the following discussion is presented to enable a person skilled in the art to make and use the invention . various modifications to the preferred embodiments will be readily apparent to those skilled in the art , and the generic principles herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention as defined by the appended claims . thus , the present invention is not intended to be limited to the embodiments shown , but is to be accorded the widest scope consistent with the principles and features disclosed herein . furthermore , “ automated external defibrillator ” or “ aed ” is any defibrillator that determines whether a patient has a shockable heart rhythm . [ 0029 ] fig2 is an exploded view of a modular aed system 40 , which includes a pad - cartridge module , i . e ., cartridge assembly , 42 and an aed base unit 44 according to an embodiment of the invention . for clarity , like numerals refer to elements common to the system 10 of fig1 . the modular aed system 40 is often easier and less expensive to manufacture than the integrated aed system 10 of fig1 . for example , multiple models of the modular aed system 40 may incorporate the same base unit 44 . therefore , the manufacturer can often purchase components for the base unit 44 in relatively large lots , and have a single assembly / testing line for the base unit . furthermore , once the fda has approved the base unit 44 , the manufacturer typically need only obtain fda approval for new modules to be incorporated into the aed system 40 . similarly , once the fda has approved a module , the manufacturer typically need only obtain fda approval for new base units to be incorporated into the aed system 40 . the cartridge assembly 42 includes the electrode pads 16 a and 16 b and a cartridge 46 . the cartridge 46 has a bottom , ie ., tray , 48 , side walls 50 a - 50 d , and lid 52 , which may be hinged to a side wall such as the side wall 50 a with one or more hinges 53 . the cartridge 46 also includes an electrode - pad connector 54 , which may extend through a side wall such as the side wall 50 a , helps to secure the cartridge 46 to the aed base unit 44 , and electrically connects the electrode pads 16 a and 16 b to the base unit via electrode - pad wire leads 56 a and 56 b . alternatively , the connector 54 may extend through the tray 48 . the leads 56 a and 56 b are conventionally attached to the connector 54 . the connector 54 may include an information provider such as a groove 57 , which provides information , such as the type ( e . g ., pediatric , adult , or training ) of pads 16 a and 16 b , to the base unit 44 . the cartridge 46 may also include a conventional latch mechanism ( not shown ) for latching the lid 52 to one or more of the side walls 50 a - 50 d . this and other embodiments of the cartridge assembly 42 are further discussed in u . s . patent application ser . no . 09 / 746 , 123 , entitled cartridge for storing an electrode pad and methods for using and making the cartridge , filed on dec . 22 , 2000 , which is incorporated by reference . still referring to fig2 in addition to the battery 18 , on / off switch 20 , speaker 24 , shock button 28 , microphone 34 , and data card 36 , the aed base unit 44 includes a receptacle 58 and a connector 60 for respectively receiving the cartridge 46 and the connector 54 . the base unit 44 may read the information provided by the groove 57 using conventional techniques or a technique such as that disclosed in u . s . patent application ser . no . 09 / 746 , 123 , entitled cartridge for storing an electrode pad and methods for using and making the cartridge , filed on dec . 22 , 2000 , which is heretofore incorporated by reference . the connectors 54 and 60 , which electrically interconnect the cartridge assembly 42 and the base unit 44 , may be the sole means by which the cartridge assembly and the base unit are attached to one another . alternatively , means such as velcro ® strips ( not shown ), mating grooves ( not shown ) in the side walls of the receptacle 58 and the side walls 50 b and 50 d of the cartridge 46 , or other conventional means may be included to attach the cartridge 46 to the base unit 44 . furthermore , the manufacturer may permanently attach the cartridge 46 to the base unit 44 to prevent one from taking the modular aed system 40 apart . one would , however , be able to replace the pads 16 a and 16 b without replacing the cartridge 46 . or , the manufacturer may allow one to remove the cartridge 46 from the base unit 44 such that he / she can replace the cartridge assembly 42 with another cartridge assembly or module ( not shown in fig2 ). furthermore , the aed base unit 44 may include a compartment 62 for storing defibrillator electrode pads , such as the pads 16 a and 16 b , when a module other than the cartridge assembly 42 is in the receptacle 58 . the connector 60 or another connector ( not shown ) may connect the pads in the compartment 62 to the base unit 44 . in addition , the compartment 62 may include a lid or other cover ( not shown ). the operation of the modular aed