WO 97/24704 PCT/US96/20602
TRAIN PROXIMITY DETECTOR RELATED APPLICATIONS
This is a continuation-in-part of provisional patent application entitled "Locomotive Detection System, filed August 22, 1995, and accorded Serial No 60/002,614, and attorney docket No DZ-1138, and provisional patent 5 application entitled "Train Proximity Detector", filed December 29, 1995 and accorded Serial No 60/009,441, and attorney docket No B-37824, the subject matter of each provisional application of which is incorporated herein by reference
TECHNICAL FIELD OF THE INVENTION
The present invention relates in general to detectors, and more particularly to FSK detectors for sensing signals transmitted by a tram to determine the presence of the tram
Printed from Mimosa
WO 97/24704 PCT/US96/20602
2
BACKGROUND OF THE INVENTION
A constant concern exists as to the safety of vehicles where highways, streets and the like, intersect with railroad crossings Despite the significant advances in technology utilized in both highway vehicles and trains, accidents 5 involving collisions between trains and mghway vehicles continue to occur,
which accidents are generally catastrophic in nature
Attempts to warn passenger vehicles and the like of oncoming trains involve many techniques that are old and well-known For example, in U S Pat No 1,978,286 by Sommer, the system includes audio receiver equipment 10 located on the train to detect the sound of whistles, warning bells and sounds to catch the general nimble of the train Such sounds are coupled to the train-mounted receiver, which transmits the sounds by way of a radio transmitter A receiver mounted in the vehicle then receives the transmission and alerts the vehicle occupants of the approaching train 15 In U S. Pat No 3,735,342 by Helliker et al, an alerting system is disclosed for alerting the occupant of a motor vehicle of the presence of an emergency vehicle siren The frequencies generated by a typical siren are m the range of about 400-1500 Hertz Three frequency-selective circuits in the receiver jure responsive to sequentially detect the 600 Hz, 900 Hz and then 1200 20 Hz tones of the siren On the detection of the specific sequence of frequencies, the motorist is alerted of the approaching emergency vehicle
In U S Pat No 3,760,349 by Keister et al , an emergency warning system is disclosed in which a transmitter is mounted on an emergency vehicle for transmitting 500 Hz and 1000 Hz signals alternately modulated on an RF 25 earner The transmitter is triggered when the siren is operated A receiver in the motor vehicle receives the modulated signals, demodulates them and produces corresponding alternating audio signals to the vehicle operator,
indicating the existence of a nearby emergency vehicle
U S Pat No 4,942,395 by Ferrari et al , discloses a railroad grade 30 crossing and motor vehicle warning system In such system, a locomotive-
Printed from Mimosa
3
pct/us96/20602
mounted transceiver transmits a coded radio signal to a transceiver mounted at the railroad crossing The railroad crossing transceiver, in turn, transmits a shortwave radio signal to a vehicle-mounted receiver The signal transmitted by the locomotive is apparently transmitted as long as the train is in motion. 5 US Pat No 5,270,706 by Smith discloses a passive aircraft proximity detector for use with highway vehicles According to this detector, a superheterodyne receiver mounted in the vehicle detects frequencies emitted from the aircraft, in the region of 900-1300 megahertz On the detection of such frequencies, the receiver provides an indication to the vehicle when the aircraft is 10 in range
U S Pat No 5,235,329 by Jackson discloses an emergency vehicle detection device Here, a signal in the citizens band frequency is transmitted by the emergency vehicle, in response to the actuation of a siren, and received by a receiver mounted in a near-by vehicle The vehicle employs a band-selective 15 receiver for detecting the particular frequency of transmission, or band of frequencies
U S Pat No 5,278,553 by Comett, et al discloses a system of warning an approaching emergency vehicle The system detects two frequencies that fall within the range of siren frequencies When detection of such frequencies is 20 sensed, audible and visible alarms are provided, and the vehicle sound system is de-energized
Despite the disclosure of these warning systems, there is nevertheless a reluctance to adopt any one or more of the techniques on a widespread scale By and large, the reason for this is that often both the emergency vehicle or train, as 25 well as the highway vehicle to be warned, require modification or additional equipment, thereby involving an inconvenience during installation, as well as added expense Indeed, and insofar as locomotives or rail traffic is concerned, any safety equipment for use thereon is governed by federal and other regulatory authorities This necessarily incurs substantial expense in testing and approving 30 the development of new equipment or any modification or addition to existing
