehicle interface requires a 12V DC power line (1 wire), system ground (1 wire), and a system communications signal (1 wire). 
         [0045]    Although not explicitly shown in  FIG. 7 , the conventional system  400  requires a DC/DC regulator in the ECU  404  as well as in every ultrasonic sensor  402 . The DC/DC regulator in each ultrasonic sensor  402  may be integrated into an application specific integrated circuit (ASIC) but it is still present. 
         [0046]    It would be desirable to design an ultrasonic sensor which utilizes only logic level signals (typically 5V) as this would allow the removal of the DC/DC regulator in all sensors. However, all wiring running through the body of an automobile has to be 12V. This is necessary in the event the insulation of a wire is worn or a wire is pinched and the insulation is damaged. In this case, a short circuit between two or more wires might occur, and therefore all wires running in the same harness must be the same voltage level in order to prevent excessive current flow and excessive damage in such a failure case. 
         [0047]    It is therefore not feasible in the conventional ultrasonic system  400  to utilize ultrasonic sensors which communicate with lower voltage logic level signals (e.g., 5 V) since the ECU is located inside the vehicle body and the sensors are located on the outside of the vehicle. The sensor DC power line and the sensor communication signal lines are routed within the main vehicle harness to connect all sensors to the ECU, so per the requirements above they operate at 12 V. Providing a separate harness for sensor communication wires is not a practical option as such an approach would be too expensive and add labor to the vehicle manufacturing for routing the additional harness from the control module inside the passenger compartment to the ultrasonic sensors mounted to the vehicle exterior. 
         [0048]    In contrast, the ultrasonic traffic environment sensing system  300  of the invention enables the 12 V wiring of the vehicle and the 5 V wiring between ultrasonic sensors and a control module to be kept separate. More particularly, referring to  FIG. 8 , the system  300  provides a vehicle wire harnesses  302  operating at 12V that is separate from an internal bumper wire harness  304  operating at TTL or CMOS logic levels of 3.3 or 5V, as the case may be. 
         [0049]    The different voltages in the wire harnesses  302  and  304  of the system  300  are made possible through the use of a main sensor (alternatively referred to as a “smart” sensor)  310 , which communicates with a plurality of individual ultrasonic sensors  312 . As seen in the block diagram of  FIG. 9 , the main sensor  310  includes its own ultrasonic sensor  318 , which functions similar to one of the individual ultrasonic sensors  312 . In addition, the main sensor  321  assumes most tasks previously provided by the ECU. The main sensor  321  provides all interfaces to the vehicle and all connections to the other ultrasonic sensors  312 . The main sensor  321  isolates the 12 V arrangement of the vehicle from the 5 or 3.3 V logic level signals utilized by the other ultrasonic sensors  312 . 
         [0050]    As will be seen from  FIG. 8 , the main sensor  310  requires three connections to the vehicle in harness  302 : 12 V DC power (IGN_PWR), chassis ground (GND), and vehicle communication line such as LIN (or a CAN) signal, as known to those skilled in the art. The logic level internal bumper harness  304  utilizes four connections since this harness is limited to connections with the other ultrasonic sensors  312  and is located behind the bumper fascia. Since there are no other wire harnesses in this area of the vehicle, any conflict between 5 V and 12 V signals is prevented by principle. A total of seven connections are thus required in system  300  (versus nine connections to the ECU of the conventional system) for a system with four ultrasonic sensors. 
         [0051]    Each ultrasonic sensor  312  requires only two interface signals: a power communications line  314 , which is a 5 V (or 3.3 V) power line communication wire, and sensor ground  316 . The ultrasonic sensors  312  are shown with three-pin interfaces where the sensor ground  316  is looped, but a two pin interface may alternatively be utilized if the sensor ground is provided via suitable splices, as known in the art per se, in harness  304 . 
