Pay Telephone Monitoring System

1. Field of the Invention

The present invention relates to a pay telephone monitoring system which accumulates at a central office location information concerning the amount of money present in the coin collection box of one or more pay telephones, and the amounts collected from the collection box. More particularly, the system is designed to be connected with existing central office equipment to provide a passive, non-intrusive pay telephone monitoring system which provides useful information to a telephone company concerning the amount of coins present in the collection box of one or more pay telephones, as well as collection histories. The invention also relates to a pay telephone monitoring system which is able to detect certain conditions occurring in a pay telephone and/or lines connected thereto which may indicate faulty equipment.

2. Discussion of the Prior Art

Despite significant achievements in the sophistication of telephone equipment and the additional features and services afforded by such equipment, there remains a significant deficiency with respect to the monitoring of pay telephone stations. Specifically, telephone companies have, as of yet, not been able to efficiently schedule the collection of pay station coin boxes, since it is difficult for the central offices to accurately determine how much money is present in a given pay telephone coin collection box. As a consequence, because an accurate determination of the amount of money present in a collection box is not known, the telephone company is susceptible to fraud in the collection process, as well as inefficiencies and costly procedures in the scheduling and collecting of the coin boxes of the many pay telephones which it services, and in the handling, counting, guarding and accounting of the money collected. Also, the telephone companies have not yet been able to solve the problem of having pay telephones sit idle because of full collection boxes which prevent telephone operation.

The present invention has been designed to provide a passive system for connection to a pay telephone station at the central office switching equipment to which it is connected for non-instrusively monitoring the amount of money deposited and collected in a pay telephone collection box. This data can be used by a telephone company to more economically schedule collection visits, or allow for third party agent collections, and/or to minimize or prevent fraud in the collection process, and/or to more economically handle, count, guard and account for collected money.

The present invention can also be used to collect various additional data concerning the use of a pay telephone station which may be useful to a telephone company in detecting a faulty pay telephone station, and/or the connection lines, and for determining the utilization of pay telephones.

Accordingly, one object of the present invention is to provide a non-intrusive, passive pay telephone station monitoring system which is designed to accurately keep track of the amount of money present in a collection box, as well as the amount of money which has been collected.

Another object of the invention is the provision of a non-intrusive, passive pay telephone station monitoring system which is capable of providing additional useful information to a telephone company concerning some of the operations of the pay telephone.

Another object of the invention is the provision of a non-intrusive, passive pay telephone station monitoring system which can recognize when a particular collection box has been collected by an authorized collection agent.

Another object of the invention is the provision of a non-intrusive, passive pay telephone station monitoring system which provides accurate accounting information on the amount of money collected by an agent, thereby facilitating use of non-telephone company employees as collection agents.

Another object of the invention is the provision of a non-intrusive, passive pay telephone station monitoring system which can help eliminate the problem of pay telephone inactivity due to a full collection box.

Another object of the invention is the provision of a non-intrusive pay telephone station monitoring system which employs two processing levels, one using a central office processor (COP) and another using a line-monitor processor (LMP), with each being able to restore critical data in the other should that data become lost.

Another object of the invention is the provision of a non-intrusive pay telephone station monitoring system which is able to recognize proper pay telephone totalizer tones, signaling the deposit of coins, even in the presence of signal dropouts and other spurious effects.

The above and other objects, features and advantages of the invention will be more fully understood from the following detailed description which is provided in connection with the accompanying drawings.

FIG. 1 shows in block diagram form the overall arrangement of the pay telephone monitoring system of the invention;

FIG. 2 illustrates in greater detail a portion of the system illustrated in FIG. 1;

FIG. 3 illustrates in greater detail the circuits used for monitoring various signal conditions on the pay telephone line and for generating signals representing the same;

FIG. 4 is a flowchart representing the overall operation of the invention in detecting and counting money deposited and collected in a collection box, and in determining when a collection agent has collected the box;

FIG. 5 is an flowchart representing a portion of the program executed by a line monitor microprocessor employed in the invention at each of a number of recurring interrupt signals;

FIG. 6 is a flowchart representing a scheduling program used by the line monitor microprocessor;

FIG. 7 is a pay telephone coin tone envelope signal diagram useful in explaining how a proper coin tone is detected in the invention;

FIG. 8 is a signal diagram, also useful in explaining how a proper coin tone is detected in the invention;

FIG. 9 is a flowchart representing a program used by the line monitor microprocessor to detect the presence of a dial tone;

FIGS. 10A and 10B are state diagrams useful in explaining how the line monitor microprocessor detects and processes signals sent by a pay telephone to a central office;

FIG. 11 is a state diagram useful in explaining how the line monitor microprocessor detects and processes collect or return signals sent by a central office to a pay telephone;

FIG. 12 is a state diagram useful in explaining how the line monitor microprocessor detects and processes a tone signal indicating that a coin box collection has occurred;

FIG. 13 is a state diagram useful in explaining how the line monitor microprocessor detects and processes repeated collect or return signals sent by a central office to a pay telephone;

FIGS. 14A and 14B are state diagrams representing how the line monitor processor detects and processes an off-hook signal;

FIG. 15 is a state diagram representing how the line monitor processor detects and processes signals indicating an abnormal on-hook condition of a pay telephone station;

FIG. 16 is a state diagram representing how the line monitor processor detects and processes signals indicating an abnormal off-hook condition of a pay telephone station;

FIG. 17 is a flowchart representing the operations performed by the central office processor (COP) employed in the invention; and

FIGS. 18A and 18B are flowcharts representing the operations performed by the host computer employed in the invention.

The present invention is a system which monitors the signal conditions present on a telephone line pair which interconnects a pay telephone station and its associate central office switching and control equipment for the purpose of (1) determining the amount of money present in a collection box at the telephone; (2) determining when certain abnormal conditions occur, such as the telephone being on-hook or off-hook for exceedingly long periods or the use of an excessive number of collect or return signals by the central office to cause a collect or return function at the telephone; (3) determining when an agent has collected the money present in a collection box; and (4) keeping track of past histories of collected amounts and the time of collection. The system of the invention is connected to the telphone line pair, typicallY at the central office, and is non-intrusive and totally passive so that it does not interfere with the normal operations which occur at either the central office or pay telephone station.

The system incorporates at least one line monitor, each including a line monitor microprocessor (LMP) which is capable of polling, and thus monitoring, up to four telephone pay stations and developing data concerning the parameters discussed above, and a central office process (COP) which polls, and thus communicates with, and extracts that data from a plurality of line monitor processors. The COP is also capable of transmitting its data to a telephone company computer upon computer request or passing data from the telephone company computer directly to the line monitor processors.

The central office processor extracts its data from the line monitor processors by polling them in sequence, and is capable of downloading and uploading critical data to or from the line monitor processors whenever the central office processor or a line monitor processor resumes processing after being disabled, thereby reducing the risk of loss of valuable data due to a fault or the need to replace a central office processor or a line monitor processor.

Before describing the invention in detail, a brief discussion of the signals which typically pass between a pay telephone and its associated central office equipment, which are detected and used in the invention, is helpful. Included are totalizer tone signals, which are tone pair bursts generated at the pay telephone station to signal to the central office the amount of coins which have been deposited in a coin pending area of the pay telephone. Each burst in a burst sequence represents a nickel-equivalent unit. Thus, if a nickel ($0.05) is deposited, a single tone burst is sent, for a dime ($0.10), two tone bursts are sent and, for a quarter ($0.25), five tone bursts are sent. Typically, the duration of each tone pair burst is longer for nickels and dimes than for quarters. Other signals passing between the pay telephone and the central office include collect or return voltage signals sent by the central office equipment to a pay telephone station, instructing the station to either return the deposited coins held in the coin-pending area to a user or to collect the deposited coins by sending them to a collection box. Still other signals which are present include dial tone, a beep tone, which may be a tone pair, generated by a coin box collection agent when a coin box is collected, other miscellaneous ansitory tones and a voltage signal representing an off-hook condition.

