Abstract:
A wireless vehicle safety monitoring system, including a portable monitor unit and a plurality of sensor modules that can monitor vehicle tire pressure, detect presence of object and its distance behind the vehicle, and monitor the security of the vehicle. The sensor modules communicate by encoded RF wireless transmission with the monitor unit, which will display the individual tire pressure on it&#39;s LCD panel while the vehicle is moving, and also display any detected object range information during the vehicle reverse motion. When one or more monitoring situations arise (bad tire pressure, object detection, or vehicle security violation), the monitor unit will issue warnings to alert the vehicle owner. The wireless pressure sensor module is miniaturized for easy mounting on the tire valve stem with minimal obstruction. The wireless ultrasonic object detection sensor module is mounted on the rear license plate holder. The small monitor unit can be dashboard-mounted or placed on any viewable location in the vehicle, or carried by the user. The system&#39;s unique power-conservation technology enables the monitor unit to operate on a single 1.5V AA battery for over six months, and for the sensor modules to operate close to 18 months without needing to change batteries.

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of vehicle tire pressure monitoring, proximity object detection, and vehicle alarm system. Particularly, the invention relates to an apparatus for automatically monitoring tire pressure, detecting nearby objects and monitoring vehicle security, and methods for constructing and operating the apparatus. 
     BACKGROUND OF THE INVENTION 
     Numerous innovations for each parts of the vehicle monitoring system have been provided in prior arts. 
     1. Tire Pressure Monitor 
     Pressure sensors have long been used to monitor tires for determining whether the tire was properly pressurized. Known methods for monitoring tire pressure included: 
     (a) A pressure sensor module installed inside the tire and transmitted the pressure data by wireless RF signal to a monitor located in the passenger compartment of a vehicle. With this method, system installation and battery replacement would be very inconvenient. 
     (b) A pressure sensing and transmission device mounted in the inner end of the tire valve, and transmitted the pressure data to a monitor. With this method, system installation and battery replacement would also be inconvenient. 
     (c) A pressure sensing and transmission device mounted on the tire valve stem. The device has a pressure sensitive diaphragm and spring switch for triggering the transmission of low-pressure warning signal to the monitor. With this method, however, the system can&#39;t monitor the pressure data continuously. 
     U.S. Pat. No. 4,804,808 issued to Dal Cero on Feb. 14, 1989 discloses a pressure-sensing device that senses low tire pressure and signals low pressure using a transmitter and a receiver. 
     U.S. Pat. No. 4,694,273 issued to Franchino on Sep. 15, 1987 discloses a tire pressure-sensing device having a movable element to trigger a radio transmission signal, which is then received by a receiver for activating visual and acoustic alarms. 
     U.S. Pat. No. 5,289,161 issued to Huang on Feb. 22, 1994 discloses a pressure gauge having a diaphragm that pushes a spring-loaded rod between two switch devices which, when the tire is not properly pressurized, will trigger the sending of an encoded RF signal to a receiver for generating alarms. 
     U.S. Pat. No. 5,694,111 issued to Huang on Dec. 2, 1997 discloses an encoder unit and a transmitter circuit for a tire pressure sensor device for generating encoded RF signals received by a receiver with a display unit. 
     U.S. Pat. No. 4,734,674 issued to Thomas on Mar. 29, 1988 also discloses a tire pressure sensing device that, upon low pressure, transmits an encoded signal to a receiver having a plurality of display indicators on a front panel that are selectively activated to indicate the respective tire. 
     U.S. Pat. No. 4,319,220 issued to Pappas on Mar. 9, 1982 discloses a system for monitoring tire pressure of the tires having respective transmitters communicating alarm signals to a receiver. 
     U.S. Pat. No. 5,001,457 issued to Wang on Mar. 19, 1991 teaches a cab mounted monitor having a graphic display for visually indicating under-pressurized tire, which is identified by encoded signals transmitted from respective tire pressure sensing transmitters to the cab mounted central receiver. 
     Typically, these systems teach tire valve mounted pressure sensors responsive to individual tire pressures for generating encoded signals transmitted to a receiver with graphic displays. However, these teachings do not address or not able to resolve many practical issues, as described below: 
     (i) Continuous Pressure Monitoring 
     Properly pressurized tires are utmost important for safe driving and for prolonging the life of tires. Also, drivers often do not even aware that a tire is punctured and slowly leaking air, until the damaged tire went flat. A safe and practical system should monitor and display the tire pressure continuously for tire pressure maintenance and air leaking tire detection. The prior systems typically only generate alarms when the tire pressure is lower than a predetermined level and, therefore, provide very little information to the driver. 
     (ii) Sufficiently Small Pressure Sensor Size 
     A tire valve-stem mounted pressure sensor, which is usually in a cylindrical shape, must be small enough to be practical. Sensor size larger than 0.65 inch tall and 0.65 inch in diameter would present problems for sidewalk parking, car washing, and for secure mounting on the value stem. A larger sensor also would be more easily be detached from a valve stem of a fast moving vehicle due to tire rotation and airflow. It is technically very challenging to make a functional device that includes pressure sensor, motion detector, power supply, and RF signal transmission electronics in a very small package. Prior systems generally do not address methods to make small sensor modules. 
