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Systems, methods and devices are described that provide a three-state control signal across a single electrical conductor. A three-position switch provides an output signal that selects between the first reference voltage, a second reference voltage and an intermediate voltage. The output from the

Systems, methods and devices are described that provide a three-state control signal across a single electrical conductor. A three-position switch provides an output signal that selects between the first reference voltage, a second reference voltage and an intermediate voltage. The output from the switch is transmitted to a voltage divider circuit that produces a predetermined result when the switch output corresponds to the intermediate state. The output of the voltage divider is then provided to an analog-to-digital converter to decode the state of the switch. The three-state control signal may be used, for example, to place a vehicle component such as a windshield temperature controller or rear-window defogger into a desired one of three operating states. Similarly, the three-state concepts may be widely applied in many automotive, industrial, consumer electronics and other settings.

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What is claimed is: 1. A signal communications apparatus having an output that is switchable between three states, the signal communications apparatus comprising: a three-position input device having a first terminal coupled to a first reference voltage and a second terminal coupled to a second ref

What is claimed is: 1. A signal communications apparatus having an output that is switchable between three states, the signal communications apparatus comprising: a three-position input device having a first terminal coupled to a first reference voltage and a second terminal coupled to a second reference voltage, wherein the three-position input device is configured to select a switch output signal from the first reference voltage, the second reference voltage and an intermediate state; and a voltage divider circuit coupled to the first and second reference voltages and having a common node therebetween, wherein the voltage divider circuit is configured to receive the switch output signal at the common node and to produce a predetermined voltage at the common node when the switch output corresponds to the intermediate state to thereby produce the output of the signal communications apparatus. 2. The signal communications apparatus of claim 1 wherein the output of the signal communications apparatus is produced at the common node. 3. The signal communications apparatus of claim 1 wherein the voltage divider circuit comprises a first resistor and a second resistor coupled to the first and second reference voltages, respectively. 4. The signal communications apparatus of claim 3 wherein the switch output signal is a continuous signal. 5. The signal communications apparatus of claim 3 wherein the switch output signal is a momentary signal. 6. The signal communications apparatus of claim 3 further comprising a second voltage divider electrically coupled between the common node and the output of the signal communications apparatus, wherein the second voltage divider is configured to adjust the output of the signal communications apparatus when the switch output corresponds to the intermediate state. 7. The signal communications apparatus of claim 6 wherein the second voltage divider comprises a third resistor coupled between the common node and the output of the signal communications apparatus and a fourth resistor coupled between the output of the signal communications apparatus and the second reference voltage. 8. The signal communications apparatus of claim 1 wherein the intermediate state corresponds to an open circuit. 9. The signal communications apparatus of claim 1 wherein the switch output signal is produced from the first and second reference voltages and the intermediate state without voltage division in the three-position input device. 10. The signal communications apparatus of claim 9 wherein the three-position input device is further configured to provide mechanical interlocking between the three output states of the three-position input device. 11. A circuit for providing a three-state input to an analog-to-digital converter, the circuit comprising: a three-position switch having a first terminal coupled to a first reference voltage and a second terminal coupled to a second reference voltage, wherein the three-position switch is operable to select a switch output signal from the first reference voltage, the second reference voltage and an intermediate state; and a voltage divider circuit comprising a first resistor and a second resistor coupled to the first and second reference voltages, respectively, and having a common node therebetween corresponding to the input of the analog-to-digital converter, wherein the voltage divider circuit is configured to receive the switch output at the common node and to provide a predetermined voltage at the common node when the switch output corresponds to the intermediate state. 12. An electrical switching apparatus comprising: a switch having three operating states; a wire coupled to the switch to transmit an analog signal corresponding to one of the three operating states; a voltage divider coupled to the wire to receive the analog signal; and an analog-to-digital (A/D) converter coupled to the voltage divider, wherein the A/D converter is configured to determine the operating state of the switch from the analog signal. 13. A electronic switching system for placing a vehicle component into a desired one of three states, the switching system comprising: a three-position input device having a first terminal coupled to a first reference voltage and a second terminal coupled to a second reference voltage, wherein the three-position input device is operable to select a switch output signal from the first reference voltage, the second reference voltage and an intermediate state; a voltage divider circuit configured to receive the first and second reference voltages and having a common node located therebetween, wherein the voltage divider circuit is configured to receive the switch output at the common node and to provide a voltage divider output corresponding to a predetermined voltage when the switch output corresponds to the intermediate state, and otherwise to provide the voltage divider output corresponding to the switch output; and an analog-to-digital converter configured to receive and decode the voltage divider output to thereby place the vehicle component into the desired state. 