Remote wireless switch sensing circuit using RF transceiver in combination with a SAW chirp processor

A circuit assembly senses a state of a variable state device, wherein a data signal representative of the state is communicated via wireless telegraphy. A surface acoustic wave (SAW) device, having a plurality of interdigital transducers (IDTs) comprises a wave launching IDT and a state information IDT, wherein the plurality of IDTs are in acoustical communication and the state information IDT is in electrical communication with an antenna through the variable state device. An RF transceiver communicates a trigger signal to the SAW device, wherein the trigger signal causes a launching of a SAW wave from the wave launching IDT towards the state information IDT. The state information IDT generates a signal pulse in response thereto and communicates the pulse to the antenna through the variable state device. A transceiver control module, in operative communication with the RF transceiver enables communication of the trigger signal and reads the data signal, wherein the trigger signal and data signal are communicated between the RF transceiver in the SAW device via wireless telegraphy.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The subject invention pertains to the field of control circuits, and more 
particularly to a circuit for sensing the state of a variable state device 
such as a switch. The invention is particularly applicable to sensing the 
state of an operator controlled switch of the type that are typically 
located on a steering wheel of a vehicle, but is also applicable to any 
environment where hard wire signal communication is particularly 
undesirable due to structural restrictions or a particularly harsh 
environment. 
2. Description of the Related Art 
The continuous increase of convenience features in passenger cars makes the 
wiring harness and connecting problems thereto a more important issue in 
terms of safety, reliability, cost and complexity of management. If 
multiplexing of such communication signals provides a solution in some 
cases, the vulnerability of this solution in case of bus wiring breakage 
in areas where numerous functions play a safety role is of significant 
concern. Examples are safety related switches in the steering wheel/stalk 
area, or the window lifter switches which are located off doors and 
control the window motors through the bus. A wireless solution would 
reduce the risk of wiring breakage, and permit easy relocation by OEMs of 
switches that do not have a dedicated location (mirrors, seats, windows, 
etc.) and are remote from the actuators. 
Communication of control signals from a steering wheel through the steering 
column of a vehicle control module has long been a matter of special 
concern due to the difficulties in maintaining dependable signal 
communication from a rotating wheel and due to the sever space constraints 
occurring as a result of the requirement of airbag deployment from the 
wheel. A detailed discussion of the various hardware techniques, as well 
as communication through a rotary transformer are disclosed in 
commonly-assigned U.S. Pat. No. 5,636,863. Ideally, all communication 
would occur through wireless transmission to avoid the problems of a 
wiring harness disposal in a rotating wheel, but the relatively 
electrically noisy environment of an automotive vehicle has generally 
presented too difficult a setting to provide acceptably reliable 
communication for control circuitry. 
Surface Acoustic Wave (SAW) devices are well known as passive devices that 
are typically useful for providing an easily recognizable identification 
signal without need of active electrical power supply to the SAW device 
itself. The use of a signal communication device that is essentially 
passive in nature would be particularly advantageous in a steering column 
application, and such an assembly has already been suggested. However, 
such suggested applications have not been able to employ such a SAW device 
in combination with wireless signal communication. Specifically, coupling 
between a control module and a SAW device has required hard wired signal 
communication or coupling coils to accommodate relative rotation between 
the wheel and steering column. Thus, problems still remain in such a 
system of accommodating coil disposition in the steering column and the 
signal wires thereof running among operator actuated control switches, the 
SAW device and the coupling coil. 
The present invention contemplates a new and improved wireless switch 
device and control assembly which overcome the problems of hard wire or 
coupling coil signal communication while including a SAW device for 
monitoring switch conditions to provide a new device and circuit assembly 
which is simple in design, economical to manufacture, readily adaptable to 
a plurality of uses for control communication or signal monitoring in a 
wide variety of applications and which provides improved ease of signal 
communication with high reliability and communication integrity. 
BRIEF SUMMARY OF THE INVENTION 
It is desirable to have the state of switches located in a car passenger 
compartment monitored by the automotive body computer without the use of 
communication wires to lower cost, weight, and increase reliability. The 
proposed invention accomplishes this task. It is very noise immune and 
operates without a power supply. Power is derived from a received RF 
signal which is chirped to provide noise reduction. 
