Microphone controller with multifunction single conductor

~ - l - CE00207R~ ~ 4 ~ .,-,. ~ ,, MICROPHONE-CONTROLLER WIl~I MULTIFUNCTION, SINGLE CONDUCTOR 1 0 Field of the Invention The present invention relates generally to the commur~ications field and particularly to the cellular radiotelephone field.

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Cellular moWe radiotelephones allow users in car~ to remain in contact with the landline telephone system while 2 0 traveling.

This form of communication typically has the disadvsntage of requiring the user to hold a telephone handset to communicate.

This can cause problems when another task must be performet simultaneously with communicating, such as dri~ring or writing.

2 5 This problem has been solved by the implementation of ;:a hand~free mode of operation for the cell~ar radiotelephone.

is sccompli3hed by using a speaker and microphone eparab &om the ~peaker and microphone in the radiotelephone'~ handset.

The e~ctra ~peaker can be built in to ; ~;

3 0 the radiotelephone housing or in 8 separate housing.

The hand3-free microphone, for improved voice reception, is . typically separate from t~e radiotelephone housing and i9 mountet near the user, such as on the driver's visor.

While the external speaker ant microphone free the :~ ~ 3 5 user's hands tunng a call, the user must still look down at - ~- the radiotelephone to operate the control~ for dialing a ~ ,~ ......

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~, -~,,,- ^.; -2- CE00207R '" '" ' 204204~ number.

If the user is driving at the time a csll is made, a dangerou3 situation csn result because of the time required to look down to dial a number. One solution to thi3 problem i3 to locate a limited 5 number of control bu~tons in the hands-free microphone housing.

If the microphone is mounted near the u~er, the ;

need to look away from the road is reduced and, if a relatively small number of button~ are used, the user may even be able to use the buttons by memorizing their locations.

The mounting of controls in the microphone housing require~ a greater number of wires in the interface csble to the ratiotelephone than if only the microphone were present. A lsrger number of wires in the cable will result in a thicker cable, creating a problem of instslling the cable between the 15 radiotelephone and the hands-free microphone without detracting from the automobile interior's appearance.

There is a resulting need, therefore, to pro~nde control functions in ; the hands-free microphone using a minimum number of ~ ~ wires. ~;

2 0 ~mmar~ of th~ InYention ~ :,,; .' :, The present invention provides a method and apparatus of atding control buttons to a hands-free microphone using 2 5 oDly power and ground conductors.

The power conductor acts as an audio sigIIal conductor and a serisl data bus in addition to being a power conductor. The apparatu~ con~ists of the power conductor and its associated ground conductor.

The power conductor is ;

3 0 connected to a voltage regulator that provides the voltages to power the circuitry, inclnding a microproces~or and an audio amplifier, in the hands-free microphone housing.

The microphone is connected to the power conductor through the audio amplifier.

Both the voltage regulator and the audio 3 5 amplifier can be isolated from the power conductor by a FET switch that i8 controlled by the microproce~sor.

:

- 3 - CE00207R . : ~ 2042~0 A number of input switche~ are connectet to the microproce~sor.

The microprocessor determine~ which input s~vitch was closed and encodes this into a signal to be transmitted on the power conductor by a bu8 driver.

The bu~ S driver i8 not isolated fi om the power conductor by the FET switch.

ief Descri~2tio~2f the Drawin~ 1 0 E ig. 1 shows a block diagram of the preferred embodiment of the present invention.

Fig. 2 shows a timing diagram of the relationship between the FET switch and the serial data bus.

E ig. 3 shows a block diagram of an alternate embodiment ofthe presentinvention.

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~iaiL~d~i~ Prefe~ed Em~Q~mtnt The present invention allows push-button switches to be 2 0 added to a hands-free microphone without increasing the ~ ~ number of conductors in the interface between the microphone and the radiotelephone.

This is accomplished by using the power conductor as a serial data bus and for conducting the audio signal from the microphone in addition ~;

2 5 to 3uppl~ power to the apparatus.

T'ne preferred embodiment of the apparatus i~ illustrated i~ Fig. 1. ~ addition to the power conductor (108), which also acts as a senal data bus, and its a~sociated ground conductor (109), the apparatus consists of a microphone (101), ~ ~ 3 0 an audio amplifier (102), a field-effect transistor (FET) switch ;-;

(104), and a voltage regulator (103). A microprocessor (105) - controls the apparatus and a number of input s~ritches (106) connected to the microprocessor (105) enter data to ba ; ~ transmittet on the power conductor by a bus driYer (107). ~ ~ ~ 3 5 In operation, the hands-free microphone and its related ; - -circuitr~ i8 powered by the power conductor (108) with its '''''''`'''''''''';' -,.. ~ 4- CE00207R ~ ~ t~ associated ground conductor.

In the preferred embodiment, the ratiotelephone pro~ide3 a 9.50 VdC supply voltage, through a 1.0 kQ resi~tor, between the power and ground (109) conductors.

Tlse voltage regulator (103) u~e8 the supply voltage to provide appro~imately 7.60 VtC to power the amplifier (102) and 3.30 Vdc to power the microproce~sor ~105).

The power conductor (108) al80 CaITie9 the audio from the microphone (101).

The amplifier (102) amplifies the audio signal that has been input through the microphone (101).

The amplified audio signal rides on the supply voltage, 8.2 volts, on the power conductor (108).

