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United States Patent5583933
MarkDecember 10, 1996
Title
Method and apparatus for the secure communication of data
Abstract
An auto-dialer suitable for use as a smart card capable of being acoustically coupled to a telephone and being reprogrammed in response to acoustic signals. The programming and other features of the auto-dialer can be enabled or disabled by the auto-dialer in response to persecuted signals, e.g., a string of DTMF tones. Encryption of calling card and other data into destination telephone numbers is achieved by selectively altering persecuted characteristics of a DTMF tone sequence, such as the duration of tones, the period of silence between tones and the twist between Lo-band and Hi-band tones of DTMF tone pairs in a DTMF tone sequence representing a telephone number. The encryption of data into the telephone number does not affect the ability of standard telephone switching circuitry to recognize the destination number. However, information encrypted into the DTMF signals is undetectable to standard telephone switching circuitry because it is encrypted using DTMF signal characteristics not normally used to represent data. The auto-dialer has a system clock used to drive a pseudo random number generator used in various data security schemes. Calibration features permit the calibration of the audio output and system clock with adjustments being made via the acoustic programming of the auto-dialer with various calibration factors.
Inventors:Mark; Andrew R. (New York, NY)
Appl. No.:286825
Filed:August 5, 1994
Current U.S. Class:379/357.04 379/361 379/418 379/444 379/93.28 713/184 235/380 379/257 379/354 
Field of Search:379/361,257,418,96,355,283,97,98,354,357,386,368,444,93 340/825.44,825.48 380/6,9 235/380
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Other References
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Primary Examiner: Zele; Krista M.
Assistant Examiner: Wolinsky; Scott
Attorney, Agent or Firm:Testa, Hurwitz & Thibeault, LLP
Claims

What is claimed is:
1. A device for generating a set of tones encoded with data, each tone in the set being separated by an interdigit period, the device including:
memory storing encoding information relating to alterable tone characteristic values and storing corresponding data items; and
an encoding generator electrically coupled to said memory, said encoding generator generating a set of tones encoded with said alterable tone characteristic values in response to said encoding information and said data items.

2. The device of claim 1, further comprising:
a system clock generating a system time;
a clock setter responsive to a first pre-defined acoustic signal to set the system clock;
a calibrator responsive to a second pre-defined acoustic signal to calibrate said system time as a function of the deviation in time from the last setting; and
an acoustic signal receiver electrically coupled to said clock setter and said calibrator.

3. The device of claim 1, further comprising:
memory storing information relating to the insertion of a timing space between a string of tones conforming to the time necessary for one call switching system to make contact with another;
an information controller responsive to a preselected sequence of tones to alter the stored information relating to the insertion of a timing space; and
a tone receiver electrically coupled to said information controller,
said generator generating said tones as a function of the stored information relating to the timing space.

4. The device of claim 1, further comprising:
a limiter limiting user accessibility to features of the device, said limiter being responsive to the receipt of a signal including a string of pre-selected tones to alter, as a function of the received signal, the features to which the user is given access; and
a signal receiver electrically coupled to said limiter.

5. The device of claim 1, further comprising:
a system clock generating a system time;
a pseudo random number generator generating a pseudo random number as a function of the system time; and
an output device outputting the pseudo random number.

6. The device of claim 1 further comprising:
an audio transducer receiving audio signals and converting the audio signals into electrical signals;
memory storing information relating to the amount of amplification that is to be applied to the electrical signals generated by the audio transducer; and
an information controller altering the information stored in said memory relating to the amount of amplification that is to be applied to the electrical signals in response to the receipt of a preselected series of audio signals stored in said memory.

7. The device of claim 1, further comprising an indicator device indicating when the device is outputting the tones.

8. The device of claim 1, further comprising:
a decoder circuit receiving and decoding encoded tones to obtain paging information from received tones; and
a display device displaying the paging information.

9. The device of claim 1 further comprising:
a number generator selected from the group consisting of a pseudo random number generator, a random number generator and an incrementing register; and
a generated number output device electrically coupled to said selected number generator.

10. The device of claim 1, further comprising:
memory storing information relating to an acoustic device access control signal;
a receiver receiving an acoustic signal, said receiver including an audio transducer;
a detector comparing a received acoustic device access control signal to the stored information relating to the acoustic device access control signal to detect the receipt of the acoustic device access control signal; and
a controller placing the device into a functional mode not otherwise available to a user of the device upon the receipt of the acoustic device access control signal.

11. The device of claim 10, wherein the information relating to the access control signal includes information identifying a preselected set of tones.

12. The device of claim 1, further comprising:
a calibrator monitoring, processing and storing transmission related characteristics of tones and calibrating the output of the device as a function of the stored transmission related characteristics.

13. The device of claim 12, further comprising:
a calibration controller enabling the calibrator to calibrate the output of the device in response to the receipt of a preselected set of tones.

14. The device of claim 1, further comprising:
memory storing a string of network address codes and dialing sequences intended for use when initiating a telephone call;
a reprogrammer responsive to a pre-selected set of tones, to alter said stored string of network address codes and dialing sequences; and
a tone receiver electrically coupled to said reprogrammer.

15. The device of claim 14, wherein said reprogrammer is responsive to received tones to reprogram the device with information encoded into the received tones.

16. The device of claim 1, further comprising:
a speaker outputting the tones as an audio signal;
a housing surrounding said speaker, the housing including audio outlets, said audio outlets permitting the audio signal generated by the speaker to exit the housing; and
a device indicator mounted on the housing in close proximity to the audio outlets, said device indicator being adapted to indicate to a receiver the presence of the device.

17. The device of claim 16 wherein the device indicator is a strip of highly reflective material mounted on the housing in close proximity to the audio outlets, said reflective material being adapted for reflecting light to the receiver to thereby indicate to the receiver the presence of the device.

18. The device of claim 1, further comprising:
a decoder circuit receiving and decoding encoded tones to obtain paging information from received tones; and
a transmitter device transmitting the paging information to a pager device.

19. The device of claim 18, wherein the transmitter device is a radio frequency transmitter.

20. The device of claim 1, wherein the generator generating the set of tones includes circuitry generating a single tone and only a single tone during at least one of the interdigit periods separating the tones in the set.

21. The device of claim 20, wherein the single tone is a tone having a frequency less than 672 Hz or greater than 1590 Hz.

22. The device of claim 20, wherein the single tone has a frequency less than 672.61 Hz or greater than 1690.16 Hz.

23. The device of claim 1, further comprising:
an activator responsive to an activation signal, said activator causing the device to become fully active upon receipt of the activation signal.

24. The device of claim 10, further comprising:
memory storing information representing a preselected set of tones corresponding to the activation signal; and
wherein the activator includes a detector detecting a received signal, said detector including a comparator comparing the received signal to the stored information corresponding to the activation signal.

25. The device of claim 23, wherein the activation signal comprises a light signal.

26. The device of claim 1, further comprising:
a receiver receiving signals representing computational instructions;
a data item calculator performing computational operations on a data item as a function of the received signals representing computational instructions; and
an output device outputting the result of the computational instructions.

27. The device of claim 26, wherein said device is capable of performing a plurality of functions and wherein said memory includes memory space storing information relating to a user, the stored information including information regarding the device functions which the user is permitted to use.

28. The device of claim 27, further comprising:
an optical sensor receiving optically transmitted data.

29. The device of claim 1, further comprising:
an audio transducer receiving audio signals; a memory device storing information relating to a first and second predetermined control signal;
a detector circuit detecting the receipt of the first and second predetermined control signals; and
a controller causing the device to cease operation in response to the detection of the first predetermined control signal.

30. The device of claim 29, further comprising:
an audio output circuit; and
wherein the controller controls the audio output circuit to output a predetermined set of tones in response to the detection of the second control signal.

31. The device of claim 29, further comprising:
an audio output circuit; and
wherein the controller controls the audio output circuit to output a diagnostic signal indicative of the operational status of the device in response to the detection of the second control signal.

32. The device of claim 29, wherein the memory stores a plurality of signal characteristics relating to signals which the device is capable of decoding, said device further comprising:
an adjustable filter circuit filtering out received signals that fail to conform to the plurality of signal characteristics stored in the memory.

33. The device of claim 1 wherein the set of tones comprises a series of tone pairs.

34. The device of claim 33, wherein the series of tone pairs is a DTMF signal and wherein the information relating to the alterable tone characteristic values includes tone pair duration values.

35. The device of claim 33, wherein the series of tone pairs is a DTMF signal and wherein the information relating to the alterable tone characteristic values includes aggregate tone pair signal power levels.

36. The device of claim 33, wherein the series of tone pairs is a DTMF signal and wherein the information relating to the alterable tone characteristic values includes differences in signal levels between the highest and lowest levels of each tone in a tone pair.

37. The device of claim 33, wherein the series of tone pairs is a DTMF signal, and wherein the information relating to the alterable tone characteristic values includes interdigit duration values.

