Modem interface device

An apparatus for connecting a telecommunications device, such as a computer or facsimile machine modem, to a telephone line via a telephone set. The telephone set includes a base and a handset connected to the base by a handset cord. The handset cord has at one end a handset plug and the base has a base jack for receiving the handset plug. The apparatus selectively electrically couples one of the handset and the telecommunications device to the base. The apparatus includes a first plug for electrically coupling with the base jack, a first jack for electrically coupling with the handset plug, and the second jack for electrically coupling with the telecommunications device connecting plug. A switch, manually selectable between a first position and a second position, electrically couples the first plug with the first jack when in the first position. A converter is coupled to the switch and the second jack such that when the switch second position is selected, the switch electrically interfacing the first plug with the second jack.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
The present invention relates to telecommunication systems. More 
specifically, the present invention relates to a novel and improved 
apparatus for selectively coupling one of a telecommunications device, 
such as a modem, or a telephone handset to a telephone system via the 
telephone base handset interconnection jack. 
II. Description of Related Art 
Modems are commonly used to permit a computer or facsimile machine to 
communicate with another like device over the telephone line. Conventional 
modems use a two-wire communications connection that is typically 
connected directly to a two-wire telephone line. 
In many applications it is not possible to utilize a dedicated telephone 
line for interconnection with the modem. In telephone systems using a PBX 
arrangement, where many lines are serviced by a central controller, it is 
difficult to achieve dedicated line service for modem communications. In 
the PBX arrangement, various lines are required for voice communication. 
The providing of dedicated telephone lines for modems which are not 
constantly communicating over the dedicated lines, may result in 
additional telephone lines that are not used to their full capacity. This 
system deficiency is especially true when additional voice communication 
lines are in use and more are needed, although the dedicated modem lines 
are currently not used. Furthermore, the telephone base usually needs to 
be coupled to the PBX system to accomplish line selection for outgoing 
communications. 
In the conventional telephone set environment, the user may desire to have 
both voice and data communication capabilities over the telephone line. 
The coupling of a modem to the telephone line forms a dedicated line 
solely for use by the modem, unless the modem includes provisions to 
couple to the telephone set thereto with a switch for selecting between 
telephone set or modem interconnection to the telephone line. Otherwise, 
the modem must be disconnected and the telephone set reconnected to the 
telephone line. In the latter situation, one must physically interconnect 
one or the other of the telephone or modem to achieve the selected 
communication status. In many situations, coupling of the modem to the 
telephone line may be physically difficult, or impossible, without 
damaging the existing telephone set-telephone line interconnection. For 
example, many businesses and hotels have the telephone sets that are 
hard-wired directly to a corresponding telephone line rather than having a 
modular plug and jack interconnection. Without the availability of a 
modular jack in which the telephone set normally plugs into for 
interconnection to the telephone line, the modem is rendered useless. 
The present invention successfully overcomes the difficulties realized in 
using both modem and voice communications from a single telephone line or 
through a PBX system. The present invention is a unique apparatus for 
enabling selected communications through the telephone set over a single 
telephone line both voice and data communications. 
SUMMARY OF THE INVENTION 
The present invention is a novel and improved device for connecting a 
computer or facsimile machine modem to a telephone line via a telephone 
set so as to both enable data or voice communications. In the typical 
telephone set, a telephone base is coupled to the two-wire telephone line. 
The base typically includes the dialing and ringer hardware. The telephone 
set also includes a handset which is coupled via a handset cord to the 
telephone base. The handset cord typically has a modular plug at one end 
thereof which mates with a handset interconnect jack mounted in the 
telephone base. The telephone base typically converts the two-wire 
telephone line connection to a four-wire connection at the handset 
interconnect jack. The wiring between the base and handset typically 
include a pair of microphone lines and a pair of speaker lines which 
respectively couple the base hardware to a microphone and speaker mounted 
in the handset. 