14. The electrical switching system of claim 13 wherein the intermediate state corresponds to an open circuit. 15. The electrical switching system of claim 14 wherein the open circuit condition corresponds to a diagnosable state of the vehicle component. 16. The electrical switching system of claim 13 wherein the vehicle component is a windshield temperature controller. 17. The electrical switching system of claim 16 wherein the first reference voltage corresponds to a high temperature state, the second reference voltage corresponds to a low temperature state, and the intermediate state corresponds to an "off" state of the windshield temperature controller. 18. The electrical switching system of claim 16 wherein the second reference voltage corresponds to an electrical ground and the intermediate state corresponds to an open circuit. 19. The electrical switching system of claim 13 wherein the vehicle component is a rear window defogger. 20. The electrical switching system of claim 19 wherein the first reference voltage corresponds to a high temperature state, the second reference voltage corresponds to a low temperature state, and the intermediate state corresponds to an "off" state of the rear window defogger. 21. The electrical switching system of claim 20 wherein the second reference voltage corresponds to an electrical ground and the intermediate state corresponds to an open circuit. 22. The electrical switching system of claim 13 wherein the vehicle component is a heater for a seat in the vehicle. 23. The electrical switching system of claim 22 wherein the seat is a driver's seat. 24. The electrical switching system of claim 22 wherein the seat is a passenger's seat. 25. The electrical switching system of claim 22 wherein the first reference voltage corresponds to a high temperature state, the second reference voltage corresponds to a low temperature state, and the intermediate state corresponds to an "off" state of the heater. 26. The electrical switching system of claim 13 wherein the vehicle component is a power mirror selector. 27. The electrical switching system of claim 26 wherein the first reference voltage corresponds to a passenger mirror selected, the second reference voltage corresponds to a driver mirror selected, and the intermediate state corresponds to neither mirror being selected. 28. The electrical switching system of claim 13 wherein the vehicle component is a windshield wiper speed selector. 29. The electrical switching system of claim 28 wherein the first reference voltage corresponds to a first speed of the windshield wiper, the second reference voltage corresponds to a second speed of the windshield wiper, and the intermediate state corresponds to an off state of the windshield wiper. 30. The electrical switching system of claim 13 wherein the vehicle component is a power window controller. 31. The electrical switching system of claim 30 wherein the first reference voltage corresponds to a window lowering function, the second reference voltage corresponds to a window raising function, and the intermediate state corresponds to no window actuation. 32. The electrical switching system of claim 13 wherein the vehicle component is a power door lock controller. 33. The electrical switching system of claim 32 wherein the first reference voltage corresponds to a door unlocking function, the second reference voltage corresponds to a door locking function, and the intermediate state corresponds to no door lock actuation. 34. The electrical switching system of claim 13 wherein the vehicle component is a power lumbar function controller. 35. The electrical switching system of claim 34 wherein the first reference voltage corresponds to a decrease in the lumbar support, the second reference voltage corresponds to an increase in the lumbar support, and the intermediate state corresponds to no actuation of the lumbar support. 36. The electrical switching system of claim 13 wherein the vehicle component is an exterior light controller. 37. The electrical switching system of claim 36 wherein the first reference voltage corresponds to parking lamp on condition, the second reference voltage corresponds to a headlamps on condition, and the intermediate state corresponds to a no exterior lights on condition. 38. The electrical switching system of claim 37 wherein the headlamps on condition comprises both headlamps and parking lamps being in an on condition. 39. The electrical switching system of claim 13 wherein the vehicle component is a power sunroof control. 40. The electrical switching system of claim 39 wherein the first reference voltage corresponds to a sunroof close actuation, the second reference voltage corresponds to a sunroof open actuation, and the intermediate state corresponds to no actuation of the power sunroof. 41. The electrical switching system of claim 13 wherein the vehicle component is a personalization selector. 42. The electrical switching system of claim 41 wherein the first reference voltage corresponds to a first personalization, the second reference voltage corresponds to a second personalization, and the intermediate state corresponds to neither personalization. 43. The electrical switching system of claim 41 wherein the personalization selector is a selector for a seat in the vehicle. 44. The electrical switching system of claim 13 wherein the vehicle component is a power extended mirror control. 45. The electrical switching system of claim 44 wherein the first reference voltage corresponds to a retraction of the power extended mirror, the second reference voltage corresponds to extension of the power extended mirror, and the intermediate state corresponds to no power extended mirror actuation. 46. The electrical switching system of claim 13 wherein the vehicle component is a power seat control. 47. The electrical switching system of claim 46 wherein the first reference voltage corresponds to an actuation of the power seat in a first direction, the second reference voltage corresponds to an actuation of the power seat in a second direction, and the intermediate state corresponds to no actuation of the power seat. 48. The electrical switching system of claim 13 wherein the vehicle component is a power seat incline control. 