Automatic Radio Telephone Encoder/Decoder

This invention relates to an automatic radio telephone encoder/decoder which utilizes a microcomputer to create and control the interface between a radio telephone station and an automatic radio telephone system. The decoder portion of the interface system decodes incoming telephone numbers and in response to a proper sequence of digits, provides a coded response to indicate that the proper radio telephone station has been reached and establish a communication link. The encoder portion of the interface system creates coded signals which are transmitted by the associated radio telephone station to enable the station to engage an automatic radio telephone system by securing a channel for its unique use and transmitting over the secured channel a code representing the telephone number of the station which is to be reached.

The device disclosed herein is adapted to function with automatic radio telephone (ART) systems which are tied directly into telephone transmission networks. ART systems permit a user to place a call by direct dialing via a standard telephone or radio telephone and reach a standard telephone station or radio telephone station. If the number dialed is a radio telephone station, the area code routes the call in the standard way and the exchange code identifies a radio telephone terminal which transmits the last four digits of the dialed number as a user identification code. In some systems, the area code identifies a radio telephone terminal which transmits the last seven digits of the dialed number as a user identification code. This code, either four or seven digits, is in the form of a pulsed 2805 HZ tone on a radio telephone channel carrier frequency.

Radio telephone receivers tuned to the channel decode the pulses and if they represent the proper telephone number, a ring tone is generated. The 2805 HZ tone remains on the channel carrier until the telephone call is terminated. After being pulsed and providing the dialing code, the tone remains constant and functions as a busy tone which blocks all other channel users except the one which received the call. The channel is protected against other stations transmitting as well as receiving to provide privacy on used channels. Notch filters are used in the audio section of the system to mask or block out the 2805 HZ busy tone so that it does not interfere with normal use of the radio telephone link completed between stations.

The radio telephone station which decodes the number sends an identification coded signal back to the calling station to indicate that the number has been decoded by the party called. The signal is decoded by the call originating station which then locks up the channel until the call is terminated as signaled by a positive disconnect code signal. Upon receiving a positive disconnect signal, the system is automatically shut down to free the channel for other uses.

One ART system for which the present invention is adapted to function in conjunction with is the Secode Modular Automatic Radio Telephone System provided by Secode Electronics of Dallas, Tex. A number of encoder/decoder systems are available to function in conjunction with that system as well as other ART systems but they all create excessive power drain on battery systems providing power to associated mobile receiver transmitters.

In addition to creating excessive power drains, existing encoder/decoders require full duplex operation, do not provide audio or visual ques to an operator to indicate when a channel has been secured, when keyboard entries are being made, when a channel is busy or when a station has been called.

In view of the preceding, it is a primary objective of the present invention to provide an automatic radio telephone encoder/decoder utilizing a microcomputer in combination with a power saving means which inhibits power application to the microcomputer except during the specific periods of time when the computer is required.

A primary objective of this invention is to provide a radio telephone encoder/decoder which will permit automatic simplex operation.

A further objective of the present invention is to provide an encoder/decoder which incorporates a notch filter to remove busy tones from received audio signals.

A further objective of the present invention is to provide a decoder which has the capability of decoding four digit or seven digit phone numbers.

A still further objective of the present invention is to provide a yellow call indicator lamp that is activated in response to the system decoding a proper phone number.

Another objective of the present invention is to provide an encoder/decoder wherein the phone number to which the system is to be responsive to is set by ANI strapping.

A still further objective of the present invention is to provide a system which decodes signalling transmitted over voice channels.

Another objective of the present invention is to provide an automatic telephone encoder/decoder which provides a choice of a plurality of ring tones or signals which may be selected as a user option.

A still further objective of the present invention is to provide an encoder/decoder which provides an output capable of activating a remote signalling means for a predetermined period of time.

Another objective of the present invention is to provide a busy lock out signal which inhibits push-to-talk and monitoring during the presence of a busy tone.

A still further objective of the present invention is to provide a busy tone when any keyboard entry is attempted on a used channel.

Another objective of the present invention is to provide a red busy indicator lamp for indicating to a potential user that a channel is busy.

Another objective of the present invention is to provide a yellow call indicator lamp which will indicate to a user that the station has been called up.

Another objective of the present invention is to provide a lock out means for the power supply to the microcomputer which will keep it from receiving power during the presence of a busy signal which occurs after dialing and during the duration of the telephone call.