38. The device of claim 33, wherein the generator generating the set of tones includes circuitry generating a third tone simultaneously with the generation of a tone pair to represent information to be encoded into the set of tones, the third tone having a frequency less than 672 Hz or greater than 1590 Hz.

39. The device of claim 33, wherein the series of tone pairs is a DTMF signal, each tone pair including a first tone and a second tone, and wherein the generator generating the set of tones includes:
a first amplification circuit amplifying the first tone; and
a second amplification circuit amplifying the second tone.

40. The device of claim 39, further comprising:
a data table in the memory storing information about amplification levels to be used for each of said first and second tones when generating one of a plurality of tone pairs; and
an amplification controller electrically coupled to said memory, said first amplification circuit and said second amplification circuit, said amplification controller controlling the amplification levels of the first and second tones of each tone pair being generated as a function of the information stored in the data table.

41. The device of claim 40, wherein the data table further includes:
a list of tone frequencies that may be used to generate the DTMF signal.

42. The device of claim 41 further comprising:
a programmer reprogramming the information stored in the data table in response to receipt of a signal including a pre-selected set of tones.

43. The device of claim 1, further comprising:
a proximity sensor electrically coupled to said generator, said proximity sensor detecting the proximity of said device to said receiver.

44. The device of claim 43 wherein said receiver is a microphone of a telephone handset, said device further comprising:
a proximity indicator coupled to said proximity sensor, the proximity indicator indicating when the device must be placed closer to said microphone to provide satisfactory acoustic communication between the device and the microphone of the handset.

45. The device of claim 44, wherein the proximity indicator is a light.

46. The device of claim 44, wherein the proximity indicator is an audio signal generator generating an audio signal indicating when the device must be placed closer to the microphone.

47. The device of claim 43 further comprising:
a speaker electrically coupled to said generator, said speaker outputting the tones as an audio signal; and
a housing surrounding said speaker, said housing including audio outlets, said audio outlets permitting the audio signal generated by said speaker to exit said housing,
wherein said proximity sensor is a pressure switch located on said housing.

48. The device of claim 43 further comprising:
a speaker electrically coupled to said generator, said speaker outputting the tones as an audio signal; and
a housing surrounding said speaker, said housing including audio outlets, said audio outlets permitting the audio signal generated by said speaker to exit said housing,
wherein said proximity sensor is a series of pressure switches encircling said audio outlets.

49. The device of claim 43 wherein said proximity sensor is a light sensor.

50. The device of claim 49 wherein said proximity sensor is activated when the device is placed in close proximity to a microphone of a telephone handset thereby reducing the amount of light received by the proximity sensor.

51. The device of claim 43 wherein said device has a predetermined operating proximity to said receiver, said device enabling said generator upon said proximity sensor detecting said proximity of said device to said receiver to be within said operating proximity, and disabling said generator upon said proximity sensor detecting said proximity of said device to said receiver to be outside said operating proximity.

52. The device of claim 51 further comprising a proximity indicator electrically coupled to said proximity sensor, said proximity indicator indicating to a user that said device is outside said operating proximity upon said proximity sensor detecting said proximity of said device to said receiver to be outside said operating proximity.

53. The device of claim 52 wherein said proximity indicator is an indicator selected from the group consisting of a speaker, a display and a light;
wherein said speaker outputs an audible signal to indicate that said device should be moved closer to said receiver;
wherein said display displays a message to indicate that said device should be moved closer to said receiver; and
wherein said light illuminates to indicate that said device should be moved closer to said receiver.

54. A device -for generating DTMF tone pairs encoded with data, the device comprising:
memory storing information elements and non-frequency DTMF tone pair characteristic values, each one of the information elements being associated with one of the non-frequency DTMF tone pair characteristic values;
a signal generator controllably generating DTMF tone pairs with non-frequency DTMF tone pair characteristic values corresponding to ones of said values stored in said memory; and
a processor coupled to said memory and said signal generator, said processor controlling the signal generator to generate said DTMF tone pairs as a function of said stored values.

55. The device of claim 54, wherein the non-frequency DTMF tone pair characteristic values include the duration of delay periods between DTMF tone pairs.

56. The device of claim 54, wherein the non-frequency DTMF tone pair characteristic values include tone pair durations.

57. The device of claim 54, wherein the non-frequency DTMF tone pair characteristic values include tone pair signal levels.

58. The device of claim 54, wherein the DTMF tone pairs each have a twist level, and wherein the non-frequency DTMF signal characteristic values include DTMF tone pair twist levels.

59. A device for decoding data encoded into a set of tones having non-frequency tone characteristic values representing encoded information, said device comprising:
a data table storing a plurality of non-frequency tone characteristic values and a data element associated with each of the stored non-frequency tone characteristic values;
a detector detecting the non-frequency tone characteristic values representing the encoded information; and
a processor coupled to said data table and said detector, said processor decoding said encoded information as a function of the data stored in the data table and the detected non-frequency tone characteristic values.

60. The device of claim 59, further comprising:
a transducer coupled to said processor, said transducer receiving an acoustic signal representing the set of tones.

61. The method of claim, 59 wherein the set of tones comprises a series of tone pairs.

62. The device of claim 61, wherein the series of tone pairs is a DTMF signal and wherein the tone characteristic values include tone pair duration values.

63. The device of claim 61, wherein the series of tone pairs is a DTMF signal and wherein the tone characteristic values include aggregate tone pair signal power levels.

64. The device of claim 61, wherein the series of tone pairs is a DTMF signal and wherein the tone characteristic values include differences in power levels between the highest and lowest power levels of each tone in a tone pair.

65. The device of claim 61, wherein the series of tone pairs is a DTMF signal and wherein the tone characteristic values include differences in amplitude levels between the highest and lowest amplitude levels of each tone in a tone pair.

66. The device of claim 61, wherein the series of tone pairs is a DTMF signal and wherein the tone characteristic values include durations of interdigit periods.

67. The device of claim 61, wherein the tone pairs are separated by interdigit periods, further comprising a detector detecting a single tone asserted during at least one of the interdigit periods separating the tone pairs in the signal.

68. The device of claim 67, further comprising a detector detecting signal characteristics of the single tone and decoding information represented by the single tone.

69. A device for generating a series of tone signals providing non-frequency modulation of data, each tone signal including simultaneously asserted first and second tones, the device comprising:
a first tone generator circuit generating a first tone;
a second tone generator circuit generating a second tone;
a first amplification circuit coupled to said first tone generator circuit amplifying the first tone;
a second amplification circuit coupled to the second tone generator circuit amplifying the second tone, said first and second amplification circuits operating independently to provide non-frequency modulation of data;
a control circuit controlling the first and second tone generator circuits and the first and second amplification circuits to generate a series of first and second tones; and
an output circuit coupled to said first and second amplification circuits combining the series of first and second tones to generate a series of tone signals.

70. A device for generating a series of tone signals providing non-frequency modulation of data, each tone signal including simultaneously asserted first and second tones, the device comprising:
a first tone generator circuit generating a first tone;
a second tone generator circuit generating a second tone;
a first amplification circuit electrically coupled to said first tone generator circuit, said first amplification circuit amplifying the first tone;
a second amplification circuit electrically coupled to the second tone generator circuit, said second amplification circuit amplifying the second tone, said first and second amplification circuits operating independently to provide non-frequency modulation of data;
a control circuit electrically coupled to said first and second amplification circuits and said first and second generator circuits, said control circuit controlling the first and second tone generator circuits and the first and second amplification circuits to generate a series of first and second tones;
an output circuit coupled to said first and second amplification circuits, said output circuit combining the series of first and second tones to generate a series of tone signals;
memory storing a plurality of twist levels, each twist level representing the difference of the amplification of a first tone and a second tone of a tone signal; and
wherein the control circuit includes a processor coupled to said memory and said first and second amplification circuits, said processor accessing said memory and controlling the amplification levels of said first and second amplification circuits to introduce into the tone signals being generated the level of twist stored in the memory for the tone signal being generated.

71. The device of claim 70, wherein each tone signal further includes a third tone signal and wherein the device further comprises:
a third amplification circuit amplifying the third tone of each tone signal being generated independently of the amplification of said first and second tone signals.

72. A device for generating a series of tone signals providing non-frequency modulation of data, each tone signal including simultaneously asserted first and second tones, the device comprising:
a first tone generator circuit generating a first tone;
a second tone generator circuit generating a second tone;
a first amplification circuit electrically coupled to said first tone generator circuit, said first amplification circuit amplifying the first tone;
a second amplification circuit electrically coupled to the second tone generator circuit, said second amplification circuit amplifying the second tone, said first and second amplification circuits operating independently to provide non-frequency modulation of data;
a control circuit electrically coupled to said first and second amplification circuits and said first and second generator circuits, said control circuit controlling the first and second tone generator circuits and the first and second amplification circuits to generate a series of first and second tones;
an output circuit coupled to said first and second amplification circuits, said output circuit combining the series of first and second tones to generate a series of tone signals;
a speaker coupled to the output circuit converting the series of tone signals into acoustic signals; and
a microphone located in proximity to the speaker and coupled to the control circuit converting the acoustic signals into an electrical feedback signal,
wherein the series of tone signals are electrical signals.