A modem typically has a single pair of communications lines that are 
readily adaptable for direct coupling to the telephone line via a 
conventional RJ-11 modular plug. However, for the reasons discussed 
previously, the telephone base is typically coupled directly to the 
telephone line or a PBX system. With the telephone base coupled directly 
to the line, one using the present invention need not inconveniently 
couple and decouple the telephone set when data communications via the 
modem are required. 
In a PBX system, one needs outgoing line selection capability from the 
telephone base prior to engaging in outgoing data communication. 
Decoupling of the telephone base from the line may disrupt the controller 
such that line selection and the dial tone is lost. The present invention 
permits coupling of the modem through the telephone base to the telephone 
line so as to overcome problems associated with using a modem in the PBX 
environment. 
In one embodiment of the present invention a module is connected between 
the telephone base and, the modem and telephone handset, so as to provide 
manually selective control between data and voice communications. The 
selected communication, i.e. data or voice, is provided through the module 
to the telephone base and telephone line. 
The modem, a two-wire device, is coupled along with the telephone handset, 
a four-wire device, into the module. The module provides a four-wire 
output to the telephone base handset interconnect jack. The module of the 
present invention interfaces both the modem and handset to the telephone 
base along with providing manually selective control between voice and 
data communications. When the module is placed in the data communication 
mode, the module functions for interfacing between the two-wire modem 
communications lines and the four-wire telephone base/handset 
communications lines. When the module is in the voice mode, the four-wire 
handset lines are directly coupled to the telephone base/handset 
communications lines. 
In another exemplary embodiment, the present invention comprises an 
apparatus for connecting a modem, having a connecting plug, to a telephone 
set having a base and a handset connected to the base by a handset cord. 
In the telephone set, the handset cord is connected at one end to the 
handset and has at the other end a handset plug. The base has a handset 
jack for receiving the handset plug. The module is interconnected between 
the base, handset and modem for selectively electrically coupling one of 
the handset and modem to the base. The module includes a first plug for 
fitting into the base handset jack, and first and second jacks for 
respectively receiving the handset plug and the connecting plug and for 
selective electrical coupling to the handset jack. A switch is provided 
for manual selection between a voice position and a data position so as to 
respectively electrically couple the first plug with the first jack when 
in the voice position and electrically couple the first plug with the 
second jack when in the data position. A converter is disposed between the 
switch and the second jack for electrically interfacing the first plug 
with the second jack. 
In summary, a device constructed according to the teachings of the present 
invention converts a telephone base handset jack into a telephone line 
connection. Accordingly, the device of the present invention permits the 
coupling of any telephone line compatible device, i.e. modem, facsimile 
machines, speaker phones, etc. 
It is, therefore, an object of the present invention to provide a novel and 
improved apparatus for selectively interconnecting one of telephone 
handset and a modem to a telephone line via a telephone base connection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to the drawings, FIG. 1 illustrates the arrangement of modem 
interconnect module 10 of the present invention in relation to telephone 
set 12. Telephone set 12 includes base 14 and handset 16. Module 10 is 
disposed between base 14 and handset 16 to couple modem 18 to base 14. 
Although a modem is illustrated in FIG. 1, it is understood that any 
device that is capable of connection directly to a telephone line can be 
coupled to module 10. As illustrated in FIG. 1, modem 18 is a computer 
external modem, and it should be understood that the modem may be a 
computer internal modem or a modem that is typically internal to a 
facsimile machine. Base 14 includes the traditional dialing and receiving 
hardware and is coupled by a two-wire line, line 20, to a telephone line 
directly or through a PBX controller. Base 14 also includes a modular 
telephone handset jack 22. 
In the conventional configuration of telephone set 12, a handset cord 24 is 
coupled at one end to handset 16 which includes a microphone (not shown) 
and speaker (not shown). The other end of handset cord 24 is coupled to a 
modular telephone handset plug 26. In the conventional configuration of 
telephone set 12 for voice only communications, handset plug 26 is 
inserted into handset jack 22 for electrically connecting to corresponding 
pairs of microphone and speaker lines. 