Printed from Mimosa
4
equipment Further, in the event an alerting system is accepted on a widespread basis, such system must be low-cost, reliable and easily implemented
From the foregoing, it can be seen that a need exists for the provision of a detector for detecting the proximity of a train, without requiring any 5 modification to the tram at all, or at least only small modifications for enhanced performance A further need exists for utilizing present train-transmitting facilities which are of high quality, which are reliable and time-tested type of equipment, where the transmissions thereof are received by remotely-located receivers In this manner, on the routine transmission by a train, such as from 10 the head end to the rear end thereof, or vice versa, such frequency can be detected by the remotely located receiver A further need exists for a receiver utilizing conventionally available circuits, but provides a high degree of reliability and selectivity as to the transmissions by trains Yet another need exists for utilizing frequencies allocated only to rail-type vehicles, thereby 15 reducing the likelihood that other spurious frequencies will be received
Printed from Mimosa
WO 97/24704 PCT/US96/20602
SUMMARY OF THE INVENTION
In accordance with the principles and concepts of the invention, there is disclosed a train proximity detector which substantially reduces or overcomes the shortcomings of the prior ait devices In accordance with an important feature of 5 the invention, a detector includes an amplifier tuned to the specific earner frequency authorized for use only by trains When a train normally provides an FSK transmission from the head end thereof to a receiver mounted on the last car, a remotely located receiver, such as m a vehicle, intercepts the transmission Further, the detector according to the preferred embodiment of the invention, 10 verifies that the transmitted earner frequency is present for a predefined period of time On the detection of the earner frequency for the predefined penod of time, a yellow LED is illuminated The FSK data transmitted by the head end transmitter is decoded and compared with a prestored pattern of data that is characteristic of every train transmission On the detection of the predefined 15 pattern of data encoded on the carrier, a red LED is illuminated With the precise detection of the parameters characteristically transmitted by trains, the remotely-located receiver prow <es both visual and audio alarms indicating the presence of a train
In accordance with another feature of the invention, the train equipment 20 can be modified in a minor manner so that when the whistle is blown at about 1500 feet before an intersection, a redundant transmission by the head end transmitter is caused to be made, thereby assuring that any nearby motorist with the receiver is warned of the presence of the train in the immediate vicinity
Printed from Mimosa
6
BRIEF DESCRIPTION OF THE DRAWINGS
Further features and advantages will become apparent from the following and more particular description of the preferred embodiment of the invention, as illustrated in the accompanying drawings in which like reference characters 5 generally refer to the same parts, elements or functions throughout the views, and in which
FIG. 1 is a detailed block diagram of the train proximity detector according to the preferred embodiment of the invention,
FIG 2 is a flow chart showing the programmed operations of the 10 microcontroller that controls the detector,
FIG 3 illustrates a multi-field frame of bits transmitted by a train according to the American Association of Railroads protocol,
FIG 4 is a block diagram of the computerized operation of a fiain for activating a transmitter when the whistle button is pushed, and 15 FIG 5 illustrates a modification of control circuits of certain train systems, wherein both the whistle and transmitter are activated when the whistle button is pushed
Printed from Mimosa
DETAILED DESCRIPTION OF THE INVENTION
