Abstract:
A sensing and control circuit for power line shorts works especially well for sensor or actuator devices controlled through a microcontroller. A power control circuit is placed between a pin of a programmable microcontroller and a sensor or actuator device to act as a short detector and switch to control power to the device. A capacitor in the power control circuit is charged and sensed by a single pin of the microcontroller to regulate a transistor which switches power to the device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to connecting devices such as sensors or actuators to an electronic interconnecting apparatus. The invention relates specifically to an interconnect device having an efficient means for detecting and breaking short circuits in an actuatable device with minimal usage of pins from a microcontroller contained within the interconnect device. 
     2. Description of the Related Art 
     Commercial bus devices for industrial usage such as SMART DISTRIBUTED SYSTEM™ by Honeywell Inc. are made for large scale material handling or the like. These bus systems comprise 4-wire buses with two wires for power and 2 wires for communication and control. The bus may operate, for example, a conveyor line having a plurality of sensors for sensing packages and/or a plurality of actuators such as, for example, controllable routers for routing the packages onto and off the conveyor. The sensors and actuators, hereinafter referred to simply as “devices”, are often connected to the main bus lines by means of bus interconnect apparatus. These interconnect apparatus can handle a plurality of connections between the main bus line and the devices. The interconnect apparatus can contain microcontrollers for timing and routing signals to the devices. Alternatively, the devices themselves may contain the microcontroller to enable a variety of features such as counting, operator interface enablement, or the like. 
     It will be appreciated that the devices under discussion need not be connected to a bus, per se. They could for example be stand alone devices, or grouped devices, operating without the benefit of a full communications bus architecture. Therefore the term “bus” as used herein is better thought of in its broadest sense as a “communications or data line” which enables a sensing and control assemblage, or network, to communicate the data produced by the sensor or which carries the actuation pulses to the actuators. 
     In order to keep the cost of the devices or their interconnect apparatus low, while maximizing the features, great efficiency should be exercised in the use of the pin assignments on the microcontroller to enable the use of the least expensive microcontroller for the tasks at hand. 
     In the case where a device short circuits, it is desirable that the device be turned off as rapidly as possible in order to avoid damage to any of the components in the devices or interconnect apparatus, and also eliminate power drains, incorrect information, or false actuations. 
     In the past, short circuit sensing and control mechanisms have less efficiently utilized the microcontroller contained within the interconnect device. However, as previously stated, it is desirable to utilize the least amount of microcontroller pins in order to achieve such functionality. Further, a typical prior device would utilize an interrupt detection method which slows reaction time to short circuit conditions, as well as consuming valuable microcontroller resources in the form of software interrupts to the I/O pins of the microcontroller. 
     Therefore, it is desirable to have a means for more immediately detecting and shutting down short circuited sensing and control network devices while utilizing the least number of microcontroller pins. 
     SUMMARY OF THE INVENTION 
     The present invention in a first embodiment includes a short circuit detect and control circuit placed between a microcontroller and its sensor or actuator device for sensing short circuits in the device and immediately removing power thereto to protect the sensing and control network. This may be accomplished by means of an active switch such as a FET circuit placed in the power line and controlled by circuitry for biasing the active switch. One pin of the microcontroller activates the control circuitry via a pulse to a capacitor, enabling the active switch. The microcontroller then utilizes the same pin thereof to sense the condition of the current sensing circuit to determine a short has occurred. When excessive current is detected, the active switch is immediately shut down. In a full bus arrangement the microcontroller, having detected this situation, can report back to the bus system controller. 
     In another embodiment of the invention, the invention includes the bus device interconnect system utilizing the active switch and short circuit detect and control circuit in order to provide an efficient and inexpensive means for controlling short circuit conditions in an industrial bus application. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the Description of the Preferred Embodiment in conjunction with the drawings, in which: 
     FIG. 1 is a perspective view of a sensing and control network interconnect apparatus exterior according to the present invention. 
     FIG. 2 is a block diagram detailing the major components of the detect and control system circuit as related to the interconnect apparatus microcontroller and the connected device. 
     FIG. 3 is a detailed electrical schematic of the current sensing and active switch portions of the short circuit detect and control circuitry of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the Description of the Preferred Embodiment, like components will be identified by like reference numerals. 
     Referencing FIG. 1, an industrial sensing and control network bus interconnect apparatus  11  has a case  13  supporting a multiplicity of connectors  15  to which sensors or actuatable devices such as, package diverters, or the like, may be connected. A connector  17  for power and communications connection to the main bus is also provided. A third connector  19  is provided for power supply to the internal circuitry of the bus interconnect apparatus  11 . 