         [0052]    In alternative embodiments the ultrasonic sensors  312  may be connected to the main sensor  310  in a daisy chain arrangement, which would reduce even further the number of wires present in the internal bumper harness  304 . However, it is more preferred that the ultrasonic sensors  312  be connected in a star topology with the main sensor  310  so that parallel communications can occur between the main sensor  310  and each of the individual ultrasonic sensors  312 . 
         [0053]    Referring additionally to  FIG. 9 , the main sensor  310  includes a protection circuit  321  that protects the sensor  310  from electrostatic discharge, reverse voltage and/or other causes that could damage the main sensor  310  or the other sensors  312 . The input to the protection circuit  321  is the 12 V DC power IGN_PWR, and the output is fed to a DC/DC voltage regulator  322 . The voltage regulator  322  converts the 12 V systems DC Power into a lower logical level voltage used by other functional blocks. The regulator  322  powers not only the internal functional blocks of the main sensor  312  as indicated, but also each individual ultrasonic sensor  312  through its respective power communications line  314  connection. 
         [0054]    A main microcontroller  320  connects all the functional blocks. The microcontroller  320  controls the internal ultrasonic transducer  318  and the other external ultrasonic sensors  312  by means of a main-side power line communication interface  326 . The interface  326  includes, in this embodiment, four instantiations of the circuit arrangement shown in  FIG. 1  between the ECU  12  and the power communications line  22  such that the main microcontroller can communicate in parallel with four ultrasonic sensors. (Thus, the interface  326  includes four low impedance lines  32 , each having impedance switch  36  controlled by the main microcontroller  320 . The high impedance line  28  may be common, or a separate high impedance line may be associated with each ultrasonic sensor.) Three power line communications wires  314 , which are incorporated in the bumper internal harness  304 , are connected to the main-side power line communication interface  326  (each to one of the low impedance lines  32 ), and one output  327  of the interface  326  is routed internally in the main sensor  310  for powering and communicating with the internal ultrasonic transducer  318 . 
         [0055]    In alternative embodiments where the external ultrasonic sensors  312  are connected in daisy chain fashion the bumper internal harness  304  includes a single power line communications wire  314  that is connected to the main-side power line communication interface  326 , which incorporates a single low impedance line  32  and impedance switch  34 . In this arrangement, the preferred master/slave communications protocol above requires an addressing scheme to identify each external ultrasonic sensor  312  for communication. 
         [0056]    The main microcontroller  320  processes all raw data provided by the ultrasonic sensors  312  and  318 , and provides the processed data to the vehicle by means of a vehicle communication interface  324 . The vehicle communication interface  324  is used to receive data from the vehicle such as activation status or other required parameters necessary for the operation of the system  300 . The vehicle communication interface  324  is also used to provide data relating to the vehicle environment such as distance to the closest obstacle, and information regarding parking maneuvers, etc (System Outputs). The vehicle communication interface could be a LIN, CAN or any other vehicle communication interface used in the automotive industry, and in the preferred embodiment is a slave type of interface that, as shown in  FIG. 8 , communicates with a main communication interface that could be located, for instance, in the vehicle radio. 
         [0057]    The internal ultrasonic sensor  318  and external ultrasonic sensors  312  preferably have the same functional blocks, including, as shown in  FIG. 10 , an ultrasonic transducer  330 , driver hardware  332  for the ultrasonic transducer, and a microcontroller  334  that connects all the functional blocks. In addition, each ultrasonic sensor  312 ,  318  includes a sensor or slave power line communication interface  336  which, as seen in  FIG. 10 , is basically a reproduction of the circuit arrangement shown in  FIG. 1  between power communications line  22  and the sensor  16 . The microcontroller  334  monitors the power line communication wire  314  for commands issued by the main sensor  310  and controls the connected ultrasonic transducer  330 . 
         [0058]    It will be appreciated by those skilled in the art that the ultrasonic transducer  330 , driver hardware  332  and microcontroller  334  may all be implemented as an application specific integrated circuit. 
         [0059]    While the above describes a particular embodiment(s) of the invention, it will be appreciated that modifications and variations may be made to the detailed embodiment(s) described herein without departing from the spirit of the invention.