These signals are detected and processed by the line monitor processor of the invention to develop data representing the following information for a pay telephone: the amount of money, if any, presently deposited in a pending coin area in nickel-equivalent units; the accumulated amount of money presently in a collection box (in nickel-equivalent units); the time when the collection box was last collected; the accumulated amount of money present in the collection box at the time of last collection; the number of times the box was collected; and past histories, typically for the three last collections, of the amount of money present in a collection box at the time of collection and the time when the box was collected. In addition, data can also be developed representing the average number of collect or return signals which a central office was required to generate to effect a collect or return operation at the pay telephone, and the amount of time a pay telephone was on-hook or off-hook. The collect/return number and amount of one-hook and off-hook time is used to determine certain faulty conditions which may be occurring at a pay telephone station, or in the lines connected thereto.

The system of the invention is illustrated in FIGS. 1-3. Starting with the overall system diagram illustrated in FIG. 1, a plurality of pay telephones are illustrated by numerals 11, 13, 15 and 17. Each is respectively connected to a central office 20 switching equipment 19 by a respective telephone line wire pair 12, 14, 16 and 18. Central office 20 includes, in addition to the switching equipment 19, passive monitoring equipment constructed in accordance with the invention and depicted in FIG. 1 as line monitors 23, 25, 27 and 29, each monitoring up to four telephone lines connected with respective pay telephones, a central office processor (COP) 30 which scans the line monitors 23, 25, 27 and 29 communicating with and assembling data therefrom, and a modem 31 for enabling the central office processor to communicate with a business office host computer 37, located at business office 33, via a business office modem 35.

Each of the line monitors 23, 25, 27, 29, as noted, is adapted to monitor the telephone lines of up to four associated pay telephones. Although four-line monitors are illustrated in FIG. 1, it should be appreciated that other numbers of line monitors, e.g., 128, can be employed, all being polled by and thus communicating with the central office processor 30.

The structure of each line monitor is illustrated in greater detail in FIG. 2, which depicts line monitor 23 of FIG. 1. Each line monitor includes up to four channels, each connected to a respective telephone line pair (T,R) of a pay telephone station. The four channels communicate over a bus 53 via an electronic switch 54 with a line monitor microprocessor 55, which in turn also communicates with a ROM program memory 57 and a RAM data and program memory 59. The microprocessor 55, in turn, also communicates, when polled, through a serial buffer 56 with the central office processor 30.

Each channel of the line monitor includes connector terminals 34, 35 for connection with a telephone line pair (tip and ring) of a pay telephone station, the connection being made at the central office between the pay telephone station and the switching equipment associated therewith, as shown in FIG. 1. A connector 36, for connection with a telephone company battery, is also provided. The connector terminals 34, 35 are connected to operational amplifiers 43, 44, the tip line to attenuating, inverting amplifier 43, and the ring line to attenuating, inverting and summing amplifier 44. The tip signal at the output of amplifier 43 is used by a collect/return sensor 45 to determine if the telephone company central office equipment is applying a collect or return signal to the tip lead. The collect/return sensor 45 detects the attenuated voltage level of approximately plus or minus 130 volts on the tip lead to respectively indicate collect or return, and passes the resultant digital output on line 22 for return and on line 24 for collect to the line monitor processor 55.

The output of amplifier 43 is also applied as an input to the attenuating, inverting and summing amplifier 44. This amplifier attenuates the ring signal by the same amount as the attenuation of amplifier 43 so that the resultant output of amplifier 44 provides a differential amplification of the tip/ring signal used by the telephone company to convey speech information. The audio output of amplifier 44 is applied to amplifier 46, which amplifies the tip/ring differential signal to the approximate level it was at the input of connectors 34, 35. The output of amplifier 46 is used by coin detector 49 to determine when coin tone bursts are present in the audio data. When coin tone bursts are detected, detector 49 generates a coin tone detect signal on line 26, together with a multi-bit code signal on lines 28, representing the detected tone pair frequencies. Microprocessor 55 uses the signals on lines 26, 28 to detect coin tone signals representing coins deposited in a pay telephone.

A limiter 47 is also driven from the output of amplifier 46 and is used as an audio zero crossing detector. The output of limiter 47 on line 30 is used by the microprocessor 55 to determine the crossing interval, and thereby the frequency of audio signals at the output of amplifier 46. The signals on line 30 are used by microprocessor 55 to detect the presence of other single frequency tones on the telephone line, that is, tones other than those used for coin counting by coin detector 49. One such tone used in the invention is dial tone. Other tones which could be detected are busy signals, 60 Hz hum, or DTMF touch tones present on the line.

The output of amplifier 44, along with the telephone company battery applied at connector 36, is also used by a summing amplifier 41 to determine if the DC tip/ring voltage has decreased sufficiently from the battery voltage to indicate an off-hook condition. Amplifier 41 thus operates as a comparator to generate an off-hook signal on line 32, which is also applied to and used by microprocessor 55.

The microprocessor 55 is adapted to poll each of the four channels to which it is assigned, applying the output signals from a polled channel on lines 22, 24, 26, 28, 30 and 32 to inputs of the microprocessor 55.

FIG. 3 illustrates in somewhat greater detail the analog circuitry used in one channel of the line monitor. Operational amplifier 43 receives the tip signal and a reference voltage VREF and amplifies the tip signal by a gain factor of k. The gain factor k is much less than 1, so the output voltage of amplifier 43 will remain within the input range of comparators 105 and 106, described below, which are used in the collect/return sensor 45. The amplified and inverted tip signal is summed together with the ring signal in operational amplifier 44, which also receives the reference voltage VREF, in such a manner that a differential output signal of the tip and ring signals is formed. This differential signal is passed through a high pass filter formed by C.sub.1 and R.sub.8 to eliminate DC and low frequency components, and is then amplified in operational amplifier 46 using a gain of approximately 1/k in order to generate a differential audio output AUDIO=tip-ring. The output signal of amplifier 44 is also added to the central office battery reference voltage, BAT, using the attenuating resistor network R.sub.11 /R.sub.10 to create an off-hook sensing voltage. Operational amplifier 41, functioning as a comparator, senses whenever this voltage is greater than a pre-defined threshold, Voff-hook, in order to generate an OFF-HOOK signal on line 32.

A comparison operational amplifier 105 provides at its output a return signal, while a comparison operational amplifier 106 provides at its output a collect signal. Amplifiers 105 and 106 are responsive to respective threshold voltages V.sub.ret, V.sub.col, and to voltages applied to the TIP line by central office equipment which appear at the output of amplifier 43, to instruct a pay telephone station to collect deposited money in a collection box or return deposited money to a customer. Typically, a voltage of +130 volts between tip and earth ground is used to signal a coin collection, while a voltage of -130 volts between tip and earth ground is used to actuate a coin return within a pay telephone. Operational amplifier 43 is designed to reduce these large voltages to lower voltages, which can be sensed by comparison amplifiers 105 and 106 and used to provide collect and return signals at their respective outputs.

The coin tone detector 49 is formed by a tone detector which is capable of recognizing the tones used by a totalizer in a pay telephone to signal the deposit of money. Typically, a tone pair of audio frequencies f.sub.1 and f.sub.2 is used by the pay telephone totalizer to signal to the central office a "nickel-equivalent" unit of money, with the number of bursts of this tone pair indicating the number of "nickel" units deposited. The coin detector 49 detects the presence of the tone pair and provides two separate output signals, one on line 26 indicating the detection of a tone pair, and another multi-bit, e.g., 4 bit, digital code signal on lines 28 representing a specific tone pair which is detected. Detector 49 may be a conventional touch-tone multi-frequency (DTMF) receiver used to detect touch-tone dialing signals, such as a MITEL 8870 DTMF, in which case detection of the tone pair of f.sub.1 and f.sub.2 can be accomplished by using a crystal of the frequency 6.513646 MHz, instead of the usual crystal frequency of 3.58 MHz. Use of a dual-tone multi-frequency receiver also permits use and detection of other tone pairs which may be used for various sensing and control operations, with the other detected tone pairs being uniquely identified by the multi-bit code present on lines 28. One such tone pair may be used by a collection agent, or by the pay telephone itself, to signal a box collection operation. Detection and use of such a signal is described below.

In summary, the signals present in the line monitors, for each channel, are a coin tone present signal on line 26, a multi-bit code signal representing a detected tone pair of lines 28, return or collect signals from the collect/return detector 45 on respective lines 22 and 24, a digital zero crossing signal at the output of the limiter 47 on line 30, and an off-hook signal at the output of operational amplifier 41 on line 32.

