Electronic parking meter and system - Patent Review 5407049

I claim:

1. An electronic parking meter comprising:

(a) a stanchion;

(b) a clam-shaped member, mounted on said stanchion, comprising a front wall and a rear wall, and a hollow area between said walls, a board mounted in said hollow area, a coin slot mounted in said front wall, and a coin chute in said hollow area in communication with said slot;

(c) means, mounted in said chute, for sensing the insertion of said coin in said slot;

(d) means, mounted in said chute, for determining the denomination of said coin, comprising a first pivotable arm and a first Piezo strip in contact with said first pivotable arm;

(e) processing means mounted on said board;

(f) display means, mounted on said board, connected to said processor; and

(g) power source means for providing power to said electronic parking meter.

2. The parking meter of claim 1 wherein said parking meter further comprises means, mounted on said board, for determining the presence of a vehicle at said parking meter.

3. The parking meter of claim 2 wherein said parking meter further comprises means, mounted on said board, for transferring data from said processing means to external devices.

4. The parking meter of claim 3 wherein said parking meter further comprises means, mounted in said chute, for determining whether said coin contains ferrous material.

5. The parking meter of claim 4 wherein said parking meter further comprises means for determining the presence of a jam in the chute.

6. The parking meter of claim 5 wherein said chute comprises a pair of opposing transparent blocks which define the bounds of said chute and said first pivotable arm is mounted on said blocks.

7. The parking meter of claim 6 wherein said means for sensing the insertion of a coin in said slot comprises a second pivotable arm mounted on said blocks, and a second Piezo strip, in contact with said second pivotable arm.

8. The parking meter of claim 7 wherein said means for determining the presence of ferrous material in said coin comprises a reed switch mounted in one of said pair of blocks and a permanent magnet mounted in the other one of said pair of blocks, opposite said reed switch.

9. The parking meter of claim 8 wherein said means for detecting the presence of a jam comprises at least one IR diode emitter mounted in one of said pair of blocks and at least one photo-cell mounted opposite said at least one IR diode emitter in the other of said pair of blocks.

10. The parking meter of claim 9 wherein said means for determining the presence of a vehicle at said parking meter comprises a sonar transducer connected to said processing means.

11. The parking meter of claim 10 wherein said display means comprises a liquid crystal display connected to said processing means.

12. The parking meter of claim 11 wherein said power source means comprises at least one non-rechargeable battery which provides the full power requirements of said parking meter.

13. The parking meter of claim 1 wherein said power source means comprises at least one non-rechargeable battery which provides the full power requirements of said parking meter.

14. The parking meter of claim 13 wherein said parking meter further comprises means, mounted on said board, for determining the presence of a vehicle at said parking meter.

15. The parking meter of claim 14 wherein said parking meter further comprises means, mounted on said board, for transferring data from said processing means to external devices.

16. The parking meter of claim 15 wherein said parking meter further comprises means, mounted in said chute, for determining whether said coin contains ferrous material.

17. The parking meter of claim 16 wherein said parking meter further comprises means for determining the presence of a jam in the chute.

18. The parking meter of claim 17 wherein said chute comprises a pair of opposing transparent blocks which define the bounds of said chute and said first pivotable arm is mounted on said blocks.

19. The parking meter of claim 18 wherein said means for sensing the insertion of a coin in said slot comprises a second pivotable arm mounted on said blocks, and a second Piezo strip, in contact with said second pivotable arm.

20. The parking meter of claim 19 wherein said means for determining the presence of ferrous material in said coin comprises a reed switch mounted in one of said pair of blocks and a permanent magnet mounted in the other one of said pair of blocks, opposite said reed switch.

21. The parking meter of claim 20 wherein said means for detecting the presence of a jam comprises at least one IR diode emitter mounted in one of said pair of blocks and at least one photo-cell mounted opposite said at least one IR diode emitter in the other of said pair of blocks.

22. The parking meter of claim 21 wherein said means for determining the presence of a vehicle at said parking meter comprises a sonar transducer connected to said processing means.

23. The parking meter of claim 22 wherein said display means comprises a liquid crystal display connected to said processing means.

