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Description  |
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FIELD OF THE INVENTION
The present invention relates in general to communication systems, and more
particularly, to digital communication systems for communicating a vehicle
parameter.
BACKGROUND OF THE INVENTION
Due, in part, to the weight restrictions being placed on vehicles by local,
state, and federal agencies, the need to equip vehicles engaged in
transporting heavy loads with a means to measure and communicate the
weight of the load being carried by the vehicle has increased. This has
become especially important in situations where the vehicle is adapted for
both highway and off-road travel, and the load to be transported is loaded
at remote off road locations where conventional weight stations are
nonexistent. In the past, an apparatus measuring and communicating the
weight carried by a vehicle, such as a tractor-trailer type vehicle or the
like used a conventional load cell to measure the load carried by the
trailer portion of the vehicle. The output of the load call was thereafter
transmitted to the operator of the vehicle along an expensive and custom
made cable interconnecting the load cell with the tractor portion of the
vehicle. This approach has several disadvantages in that uncoupling the
tractor and trailer without disconnecting the cable between same broke the
cable resulting in replacement of the expensive item. In addition, if the
cable were disconnected, the environment in which the vehicle was operated
frequently introduced mud or the like in the ends of the cable producing
inaccuracies in the apparatus.
The present invention overcomes these problems of the prior art. By using
data transmitter and receiver units disposed on the trailer and tractor
portions of the vehicle, the present invention measures and communicates
the weight of the load to the vehicle operator along a spare wire in the
reach cable interconnecting the tractor and trailer and typically provided
as standard equipment by the vehicle manufacturer. The present invention
alternately can communicate the weight of the load to the vehicle operator
along one of the trailer lighting circuit wires. In addition, the
electronic circuitry within these units enables the present invention to
operate with minimal susceptability to error introduced by the effects of
the environment in which the vehicle is used.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, an apparatus for
communicating a vehicle parameter to a location remote and apart from the
parameter comprises sensor means responsive to the parameter to be
communicated. The sensor means produced an output analog signal
proportional to the parameter. Means periodically converts the output
analog signal into a digital signal whereby the parameter to be
communicated is represented by an N-bit digital code. Means transmits the
digital signal to a location remote and apart from the parameter. Means
periodically converts the N-bit digital code representative of the
parameter into a form suitable for driving a display device. Visual
display means presents in a user viewable form the converted N-bit digital
code.
It is an object of the present invention to provide an apparatus accurately
and quickly communicating a vehicle parameter to the operator of the
vehicle.
A further object of the present invention is to provide an apparatus
communicating a vehicle parameter from one point on the vehicle to another
without the use of expensive cabling between the vehicle's points.
A still further object of the present invention is to provide an apparatus
communicating a vehicle parameter from one point on the vehicle to another
having minimal susceptibility to transmission errors introduced by the
vehicle's environment.
These and other objects, features and advantages of the present invention
will become more apparent in light of the detailed description of the
preferred embodiment set forth hereafter, and illustrated in the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a vehicle showing the typical location of a
data transmitter unit according to the present invention.
FIG. 2 is a perspective view of a vehicle with portions broken away showing
the typical location of a data receiver unit according to the present
invention.
FIG. 3 is a block diagram of the present invention.
FIG. 4 is an electronic schematic diagram showing a typical data
transmitter unit of the present invention.
FIG. 5 is an electronic schematic diagram showing a typical data receiver
unit according to the present invention.
BEST MODE OF CARRYING OUT THE PRESENT INVENTION
With reference to FIGS. 1, 2, an apparatus for communicating a vehicle
parameter from one point on the vehicle to a location remote and apart
from the parameter is shown disposed at a typical location on a vehicle.
For illustrative purposes, the vehicle is shown as a logging truck having
a trailer portion 11 connected to and movably pulled by a tractor portion
12. As illustrated, the vehicle carries a plurality of logs with the logs
coming in contact with the trailer 11 substantially at a point above the
rear axles where the weight of the logs are concentrated. The logs are
restrained from lateral movement both on the trailer and the tractor by a
plurality of log bunks 13. The present invention comprises a data
transmitting unit 20 disposed generally rearwardly on the trailer 11 in
close proximity to the log bunks 13. The data transmitting unit converts
an analog signal representative of the vehicle parameter to be
communicated into a digital form for subsequent transmission. A data
receiving unit 40 is spaced apart and remote from the data transmitting
unit and is typically carried in the cab portion of the tractor 12. The
data receiving unit periodically converts the digital signal
representative of the vehicle parameter into a continuous analog signal.