Software programs which are used by both the line monitor microprocessor 55 and the central office microproceassor 30 to acquire and transmit coin deposit and collection date is attached as an Appendix hereto. To facilitate subsequent description of the invention, the operations executed by the line monitor microprocessor 55 and central office processor 30 in carrying out those programs will be summarized with reference to the flowcharts and processor state diagrams depicted in FIGS. 4-6 and 9-17. FIGS. 4-6 and 9-16 represent operations performed by line monitor microprocessor 55, while FIG. 17 represents operations performed by the central office processor 30.

FIG. 4 illustrates, in simplified flowchart form, an overview of the operation performed by microprocessor 55 in connection with formulating date on the amount of money present in a collection box, as well as collection histories. As illustrated in step 81, the microprocessor 55 basically checks for a valid coin deposit and, when the same is found, proceeds to step 83 where a pending nickels count PN, which is a count of the amount of money deposited in the pending area of a pay telephone in nickel-equivalent units, is augmented by adding to an old pending nickels count the amount of money represented by the valid coin detected in step 81. Thereafter, the microprocessor proceeds back to step 81 and waits to see if additional valid coins are deposited. If, after a predetermined amount of time, there is no additional money deposited, the microprocessor determines this in step 81 as a no response to the inquiry and then proceeds to step 85, where it determines whether a collect signal has been sent from a central office to a pay telephone station. If a collect signal is detected, the microprocessor proceeds to step 87, where it augments a cumulative nickels CN count by adding to a previous cumulative nickels CN count the amount of money which has been retained in the pending nickels PN count (CN=CN+PN). In other words, once a collection signal has been detected, the microprocessor 55 determines that the amount of money then held in the pending area of the pay telephone has been transported to the collection box. Accordingly, the cumulative nickels CN counter is augmented. Thereafter, microprocessor 55 proceeds to step 91, where it clears the pending nickels PN count to zero and then returns to step 81, where is again awaits for valid coin tone deposit signals.

If, in step 85, the microprocessor does not detect that a collect signal has been received, it then proceeds to step 89, where it determines whether a return signal is received by the pay telephone from the central office. If a return signal is received, indicating that the coins in the pending area of the telephone are to be returned to a user, microprocessor 55 then clears the pending nickels PN count to zero in step 91 and returns to step 81. If, on the other hand, a return signal is not received in step 89, the microprocess then proceeds to step 93, where it determines whether or not a collection beep has been detected on the line. This beep is present when a collection agent, either through manipulation of the tone pad at the pay telephone or through the provision of a portable tone beeper, signals that a collection has occurred. If the collection beep is detected in step 93, the microprocessor proceeds to step 95, where it augments a coin collection CC count by the amount of money in the cumulative nickels counter CN (CC=CN). In addition, a time of collection is noted by reading the CPU clock. Also, in step 95, previous coin collection counts and times of collection are stored for the past several times that a collection beep has been recognized. If no collection beep is detected in step 93, the microprocessor returns to step 81 and awaits the deposit of valid coins.

The summary shown in FIG. 4 is merely an overview, and is not intended to represent the detailed step-by-step operations performed by microprocessor 55. These are provided by the attached actual programs in the Appendix. A more detailed understanding of the workings of the microprocessor 55, as well as the central office processor 30, in executing these programs will now be provided with the assistance of FIGS. 5-17.

The overall operation of the line monitor microprocessor 55 is governed by a program called a task scheduler, which in turn utilizes and controls timing information in five counters identified by the designations TFF, TF, TS, T2M and T9H. These respective counter count clocking signals of a frequency of approximately 500 microseconds, 2 milliseconds, 0.5 seconds, 2 minutes, and 9 hours. The task scheduler program executed by the line monitor microprocessor 55 controls the incrementing of these counters upon the occurrence of 500 microsecond interrupt signals, and also detects various states thereof in order to control execution of various other subprograms which are called for by the task scheduler during its execution.

There are several sub-programs which are executed by microprocessor 55 in carrying out its assigned tasks, and the times at which these sub-programs are executed are governed by the task scheduler. This program will now be described with reference to FIGS. 5 and 6.

FIG. 5 illustrates a program executed by miroprocessor 55 at the occurrence of each interrupt, which is generated by an interrupt clock at 500 microsecond intervals. In the first step 99 of this program, the microprocessor 55 increments the counter TFF, after which it executes a signal tone detect routine in step 101. This routine is used in the present invention to detect the presence of dial tone on the line, and is described in detail below with respect to FIG. 9. Upon completion of the signal tone detect routine in step 101, the microprocessor returns in step 103.

The microprocessor also, while processing the program of FIG. 5 upon the occurence of an interrupt, is also processing the program illustrated in FIG. 6, which is the task scheduling program. When an interrupt occurs, execution of the FIG. 6 task scheduling program is interrupted, while the FIG. 5 program is executed, after which processing of the task scheduler resumes. The task scheduler program of FIG. 6 is entered whenever a return is encountered in a sub-program executed during execution of a task scheduler program or after power-up of the microprocessor 55 once an initialization program, in which various parameters are initialized, is executed.

In the first step 105 of the task scheduler program, the microprocessor reads the contents of the TFF counter and, if the value thereof is less than 3, the microprocessor remains in step 105. Once a value of 3 has been detected, the microprocessor proceeds from step 105 to step 107, wherein it decrements the TFF counter by a value of 4. After that, the microprocessor proceeds to step 109, where it increments a TF counter, and thereafter proceeds to step 111, where it determined whether the TF counter has overflowed or not. The TF counter overflows approximately every half second. If the TF counter has overflowed, the microprocessor proceeds to step 113, where it increments a TS counter, and from three proceeds to step 115 where it determines whether the TS counter has overflowed. The TS counter overflows in intervals of approximately every two minutes. If the TS counter has overflowed, the microprocessor proceeds to step 117, where it increments a T2M counter, and from there proceeds to step 119 where it tests whether the T2M counter has overflowed. The T2M counter overflows approximately every 9 hours. If, in step 119, a yes response is detected, the microprocessor proceeds to increment the T9H counter in step 121, following which it proceeds to step 123. If a no response was received at steps 111, 115 or 119, the microprocessor also proceeds to step 123.

In step 123, the microprocessor executes, for all four channels to which it is connected, a coin filter program. This program is described in greater detail below with respect to the state diagrams of FIGS. 10A and 10B. After this program is executed, microprocessor 55 proceeds to step 125, where it determines whether the first bit (LSB) position TF.0, that is, bit zero, of the TF counter equals one. If it does not, microprocessor 55 proceeds to step 127, where it executes a communications program, following which it returns to step 128. The returns in the task scheduler program are denominated return 2 to distinguish them from the return at step 103 in FIG. 5. A return 2 indicates a return to the task scheduler program of FIG. 6 and entry thereof in step 105.

If a yes response is received in step 125, the microprocessor 55 proceeds to step 129, where it tests the next most significant bit position, that is, TF.1, to determine whether it equals one or not. If it does not, microprocessor 55 then proceeds to step 131, where it increments a modulo-4 counter M by a value of one. The modulo-4 counter will count the value 0, 1, 2, 3, 0, 1, etc. After executing step 131, microprocessor 55 proceeds to step 133, where it executes an off-hook line processing routine for line (M), which is described in greater detail below with respect to the state diagram of FIG. 14. Following this, it returns in step 134. It should be apparent that each time the off-hook processing routine is executed in step 133, it is for a different channel.

If, in step 129, a yes response was received, microprocessor 55 proceeds to step 135 where it tests the third bit position of the TF counter TF.2 for a value of one. If a no response is received, microprocessor 55 proceeds to step 137, where it increments a modulo-2N counter by a value of one. This counter counts the value of 0, 1, 0, 1, etc. Thereafter, microprocessor 55 proceeds to step 139, where it executes a collect/return program for the channel 2(N). Following this, microprocessor 55 proceeds to step 141, where it executes a collect/return program for channel 2(N)+1. Thereafter, it returns at step 142. It should be apparent that in steps 139 and 141 the microprocessor is executing the collect/return program for two channels of the four channels which are capable of being processed. On the next pass through the task scheduler program of FIG. 6, the other two lines or channels will be processed.