24. A coin receptor for accepting and detecting coins of various denominations comprising:

(1) a slot;

(2) a chute in communication with said slot;

(3) means, mounted in said chute, for detecting the insertion of said coins into said slot;

(4) means, mounted in Said chute, for determining the denomination of each of said coins;

(5) means, mounted in said chute, for detecting the presence of ferrous material in said coins, said means comprising a permanent magnet and a reed switch: and

wherein said means for detecting the insertion of said coins comprises a first pivotable lever arm and a first Piezo strip in contact with said first pivotable lever arm.

25. The coin receptor of claim 24 wherein said means for determining the denominations of said coins comprises a second pivotable lever arm and a second Piezo strip in contact with said second pivotable lever arm.

26. The coin receptor of claim 25 wherein said coin receptor further comprises means, mounted in said chute, for detecting the presence of a jam in said chute.

27. The coin receptor of claim 27 wherein said means for detecting the presence of a jam in said chute comprises at least one IR diode emitter and at least one photo-cell, each one of said at least one photo-cell being mounted opposite a respective one of said at least one IR diode emitter to receive the IR light transmitted by said respective one IR diode emitter.

28. The coin receptor of claim 27 wherein said chute comprises a first and a second side wall, said side walls comprising a transparent material and having a gap therebetween, said permanent magnet being mounted in said first side wall and said reed switch being mounted in said second side wall opposite said permanent magnet.

29. The coin receptor of claim 28 wherein said chute further comprises a first rod connected to said side walls and bridging said gap and wherein said first pivotable lever arm is pivotably connected to said first rod.

30. The coin receptor of claim 29 wherein said chute further comprises a second rod, connected to said side walls and bridging said gap, and wherein said second pivotable lever arm is pivotably connected to said second rod.

31. The coin receptor of claim 30 wherein each said at least one IR diode emitter is mounted in said first side wall and each of said at least one photo-cell is mounted opposite said at least one IR diode emitter in said second side wall.

32. The coin receptor of claim 31 wherein said coin receptor generates electrical signals which are connected to processing means for processing said electrical signals, and wherein said first Piezo strip is connected by electrical conductors to said processor.

33. The coin receptor of claim 32 wherein said second Piezo strip is connected by electrical conductors to said processing means.

34. The coin receptor of claim 33 wherein said reed switch is connected by electrical conductors to said processor.

35. The coin receptor of claim 34 wherein said at least one IR diode emitter and said at least one photo-cell are connected by electrical conductors to said processor.

36. A low powered electronic parking meter system, accepting coins of various denominations, said system comprising:

(a) a coin receptor comprising a coin slot, a chute in communication with said coin slot, a coin detector mounted in said chute, first means, mounted in said chute, for determining the denominations of said coins, and for sensing the insertion of said coins in said slot, means for determining the ferrous content of said coins, and second means for determining the presence of a jam in said chute, all of said means generating information in the form of electrical signals, said first means comprising at least one pivotable lever arm and a Piezo Strip in contact with said at least one pivotable lever arm;

(b) processing means, connected to said coin receptor, for accepting and processing said information, said processor means further comprising means for storing said processed information;

(c) vehicle detection means for detecting the presence of a vehicle at said coin receptor location, said vehicle detection means comprising and ultrasonic transducer responsive to control signals from said processor means;

(d) means for communicating said stored information to a hand-held computer;

(e) display means connected to said processor means, said display means comprising a liquid crystal display;

(f) flasher means for indicating overtime parking by a vehicle at said location; and

(g) at least one standard, commercially available non-rechargeable battery for providing the full power requirements of said coin receptor, processor means, vehicle detection means, communicating means, display means and flasher means.

37. The system of claim 36 wherein said means for communicating comprises a first transceiver connected to said processor means and a second IR transceiver in said hand-held computer.

38. The system of claim 37 wherein said processor means and communication means provides data of pre-determined categories to said hand-held computer and wherein said hand-held computer further comprises means for storing said data.

39. The system of claim 38 wherein said hand-held computer further comprises second means for communicating said stored data to a central computer facility.

40. The system of claim 39 wherein said stored data includes low battery indication, equipment failure indication, coin jam indication, total revenue, number of parked cars, time bought, expired time and number of cars with expired time.

41. The system of claim 40 wherein said system comprises power conservation means for operating said coin receptor selector, said processor means, said display means, said flasher means, said communicating means, and said vehicle detection means in power-off, inactive or active states.

42. The system of claim 41 wherein said system comprises means for checking the power voltage level of said at least one battery at pre-determined intervals and for providing an indication of a low battery condition when said voltage level drops below a pre-determined level.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

This invention relates generally to parking meters and systems and more specifically to electronic parking meters and systems.