In the embodiment as illustrated in FIG. 1, module 10 includes a housing 28 
and a series of user accessible selector switches, mode switch 30, phone 
type 32 and polarity switch 34 which permit manual selection of various 
modes and operational settings of the module. The functions of switches 
30, 32 and 34 will be described later herein with reference to FIGS. 2 and 
3. Mounted within housing 28 is circuitry (not shown) also discussed with 
reference to FIGS. 2 and 3. Mounted at one end of housing 28 is a modular 
telephone handset jack 36 for receiving handset plug 26. Extending 
outwardly from housing 28 is a four-wire interconnecting cable 38. Coupled 
at the end of cable 38 exterior to housing 28 is handset plug 40. Handset 
plug 40 is coupled within handset jack 22 in base 14 so as to electrically 
couple the telephone set microphone and speaker lines with module 10. Also 
mounted at housing 28 is a jack (not shown) adapted for receiving and 
electrically coupling a modular plug (not shown) coupled to an end of 
cable 42. Cable 42 is a two-wire interconnecting cable which connects the 
communications lines of modem 18 to module 10. Although module 10 is 
illustrated in FIG. 1, it is readily envisioned that the module circuitry 
may be incorporated with the computer or facsimile machine itself along 
with the modem. It is to be further understood that the telephone base may 
be of a cellular telephone type. 
FIG. 2 illustrates a schematical diagram of the circuitry of module 10 in 
an embodiment configured for coupling a telephone handset and modem to the 
telephone base as discussed with reference to FIG. 1. Module 10 is coupled 
by plug 40, a four-wire modular telephone handset plug, and cable 38 to 
handset jack 22 in base 14. Module 10 also includes a pair of jacks 36 and 
44 which respectively receive handset plug 26 and a plug connected to 
cable 42 from modem 18. Plug 40 and jacks 36 and 44 are each configured 
with four separate contacts or pins to provide a four-wire connecting 
capacity. With both plug 40 and jack 36, all four pins are required, 
however, with jack 44 only the two center pins are used. 
Module 10 further comprises a mode switch means, mode switch 30, for 
selecting between voice or data communications, i.e. modem or handset 
connection to the base. In the data mode, a signal level selector means, 
i.e. phone type switch 32, determines the voltage level of the signal 
coupled from the modem as output to the base. A polarity switch means, 
polarity switch 34, is used in the data mode for telephone handsets having 
carbon microphones so as to ensure proper interconnection with various 
telephone sets. A transformer 46 is included in module 10 as a 
two-wire-to-four-wire converter means. Transformer 46 converts the 
two-wire modem interconnection to the four-wire telephone handset 
connection while providing signal gain and signal isolation features. In 
summary, transformer 46 enables four-wire-to-two-wire conversion in a 
single component that provides both signal amplification and impedance 
transformation. 
In FIG. 2, module 10 is illustrated with switch 30 in a voice position for 
voice communications. A modem connected at jack 44 is thus electrically 
bypassed by mode switch 30, a triple-pole, double-through slide switch, to 
permit voice only communication. In the voice mode, mode switch 30 couples 
corresponding base and handset microphone and speaker lines. In the voice 
mode, mode switch 30 electrically couples the base microphone lines 
connected at plug 40, pins 1 and 4, respectively to corresponding handset 
microphone lines connected at jack 36, pins 1 and 4. Similarly, mode 
switch 30 also electrically couples the base speaker lines connected at 
plug 40, pins 2 and 3, respectively to corresponding handset speaker lines 
connected to jack 36, pins 2 and 3. In particular, plug 40, pin 1 is 
coupled by microphone line 48 through one switch portion of mode switch 
30, switch 30a, via contact 50, wiper 52 and contact 54, to jack 36, pin 
1. Plug 40, pin 2 is coupled directly by speaker line 56 to jack 36, pin 
2. Plug 40, pin 3 is coupled by speaker line 58 through another switch 
portion of mode switch 30, switch 30b, via contact 60, wiper 62 and 
contact 64, to jack 36, pin 3. Similarly, plug 40, pin 4 is coupled by 
microphone line 66 through switch 30c, via contact 68, wiper 70 and 
contact 72, to jack 36, pin 4. 