Another objective of the present invention is to provide a signal which will squelch an associated receiver and the internal notch filter to minimize undesired reception.

A still further objective of the present invention is to provide a system capable of producing ten ANI call routing codes and positive disconnect signals.

Another objective of the present invention is to provide a hang-up hook switch positive disconnect for mobile control heads.

A still further objective of the present invention is to provide an automatic reset for call-up, push-to-talk pulser, and muting following a positive disconnect.

A still further objective of the present invention is to provide a pulse dialing means for a 2805 HZ tone capable of operating at ten pulses per second or twenty pulses per second at user option.

A still further objective of the present invention is to provide a pulse dialing system or alternately a touch-tone dialing system.

Another objective of the present invention is to provide a means to store a dialed number so that it may be redialed on command.

A still further objective of the present invention is to provide an encoder/decoder that provides an automatic push-to-talk output control function.

Another objective of the present invention is to provide a delayed ANI signal 100 milliseconds after initial push-to-talk to provide lock up time for satellite receiver voting systems.

Another objective of the present invention is to provide a synchronous push-to-talk pulser which will key a transmitter during receive for 650 milliseconds every nine seconds to refresh the automatic radio telephone system COR circuit which terminates a telephone link when not used.

Another objective of the present invention is to provide a green indicator lamp for indicating when transmission occurs.

Another objective of the present invention is to provide an audible tone in response to each keyboard entry.

Another objective of the present invention is to provide a busy tone with each keyboard entry made on a marked busy channel currently being used by another party.

The preceding, and other objectives of the present invention will become apparent in light of the specification, drawings and claims which follow.

The automatic radio telephone encoder/decoder disclosed herein employs a microcomputer which is programmed to accomplish, through associated circuitry, the various decoder functions and encoder functions required for a radio telephone to function in an automatic radio telephone system environment where dialing codes are modulated on audio dialing code carrier tones.

The systems is programmed to decode pulsed dialing codes and encode pulsed and/or touch-tone dialing codes, alert a user when his number is decoded and via audio and visual means provide an indication as to the status of the communications channel which the radio telephone is tuned. In response to keypad operation, the system provides telephone codes acceptable by related system networks.

The controlling program within the computer in combination with associated circuitry keeps the microcomputer de-energized except during the actual periods of time when the services of the computer for encoding or decoding are required. The system also provides an automatic refresh signal that is transmitted periodically while the system is receiving or listening for incoming data to prevent the network terminal from automatically disconnecting the circuit through its COR delay disconnect during simplex operations.

A keypad provides a means to enter telephone number data and related codes in the microcomputer and also contains a green indicator which is energized during transmission, a red indicator which is energized when the channel is busy and a yellow indicator which is energized when the system has been called up.

FIG. 1 is a schematic of the audio circuits.

FIG. 2 is a schematic of the microcomputer and power control means.

FIG. 3 is a schematic of the control logic circuits.

FIG. 4 is a top view of the present invention.

In its normal quiescent state the microcomputer of the encoder/decoder is off. However, when the system is connected to a radio telephone receiver-transmitter, the receiver audio line is interrupted and patched into the encoder/decoder at audio input jack 11 of FIG. 1 and returned via audio output jack 12. Thus when a 2805 HZ tone is received, it is applied to the positive input of operational amplifier 13. The output of operational amplifier 13 is applied to a bridge differentiator filter comprised of operational amplifier 14 and related resistor and capactive components. This differentiator blocks the 2805 HZ tone but passes all other audio signals back to the receiver audio circuits via output jack 12 as previously stated. Potentiometers 15 and 16 provide a means for adjusting the bridge differentiator filter for the precise frequency to be blocked.

The audio amplitude of the signal emerging from the output of operational amplifier 13 is controlled by potentiometer 17. The variable tap on potentiometer 17 couples the 2805 HZ tone to a band pass filter comprised of operational amplifier 18 and its related resistive and capacitive components. This filter functions as a bandpass filter which passes only the 2805 HZ tone. Hence the filters comprised of operational amplifier 14 and related components and operational amplifier 18 and related components function to split received audio into two channels, a first channel containing everything except the 2805 HZ tone and a second channel containing only the 2805 HZ tone.

