fig1 is a perspective view of a defibrillator system of a type in which the present invention may be employed . the defibrillator system includes a base unit 18 for providing electrical energy to shock a patient . various types of pads or paddle assemblies may be used with this system . in fig1 external paddle assemblies 40 , 42 are illustrated . the paddle assemblies are disposed in respective recesses 41 , 43 which are provided in the base unit 18 for storing the external paddles when they are not in use . the paddles are connected to the base unit by a cable assembly which includes a cable 24 fixed to a plug assembly 30 . the plug assembly 30 is shown engaged in the base unit as will be further described below . referring now to fig2 the external paddles are illustrated in a top plan view , along with the associated cable assembly 16 . cable assembly 16 includes the plug assembly 30 and a pair of cables , for example cable 24 , for connecting the paddle assemblies 40 , 42 to the plug assembly . a strain relief interface 26 , formed of a sturdy yet pliable material , is provided where the cable 24 enters the plug assembly . the plug assembly 30 and its interface with the base unit will be described further below , following a description of alternative types of pads and paddle assemblies . fig3 illustrates a pair of internal paddles 78 , which may be connected to the base unit by means of an associated cable assembly 70 . cable assembly 70 includes a cable 72 fixed to a plug assembly 76 . plug assembly 76 , like plug assembly 30 , is arranged for interfitting engagement with a connector in the base unit . a coupler 74 is provided for removably connecting the internal paddles to the cable assembly 70 . fig4 illustrates a pair of patient adhesive pads 112 . the patient pads 112 may be connected to the base unit via an associated cable assembly 100 . cable assembly 100 includes a cable 102 fixed to a corresponding plug assembly 116 . a pads coupler 104 is provided for connecting the patient pads to the cable assembly 100 . note that the patient pads coupler 104 is mechanically keyed differently ( not shown ) from the internal paddles coupler 74 shown in fig3 . this arrangement prevents connection of the internal paddles 78 to the patient pads cable assembly 100 , and likewise prevents mechanical connection of the patient pads 112 to the internal paddles cable assembly 70 . fig5 is an enlarged , partially cut - away view showing the plug assembly 30 engaged in a connector assembly 20 . connector assembly 20 is fixed in position within the base unit 18 and arranged to receive any of the plug assemblies 30 ( external paddles ), 76 ( internal paddles ), or 116 ( patient pads ) in interfitting engagement . plug assembly 30 is shown in fig5 for purposes of illustration . referring now to fig2 and 5 , plug assembly 30 includes a plug body 32 and a cover 35 coupled to the plug body . a plurality of pins 56 extend from the plug body 32 for electrical connection between the cable assembly and the base unit . corresponding receptacles 57 are provided in the connector assembly 20 for receiving the pins 56 in an electrical content . fig6 is a schematic diagram of electronic circuitry used for identifying pads or paddles connected to the base unit . the plug assembly 32 and connector assembly 20 are indicated generally in the center of the drawing , representing the interface between the base unit and the connected pads or paddles . circuitry shown to the left of connector assembly 20 thus illustrates circuitry disposed within the base unit 18 . circuitry 66 , on the right side of the diagram , is electrically coupled through cable 24 to the plug assembly 32 . in the defibrillator base unit , a charge - done driver circuit 82 comprises an npn transistor 84 which is controlled by a charge - done signal ( chdone ) coupled to the transistor through a base resistor 86 . transistor 84 has a collector terminal coupled through a collector resistor 88 to vcc , which may be , for example , 5 volts dc . the emitter terminal is coupled through an emitter resistor 92 to the charge - done signal line 60 . the charge - done signal line 60 is coupled to the connector assembly 20 for connection to any of the various plug assemblies 30 , 76 or 116 . the charge - done signal line 60 also is coupled through a pull - up resistor 90 to vcc . the charge - done signal line also is coupled through an input resistor 94 to an analog - to - digital conversion circuit 96 . the a / d circuit 96 is coupled to or disposed within a defibrillator controller 80 which asserts the charge - done signal when a patient circuit ( not shown ) is charged to a selected energy level . turning now to the right side of fig6 identification