Parking meters permit vehicles to be parked on streets for an allowable time determined by the number and denominations of coins which are placed in the parking meter. A clock mechanism in the parking meter runs down the allowable time until it reaches zero, and an overtime parking indication appears.

The coin receiving devices of the parking meters perform various tests to determine whether an acceptable coin has been inserted, and the denomination of the coin. Circuitry which tests for the presence of ferrous material (i.e., slugs) includes Hall-effect sensors, and frequency shift metallic detectors. The denomination is determined by devices which measure the diameter of the coin such as infra-red emitting diodes and photo-diodes, or which measure the weight of the coin using strain gauges, and the like.

Coin receiving mechanisms which use IR detectors, Hall-effect circuitry, magnetic fields and light sensing rays with microprocessors include U.S. Pat. No. 4,483,431 (Pratt); U.S. Pat. No. 4,460,080 (Howard); U.S. Pat. No. 4,429,648 (Meyer) and U.S. Pat. No. 5,119,916 (Carmen et al.).

In recent years, electronic parking meters and systems have been developed which use microprocessors in conjunction with electronic displays, IR transceivers to communicate with auditors, and ultrasonic transceivers to determine the presence of vehicles at the parking meter. U.S. Pat. Nos. 4,823,928 and 4,967,895 (Speas) disclose electronic parking meters which use microprocessors, electronic displays, IR transceivers, solar power and sonar range finders.

The sophisticated devices which use microprocessors, electronic displays and IR and ultrasonic transducers consume too much power to operate by non-rechargeable batteries alone. Thus, the Speas' patents disclose the use of solar power cells which charge capacitors or rechargeable batteries.

Various problems exist with the use of solar power sources including the use of parking meters in shady areas, or the use of parking meters during periods in which there is very little sunlight. This causes the rechargeable batteries to run down, and they require frequent replacement. Or, in the case of the use of capacitors, the lack of power causes the meter to become inoperative.

There is therefore a need for an electronic parking meter, with a microprocessor, electronic display, ultrasonic and IR transceivers, which is specifically designed for low power drainage so that it can operate for extended periods of time with ordinary batteries. The parking meter of this invention utilizes unique low-power coin sensing and detecting devices and circuitry as well as several conditions or states of operation to minimize power requirements in usage. This enables the electronic parking meter to operate strictly on battery power without the use of unreliable solar power sources or the requirement to run and connect power cables to the meters.

OBJECTS OF THE INVENTION

Accordingly, it is the general object of this invention to provide an electronic parking meter which improves upon, and overcomes the disadvantages of the prior art.

It is a further object of this invention to provide an electronic parking meter with unique coin sensing and detection circuitry which is simple, inexpensive, and uses very little power.

It is still a further object of this invention to provide an electronic parking meter which operates in several states to minimize power consumption.

It is yet a further object of this invention to provide an electronic parking meter which utilizes a vehicle detector to determine the presence of a vehicle at the parking meter.

It is still yet a further object of this invention to provide an electronic parking meter with an electronic display which shows allowable time and which resets the allowable time to zero when the vehicle at the parking meter location is removed.

It is another object: of this invention to provide an electronic parking meter which has automatic diagnostic testing to determine the presence and category of failures.

It is still another object of this invention to provide an electronic parking meter which enables an auditor to receive stored information relating to the value of the coins deposited, the amount of overtime parking, and the operational status of the meter for central processing.

It is yet another object of this invention to provide an electronic parking meter with an electronic display which incorporates a flashing signal to indicate overtime parking.

It is still yet another object of this invention to provide an electronic parking meter which enables a parking enforcement officer to communicate with the meter.

SUMMARY OF THE INVENTION

These and other objects of this invention are achieved by providing an electronic parking meter which has an electronic display, an ultrasonic transceiver to determine the presence of vehicles, an IR transceiver for communicating information to and from parking enforcement officers and auditors, and a flashing signal to indicate overtime parking. The meter is designed for very low power drain to enable the use of common batteries only for extended periods of time without the requirement for external power cables or solar power systems.