     (iii) Long Sensor Operating Life Between Battery Changes 
     A small sensor module can only have a mini-scale power supply. Therefore, a practical system must manage power consumption for providing a longer sensor operating life (preferably 18 months or more of normal usage) between battery changes. The few prior systems that discussed power saving at all did not present satisfactory methods. 
     (iv) Long and Large Vehicle Tire Pressure Monitoring 
     Prior arts generally do not address the problem of how to monitor tire pressures in larger vehicles with wheels far away from the receiver in the driver cab. A small sensor module physically can not be equipped with a very efficient antenna for RF message transmission, and the RF signal power is limited by the FCC regulations. Tire rotation would also create interference to further weaken the signal. Therefore, it is very difficult for a cab-mounted monitor to have a good reception for the weak data messages from the rear tire pressure sensors of a long truck or a trailer. Therefore, prior-art valve stem mounted sensors can not be successfully used on monitoring tire pressures in larger vehicles. 
     2. Object Detection Monitor 
     Safety concerns have led to numerous proposals for devices to be used in automobiles to detect the proximity of other vehicles or objects for collision avoidance. Known methods for object detection included: 
     (a) A radar-liked device that transmitted high frequency RF signals and then detected the object echo-reception signals; the signal travel time can be used to determine the object distance. However, with this method, the system is complicated, expensive, and has low range resolution for nearby objects. 
     (b) A device that transmitted infrared signals and then detected the intensity of the reflected signals to determine the object distance. However, with this method, the monitoring range is very short, and the system performance would be unstable due to environmental interference. 
     (c) A device that transmitted ultrasound signals and then detected the object echo-reception signals; the signal travel time can be used to determine the object distance. 
     U.S. Pat. No. 4,450,430 issued to Barishpolsky on Apr. 24, 1981 discloses a method for a diaphragm-type transducer assembly is mounted on the rear of an automobile to transmit ultrasound into left-and-right-hand target regions near the automobile. When the turn signal is turned on, it will transmit ultrasound pulse and listens for echo response from object. 
     U.S. Pat. No. 4,450,430 issued to Bonnefoy on Mar. 20, 1997 discloses a method for controlling a device for the ultrasound detection of objects in air, and to monitor object range during the vehicle reverse motion. 
     Typically, these systems teach ultrasonic object detection methods. However, these systems do not provide continuous visual range readings to the driver using wireless transmittal of detected object data, and the system installation would be difficult. 
     3. Vehicle Alarm System 
     Most automobile security systems relied on siren alarms for audio notification of vehicle security violation. If the vehicle owner was out of the hearing range, however, he or she will be unable to know whether the car alarm has been trigged. A known method of remote notification was to transmit a coded RF signal, upon alarm activation, to a portable receiver carried by the vehicle owner. 
     U.S. Pat. No. 5,905,432 issued to Greene on May 8, 1998 discloses a method for a vehicle anti-theft alarm system having a vehicle monitor with a battery, microprocessor, transmitter, audio generator and motion sensor, and the system also having a portable receiver. 
     U.S. Pat. No. 6,028,506 issued to Xiao on Feb. 22, 2000 discloses a method for a car alarm paging system, comprising an improvement of a conventional wireless phone pager and transmitter. The modified pager can be used both as a phone pager and also as a vehicle alarm transmitter for the notification of alarm activation to the pager carrier. A sample alarm trigger sensor module is provided in this invention. 
     Typically, these prior-arts teach vehicle alarm systems with a portable receiver, or a receiver with multiple uses. However, there are already many excellent vehicle, alarm systems available, and what these systems lacking is a method to remotely notify the user upon vehicle security violation. Therefore, a practical notification solution is not necessary to invent a more sophisticate alarm system with a remote receiver, but to invent a stand-alone notification system that can be coupled with a user-chosen alarm system. 
     Even though prior innovations may be suitable for the specific individual purpose to which they address, they differ from the present invention as hereinafter contrasted. 
     SUMMARY OF THE INVENTION 
     A main object of the present invention is to provide a wireless vehicular safety monitoring system, which can monitor tire pressure, detect objects behind the vehicle, and remotely notify vehicle security violations. 
     Another object of the invention is to provide a small battery-operated monitor unit, which can display individual tire pressure and detected-object range, and which can be carried by the vehicle owner for learning about car alarm activation from as far as 1000 feet away. 
     Another object of the invention is to provide a power-conservation method and apparatus, which allow the monitor unit to use minimal power when the vehicle is turned off. When a car is operating, its battery voltage is higher than when the engine is turned off. This system used a battery-voltage sensor module to detect the vehicle engine on/off status, and then transmit the status via RF signal to the monitor unit. Therefore, in engine-off time, the monitor unit can go to sleep and only wake up 10 milliseconds for every 2 seconds to detect any new engine-on message or alarm trigger message. This power-saving method enables the monitor unit to operate on a single 1.5V AA size battery for over six months. 