73. The device of claim 72 wherein said electrical feedback signal has actual signal characteristic values, said device further comprising:
memory including a first set of memory locations storing control parameters for controlling the generation of the first and second tones, and a second set of memory locations storing signal characteristic values, and
wherein the control circuit operates to compare the actual signal characteristic values of the electrical feedback signal to characteristic values stored in the second set of memory locations and to adjust the control parameters stored in the first set of memory locations to adjust the first and second tone generator circuits to reduce the differences between the stored signal characteristic values and the actual signal characteristic values of the electrical feedback signal.

74. A device for generating and dynamically encrypting data into a set of tones, said device comprising:
memory storing data, information relating to alterable tone characteristic values and a plurality of encryption methods, each of said plurality of encryption methods being valid for use at different times;
an encryptor electrically coupled to said memory, said encryptor selecting which of said encryption methods is valid for use and using said valid encryption method to associate each of said alterable tone characteristic values with a data item; and
a tone generator in electrical communication with said encryptor.

75. The device of claim 74 further comprising:
a system clock electrically coupled to said encryptor,
wherein said encryptor selects said valid encryption method in response to said system clock.

76. The device of claim 74 further comprising:
a number generator electrically coupled to said encryptor,
wherein said encryptor selects said valid encryption method in response to said number generator.

77. The device of claim 74 wherein said set of tones comprises a series of tone pairs.

78. A device for generating a set of tones encoded with data, each tone in the set being separated by an interdigit period, the device including:
memory storing encoding information relating to alterable out-of-band tone characteristic values and storing corresponding data items; and
an encoding generator electrically coupled to said memory, said encoding generator generating a set of tones encoded with said alterable out-of-band tone characteristic values in response to said encoding information and said data items to provide out-of-band transmission of said data items.

79. The device of claim 78 wherein the set of tones comprises a series of tone pairs.

80. A method of generating a set of tones encrypted with data, wherein the tones are separated by interdigit periods, said method comprising the steps of:
storing information in a data table, the information relating to a set of N variations of a first tone characteristic value, wherein the first tone characteristic value can be selectively altered and wherein N is a positive integer; and
generating, as a function of the stored information and the data to be encrypted, the set of tones wherein the first tone characteristic value is varied, as a function of the data to be encrypted, with the generation of each tone, to correspond to one of the set of N variations of the first tone characteristic value.

81. The method of claim 80, further comprising the step of:
accessing the stored information using the data to be encrypted as an index into the data table of stored information, the accessed information indicating which variation of the set of N variations of the first tone characteristic value corresponds to the data to be encrypted.

82. The method of claim 80, further comprising the step of generating as a function of the information to be encrypted, a single tone during at least one of the interdigit periods separating the tones in the set.

83. The method of claim 82, wherein the single tone is a tone having a frequency less than 672 Hz or greater than 1590 Hz.

84. The method of claim 80 wherein the set of tones comprises a series of DTMF tone pairs.

85. The method of claim 84, further comprising the step of generating a third tone, as a function of the information to be encrypted, at the same time a DTMF tone pair is generated, the third tone having a frequency less than 672 Hz or greater than 1590 Hz.

86. The method of claim 84, wherein the first tone characteristic value is the time period between the generation of each sequential DTMF tone pair and wherein the step of storing information in the data table includes the step of storing in the data table N different time periods representing the time periods between the generation of each sequential DTMF tone pair.

87. The method of claim 84, wherein the first tone characteristic value is the duration a DTMF tone pair is asserted and wherein the step of storing information in the data table includes the step of storing in the data table N different durations representing the durations a DTMF tone pair can be asserted.

88. The method of claim 84, wherein each DTMF tone pair includes a Lo-band tone and a Hi-band tone and wherein the first tone characteristic value is the twist between the Lo-band and Hi-band tones of a tone pair, the step of storing information in the data table including the step of storing in the data table N different twist values.

89. A method of generating a set of tones encoded with data, comprising the steps of:
storing in a data table a plurality of information elements and a plurality of alterable tone characteristic values, each one of the information elements being associated with one of the plurality of alterable tone characteristic values;
using the data to be encoded to obtain the alterable tone characteristic value associated with the data to be encoded from the data table; and
generating, as a function of the alterable tone characteristic value obtained from the data table, a set of tones.

90. The method of claim 89 wherein the set of tones comprises a DTMF signal.

91. The method of claim 90, wherein the step of generating a set of tones includes the step of generating a series of tone pairs, each tone pair having a twist level, and wherein the step of storing in a data table a plurality of alterable tone characteristic values, includes the step of storing a plurality of twist level values.

92. The method of claim 90, wherein the step of generating a set of tones includes the step of generating a series of tone pairs separated by delay periods, and wherein the step of storing in a data table a plurality of alterable tone characteristic values, includes the step of storing a plurality of delay period values, each delay period value representing a different delay following the generation of a tone pair.

93. The method of claim 92, wherein the step of storing in a data table a plurality of information elements includes the step of storing a plurality of alphanumeric values in the data table.

94. The method of claim 90, wherein the step of generating a set of tones includes the step of generating a series of tone pairs, each tone pair having a period of signal duration, and wherein the step of storing in a data table a plurality of alterable tone characteristic values, includes the step of storing a plurality of tone pair signal duration values, each signal duration value representing a different period of tone pair signal duration.

95. The method of claim 94, wherein the step of storing in a data table a plurality of information elements includes the step of storing a plurality of alphanumeric values in the data table.

96. The method of claim 90, wherein the step of generating a set of tones includes the step of generating a series of tone pairs, each tone pair having a signal level, and wherein the step of storing in a data table a plurality of alterable tone characteristic values, includes the step of storing a plurality of signal level values.

97. The method of claim 96, wherein the step of storing in a data table a plurality of information elements includes the step of storing a plurality of alphanumeric values in the data table.

98. A method of generating an audio DTMF signal providing non-frequency modulation of data, comprising the steps of:
generating a Lo-frequency tone signal;
amplifying the Lo-frequency tone signal to create a Lo-frequency tone signal having a first power level;
generating a Hi-frequency tone signal;
amplifying the Hi-frequency tone signal separately from said Lo-frequency tone signal to generate a Hi-tone signal having a second power level that differs from the first power level to provide non-frequency modulation of data;
combining the Lo-frequency and Hi-frequency tone signals to form a tone pair;
amplifying the tone pair; and
supplying the amplified tone pair to a speaker to generate said audio DTMF signal.

99. The method of claim 98, wherein the tone pair corresponds to the digit 1, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately nine dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
100. The method of claim 98, Wherein the tone pair corresponds to the digit 2, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately three dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
101. The method of claim 98, wherein the tone pair corresponds to the digit 3, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately five dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
102. The method of claim 98, wherein the tone pair corresponds to the digit 4, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately one dB lower than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
103. The method of claim 98, wherein the tone pair corresponds to the digit 5, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately seven dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
104. The method of claim 98, wherein the tone pair corresponds to the digit 6, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately seven dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
105. The method of claim 98, wherein the tone pair corresponds to the digit 7, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately five dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
106. The method of claim 98, wherein the tone pair corresponds to the digit 8, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately three dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
107. The method of claim 98, wherein the tone pair corresponds to the digit 9, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately seven dB higher than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
108. The method of claim 98, wherein the tone pair corresponds to the digit 0, and the Lo-frequency tone component of the audio DTMF signal has a sound pressure level that is approximately two dB lower than the sound pressure level of the Hi-frequency tone signal component of the audio DTMF signal.
109. A method of dynamically encrypting data into a set of tones, said method comprising the steps of:
storing data items, information relating to alterable tone characteristic values and a plurality of encryption methods, each of said plurality of encryption methods being valid for use at different times;
determining which of said plurality of encryption methods is valid for use;
using said valid encryption method to associate each of said alterable tone characteristic values with a data item; and
generating a set of tones as a function of the alterable tone characteristic values associated with each data item to be encrypted.
110. The method of claim 109 wherein the step of determining which of said plurality of encryption methods is valid for use further comprises the steps of:
obtaining a current system time from a system clock; and
using said current system time to determine which of said plurality of encryption methods is valid for use.
111. The method of claim 109 Wherein the step of determining which of said plurality of encryption methods is valid for use further comprises the steps of:
generating a pseudo random number; and
using said pseudo random number to determine which of said plurality of encryption methods is valid for use.
112. The method of claim 109 wherein the step of generating a set of tones further comprises the step of generating a series of tone pairs.
Description
FIELD OF THE INVENTION

The present invention is directed to methods and apparatus for communicating data, telecommunications access methods, and, more particularly, to auto-dialers, security and information devices that can transmit and receive data.