The audio Bigllal can be up to 4 volts peak to peak.

The radiotelephone's tran~ceiver uses this audio signal for transmission.

The power conductor (108) additionally acts as a serial 1 5 data bus.

The bw (108) interfiace~ to receive and decode circuitry at the ratiotelephone end of the bu~ (108).

The tecode circuut~y begins looking for the start of a ~erial data me3sage, a low going edge, after a bu~ re~et, which is a 5 ms high on the bw ~108).

Since the audio i9 transmitted on the same 2 0 contuctor (108), the low for the message start has to be below the worst ca~e lov~ for the audio ~ignal to avoid causing a -;

message start when the audio goe~ low.

In the preferred embodiment, a low l~vel is 4.3 Vd,. A high level is defined as 8.2 Vdc.

2 5 I~ preferred embodiment, the tata to be tran~mitted f~om the controller end o~ the bw (108) is entered by four push-button nvitches (106).

The ~witches (106) are connected to the m~croprocessor (105).

The first thres switches (106) are used for memory recall of telephone numbers.

The fourth 3 0 switch (106) is a multifunction switch that i~ used for st~rting : ;

and ending a telephone call, clearing entered digits, and muting the handset microphone during a telephone call.

Each ~witch (106) is asdgnet a unique two bit code that is ~ent four times in ~uccession, the secont and fourth pair being the 3 5 complement of the switch code.

The microprocessor (105) determines which switch (106) ha~ been depressed, and ~ends - 5 - CE00207R ~2~ ~ii,3 , the sppropriate code on the power conductor (108) in serial form.

Every 8witch (106) clo8ure i8 followed by a release code.

Table 1 illu~trates the codes assigned to the re~pective switche~ (106) in the preferred embodiment.

s SWlTCH 1 (10X01XlOX01) SWrrCH 2 (01)(10XOlX10) SWITCH 3 (OOX11XOOX11) MULTIl?UNCTION SWITCH (llXOOXllXOO) 1 0 R~3LEASE (llXllXllXll) TABLE 1. :

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As illustrated in Fig. 2, each bit of a switch code is sent 1 5 in 1 ms 1 50 ,U8 and i8 represented by a different length low going pulse of the 8upply voltage that begins at the start of the bit time. A zero is defined a~ a 250 - 450 ~9 low going pulse ;

(203) and a one i8 defined as a 650 - 850 118 low going pulse (202).

The remainder of the bit time of both the zero snd one 2 0 digit after the low pul~e i8 a high level (204).

The El~T switch (104), controlled by the microprocessor ~.

~: (105), i~ used to isolats the po~ver conductorltlata bus (108) ~ ~;

from the circuitry, wit~ th0 e~ception of the bu~ driver (107),' " ! ~' ,' "',' on the hand~-free microphone end of the bw.

This ensure~ :~ 2 5 that the capacithre load on the bu~ (108) at the hands-free - microphone end doe~ not COlTUpt the rise and fall time of the data when transmitting on the bu~ (108). ~ :~ illwtratet in the timing diagram in Fig. 2, the :; :

switch (lo?) is turned off, which opens the line and isolates;the 3 0 bw (108), 10 ms before the microproces~or (105) 3ta~1 to .~ ~ transmit its ~erial data stream.

The 10 m~ delay, in case the . -; :

-~ audio signal plus coupled noise goes below the low threshold ` ~ ~ i of the decode circ~utry thereby starting a decode sequence, ensure~ that the receivc ent is in a reset ~tate prior to 3 5 msi~ing the data stream.

In addition, the decode circuitry must recei~e three cf the four data bit pair~ correctly before ,~.." ..~. ~ .. ..... ...

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~ 0 4'~ . :,, , decoding is started. A190, there must be a complete ~transmission of eight total bits before the decode is performed.

Since power to the microprocessor (105) is cut off when the El~T switch (104) i9 off, the microprocessor (105) n~ns off a S capacitive charge stored in the voltage regulator (103).

With this charge, the worst case minimum time the microprocessor (105) will continue to run iB 50 ms.

This is enough time for the microproces~or (105) to complete its transmis~ion since the FET switch (104) is only off for 18 ms.

10 The FET switch (104) is turned on after the bus transmission to allow the audio sig~al acce~s to the power conductor (108) and to allow the power conductor ( 108) to supply power to the circuitry.

In alternate embodiments, the number of push button 15 switches on the hands-free microphone-controller can be increased or decreased without departing from the scope of the pre~ent invention.

In addition, the codes sent when the buttons are pushed and the length of ths data word may vary for different application~. A display (302), such a8 an LCD as 2 0 illustrated ~n Fig. 3, can be added to the microphone-controller to display data sent over the bua A receiver (301) can also be added, to make the serial data bus bidirectional.

This would allow data to be ~ent from the radiotelephone end to the microphone controller a~ well a~ from the microphone25 controll~rto the radiotelephone.

rne multifimction interface descrbed above permits control function~ to be added to a hands-f~ee microphone ~;

- witllout increa~ing the number of conductors required to interface the microphone to the main unit.

The present 3 0 invention provide~ power, audio, and a serial data bu~ on the same conductor.

Wbile the preferret embodiiment uses a radiotelephone as the main u~it, any communication transceiver having the required decoding ~rc ~itry can be used; an alternate embodiment being a radio.