The 2805 HZ tone emerging from operational amplifier 18 is applied to tone decoder 19, which in the disclosed embodiment is a type L567 tone decoder made by EXAR. The output at pin 8 of tone decoder 19 goes low in respone to the application of a 2805 HZ tone to pin 3 as a function of the timing resistors 21 and 22 and timing capacitor 23.

The low output of tone decoder 19 is applied via isolation diode 26 of FIG. 3 to a timing circuit comprised of capacitor 24 and resistor 25. This RC timing network is coupled to one input of NOR gate 27. (All NOR gates illustrated in FIGS. 2 and 3 may be of a similar type such as CD4001). The low at one input of NOR gate 27 causes the output to go high and turn on transistor 28. This energizes light emitting diode 29 which is adapted to provide a real indication that a 2805 HZ tone is being received. This indicates that the channel is busy.

The high output of NOR gate 27 is also applied to one input of NOR gate 30. This causes the output of NOR gate 30 to go low and inhibit transistor 31 which controls the push-to-talk output at jack 32 and light emitting diode 33 which provides a green indication of transmission.

The output signal at pin 8 of tone decoder 19 is also applied to pin 39 of the microcomputer 34 of FIG. 2. In the disclosed embodiment, the microcomputer is a type 8048 system and it is programmed in accordance with instructions provided later in this specification to decode pulsed input data applied to pin 39. However, as previously stated microcomputer 34 is normally maintained in an off state. The initial negative going pulse or phase transition which occured at pin 8 of tone decoder 19 when the 2805 HZ signal was first received is delayed by resistor 25 and capacitor 24 and then coupled to one input of NAND gate 35 and one input of NAND gate 36 of FIG. 2. (These NAND gates and the other NAND gates illustrated in FIGS. 2 and 3 may be of a common type such as CD4093). The negative potential at the input of NAND gate 35 causes the output of that NAND gate to be driven high but due to the blocking diode 38, the high at the output of NAND gate 35 has no effect on NOR gate 37. The low at one input of NAND gate 36 causes that NAND gate to go high also and commence charging capacitor 39. As capacitor 39 begins charging, the associated input to NOR gate 37 goes high and the output of NOR gate 37 goes low which causes transistor 40 to begin conducting. This supplies 5 volts from regulated power source 41 to microcomputer 34. If a low input from tone decoder 19 is present at input pin 39 of microcomputer 34 at this time, pin 24 of microcomputer 34 will go high for a period not exceeding three seconds. If within that three seconds, a transition occurs at the input to pin 39 from a dialing code pulse, the repeat transition from high to low will have the effect of causing the three second period to be refreshed so that the high at pin 24 of microcomputer 34 will be present for another three seconds. It should be noted at this point that the program for microcomputer 34 contains instructions whereby if the code creating the three second keep-alive potential at pin 24 is detected as being an erroneous pulse, the keep-alive potential at pin 24 is immediately removed.

When transistor 40 was first caused to start conducting by the output of NAND gate 36 going high, capacitor 39 began to charge. Capacitor 39 charges relatively rapidly with respect to the three second keep-alive potential duration and when capacitor 39 is charged, the associated input to NOR gate 37 goes low. Therefore NOR gate 37 will not receive a high input from NAND gate 36 until such time as the dialing tone carrier detected by tone detector 19 is interrupted long enough for capacitor 39 to become substantially discharged. Thus the only way for the computer to receive constant power and perform its decoding functions is for a keep-alive positive potential to be applied to the other input to NOR gate 37 from pin 24 of the computer. Three seconds after the final digit of the incoming code, the keep-alive potential at pin 24 drops to low and the computer is shut down. If the 2805 HZ signal is still present on the channel because the channel is active, the computer will still not be energized because the high output of NAND gate 36 is blocked by the fully charged capacitor 39 which functions as a means to inhibit the reactivation of the microcomputer. However, depression of any key on the key panel 53 will cause a negative potential to be reflected through capacitor 54 and this will cause transistor 40 to begin conducting. Once transistor 40 begins conducting, the computer will turn on for three seconds due to the low provided by tone decoder 19 to input pin 39. This period of time is sufficient for the computer to generate the codes required for a call termination which will free the channel and allow capacitor 39 to discharge so that the system will be ready to respond to a second call.