system 40 is discussed according to an embodiment of the invention . during an emergency where it is determined that a patient ( not shown ) may need a shock , the operator ( hands shown in fig2 ) retrieves the aed base unit 44 and installs the battery 18 if it is not already installed . next , the operator inserts the connector 54 into the connector 60 , and thus inserts the cartridge 46 into the receptacle 58 , if the cartridge 46 is not already installed . then , the operator opens the lid 52 and removes the electrode pads 16 a and 16 b from the cartridge 46 . next , the operator activates the base unit 44 by turning the on / off switch 20 to the “ on ” position , and in response to written or spoken instructions , places the electrode pads 16 a and 16 b on the patient ( not shown ). the base unit 44 then analyzes the patient &# 39 ; s ecg to determine whether the patient is suffering from a shockable heart rhythm . if the base unit 44 determines that the patient is suffering from a shockable heart rhythm , it then instructs the operator to press the shock button 28 . conversely , if the base unit 44 determines that the patient is not suffering from a shockable heart rhythm , it may inform the operator to seek appropriate non - shock treatment for the patient and may disable the shock button 28 . after the operator has treated the patient , he / she typically installs new pads 16 a and 16 b or an entire new cartridge assembly 42 . thus , with new pads or a new cartridge assembly installed , the modular aed system 40 is ready for its next use . alternatively , one may wait until the next use of the aed system 40 to install new pads or a new cartridge assembly . although the modular aed system 40 is discussed , other modular medical devices or systems are contemplated . furthermore , although the aed system 40 is discussed having a pair of pads 16 a and 16 b , the system may have more or fewer pads . or , the system 40 may be capable of , and include pads that are suitable for , electrotherapies other than or in addition to defibrillating . such electrotherapies may include monitoring , cardioverting , or pacing . moreover , the system 40 may include a manual override that allows the operator ( hands shown in fig2 ) more control over otherwise automated functions . in one embodiment , the modular system 40 is configured with a certain set of one or more modules ( such as the cartridge assembly 42 ) in conjunction with the base unit 44 . this configuration is typically determined by the type of aed features the customer / operator desires or the particular model of the aed system 40 that the manufacturer produces . such a configure - to - order ( cto ) scenario allows the customer / operator to choose a modular aed system 40 having the features and functionality he / she needs . [ 0035 ] fig3 is a control module 70 that can replace the cartridge assembly 42 of fig2 according to an embodiment of the invention . the manufacturer may give an operator ( not shown in fig3 ) the ability to configure the aed system 40 ( fig2 ) to meet his / her needs . specifically , the operator can configure the system 40 by inserting the module 70 into the receptacle 58 ( fig2 ) of the aed base unit 44 ( fig2 ) in place of the cartridge assembly 42 . the module 70 typically receives power from the base unit 44 , and provides additional features to the modular aed system 40 ( fig2 ) as described below . the control module 70 includes a display 72 , status indicator 74 , control knob 76 , pad connector 78 , indicator light - emitting diodes ( leds ) 80 , a connector 82 , and push buttons 84 . the display 72 displays operator information such as patient - treatment instructions or an aed function - select menu . the indicator 74 and leds 80 provide the status of the aed 40 . for example , the indicator 74 , leds 80 , or both may indicate when the shock circuitry ( fig8 ) is ready to deliver a shock to the patient ( not shown ). the control knob 76 allows the operator to manipulate the display 72 . for example , the operator may control the brightness or contrast of the display 72 by turning the knob 76 . the connector 78 allows one to connect a set of pads , such as the pads 16 a and 16 b ( fig2 ), to the aed system 40 . the connector 82 is similar to the connector 54 ( fig2 ) and mates with the base - unit connector 60 ( fig2 ). although not shown , the connector 82 may include an information provider such as the groove 57 ( fig2 ). the push buttons 84 allow the operator to select software - menu items from the display 72 , or may provide other features . alternatively , the display 72 may include a touch - sensitive screen so that the manufacturer can omit the buttons 84 . other embodiments of the control module 70 may have a different layout or different controls , or may provide different features . for example , the positions of the display 72 , status indicator 74 , selection knob 76 , pad connector 78 , indicator leds 80 , connector 82 , and push buttons 84 may be rearranged . furthermore , the knob 76 may control defibrillation functions