The coin sensing and discrimination circuitry requires very little power. It comprises a coin pre-sensor, a coin diameter measuring device, a ferrous coin (i.e., slug) detector and a coin jam detector. The pre-sensor uses a lever mechanism to deflect or flex a Piezo electric strip, as does the coin diameter measuring device. The coin ferrous detector uses a permanent magnet and a reed switch. When a coin with ferrous material passes between the magnet and the reed switch, it affects the magnetic field, thereby releasing the reed switch. The coin jam detector comprises IR diode emitters and photo-electric cell receivers to detect the presence of a jam in the coin slot. Also, the meter and its components operate in several states including off, inactive and active states to further minimize power requirements.

DESCRIPTION OF THE DRAWING

Other objects and many of the intended advantages of this invention will be readily appreciated when the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a rear elevation view of the parking meter of this invention;

FIG. 2 is a front elevation view of the parking meter;

FIG. 3 is a side view, partially in section, of the parking meter taken along the lines 3--3 of FIG. 1;

FIG. 4 is a sectional view of the invention taken along the lines 4--4 of FIG. 3;

FIG. 5 is a sectional view of the parking meter taken along the lines 5--5 of FIG. 3;

FIGS. 6a and 6b show an overall block diagram of the electrical and electronics portion of the parking meter;

FIGS. 7a and FIG. 7b show, in schematic form, the auto detector of the parking meter of this invention;

FIGS. 8a and 8b show, in schematic form, the processor portion of the parking meter;

FIG. 9 is a schematic of the circuitry which controls the red display (LCD) flasher of the parking meter;

FIG. 10 is a schematic of the predetection section of the coin detector circuitry of the parking meter;

FIG. 11 is a schematic of the coin size and ferrite or slug determination circuitry of the parking meter;

FIG. 12 is a schematic of the infra-red transceiver circuitry of the parking meter.

FIG. 13 is a schematic of the coin jam detection circuitry of the parking meter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now in greater detail to the various figures of the drawing, wherein like reference characters refer to like parts, there is shown in FIGS. 1 and 2 the parking meter 2 constructed in accordance with this invention.

The parking meter 2 comprises a clam shell shaped member 4 which is mounted on a stanchion 6. The member 4 has a lower portion 8 with an opening 10 at its rear which is covered by a protective mesh 12. As will be explained later, a sonar transducer is mounted behind the protective mesh 12 to detect the presence of vehicles at the parking meter location.

The clam shell shaped member 4 also has an upper portion 14 which comprises a window 16 for viewing an electronic LCD display 18. The LCD display 18 is mounted on a board 20 which holds the electrical and electronic components of the system. The board has openings 22 and 23 behind which are mounted an IR transceiver for receiving information from, and conveying information to, parking authority enforcement and auditor personnel, as will be explained in detail later. Finally, a coin slot 24 is mounted in the front of the lower portion 8 of the member 4.

FIGS. 3-5 show the mounting of the various components within the area enclosed by the clam shell shaped member 4. The coin slot 24 provides entry for coins into a chute 26. A stationary guide member 28, mounted by screws 29 in one of a pair of transparent plastic blocks 72 (see FIG. 5), defines one boundary of the chute 26 and directs the coin downward as shown by the arrow.

The coin sensing and detecting circuitry comprises four principal elements: a pre-sensor 30, a ferrous material or slug detector 32, a coin size detector 34, and a coin jam detector 37. The pre-sensor 30 comprises a pivotable pre-sensor arm 36, a pivot 38 and a screw 40 mounted on the pre-sensor arm 36. The screw 40 holds a bracket 42 through which a Piezo mylar strip 44 has been placed. As will be explained later, the deflection of the presensor arm 36 causes the bracket 42 to move and flex the Piezo strip 44 creating a current which is detected by a processor to alert the equipment that a coin has been inserted into the coin slot 24.

The slug detector 32 comprises a permanent magnet 66 mounted in the hole 55 and a reed switch 68 mounted opposite the permanent magnet 66 in the blocks 72. The coin size detector 34 comprises a pivotable size measurement arm 46, a pivot 48 and a screw 50. The screw 50 is in contact with a Piezo strip 56. The jam detector 37, comprises IR emitters 39 and photo-cells 41, which are also mounted on plastic blocks 72, as are the pre-sensor 30, and the coin size detector 34.

At this time, the operation of the coin sensing and detection system will be described. When a coin is inserted into the slot 26, it proceeds to progress downward through the chute 26 and is deflected by the guide member 28 so that it impinges upon a pre-sensor arm 36. The pre-sensor arm 36 rotates about the pivot 38 into the position shown in dashed lines in FIG. 3. The screw 40 mounted on the pre-sensor arm 36 moves the bracket 42 which flexes the Piezo strip 44.