The needed features provided by capacitor 39 are not sufficient to ensure that the computer will remain shut off during a complete call due to various tone interrupts as might be caused by a mobile unit travelling under a bridge etc.. Therefore, to compensate for such problems a crow bar circuit is included. This crow bar circuit includes the RC network comprised of capacitor 75, resistor 76 and diode 77. When VCC or the regulated 5 volt potential is made available at distribution point 42 to be applied to the microcomputer, it is also applied to this RC network and causes capacitor 75 to commence charging. The values of the resistor 76 and capacitor 75 are selected such that the capacitor will require approximately eighteen seconds to charge. Once charged, the output of NAND gate 35 goes low which causes diode 38 to effectively ground the keep-alive potential at pin 24 so that the system cannot be turned on again via NAND gate 36 as might be caused by a brief signal interruption which would permit capacitor 39 to discharge and then be recharged again. If this occurs, the computer would come on the line for a very brief period of time but the keep-alive voltage would not be present and therefore the microcomputer would immediately shut down. This crow bar function is bypassed as previsouly explained by depression of any one of the keys on the keypad through capacitor 54 to that the computer can be brought back on line to send the terminating code when a call has been terminated.

The regulated power source 41 normally produces 5.6 volts which is dropped by the resistance of transistor 40 to a regulated 5 volts. The 5 volts is present at voltage distribution point VCC indicated by numeral 42 in FIG. 2 and is applied to the power inputs pins 26 and 40 of microcomputer 34 under conditions previously explained.

When the system is in its quiescent, normally cut off state and no detected tone signal is creating a low output from tone detector 19, the system may be brought on line by depressing any one of the keys on keypad 53. The keys on the keypad function to connect a ground potential to one input of NAND gate 36. This causes the output of NAND gate 36 to go high and while capacitor 39 is charging, a high input is applied to the associated pin of NOR gate 37 which causes its output to go low and cause transistor 40 to start conducting so that a regulated 5 volts is applied to the system as previously described. However, in this instance a low potential is not present at input pin 39 of the microcomputer because the tone decoder has not detected a 2805 HZ signal. In this situation, the microcomputer is programmed to provide a keep-alive potential or high at pin 24 for a period of seven seconds. It is anticiapted that the seven second keep-alive potential at pin 34 will maintain a low output at NOR gate 37 for a period sufficiently long to enable the dialing of a telephone number.

If the received pulsed code represents the telephone number for which the system has been strapped, a ring signal is provided at output pin 37 of microcomputer 34. This output pin is connected to the bridge differentiator of FIG. 1 from where it is coupled via operational amplifier 14 to the audio output jack 12. The computer is programmed to provide one of a plurality of output ring tones as selected by connecting the jumper from pin 34 of microcomputer 34 to either one of pins 0 or 1 through 7 of diode matrix 43 of FIG. 2.

The microcomputer 34 is programmed to provide a standard Bell System ring tone if the jumper connected to pin 34 of microcomputer 34 is not connected. However, if it is connected the ring tone will be a 2400 HZ pulsating ring tone or one of the following tunes depending on jumper wire connection:

Dixie, Shave and a Haircut Two Bits, Westminster chime, William Tell Overture, Theme from Laurel and Hardy, America, or a bugle call.

The selected ring tone will be inhibited by the band pass filter including operational amplifier 18 but it will pass through the bridge differentiator filter including operational amplifier 14 and thus it will be applied to the audio circuit of the radio telephone.

In addition to the ring tone, microcomputer 34 will provide a high level output at pin 35 for a period of two seconds. This output will cause transistor 44 of FIG. 3 to conduct and provide an activation signal to a remote indicator such as a light or horn. In mobile units, this signal is generally connected to the automobile horn to provide an alert to an operator not in his vehicle at the time the signal is received.

The positive output from pin 35 of microcomputer 34 is also applied to one input of NOR gate 45 which, combined with NOR gate 46 functions as a relatively slow flip-flop that will inhibit the bridge differentiator filter circuit including operational amplifier 14 via diode 47 so long as the output of NOR gate 30 is low so that messages for other stations will not be passed to the speaker of the radio telephone. However, when the flip-flop is reset by the output of pin 35 of microcomputer 34 as a function of the microcomputer having properly decoded an incoming telephone call, the bridge differentiator filter circuit is not inhibited and the output of NOR gate 46 goes high to cause transistor 48 to begin conducting. When transistor 48 is conducting, light emitting diode 49 is energized and a yellow visual indication of a call is given. The high at the output of NOR gate 46 is also applied to one input of NOR gate 27 which causes the output of NOR gate 27 to go low. This turns off transistor 28 and the busy LED 29 and enables NOR gate 30 so that when it receives a low from NOR gate 50, it will provide a high output that will cause transistor 31 to begin conducting. This provides a push-to-talk output at pin 32 and energizes LED 33 which provides a visual green indication of transmission.