BACKGROUND OF THE INVENTION

In the modern world, telephone transactions involving extensions of credit, payment of bills, fund transfers and the providing of other types of services are commonplace. Generally, such services are provided in response to a user dialing the telephone number of a service and by then entering identification information and/or credit card information using standard "touch tones", i.e., dual tone multi-frequency signals ("DTMF tones"), to represent the identification information being entered and transmitted. Normally, such touch tone signals are produced using a standard telephone keypad input device.

Touch tones are generated using a dual tone multi-frequency (DTMF) encoding technique, as opposed to a frequency shift key (FSK) encoding, which is frequently used for data transmission purposes. In accordance with the DTMF technique used to generate touch tone signals, tone signals are produced by generating two tones such that one tone is selected from a high frequency band group and the other tone is selected from a low frequency band group. In standard telephone systems, the high frequency band group includes four high frequencies (1209, 1336, 1477, and 1633 Hz) while the low band frequency group includes four low frequencies (697, 770, 852 and 941 Hz). Each of the high and low frequencies is referred to as a fundamental frequency.

Each one of the low frequencies corresponds to one of the four rows of keys on a standard extended telephone keypad while each one of the four high frequencies corresponds to one of the four columns of keys on standard extended telephone keypads. Accordingly, low frequency tones represent row tones and high frequency tones represent column tones. It should be noted that extended and non-extended keypads differ in that extended keypads include the additional fourth column of keys not found on non-extended standard keypads such as those commonly used with public telephones and household telephones, although these additional tones are found in most modem hardware/software systems.

Each different telephone key is represented by a signal including a unique combination of one tone from the high band and one from the low band. Sixteen different signal states may be represented by this encoding technique with one signal state corresponding to each one of the sixteen keys that can be found on a standard telephone keypad. Referring now to FIG. 8A, there is illustrated a chart which lists the 16 different numbers/symbols that are represented by the 16 different signal states and the Hi-tone and Lo-tone frequency associated with each of the 16 different signal states.

A received DTMF tone signal is determined, in telephone switching and DTMF tone signal detection devices, as having a valid signal state if five conditions are met. The first of these is that the tone signal contain exactly one valid tone, and only one valid tone, from each of the low and high band frequency groups, i.e., the signal must contain only one valid Hi-tone and one valid Lo-tone frequency. The second condition is that the low and high tones are present for a predetermined minimum time duration, i.e., at least 35-40 milliseconds. Third, the difference in power (level), commonly referred to as "twist", between the low and the high tone must fall within a predetermined range, i.e., the Hi-band tone signal power level can not be more than 4 dBm greater or 8 dBm less than the Lo-band tone signal power level, where dBm is a logarithmic measure of power with respect to a reference power of 1 milliwatt. Fourth, the amplitude level of each tone signal in the tone pair must be in the range of 0 to -25 dBm. Fifth, consecutive tone-pairs must be separated by a period of silence for at least 35-40 milliseconds.

Thus, if too many or too few tones are detected the detection criteria will not be met and a valid signal state will not be indicated. When a valid signal state does occur, the particular combination of low and high tones is decoded to produce an indication of the corresponding key or signal state that was responsible for the generation of the DTMF tone signal. It is this key or signal state information that represents, e.g., one of the numerical digits comprising a telephone or credit card number.

Placing a voice call, using a calling card number or other credit card number, is exemplary of one of the most common types of telephone credit transactions involving the use of DTMF tones.

Referring now to FIG. 1, there is illustrated a flow chart illustrating a standard telephone call transaction involving the use of a credit card for billing purposes. As illustrated, the standard telephone call transaction comprises the first step of making a decision to place a credit card call 1001 followed by the actual step of dialing 1002. As part of the dialing step 1002 a user enters, using, e.g., the telephone keypad, an access code identifying the desired long distance telephone carrier, and a destination number, i.e., the telephone number of the party being called. Both the access code and telephone number are represented as DTMF tones, i.e., touch tones, generated by the telephone in response to the keypad input.

The telephone system, e.g., the local switching office to which the telephone is linked, connects the caller to the appropriate long distance carrier represented by the access code input by the user. The long distance carrier then generates an audible signal/message indicating to the caller that it is ready to receive billing information as indicated in step 1003.

In response to the audible signal/message generated by the long distance carrier, the caller then inputs, e.g., using the telephone keypad, a credit card number as illustrated in step 1004. In response to receiving DTMF tones representing the credit card number, generated by the telephone, the long distance carrier checks the credit card number for validity as illustrated in step 1006. If the credit card number is determined to be valid, the call is placed as illustrated in step 1008. However, if the credit card number is determined to be invalid, the call is rejected and the telephone connection is disconnected as illustrated in step 1010.

The standard procedure for placing a call using a credit card has several drawbacks. For example, requiring a caller to manually input through the telephone keypad a carrier access number, a destination number, and a credit card number introduces into the calling procedure ample opportunity for a user to accidentally input an incorrect number for any one of the required values, which can exceed, e.g., 35 required inputs--more if the call is placed to or from a foreign country.

It is generally understood that the likelihood of entry errors increases in proportion to the number of digits to be entered. Such an error normally results in the call being rejected by the telephone carrier, requiring the caller to repeat the entire calling procedure from the point of connection to the long distance carrier. Generally, the long distance carrier pays fees to the company which owns the originating local switching office of the caller from the moment of connection, and is unable to start billing for the ultimate connection until the moment of connection. In such a case, each entry error is an increase in the unbillable time that a long distance carrier must absorb without any offsetting revenue.

Generally, the requirement that a caller manually input a large series of numbers to place a call leads to a higher error rate during call placement than results when the caller has to input fewer numbers, e.g., when calls are placed without the use of credit cards. In addition, requiring a caller to manually input a calling card number discourages some callers from using a credit card to place a call because of the additional time and frequent input errors associated with the initiation of a call as compared to calls placed without using credit cards.

In addition to error problems associated with the manual input of credit card number information, security problems are also associated with the manual input of credit card data into a telephone using a standard keypad. For example, a person viewing the initiation of a telephone transaction can record the credit card number input to the telephone keypad and then later use the calling card number to place unauthorized calls.

Portable electronic information cards and auto-dialers that are capable of being acoustically coupled to telephone systems to perform dialing functions are well known in the art.

Such known devices which generate a series of DTMF tones representing the numbers which must be input to initiate a call, have reduced or eliminated the need to input telephone number, carrier number, and credit card number information manually each time a call is placed.

Frequently, to enhance the versatility of such devices, they are made programmable with individual devices being programmed to store different telephone numbers, and/or calling card, credit card or personal identification numbers (PINs). While such programming is generally performed by electronically coupling such programmable devices to a programming unit, for example, as described in U.S. Pat. No. 4,882,750 to Henderson et al., it has been suggested that such devices should be designed to be capable of being programmed by acoustic signals received from a telephone. For example, PCT Patent Application Number 02837, now abandoned, suggests a portable electronic information card capable of being programmed in response to acoustic signals.

While known portable electronic information cards and auto-dialers that can be acoustically coupled to telephone systems facilitate telephone dialing and the supplying of billing information over the phone, the lack of a practical workable device which deals with past data transmission errors and security problems has inhibited widespread acceptance and use of such auto-dialer devices.

The introduction of errors into the data being sent to the telephone system, e.g., as the result of the use of an acoustic coupling, is one example of a data error problem that may prevent the telephone system from completing a call. As will be discussed in detail below, errors associated with the use of an acoustic coupling result from various factors affecting the acoustical transmission of DTMF tones. Such factors include variations between components used in present auto-dialers to generate the DTMF tones, temperature variations affecting battery voltages and the amplification levels applied to DTMF signals, speaker proximity to a telephone handset's microphone used to receive the acoustic DTMF tones, distortions introduced by the microphone receiving DTMF tones output by an auto-dialer, as well as, ambient noise levels. Errors may also be introduced from the lines that connect a caller to the ultimate telephone call destination as well as from other sources.

In addition to the error problems associated with the use of known auto-dialers, known devices for providing calling card and caller identification information acoustically to a telephone system present many security problems. For example, an unauthorized tape recording of a calling card number generated by the known systems, can easily be created by connecting an input cable to the telephone cable connected to a coin phone and then played back by an unauthorized user seeking to obtain access to the telephone system. Generally, the known calling card systems fail to provide a security method for preventing unauthorized users from gaining access to the telephone system via the use of such an unauthorized recording. Furthermore, known systems fail to prevent an unauthorized person from obtaining a calling card number and its related Personal Identification Number (PIN), both of which can be repeatedly used in their identical form for subsequent calls, through other methods, e.g., video-taping an authorized caller in a public place, going through the trash outside of large office facility, etc. Once known, calling card number and PIN data can be used to initiate multitudes of calls, often to foreign countries. The aggregate cost of the fraudulent use of unauthorized calling card calls in the United States is estimated to exceed $1 billion per year. While long distance carriers are now providing software analysis of many calls placed on their network to determine if there is a likelihood of unauthorized use, many such calls are paid by authorized customers who fail to notice the unauthorized calls on their bills.