If a yes response is received in step 135, the microprocessor proceeds to step 143, where it tests the fourth bit position TF.3 of the TF counter to see if it equals one or not. If a no is detected, a return is executed in step 145, while if a yes is detected, the microprocessor proceeds to step 147, where it tests the fifth bit position TF.4 to see whether it equals one or not. If no, the microprocessor returns at step 149, if yes the microprocessor returns at step 151. The returns provided at steps 145, 149 and 151 are designed to handle optional programs which may later be added in the system. These optional programs can be executed ahead of the returns shown at these steps.

As evident from the above, the task scheduler program will call for and execute coin filter, communications, off-hook, and collect/return programs at various times as called for by the contents of the TF counter. In addition, a signal tone detect program is executed at step 101 upon the occurrence of each interrupt. These programs which are called and executed will now be described.

The signal tone detect program is illustrated in greater detail in FIG. 9. It is executed by the microprocessor 55 in order to determine the presence of dial tone. A determination of whether dial tone is present is not actually made in FIG. 9, but is made elsewhere in the collect/return program described below.

In the first step 251 of the signal detect program of FIG. 9, a period counter is incremented. Thereafter, the microprocessor 55 proceeds to step 253, where it determines whether the signal being monitored, which is on line 30 of the line monitor, is at its leading edge or not. This is done by comparing a present sample with a previous sample of this line. If it is not at a leading edge, the program does nothing further and proceeds to a return in step 265. Consequently, the next time the program is executed, the period counter will again be incremented in step 251. The period counter will continue to be incremented until a leading edge is detected at step 253. In other words, the period counter is being used to measure the period between leading edges of the signal on line 30. Once a leading edge is detected at step 253, the contents of the period counter are then compared with a predetermined range to determine whether the period of the signal falls within a range assigned to a dial tone. If it does not, the microprocessor 55 proceeds to step 257, where it determines whether or not a value denominated DIAL is at a minimum value. It it is not, the DIAL value is decremented in step 259 and then the microprocessor proceeds to clear the period counter at step 264 and then return at step 265. If, on the other hand, the DIAL value is at its minimum value, then the microprocessor clears the period counter at step 264 and returns at step 265 and does not further decrement this value.

If, in step 255, the microprocessor 55 determines that the period was within a predetermined range, it then proceeds to step 263 where it tests whether the DIAL value has reached a maximum value or not. If not, it increments the DIAL value in step 261, clears the period counter at step 264 and returns at step 265, while if the DIAL value has reached its maximum value, the microprocessor 55 simply clears the period counter at step 264 and returns at step 265.

The program of FIG. 9 is designed to increment or decrement the value DIAL, which will be later used as a test value to determine whether dial tone is present. In order to eliminate the possibility of a spurious signal being on the line at the same frequency as dial tone, the program of FIG. 9 performs a statistical analysis, whereby the period of the applied signal is repeatedly checked to see whether it falls within the predetermined range corresponding to a dial tone. If it does, the DIAL value will be continuously incremented from its initialized value, at step 261, and eventually will reach a DIAL value which exceeds a threshold assigned for a determination that dial tone is present. If, on the other hand, a spurious signal is detected, the DIAL value will be decremented in step 259 and, if a sufficient number of spurious signals are found, the DIAL value will be decremented to a value below a threshold which indicates dial tone. The comparison of the value of DIAL with the threshold is done in the collect/return program discussed in detail below.

The sub-program executed by microprocessor 55, at step 123 of the task scheduler, is a coin tone filter program, which is designed to detect the presence of a coin tone pair and to properly increment a tone counter TC when a tone pair of the proper signal specifications has been recognized. The coin tone filter program is particularly adapted to recognize a valid coin tone, even if the same is subjected to minor dropouts therein. In addition, the coin tone filter program is adapted to detect multiple coin tones, each representing a nickel-equivalent unit, and to properly count the same and, while doing so, to ensure that proper gaps are present between successive tones of the tone burst for a single deposited coin and proper gaps are present between tone bursts of successively deposited coins. In addition, the coin tone filter program is designed to recognize certain fault conditions and either ignore tone signals which the microprocessor 55 judges to be invalid, or to force a recognition of a local call rate when a struck coin is detected, even if less than the requisite number of tone bursts have been received for that local rate.

The signal diagram of FIG. 7 illustrates various signal conditions either recognized or ignored by microprocessor 55. A coin tone detect signal is illustrated which is generated when microprocessor 55 detects the presence of a coin present signal on line 26 and the proper four-bit code for coin deposits on line 28. The coin tone detect signal illustrated represents the deposit of a dime.

Also illustrated in the coin tone detect signal is a signal dropout condition at A, which the microprocessor 55 ignores, provided it is of short enough duration. The interpulse gap, that is, the spacing between bursts for a deposited coin, is shown at B. This period is measured by the coin tone filter to ensure that it is within predetermined parameters. An inter-coin gap, that is, the tone gap between successively deposited coins, is also illustrated at C in FIG. 7, and this period is also measured in the coin tone filter of the invention to ensure it is within predetermined parameters.

The coin tone filter uses two timers, one labeled a tone timer and one labeled a gap timer, to assist in recognizing proper coin tone detect signals. The signal pattern for the tone timer is illustrated in FIG. 7, as are signal patterns for the gap timer, which is shown as used for two different gap timing functions. The tone timer is started when the coin detect signal goes high. It times out when the minimum continuous signal duration to qualify a tone as valid is reached. The gap timer starts whenever the coin detect signal disappears. If the coin detect signal is present for a sufficient duration and before the tone timer times out, and there were no signal dropouts or, if so, if they were of sufficiently short duration, such as shown at D, as measured on the gap timer, a valid tone signal is recognized and a tone counter TC is incremented. If thereafter the coin tone detector goes high again, after a predetermined interpulse gap B, and the conditions to detect a proper tone are present again, another tone will be recognized as part of the burst for a single deposited coin and the tone counter TC will be incremented again. If an inter-coin gap C is recognized, the next validated tone will be recognized as being the beginning of a new burst for a next deposited coin. Thus, in the coin filter portion of the invention, the tone timer is turned on and off, as is the gap timer, while the condition of the coin tone detect line is monitored to determine if an applied coin tone detect signal falls within predetermined characteristics to ensure that a proper coin tone detect signal has been identified. Once it has, the tone counter TC is incremented.

An activity timer signal pattern is also illustrated in FIG. 8. This timer is used to check if any coins are deposited within a predetermined period, e.g., thirty seconds, after recognition of the last valid tone. If, for example, a single tone pulse is validated, but thereafter no tones are recognized, i.e., no coins recognized as being deposited, within this period, the activity timer times out and the microprocessor 55 will ignore the tone pulse first recognized, since it would represent a single nickel, which would be much less than the rate required for even a local telephone call. The isolated tone is thus considered a spurious signal and discarded by the system.

The state diagrams of FIGS. 10A and 10B illustrate in greater detail the operation of the microprocessor 55 in implementing the coin filter program. Upon power-up, or upon the occurrence of certain conditions discussed below, the first state that microprocessor 55 assumes in the coin tone filter program is an idle state 201. The microprocessor 55 will remain in state 201 as long as there is no coin present (CP) signal detected on the telephone line, that is, the coin tone detect signal in FIG. 7 is at a zero "0" level. This is illustrated by the return line CP=0, forming a closed loop in the idle state 201. When the coin filter program is called by the task scheduler and the microprocessor 55 is in idle state 201 and a coin present is detected (CP=1), by the microprocessor 55 detecting a signal on line 26 and the proper four-bit code for a touch-tone coin tone pair indicating a deposit on lines 28, then the microprocessor 55 transitions to state 203. It remains here until the next time the coin filter program is called from the task scheduler. At that time, assuming the coin present signal remains at 1, the microprocessor will then transition from state 203 to state 207, but, while doing so, it will turn on the tone timer (TONE TMR) at step 205.