When data communications are desired, module 10 is placed in the data mode 
by manually changing switch 30 to a data position. The wipers of mode 
switch 30 are ganged such that movement of the switch from one position to 
another results in changing of contacts in each of switches 30a, 30b and 
30c. In the data mode, wiper 52 breaks continuity with contact 54 while 
connecting contact 50 with contact 74. Similarly, wiper 62 breaks 
continuity with contact 64 and connects contact 60 to contact 76. 
Furthermore, wiper 70 breaks continuity with contact 72 and connects 
contact 68 with contact 78. 
With switch 30 in the data position, microphone line 48 is connected to tap 
80 of secondary winding 82 of transformer 46. The other microphone line, 
line 66, is coupled directly or through a resistor to a pair of contacts 
of a single-pole, triple-throw slide switch, i.e. phone type switch 32. 
Specifically, line 66 is coupled through resistor 84 to contact 86 while 
also being coupled directly to contact 88. For digital telephone sets, 
switch 90 is positioned with wiper 90 electrically coupling contact 86 to 
contact 92. Contact 92 is electrically coupled through resistor 94 to end 
96 of secondary winding 82. The position of wiper 90 in connecting contact 
86 and 92 couples resistors 84 and 94 in series with the microphone line 
66 so as to provide proper voltage levels. 
For a telephone set using a handset having an Electrolet microphone, wiper 
90 would be positioned between contacts 92 and 88. In this position only 
resistor 94 is in series with microphone line 66 and end 96 of secondary 
winding 82. For a telephone set using a handset having a carbon type 
microphone, wiper 90 is positioned between contacts 88 and 98. In this 
position, microphone line 66 is directly coupled to end 96 of secondary 
winding 82. 
In the data mode, speaker line 56 is connected directly to center tap 100 
of primary winding 102 of transformer 46. Speaker line 58 is coupled by a 
single-pole slide switch, polarity switch 34 to either modem communication 
line 104, which is coupled to pin 2 of jack 44, or modem communication 
line 106, which is coupled to pin 3 of jack 44. Polarity switch 34 is only 
required when module 10 is coupled to a telephone set having a handset 
that uses a carbon type microphone. Polarity switch 34 has a set of 
contacts 108, 110 and 112 and a wiper 114. Line 58 is coupled to contact 
110, with contact 108 coupled to line 106 and end 116 of primary winding 
102. The other end of primary winding 102, end 118, is coupled to contact 
112 with contact 112 coupled to line 104. Line 58 is also coupled through 
mode switch 30B, via contact 60, wiper 62 and contact 76 and through a 
series coupled speaker deloading resistor 120 to jack 36, pin 3. It is 
further envisioned that polarity switch 34 may be positioned in the 
transformer secondary circuit. With polarity switch 34 positioned in the 
transformer secondary circuit, the output from phone type switch 32, 
and/or resistor 94, is coupled to either end 96 or end 97 of secondary 
winding 82. 
When module 10 and modem are used with a telephone set having a carbon type 
microphone, phone type switch 32 is positioned with wiper 90 positioned 
between contacts 88 and 98. The phone type switch is used to determine the 
modem outgoing signal level which is ultimately determined by the type of 
microphone used by the telephone. In a telephone set using the carbon type 
microphone, the microphone and speaker lines have a direct connection. 
When the data mode is selected, polarity switch 34 is used to selectively 
couple speaker line 58 to either transformer ends 116 or 118. The user 
upon selecting the data mode listens for the dial tone in the handset 
speaker so as to select the correct polarity switch position. The user 
sets the polarity switch to a position in which the dial tone is the 
loudest. 