Accordingly, there is a need to provide a secure device and method for storing and providing information regarding a user, and, more specifically, for providing such information locally or transmitting it remotely by, e.g., calling card, credit card, and user identification information either through or to a telephone system.

In addition to the reliability and security issues discussed above, there are also several convenience problems associated with known auto-dialer devices some of which are inherent in the standard credit card calling transaction illustrated in FIG. 1. These convenience problems include the need to generate and/or input separate telephone number and calling card identification information when attempting to place a credit card call. Furthermore, the procedures often used to initiate a calling card call often require that a user interlace carrier access codes (up to 20 digits) followed by the user's desired destination number (up to 17 digits) followed by an account/pin number array (usually at least 14 digits). These input sequences, which may expand in the future to accommodate greater call/user volumes are difficult sequences for a user to supply without input errors, and because of their complexity often result in users holding a publicly viewable card showing the account number and dialing sequences needed, creating security risks from unscrupulous users of calling card account and access data.

Additionally, because many countries have a distinct dialing sequence and numbering plan, carrier access codes are rarely identical from country to country, thereby increasing the difficulty that a traveler experiences when placing a calling card call.

Other convenience problems with the known devices relate to size and general ease of use issues. For example, known devices may be of such a size that it is inconvenient for a user to keep the device with them throughout the day. In addition, the size and shape of many of the known auto-dialers makes it difficult to properly align the auto-dialer with the microphone of a standard telephone handset making it somewhat difficult to use if accurate transmission of DTMF signals is to be achieved. Furthermore, the number of keys and the complexity of the controls frequently encountered on the known portable electronic information cards and auto-dialers have tended to inhibit the known devices from gaining widespread acceptance.

While the problems described above mainly refer to the problems and errors associated with the initiation of calling card calls, each of these problems may also affect access security and convenience in relation to any telephone based transaction (e.g. credit card purchases of over the phone, access to secure voice and data networks, etc.).

SUMMARY OF THE PRESENT INVENTION

The present invention provides a communication device capable of transmitting and receiving data. In accordance with the present invention, data may be encoded into a signal comprising a series of tones or tone pairs, e.g., a conventional DTMF signal, by controlling various identifiable components or aspects of the signal, e.g, the amplitude, frequency, lack of tone, or the period between tones, etc. When multiple signals are used, e.g., a combined Lo-frequency tone signal and a Hi-frequency tone signal, the twist, i.e., amplitude difference between the signals, may also be used to encode data.

In accordance with one embodiment of the present invention, the signal characteristics described above are used to encode data into a DTMF signal which is still detectable by a standard DTMF signal detector. In this manner, the present invention permits data to be embedded or encoded into a DTMF signal being used, e.g., to place a call. The embedded data may represent, e.g., a telephone calling card number, destination telephone number information or other data.

In one embodiment, the present invention is implemented as an auto-dialer also suitable for use as a smart card which is capable of transmitting and receiving information over conventional telephone lines, e.g., between a database and the auto-dialer, without the need for a specialized interface (other than a standard telephone). The auto-dialer of the present invention is capable of being acoustically coupled to the receiver of a telephone and being reprogrammed in response to acoustic signals. The programming and other features of the auto-dialer can be individually enabled or disabled in response to pre-selected signals, e.g., a string of DTMF tones received by the auto-dialer. In this manner, in one embodiment, the auto-dialer of the present invention requires an acoustic "key" to enable/disable some functions.

Using the encoding technique described above, an auto-dialer according to the present invention can encrypt calling card and other data into, e.g., destination telephone numbers by selectively altering pre-selected characteristics of a DTMF tone sequence, such as the duration of tones, the period of silence between tones and the twist between Lo-band and Hi-band tones of DTMF tone pairs in the conventional DTMF protocol which represent the desired destination telephone number. In accordance with the present invention, the encryption of data into the destination telephone number does not affect the ability of standard telephone switching equipment to recognize the destination number. However, information encrypted into the DTMF signals will be undetectable to standard telephone switching circuitry because it is encrypted using DTMF signal characteristics not normally used to represent data related to conventional call processing. In one embodiment, other tones or frequencies are also used to transmit data which cannot be detected by standard DTMF tone detectors.

In addition to the encryption capability described above, the auto-dialer of the present invention, in one embodiment, has a system clock that is used to drive a pseudo random number generator used in various data security schemes.

The auto-dialer of the present invention incorporates various calibration features which permit the calibration of the audio output and system clock. In one embodiment calibration adjustments are made by programming the auto-dialer with various calibration factors. This programming may be done by an acoustic coupling device incorporated into the auto-dialer or via another input device, e.g., wired to the auto-dialer either at the time of manufacture or over the phone at a later time. The calibration features permit the easy calibration of both the system clock and various characteristics of the tones generated by the auto dialer.

In addition to the various encoding and calibration features of the present invention, the present invention is also directed to a variety of security schemes and features which are designed to generally increase security when placing a telephone call and/or when providing other confidential or user-identification-related information.

Each of the above described features of the present invention, as well as numerous other features, will be described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating the steps involved with placing a standard telephone call using a credit card.

FIG. 2 is a schematic block diagram of an exemplary embodiment of an auto-dialer in accordance with one embodiment of the present invention.

FIG. 3 is a more detailed diagram of the auto-dialer illustrated in FIG. 2.

FIG. 4 is a diagram illustrating DTMF decoder circuitry suitable for use in the auto-dialer of FIGS. 2 and 3.

FIG. 5 is a diagram illustrating DTMF encoder circuitry suitable for use in the auto-dialer of FIGS. 2 and

FIG. 6 is a flow chart illustrating the steps associated with the placing of a credit card call using the auto-dialer of the present invention.

FIG. 7 is a block diagram of the auto-dialer of the present invention being coupled to a destination telephone via a carrier switching center.

FIG. 8A is a chart illustrating the fundamental difference between the tones of various DTMF tone pairs generated by standard DTMF generators.

FIGS. 8B-8E are charts illustrating the accept/reject and out-of-range frequencies, of a standard DTMF detector circuit, in relationship to each of the four fundamental Lo-band frequencies and four fundamental Hi-band frequencies used to generate standard DTMF signals.

FIG. 8F is a chart illustrating exemplary output levels of both carbon and electret microphones when receiving acoustic high-frequency tones associated with the DTMF tone pair representing the indicated digits.

FIG. 8G is a chart illustrating exemplary output levels of both carbon and electret microphones when receiving acoustic low-frequency tones associated with the DTMF tone pairs representing the indicated digits.

FIG. 9A is a chart illustrating the fundamental difference between the various tone pairs when the frequency of the Lo-band and Hi-band tones are selected, in accordance with the present invention, to reduce third tone errors.

FIG. 9B is a chart illustrating twist values of DTMF tone pairs generated in accordance with one embodiment of the present invention.

FIG. 9C illustrates acoustic output levels of Hi and Lo tones.

FIG. 10A is an illustration of a bottom view of one embodiment of the auto-dialer of the present invention.

FIG. 10B is an illustration of a top view of the auto-dialer illustrated in FIG. 10A.

FIG. 10C is an illustration a side view of the auto-dialer illustrated in FIG. 10A.

FIG. 10D is an illustration of a cut away side view of the auto-dialer illustrated in FIG. 10A.

FIG. 10E is an illustration of the auto-dialer illustrated in FIG. 10A mounted on a key ring.

FIG. 11 is a chart illustrating exemplary signal characteristic values, for a DTMF tone pair representing the digit 3, that can be used to represent data in accordance with the present invention.

FIG. 12A illustrates an exemplary Lo-band tone level to data conversion table in accordance with the present invention.

FIG. 12B illustrates an exemplary Hi-band tone level to data conversion table in accordance with the present invention.

FIG. 12C illustrates an exemplary tone duration to data conversion table in accordance with the present invention.

FIG. 12D illustrates an exemplary interdigit period duration to data conversion table in accordance with the present invention.

FIG. 12E illustrates an exemplary Lo-band tone frequency deviation to data conversion table in accordance with the present invention.

FIG. 12F illustrates an exemplary Hi-band tone frequency deviation to data conversion table in accordance with the present invention.

FIG. 12G illustrates an exemplary tone pair twist level to data conversion table in accordance with the present invention.

FIG. 13 illustrates a chart which displays the data conversion results obtained by using the signal characteristic values of chart 11 in conjunction with the conversion tables of FIGS. 12A through 12G to decode information encoded into a DTMF tone pair in accordance with the present invention.