49. The electrical switching system of claim 48 wherein the first reference voltage corresponds to a recline of the power seat, the second reference voltage corresponds to an incline of the power seat, and the intermediate state corresponds to no actuation of the power seat. 50. The electrical switching system of claim 13 wherein the vehicle component is a channel seek selector for a vehicle audio system. 51. The electrical switching system of claim 13 wherein the vehicle component is a volume control for a vehicle audio system. 52. The electrical switching system of claim 13 wherein the vehicle component is a vehicle temperature control. 53. The electrical switching system of claim 13 wherein the vehicle component is a set/resume selector for a vehicle cruise control. 54. The electrical switching system of claim 13 wherein the vehicle component is a transmission up/down shift selector. 55. An electrical switching system capable of diagnosing a fault condition relating to a vehicle component, the electrical switching system comprising: a switch operable to select a switch output signal from a first state and a second state; a voltage divider circuit configured to receive the switch output signal and to provide a voltage divider output in response to the switch output signal, wherein the three-state voltage divider output comprises one of three states corresponding to the first and second states of the switch output signal in addition to a diagnosable state, wherein the diagnosable state corresponds to the fault condition; and an analog-to-digital converter configured to receive and decode the voltage divider output to thereby place the vehicle component into the desired state and to identify the fault condition if the diagnosable state occurs. 56. The electrical switching system of claim 55 wherein the diagnosable state comprises an open circuit condition. 57. The electrical switching system of claim 56 wherein the first and second states comprise a short to power and short to ground, respectively. 58. The electrical switching system of claim 55 wherein the diagnosable state comprises a short to ground. 59. The electrical switching system of claim 58 wherein the first and second states comprise an open circuit and short to power, respectively. 60. The electrical switching system of claim 55 wherein the diagnosable state comprises a short to power. 61. The electrical switching system of claim 60 wherein the first and second states comprise a short to ground and open circuit, respectively. 62. The electrical switching system of claim 55 wherein the vehicle component is a hazard control. 63. The electrical switching system of claim 55 wherein the vehicle component is an airbag on/off control. 64. The electrical switching system of claim 55 wherein the vehicle component is a fog lamp control. 65. The electrical switching system of claim 55 wherein the vehicle component is a passenger sensor. 66. The electrical switching system of claim 55 wherein the vehicle component is a seat belt latch indicator. 67. The electrical switching system of claim 55 wherein the vehicle component is a traction control system on/off switch. 68. The electrical switching system of claim 55 wherein the vehicle component is an overdrive on/off control. 69. The electrical switching system of claim 55 wherein the vehicle component is a displacement on demand (DoD) selector. 70. The electrical switching system of claim 55 wherein the vehicle component is a rear defogger control. 71. The electrical switching system of claim 55 wherein the vehicle component is a rear tow selector. 72. The electrical switching system of claim 55 wherein the vehicle component is a request switch for a vehicle emergency communications service. 73. The electrical switching system of claim 72 wherein the vehicle component comprises an emergency selection, call and initiate/end request switch. 74. The electrical switching system of claim 55 wherein the vehicle component is a seat belt latch sensor. 75. The electrical switching system of claim 55 wherein the vehicle component is a horn actuation control. 76. The electrical switching system of claim 55 wherein the vehicle component is HVAC on/off control. 77. The electrical switching system of claim 55 wherein the vehicle component is an audio system on/off control. 78. The electrical switching system of claim 55 wherein the vehicle component is a compact disk accept/eject control. 79. The electrical switching system of claim 55 wherein the vehicle component is a cassette eject control. 80. The electrical switching system of claim 55 wherein the vehicle component is an air conditioning request switch. 81. The electrical switching system of claim 55 wherein the vehicle component is a re-circulated air selector. 82. The electrical switching system of claim 55 wherein the vehicle component is an external/internal temperature switch. 83. The electrical switching system of claim 55 wherein the vehicle component is a redundant steering wheel control. 84. The electrical switching system of claim 83 wherein the redundant steering wheel control is an audio system control. 85. The electrical switching system of claim 83 wherein the redundant steering wheel control is a climate control system control. 86. The electrical switching system of claim 55 wherein the vehicle component is a dome light override. 87. The electrical switching system of claim 55 wherein the vehicle component is a trip odometer reset. 88. The electrical switching system of claim 55 wherein the vehicle component is a door ajar indicator. 89. The electrical switching system of claim 55 wherein the vehicle component is a manual door lock status indicator. 90. The electrical switching system of claim 55 wherein the vehicle component is an audio system auxiliary function selector. 91. The electrical switching system of claim 55 wherein the vehicle component is an audio system band selector. 92. The electrical switching system of claim 55 wherein the vehicle component is an audio system mute button. 93. The electrical switching system of claim 55 wherein the vehicle component is a cruise control on/off selector. 94. The electrical switching system of claim 55 wherein the vehicle component is a overdrive selector. 95. The electrical switching system of claim 55 wherein the vehicle component is a trip reset button.