The train proximity detector descnbed below receives a earner and frequency shift key (FSK) data typically transmitted by the "head of tram" or head end device which is typical of free space transmissions of data from the 5 locomotive to a receiver mounted to the last car of the tram The frequency band allocated specifically to such transmissions is 450-460 MHz, with the frequency of 452 9375 megahertz being one frequency presently of interest in the employment of the invention The earner frequency of 452 9375 MHz is allocated for transmission of FSK data from the head of tram to the rear of tram 10 Conversely, the earner frequency of 457 9375 MHz is allocated for the transmission of an acknowledgment and other data from the rear of tram to the head of train The encoded FSK data transmitted between the locomotive and the rear-most car monitors the status of vanous parameters such as brake pressure, speed, etc , while the tram moves along the track The earner 15 frequency is modulated by 1200 hertz and 1800 hertz signals to eacode digital data on the earner The encoding of data is in accordance with the protocol specified by the AAR, dated 1994, and identified as "Recommended Guidelines, Considerations and Radio Frequency Requirements for Train Information Systems", Part 12-15, pages 1-45, the subject matter of which is incorporated 20 herein by reference
A typical frame of data, including synchronizing bits, data bits, panty bits, etc , typically include 672 bits of FSK data transmitted within a 560 millisecond penod of time According to the invention, the tram proximity detector receives the FSK data frame, checks the baud rate, verifies that the 25 earner is present for a predefined penod of time, and verifies a specific bit pattern or "signature" of the data to thereby verify that the transmission was from the head end transmitter of a tram Further, the train is contemplated to be modified in a maimer so that when the whistle button is activated at a predefined distance from a crossing, the whistle not only blows, but the head end transmitter 30 is caused to transmit a frame of data In this manner, when the tram whistle is
Printed from Mimosa
WO 97/24704 PCT/US96/20602
blown at about 1500 feet from a crossing, any nearby vehicle equipped with the train proximity detector of the invention will be alerted by both audio and visual indicators The prevention of accidents between trains and vehicles at crossing intersections is thereby facilitated 5 With reference to FIG 1, there is illustrated a block diagram of the train proximity detector according to the preferred form of the invention The detector includes a UHF receiver 10 of the type adapted for receiving FSK modulated carrier frequencies transmitted by trains, namely 452 9375 megahertz The UHF receiver 10 is of the type A04CJC/A04CJB utilized in pagers of the 10 same type Such pagers are obtainable from the Motorola Corporation This type of pager employs a receiver board and a decoder board The modification thereto according to the invention involves the use of only the receiver board having the UHF receiver and the crystal replaced so as to operate with an incoming earner frequency of 452 9375 MHz, i e , the head of train transmitting 15 frequency The receiver board 14 includes an internal antenna 12 and other circuits, as well as RF amplifiers, oscillators, mixers, a demodulator,
multipliers, first and second IF amplifiers, an audio frequency output, etc According to a feature of the invention, the antenna and/or the front end receiver of the UHF receiver 10 is detuned to make the train proximity detector 20 responsive to signal strength transmissions only within the general location of the detector, such as within about 1/2-1/4 mile This is advantageous, as it is undesirable to detect transmissions from the head end transmitter of trains more than about three miles from the detector Moreover, the bandpass characteristics of the UHF receiver 10 provide a first IF center frequency of 45 MHz, with a 25 bandpass of only 6-7 KHz about the center frequency This sharp bandpass characteristic allows a very narrow band around the train transmission earner frequency to be received, with the out-of-band frequencies being rejected Thus, if the earner frequency received by the UHF receiver 10 is not substantially 452 9375 MHz, it is rejected, even if the other transmitted parameters are 30 correct
Printed from Mimosa
WO 97/24704 PCTWS96/20602
The audio output of the UHF receiver 10 is coupled via a blocking capacitor 16 to a single-transistor amplifier 18 for amplifying the AC signals Essentially, the output of the UHF receiver is the demodulated analog audio signals comprising the FSK data The output of the amplifier 18 is coupled via a 5 capacitor 20 to an FM demodulator 22 for converting the FSK signals to corresponding digital signals. In the preferred form, the FM demodulator 22 is an integrated circuit type XR-2211, obtainable from EXAR Corporation, San Jose, California A potentiometer 24 is connected to the VCO input of the FM demodulator 22 to fine tune the free-running frequency of the voltage controlled 10 oscillator with the frequency of the FSK signals Other components, such as capacitors and resistors, are utilized to adjust the free-running frequency, the value of such components being selected according to the data sheets provided with the XR-2211 demodulator chip Thus, the potentiometer 24 is therefore only illustrative of the components connected to various pms for fine timing the 15 VCO frequency