FIG. 14 is a schematic block diagram of an access control device implemented in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention is directed to methods and apparatus for communicating data through the use of acoustic or electrical signals including, e.g., DTMF signals. Various embodiments of the present invention are directed to, e.g., portable acoustically coupled auto-dialers, calling cards, credit cards, paging devices, smart cards, and other information card type devices, debit cards, etc. In addition to such portable embodiments, several embodiments of the present invention are directed to telephone switching circuitry and DTMF and other tone recognition circuitry which may be incorporated into existing telephone systems, as well as other data systems.

Referring now to FIG. 2 there is illustrated an auto-dialer device, generally indicated by the reference numeral 100, in accordance with one exemplary embodiment of the present invention. As illustrated, the auto-dialer 100 comprises a microprocessor 104 coupled to a read only memory (ROM) 106, device control keys 105, and a random access memory (RAM) 108. The ROM 106 may be located within the microprocessor 104 or externally thereto.

Via device control keys 105, the microprocessor 104 receives input signals from a user, which input is stored in the RAM 108 or processed by the microprocessor 104 using other information stored in the ROM 106. In addition, in various embodiments, the RAM 108 is used to store data relating to voice signals and/or tone signals.

The auto-dialer 100 further comprises a DTMF encoder 110 and a DTMF decoder 112 which are coupled to the microprocessor 104 and to a speaker/microphone 114. In the illustrated embodiment, the speaker/microphone 114 serves as both an input device for receiving acoustic signals, such as DTMF tones, and as an output device for outputting signals such as DTMF tones and other signals generated by the encoder 110. In other embodiments, a separate microphone is used for receiving audio signals and the speaker/microphone 114 is used only for outputting signals.

As illustrated in FIG. 2, the auto-dialer 100 may be acoustically coupled to a standard telephone 122 such as a public pay phone. While the speaker/microphone 114 is illustrated in FIG. 2 as receiving a signal from and sending a signal to, a telephone handset 121, it is to be understood that the speaker/microphone 114, in this embodiment, can not be used to perform these operations simultaneously. Furthermore, it should be noted that when receiving signals from the handset 121, the speaker/microphone 114, which serves as a transducer, is positioned in close proximity to the handset's speaker 120 and while sending signals to the handset's microphone 118 the speaker/microphone 114 is positioned in close proximity to the microphone
118. Thus, to change between the send and receive functions, in the illustrated embodiment, a user must move the auto-dialer 100 from being in close proximity to the microphone 118 to a position where it is in close proximity to the speaker 120. However, in another embodiment, a separate microphone is included for the receipt of data in addition to the speaker/microphone 114. In accordance with such an embodiment, data may be received and transmitted simultaneously by the auto-dialer 100, without the requirement of moving the auto-dialer 100.

In another embodiment, the auto-dialer 100 is designed to acoustically monitor its output and perform an auto-calibration sequence prior to or at the beginning of each period of use of the auto-dialer 100 which follows a period of dormancy of a preselected time period, e.g., a selected number of hours or days or when the autodialer 100 senses a temperature outside of a preselected temperature range, e.g., representing the temperature the autodialer 100 is expected to work at.

As is well known, battery voltage output varies as a function of temperature. Variations in voltage output are particularly noticeable in cold weather. Additionally, other components of the autodialer 100 are subject to the effects of temperature. Accordingly, in one embodiment, the autodialer 100 incorporates an auto-calibration feature which causes the generation of a preselected group of tones used for calibration purposes. As these tones are generated, the microphone 109
receives the tones and converts them to electrical signals which are analyzed by the microprocessor 104. The microprocessor 104 analyzes the generated signal levels and compares them against stored desired signal level values. In the event that an adjustment is required in any tone output level, or other signal characteristic, the microprocessor 104 calculates the appropriate change, and alters a tone generation control parameter stored in the RAM 108 to correct the output signal level. The autodialer 100 may then re-test the generation of the tone which had a tone signal level problem to insure accurate generation of the tone to insure that the calculated parameter change produced the desired result. If the desired output level was not achieved, the microprocessor 104 repeats the calibration sequence. In one embodiment, when it is detected that a tone signal level fails to achieve the pre-determined level, e.g., desired signal level after one or more attempts to adjust the output level, the auto-dialer 100 indicates a "don't use" condition on a display device 202.

Referring now to FIG. 3, the auto-dialer 100 of FIG. 1 is illustrated in greater detail. In FIG. 3, components that are the same or similar to those of FIG. 2, will be referred to using the same reference numerals as used in FIG. 2. As illustrated in FIG. 3, the auto-dialer 100 may further comprise the display device 202 for displaying data and other information output by the microprocessor 104 and/or system components, a main battery 208 for powering the auto-dialer 100, a back-up battery 206 for supplying power to the microprocessor 104 as well as other system components when the main battery fails, and a voltage comparator 210 for detecting the condition of the main and backup batteries 206, 208.

As illustrated in FIG. 3, the auto-dialer further includes a micro-power amplifier 226 coupled to the output of the speaker/microphone 114. The amplifier 226 serves to provide a wake-up signal to the microprocessor 104 as described below. The amplifier 226 generates a signal in response to a signal generated by the speaker 114 in response to received acoustic signals. The signal output by the amplifier 226 causes the microprocessor 104 to become fully active from, e.g., a sleep mode which is automatically entered into after a long period of inactivity in order to conserve power. In an alternative embodiment, an input of the microprocessor 104 is coupled to a light sensor or other activation device such as a radio frequency sensor, which causes the auto-dialer 100 to become fully active in response to an outside stimulus which may be provided by, e.g., a light or sound source associated with an automatic teller machine (ATM) or telephone device. Thus, in accordance with such an embodiment the auto-dialer 100 can be made active by the excitation of a transducer or other sensor by, e.g., a light, radio frequency signal or the receipt of an acoustic signal having a pre-defined frequency and a minimum, pre-defined intensity level. These pre-defined levels or values are a matter of design choice and may be programmed into the ROM 106 or RAM 108 at, e.g., the time of manufacture.

With regard to "wake-up" features, in one embodiment, the auto-dialer 100 incorporates a reflective surface, e.g., a reflective ring 160 as illustrated in FIG. 10A or other component which can be detected by an interface of e.g., an ATM machine. For example, an ATM machine may detect the presence of the auto-dialer 100 because of its unique shape when it is place in contact with the ATM machine. As will be discussed below, with regard to FIG. 10A, the auto-dialer 100 may include a notch or cut out designed to mate with the shape of the input area of the interface with which the auto-dialer 100 is intended to communicate. Because of the auto-dialer's reflective ring 160 shape, or other physical characteristic, the interface of the machine with which the auto-dialer 100 is designed to communicate can detect the presence of the auto-dialer 100 and signal the auto-dialer through, e.g., a series of tones, to become active, e.g., "wake-up". Accordingly, the auto-dialer 100 permits interfacing hardware to recognize the presence of the autodialer 100 by, e.g., the presence of a highly reflective material, e.g., a mirrored film or other similar material, which reflects an emitted light from the interfacing hardware in such a fashion as to cause a light detecting sensor in the interfacing hardware to sense the reflection of such light, and upon the sensation of such light, cause the interfacing hardware to emit a pre-determined set of tones which will cause the autodialer 100 to become active and enter a mode of operation which may not otherwise be available to the user.

The ROM 106 includes a series of memory locations which contain information that serves as a set of permanent data tables, as well as a computer program instructions for controlling the operation of the microprocessor 104. The permanent data tables may contain e.g., long distance carrier information, area code information, data encoding/decoding information, and/or credit service related information as will be described further below.

The RAM 108, on the other hand, is used to store information that is device dependent, is likely to change, or for other reasons is more easily stored in an alterable memory device than in a ROM. As illustrated by the representative memory map
211, the RAM 108 may dedicate memory space to storing DTMF transfer and receive parameters 214 used for encoding/decoding signals, mode tone pairs information 216, e.g., frequency information relating to supported tone pairs, display memory 218, system control data 224, e.g., calibration parameters, user data 222, (e.g., destination phone numbers and billing information relating to the individual who is authorized to use the auto-dialer 100) and device data 220, (e.g., one or more numeric or alpha-numeric sequences which identify the particular auto-dialer 100, manufacturing date information, etc.).

A circuit suitable for use as the DTMF decoder circuit 112 illustrated in FIGS. 2 and 3 will now be described with reference to the schematic block diagram of FIG. 4. As illustrated in FIG. 4, the DTMF decoder circuit 112 comprises an amplifier and filter circuit 302 that has an input coupled to the output of the speaker/microphone 114 and a received signal output coupled to the input of a Hi-band passband filter 304 and a Lo-band passband filter 306. In this embodiment, the speaker 114 acts as an inductor converting acoustic signals received from, e.g., the speaker 120 of the telephone handset 121, into electrical signals which are amplified and filtered by the amplifier and filter circuit 302 and then further filtered by the passband filters 304, 306. The Hi-band passband filter 304, is designed to pass the corresponding Hi-band frequency DTMF signals while eliminating noise and other signals. Similarly, the Lo-band passband filter 306 is designed to pass the Lo-band frequency DTMF signals and to eliminate other signals. In this manner, the Lo-band and Hi-band signals are segregated from each other with noise, i.e., signals having frequencies outside the bands of the DTMF signals being removed to facilitate the later decoding of the signals.