In accordance with the present invention, there is provided a circuit 
assembly for sensing a state of a variable state device representative of 
an operator actuated switch or a condition of the device wherein a data 
signal representative of the state is communicated via wireless 
telegraphy. The assembly comprises a Surface Acoustic Wave (SAW) device, 
an RF transceiver and a transceiver control module. The SAW device has a 
plurality of interdigital transducers (IDTs), comprising a wave launching 
IDT and a state information IDT, wherein the plurality of IDTs are in 
electrical communication with an antenna and the state information IDT is 
in electrical communication with the variable state device. The RF 
transceiver communicates a trigger signal to the device wherein the 
trigger signal causes a launching of the SAW wave from the wave launching 
IDT towards the state information IDT and the state information IDT 
generates a signal pulse in response thereto. The signal pulse is then 
communicated to the antenna through the variable state device which will 
modify the pulse to be representative of the state of the device. The 
transceiver control module is in operative communication with the RF 
transceiver and enables communication of the trigger signal and reads the 
data signal. The trigger signal and the data signal are communicated 
between the RF transceiver and the SAW device via wireless telegraphy. 
In accordance with a more limited aspect of the present invention, the data 
signal comprises a waveform including a start pulse, a stop pulse and a 
state information pulse intermediate thereof, wherein an absence or 
existence of the state information pulse is representative of the state of 
the variable state device. The variable state device includes a circuit 
switch for determining the absence or existence of the pulse. More 
particularly, an open switch precludes communication of the pulse to the 
antenna. 
In accordance with yet another more limited aspect of the present 
invention, a plurality of variable state devices are each respectively 
associated with a different state information IDT. The plurality are in 
parallel connection to the antenna so that the data signal comprises a 
wave form wherein a pulse occurring at a particular unique location in the 
waveform signifies a state of the variable state device. 
One benefit obtained by the use of the present invention is a SAW signal 
device that can communicate via wireless telegraphy a data signal 
representative of a variable state device. 
Another benefit obtained from the present invention is a wireless signal 
device that can be disposed in an electrically noisy environment such as a 
vehicle steering column. 
A further benefit of the present invention is a passive wireless signal 
device which includes a circuit component capable of communicating switch 
contact information without application of active electronics, such as a 
power signal, to the component. 
Other benefits and advantages for the subject new circuit assembly and 
device will become apparent to those skilled in the art upon a reading and 
understanding of this specification.

DETAILED DESCRIPTION OF THE INVENTION 
The system works by receiving and changing a chirped RF interrogation 
signal and by processing this signal in a SAW device. The SAW device 
converts the RF into an acoustic surface wave. The acoustic wave is 
converted back to an electrical signal on the SAW device. This electrical 
signal is sent to a contact that would either be open or closed. If the 
contact were closed, the electrical signal would then be sent on to a 
broadcast system where an RF signal would be sent out (radiated). In this 
manner the state of the switch being closed could be monitored without 
power and wires at the switch. 
The process of converting the switch open/closed output to a radiated RF 
signal could be realigned by direct connection of the switch as shown in 
FIG. 1 or could involve further processing with a SAW structure followed 
by a radiated RF signal to indicate the contact closure. 
Referring now to the drawings wherein the showings are for purposes of 
illustrating the preferred embodiments of the invention only, and not for 
purposes of limiting same, the FIGURES show a switch sensing circuit 
assembly comprising an RF transceiver in combination with a SAW chirp 
processor. With particular reference to FIG. 1, a preferred circuit 
assembly 10 is shown to comprise a transceiver module 12 and a SAW 
processor 14. The SAW processor itself is essentially conventional in 
nature and is comprised of a piezoelectric substrate, preferably of 
lithium niobate, upon which are disposed a plurality of interdigital 
transducers (IDTs). Towards one end of the SAW device 14 a set of IDTs 
comprise a SAW launching IDT assembly. Such assembly is more particularly 
illustrated in FIG. 2, wherein the plurality of IDTs are disposed to 
function as a pulse compression filter when a matching signal of the kind 
shown in FIG. 2 is impressed thereon. The result of the pulse compression 
filter 16 is an output pulse 18, comprising a wave moving across the 
piezoelectric towards the other IDTs for generating an electrical signal 
in each one of them. Such a configuration, typically referred to as a 
"delay line", will allow identification of pulses in a time domain which 
can correspond to particular IDTs, as will hereinafter be more fully 
explained. At opposed ends of the SAW device are absorption materials 20 
to minimize reflection of the wave pulse 18. Along the longitudinal length 
of the device 14, first and second bus bars 22, 24 are disposed for 
communication of electrical signals between the IDTs and the receive and 
transmit antenna 30. The IDTs, other than those used for the pulse 
compression filter, fulfill specific roles in pulse generation in the time 
domain. The IDTs at position 32 are both connected to the bus bars 22, 24, 
respectively, for purposes of generating a recognizable start pulse. The 
IDTs at positions 34, 36 and 38 are connected to switches 40, 42, 44, 
respectively. The last IDT position 50 corresponds to IDTs which are 
similarly connected to both bus bars for generating a recognizable stop 
pulse. The IDTs at positions 34, 36, 38 are connected to bus bars 22, 24 
through switches 40, 42, 44. However, any type of switch, or for that 
matter any variable state device, could be monitored by the subject 
invention. 