In FIG. 2, several modifications may be made to the circuit to provide 
various additional features and functions to module 10. For example, in 
switch 30a, contacts 50 and 74 may be shorted at all times by line segment 
48a. In this arrangement microphone line 48 is directly coupled to tap 80 
of secondary winding 82. Furthermore, in switch 30c, contacts 68 and 78 
are correspondingly shorted by line segment 66a. Line segment 66a couples 
microphone line 66 from plug 40, pin 4 directly to phone type switch 32 
contact 88, and through resistor 84 to phone type switch 34 contact 86. 
With line segments 48a and 66a in place, a modem connected to module 10 at 
jack 44 is always coupled through transformer 46 to microphones lines 48 
and 66. With the modem communication lines electrically coupled to 
microphone lines 48 and 66 via transformer 46, the computer may be used 
for computer autodialing in purposes. Furthermore, both voice and data 
communications may be selected by the operator without interruption of the 
autodialing feature. 
There are presently commercially available computer software packages which 
enable one to create a computer data base of telephone numbers. The 
computer under software control operatively communicates with the modem to 
dial the operator selected number. When the module is selected for the 
data mode, data may be transmitted directly through microphone lines 48 
and 66. When the module is selected for the voice mode, the computer and 
modem provide the autodial feature by direct coupling of the modem to 
lines 48 and 66. In the voice mode, the voice communications enabled by 
the coupling of the microphone and speaker lines as previously discussed. 
Another optional feature of the present invention is the removal or 
bypassing of switch 30B. In this arrangement, speaker line 58 is coupled 
at all times by line segment 58a through handset speaker deloading 
resistor 120 to handset jack 36 pin 3. The resistance value of deloading 
resistor 120 is substantially reduced in this embodiment. 
In the embodiment as illustrated in FIG. 2, transformer 46 is typically a 
600:600 .OMEGA. or a 600:900 .OMEGA. transformer having tapped primary and 
secondary windings. The input impedance of a modem is typically 600 
.OMEGA., and using a transformer with a 600 .OMEGA. winding impedance 
matching is achieved. With a 600 .OMEGA. primary winding, the ends of the 
primary winding would be directly coupled to the modem circuit. Typically, 
the impedance of the handset speaker is in the range of 150-300 .OMEGA. s. 
It is, therefore, preferred that the impedance across one end of the 
primary to the center tap is approximately the same for coupling to the 
handset. The impedance of the primary winding from end to end is 600 
.OMEGA. to match the impedance of the modem line. Resistors 84 and 94 are 
respectively 25K .OMEGA. and 5.6K .OMEGA. resistors while resistor 120 is 
typically a 1K .OMEGA. resistor. In the alternate embodiment where line 58 
is directly coupled through line segment 58a to resistor 120, resistor 120 
is typically a 150 .OMEGA. resistor. In either embodiment, deloading 
resistor 120 is utilized to reduce the handset speaker volume during data 
transmission or computer autodialing. Deloading resistor 120 serves to 
increase the incoming signal level to the modem. 
FIG. 3 illustrates yet another alternate embodiment of the present 
invention for use for coupling communications devices which require a 
voltage or current, such as certain types of facsimile machines to a 
telephone base at the handset jack. The embodiment illustrated in FIG. 3 
is utilized in applications where the facsimile machine communications 
circuitry requires a loop current detection before communications 
operation can occur. The circuit of FIG. 2 is in essence modified to 
provide a battery 122 disposed in series between polarity switch contact 
112' and jack 44, pin 2 in line 104'. Battery 122 is typically a 3.0 volt 
battery. In certain facsimile machines, the current provided by battery 
122 may be lowered to prolong battery life and yet provide sufficient 
current for communication purposes. In this case, a resistor 124 may be 
placed in series with battery 122. Upon the addition of resistor 124 into 
the circuit, capacitor 126 is placed in parallel across the series 
connection of battery 122 and resistor 124. Capacitor 126 provides a low 
impedance AC signal path thus enabling incoming signals to appear across 
the facsimile machine input circuit. 