other than the brightness or contrast of the display 72 . for example , the knob 76 may control the level of the shock energy or the volume of the speaker 24 ( fig2 ). furthermore , these components may be replaced with equivalent components . for example , although the pad and module connectors 78 and 82 are respectively shown as female and male connectors , they may be male and female connectors . or the knob 76 or buttons 84 may be replaced with other types of control components such as switches . in addition , the display 72 may provide the status of the aed system 40 so that the manufacturer can omit the status indicator 74 or leds 80 . moreover , although the connectors 82 and 60 ( fig2 ) may be the sole means by which the module 70 is attached to the base unit 44 ( fig2 ), means such as , screws , fasteners , or velcro ® strips ( not shown ), mating grooves ( not shown ) in the side walls of the receptacle 58 and the side walls 86 a and 86 b of the module 70 , or other conventional means may be included to attach the module 70 to the base unit 44 . furthermore , the module 70 may provide power to the base unit 44 . in addition , the manufacturer may permanently attach the module 70 to the base unit 44 to prevent one from taking the modular aed system 40 apart . or , the manufacturer may allow one to remove the module 70 from the base unit 44 such that he / she can replace the module with another module or the cartridge assembly 42 ( fig2 ). [ 0038 ] fig4 is a monitor module 90 that can replace the cartridge assembly 42 of fig2 according to an embodiment of the invention , where like numbers identify like components with respect to the control module 70 of fig3 . specifically , an operator ( not shown in fig4 ) can insert the module 90 into the receptacle 58 ( fig2 ) of the base unit 44 in place of the cartridge assembly 42 . the module 90 typically receives power from the base unit 44 , and provides additional features to the modular aed system 40 ( fig2 ) as described below . like the control module 70 of fig3 the monitor module 90 includes a display 72 , control knob 76 , pad connector 78 , indicator light - emitting diodes ( leds ) 80 , connector 82 , and push buttons 84 . the display 72 displays information such as patient - treatment instructions , an aed function - select menu , or a patient waveform such as the patient &# 39 ; s electrocardiogram ( ecg ). the display 72 may also display the status of the aed system 40 ( fig2 ). other embodiments of the monitor module 90 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . [ 0041 ] fig5 is a training cartridge assembly 100 that can replace the cartridge assembly 42 of fig2 according to an embodiment of the invention , where like numbers identify like components with respect to the cartridge assembly 42 . specifically , an operator ( not shown in fig5 ) can adjust the training - scenario selector 102 to simulate any of a number of different rescue or training scenarios . if power is needed , the selector 102 typically receives it from the base unit 44 , and provides training features to the modular aed system 40 ( fig2 ) as described below . alternatively , the cartridge assembly 100 may have its own power supply ( not shown ) such as a battery . the cartridge assembly 100 is similar to the cartridge assembly 42 of fig2 except that it includes the training - scenario selector 102 , and , to prevent accidental shock delivery , the connector 54 does not electrically couple the electrode pads 16 a and 16 b to the base unit 44 ( fig2 ). furthermore , to prevent inadvertent use of the assembly 100 during an actual rescue , an optional flag 104 indicates that the assembly 100 is a training assembly . in operation , an operator ( not shown in fig5 ) sets a selector knob 106 of the selector 102 to a desired training scenario that allows him / her to train a student ( not shown ) in the use of the aed system 40 ( fig2 ). for example , the operator can set the knob 106 so that the selector 102 causes the aed base unit 44 to behave as if it has determined that a patient ( not shown ) is suffering from a shockable heart condition . then , while the operator studies and comments on his / her performance , the student tries to revive the patient using the aed system 40 . for such training purposes , the patient can be a mannequin . aed training devices and techniques are further discussed in u . s . pat . nos . 