The FM demodulator 22 includes a lock detect complement output 26 Essentially, the lock detect complement output 26 is at a logic high state when the internal phase lock loop is out of lock with the FSK signals, and goes to a low state when the phase lock loop is locked The output 26 thus detects the 20 presence of the FSK frequency signals and is denoted "earner detect" The FM demodulator 22 also includes a data output 28 for providing logic signals corresponding to the FSK signals The digital signals provided on the earner detect output 26 and the FSK data output 28 are coupled to a microcontroller 30 According to the AAR protocol, the earner is modulated with a 1200 hertz tone 25 and an 1800 hertz tone Hie FM demodulator 22 is configured so that the digital zero is generated in response to the detection of the 1200 hertz tone, and a binary digit 1 is generated on the detection of the 1800 hertz tone
The FM demodulator of the type identified above is designed to verify the baud rate of data transmission, as well as the particular pair of FSK frequencies 30 The baud rate of data transmitted by the tram is 1200, with the FSK frequencies
Printed from Mimosa
PCT/US96/206W
being 1200 and 1800 Hertz, as noted above If the transmitted baud rate is 1200, and if the FSK frequencies received are within a small tolerance of 1200 and 1800 Hertz, then the FM demodulator 22 provides corresponding decoded data on the output If either of these parameters do not correspond to the protocol 5 the data is rejected even if the other parameter, i e , the earner frequency, i<-
found to be within Limits This feature of the invention provides a high degree of selectivity in assuring that a transmission is indeed from a train, and n^i iron:* some other source with similar parameters It can be appreciated that i<dse detections are thus substantially reduced and vehicle operator confidence in the 10 proximity detector is enhanced
In the preferred form of the invention, the microcontroller 30 is of the type PIC16C73, obtainable from Microchip Technology, Chandler, Arizona The microcontroller 30 has an interrupt input 3? for interrupting the processor when a earner detect signal is present, 1 e., on the presence of either of the 1200 15 or 1800 Hertz tones Also included is a capture input 34 for capturing the data bits output by the FM demodulator 22 A 4 0 MHz crystal 36 provides an oscillator signal to the appropriate inputs of the microcontroller 30 An output port 38 provides a reference voltage for activating an audio alarm 40, preferably of the piezoelectnc type An output port 42 can be programmed to provide an 20 output signal for illuminating a yellow light emitting diode (LED) 44 for indicating the presence of the transmitted train signal for a predefined penod of tune The illumination of the yellow LED constitutes a first level alert. Output port 46 is programmable to be driven to a logic low to illuminate a red t:rt> 48 when data is detected The illumination of the red LED constitutes a second 25 level alert Output port 50 is programmable so that it can be dnven to a logic low to illuminate a green LED 52 when DC power is applied to the train proximity detector It is contemplated that the typical automotive voltage (12 volts) will be utilized, together with series regulators to reduce the voltage, if necessary, to power the vanous circuits of the detector
Printed from Mimosa
PCT7US96/20602
11
An auxiliary relay 54 can be driven via a buffer driver 56 by way of output port 58 The microcontroller 30 can be programmed so that on the occurrence of various events, the relay 54 will be operated to simultaneously close a set of contacts and open a set of contacts With the relay 54, other 5 warning systems can be activated The warning system could be actuated without the sounding of the audible whistle and enable a "silent alarm" to equipped vehicles providing an adequate warning without causing the problems encountered in the "whistle ban" areas that have been created to avoid bothering the non-motoring residents The relay 54 can also be utilized for test purposes or 10 can be utilized by other equipment to count the number of events that have occurred, as determined by the programmed operations of the microcontroller 30 The train proximity detector includes a reset switch 60 that is manually operable by the operator to reset the microcontroller 30, such as after various alarms have been triggered, again according to the programmed routine. The 15 reset switch 60 is connected to an interrupt input port 62 of the microcontroller 30 A transmit receive (Tx/Rx) port 64 is connected to a respective SCI asynchronous receive and SCI asynchronous transmit port of the microcontroller 30 for programming the memory, or for reading data therefrom