As further illustrated in FIG. 3, switch 30' include only switches 30a' and 
30'c. Speaker line 58' is coupled directly to base plug 40', pin 3 to 
polarity switch contact 110' and directly to handset jack 36', pin 3 
through resistor 120'. In this arrangement, switch 30' may be configured 
as a double-pole double-throw switch. Furthermore, in implementing the 
autodialing feature, microphone line 48' may be coupled directly to 
secondary tap 80' of transformer 46' via line segment 48a'. Similarly, 
microphone line 66' may be coupled directly to phone type switch 32', 
directly or indirectly through resistor 84', via line segment 66a'. In 
this particular alternate embodiment, switch 30' may be implemented as a 
double pole, single-throw switch. 
FIG. 3 further illustrates the optional implementation of the polarity 
switch in the transformer secondary circuit. When optional polarity switch 
34a' is utilized, polarity switch 34' is removed from the circuit with 
speaker line 58' coupled to one or the other end of the primary winding of 
transformer 46. For example, speaker line 58' is coupled by line segment 
58a' to primary winding end 116. In the transformer secondary circuit, 
line segment 99', which couples secondary winding end 96' to contact 98' 
of phone type switch 32' and an end of resistor, is removed. In place of 
line segment 99' is polarity switch 34a'. Polarity switch 34a couples 
contact 98' and the one end of resistor 94' to a selected end, end 96' or 
97' of the secondary winding. 
FIG. 4 illustrates an embodiment of the present invention configured for 
computer modem autodialing. It is envisioned that a circuit disclosed with 
reference to FIG. 4 may be incorporated within the computer and/or modem 
hardware. 
In FIG. 4, microphone line 48" is coupled to plug 40", pin 1, to secondary 
tap 80" of transformer 46". Microphone line 48" is also coupled directly 
to jack 36", pin 1. The other microphone line, line 66", is coupled 
directly to jack 36", pin 4, and indirectly to end 96" of secondary 
winding 82" by phone type switch 32, directly or through resistor 84" 
and/or resistor 94". 
Speaker line 56" is coupled from plug 40", pin 2, to jack 36", pin 2, and 
tap 100" of primary winding 102". The other speaker line, line 58" is 
coupled at plug 40, pin 3, through polarity switch 34" to a selected end 
of primary winding 102", end 116" or end 118". Speaker line 58" is also 
coupled through deloading resistor 120" to jack 36", pin 3. End 118 of 
primary winding 102" is coupled by line 104" to jack 44", pin 2. 
Similarly, end 116" is coupled by line 106" to jack 44", pin 3. Jack 44", 
pins 2 and 3, are coupled to the modem. 
The circuit configuration of FIG. 4 permits a minimal part count circuit 
for use with an autodialer or a computer modem for autodialing purposes. 
In the embodiment illustrated in FIG. 4, a modem connected to jack 44", is 
always electrically coupled with microphone lines 48" and 66" through 
transformer 46". 
With reference to the transformer implementation as disclosed in FIGS. 2-4, 
the transformer is implemented to provide a four-wire-to-two-wire 
conversion circuit utilizing a single component. The transformer functions 
as an interface which provides autotransformation of voltage levels. In 
particular, the transformer provides amplification of a signal received on 
the base speaker lines through the primary winding to the communications 
lines. Furthermore, the transformer embodiment provides isolation between 
the microphone lines and the speaker lines, and impedance transformation 
between telephone handset, telephone base and modem. 