This flexation of the Piezo strip 44 causes an electrical current to be generated which is detected by the processor of the system. As will be explained in detail later, this enables the processor to activate electronic circuitry which has been off or in an inactive state, so that it may process the signals it receives from the remainder of the coin detection circuitry of the meter 2.

After predetection takes place, the coin progresses further down chute 26 until it passes the slug detector 32, between a permanent magnet placed in a hole 55 in one of the two blocks 72 made of clear plexiglass or similar material, and the reed switch 62.

The reed switch 62, positioned in a second hole 55 in the second block 72, is normally held in the operative position by the magnetic field of the permanent magnet. As the coin passes between the permanent magnet 66 and the reed switch 68, if the coin is a slug, i.e., it possesses ferrous material, the field will be broken and the reed will drop out causing an electrical pulse to be sent to the processor.

After slug detection has taken place, the coin then deflects the size measurement arm 46. The amount of the deflection of the size measurement arm 46 is a function of the diameter of the coin. The arm 46 rotates about pivot 48 which causes a screw 50, mounted on the arm 40 to move as shown by the dashed lines of FIG. 3 to flex the Piezo strip 56. This causes a current to flow in conductors 57 attached to the Piezo strip 56, which is proportional to the flexing of the Piezo strip 56, thereby indicating to the processor the size or denomination of the coin which has been inserted in the slot 24. The coin then progresses out of the chute 26 through an opening 53, where it is held within the meter 2.

If the chute 26 is jammed, by a coin or other material, the light between one or more of the IR emitters 39 and its associated photo-cell 41, is broken, thereby signalling the processor that a jam has occurred, as will be explained in detail later.

The coin detection circuitry of this invention is unique in that it requires almost no standby power as compared to similar existing devices. Therefore, the system may operate entirely by the use of non-rechargeable batteries with an operating life of 6 months or longer as compared to existing systems which use either a source of external power or require solar power cells which depend on continuous sunlight to maintain power.

Also shown in FIG. 3, a sonar transducer 74 is mounted behind the protective mesh 12 so that it can transmit and receive through the opening 10. It is angled downward to transmit toward the parking area adjacent the meter 2, to detect the presence of vehicles.

Referring now to FIGS. 4 and 5, which show additional sectional views of the meter 2, it can be seen that the chute 26 is defined by the opening between the blocks 72. Also within that opening, are the pivotally mounted arms 36 and 46. A set screw 52 (see FIGS. 3-5) provides a zero set position for the size measurement arm 46. Screws 29 hold the stationary guide member 28 in place.

The IR emitters 39, and the photo-cells 41 of the coin jam detector 37 are shown mounted on respective boards opposite each other so that light from the emitters 39 can flow through the transparent blocks 72 to the photo-cells 41. As explained previously, any coins or other material jammed in the chute 26 will block the light to one or more of the receivers 41, thereby indicating a jam.

The electrical and electronic circuitry of the parking meter 2 will now be described. FIGS. 6a and 6b show an overall block diagram of the circuitry. Auto detector 100 comprises the sonar transducer 74 which receives power from a connector J1 on lines 202 and 204. In order to conserve power to enable the use of a power source comprising batteries only, the transducer 74 is only turned on every ten to fifteen seconds for a few microseconds. It generates a half-millisecond pulse and then waits for approximately 50 milliseconds for a return echo. The auto detector 100 is initiated by a command signal (AUTO INIT) from a processor/LCD 102 on line 206. If the auto detector 100 receives a return echo indicating that a vehicle is present at the parking location, a signal (AUTO ECHO) is sent back to the processor/LCD 102 on line 208.

The processor/LCD 102 also receives input from, and transmits information to, coin detector circuitry 104 (see FIG. 6b). The coin detector circuitry 104 receives signal input from the Piezo strip 56 which measures coin size and from the reed switch 62 for slug detection on lines 210, 212, 214 and 216, respectively. The pre-sensor coin detector 30 receives signal input from the Piezo strip 44 on lines 215 and 217.

The coin detector 104 sends an analog coin detect signal, on line 218, to the processor/LCD 102. This signal is caused by the deflection of arm 40, causing Piezo strip 56 to generate a voltage proportional to the diameter of the coin. Signal (COIN INTER) is then sent to the processor/LCD 102 on line 220 to inform the processor that it should determine coin size.