An output of the Hi-band filter 304 is coupled to the input of a column frequency detector 308 for detecting which frequency of the set of Hi-band tone frequencies is being received. Similarly, the Lo-band filter 306 has an output coupled to an input of a row frequency detector 310 for detecting which frequency of the set of Lo-band frequencies is being received. In particular embodiments, the column and row frequency detectors 308, 310 as well as Hi and Lo band filters 304, 306 may be designed to recognize and pass additional Hi-band and Lo-band tones, respectively, which are outside the range of standard DTMF tones to thus increase the number of signals which can be used to transmit data to add additional security, increase data transmission rates, or provide additional features.

An output of the column frequency detector 308 and an output of the row frequency detector 310 are coupled to corresponding inputs of a DTMF signal detector 312. The DTMF signal detector 312 receives the Lo-band and Hi-band tones output by the column and row frequency detectors 308, 310 along with information signals indicating the frequency of the received tones. The DTMF detector 312 determines if the received tones constitute a valid tone pair or other signal which the DTMF signal detector
312 is programmed to recognize. If the DTMF signal detector 312 detects a valid tone pair or a signal it recognizes, it sends a signal to a DTMF tone to data converter circuit 316 of the microprocessor 104 to convert the detected DTMF tone or signal into the data it represents, e.g., a symbol or number.

Because the auto-dialer 100 is programmable, it may be programmed or reprogrammed to accept one or more signals as valid tones. These tones may include tones other than those used for standard DTMF signals. Furthermore, it can be programmed to reject or ignore input data which does not conform to predetermined signal characteristics which are stored in the RAM 108 of the auto-dialer 100. In one embodiment, these signal characteristics (e.g. maximum tone-length) may be remotely modified via, the acoustic reprogramming of the auto-dialer 100 in response to the auto-dialer 100 receiving a series of DTMF tones. Such tones act as a signal or key which is required to enable the reprogramming of the auto-dialer 100. In addition, because the auto-dialer 100 is designed to be both responsive to, and capable of, generating audio tones, e.g., both standard and encoded DTMF tones, as will be described below, the auto-dialer 100 is capable of receiving, storing and transmitting both standard and encoded DTMF tones for a variety of purposes including for use as passwords and "keys" to enable certain functions of the auto-dialer 100 or the device which the auto-dialer 100 is used to communicate with.

In yet another embodiment, the auto-dialer 100 is programmed to, upon the receipt of pre-selected series or group of tones, representing commands or instructions to the microprocessor 104, perform mathematical computations based on either data stored within the auto-dialer 100 and/or on data which is received by the auto-dialer 100 in response to the received commands. In such an embodiment, the performed computation(s) is in accordance with a received instruction and is performed in such a manner that a user can not effect the result of the computation by manipulating the keys on the auto-dialer 100. In this manner, the auto-dialer 100, because of its programming and ability to receive commands and data from an outside source, can perform, e.g., debit/credit calculations with the user being unable to manipulate the result from the device control keys 105 of the auto-dialer 100. Additional security features to prevent unauthorized manipulation of data stored in various locations within the memory 106, 108 of the auto-dialer 100 will be discussed below.

As discussed above, for security reasons, the reprogramming feature is, in some embodiments, enabled only upon the receipt of a pre-selected group of acoustic tones which serve as a key to indicate to the auto-dialer 100 that an authorized individual is in fact reprogramming the device. Different acoustic keys or tone sequences may be used to limit access to different memory locations. In this manner, one key, e.g., a series of tones, may be required to reprogram one memory location while another key may be required to reprogram another memory location. In this manner, the ability to alter the contents of various memory locations containing, e.g., personal identification telephone numbers, prefix information, etc. can be restricted so that the user cannot change the contents of certain memory locations and so that only services authorized to alter particular items in memory, e.g., dialing prefixes, country codes, etc. can alter such information. In such an embodiment, a first series of tones is required to alter the contents of a first memory location while a second series of tones is required to alter a second memory location. Additional tone sequences or "keys" may be associated with additional memory locations.

In one embodiment, the DTMF signal detector 312 of the present invention referred to as an enhanced DTMF signal detector is able to detect alterable characteristics of a DTMF signal, e.g., signal twist, Lo-band and Hi-band tone amplitude, Lo-band and Hi-band tone duration, tone frequency, etc. which may be used to encode information into a DTMF signal without affecting the ability of a standard DTMF signal detector to detect the symbol/number represented by a DTMF tone pair. If the DTMF signal detector 312 detects encoded information the encoded information is supplied to the DTMF tone to data converter 316 for processing. A particular signal or sequence of tones is used in some embodiments to provide an indicator signal to indicate to a receiver that encoded DTMF signals are being transmitted. In such embodiments, a DTMF signal detector detects the receipt of encoded DTMF signals by checking a received signal for such an indicator signal or indicator sequence of tones.

The DTMF signal detector 312 also has start and stop signal outputs coupled to corresponding inputs of a non-tone demodulation circuit 314 of the microprocessor 104. In this manner, the non-tone demodulation circuit 314 receives timing information concerning the starting and stopping of each received signal. As will be discussed below, this information can be used, in accordance with one embodiment of the present invention, for decoding information encoded into one or more DTMF signals and/or for distinguishing of a string of signals which represent meaningful data as opposed to nonsense signals added for security reasons as well as to enable the device to provide non-frequency dependent data that is encoded into the interdigit periods, i.e., the time between DTMF tone pairs.

Referring now to FIG. 5, DTMF encoder circuit 110, which may be used as illustrated in FIGS. 2 and 3, will now be described in detail. The DTMF encoder 110 comprises a high frequency register 424, a tone select register 426, and a low frequency register 428.

The high and low frequency registers 424, 428 have a first input coupled to a data output of the microprocessor 104, a second input coupled to a tone select output of the microprocessor 104 and a third input coupled to a tone select signal output of the tone select register 426.

The tone select register 426 receives tone signal information from a tone store output of the microprocessor 104 which is then processed to generate a control signal which is supplied to the low and high frequency registers 424, 428 through the third input of the registers 424, 428.

The high and low frequency registers 424, 428 are responsive to signals received from the microprocessor 104 and the tone select register 426 to produce a control signal indicating the fraction of the microprocessor's clock frequency the desired Hi and Lo tones correspond to.

The Hi-band DTMF tone of each DTMF tone signal pair is generated by a Hi-band frequency signal generation circuit 401. The Hi-band frequency signal generation circuit 401 comprises a programmable divider 430, which is coupled to a Johnson counter 434. The Johnson counter 434 is coupled to digital to analog converter 438 which has an output coupled to an amplifier 458 which is responsible for amplifying the Hi-band DTMF tone signals of each tone pair.

The programmable divider 430 receives as input signals the output of the high frequency register 424 and the microprocessor's oscillator. Using the control information provided by the high frequency register 424, the programmable divider generates a digital signal having the desired frequency of the Hi-band tone to be generated from the oscillator signal. This digital signal is then further processed by the Johnson counter 434 before being converted into an analog signal by the D/A converter 438.

It should be noted that to avoid the problems that may result from harmonics associated with squarewaves, the D/A converter 438 only generates pure sine waves. The analog Hi-tone output signal, output of the D/A converter 438, is amplified by the amplifier 458 which has a gain control input coupled to a Hi-band amplitude control signal output of the microprocessor 104.

As will be discussed below, the degree of amplification performed by the amplifier 458 is controlled by the microprocessor 104. In this manner, the microprocessor 104 can introduce intentional twist into the DTMF signal being generated and/or encode information into the DTMF signal by selectively varying signal strength and/or twist associated with the tone pairs comprising the DTMF signal being generated.

A Lo-band frequency signal generation circuit 403 comprising a programmable divider 432, a Johnson counter 436, a (D/A) digital to analog converter 440, and an amplifier 460 is responsive to the output of the low frequency register 428, the microprocessor's oscillator, and the microprocessor's Lo-band amplitude control signal, to generate the Lo-band DTMF tone in the same manner as described above with regard to the generation of Hi-band DTMF tones.

The output of each of the amplifiers 458 and 460 which comprise the Hi-band and Lo-band tones, respectively, of each DTMF tone pair being generated, are supplied to first and second inputs of a dual ported amplifier 462 for additional amplification. The amplifier 462 has a control input which is coupled to a timing control output of the microprocessor 104.