Step 207 is an active state wherein the tone timer is on, and the microprocessor 55 will remain in this state as long as the time that the tone timer is on is less than a maximum tone timer time period (TONE TMR MAX), and the coin present signal still equals one. This is represented by the closed loop line exiting and then returning to step 207. If microprocessor 55 is in step 207 and, at the next time the coin filter program is called by the task scheduler the coin present signal disappears, as indicated by the line CP=0, then the microprocessor 55 will transition from state 207 to state 213, termed a "trailing edge" state. However, if while in state 207 the microprocessor still receives a coin present signal, CP=1, and now the tone timer has timed out by the time being greater than or equal to the maximum tone timer time, then microprocessor 55 exits state 207 and enters state 211, and in the process it flags a stuck coin, stops the tone timer and sets a tone counter TC to a local rate, e.g., the transition from state 207 to 211 is taken whenever the coin tone is present (CP=1) after the tone timer times out, thereby indicating a coin stuck in a deposit chute. In normal operation, as shown in FIG. 7, the coin tone detect signal will normally disappear before the tone timer times out. If it does not, then, as noted, the tone counter is set to a local rate which, for a 20-cent local rate call would be a value of 4 (a value of 5 for a 25-cent local rate), the tone timer is turned off and a stuck coin condition is noted.

The microprocessor 55 remains in step 211 during the next pass through the coin filter program called for by the scheduler program, as long as the coin present signal still equals one, that is, as long as the coin tone is still on the line. However, once it disappears, the microprocessor 55 then transitions from state 211 to state 213, where it remains until the next time the coin filter program is called for by the task scheduler. At that time, a transition occurs from the trailing edge state 213 to another idle state 215, but, in doing so, the microprocessor 55 now starts a gap timer at step 214. Microprocessor 55 remains in state 215 with the gap timer on as long as the coin present signal is zero, indicating that no coin tone is present, and the time of the gap timer is less than or equal to a predetermined tone gap time. At this point, the gap timer is measuring a possible signal dropout gap, illustrated at D in FIG. 7.

If the coin present signal still equals zero and the time of the tone gap has been exceeded, which is the maximum tone break which can be tolerated before two separate tones are recognized, the microprocessor 55 then transitions through steps 219 and 223 and 217 to an idle state C. In this transition, the microprocessor 55 also determines that the time of tone duration, with bridging of minor dropouts, has exceeded a minimum time (TONE TIME) established for a tone to be recognized as valid. In step 219, the microprocessor increments the tone counter TC and then, if the time of a detected tone was less than or equal to the tone duration for a nickel, the program proceeds to step 217 where it steps the tone timer. If, on the other hand, after incrementing the tone counter TC in step 219 the microprocessor determines that the tone time was greater than the nickel time, it sets a nickel detector NIDET to one in step 223 and then stops the tone timer in step 217. In either case, the microprocessor 55 then proceeds to the idle state C indicated at state 221.

In transitioning from state 215 to state 221, by means of the increment TC step 219, the microprocessor 55 has identified a good tone, that is, one indicating a monetary nickel-equivalent unit. In addition, it it has determined whether the tone was long enough to indicate a nickel (shorter tones are used for quarters).

On the next pass through the task scheduler program, the microprocessor 55 will remain in step 221 as long as the coin present signal is zero and the time measured by the gap timer is less than an inter-coin gap time (COIN GAP), shown in FIG. 7.

When, on a subsequent pass through the program schedule, the coin filter program is called and the coin present signal returns, indicated at line CP=1, the microprocessor 55 then returns to state 203 and begins the procedure described above once again to detect another tone. At this point, it has recognized the leading edge of the next tone burst. If, while in state 221, the coin present signal remains zero, but the time of the gap timer exceeds an inter-coin gap time (COIN GAP), the gap timer is then stopped in step 225 and the microprocessor 55 then proceeds by one of four different paths determined by the state of various counters and timers.

One path from step 225 is to step 231. This path is taken if the tone counter TC equals one, and an activity timer (ACTIVITY TMR) is on, and the nickel detect flag had been set in step 223, of if the tone counter TC value is greater than one. If either of these two conditions occurs, the microprocessor 55 proceeds to execute step 231, wherein a pending nickels PN counter is augmented by adding to its old value PN the number now present in the tone counter TC. It is here that the microprocessor 55 determines the amount of money deposited in nickel-equivalent units. In addition, the tone counter TC is reset to zero. The activity timer is then either started if it is off, or restarted if it is on, in step 233. Following this, the microprocessor 55 proceeds to step 235, where it resets the nickel detector NIDET to zero and, if the activity timer is on, preceeds to an idle state 237. If, after step 235, microprocessor 55 determines that the activity timer is off, it proceeds back to idle state 201 and now awaits the presence of a new coin present signal CP= 1.

If, after stopping the gap timer in step 225, the microprocessor 55 determines that the tone counter TC equals one, and the nickel detector NIDET has been set (=1) and the activity timer is off, it then proceeds to start the activity timer in step 229, following which it executes step 235 and, since the activity timer is now on, proceeds directly to idle state 237. If, after turning the gap timer off in step 225, the microprocessor 55 determines that the tone counter TC equals zero, it proceeds directly from step 225 to step 235, where it resets the nickel detector NIDET to zero and then proceeds as described above, depending on whether the activity timer is on or off.

If, after stopping the gap timer in step 225, the microprocessor 55 determines that the tone counter TC equals one, but that the nickel detector NIDET has not been set, it then resets the tone counter TC to zero and ignores the tone, since it is too short to be recognized as a nickel. From here, microprocessor 55 then proceeds back to idle state 201 where it waits for the next coin present signal.

If microprocessor 55 is in state 237, it will remain there as long as a coin present CP signal equals zero and the activity timer has not timed out. However, if a coin present signal occurs while microprocessor 55 is at state 237, then the microprocessor transitions to state 203. If the microprocessor 55 is in state 237 when the coin filter program is next called by the task scheduler, and it determines that CP=0, and that the activity timer has timed out and that the tone counter TC equals one, this condition is recognized as a so-called "talk-off" condition, in which case a nickel is recognized by itself (no other tones detected). As a consequence, the microprocessor 55 then proceeds from state 237 to step 239 where it resets the tone counter TC to zero and flags a talk-off fault condition, following which it proceeds to step 241 where it stops the activity timer, and from there back to state 201 where it awaits the next coin present signal.

If, while in state 237, the microprocessor determines that the coin present CP signal is still off, that the activity timer has timed out and that the tone counter TC does not equal one, that is, some value greater than one is present in the tone counter, then it merely stops the activity timer in step 241 and proceeds to the idle state 201. Under this condition, since more than one tone has been detected and the activity timer has timed out, the microprocessor 55 will recognize the tones as valid tones.

It should be remembered that state transitions, illustrated in FIGS. 10A and 10B, only occur each time the coin filter program is called for from the task scheduler. At the time the program is called for, the microprocessor 55 determines whether a change of state is warranted based on monitored conditions at that time and, if so, executes whatever program steps are necessary while changing states.

The coin filter program operation depicted in the state diagrams of FIGS. 10A and 10B functions to recognize a valid tone, that is, one that has been on long enough to indicate a nickel-equivalent unit, it counts the tones by means of the tone counter TC in step 219, determines that proper gaps exist between tones by means of the gap timer, ignores tones which are too short to be a nickel-equivalent unit, ignores a tone count if only one has occurred within a predetermined period of time following its occurrence, sets the tone counter TC to a local rate count if a valid coin tone has been detected, and if detected as a stuck coin, and keeps a running tab by means of the pending nickels PN counter of the amount of money which has been deposited in the deposit chute of a pay telephone.

The microprocessor 55 operation of determining whether the deposited coins recorded in the pending nickels PN counter are collected or returned to a user will now be described with respect to the state diagram shown in FIG. 11.

FIG. 11 illustrates the state diagram for the collect/return routine which is performed by microprocessor 55. As noted in the FIG. 6 flowchart of the task scheduler, the collect/return routine is executed for line 2(N) and then immediately thereafter is reexecuted for line 2(N)+1. The reason for this is that the collect/return routine can only be executed for two lines on each pass through the task scheduler, and therefore only two lines are processed at a time due to processing speed constraints. Once again, the microprocessor 55 will remain in a particular state when the collect/return routine is called for by the task scheduler program, unless state transition conditions exist.