     Another object of the invention is to provide another power-conservation method and apparatus, which allow the tire pressure sensor module to stop consuming power when the vehicle is stationary. The tire pressure sensor module used omni-directional mercury roll motion switch for controlling its battery power supply, which will be turned on only while the vehicle is moving. This power-saving method enables the sensor module to operate on one set of button battery for over 18 months. 
     Another object of the invention is a method for constructing miniature sensor modules by first laying out print circuit and mounting components on a flexible rectangular sheet. Then the circuit sheet is vertically mounted on the base print circuit board for circularly surrounding the protruding pressure sensor, so that optimal utilization of space inside the module housing can be realized. 
     Another object of the invention is a method for mounting ultrasonic transducers on the license plate holder. And a method for transmitting range data of detected objects to the monitor unit by coded RF signal. 
     Another object of the invention is a method to re-transmit the sensor module RF signals for enhancing monitor signal reception. For example, signals from tire pressure sensor modules mounted on the rear tire stems of a long truck or trailer might be too weak for the cab-mounted monitor to receive. A RF signal repeater, installed near the rear section of the truck, can pick up the sensor module signal there and then re-transmit the signal to the monitor via a more efficient antenna. 
     The present invention is directed toward a vehicular monitoring system that gathers information through wireless sensor modules. Actual working models have been constructed to prove the practicality of the invention. The invention has provided numerous innovations to enable the making of a viable product. 
     The invention has the advantages of integrating several essential vehicle-monitoring functions into one package, and displaying the information on a battery-operated monitor unit, which can be put on any viewable location inside the vehicle, or be carried by the vehicle owner for remote notification. The monitor unit is designed to be small and durable, using one 1.5V AA battery that can support over six months of operation. 
     Another advantage of the invention is to provide a practical tire pressure monitoring solution. Prior proposals have discussed various concepts of monitoring tire pressure with a valve stem mounted sensor. Until now, however, very few (if any) such products are available on the market. This is a clear indication of its technical difficulties. The present invention overcomes the technical challenges by providing means to miniaturize the sensor module and to prolong its operational life between battery changes. The working tire pressure sensor module has a diameter and height of only 0.62 inches, and can last almost 18 months without needing to replace batteries. 
     Another advantage of the invention is to provide a practical tire pressure monitoring solution for all vehicles, large and small, by using RF signal repeaters to relay signals from farther away sensors to where the monitor is mounted. 
     Another advantage of the invention is to provide a practical solution for a driver to learn about the presence and distance of rear objects during vehicle reverse motion. The invention provided means for easy installation of ultrasonic transducers on the license plate holder, and for transmitting detected object range to the monitor unit via encoded RF signal. 
     Another advantage of the invention is to provide an effective way for vehicle owner to learn about vehicle alarm activation from as far as 1000 feet away. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is the block diagrams for the vehicle monitor, tire pressure sensor module, and object detection module. 
     FIG. 1B is the block diagrams for the engine ON/OFF sensor module, alarm trigger module, and RF signal repeater module. 
     FIG. 2A is a sketch of the mercury omni-directional motion switch, and tire sensor module installation. 
     FIG. 2B is a sketch of the miniature tire pressure sensor module assembly. 
     FIG. 2C is a sketch of the tire pressure sensor stack assembly. 
     FIG. 2D is a sketch of the object detection module installation. 
     FIG. 3 is a drawing depicting the display panel of the monitor unit. 
     FIG. 4A is a schematic of the RF section of the monitor unit. 
     FIG. 4B is a schematic of the logic section of the monitor unit. 
     FIG. 5 is a schematic of the tire pressure sensor module. 
     FIG. 6 is a schematic of the object detection module. 
     FIG. 7 is a schematic of the vehicle engine On/Off sensor module. 
     FIG. 8 is a schematic of the alarm trigger sensor module. 
     FIG. 9 is a schematic of the RF signal repeater module. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention is described herein with references to the figures using reference designations as shown in the figures. The wireless vehicle monitoring system comprises battery-powered components that are referred to as the monitor unit and sensor modules, shown by way of block diagram representation in FIG.  1 A and FIG.  1 B. Together, these devices monitor tire pressure, alarm activation, and object detection status. When the vehicle is moving, the monitor can display individual tire pressures. During vehicle reverse motion, the monitor can display detected object range with respect to the rear of the vehicle. In the events that the tire pressure drops below a predetermined level, alarm system has been tripped, or object is detected behind the vehicle, the monitor will generate warnings for alerting the system user. 
     The miniature tire pressure sensor module, shown by FIG. 2A, is securely attached to the valve stems of the respective tires. These tire pressure sensor modules are encased in a small plastic housing, shown by FIG. 2B, with suitable threads for valve stem attachment. The tire pressure sensor modules are made by vertically mounting a flexible print circuit sheet on top of a base print circuit board, and surrounding the protruding pressure sensor, shown by FIG.  2 C. The rear object detection module is shown by FIG.  2 D. The monitor unit is enclosed in a pager-sized plastic housing with a LCD display panel, shown by FIG.  3 . The small monitor unit can be dashboard mounted, rearview mirror mounted, or carried by the user. These devices are also shown by the way of schematic representation in FIG.  4  through FIG. 9, respectively. 