The display means 50 also carried in the tractor portion of the vehicle
and generally in close proximity to the data receiving unit presents in a
viewer usable form the analog signs representing the parameter. As located
in its relationship to the vehicle, the present invention is ideally
suited to communicate the weight of the logs carried by the trailer to the
operator of the tractor. However, it is to be understood that the location
of both the data transmitting unit and the data receiving unit, including
the display means may be varied without departing from the teachings of
the present invention. For example, the data transmitting unit may be
conveniently located on the vehicle to communicate other parameters such
as vehicle velocity, center of gravity or the like, while the data
receiving unit may be located apart from the vehicle on a loading dock or
some other central stationary location.
With reference to FIG. 3, the data transmitting unit of the present
invention generally comprises sensor means 22 responsive to the parameter
to be communicated. The sensor means produces an output analog signal
proportional to the parameter to be communicated. Means, generally shown
at 24, periodically converts the output analog signal produced by the
sensor means into a digital signal whereby the parameter to be
communicated is represented by an N-bit digital code. Means 27-29
transmits the digital signal to a location remote and apart from the
parameter. The data receiving unit 40 of the present invention generally
comprises a means, generally shown at 42, periodically converting the
N-bit digital code representative of the vehicle parameter into a
continuous signal. Visual display means 50 presents to the user in a user
viewable form the continuous signal representative of the vehicle
parameter. As will be discussed more fully below, the present invention
also includes a means enabling a predetermined known continuous analog
signal simulating the sensor means and switchable therewith to be
periodically converted into a continuous digital signal thereby providing
a calibration source for the invention. The means generally comprises a
tone generator 60 in communication with a tone detector 70 with the tone
detector being operable so that it activates a switch connecting a precise
calibrating resistor across the load cell bridge terminals thereby
simulating a known deflection of the load cell. These and other elements
of the present invention will next be described in more detail below.
With reference to FIGS. 3-5, the sensor means 22 typically comprises a
plurality of load cells or like devices producing an output analog signal
proportional to the weight of the load disposed above the load cells. By
way of example, the plurality of load cells are disposed rearwardly on the
trailer 11 typically directly below the point at which the weight of the
load on the trailer is concentrated. Each load cell deflects responsive to
the weight of the load directly above the load cell. Deflection produces
an analog output signal proportional to the distance the load cell has
deflected from a predetermined reference position. The output analog
signals from all load cells are electrically summed by parallel connection
at the transmitter unit input terminals to produce a single output analog
signal representing the total deflection of the load cells. It is to be
understood that although a load cell is utilized in the preferred
embodiment, other sensors responsive to other vehicle parameters, such as
temperature, vehicle velocity, or the like may be utilized to practice the
invention without departing from the teachings of the present invention.
The load cell of the preferred embodiment is a commercially available unit
such as manufactured by Structural Instrumentation, Inc.
With reference to FIG. 3, means shown generally at 24 periodically
converting the output analog signal produced by sensor means 22 into a
continuous digital signal comprises an analog to digital converter 25 in
parallel communication with a serial data converter 26. The continuous
analog signal representative of the vehicle parameter is routed through a
signal conditioning network comprising an operational amplifier (see FIG.
4), to the input of the analog to digital converter. Timing and control of
the electronics within the data transmitter, and specifically the analog
to digital converter, is provided by a crystal oscillator and frequency
divider chain in conjunction with timing circuitry within the analog to
digital converter. The analog to digital converter periodically samples
the conditioned and continuous analog input signal and provides an N-bit
digital code representative of the input. In the preferred embodiment, the
analog to digital converter is of the dual slope type producing a twelve
bit parallel output responsive to the analog input. In response to a
periodic request from its internal timing circuitry, the analog to digital
converter integrates the reference voltage for substantially 2048 clock
pulses and generates a voltage ramp whose slope and end point voltage are
directly proportional to the reference voltage. It thereafter connects the
conditioned input analog voltage to an integrator circuit in such a way as
to cause the voltage ramp to integrate each to its initial starting point.
A twelve bit digital counter contained within the analog to digital
converter counts the number of clock pulses required for the second
integration, and the binary count produced is the digital representation
of the analog input. In this manner, errors occurring as a result of a
change in the reference voltage from temperature or the like are
minimized. It is to be understood that although in the preferred
embodiment the analog to digital converter is of the dual slope type,
other types of analog to digital conversion, such as a successive
approximation or the like, may be used to provide the N-bit digital output
code representative of the parameter to be communicated. In the preferred
embodiment, the analog to digital converter is manufactured by Intersil,
Part No. ICL 7109 CPL.