The output of NOR gate 50 is driven low by activation of the push-to-talk button via push-to-talk input jack 51. This applies a low level to one input of NAND gate 52 which causes a high output to be produced by that NAND gate which is coupled to one input of NAND gate 52 which causes a high output to be produced by that NAND gate which is coupled to one input of NOR gate 50 and thus the second low is provided to true NOR gate 30.

The microcomputer 34 of FIG. 2 is programmed to decode either a four or seven digit telephone call and as a function of jumper JU 3 connecting pin 1 to ground causes the yellow call light to be activated in response to both a four and seven digit code instead of the standard response of a yellow call light only for a seven digit code. The actual phone number programming is accomplished by connecting jumpers A through G from the microcomputer 34 to the jumper connections 0 through 9 of the diode matrix 43. For instance, to program the system to be responsive to a telephone number 885-1234, the following jumper or strap connections would be made: jumpers A and B connected to diode matrix connection 8, C to 5, D to 1, E to 2, F to 3, and G to 4.

When the system is functioning as an encoder, that is when a telephone call is being originated by the associated radio telephone, activation of * on keypad 53 followed by any single digit causes the microcomputer 34 to encode the number patched in from the diode matrix 43 and convert it to a phase encoded 1402.5 HZ ASCII hamming code at pin 38 of the microcomputer. This code is generated and transmitted to the system network to identify the remote equipment generating the response or initiating a call. Depression of additional keys creates a ground connection at 2 of pins 13 through 18 of microcomputer 34 which represents a 2 out of 7 code which is encoded by the microcomputer as a 2805 HZ pulsed dialing code and applied to output pin 38. However, as previously indicated the microcomputer 34 is normally in an off condition. When a button on keypad 53 is depressed, capacitor 54 is grounded and this causes a voltage spike to be applied to the base of transistor 40. This causes transistor 40 to conduct and the microcomputer will be energized for a period of seven seconds as previously described due to the application of a keep-alive voltage to NAND gate 37 from pin 24 of the microcomputer.

In response to a user keying in * 1, 2, 3 or 4, an identification code is sent to the network system which recalls from its memory and dials user preselected telephone numbers. The system is also programmed to remember the last dialed telephone number so that it may be recalled. A * 7 input provides automatic connection to a phone exchange, * 8 activates a loop back so that another radio telephone unit may be called, * 9 provides an outside line where the user accomplishes his own dialing via keypad 53 and * 0 calls the operator for assistance. If it is desired to terminate a telephone call, the * # sequence may be entered and the radio telephone interconnection will be immediately terminated without waiting for the COR timer to automatically drop out after the prescribed delay period.

It should be noted that once the system is locked on a channel, the input to NAND gate 36 from the tone decoder via diode 26 will prevent the NAND gate from turning on transistor 40 via NOR gate 37 after the initial input spike when the system is in the decoding mode. Thus when the system is in an encoding mode, after the initial turn on which can be either via capacitor 54 or capacitor 39, the computer will shut down and remain in an off condition. Thus when * # is selected to terminate a call, the computer would be in an off condition and not responsive. However depression of one of the keys on keypad 53 will cause a voltage spike through capacitor 54 which will cause transistor 40 to conduct regardless of the output of NOR gate 37 or the mode of operation of the system.

The codes generated by microcomputer 34 in response to answering a proper incoming call or in response to activation of the keypad when originating a call or terminating a call are applied to pin 38 of microcomputer 34. This pin couples the coded 2805 HZ and 1402.5 HZ signals via an integrator and level control circuit including potentiometer 55 to output amplifier 56 which drives the high impedance output jack 57 and the low impedance output jack 58. The appropriate output jack, 57 or 58, is coupled to the audio section of the radio telephone transmitter.

Two hundred fifty milliseconds before the code to be transmitted is applied to pin 38 of the microcomputer, pin 36 of the microcomputer goes high. This pin is coupled to NOR gate 50 of FIG. 1 which provides a low output in response to the high input and trues NOR gate 30 to automatically activate the transmitter circuit. The transmitter circuit is activated via the push-to-talk circuit before the code is presented for transmission so that systems utilizing voting receivers will have time to select the proper receiver to respond.