circuitry 66 is disposed within the external paddle assembly 40 . the external paddle assembly 40 includes a charge - done indicator light 58 ( see also fig2 ), which may be provided by a light emitting diode . a light emitting diode ( led ) 58 is disposed between the charge - done signal line 60 and ground line 61 . a resistor 62 is disposed in parallel to the led 58 . and finally , a zener diode 64 also is disposed in parallel to led 58 , i . e ., between the charge - done signal line 60 and ground connection 61 . only selected signal lines at the defibrillator / plug assembly interface are illustrated in fig6 . a more complete list of the defibrillator interface connections is shown in the following table 1 : table 1______________________________________plug connector signalssignal definition______________________________________ncharge apex paddle 40 charge button 67 . charge is asserted low . charge - done voltage level indicates the type of paddlessignal 60 connected to the base unit . also used to light the apex paddle charge done led 58 . vcc + 5vdcpci patient contact impedance . a voltage which turns on a specific number of leds on the sternum pci led bar ( not shown ). logic gnd groundndischarge a signal asserted when the apex paddle 40apex shock button 67 is pressed . ndischarge a signal asserted when the sternum paddlesternum 42 shock button 68 is pressed . hi voltage connects the apex paddle ( pad ) to the outputapex (-) side of the patient ( transfer ) circuit and to the pacer (-) terminal ( if a pacer is installed ). hi voltage connects the sternum paddle ( pad ) to thesternum output (+) side of the patient ( transfer ) circuit and to the pacer (+) terminal if a pacer is installed . ______________________________________ in operation , when the patient charging circuit in the defibrillator reaches a selected energy level , the defibrillator controller 80 asserts the charge - done signal chdone to turn transistor 84 on . transistor 84 drives the charge - done signal line 60 up toward vcc , thereby actuating led 58 so as to turn on the indicator light , indicating &# 34 ; charge - done &# 34 ; to a user . this occurs only when the external paddles are connected to the base unit , as the other paddles and pads do not have the led . nonetheless , the charge - done signal line may be asserted in all cases . while the charge - done signal is not being asserted by the controller 80 , transistor 84 is off . during such times , the charge - done signal line 60 essentially is coupled through pull - up resistor 90 to vcc . referring now to the identification circuit 66 in fig6 the charge - done signal line 60 is coupled through resistor 62 to ground . resistors 90 and 62 thus form a resistive divider circuit which provides a voltage calculated as follows . if resistor 90 has a value of 10 kω and resistor 62 has a value of 2160ω then the divided value equals 0 . 178 times 5 volts ( vcc ) or 0 . 888 volts . resistor 62 thus pulls the voltage down to a level which keeps the led 58 turned off . the voltage at the charge - done signal line 60 is presented through resistor 94 to an analog - to - digital ( a / d ) converter 96 for sensing the voltage and providing the sensed voltage value to the defibrillator controller 80 . the defibrillator controller is arranged to recognize an analog voltage in a range of approximately 0 . 5 to 3 . volts as identifying the external paddles assembly . in case no pads or paddles are connected to the base unit , resistor 90 pulls the signal line 60 up to approximately vcc or 5 volts . the controller 80 is arranged to recognize a voltage greater than approximately 4 volts as an indication that no pads or paddles are connected to the base unit . in the case of internal paddles 78 , these are connected to the base unit through a plug assembly 76 , as noted above . plug assembly 76 includes means for connecting the single line 60 to ground , thereby driving the signal line 60 to approximately zero volts . accordingly , the controller 80 is arranged to recognize a voltage of less than approximately 0 . 5 volts as identifying the internal paddles assembly . in the case of adhesive patient pads 112 , the identifying voltage preferably falls within a range of approximately 3 - 4 volts dc . accordingly , a reference voltage circuit which provides a voltage within that range , nominally 3 . 5 vdc , is disposed in the corresponding plug assembly 116 . the voltage reference may be provided by a resistor divider , zener diode , etc . the reference voltage source may be powered by the vcc supply voltage provided to the plug assembly by the base unit . plug assemblies 76 and 116 thus contain circuitry adequate for identifying the respective pads and paddles by impressing a corresponding voltage onto the charge - done signal line . the identification voltage levels are summarized in the table 2 : table 2______________________________________analog voltage value vs paddles typeid voltage paddles type______________________________________ & lt ; 0 . 