     Now, referring to FIGS. 3, the monitor display panel shows a graphic representation of a vehicle, with icons S 1  to S 25  indicating respective tire locations in the vehicle, which included possibly a trailer. Icon S 26  is to indicate that incoming signal is out of the receivable range. Icon S 27  indicates proper monitor operation and proper operating tire pressures. Icon S 28  indicates monitor malfunction or improper tire pressure, such as a low tire pressure. Icon S 29  indicates low battery level in the monitor, or in one or more of the tire pressure sensor modules if the respective tire icon is flashing. The monitor display panel further includes a plurality of numerical indicators, such as digit  1  and digit  2 . These numerals can display a two-digit tire pressure values in PSI, as indicated by icon S 30 , or a two-digit tire pressure in BAR, as indicated by icon S 31 . Display digits  1 - 2  are also used to display the detected object range during vehicle reverse motion and, when in programming mode, to display system setup values such as the proper tire pressure level. 
     Referring to FIG. 4A, the monitor receiver obtains a +3V clean power from a J 1  at pin  6 . The incoming coded message, which is a 315 MHz RF Amplitude Shift Key (ASK) modulated signal, is received by a helical antenna ANT 1  and processed by an ASK receiver module U 1 . The receiver module U 1  is an integrated circuit with a built-in mixer, oscillator, frequency multiplier, post mixer amplifier, limiter, IF filter, demodulator, and data filters. The mixer is a single balanced emitter-coupled mixer with internal biasing. Matching of the RF source impedance to the mixer input requires an external circuit, which comprised capacitors C 1 , C 2 , C 4  and inductor L 1 . The oscillator is based on a transistor connecting in a common collector configuration, and is followed by a cascade stage driving a tuned circuit. The voltage at this tuned circuit drives the frequency multiplier, resistor R 3  sets the bias current of the oscillator, and overtone crystal Y 1  controls the frequency of the oscillator. The capacitors between base and emitter C 11  and ground C 14  caused the oscillator transistor to appear as having negative resistance at small signal levels, and thereby caused the oscillator to start. A parallel resonance circuit L 2  and capacitor C 14 , connecting to the emitter of the oscillator transistor, prevents oscillation at the fundamental frequency of the crystal. Capacitor C 15  is used for bypass to ground. The LC tank circuit by L 4 , L 5 , and C 12  at the output of the oscillator is used to select the third harmonic of the oscillator frequency. The frequency multiplier is an emitter-coupled transistor pair driving an off-chip balanced tuned circuit. Resistor R 2  sets the bias current of this emitter-coupled pair. The bias voltage is set by resistor R 4  to allow sufficient voltage swing at the mixer output. The post mixer amplifier (PMA) is a differential input, single-ended output amplifier. Amplifier gain is provided in order to reduce the influence of the limiter noise figure upon the total noise figure. The IF filtering with high selectivity is realized by means of the ceramic filter F 1 , which feeds the IF from the PMA at U 1  pin  22  through the coupling capacitor C 10  to the limiter input at U 1  pin  20 . The limiter is a single-end input, multiple stage amplifier with high total gain. Amplifier stability is achieved by means of the DC feedback capacitor C 5 , which is also used to determine the lower limiter cut-off frequency. Coming from the limiter, the ASK signal is fed into the Ask demodulator. After the demodulator, a two-stage data filtering circuit is provided in order to suppress unwanted frequency components. A RC low-pass filter by C 7 , C 8 , and C 9  with on-chip resistors is provided. Finally, the digital data output of the monitor receiver module will be sent through J 1  at pin  1 , to the monitor logic section for further processing. For power management, the monitor receiver module can be set to sleep mode, and thereby consuming less power, by pulling down the voltage at pin  3  of J 1 . 