The N-bit serial digital output provided by the analog to digital converter
is communicated in a parallel manner to the serial data converter 26. The
serial data converter is also under operational control by a crystal
oscillator and frequency divider and formats or arranges the parallel
output from the analog to digital converter into a plurality of digital
words or bytes. Within one of the bytes, the serial data converter
introduces an M-bit digital code (typically eight bits) enabling the data
receiving unit 40 to convert all N-bits of the digital code representative
of the parameter to be communicated into a continuous analog signal as
will be more fully discussed. The serial data converter thereafter outputs
the plurality of bytes containing both the N-bit digital code and the
M-bit code utilized by the data receiver unit. In the preferred
embodiment, the serial data converter is a commercially available
integrated circuit such as a Standard Microsystems COM 8017.
The digital signal including the N-bit digital code representing the
parameter to be communicated is applied directly to the means 27-29
transmitting the digital signal to a location remote and apart from the
parameter. As shown in FIG. 3, the means transmitting the digital signal
comprises a frequency shift keyed modulator 27 in a hardwire communication
with a frequency shift keyed demodulator 28. In the preferred embodiment,
the frequency shift keyed modulator typically has an output frequency
range of from between 24 kHz to 40 kHz. For example, a digital signal
input having a logic zero value causes the frequency shift keyed modulator
to produce an analog output signal at 24 kHz, while a digital input signal
having a logic one value causes the modulator to produce an analog output
signal at typically 40 kHz. The output of the frequency shift keyed
modulator is applied through a passive low pass filter to a hardwire link
29 physically connected between the data transmitted unit 20 and the data
receiving unit 40. With reference to FIG. 1, the hardwire link 29 is of a
conventional cable of the type used in automotive wiring, extending the
length of the trailer 11, such as a spare wire found in the vehicle's
reach cable. In an alternate embodiment, the hardwire link can be shared
with one of the trailer's lighting circuit wires. In this instance, the
FSK signal as well as the 200 KH.sub.3 tone signal (see below) is biased
by the voltage existing on the lighting circuit wire.
With reference to FIG. 3, the frequency shift keyed signal representing the
parameter to be communicated is applied directly to the input of a
frequency shift keyed demodulator 28. The demodulator comprises
essentially a digital frequency-phase comparator. The frequency shift
keyed input is compared with a signal of known frequency to determine if
the received signal is a binary one or a binary zero. The output of the
demodulator, a continuous digital signal is thereafter routed to the
serial data converter.
The data receiving unit 40 includes a means periodically converting the
N-bit digital code representative of the vehicle parameter into a
continuous analog signal representative of the parameter. The means
generally comprises a serial data converter 44 in communication with a
digital to analog converter 46. The serial data converter and other
electronics within the data receiver are controlled in their operation by
a free running crystal oscillator in conjunction with a frequency divider
(see FIG. 5). The serial data converter continually monitors the digital
input signal from the demodulator to detect the presence or absence of the
M-bit digital code. Upon detection of this M-bit digital code, the serial
data converter subsequently applies the N-bit digital code representative
of the parameter to a plurality of temporary storage registers or data
latches in a parallel manner. The parallel output of each temporary
storage register is applied in a parallel manner to a digital to analog
converter.
The digital to analog converter 46 of the present invention comprises a
resistive ladder network producing a continuous analog signal in
proportion to the value of the digital signal applied to each leg of the
ladder network. By electrically summing the electrical signals from each
leg of the resistive ladder, the converter produces an analog signal
representing the parameter communicated. In the preferred embodiment,
digital to analog converter is implemented by means of an integrated
circuit manufactured by Precision Monolithics No. DAC 03 CDX2. The output
of the digital to analog converter is subsequently conditioned prior to
routing to the display means.
In an alternate embodiment (not shown), the parallel output of each
temporary storage register is applied through display drivers to a
corresponding digital readout in the display means 50. In this embodiment,
the output of the temporary storage registers may require additional
processing, such as gain adjustment for zero crossing or the like, before
being presented in user viewable form. The necessary circuitry providing
this function may be separate and apart from the display means 50, or may
be integral with the display means.
In an alternate embodiment of the present invention (not shown), the analog
signal representative of the parameter to be communicated may be
communicated to a location remote and apart from the parameter by the use
of a voltage to frequency converter, and a frequency to voltage converter.