5 v internal paddles ≧ 0 . 5 , & lt ; 3 v external paddles ≧ 3 . 0 , & lt ; 4 v external paddles ≧ 4 . 0 v none______________________________________ additional types of pads or paddles may be identified in a similar fashion , by assigning a corresponding identification voltage level ( or range ) to each such assembly . even with modest voltage accuracy , say within one - half volt , several more levels could be assigned within the existing 5 volt supply range , by narrowing one or more of the existing ranges set forth in table 2 . virtually any a / d converter has ample resolution for sensing these levels . plug assemblies 76 and 116 each include a pair of discharge switches ( not shown ) for signalling the defibrillator base unit to deliver a shock to the patient through the connected cable assembly . both switches must be actuated at the same time to deliver the shock , so as to avoid accidental discharge . the discharge switches are actuated by push buttons 52 , 54 . preferably , the discharge switches are mounted on a small circuit board ( not shown ), disposed inside the plug assembly . push buttons 52 , 54 are exposed through apertures provided in the plug assembly cover 35 for that purpose . the identification circuitry described above conveniently may be disposed in the plug assemblies on the same circuit board as the discharge switches . referring now to fig7 - 10 , the plug assemblies include a latch 38 which is slidably connected to the plug body ( for example 34 ) and extends over at least a portion of the cover 35 . the base unit case 18 includes a lip 22 that extends partially over the connector assembly 20 as best seen in cross - section in fig8 . latch 38 includes means 44 defining a recess sized for engaging the lip 22 . latch 38 is slidable between a first or unlocked position as illustrated in fig7 and 8 . when the latch is unlocked , the plug assembly 76 may freely be inserted or removed from the connector assembly 20 . in the locked position , as illustrated in fig9 and 10 , means 44 engages the lip 22 so as to prevent removal of the plug assembly from the base unit . essentially the same latching arrangement is provided in all three illustrated plug assemblies 30 , 76 , 116 . plug assemblies 76 and 116 , as noted above , include buttons 52 , 54 for actuating discharge switches to shock the patient . referring to fig7 it may be observed that the latch 38 , in the unlocked position , partially obscures buttons 52 , 54 so as to prevent their actuation by a user . this prevents discharge of the defibrillator unless the plug assembly 76 is securely locked in place in the defibriilator base unit 18 . conversely , as illustrated in fig9 the latch 38 , when moved to the lock position , exposes buttons 52 and 54 for use . the latch 38 thus serves the dual purposes of maintaining the plug assembly secured in the base unit and preventing actuation of the discharge switches unless the plug assembly is locked in place . having illustrated and described the principles of my invention in a preferred embodiment thereof , it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles . i claim all modifications coming within the spirit and scope of the accompanying claims .
a defibrillator patient connection system is disclosed for automatically identifying to a defibrillator system the type of pads or paddles assembly connected to the system for conveying electrical energy to shock a patient . each of the available pads or paddles assemblies is identified by a corresponding analog voltage level provided to the base unit through a corresponding cable assembly . the identification voltage is sensed by an a / d converter in the defibrillator base unit . the identification voltage is provided to the base unit on a charge - done signal line which otherwise is asserted by the base unit to controllably actuate a charge - done indicator light in an external paddles assembly . the disclosed methods and apparatus thus maintain a simple defibrillator / cable assembly interface and require no additional signal lines for implementing automatic identification . a plug assembly latch mechanism also is disclosed that provides the dual functions of locking a plug assembly in place in the defibrillator base unit and preventing actuation of discharge buttons on the plug assembly when the latch is not in the locked position , thereby avoiding a high energy discharge unless the plug assembly is securely locked in position .