5 , 611 , 815 , 5 , 662 , 690 , and 5 , 993 , 219 , which are incorporated by reference . [ 0044 ] fig6 is a communication module 110 that can replace the cartridge assembly 42 of fig2 according to an embodiment of the invention , where like numbers identify like components with respect to the monitor module 90 of fig4 . specifically , an operator ( not shown in fig6 ) can insert the module 110 into the receptacle 58 ( fig2 ) of the aed base unit 44 in place of the cartridge assembly 42 . the module 110 typically receives power from the base unit 44 , and provides additional features to the modular aed system 40 ( fig2 ) as described below . in addition to a base - unit connector 82 , the communication module 110 includes a conventional telephone keypad 112 , female telephone connector 114 for receiving a male connector 116 , and an optional antenna 118 . after completion of the patient - rescue operation , the operator ( not shown in fig6 ) connects the connector 114 to the connector 116 and dials the telephone number of a data - collection center ( not shown ). then , the aed base unit 44 ( fig2 ) uses the module 110 as a modem to download rescue data from the card 36 ( fig2 ) or from the base unit in general to the data - collection center via a phone line 120 . alternatively , the base unit 44 uses the module 110 as a wireless modem to download the rescue data via the antenna 118 and a wireless channel . the base unit 44 may also receive data from the data - collection center via the telephone line 120 or the wireless channel . other functions of the module 110 include downloading new or updated software for the base unit 44 , module 110 , or both , or downloading rescue instructions for the operator . other embodiments of the monitor module 110 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . [ 0047 ] fig7 is an exploded view of a modular aed system 130 , which includes an electrode - pad module , i . e ., cartridge assembly , 132 , a control module 134 , and an aed base unit 136 according to an embodiment of the invention . for clarity , like numerals refer to elements common to the aed system 40 ( fig2 ). a difference between the aed system 130 and the aed system 40 is that the base unit 136 lacks a shock button and an on / off switch . therefore , in this embodiment , the aed 130 requires a control module such as the control module 134 . in addition , although not shown in fig7 the base unit 136 may include a pad storage compartment such as the storage compartment 62 of the base unit 44 ( fig2 ). the cartridge assembly 132 includes a connector 138 to which the pads 16 a and 16 b are connected via the leads 56 a and 56 b . unlike the connector 54 ( fig2 ) of the cartridge assembly 42 ( fig2 ), the connector 138 extends through the bottom 48 of the cartridge 46 . but like the connector 54 , the connector 138 may include an information provider such as the groove 57 ( fig2 ). otherwise , the cartridge assembly 132 is similar to the cartridge assembly 42 . the control module 134 typically receives power from the aed base unit 136 , and includes an on / off switch 140 , shock button 142 , and side walls 144 a and 144 b . the switch 140 and button 142 may be similar to the on / off switch 20 and the shock button 28 of fig2 respectively . the module 134 also includes a connector ( not shown ) that extends from the bottom of the module and that may include an information provider such as the groove 57 ( fig2 ). other embodiments of the module 134 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . furthermore , in addition to the battery 18 , speaker 24 , microphone 34 , and data card 36 , the aed base unit 136 includes a receptacle 146 and connectors 148 and 150 for respectively receiving the connector 138 of the cartridge 46 and the connector ( not shown ) of the control module 134 . the base unit 136 may read the information provided by information providers on the connector 138 and the connector of the module 134 . the connectors 138 , 148 , 150 , and the control - module connector , which electrically interconnect the cartridge assembly 132 , the control module 134 , and the base unit 136 , may be the sole means by which the cartridge assembly and the control module are attached to the base unit . alternatively , other attachment means , such as those described above in conjunction with fig2 and 3 , may be included to attach the cartridge 46 and the module 134 to the base unit 136 . furthermore , the manufacturer may permanently attach the cartridge assembly 132 and the control module 134 to the base unit 136 to prevent an operator ( hands shown in fig7 ) from taking the modular aed system 130 apart . or , the manufacturer may allow the operator to remove the cartridge assembly 132 or the control module 134 from the base unit 136 such that he / she can replace the cartridge assembly or control module with another cartridge assembly or module ( not shown in fig7 ). where the cartridge assembly 132 is permanently attached to the base unit 136 , the operator can replace the pads 16 a and 16 b without replacing the cartridge 46 . still referring to fig7 the operation of the modular aed system 130 is discussed according to an embodiment of the invention . during an emergency where it is determined that a patient ( not shown ) may need a shock , the operator ( hands shown in fig7 ) retrieves the aed base unit 130 and installs the battery 18 if it is not already installed . next , the operator inserts the connector 138 into the connector 148 , and thus inserts the cartridge 46 into one end of the receptacle 146 , if the cartridge 46 is not already installed . similarly , the operator inserts the control - module connector ( not shown ) into the connector 150 , and thus inserts