After the processor/LCD 102 has completed its functions with regard to the coin, it sends a coin acknowledgement signal (COIN ACK) on line 222 back to the coin detector circuitry 104 to reset the coin detector so that it can accept and process subsequent coins.

In addition, the processor/LCD 102 receives information from, and sends information out to, an IR transceiver 106 on lines 224 and 226, respectively.

Other inputs and outputs shown in FIGS. 6a and 6b for the processor/LCD 102, include input/output facilities for an RF transceiver 110 on lines 225 and 227 and for a card reader 108 on lines 229 and 231 for the use of a credit card in conjunction with, or in place of, a coin input. A solar panel 112, connected to a solar charger 114 on lines 233 and 235, may also be provided where sunlight is sufficient to operate the meter.

The RF transceiver 108 may be provided to communicate with a grid (not shown), in cases of meter failure, meter jam, or overtime parking conditions, which in turn transmits to a central facility so that repair or enforcement personnel may be dispatched. Typically, a series of repeaters, each covering an eight square block area, could be used to communicate from any parking meter to the central facility.

Also shown in FIG. 6a is the power source for the system which has four 11/2-volt batteries, 2 batteries each designated as 116A and 116B, which provide 6 volts VCC and ground on buses 230 and 232, respectively. In addition, a 11/2 volt battery 116C, may be strapped in to provide 71/2 volts to the LCD display, which may require the additional voltage in extremely cold weather.

FIGS. 7a and 7b show the circuitry of the auto detector 100. When the processor/LCD 102 decides it is time to look for the presence of a vehicle, it will make the AUTO INIT at pin 34 of the processor 100 of FIG. 8a, high. When AUTO INIT goes high, it makes pin 2 of the invertor I2 low on line 236. Line 236 is connected to the base of transistor Q2 through limiting resistor R4 (1K). When Q2 is turned on, power is applied to the auto detection circuitry.

The AUTO INIT signal is also applied through resistor R2 (10K) and capacitor C2 (0.33 uF). This R/C combination, in conjunction with two invertors I4 and I6, is used to delay the AUTO INIT signal on line 238 applied to auto detector digital circuit U2, which is the transmitter for the sonar transducer. The reason for the delay is to allow time for the power to settle after it has been applied to the circuit. Capacitors C4 and C6 (47 uF and 0.1 uF, respectively, (FIG. 7b)) are filters for the main battery power Vcc.

After the delay of approximately 20 milliseconds, AUTO INIT is applied to pin 14 of sonar transmitter U2. The transmitter U2, in this case a TL851 chip, will generate fifteen cycles of a 50 KHZ tone at pin 2 of U2. Diode D3 and capacitor C9 (10 uF) provide a filter for the internal circuitry of U2. A 420 KHZ ceramic resonator Y1 generates the base frequency for the 50 KHZ transmitter in U2. The fifteen cycles of 50 KHZ from pin 2 of U2 are applied to the base of transistor Q4 and the signal is amplified in Q4 and then applied to the primary of transformer T2. Transformer T2 has a step up ratio of 54.5, therefore the secondary of T2 will be approximately 340 VAC with a fully charged 6 volt battery input. Capacitor C10 (0.022 uF) is used to block any DC component from being applied to the transducer attached to connector J2. The two zener diodes, D1 and D2, are each 200 V zeners and they assure that the signal applied to the transducer will never exceed 400 volts.

After the signal has been transmitted, the transducer waits for a return echo. When the echo is received by the transducer, the signal passes through capacitor C10 and the secondary of transformer T2 and is applied to pin 2 of sonar receiver U4 (TL852) via line 250 (FIG. 7a). The receiver U4 amplifies the signal and send it out of pin 9 on line 248 back to pin 8 of chip U2. Capacitor C8 (3300 pF) is used as a filter cap on the receive signal.

Inductance L2 (1.8 mH) and capacitor C5 (0.01 uF) connected to pin 4 of receiver U4 form a 50 KHZ tuned circuit for the receiver. Resistor R6 (56K) is a bias resistor for the receiver U4. Resistors R8 and R10 (18K and 1.5K, respectively) provide a fixed gain setting for the receiver. Potentiometer P2 (10K) and resistor R12 (39K) are used to vary the gain of the receiver from its fixed point.