The transceiver module 12 generates a trigger signal and receives a 
responsive waveform from the SAW device 14. In particular, transmitter 60 
sends out an RF signal through transmit and receive antenna 62 of a type 
that will generate the matching signal in the SAW device, such as 
illustrated in FIG. 2. Switch 64 is used to isolate the receiver 66 when 
the transceiver module is in the transmit mode and, alternatively, to 
isolate the transmitter 60 when the module is in the receive mode. Timing 
electronics 68 control the state of switch 64 and the timing operations of 
the transmitter and receiver in a conventional manner which would be known 
to one of ordinary skill in the art. It is preferred that the RF signal be 
of relatively high frequency to reduce the size requirements of the 
antennas 30, 62. 
A proof-of-concept prototype operated successfully at distances greater 
than six (6) feet at 75 MHz. However, SAW devices will operate at higher 
frequencies in the range of 900 MHz and offer the advantage of significant 
reduction in the size of the antenna required. 
With particular reference to FIGS. 1 and 3, circuit operation will be 
explained. FIG. 3 illustrates s chirp signal comprising a high frequency 
RF signal transmitted from the transceiver module 12 and received by the 
SAW device 14. The IDTs of the pulse compression filter 16 convert the 
electromagnetic energy of the chirp signal into an acoustic waveform 
trigger signal, such as illustrated in FIG. 3B. A data signal 
representative of the state of the switches 40, 42, 44 is illustrated in 
FIG. 3C. Deflection of the piezoelectric substrate by the acoustic wave of 
FIG. 3B will generate an electrical signal which can be communicated back 
out from the SAW device 14 via antennas 30. In particular, as the acoustic 
pulse contacts the IDTs at position 32, a start pulse 70 can be recognized 
by the receiver 66 in the receiver module 12. At position 72, no pulse is 
detected which indicates that the switch 40, corresponding to IDT position 
34 is open so that electrical energy detected by the IDTs at position 34 
cannot be communicated back to the antenna 30. At position 74, a pulse is 
recognized indicating that the switch 42 is closed to thereby communicate 
the electrical energy sensed by the IDTs at position 36 back out by the 
antennas 30. Similarly, switch 44 is detected as being closed by the 
occurrence of the pulse at position 76 in FIG. 3C. Lastly, the pulse in 
the data signal at position 78 is representative of the stop pulse in the 
data signal. Thus, control circuitry which identifies an existence or 
absence of a pulse at the respective positions shown in FIG. 3C, can be 
used to identify the particular state of variable state devices such as 
the switches shown in FIG. 1. 
It is a particular feature of the invention that the RF trigger signal, as 
well as the data pulse signal are communicated between the transceiver 
module 12 and the SAW device 14 via wireless telegraphy. Such an assembly 
is particularly applicable to monitoring operator control switches such as 
are typically disposed on a vehicle steering wheel. Such switches relate 
to items such as cruise control, horn, turn signals and the like. 
Various alternative modes are known for implementing the circuit of the SAW 
device 14. For example, even though both bus bars are shown being disposed 
on the piezoelectric substrate, it is possible to remove one of the bus 
bars from the piezoelectric material itself and dispose it elsewhere. It 
is only important that the data signal be somehow communicated back to the 
antennas 30 for reception by the transceiver module 12. 
It is most convenient when the variable state device being sensed by the 
subject invention is disposed serially between the state information IDTs 
at positions 34, 36, 38 so that when the variable state device comprises a 
switch, and when the switch is in an open state, the transmission of the 
data signal from the particularly associated state information IDT to the 
antenna is precluded. However, alternative circuit arrangements may also 
occur to those of ordinary skill in the art to accommodate other types of 
variable state devices. 
The invention has been described with reference to preferred embodiments. 
Obviously modifications and alterations will occur to others upon the 
reading and understanding of this specification. It is our intention to 
include all such modifications and alternations insofar as they come 
within the scope of the appended claims or the equivalents thereof.