Having set forth the electrical circuits of the train proximity detector, 20 reference is now made to FIG 2 where there is illustrated the programmed operations of the microcontroller 30 The microcontroller includes an on-board electrical programmable read only memory (EPROM) for storing an operating program
In the program flow chart of FIG 2, the microcontroller 30 starts at 25 block 100 and proceeds to block 102 when battery power is applied to the detector. Power is applied to the tram proximity detector by way of a toggle switch (not shown) on the face plate, which also supports the audio alarm 40, the yellow earner detect LED 44, the red data detect t.bd 48, the green power on LED and the reset button 60 Once power to the unit is detected, the 30 microcontroller 30 proceeds to block 104, where initialization procedures are
Printed from Mimosa
lz earned out During initialization, a software up-counter is reset, the green LED 52 is illuminated via output port 50, the microcontroller ou-board memory is checked, as are various registers, according to a programmed diagnostics routine If the diagnostics fail, a single audio tone is emitted from the audio alarm 40, and all LEDs are extinguished Once a successful initialization has been established, the microcontroller 30 proceeds to block 106, where the up-counter is started The counter is incremented in software once every minute, and thus constitutes a time counter Sufficient digits are provided to count up to 45 days, or more As will be described more fully below, the time counter measures an elapsed penod of time after the occurrence of a level two alert The contents of the time counter can be externally read, via the Tx/Rx port 64
After the time counter is started, the microcontroller 30 proceeds to the idle mode, as shown in program flow block 108 In the idle mode, the microcontroller 30 waits for the detection of an RF earner and a FSK data stream, as provided by the FM demodulator 22 In program flow block 110, when the RF earner lope signal is detected on input port 32 and data is detected on the input port 34, the microcontroller 30 proceeds to decision block 112 Here, it is determined whether or not the earner signal on input port 32 is present for a predefined penod of time. In the preferred embodiment of the invention, the predefined penod of time is about 25 milliseconds. However,
such time is arbitrary and thus other time penodi may be more suitable for particular purposes If the earner is not present for the predefined penod of time, the microcontroller 30 branches back to the idle mode 108 If, on the other hand, the earner signal is detected for at least the predefined penod of time, processing proceeds to block 114 The yellow LED 44 on the face plate of the detector indicates to the vehicle operator that an RF earner transmitted by a train has been detected Also, the audio alarm is sounded once The detection of the earner signal transmitted by a tram constitutes yet another parameter that must be met in order to assure that a detection was indeed that transmitted by a train
Printed from Mimosa
13
From program flow block 114, the microcontroller 30 proceeds to decision block 116 where it determines if the received data pattern constitutes a specified data signature In this group of instructions, the microcontroller 30 compares the pattern of data bits received on input port 34 with a predefined 5 pattern, as stored in the EPROM memory The predefined data pattern can be any group of bits routinely transmitted by a tram, such as that shown by the AAR protocol of FIG 3 The 672-bit frame 130 transmitted on the earner of 452.9375 MHz is characteristic of the format transmitted by tram head end transmitters As noted above, the 672 bits of the frame are transmitted in a 560 10 millisecond time penod