FIG. 5 illustrates a circuit embodiment similar to that of FIG. 2 
incorporating an alternate transformer implementation. In FIG. 5, 
microphone line 48'" is coupled to plug 40, pin 1'", through switch 30a'" 
to jack 36'", pin 1, when switch 30'" is selected for the voice mode. When 
switch 30'" is selected for the data mode, line 48'" is coupled through 
switch 30a'" to tap 166 in secondary winding 160 of transformer 150. When 
the circuit is configured for the autodialing, line segment 48a'" is used 
to directly couple microphone line 48 to tap 166. 
The other microphone line, line 66'", couples plug 40'", pin 4, to switch 
30'". When switch 30'" is selected for the voice mode, switch 30c'" 
couples line 66'" to jack 36'", pin 4. When switch 30'" is selected for 
the data mode, switch 30c'" couples line 66'" either to end 162 of 
secondary winding 160 phone type switch 32'", directly or through resistor 
84'" and/or resistor 94'". When the circuit is configured for the 
autodialing, line segment 66a'" is used to couple line 66'" either through 
resistor 84'", or directly, to phone type switch 32'". The modem 
communication lines (not shown) are coupled to jack 44'", pins 2 and 3. 
Jack 44'", pins 2 and 3, are coupled respectively by lines 104'" and 106'" 
to ends 164 and 162 of secondary winding 160. 
Speaker line 56'" is coupled to plug 40'", pin 2, directly to jack 36'", 
pin 2, and center tap 158 of primary winding 152 of transformer 150. The 
other speaker line, line 58'", is coupled to plug 40'", pin 3, through 
polarity switch 34'" to either end 154 or end 156 of primary winding 152. 
In addition, speaker line 58'" is coupled to switch 30b'" for direct 
coupling to jack 36'", pin 3, when mode switch 30'" is positioned in the 
voice mode. When mode switch 30'" is positioned for the data mode, speaker 
line 58'" is coupled by switch 30b'" through deloading resistor 120'" to 
jack 36'", pin 3. In the autodialing configuration, microphone line 58'" 
is coupled by line segment 58a'" through deloading resistor 120'" to jack 
36, pin 3. 
The configuration illustrated in FIG. 5 utilizes transformer 150 in a 
coupled transformation configuration. Transformer 150 provides a 
four-wire-to-two-wire conversion circuit in a single component. 
Transformer 150 also provides both signal amplification and impedance 
transformation. In the embodiment in FIG. 5, polarity switch 34 may be 
either in the primary winding circuit, as illustrated, or in the secondary 
winding circuit. Similarly, in the embodiment illustrated in FIGS. 2-4, 
the polarity switch may be also located in the secondary winding circuit. 
In certain applications, the individual may not only find the telephone set 
hardwired directly to the telephone line or PBX system, but also the 
telephone handset hardwired directly to the base. FIG. 6 illustrates an 
accessory 130 for use in coupling through module 10 a modem or facsimile 
machine to the telephone line via the handset. Accessory 130 includes a 
modular jack 132 for receiving plug 40 (FIG. 2). Coupled to jack 32 are a 
pair of leads 134 and 136 which have respectively coupled, at an end 
opposite jack 132, clips 138 and 140. In using accessory 130, the 
mouthpiece and microphone (not shown), typically a carbon microphone, are 
removed from handset 16'. The mouthpiece portion of handset 16' includes 
microphone contacts 142 and 144 which in normal use of handset 16' connect 
the microphone to the handset microphone lines. Accessory 130 is coupled 
by clips 138 and 140 respectively to contacts 142 and 144. Plug 40 is then 
inserted into jack 132 so as to couple module 10 speaker lines 56 and 58 
to the handset microphone lines. 
The previous description of the preferred embodiments are provided to 
enable any person skilled in the art to make or use the present invention. 
Various modifications to these embodiments will be readily apparent to 
those skilled in the art, and the generic principles defined herein may be 
applied to other embodiments without the use of the inventive faculty. 
Thus, the present invention is not intended to be limited to the 
embodiments shown herein, but is to be accorded the widest scope 
consistent with the principles and novel features disclosed herein.