     Referring to FIG. 4B, the monitor logic section includes a U 2 , which is a high performance eight-bit CMOS microprocessor with internal 4 K EPROM program memory, 160 bytes of RAM data memory and on-chip LCD driver. Microprocessor U 2  is clocked by a 4 MHz crystal oscillator Y 2 . A one kilo bit serial electrically erasable programmable read only memory (EEPROM) U 3  stores user-programmed low tire pressure trigger values, sensor module identification codes and other important parameters. EEPROM U 3  is connected to microprocessor U 2  at pins PA 3 , PA 4 , PA 5 , and PA 6 , respectively. The PC communication port for programming EEPROM U 3  is provided by connectors J 3 , J 4 , and J 5 . Microprocessor U 2  is powered by the reference VCC +3.3V having filter capacitors C 23 , C 24 , and C 25 . Upon power up, resistor R 13  and capacitor C 22  reset the microprobe of U 2  to start execution of an operating program stored in the U 2  EPROM. Microprocessor U 2 &#39;s LCD segment output seg 0 - 13  and com 0 - 3  are connected through a flexible cable to a display panel LCD 1 . Output at PC 3  drives switch transistor Q 1  through resister R 5  to control the LCD backlight lamp LP 1 . Capacitors C 18 , C 19  and C 20  are used for on-chip LCD voltage pump. Resistors R 6  and R 7  provide a voltage for the LCD power supply. Microprocessor U 2  output at pin PC 1 , connecting to pin  3  of J 2 , controls the power-up and power-down of monitor receiver FIG.  4 A. To wake up microprocessor U 2  itself from sleep mode, transistor Q 2  and resistors R 8 , R 9 , R 10  are used as an inverter for the input data so that a pull down level at J 2  pin  1  will be provided to PA 7  when the data preamble signal is presented. The input data from J 2  pin  1  is sent to PB 7  for decoding. Microprocessor U 2  pins PB 1 , PB 2 , and PB 3  are connected to monitor key-switches S 1 , S 2  and S 3 , respectively, for receiving user manual inputs. A buzzer LS 1  is a piezoelectric ceramic device driven by transistor Q 3 , which has a base resistor R 14  connecting to microprocessor U 2  at an output pin PA 1 . Buzzer LS 1  is energized by microprocessor U 2  to alert the user when the monitor receives and decodes a low tire pressure message from a tire sensor module, or a car alarm tripped message from the alarm trigger sensor module. To operate the monitor by a single 1.5V battery BT 1 , the DC—DC converter that consists of U 4 , L 6 , C 26  and C 27  converts BT 1  power to a constant +3.3V voltage VCC. When BT 1  voltage drops to lower than 0.9V, U 4  generates a battery low signal at pin  4 , which will then be provided to microprocessor U 2  input pin PC 0 . In this case, the monitor lights up the battery low icon S 13  and generates battery low alert to inform user for replacing the battery. 
     Referring to FIG. 5, the tire pressure sensor module is housed in a plastic enclosure, shown by FIG. 2B, and is securely fastened to a respective tire valve stem, also shown by FIG.  2 A. The tire pressure sensor module is assembled with a base print circuit board and a flexible print circuit board, shown by FIG.  2 C. FIG. 2C shown a unique way of constructing miniature assembly, wherein the pressure sensor is installed on a circular base print circuit board, while the other components are installed on a flexible print circuit sheet. The flexible sheet is then mounted vertically on the base circuit board and surrounded the protruding pressure sensor, thereby achieving optimal space utilization within the small cylindrical enclosure. The tire pressure sensor module electronics support sensory logic and transmitter functions. Sensory electronics include a piezo-resistive pressure sensor U 9 , which comprises four strain resistive sensitive resistors diffused in silicon. These resistors are connected in a Whetstone bridge configuration, whereby two resistors increase resistance with positive pressure while the other two decrease in resistance. When pressure is applied to sensor U 9 , the resistors in the arms of the bridge of sensor U 9  changed resistance by an amount directly proportional to the pressure applied. When a voltage is applied to the bridge, there will be a resulting differential output voltage indicating sensed tire pressure. Sensory logic consists of (1) a micro-power dual amplifier U 8  connected to the sensor bridge U 9  and to resistors R 21  through R 26 , (2) a voltage regulator U 5  having filter capacitor C 28 , and (3) another high performance CMOS eight-bit microprocessor U 6  with an attached EEPROM U 7  using a pull up resistor R 16  on GP 1  input. A six-volt battery pack BT 2  having filter capacitor C 30  is connected to switch S 4 , which is a mercury roll omni-directional motion switch activates by gravitational forces. In S 4 , pure hydrogen gas is contained in a small glass container, shown by FIG. 2A, encapsulating first and second electrical contacts. Under gravitational or centrifugal forces, mercury disposed on the first electrical contact flows to make contact with the second electrical contact and thereby closes switch S 4 . A tire value stem mounted switch S 4  can detect sufficient motion and close switch contacts within 100 milliseconds after the vehicle reaches between 12 to 15 miles per hour. Those skilled in the art are adept at making motion detection switches sized to a small valve stem plastic casing. Battery BT 2  output voltage level is divided by resistors R 18  and R 20  to provide an analog battery voltage value to microprocessor U 6 , which can then convert it into a digital value for monitoring battery BT 2  usage. The micro-power amplifier U 8  conditions the sensed tire pressure voltage signal for input to the on-chip A/D converter of microprocessor U 6 , as an indication of the tire pressure sensed by sensor U 9 . The radio frequency transmitter consists of transistor circuit Q 4 , resistors R 19 , inductor antenna ANT 2 , capacitors C 29 , C 31 , and C 32 , and a SAW resonator Y 3  for providing a transmitter frequency signal at 315 MHz. The transmitter is modulated by microprocessor U 6  at pin GP 5  through resistor R 17 . The GP 0 -GP 5  terminals of microprocessor U 6  are bi-directional inputs and outputs. Terminal GP 0  is used to receive the analog pressure signal for the on-chip A/D converter. Terminal GP 1  is used to send or receive data to EEPROM U 7 . Terminal GP 2  receives the battery voltage level reference and can output a digital clock signal to EEPROM U 7 . Terminal GP 3  is connected to U 5  at VOUT pin for the on-chip power-on reset. Terminal GP 4  is an output used to power sensor U 9  and amplifier U 8 . 