The first state 271 in the collect/return routine is a state wherein the microprocessor 55 is looking for a collect or return signal sent from the central office to a pay telephone station. If neither a collect nor return signal is sensed, microprocessor 55 proceeds to step 273 where it executes a retry monitor routine, described below in connection with FIG. 13, and from there proceeds to execute a box monitor routine in step 275, which is described below with respect to FIG. 12. Upon finishing the box monitor routine in step 275, the microprocessor then will either return to idle state 271, if the dial tone counter value, which was incremented or deincremented in the FIG. 9 program, is less than or equal to a set point, indicating that no dial tone is present, or if dial tone is present (the dial tone counter set point), microprocessor 55 proceeds from step 275 to step 277 where it sets a force flag equal to one, following which it then returns to the idle state 271.

If, while in idle state 271, the microprocessor 55 senses that a collect or return signal has been sent from the central office to the pay telephone, it then proceeds to step 279 where it starts a collect/return timer, following which it takes one of two paths depending on whether a collect or return signal is detected. If a collect (AC) signal is detected, microprocessor 55 proceeds from step 279 into state 293, which is a collect monitor state. If a return (RJ) signal is detected, microprocessor 55 proceeds from step 279 to state 281, which is a return monitor state.

The microprocessor 55 will remain in the collect monitor state 293 as long as the collect signal is present and the collect/return timer has not yet timed out. If the collect signal disappears while the microprocessor is in state 293, then the microprocessor will stop the collect/return timer in step 295 and return to the idle state 271. If, when in state 293, microprocessor 55 determines that the collect signal is still present and that the collect/return timer has not yet timed out, and that either the force flag F has not been set or the pending nickels counter is greater than or equal to the local rate, then it proceeds from state 293 to step 301, wherein a cumulative nickels count CN is augmented by adding to the previous cumulative nickels count CN the pending nickels PN count. Thus, in step 301, the microprocessor is able to augment the amount of money in the collection box by the amount of money which was in the deposit chute, since it is now recognized that a valid collect signal has been transmitted and the money has been collected in the collection box.

Following execution of step 301, microprocessor 55 proceeds to step 285 where if stops the collect/return timer, initializes the pending nickels PN counter to zero and the tone counter TC to zero, and sets the force flag F equal to zero. Following this, it proceeds to step 287 where it stops the activity timer (started in FIG. 9), after which it proceeds to step 289 where it increments a retry counter and starts a retry timer, or restarts a retry timer if it is already on. The function of the retry count and retry timer will be described in greater detail below in connection with FIG. 13. The microprocessor then proceeds to a wait state 291. The microprocessor will remain in wait state 291 as long as a collect or return signal is present, and as soon as both signals disappear, microprocessor 55 proceeds from state 291 to idle state 271.

If, when in state 293, microprocessor 55 determines that the collect signal is present and the collect/return timer has timed out, and the force flag F has been (=1) and the pending nickels PN count is less than the local rate, it then sets, in step 303, the pending nickels PN count to the local rate. Thus, in step 303, the microprocessor has recognized a valid collect signal, and that the collect/return timer has not yet timed out and that dial tone is present (F=1), indicating that the central office has authorized the making of a telephone call. In this instance, the system assumes that even though the pending nickels PN count is less than the local rate, that a sufficient number of nickel-equivalent units have been detected to assume that a sufficient amount of money has been deposited to equal the local rate. This is why the pending nickels count is set at the local rate and thereafter, in step 301, microprocessor 55 updates the cumulative nickels CN count with the new pending nickels CN rate, following which the microprocessor proceeds to step 285 and executes that step and subsequent steps, as described above.

If microprocessor 55 is in the return monitor state 281, it will remain there as long as a return signal is present and the collect/return timer has not yet timed out. If the return signal is present and the collect/return timer times out, microprocessor 55 then exits state 281 and enters state 291, executing in the transition steps 285, 287 and 289 in the manner described above. In this case, a return signal emanating from the central office has been sensed, in which case the deposited coins have been returned to the user, thereby requiring a resetting of the pending nickels PN counter, the tone counter TC and the force flag F. If, while in state 281, the microprocessor 55 recognizes that the return signal has disappeared, it stops, in step 287, the collect/return timer and proceeds back to idle state 271. The purpose of the collect/return timer is to ensure that the collect or return signal is present for a predetermined period of time before it will be recognized as a valid signal by the system.

The box monitor program executed in step 275 is illustrated in greater detail in FIG. 12 by means of a state diagram. The box monitor program is designed to detect a valid beep tone on the line which is used by a collection agent, or the pay telephone itself, by, for example, a collection box switch, to signal the collection of a coin box. When the beep signal is recognized, the system takes, in effect, a snapshot of the amount of money in the cumulative nickels CN counter, as well as the time at which the beep, that is, collection, occured. In addition, a two minute blackout window is set wherein further beeps by a collector or pay telephone will not be recognized once a valid beep has been detected.

The first state 305 that the microprocessor 55 assumes in the box monitor program is an idle state 305. Microprocessor 55 will remain in this state as long as the beep signal is not detected. However, when a beep signal is detected, the microprocessor will start a box timer, in step 307, and then proceed to a box-active state 309. It will remain here as long as the beep tone is still present and a box timer has not timed out. If, when in state 309, microprocessor 55 detects that the beep signal has disappeared, it stops the box timer, in step 311, and then returns to the box idle state 305. The box timer is used to ensure that the box timer tone is on the line for a sufficient duration to be recognized as a valid tone. If, while in state 309, microprocessor 55 recognizes that the box timer has timed out and that the box signal is still present, it recognizes this as a valid coin box collection signal and, as a result, stores the cumulative nickels CN count in a coin collection CC counter, as well as the time of collection. Microprocessor 55 maintains the just-stored coin collection count and time together with the coin collection counts and times of collection for at least three previous collections by means of a push-down register, wherein the oldest data is lost as new data is added. In addition, in step 313, microprocessor 55 increments a box collection counter, thereby keeping track of the number of collections which have occured, following which it proceeds to step 315 where it starts a blackout timer, and then to state 317 where it waits until the blackout timer has timed out. Once the blackout timer has timed out, microprocessor 55 exits state 317 and, in the process, stops the box timer in step 319 and then returns to the idle state 305.

As should be apparent, the beep signal, illustrated in FIG. 12, really represents the presence of a tone detect signal on line 26, and the proper four-bit code on lines 28 representing the tone pair of the generated beep signal. Also, in step 313, the cumulative nickels CN count, which is the amount of money then residing in the collection box, is placed in the coin collection CC counter and the cumulative nickels CN count is also reset.

FIG. 13 illustrates the retry monitor routine which is executed at step 273 in FIG. 11. The purpose of this routine is to keep track of the number of collect or return pulses which are required to have a collect or return operation take place at the pay telephone station. In some instances, due to malfunctioning or sticking components, it may be necessary for a central office to emit more than one collection or return pulse before the coins in the deposit chute are deposited in the collection box or returned to a customer. The retry monitor routine, illustrated by the FIG. 13 state diagram, is designed to keep track of the number of collect or return pulses required for each collection or return operation as a running average. This information is useful for fault monitoring purposes.

The first state 321 of the retry monitor is an idle state which microprocessor 55 remains in until a retry timer, set in FIG. 11, times out. Once the retry timer is activated, microprocessor 55 exits from state 321 into state 323, which is a collect/return count state. The microprocessor 55 will remain in this state as long as the retry timer is on. Once the retry timer times out, the microprocessor executes step 325 wherein it performs a recursive filtering of the retry count data, illustrated in step 325 as X=(1-K)X+K(Y), where Y is the new value of the retry count and K is a constant. The value X is initialized at zero and, after repeated executions of the recursive filter in step 325, microprocessor 55 has a value which represents the average number of collect or return pulses which a central office must emit to effect either a collect or return operation at a pay telephone. After executing step 325, the microprocessor proceeds to step 327 where it determines whether the average value of collect or return pulses exceeds a threshold and, if it does, it sets a flag representing this. Thereafter, microprocessor 55 proceeds to step 329 where it clears a retry counter (incremented in FIG. 11), following which it proceeds to step 331 where it stops the retry timer and then proceeds back to idle state 321. Thus, with the retry monitor routine, the microprocessor creates and maintains a running average of collect or return pulses required to activate a collect or return operation at a pay telephone, and has also flagged a fault condition when this average exceeds a predetermined value.