the control module 134 into the other end of the receptacle 146 , if the control module is not already installed . then , the operator opens the lid 52 and removes the electrode pads 16 a and 16 b from the cartridge 46 . next , the operator activates the control module 134 and the base unit 136 by turning the on / off switch 140 to the “ on ” position , and in response to written or spoken ( via the speaker 24 ) instructions , places the electrode pads 16 a and 16 b on the patient ( not shown ). the base unit 136 then analyzes the patient &# 39 ; s ecg to determine whether the patient is suffering from a shockable heart rhythm . if the base unit 136 determines that the patient is suffering from a shockable heart rhythm , then it instructs the operator to depress the shock button 142 . conversely , if the base unit 136 determines that the patient is not suffering from a shockable heart rhythm , it may inform the operator ( e . g ., via the speaker 24 ) to seek appropriate non - shock treatment for the patient and may disable the shock button 142 . after the operator has treated the patient , he / she installs new pads 16 a and 16 b , or an entire new cartridge assembly 132 . thus , with new pads or a new cartridge assembly installed , the aed system 130 is ready for its next use . alternatively , the operator may wait until the next use of the system 130 to install a new cartridge assembly or pads . typically , the operator does not detach the control module 134 from the base unit 136 once the control module is installed . [ 0052 ] fig8 is an enhanced control module 160 that can replace the cartridge assembly 132 or the control module 134 of fig7 according to an embodiment of the invention , where like numbers reference like components with respect to the control module 134 . typically , an operator ( not shown in fig8 ) inserts the module 160 into the base - unit receptacle 146 ( fig7 ) in place of the control module 134 . the control module 160 has more features than the control module 134 as described below . the control module 160 typically receives power from the aed base unit 136 ( fig7 ), and , in addition to the on / off switch 140 and shock button 142 , includes a display 162 , control knob 164 , and push buttons 166 , which are respectively similar to the display 72 , control knob 76 , and push buttons 84 of fig3 . the module 160 also includes a connector ( not shown ) that extends from its bottom and that mates with the connector 150 ( fig7 ) of the base unit 136 . this connector may include an information provider such as the groove 57 ( fig2 ). other embodiments of the control module 160 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . [ 0055 ] fig9 is a full - featured control module 170 that can replace one or both of the cartridge assembly 132 and the control module 134 of fig7 according to an embodiment of the invention , where like numbers reference like components with respect to the control module 160 ( fig8 ). typically , the module 170 is sized to occupy the entire base - unit receptacle 146 ( fig7 ). therefore , the operator ( not shown in fig9 ) inserts the module 170 into the base - unit receptacle 146 in place of the cartridge assembly 132 and the control module 134 . the control module 170 has more features than the enhanced control module 160 as described below . the control module 170 typically receives power from the aed base unit 136 ( fig7 ), and , in addition to the on / off switch 140 , shock button 142 , display 162 , control knob 164 , and push buttons 166 , includes a status indicator 172 , indicator leds 174 , and a pad connector 176 , which are respectively similar to the status indicator 74 , leds 80 , and pad connector 78 of fig3 . the module 170 also includes a pair of connectors ( not shown ) that extend from its bottom and that respectively mate with the connectors 148 and 150 of the base unit 136 . one or both of these connectors may include an information provider such as the groove 57 ( fig2 ). alternatively , the module 170 may include a single connector ( not shown ) that extends from the its bottom and that mates with one of the connectors 148 and 150 of the base unit 136 . other embodiments of the control module 170 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . furthermore , the module 170 may be sized to occupy only a portion of the base - unit receptacle 146 ( fig7 ) such that the cartridge assembly 132 or another module ( not shown ) can simultaneously occupy the receptacle 146 with the module 170 . [ 0058 ] fig1 is a monitor module 180 that can replace one or both of the cartridge assembly 132 and the control module 134 of fig7 according to an embodiment of the invention , where like numbers identify like components with respect to the control module 170 ( fig9 ). typically , the module 180 is sized to occupy the entire base - unit receptacle 146 ( fig7 ). therefore , the operator ( not shown in fig1 ) inserts the module 180 into the receptacle 146 of the base unit 136 in place of the cartridge assembly 132 and the control module 134 . the module 180 