     For reducing the circuit size, an internal 4 MHz RC oscillator is used to clock microprocessor U 6 . Terminal GP 5  outputs data to the transmitter for amplitude modulation of the 315 MHz radio frequency carrier signal. Under program control, microprocessor U 6  outputs an encoded digital message data string for amplitude shift key modulating the carrier signal from the RF transmitter circuit. To minimize power consumption, the tire pressure sensor module operates in a dormant mode and is only powered up when the tire is in motion, as detected by motion switch S 4  that operates to connect battery BT 2  to the electronic components of sensor module. Microprocessor U 6  is programmed to periodically read the tire air pressure from sensor U 9  through amplifiers U 8 . If there has been a significant pressure change, such as +/−2PSI, from the previous reading, the sensor module transmits an ASK modulated radio frequency signal to the monitor using inductor antenna ANT 2 . The RF message consists the sensor module ID, tire air pressure value, battery level data, and checksum. Upon receiving the RF message from the tire sensor module, the monitor compares the tire pressure value received to a pre-programmed value stored in the EEPROM U 7 . If the received value is less than a predetermined low-pressure trigger value, the monitor alerts the driver by displaying the low tire pressure value on LCD, by flashing the corresponding tire icon for the respective tire, and by sounding an alarm using buzzer LS 1 . 
     Referring to FIG. 6, the object detection module is powered by the vehicle reverse lamp&#39;s +12V power, which will be present when the vehicle is in reverse motion. Diode D 2  is used for the +12V input protection. The +12V power is converted to VCC +5V power by regulator U 13 , and capacitors C 40  and C 41 . U 12  is a gain control amplifier for use with microprocessor U 11  to receive the sonar echo signal. Resistor R 31  connects amplifier U 12  at pin  8  to ground for providing the internal biasing reference. The amplifier U 12  gain can be set with a resistor R 30  from GIN to GADJ. Digital control of amplifier U 12  gain is provided with gain control inputs at amplifier U 12  pin GCA, GCB, GCC and GCD. These inputs have to be driven synchronously (all inputs were stabilized within 1 us) by microprocessor U 11  at pins PA 0 -PA 3 . Capacitor C 38  provides an AC coupling between different amplifier U 12  stages for proper biasing. A parallel combination of inductor L 7  and capacitor C 37 , between amplifier U 12  at pin LC and pin Vcc, provides amplifier U 12  with an externally controlled gain. This circuitry allows the gain control to compensate for the attenuation of distant signals and, at the same time, also maximizes noise and side lobe rejection. Amplifier U 12 , at pin XIN, and diode D 1  provide clamping for the transformer T 1  secondary when used for transducer during the ultrasonic transmitting. The amplifier U 12  output is normally held at a low level by an internal 1 uA current source. When an input of sufficient amplitude is received, the 1 uA discharge current and a 50 uA charging current alternately drive the output. A capacitor C 42  is required to connect amplifier U 12  at pin REC to ground for integrating the received signal, so that one or two noise pulses are not recognized. To cover a larger area behind the vehicle, two ultrasonic transducers are used, shown by FIG.  2 D. The transducer pair can be mounted on the license plate holder and be secured by the existing anchoring screws, shown by FIG.  2 D. The two ultrasonic transducers are both connected to an I/O port J 6  at pin  6  and pin  7 . During vehicle reverse motion, microprocessor U 11  generates 15 pulses of 49.4 KHz burst signal, and outputs this ultrasonic signal at pin PB 4  to a transformer T 1  at pin  2 , first through a resistor R 32  and then a transistor Q 6 . Transformer T 1  outputs the transformed signal at pin  4 , through an AC coupling capacitor C 39 , to I/O port J 6  at pin  6 , and thereby trigger the transducers to send out ultrasonic pulses. After the ultrasonic pulses are sent, these transducers are used as sensors to pickup the echoed back ultrasonic signals from nearby objects. The echo signals are then fed to amplifier U 12  pin G 1 IN through capacitor C 39 , transformer T 1  secondary, and resistor R 29 . When the echo signals reached a predetermined strength level, amplifier U 12  pin REC provides a high level output to microprocessor U 11  pin  13  to inform that an object echo was detected. The echo time, then, is the time differential between sending out ultrasonic pulse and receiving its echo. After the echo time is computed, microprocessor U 11  then calculates the detected object range with the following equation: 
     
       
         Distance (in inches)=Echo time/147.9 microseconds. 