An off-hook routine is also executed by microprocessor 55 at step 133 of the task scheduler program illustrated in FIG. 6. This off-hook routine is executed on each pass through the task scheduler for only one telephone line, so that four passes through the task scheduler are required for an off-hook routine to be executed for each of the four telephone lines. The off-hook routine is illustrated in greater detail by means of a state diagram in FIG. 14. The routine is used to detect an extended off-hook condition or extended on-hook condition. It also can be used to gather various statistical data on how frequently a phone goes off-hook or on-hook, etc., and other problems with the phone line. For the purpose of implementing the present invention, only extended off-hook or on-hook conditions are recognized and flagged to indicate potential fault conditions.

The first state the microprocessor assumes when in the off-hook routine illustrated in FIG. 14 is an idle state 341. Microprocessor 55 will remain in this state as long as it does not detect an off-hook signal OFHKRT at the output of line 32 of the line monitor. In addition, on each pass through the off-hook routine of FIG. 14, if an off-hook signal is not detected, the microprocessor will remain in the idle 341, but executing a phone idle monitor routine 345, which is discussed below with respect to FIG. 15. If, when in state 341, microprocessor 55 recognizes an off-hook signal OFHKRT, it starts a hook timer in step 343 and then proceeds to state 347, which is an on-hook state. Microprocessor 55, once in state 347, will remain there as long as an off-hook signal is present and the hook timer started in step 343 does not time out. However, it does execute, in step 351, the phone idle monitor routine, discussed above with respect to step 345, on each pass through the FIG. 14 routine if it is in state 347. If, while in state 347, the microprocessor 55 recognizes that an off-hook signal is still present and that the hook timer has timed out, it then sets a call time (CALL TM) counter equal to zero and restarts a phone timer (PHONE TMR), in step 353. It then proceeds to step 355, where it stops the hook timer and sets an off-hook flag OFHKB equal to one. It then proceeds to state 359, which is an off-hook state. The microprocessor 55 will remain in state 359 as long as the off-hook signal is still present, but will execute a call monitor routine in step 363 (FIG. 16) while it remains in state 359 on each pass through the FIG. 14 routine.

If, while in state 359, the microprocessor 55 recognizes than an off-hook signal OFHKRT has disappeared, it starts the hook timer in step 361 and proceeds to an off-hook state 371. Microprocessor 55 will remain in this state as long as there is no off-hook signal and the hook timer has not timed out, and it will execute a call monitor routine in step 373 on each call of the FIG. 14 routine while the microprocessor is in state 371. When, in state 371, if microprocessor 55 recognizes that the off-hook signal is absent, but the hook timer times out, it now proceeds to step 377 where it sets a phone idle time equal to zero and restarts the phone timer. It then proceeds to step 379 where it stops the hook timer, and from there to step 381 where it sets an off-hook flag OFHKB equal to one, following which it returns to state 341. If, while in state 371, the microprocessor recognizes that the off-hook signal appears, it stops the hook timer in step 375, and then proceeds to the off-hook state 359.

If, while in the on-hook state 347, the microprocessor detects that the off-hook signal disappears, it then stops the hook timer in step 349 and returns to state 341. The routine illustrated in FIG. 14 by the state diagram is designed to detent on-hook and off-hook conditions and start and stop various timers, the consequences of which will become more apparent by the discussion below of the phone idle monitor routine of FIG. 15 and the call monitor routine of FIG. 16, which are executed at steps 345 and 351 and 363 and 373 in FIG. 14.

In the phone idle monitor routine of FIG. 15, the microprocessor 55 begins in a phone idle monitor state 401 and will remain there as long as the phone timer value is less than or equal to a predetermined idle time. When the phone timer value exceeds a predetermined idle time, for example, a two minute time period, microprocessor 55 exits from state 401 and proceeds to restart the phone timer in step 403, and then to step 405 where it increments the phone idle time counter, following which it returns to the idle state 401. By incrementing the phone idle time counter in step 405, the microprocessor is now keeping a running tally on the time that the phone is idle, as measured in two minute time increments. This value can be examined at any time to determine if the phone is idle and for how long to potentially flag a fault condition.

FIG. 16 illustrates a call monitoring routine, in which the first state 407 is a call monitor state. The microprocessor 55, once in this state, will remain there as long as the phone timer is less than or equal to a preset call time. When the phone timer is greater than the preset call time, which may, for example, be as little as two seconds, the microprocessor exits state 407 and restarts the phone timer in step 409, following which it increments the call time counter in step 411, following which it returns to the call monitor state 407. Thus, the call time counter incremented in step 411 will contain a running tally of the time of use of a phone, which is incremented in two second intervals. This too can be used to indicate how long a phone is used and can be monitored at various periods of time to obtain information on how long the phone is in use.

The final routine which is called by the task scheduler is a routine executed by the central office processor 30. It monitors the TF0 bit at step 125 of the task scheduler program and, when this bit is not equal to a one value, it executes a communications program at step 127.

The communications program for the central office processor 30 is best illustrated in flowchart form and is depicted in FIG. 17. The central office processor 30 executes the FIG. 17 program and, during execution thereof, communicates with the line monitor microprocessors to provide data thereto or receive data therefrom. During execution of the communication program at step 127 of the task scheduler of FIG. 6, the line monitor microprocessors 55 act on a data block received from the central office processor 30 and formulate an appropriate response to be returned to the central office processor 30.

In the first step 420 of the central office processor program, a determination is made if the central office processor has just been powered up. If it has, the central office processor 30 executes an initialization step 421 in which various flags and registers are set to predetermined initialized parameters. In the next step 423, input parameters from all line monitor microprocessors 55 are loaded into the central office processor 30 data base, and a line monitor power-up flag is reset. The parameters which are input from the line monitor microprocessor 55 include the current value of the cumulative nickels CN count, the cumulative coin CC count at most recent collection, the time of the most recent collection, the collection count representing the number of times a collection has occurred, the local rate, the collect/return threshold, cumulative phone usage data, cumulative phone idle data, a maximum call time threshold, and a maximum idle time threshold. Since these input parameters are loaded in step 423 each time the central office processor 30 is powered-up, should the central office processor 30 be replaced or removed from service, it will automatically have its data base restored with the most current line monitor microprocessor 55 data when powered-up.

If the central office processor 39 was not powered up, then the central office processor 30 proceeds from step 420 directly to step 425, wherein it determines whether or not there is an incoming call from host computer 37 at the telephone company business office. If there is no incoming call from the host computer, then the central office processor 30 begins its polling of the various channels of the line monitors to collect data concerning cumulative nickels CN, cumulative coin CC count at most recent collection, time of most recent collection, and collection count, cumulative phone usage and cumulative idle time.

After polling one channel n in step 427 for this data, the central office processor 30 then proceeds to step 431, where it determines whether a power failure flag in the line monitor microprocessor it is currently polling is on or not. The power failure flag will be set to a one state whenever a line monitor microprocessor is powered-up, and thus needs to have its data restored from the data base of the central office processor 30. If the line monitor power failure flag is not on, the various input parameters noted above are input from the polled channel of the line monitor microprocessor to the central office processor 30. After this, the central office processor 30 proceeds to execute step 435, where it increments the channel counter n so that on the next pass through step 427 the next channel of the line monitor microprocessor will be polled. Thereafter, the central office processor proceeds to step 425. If, in step 431, the central office processor 30 determines that the line monitor power failure flag has been set, it proceeds to step 437, where it initializes the line monitor microprocessor channel data from the data contained in the central office processor data base. This includes data concerning cumulative nickels CN count, the cumulative coin CC count at most recent collection, the time of most recent collection, the collection count, the local rate, collect/return threshold, the maximum call time threshold, the maximum idle threshold, the cumulative phone usage and the cumulative idle usage. After this data is downloaded from the central office processor 30 to the line monitor microprocessor 55 for the line then being polled, the central office processor 30 then proceeds to step 435, incrementing the next channel counter, and the proceeds back to step 425.

If, in step 425, central office processor 30 determines that there is an incoming call from the host computer 37, it then proceeds to examine whether there is a request from the host computer for a transfer of data in the central office processor 30 data base to the host computer. If no transfer request is found, the central office processor 30 proceeds to step 439, where it places itself in a so-called "invisible" mode where it merely buffers data to and from the host computer 33 and the line monitor microprocessors 55. If a request from the host computer for data from the central office processor is found in step 429, the central office processor 30 then transmits to the host computer the requested data, in step 441, after which it proceeds back to step 425.