The positive pulse applied at pin 36 of microcomputer 34 is also applied to one input of NOR gate 59 which forms a flip-flop with NOR gate 60. The effect of the positive pulse at the input of NOR gate 59 causes the output of NOR gate 60 to go high and this enables NAND gate 61. When enabled, NAND gate 61 functions with NAND gate 52 as a non-symmetrical oscillator which is an automatic refresh pulse generator with a 20 to 1 duty cycle. It sends a pulse having a width exceeding 500 milliseconds every eight to nine seconds as set by the time constant provided by capacitor 71 and resistors 72 and 73 which vary the pulse width and repetition rate. This automatic refresh pulse is sent out periodically to prevent the automatic COR disconnect from terminating the radio telephone circuit if the listening period exceeds the COR delay. The refresh pulse generator is turned on by the output of a flip-flop comprised of NOR gates 59 and 60 which are controlled by the push-to-talk output at pin 36 of microcomputer 34. The refresh pulse generator remains on during the length of the call after the microcomputer has shut down as previously explained to conserve power. The refresh pulse generator uses low power drain CMOS circuitry to minimize battery drain. The refresh pulse generator is synchronized to the push-to-talk output at input jack 51 and by microcomputer 34 through its push-to-talk output at pin 36. An output at pin 36 of the microcomputer causes the flip-flop comprised of NOR gates 59 and 60 to provide an input from the output of NOR gate 59 via capacitor 74 to the push-to-talk input of NAND gate 52. The output of the flip-flop at the output of NOR gate 60 enables the refresh pulse generator and causes it to continue producing a refresh pulse which energizes the push-to-talk circuit at eight to ten second intervals continually until the flip-flop is reset, even though the computer is no longer on the line.

Crystal 62 provides a timing or clock circuit for microcomputer 34.

The microcomputer is programmed to interpret an input at pin 6 as a positive disconnect signal and in normal installations, this pin is connected to a hangup hook switch so that when the microphone is hung up, the microcomputer responds as if the positive disconnect signal * # was inserted by the keypad 53 and the call is terminated.

To prevent excessive battery drain, the microcomputer 34 is programmed to remove the keep-alive potential at pin 24 during the decode mode if a code pulse is not received within three seconds of power up. This prevents the computer from staying on line when the channel is marked busy with the 2805 HZ dialing tone. A further battery saving feature is included in the microcomputer program wherein the keep-alive potential at pin 24 of the microcomputer is terminated during the decode mode as soon as an erroneous pulse position is detected. Therefore, when the microcomputer begins to decode an incoming signal, the computer will remain on until the first wrong digit is detected and then it will immediately shut down with the red LED indicator 29 indicating a busy channel.

The program for microcomputer 34 causes it to provide an audio tone output at pin 37 each time a key is depressed on keypad 53. This provides an audio indication of keypad activation.

FIG. 4 illustrates a preferred embodiment of the present invention wherein the electronic components of the system are incorporated in a keypad housing 153. A red busy indicator 129 illuminated by diode 29 of FIG. 3, a yellow channel capture indicator 149 illuminated by diode 49 of FIG. 3, and a green transmit indicator 133 illuminated by diode 33 of FIG. 3 are positioned on the face of the housing.

Jumper JU 1, when installed between ground and pin 22 on microcomputer 34 changes the dialing speed from ten pulses per second to twenty pulses per second for radio telephone systems located in ESS offices.

Jumper JU 2, when installed between ground and pin 23 of microcomputer 34 disables the annunciated keyboard beat tones and the busy tone normally provided at output pin 37 of the microcomputer.

Jumper JU 4, when installed between ground and pin 19 disables the pulse code dialing system within the microcomputer and activates the microcomputer to control an operational touch-tone encoder.

In the exemplary system presented herein, the microcomputer 34 is a standard type 8048 microcomputer programmed to provide the encoding, coding and control functions described herein in accordance with the following instructions: ##SPC1## ##SPC2##

While preferred embodiments of this invention have been illustrated and described, variations and modifications may be apparent to those skilled in the art. Therefore, I do not wish to be limited thereto and ask that the scope and breadth of this invention be determined from the claims which follow rather than the above description.