       
     
     When the object range data is obtained, microprocessor U 11  produces a data stream, incorporating with an identification code, range data and a checksum, and sends it over to a RF transmitter circuit, which consists a transistor Q 5 , resistors R 27  and R 28 , capacitors C 33 -C 35 , and a resonator Y 5 . Microprocessor U 11  sends the data stream out at output pin PB 6  to transistor Q 5  through resistor R 28  to modulate the 315 MHz RF. The modulated RF signal is then transmitted by antenna ANT 3 . Microprocessor U 11  also provides an audio output control at pin PB 3  to I/O port J 6  pin  3  for generating different acoustic tones to represent the detected object distance. 
     An oscillator consisting of a 4 MHz crystal Y 4  clocks microprocessor U 11 . A capacitor C 32  provides the AC de-coupling for U 10  and U 11 . A 1 K bits EEPROM U 10  is used to store sensor module ID and some important parameters. For writing the ID and parameters to EEPROM U 10 , microprocessor U 11  supports a RS232 TX/RX connection to I/O port J 6  at pin  4  and pin  5  for communication between a PC and the sensor module. 
     Referring to FIG. 7, the vehicle engine On/Off sensor module is housed in a miniature enclosure, not shown, and is mounted near the vehicle battery power line to monitor the battery voltage change. For passenger vehicles, there is about a two-volt battery voltage difference when the engine is on versus when it&#39;s off. When the engine is off, the battery voltage power is at around +12V and, when the vehicle engine is turned on, the battery voltage power is increased to around +14.4V. For sensor module power supply, a voltage regulator U 14  at pin VIN is connected to the vehicle battery through a resistor R 33  and, at pin VOUT with a filter capacitor C 42 , outputs a +5V voltage. In addition, the vehicle voltage power is applied to a resister diver R 36  and R 38  to provide an analog voltage value for a microprocessor U 15 &#39;s on-chip A/D at pin GP 2 . The high performance CMOS eight-bit microprocessor U 15  has an on-chip A/D pin at GP 2  to convert the analog voltage value to a digital value. A 16-byte EEPROM U 16  with a pull up resistor R 34  provides memory space to store module ID and some important parameters. The radio frequency transmitter consists of transistor Q 7 , resistors R 37 , inductor antenna ANT 4 , capacitors C 43 , C 44 , and C 45  and a SAW resonator Y 6  for providing a transmitter frequency signal at 315 MHz. The transmitter is modulated by microprocessor U 15  at pin GP 5  through a resistor R 35 . When microprocessor U 15  detected the vehicle battery voltage changed to above +12V and near +14.4V, an engine-on message is sent to the monitor, otherwise, an engine-off message is sent to the monitor. When the vehicle engine is turned off, the monitor is put to sleep for reducing its battery power consumption. The monitor can still receive messages in sleep mode if the incoming signal had a long enough preamble period of over 2 seconds. Upon receiving the engine-on message, the monitor wakes up and resumes normal operation, until receiving the engine-off message and going back to sleep again. 
     Referring to FIG. 8, the vehicle alarm trigger sensor module is used to monitor the car alarm system, and is mounted near the existing vehicle alarm system. For module power supply, a voltage regulator U 17  at pin VIN is connected to the vehicle battery through a resistor R 33  and a protection diode D 3  and, at pin VOUT with a filter capacitor C 46 , outputs a +5V voltage. A 16-byte EEPROM U 16  with a pull up resistor R 40  provides memory space to store module ID and some important parameters. A transmitter circuitry sends RF messages to the monitor. The transmitter consists of a RF oscillator, a low pass filter match network, and a RF power amplifier U 20  to keep the RF signal strength at a range of over 1000 feet. The RF oscillator consists of a-transistor Q 8 , a resistor R 44 , a resonator Y 7 , and capacitors C 47  and C 48 . The low pass filter match network consists of a resistor R 47  and capacitors C 49 , C 50 , C 51 , C 52 , L 9 , and L 10 . The RF power amplifier U 20  is a medium power linear amplifier IC. When the car alarm system is trigged, it sends a high DC voltage to the audio alarm siren. This DC voltage source at the siren terminal provides an alarm trigger input signal to a microprocessor U 18  at pin GP 2 , through a resistor diver R 46  and R 45 . When microprocessor U 18  sensed the trigger voltage, it sends out an “alarm system trigged” message at pin GP 5 . The message data, which includes a module ID, trigger data, and a checksum, is sent to transistor Q 8  through resistor R 42  to modulate the 313 MHz RF oscillator. Output from the oscillator goes through the low pass filter match network onto the RF power amplifier U 20 , at pin ‘RF1 IN’. The power-down pin at amplifier U 20  pin PD is controlled by the microprocessor U 18  pin GP 0  having an AC de-coupling capacitor C 57 . A capacitor C 55  provides the coupling between pre-amplifier output pin ‘RF1 OUT’ and RF power stage input pin ‘RF2 IN’. An inductor L 14  and a resistor R 48  provide a match load impedance for the two stages. Capacitors C 56 , C 59 , C 60 , C 61 , and C 62  are used for RF de-coupling. A capacitor C 58  and inductors L 12  and L 13 , together, is an AC de-coupling network between the DC power and RF power amplifier U 20  output, which provides filtered DC power for the RF power amplifier U 20 . Finally, RF power amplifier U 20  sends out a RF output through a match network of L 11 , C 53  and C 54  to the antenna ANT 5  for transmission. 