typically provides additional features to the modular aed system 130 ( fig7 ) as described below . the monitor module 180 typically receives power from the aed base unit 136 ( fig7 ), and includes on / off switch 140 , shock button 142 , display 162 , control knob 164 , push buttons 166 , indicator light - emitting diodes ( leds ) 174 , and pad connector 176 . the display 162 displays information such as patient - treatment instructions , an aed function - select menu , or a patient waveform such as the patient &# 39 ; s electrocardiogram ( ecg ). the display 162 may also display the status of the aed 130 . furthermore , the module 180 may include a single connector ( not shown ) that extends from the bottom of the module and that mates with one of the base - unit connectors 148 or 150 ( fig7 ). alternatively , the module 180 may include two such connectors that each mate with a respective one of the base - unit connectors 148 and 150 . one or both of these connectors may include an information provider such as the groove 57 ( fig2 ). other embodiments of the monitor module 180 are contemplated . these embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . furthermore , the module 180 may be sized to occupy only a portion of the base - unit receptacle 146 ( fig7 ) such that the cartridge assembly 132 or another module ( not shown ) can simultaneously occupy the receptacle 146 with the module 180 . [ 0061 ] fig1 is a modular aed system 188 , which includes an aed base unit 190 and communication module 192 according to an embodiment of the invention , where like numbers identify like components with respect to the aed system 130 ( fig7 ). the base unit 190 is similar to the base unit 136 except that it includes a receptacle 194 for receiving the communication module 192 . the receptacle 194 includes a connector 196 for mating with a corresponding connector ( not shown ) on the bottom of the module 192 . the communication module 192 allows an operator ( hands shown in fig1 ) to communicate with someone , such as a doctor ( not shown ), at a remote location , such as a hospital ( not shown ), before , during , or after a rescue operation . the module 192 includes a microphone 198 for picking up the operator &# 39 ; s voice , an antenna 200 , which allows wireless communication between the operator and the remote location , and an optional speaker 201 . the speaker 24 , the speaker 201 , or both the speakers 24 and 201 may allow the operator to hear the voice of a person at the remote location . the module 192 may receive power from the base unit 190 , or may include a power supply such as a battery ( not shown ). furthermore , where the wireless communication is over a wireless telephone network , the base unit 190 or module 192 includes circuitry ( not shown ) for dialing a predetermined telephone number . the base unit 190 or module 192 may cause the this circuitry to dial the telephone number automatically when the operator powers on the base unit , or may wait for a specific instruction from the operator . alternate embodiments of the base unit 190 and module 192 are contemplated . for example , the module 192 may include a telephone keypad and telephone line connector like the module 112 ( fig6 ). in such an embodiment , the module 192 can be used for voice communications and for downloading rescue data as discussed above in conjunction with fig6 . furthermore , the module 192 may include a speaker separate from the speaker 24 to allow the operator to hear the voice of a person at the remote location . in addition , the module 192 may lack the microphone 198 , and the microphone 34 may pick up the operator &# 39 ; s voice for transmission to the remote location . moreover , the microphone 198 , the antenna 200 , the communication circuitry ( not shown ) within the module 192 , and other components ( not shown ) of the module 192 may be integral with the base unit 190 . furthermore , the aed base unit 44 of fig2 can be modified to receive the module 192 . in addition , other embodiments may incorporate modifications similar to those discussed above in conjunction with fig3 for the other embodiments of the control module 70 . [ 0065 ] fig1 is a schematic block diagram of a base - unit circuit 210 , which the base units 44 ( fig2 ), 136 ( fig7 ), and 190 ( fig1 ) may incorporate according to an embodiment of the invention . the circuit 210 includes a functional circuit 212 and one or more — here n — module interfaces 214 . the functional circuit 212 may include and execute software , and performs functions such as turning on and off the modular aeds 40 , 130 , and 188 , analyzing a patient &# 39 ; s heart rhythm and determining whether it is a shockable rhythm , generating a defibrillation shock if the rhythm is shockable , and sending rescue data to a remote location directly or via a module such as the control module 110 ( fig6 ). the circuit 212 may also control the speaker 24 and the microphone 34 , interface with the data card 36 , and manage the power supply for the base unit and any connected control modules . each module interface 214 interfaces the functional circuit 212 to a respective module such as the control module 134 ( fig7 ). each interface 214 typically includes at least one connector such as the connector 150 ( fig7 ), and may include an interface circuit ( not shown ). for example , the base unit 136 ( fig7 ) may include a single module interface 214 having the two connectors 148 and 150 , or may include two interfaces 214 each having a respective one of the connectors 148 and 150 . [ 0066 ] fig1 is a schematic block diagram of a module circuit 220 , which the modules 42 ( cartridge assembly of fig2 ), 70 ( fig3 ), 90 ( fig4 ), 100 ( training cartridge assembly of fig5 ), 110 ( fig6 ), 132 ( cartridge assembly ) and 134 ( fig7 ), 160 ( fig8 ), 170 ( fig9 ), 180 ( fig1 ), and 192 ( fig1 ) may incorporate according to an embodiment of the invention . the circuit 220 includes a functional circuit 222 and one or more — here n — base - unit interfaces 224 . the functional circuit 222 may include and execute software , and performs functions such as turning on and off the modular aed systems 130 and 188 ( fig7 and 11 ), controlling the display of information from the base unit ( e . g ., base unit 136 of fig7 ) on a display screen ( e . g ., display screen 72 of fig3 ), allowing an operator to select menu items or aed functions from the display screen ( e . g . via buttons 84 of fig3 ), providing a status of the aed ( e . g ., via indicator 74 or leds 80 of fig3 ), instructing the base unit to deliver a shock in response to an operator ( not shown in fig1 ) pushing the shock button 142 ( fig7 - 10 ), and dialing a telephone number ( e . g ., via the key pad 112 of fig6 ). each base - unit interface 224 interfaces the module functional circuit 222 to the base - unit functional circuit 212 ( fig1 ) of a base unit , such as the base unit 136 ( fig7 ), via one or more respective module interfaces 214 ( fig1 ). each base - unit interface 224 typically includes at least one connector such as the connector 82 ( fig3 ), and may include an interface circuit ( not shown ). for example , the full - featured control module 170 ( fig9 ) may include a single base - unit interface 224 having two connectors ( not shown ) that respectively mate with the base - unit connectors 148 and 150 ( fig7 ), or may include two interfaces 224 each having a connector that mates with a respective one of the connectors 148 and 150 . alternatively , for modules such as the cartridge assemblies 42 , 100 , and 132 , of fig2 , and 7 respectively , the functional circuit 212 may be an energy - attenuation circuit , power circuit , or other type of circuit . or , these modules may altogether omit the functional circuit 212 . [ 0068 ] fig1 is a schematic block diagram of an aed circuit 230 , which the modular aed systems 40 ( fig2 ), 130 ( fig7 ), and 188 ( fig1 ) can incorporate according to an embodiment of the invention . table i below gives examples of which of the circuit blocks are disposed in the base unit 44 , 136 , or 190 and which of the circuit blocks are disposed in the module or modules connected to the base unit . furthermore , the defibrillator electrode pads 16 a and 16 b are typically coupled to the base unit via a module . but there is no requirement that a particular circuit block be disposed in the base unit or in a module , or that the pads be connected to or be part of a module . therefore , circuit blocks disposed in the base unit may be disposed in the module or modules , and vice versa , and the pads may be connected directly to the base unit . for clarity , unless otherwise noted , the aed circuit 230 is described as being part of the modular aed system 130 with the cartridge assembly 132 and the enhanced control module 160 ( fig8 ) attached , it being understood that the circuit 230 is similar when part of the modular aed systems 40 and 188 . referring to fig1 , the defibrillator electrode pads 16 a and 16 b are coupled to the circuit 230 via the connectors 138 and 148 and are operable to sense a patient &# 39 ; s ecg ( not shown ) and to apply an electrical shock to the patient ( not shown ). a shock - delivery - and - ecg front - end circuit 232 samples the patient &# 39 ; s ecg during an analysis mode of operation , and provides a shock to the patient via the connectors 138 and 148 and the electrode pads 16 a and 16 b during a shock - delivery mode of operation . a gate array 234 receives the ecg samples from the circuit 232 and provides them to a first processor unit ( pu ) 236 , which stores and analyzes the samples . if analysis of the patient &# 39 ; s ecg indicates that the patient is suffering from a shockable heart rhythm , then the processor unit 236 instructs the circuit 232 , via the gate array 234 , to enable delivery of a shock when an operator ( not shown in fig1 ) presses the shock button 142 ( which is coupled to the processor unit 236 via the connector 150 of fig7 ). conversely , if analysis of the patient &# 39 ; s ecg indicates that the patient is not suffering from a shockable heart rhythm , then the processor