The timing control signal is used to control the amount or level of amplification the amplifier 462 provides. In addition, by asserting the timing control signal the microprocessor 104 enables the amplifier 462 during periods of data transmission. On the other hand, when the speaker/microphone 114, which has an input coupled to the output of the amplifier 462, is being used as a receiving device or microphone, the microprocessor 104 de-asserts the timing control signal thereby deactivating the amplifier 462 and thus the output of the DTMF tone encoder 110. The timing control signal may also be used to inhibit signal output during the interdigit periods.

Various features of the present invention, directed to overcoming the data error, security and convenience problems associated with known auto-dialer devices will now be described with reference to the auto-dialer 100.

Each feature of the present invention will be discussed in detail below beginning with a discussion of the features of the present invention which are directed to reducing the error rate associated with the acoustic transmission of information represented by DTMF signal tones, e.g., telephone number and credit card number information, from the auto-dialer 100 of the present invention to a DTMF signal receiver such as a telephone handset 121. This particular feature of the present invention may be described as an error avoidance feature.

I. Error Avoidance Features

In accordance with the present invention, several methods are used to avoid or compensate for the occurrence of errors commonly associated with the acoustic transmission of a DTMF signal to a standard telephone system, e.g., a handset. These methods are directed to eliminating, or compensating for, common sources of errors that are associated with acoustic transmission of a DTMF signal. The methods of error avoidance of the present invention will generally be discussed according to the source of the error and the particular method of the present invention directed to eliminating or compensating for such error sources.

A. Third Tone Errors

One of the most common sources of errors associated with known acoustically coupled auto-dialers is generally referred to as the "third tone" problem. This problem is, as the name suggests, associated with the detection of a third, otherwise valid tone, at the detector stage of a receiver where a DTMF tone signal is being decoded. As described above, a DTMF tone signal is only considered valid if it includes a single pair of valid tones, i.e., one valid Hi-band tone and one valid Lo-band tone. Thus, when multiple valid Hi-band or Lo-band tones are received at the same time, the DTMF signal is considered invalid and can not be properly decoded. The relative amplitude of a received tone compared to the other received tones may, in some cases, be used to distinguish valid tones from erroneous invalid tones.

When used as collectors of DTMF tones, carbon based microphones, which are commonly used in standard telephone handsets because of their low cost and high degree of reliability, often generate and transmit erroneous tones, e.g., third tones, in addition to the tones actually received by the microphone. Such errant third tones can cause errors in some tone detection receivers, and particularly those systems which do not utilize digital signal processing equipment for tone detection.

The transmission of DTMF tone signals through carbon microphones causes the carbon granules within the carbon microphone to vibrate in relation to the driving frequencies. As a result of the harmonic effect of the varying vibrations of the granules, various residual tones are generated, with the third tone being the most powerful of these residual tones. This third tone can be relatively powerful, e.g. as much as one half the power level of the higher of the two received acoustic DTMF tones passing through the microphone. The frequency of this third tone will normally be the arithmetic difference between the frequencies of Hi-band and Lo-band tones being received by the carbon microphone.

Referring now to FIG. 8A, there is illustrated a chart with four columns. In the chart, the number or symbol in the first column 11 represents those numbers or symbols available on a standard telephone keypad. The second column 13 represents the Lo-band frequency associated with the corresponding number or symbol in the first column 11 while the third column 15 represents the corresponding Hi-band frequency. The fourth column 17 represents the fundamental difference between the Lo-band and Hi-band frequencies listed in columns two and three 13, 15. It is this fundamental difference in frequency that represents the frequency of the third tone that is generated by a carbon microphone when the corresponding Lo-band and Hi-band frequencies are received. As will be discussed further below, the fundamental difference frequency, or third tone frequency associated with the symbols/numbers 3, 6, a, b, c, and d will fall within the passband of the filters of many standard DTMF detectors.

The third tone error problem is particularly significant with regard to the tone pairs representing the numbers symbols 3, 6, a, b, c, and d because, in their case, the third tone created from the harmonic effect associated with the carbon microphone falls within the tolerance range of the low frequency band tones and the band pass filters corresponding to these frequencies. Thus, in the case of these numbers and symbols, the third tone signal will fall within the passband of the filters of many standard DTMF detectors and will therefore not be filtered out.

As discussed above, the presence of such an errant tone within the frequency range of valid tones, may cause a detector to detect two valid Lo-band tones, when only one should be present. While the power level of the deliberately generated tone will normally be much higher than the errant signal tone, without the use of digital signal processing which is able to select the tone with the higher power level, a detector will have difficulty in determining which of the two Lo-band tones received should be used. Normally, when the DTMF detector is unable to select the valid or deliberate tone from the two Lo-band tones, the DTMF tone detector will ignore the tone-pair signal which includes the third tone, causing the entire dialed string to be lacking the errant digit and, thus, preventing the connection of the call or the completion of a data string being used for other purposes.

While the third tone will not always be of such an intensity that it results in an error, and while digital signal processing in DTMF detectors is becoming more common, for an acoustically coupled auto-dialer 100 to offer maximum versatility it must be capable of transmitting telephone and credit card number information accurately to the vast majority of existing telephone systems including those that do not perform such digital signal processing. Accordingly, the third tone problem associated with carbon microphones needs to be reduced or compensated for to increase the reliability of acoustically coupled auto-dialers if such auto-dialers are to work reliably with the vast majority of existing telephone systems.

The present invention, addresses the third tone problem in two ways. The first approach is directed to avoiding using symbols/numbers which are likely to produce third tone errors. The second approach is directed to altering the nominal frequency of the tones which are likely to generate third tone errors in an attempt to avoid such errors.

i. Avoidance of the Use of Symbols/Numbers Likely to Produce Third Tone Error Problems

As discussed above, the first approach of the present invention for dealing with the third tone problem revolves around avoiding the use of numbers/symbols that are most likely to produce the problem in the first place, i.e., the numbers/symbols
3, 6, a, b, c, and d. Because most credit card, calling card, and telephone numbers use only the digits 0 through 9 found on standard, non-extended keypads such as those found on pay phones, most third tone problems can be eliminated by merely avoiding the use of the numbers 3 and 6.

Thus, in accordance with one embodiment of the present invention, when assigning numbers, e.g., telephone numbers which must be used to obtain connection, e.g., via a local telephone switching office which may not contain digital signal processing equipment, to a central office, only the digits 0, 1, 2, 4, 5, 7, 8, and 9 are used. In this manner, third tone problems associated with the numbers/symbols 3, 6, a, b, c, and d are avoided when sending information to telephone switching offices which may not have digital signal processing equipment capable of distinguishing the actual tone from the undesired third tone signal.

Once a connection has been made to a telephone switching network with digital signal processing equipment, such as the type currently found in most long distance carrier telephone switching offices, the risk of errors due to third tone problems will be greatly reduced. Thus, all digits may be used including 3, 6, a, b, c, and d once a connection has been established to a system known to include digital signal processing equipment. Accordingly, the primary time for avoiding the digits associated with third tone problems is when establishing connections to local offices or other telephone switching networks which may not contain the digital signal processing circuitry required to avoid third tone problems.

By avoiding the use of the numbers/symbols 3, 6, a, b, c, and d in the above described manner, the vast majority of third tone problems can be avoided without the need for digital signal processing circuitry in a DTMF detector and without modifying the DTMF signal generator.

ii. Generation of Tone Pairs Wherein the Arithmetic Difference of the Generated Tones Comprising Each Tone Pair Will Fall Outside the Range of the Bandpass Filters Included in Standard DTMF Detectors

The second approach of the present invention to avoiding third tone error problems involves the generation of tone pairs wherein the arithmetic difference between the generated tones comprising each tone pair will fall outside the range of the bandpass filters included in standard DTMF generators.

Because of manufacturing tolerances and component differences, DTMF generators will vary slightly in output frequency from one DTMF signal generator to another even though the nominal frequencies, which represent the frequencies the DTMF generators are designed to produce, will normally be the same. Thus, DTMF detectors are designed to detect, i.e., accept as valid, a range of frequencies corresponding to the Lo-band and Hi-band DTMF tone frequencies.

Referring now to FIG. 8B, there is illustrated a chart of the frequency accept range of a standard DTMF detector circuit. As illustrated, the accept range is .+-.1.5%+2 Hz of the nominal frequency illustrated in the center column of the chart shown in FIG. 8B. Referring now to FIG. 8C there is illustrated a chart of the frequency reject range of a standard DTMF detector circuit. As illustrated, the reject range is .+-.3.5% of the nominal frequency illustrated in the center column of FIG.
8C. Referring now to FIG. 8D, there is illustrated a chart of the out of range frequencies of a standard DTMF detector circuit. These frequencies represent frequencies outside the accept/reject ranges of a standard DTMF detector which cannot be recognized by a standard DTMF detector circuit in a reliable manner. Referring now to FIG. 8E, there is illustrated a composite chart of standard DTMF tone detector circuit reject and acc