The received signal which is sent from U4 to U2 (pin 9 to pin 8, respectively) sets a latch in the U2 chip which puts out the ECHO signal on pin 9 of U2. This signal is sent back to the processor/LCD 102 at pin 29 (FIG. 8) on line 252 via invertor I8. When the processor/LCD 102 receives the ECHO signal, it deactivates the AUTO INIT signal at pin 34 of U6 which turns off transistor Q2 removing power from the transmitter and receiver. Upon receiving the ECHO signal, the processor/LCD 102 will calculate the distance to the vehicle, or if no echo is received within 50 milliseconds, the micro-controller will time-out and deactivate the AUTO INIT signal.

By definition, a vehicle is detected if the distance reading is three to eight feet, and a consistent reading for three consecutive transmissions is required.

The operation of the processor/LCD 102 will now be explained. Referring now to FIGS. 8a and 8b, the processor comprises 8k of internal ROM and 192 bytes of internal RAM. In addition, the processor has two parallel eight bit I/O ports, any of which could be interrupt inputs. The processor also has a direct drive to the LCD display which will be used to display time and information concerning the operation and status of the parking meter.

U5 is a temperature sensor which, together with diodes D4 and D5 and resistor R14 (100K), is used by the processor/LCD 102 to determine the temperature of the meter in order to adjust any parameters that are sensitive to changes in temperature. Zener diode D6 and resistor R16 (100K) provide a reference voltage to the micro-controller to determine the battery voltage level and to report when a battery falls below a predetermined level. To further conserve power, although this zener diode D6 draws very little current (22 micro-amps on average), the power to the zener diode is turned off when the power is removed from the LCD display. The power reference voltage is connected to pin 19 of the processor/LCD 102 chip U6.

The power to the LCD display is turned on and off by the processor/LCD 102. In order to turn on the LCD display, the processor/LCD 102 makes the voltage at pin 37 of processor/LCD 102, chip U6, positive. This turns on transistors Q5 and Q6 applying power (VLCD) to the LCD display (See FIG. 9). Although the processor/LCD 102 has an internal resistor network to power the LCD display 18, if the battery voltage drops below 4.5 volts, it is necessary to have an external resistor network to deliver one microamp of current. This network comprises resistors R18 (1M), R20 (1M) and R22 (1M). Jumper J2 (FIG. 9) is used to apply either 6 volt battery or 7.5 volt battery to the LCD depending on which one is required. Resistor R25 (220K) is used to pull up the watchdog timer to force the processor/LCD 102 to use the software watchdog timer.

There are two crystals attached to the processor/LCD 102. These are crystal Y3 which provides a base oscillator of 1.8432 MHZ when the micro-controller is awake, and crystal Y2 which provides 32.6768 KHZ which is used to keep the LCD display and the watchdog timer active when the micro-controller is asleep. Each side of the crystal Y2 is connected to ground via capacitor C14 (15 pF) and capacitor C16 (15 pF), respectively. Similarly, each side of crystal Y3 is connected to ground via capacitors C18 (15 pF), and C20 (15 pF).

The circuitry to control the red LCD flasher to alert the parking authority when a vehicle is parked at a meter and the time has expired is also shown in FIG. 9. If there is no vehicle parked at the meter, or if there is a vehicle parked with time on the meter, the flasher will be off. If the parking meter detects a problem within itself, it will turn the flasher on solid in order to alert the parking enforcement officer. The LCD flasher must never have a DC voltage applied to it. Therefore, chip U10, with resistors R30 and R32 (536K and 100K, respectively) and capacitors C22 and C24 (each 0.01 uF) is set up as a 100 cycle multi-vibrator. Gates G2 and G4 are used as a buffer and invertor, respectively, in order to always have opposite polarity applied to the back plate and segments of the flasher U12. In order to conserve power, whenever the flasher is flashed off or turned off, the power (V FLASH) is removed from the entire circuit. When pin 38 is (FLASHER EN) deactivated, transistor Q3 is turned off which then turns off transistor Q4 and removes power from the entire flasher circuit. Resistors R34 and R36 (1M and 220K, respectively) limit the current flow through the transistors Q3 and Q4 when they are on.

The circuitry of the coin detector is shown in FIGS. 10 and 11. When the presensor arm 30 rotates due to the presence of a coin, it will flex the Piezo strip 44, causing the coin detection voltage to appear at connector J3 (see FIG. 9). The voltage is applied to pin 2 of operational amplifier