unit 236 may disable the circuit 232 from delivering a shock to the patient , and may instruct the operator via the speaker 24 or display 162 to seek non - shock treatment for the patient . furthermore , the processor unit 236 can detect and signal the operator ( e . g ., via the speaker 24 , the leds 252 , or status circuit 242 ) when a module is not coupled to the module connector 148 or 150 ( fig7 ). the circuit 230 also includes a power - management circuit 238 for distributing power from the battery 18 to the subcircuits of the circuit 230 . the on / off switch 140 turns the circuit 230 “ on ” and “ off ”, a status circuit 242 indicates the status of the circuit 230 , and a second processor unit 244 interfaces the power - management circuit 238 , the on / off circuit 140 ( via the connector 150 of fig7 ), and the status circuit 242 to the circuit 232 , the first processor unit 236 , and the gate array 234 . as discussed above in conjunction with fig2 - 3 , the display 162 ( comparable to the display 72 of fig3 in one embodiment ) displays information to the operator , the speaker 24 provides audio instructions to the operator , and the microphone 34 records the operator &# 39 ; s voice and other audible sounds . the data card 36 is connected to the gate array 234 via a port 248 . the card 36 stores the operator &# 39 ; s voice and other sounds along with the patient &# 39 ; s ecg and a record of aed events for later study . alternatively , another storage device such as magnetic tape ( not shown ) may store this data . a status - measurement circuit 250 provides the status of the circuit 230 subcircuits to the processor unit 236 , and leds 252 provide information to the operator such as whether the processor unit 236 has enabled the circuit 232 to deliver a shock to the patient . a contrast control 254 , which the operator may manipulate via the control knob 164 ( fig8 ), allows the operator to control the contrast of the display screen 162 , and a memory such as a read only memory ( rom ) 256 stores programming information for the processor units 236 and 244 and the gate array 234 . still referring to fig1 , the circuit 230 also includes the optional microphone 198 , a data transmitter / receiver 258 , and a training - scenario selector circuit 260 . as discussed above in conjunction with fig6 and 11 , the transmitter / receiver 258 allows communication of data between the aed circuit 230 and a remote location ( not shown ) such as a hospital via a landline ( fig6 ) or wireless telephone channel . for example , the transmitter / receiver 258 may receive data from the data card 36 via the gate array 234 and transmit the data to the remote location . or , the transmitter / receiver 258 may receive voice data from the microphone 34 or 198 and transmit this data to the remote location . alternatively , the transmitter / receiver 258 may provide data received from the remote location to the processor 236 via the gate array 234 . the processor unit 236 may convert the received data into a voice using the speaker 24 . the training - scenario selection circuit 260 allows training of a student in the operation of the aed system 130 ( fig7 ), when the training cartridge assembly 100 is attached to the base unit 136 ( fig7 ) in a manner similar to that discussed above in conjunction with fig5 . when the circuit 260 is coupled to the connector 148 , the pads 16 a and 16 b typically are not electrically coupled to the connector 148 to prevent inadvertent delivery of a shock during the training exercise . but the circuit 260 “ fools ” the processor unit 236 into determining that a selected scenario exists such that the processor unit causes the circuit 230 to operate according to this scenario . for example , the circuit 230 may cause the processor unit 236 to determine that a “ patient ” is experiencing a shockable heart rhythm , and thus to cause the circuit 230 to operate accordingly . this allows the student to learn the operation of the aed without putting a test patient at risk . once can modify the circuit 230 according to known principles such that the aed system 130 can provide electrotherapies other than defibrillation , such as pacing and cardioversion , or includes a manual override that allows an operator ( not shown in fig1 ) more control over otherwise automated functions . an aed circuit similar to the aed circuit 230 and other aed circuits are further discussed in the following references , which are incorporated by reference : u . s . pat . no . 5 , 836 , 993 , u . s . pat . no . 5 , 735 , 879 entitled electrotherapy method and apparatus , u . s . pat . no . 5 , 607 , 454 entitled electrotherapy method and apparatus , and u . s . pat . no . 5 , 879 , 374 entitled defibrillator with self - test features . table i describes the locations of the circuit blocks of the aed circuit 230 ( fig1 ) and other circuits and components of the base unit and module ( s ) according to respective embodiments of the invention . unless otherwise stated , reference numerals in table i refer to circuit blocks or components in fig1 .