     Referring to FIG. 9, the RF signal repeater module is used to re-transmit the sensor module RF signals for enhancing monitor signal reception. For example, signals from tire pressure sensor modules mounted on the rear wheels of a long truck or trailer might be too weak for the cab-mounted monitor to receive. A RF signal repeater, installed near the rear section of the truck, can pick up the sensor module signal and then re-transmit the signal to the monitor via a more efficient antenna. The repeater works in a half-duplex mode. Any sensor signals picked-up by the repeater will be transmitted out in the same signal format. Therefore, the receiver and transmitter of the repeater can share the same antenna ANT 3 . The receiver circuit is the same as the RF section of the monitor. The transmitter circuit is same as in FIG.  8 . The received sensor signal is sent to the receiver through a capacitor C 63 . The demodulated digital data is sent to a microprocessor U 18  pin  5  by a resistor network of R 46  and R 45 . Upon receiving the signal, microprocessor U 18  will send out the received data, in its original format, to the transmitter for transmission. 
     The message protocol starts with a preamble period and a synchronization period, then followed by sensor group ID, sensor ID, message data, parameter data, and lastly the checksum. The sensor group ID represented difference sensor module. The sensor ID is an identification number of the respective sensor module within same sensor group ID. The preamble period is 4 milliseconds for the tire pressure sensor module and 2.5 seconds for all other sensor modules. Base on the preamble period design, a power saving scheme is used in the monitor. When the monitor detected a vehicle engine ‘Off’ message, it goes into a long sleeping mode. Thereafter the monitor wakes up every 2 seconds and powers up the receiver to determine whether any engine ‘On’ or alarm trigger signal is present. If there is an “alarm trigger” message, the monitor will generate a 80 dB audio alert and display the alarm icon on LCD, then the monitor will go back to sleep. If it is an engine ‘On’ message, monitor will go into a short sleeping mode, waking up every 4 milliseconds and powering up the receiver to check for new messages. The monitor will once again go back to long sleep upon receiving an engine ‘off’ message. 
     The wireless data communication is one-way from the sensor modules to the monitor. The transmission signal is in bits having logic one or logic zero as value, and is represent by variations in the signal amplitude modulation level. A bit time period is divided into 3 T&#39;s, with each T at about 270 microseconds. When the amplitude modulation level is high for two T and low for one T, the signal is logic one. Otherwise when the amplitude modulation level is high for one T and low for two T, the signal is a logic zero. Messages are preferably transmitted with the most significant bits first. It is difficult for the monitor microprocessor to synchronize the receiving data message without know the timing. Therefore, a 10 T synchronization period will be sent by a sensor module after the preamble period, so that the monitor microprocessor can calculate the pulse period with the following equation: 
     
       
           T =(detected synchronize period)/10. 
       
     
     Since the tire pressure sensor module is mounted on the tire valve stem, it is very difficult to use traditional mechanical roll motion switch to detect vehicle motion with a 360-degree tire rotation. The usage of omni-directional mercury roll motion detection switch is a key invention to solve this problem. Until now, there is no sufficiently small tire valve stem mounted sensors available. The present invention provided a miniature assembly design for the tire pressure sensor module. In the present invention, the height of the tire pressure sensor module for the valve stem is contributed mainly by the heights of the silicon sensor and the battery pack. Most other components are mounted on a rectangle flexible print circuit board, shown by FIG. 2C, like a donut around the silicon sensor. The total height of the sensor over the top of valve stem is only 0.62 inch in the present invention. 
     The above system and methods describe a preferred embodiment using exemplar devices and methods that are subject to further enhancements, improvement and modifications. However, those enhancements, improvements modifications may nonetheless fall within the spirit and scope of the appended claims. 
     ADDITIONAL PREFERRED EMBODIMENTS AND SCOPE 
     The above-preferred embodiment illustrated a typical embodiment of the present invention. There are various possibilities with regard to additional embodiments. 
     An additional embodiment for a tire pressure monitoring system can be illustrated with a combination of a monitor unit with tire pressure sensor modules, shown in, FIG. 1, FIG. 2A, FIG. 2B, FIG. 2C, FIG. 3, FIG. 4A, FIG. 4B, FIG. 5, and FIG.  7 . 
     Another additional embodiment for an object detection system can be illustrated with a combination of a monitor unit with object detection modules, shown in FIG,  1 , FIG. 2D, FIG. 3, FIG. 4A, FIG. 4B, FIG. 6, and FIG.  7 . 
     Another additional embodiment for an alarm remote notification system can be illustrated with a combination of a monitor unit with an alarm trigger sensor modules module, shown in FIG. 1, FIG. 3, FIG. 4A, FIG. 4B, FIG. 7, and FIG.  8 . 
     Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the following claims and their legal equivalents, rather than by the examples given.