     Referencing the block diagram of FIG. 2, the bus interconnect apparatus  11  is surrounded by a dashed line  21 . The communication bus, or other communications line for a sensing and control network,  23  is shown connected to the microcontroller  27 . The sensor or actuator device  25 , again hereinafter referred to collectively as the “device”  25 , is shown as connected to another side of the bus interconnect apparatus  11 . Appropriate power connections from the bus and from the separate power supply necessary for powering the components internal to the interconnect apparatus have been left off for clarity of illustration, but are within the ordinary skill of the art. 
     As stated, connected to communications bus is a microcontroller  27  for controlling the plurality of connected devices, such as device  25 , which may be connected to the interconnect apparatus  11 . The microcontroller manages timing cycles and information management between the interconnect apparatus  11  and the main bus controller (not shown). Individual devices in a sensing and control network may of course have individual microcontrollers therein. The microcontroller  27  is connected through a single pin or electrical run  29  to the short circuit detect and control circuitry  31  as further explained below. The short circuit detect and control circuit  31  is connected in the voltage power line  33  between the main power bus and the power lines to the actuatable device  25 . The short circuit detect and control circuitry includes current sensing portions  35  and a controllable switch  37 . Thus, there is interposed between the microcontroller and the actuatable device, separate circuitry for controlling power to the actuatable device with utilization of only one pin of the microcontroller  27  and providing short circuit sensing and control on an instantaneous basis as further explained below. 
     Referencing FIG. 3, the control switch  37  is represented by P-Channel enhancement-mode FET, such as IRLMS5703 from International Rectifier, circuit  39  labeled as Q 1 . The choice for the P-Channel enhancement-mode FET is necessary for the operation of the circuit as configured. This is necessary so that the normal condition of the FET is off until activated by applying a negative Gate to Source voltage. The gate is pulled low when Q 5  turns on thus enabling the FET to pass current to the connected device. 
     The remaining components are part of the current sensing circuit of the short circuit detect and control circuitry. Connected to the single pin or line  29  of the microcontroller  27  through the 1 KΩ resistor R 24  is a 0.22f capacitor C 6  which is the charge and hold capacitor for the current sensing circuit. Connected on either side of the sense and hold capacitor C 6  is the emitter and collector of transistor Q 7  which, when turned on, quickly drains the capacitor C 6 . C 6  is connected to the base of a Darlington transistor Q 5 , the collector of which is connected to the gate of the control switch Q 1 . Transistor Q 3  is connected through R 1  at its emitter to the source of Q 1  and at its collector to the base of Q 7  through biasing resistors R 15  and R 36 . Microcontroller  27 , at its single pin  29 , pulses the pull-up-and-hold capacitor C 6  which turns on Q 5 , which pulls the gate of Q 1  low, turning on the active switch and putting power to the device  25 . Should the device  25  short and begin overdrawing current, the increased voltage drop across R 1  will turn on Q 3  and increase the current through R 15  thereby putting a base drive on Q 7  and turning on Q 7  to quickly drain capacitor C 6 . It will be appreciated that power is shut down wherever a short circuit occurs beyond the power input to the device circuit, so that when the phrase “short circuit in the device” is used, the reader will understand that such short circuit may occur anywhere in the device circuit, not just the device itself, in order to activate the detect and control circuit of the present invention. 
     The microcontroller  27  is programmed to check the voltage on C 6  utilizing a high impedance phase so that C 6  does not discharge through the pin  29 . When the voltage check reveals that the capacitor has drained, it recognizes a shorted condition and takes appropriate measures to indicate to the operator and system controller that the event has occurred. In the meantime, power to the device  25  has been shut down through control switch  37  as soon as the capacitor C 6  has drained. Alternative embodiments may have application specific integrated circuits, multivibrators, timing ICs, or the like, where the application does not require the functionality of the microcontroller. 
     Thus it will be recognized that two important functionalities are obtained with the short circuit detect and control circuit of the present invention. First, short circuit control to the device  25  is placed outside the microcontroller, and second, all short circuit sensing and control functionality is accomplished through utilization of only one pin of the microcontroller. 
     It will be recognized that the short circuit detect and control circuit of the preferred embodiment may have other applications not strictly limited to the control of an actuatable device in an industrial bus system. Many such utilizations and variations on the present invention and its basic structure will occur to those skilled in the art. Accordingly, the present invention is to be limited only by the appended claims.