In this embodiment, the analog signal from sensor means 22 is applied to a
voltage to frequency converter producing a frequency modulated output
signal in response to the analog voltage at its input. The frequency
modulated output signal is then applied through a cable or the like to the
input of a frequency to voltage converter. This converter outputs an
analog voltage responsive to the frequency of the signal appearing at its
input. The resulting analog signal is then applied directly to the display
means 50.
Display means 50 located within the tractor portion 12 of the vehicle
presents to the user in a viewable form the continuous analog signal
representative of the vehicle parameter communicated. In the preferred
embodiment, display means typically has a numeric readout responsive to
the analog input, but it is to be understood that other forms of the
display means may be utilized to practice the present invention.
The present invention includes a means enabling a predetermined and known
continuous analog signal simulating the output of the sensor means 22 and
switchable therewith to be periodically converted into a continuous
digital signal thereby providing a calibration source for the present
invention. The means comprises a tone generator 60 in communication with a
tone detector 70 with the tone detector being switchably connectable to
the analog to digital converter 25 input. A switch or the like on the
display means is activated by the driver of the tractor. When this occurs,
an oscillator within the frequency shift keyed demodulator 28 of the data
receiver unit generates a tone of typically 200 kHz. The 200 kHz tone is
applied directly to the hardwire link 29 connecting the data transmitter
unit with the data receiver unit. The tone is additive to the data being
propogated along the data link. A detector circuit within the data
transmitter unit detects the presence of the 200 kHz tone, in part by a
high pass filter disposed at the input of the detector circuit, and
provides the requisite voltage excitation to a switching means disposed
across the input of the analog to digital converter. When active, the
switching means causes a known and predetermined analog signal, such as
the excitation used to power the data transmitter unit, directly into a
conditioning network (see FIG. 4) prior to being converted into a digital
code simulating the sensor output.
With reference to FIGS. 4-5, and Tables 1 and 2 below listing the typical
component valves of the present invention, the operation of the present
invention will next be described for both the data transmitter unit and
the data receiver unit.
DATA TRANSMITTER UNIT
Differential input signals coming from the bridge type load cell are
amplified by operational amplifier U1. The gain of the amplifier is
determined and set by resisters R2, R6, R7, and R9. Capacitor C20 removes
high frequency noise appearing on the differential input signals. Resister
R5 biases the output of amplifier U1 such that with no load applied to the
load cell, the analog to digital converter input is biased to
approximately twenty-five percent of this full-scale range. The analog to
digital conversion process is performed by component U2. The reference
voltage for U2 is supplied through a voltage divider comprising resistors
R10 and R11. Resister R12 and capacitor C2 filter input noise appearing on
the reference voltage. Resister R13 and capacitor C3 establish integrator
and constants for the analog to digital convertor. Capacitor C4 stores the
analog digital converter's auto-zero cycle voltage.
Component U3 is a universal asynchronis receiver and transmitter circuit
which converts the parallel digital output of the analog to digital
converter into a serial code. Timing and clock signals for the analog to
digital converter and the universal asynchronis receiver/transmitter
circuit are provided by an oscillator/divider circuit shown at U8. An
oscillator Y1 provides a master clock frequency of substantially 32.768
kHz. The output of U3 is coupled through resister R22 through a voltage
control oscillator U4, which generates frequency shift keyed (FSK) signals
with a 40 kHz mark frequency in a 24 kHz space frequency. These
frequencies are determined and set by resisters R20 through R22, and
capacitor C10. The FSK signal is filtered by a low pass filter comprised
of elements C17, C18, and routed through a coupling capacitor C19 to the
input line. Component L3 decouples the input line for the data
transmission frequency and allows them to be superimposed on the DC power.
The output side of L3 is connected to a terminal that may be used to
receive the power for external lighting circuit purposes. Capacitors C6
and C7 are used to suppress any switching transients.
A diode bridge comprising diodes CR1 through CR4 selects power of the
appropriate polarity for the data transmitter unit circuits. Regulator
circuit U5 supplies the positive DC voltage. Oscillator U6 and a rectifier
circuit, comprising diodes CR7 through CR8, form a DC/DC voltage converter
circuit used to generate a negative supply for the data transmitter unit.
Regulator U7 regulates the negative voltage to a controlled negative DC
value.