The frame 130 of FIG 3 mcludes a number of fields, the first field 132 being a 456-bit synchronization field In the preferred form of the invention, the authorized synchronization signal transmitted by trams mcludes 456 bits of alternating zeros and ones In decision block 116, the microcontroller 30 15 determines if at least the first eight bits of the synchronization field constitutes alternating ones and zeros or alternating zeros and ones Those skilled in the art may find that it is more advantageous to compare the bits of other fields of the frame, or vanous bits from several fields Indeed, it w <ld be advantageous if the frame of bits included a field showing the activation of the train whistle at the 20 specified 1500 feet from every crossing In this manner, the train proximity detector could not only detect the presence of the frame, but also detect that the train is about 1500 feet from the crossing Other data or bit patterns within the frame can also be detected, as the need arises
The AAR head end transmission frame 130 mcludes a 24-bit field 134 for 25 frame synchronization purposes, and then three groups of a pair of fields constituting a 63-bit field 136 for a data block and a 1-bit field 138 for odd panty The three data blocks have identical data and represent a rear unit address code, a command block and a batch code block While the format of FIG. 3 represents a front end transmission format, the detector can also be 30 configured to also detect the format of a rear-to-front transmission which is on a
Printed from Mimosa
FCT/US96/20602
14
different earner frequency Further, when the head end transmitter transmits to the rear car of the train, the rear transceiver acknowledges the transmission with a "handshake" rear-to-front transmission Those skilled in the art may prefer to also detect one or more of these transmissions to improve the reliability of the detection scheme
If the data signature stored in the EPROM memory matches that received on the data input port 34, the microcontroller 30 proceeds to block 118 where the green LED 52 is alternately illuminated with the red LED 48 This is a warning of a second level alert Further, the audio alarm 40 is activated to provide an audio indication to the vehicle operator that a bona fide train signal has been received The LEDs 48 and 52 are alternately illuminated at a perceptive rate of about 200 ins, and the audio alarm is activated As noted above, the UHF receiver 10 can be adjusted to detune the sensitivity of the detector In other words, the gain or sensitivity of the UHF receiver 10, or other circuits, can be adjusted so that the train proximity detector is less sensitive to the reception and detection of train RF transmissions In this manner, trams further than about 1/2-1 mile from the detector will not be detected, even if such trams transmit on the allocated frequency This prevents the tram proximity detector from providing detections of trams that axe of no real danger to the vehicle operator, in that too great a distance exists between the tram and the detector Yet other techniques are available for desensitizing the detector to limit the range of operation thereof From the foregoing, with the yellow TP.r> 44 indicating the detection of a earner, and with the red LED 48 and green LED 52 alternately blinking to indicate the detection of the data signature, the operator is fully aware that extreme caution should be exercised, l e , a second level alert Not only is the red LED 48 and the green LED 59 alternately illuminated, but the audio alarm 40 also provides an audio indication of the second level alert
From program flow block 118, the microcontroller 30 proceeds to block 120, where the time counter is reset In other words, once a second level alert is reached, the tune counter started m block 106 is reset to start the time anew
Printed from Mimosa
pct/us96/20602
The counter remains counting in one minute increments until the detector is either initialized (block 104) or a subsequent second level alert is detected In the event an accident occurs between the train and the vehicle equipped with the detector, the contents of the time counter, which are stored in a register, are read 5 via port 64 to determine the approximate time elapsed since the detector sensed a second level alert An accident sensing device may comprise an air bag type actuation switch, which signals the microcontroller 30 While not shown above, it is contemplated that the tram proximity detector will be equipped with a backup supply voltage, in the nature of a lithium battery Thus, even if the battery 10 voltage of the vehicle is removed from the detector, the detector will maintain minimum operations To that end, provisions can be made for placing the microcontroller 30 in a sleep mode on the occurrence of the removal of the vehicle battery supply voltage In the sleep mode, the microcontroller 30 can turn off the audio alarm 40 and any LEDs that are illuminated to conserve 15 power Further, in the sleep mode, the microcontroller 30 can be programmed to maintain the one-minute increments to the counter, and the storage of the same m an internal register