The communications program is designed to upload data collected by the line monitor microprocessors 55 into the central office processor for retransmission to the host computer 37 upon request. In addition, if the central office processor loses data it is capable of requesting that the line monitor microprocessors update the central office processor 30 with all data which was lost. If, on the other hand, the line monitor microprocessors are taken out of service, the central office processor is capable of recognizing this by means of the power flag which is set in the line monitor microprocessors to download relevant data to the line monitor microprocessors. It is also possible for the central office processor 30 to be invisible and act as a buffer to allow direct communications from the host computer 37 to the line monitor microprocessors 55.

The host computer 37 is used to accumulate information on all the phone channels monitored by each central office processor 30 in the system. The host computer 37 also maintains a data base containing pertinent information on a phone channel and relates the accumulated data to the telephone number for that channel.

The host computer 37 executes the FIGS. 18A, 18B program beginning in step 501 and assumes an idle condition, awaiting the proper time to initiate a poll sequence for all central office processors 30 within the system. Thus, the host computer 37 waits in step 503 until it detects the time for polling from a timer control 502. Typically, the collection program is initiated daily. When it is time for a poll, computer 37 initializes a central office processor pointer (n) to the first central office processor to be polled in step 505. Thereafter, it checks, in step 507, whether the pointer has reached a maximum value. If not, computer 37 establishes a connection with central office processor (n) in step 509. If the pointer value (n) has exceeded a maximum value, indicating that all central office processors have been polled, computer 37 proceeds from step 507 to step 503 and awaits the next polling time.

Once computer 37 establishes a communications link with a central office processor, it then initializes the phone pointer (p) in step 511. It then proceeds to acquire and process data for each phone channel in turn, provided there are more phone channels to process, as determined in step 513 by the (p) value reaching a maximum. When phone data is processed and stored for all phone channels maintained by the central office processor (n), the pointer (n) is incremented in step 515 and the process then repeats until all central office processor information for all phone channels has been acquired and processed. When data for a phone channel is updated, a data base record for the phone PH REC (n,p) is accessed in step 517 which is entered from step 513. Data contained in the record is illustrated below:

CN.sub.-- DB: Cumulative nickels collected by phone since installation

CNMR.sub.-- DB: Cumulative nickels at time of most recent collection

Tmrc.sub.-- DB: Time of most recent collection

CNPC.sub.-- DB: Cumulative nickels at time of collection previous to most recent one

Tpvc.sub.-- DB: Time of collection previous to most recent one

CCT.sub.-- DB: Count of number of collections made

Tinst.sub.-- DB: Time of line monitor installation on phone.

The host computer also accesses data base information common to all phones associated with a central office processor, which is as follows:

CBWT.sub.-- DB: Coin box warning level threshold set point

Tproj.sub.-- DB: Projection time for full box test

Tpp.sub.-- DB: Time of previous poll of central office processor.

The data for phone channel (p,n) is next retrieved in step 519. This data includes:

OCT: Present collection count

CN: Present cumulative nickels count

A check is then made in step 521 to see if the collection count CCT is the same as it was at the time of the last poll. If so, it is not necessary to collect the remainder of the information on the phone, since it has not changed since the time of the last poll. This method of checking for changes greatly reduces the communication overhead burden in the system, and enhances the time efficiency of communications. If the collection count CCT has changed, a flag is set to indicate that a collection has been made so that a report can be later generated, identifying collected phones together with the collection amount and the time of collection. If the data has changed, as determined in step 521, computer 37 then also collects the following data from the phone channel of the active central office processor:

CNMR: Coin count at time of most recent collection

Tlmmrc: Line monitor time at time of most recent collection

Tlml: Line monitor local time.

Once this information has been collected in step 523, all data is entered in the phone record. Thereafter, in step 525, the time and cummulative nickels CN count at the time of most recent collection is moved down to the previous collection data so that the newest, most recent collection information can be entered. That is,

Next, the new collection information is entered as follows:

CNMR.sub.-- DB=CNMR

BOX.sub.-- VAL=CNMR.sub.-- DB-CNPC.sub.-- DB

where BOX.sub.-- VAL equals the amount of money in the coin box as collected

Tmrc.sub.-- DB=Tcpu-(Tlml-Tlmlrc)

where Tcpu equals computer 37 time in year, month, day, hour and minute

Tinst=Tcpu-Tlml.

The time of most recent collection (Tmrc DB) is calculated based on the present time of day utilized by the computer 37 and subtracting from that the difference between the two minute tick time that is presently in the line monitor and the line monitor tick time when the collection was identified. This difference, therefore, identifies how long ago the collection occurred in two-minute increments. Subtracting this from the present time, therefore, provides the time at which the collection was made. This is accomplished without having to load the line monitoring microprocessors 55 with the correct time and date, thereby lowering the complexity of initialization, line monitor time data storage, and communication overhead associated with time transmission.

The coin box level (CBL) and percentage of full box (% FULL) is thereafter calculated by computer 37, in step 529, as follows:

CBL=CN-CNMR.sub.-- DB

where CBL equals coin box level, i.e., the dollar value (in nickel counts) presently in the money box

% FULL=CBL/FULL.sub.-- LEVEL

where FULL.sub.-- LEVEL is a dollar value at which the money box cannot hold additional coinage.

Since the dollar value which can be held differs between nickels, dimes and quarters, this value represents a statistical average of different coin denominations in determining the full box level. If there was no change detected in step 521 by computer 37, then the computer proceeds immediately to step 529.

A warning is issued if the projected money box level exceeds a predetermined threshold within the projected time interval. The projection formula is based on the present coin box level CBL, and weighting the following collection rates which can be derived from the data in the phone base and in the phone channel:

DR: Collection rate from the time of the previous poll, typically a daily rate

RSMRC: Rate since most recent collection

RSPC: Rate since previous collection

RSI: Rate since installation.

These rates are obtained in step 531 as follows:

The projected coin box level CBL PROJ can then be calculated in step 533 as follows:

where K1-K4 are weighting constants necessary to place the appropriate emphasis on the four rates available. These weights will change depending on the specific conditions of the phone company.

CBL.sub.-- PROJ is then compared to a threshold value in step 535 to determine if the projected fullness level will exceed CBWT threshold. Since the calculated value CBL.sub.-- PROJ includes a factor based on projected collection over time, the test in step 535 is one of whether the box will be full within Tproj hours. If so, a warning flag is issued in step 537 to indicate that the phone should be collected prior to Tproj.

Following the test and possible warning for CBL.sub.-- PROJ, the value CN DB is updated, in step 539, as follows:

The updated phone record is then stored back in the data base in step 541, and thereafter the phone pointer (p) is incremented in step 543 and a determination is made in step 513 if more phones remain to be updated in the central office processor 30.

In summary, the host computer periodically polls for information on each phone channel in the system. A data base record for each phone is updated to reflect the newest values, and the other useful information is derived from the combination of data in the data base and obtained from the phone channel. This information includes: the amount of money presently in the coin box (CBL), the fullness percentage for the money box, a projection of whether the coin box will overflow within a projected time interval, a report on the money boxes projected to overflow, a report identifying phones collected since the last poll, together with the amount collected and the time of collection along with other archival data which can be used in phone studies.

As is evident from the foregoing description, the present invention is able to provide a system for monitoring the collection of coins at a pay telephone, for indicating the amount of money in the collection box, for noting the time and number of collections which have been made, for discriminating between false tones and valid tones for the purpose of coin counting, and for monitoring several fault conditions, including excessive on-hook or off-hook conditions. In addition, data concerning the amount of money which has been collected is maintained for later comparison with the amount of money returned by a collection agent. The system is also capable of being configured for various other optional fault sensing conditions by the use of additional call points in the task scheduler program which may be implemented.

While a preferred embodiment of the invention has been described and illustrated with respect to various figures of the application, it should be understood that many modifications can be made to the invention without departing from the spirit and scope thereof. Accordingly, the invention is not to be considered as limited by the foregoing description, but is only limited by the claims which are appended hereto. ##SPC1##