The calibration function is performed by shunting a calibration resister R3
across the load cell input. This is done by an electronic switch
comprising a transistor Q1 which is activated when a 200 kHz tone is
detected by the detector circuit comprising diodes CR9, CR10 and capacitor
C11. The 200 kHz tone is picked off the input line by a high pass filter
comprising capacitor C14 through C16, and the inductor L2. The output of
the filter is amplified by amplifier Q2.
DATA RECEIVER UNIT
Input data is picked off the power line by capacitor C104 and applied
through a low pass filter comprising inductor L101, and capacitor C105
through C106. The input data is amplified by amplifier Q101. The input
signal is squared up by a digital inverter U109 and subsequently applied
to the input of the frequency comparator section of component U101. A
reference frequency input for U101 is provided by an oscillator U102 whose
output frequency is substantially 32.768 kHz. The frequency comparator in
U1 determines if the FSK input signal is either above or below the
reference frequency, and outputs a logic one or a logic zero for a mark or
a space, respectively. The output of U1 is buffered by a digital inverter
and applied to the serial data input of data converter U103.
Data converter U103 converts the serial data stream at its input into a
parallel binary data source. Because the data being received is contained
in more than one byte, the output of the data converter is stored in a
plurality of latches comprised of components U105 through U107. Gate
circuit U108 picks off the byte identification bit contained in the
received data strain, and combines it with a strobe signal from the data
converter U103. The gate unit further generates control signals at low
data into the latches.
Component U111 is a digital to analog converter. Operational amplifier U112
inverts the output of the digital to analog converter and adjusts its
slope and bias point.
A five volt DC power supply for the logic circuit and the data receiver
unit is supplied by a regulator circuit U104. The necessary negative
voltage for the data receiver unit is generated by an oscillator circuit
comprising component U110, and a voltage doubler circuit comprising diodes
CR105 through CR108, and capacitor C115 through C118. The voltage is
regulated to a minus 12 volts by diode CR109 and resistor R116. Inductor
L102 together with transient suppressors CR102 through CR102 provide
isolation between the DC power and the frequency used for data
transmission.
The 200 kHz tone used to operate the calibration circuit is generated by
the oscillator section of component U101. Its frequency is determined by
capacitor C102 and resistor R103. The oscillator is switched by grounding
the CAL ENABLE line. Its output is coupled into the output line through
capacitor C101 and resistor R102.
TABLE 1
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TYPICAL COMPONENTS FOR DATA
TRANSMITTER UNIT
Reference Designation
Description
______________________________________
R14, 23 330 ohm, 5%, 1/4 Watt
R27 1,5K ohm, 5%, 1/4 Watt
R24, 26 4.7K ohm, 5%, 1/4 Watt
R20 4.1K ohm, 5%, 1/4 Watt
R22, 16 10K ohm, 5%, 1/4 Watt
R21 18K ohm, 5%, 1/4 Watt
R13, 1, 2 22K ohm, 5%, 1/4 Watt
R17 100K ohm, 5%, 1/4 Watt
R12, 19 470K ohm, 5%, 1/4 Watt
R18 22 Meg. ohm, 5%, 1/4 Watt
R11, 15, 25 2200 ohm, 1%
R6, 7 3650 ohm, 1%
R3, 8, 9, 10 51.1K ohm, 1%
R5 2.2 Meg. ohm, 1%
C1 1 .mu.f. 16 v.
C6, 7 10 .mu.f. 16 v.
C8 10 pf.
C9 22 pf.
C14, 15 680 pf.
C17, 18 6800 pf.
C10 1000 pf.
C5, 11, 12, 13 .01 disc
C2, 16 .01 .mu.f film
C3 .15 .mu.f film
C4 .33 .mu.f film
C19, 20 .1 .mu.f disc
U1 OP-05CP
U2 1CL7109CPL
U3 COM 8017
U4, 6 LM 555
U5 78L05
U7 79L05
U8 CD4060A
CR1-4 MDA 100
CR 5, 6 1N4001
CR7-10 1N4148
Q1 2N3640
Q2 2N3563
Y1 32.768 kHz. crystal
L2 1 mhy
L1 2.7 mhy
L3 500 .mu.hy.
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TABLE 2
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TYPICAL COMPONENTS FOR DATA RECEIVER UNIT
Reference Designation
Description
______________________________________
R116 330 ohm, 1/4 Watt, 5%
R107 1.5K ohm, 1/4 Watt, 5%
R106, 108 4.7K ohm, 1/4 Watt, 5%
R103, 114 10K ohm, 1/4 Watt, 5%
R101, 104, 112 100K ohm, 1/4 Watt, 5%
R111 | | |