From block 120, the microcontroller 30 proceeds to decision block 122 to determine if the reset button 60 has been pushed If the reset button 60 has not 20 been pushed, the program flow branches back to the idle mode 108 If, on the other hand, the reset button 60 has been depressed by the vehicle operator, program flow block 124 js encountered Here, the yellow and red LEDs are extinguished and the green LED 52 is illuminated to indicate that power remains applied to the detector From program flow block 124, the processor branches 25 back to the idle mode 108
While the foregoing illustrates the basic software operations m controlling the microcontroller 30, many other instructions, subroutines and decisions can be implemented to streamline the operation or to supplement the detector with additional features Indeed, it may be found that not all of the parameters 30 detected are necessary to assure that a sensed transmission was from a tram In
Printed from Mimosa
16
addition, the detector can be designed to demodulate or decode and/or identify digital encoding, analog encoding, phase modulation, etc
Reference is now made to FIGS 4 and 5, where there is illustrated modifications to the train equipment to further facilitate the detection of a train in 5 close proximity to the detector, 1 e , near a crossing While the detector of FIG 1 is effective to detect train head end transmissions in the area of reception, irrespective of the proximity to crossings, the inventions of FIGS 4 and 5 cause head end train transmissions to occur when the tram whisde is blown, which is required at about 1500 feet from crossings 10 In FIG 4, there is diagrammatically illustrated the train whistle button
160 for activating the train whistle 162 In actual practice, the button 160 can be a pull string, a manually operated button, a switch, etc Further, the tram whistle 162 can be an audio signal that is mechanically, electrically or electronically generated Modern trams are equipped with a computer 164 that 15 controls or monitors many of the operator switches Indeed, a computer interface (not shown) can be provided so that the computer 164 can scan the operator input devices When the computer 164 detects that the whistle button 160 has been activated, a signal is forwarded to the head end transmitter 166 to cause a transmission on the allocated frequency. The transmitter 166 transmits 20 frames of data, such as shown in FIG 3, by way of an antenna 168 On activation of the whistle button 160, the computer 164 also signals a driver 170 for driving the tram whistle 162 It is contemplated that the configuration of FIG 4 can be implemented by minor modification of the software of the train computer 164 to not only activate the whistle 162 when the button 160 is 25 depressed, but also to cause a transmission via the head end transmitter 166 Although there is no necessity, as to the tram itself, of causing a transmission when the whistle button 160 is pushed, such transmission may be redundant but nevertheless provides a medium for communicating to the tram proximity detector an indication of the proximity of a tram, even if the whistle cannot be 30 heard by the vehicle operator
Printed from Mimosa
17
In FIG 5, there is shown other train apparatus reconfigured to cause an RF transmission when the train whistle button 160 is depressed Here, the whistle button 160 is coupled via a driver 170 to the train whistle 162 In addition, the output of the train whistle 160 is coupled by way of conductor 172 5 to the head end transmitter 166, via a diode 174 Also shown connected to the same input of the head end transmitter 166 is a conventional communication test button 176 To test the train communications equipment, the engineer depresses the communication test button 176 which enables the head end transmitter 166 to transmit a test frame of data The diode 174 prevents the whistle 162 from being 10 activated in response to the depression of the communication test button 176
However, when the whistle button 160 is depressed, the head end transmitter 166 is also enabled, thereby providing a test communication whenever the whistle 162 is blown While FIGS 4 and 5 show basic modifications of locomotives to provide transmissions of data in response to the depression of the whistle button 15 160, many other techniques and variations of the foregoing are available to those skilled in the art
While the preferred embodiment of the invention has been disclosed with reference to a specific train proximity detector, and methods of operation thereof, it is to be understood that many changes in detail may be made as a 20 matter of engineering or software choices, without departing from the spirit and scope of the invention, as defined by the appended claims
Printed from Mimosa