JPS6156910B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention monitors whether or not the billing signal sent from the exchange is normally received on the public telephone side, and automatically disconnects the call circuit if it is not received normally. This invention relates to a charge signal monitoring circuit for public telephones.

In the case of a paid call, a public telephone receives a billing signal sent from an exchange by a billing signal receiving circuit inside the public telephone, and performs operations such as collecting the call charge based on this signal. However, if the ground connected to the ground terminal is cut off outside the public telephone for some reason when this billing signal is sent between the telephone call line and the ground, the ground and the telephone line may be shorted outside the public telephone. or if the call lines are shorted for some reason when the billing signal is sent to the call line, or even if the billing signal reaches the billing signal receiving circuit, this billing signal receiving circuit is malfunctioning. In cases where the public telephone is in use, the billing signal sent from the exchange is not received, and therefore the public telephone does not collect the call charge, resulting in a shortcoming in the case of a paid call.

The present invention corrects the above-mentioned drawbacks and monitors billing signals of public telephones by automatically disconnecting the call circuit if a billing signal is not properly received within a predetermined time in the case of a paid call to prevent call-outs. The purpose is to provide circuits.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the invention.

In the figure, Ta and Tb are the call line terminals of the public telephone, Te is the ground terminal of the public telephone, a and b are the call lines, e is the ground wire, 1 is the call circuit, 2 is the call between the call lines a and b, or the call A billing signal receiving circuit receives a billing signal sent from the exchange between lines a and b and ground wire e and outputs a billing signal arrival detection signal; 3 is a paid call sent from the exchange between call lines a and b; A pay call identification signal which receives the signal and outputs a pay call signal arrival detection signal; 4 receives the charge signal arrival detection signal from the charge signal receiving circuit 2, stores it, and detects that a charge signal has been received; A storage circuit 5 outputs a reception detection signal for the purpose of detecting a reception when the reception detection signal from the storage circuit 4 is not received within a predetermined period of time after receiving the detection signal for the arrival of a pay call signal from the pay call identification circuit 3. A timer circuit 6 outputs a disconnection signal and is a forced disconnection circuit that forcibly disconnects the communication circuit 1 upon receiving the disconnection signal.

FIG. 2 shows an example of a specific circuit configuration of the block diagram shown in FIG.

The billing signal receiving circuit 2 includes a filter circuit 21 for extracting an AC signal sent from the exchange between the telephone lines a and b and the ground wire e or between the telephone lines a and b as a billing signal; It is comprised of a signal processing circuit 22 that processes AC signals and outputs one pulse "L" as a charge signal arrival detection signal for AC signals continuously arriving from the exchange.

The memory circuit 4 is a flip-flop consisting of two NAND circuits 41 and 42, and the output signal of the signal processing circuit 22 is connected to the set terminal, and the signal RST that becomes "L" momentarily when the handset is raised is connected to the reset terminal. When it receives the billing signal arrival detection signal from the signal processing circuit 22, it is configured to memorize it and thereafter hold the output "L" as the reception detection signal.

The toll call identification circuit 3 inserts photo diodes of a photocoupler PC into the call lines a and b, so that the call line a is supplied as a pay call signal by a DC power supply (not shown) in the exchange when the called party answers. , b is detected as a change in the emitter output of the phototransistor of the photocoupler PC, and the emitter output of the phototransistor is detected by the resistor R1 and the inverter 31,
32, and is output to the timer circuit 5 via a waveform shaping circuit consisting of a resistor R2. Note that VR is a varistor that protects the photodiode by preventing application of an excessive reverse voltage to the photodiode of the photocoupler PC, and R3 and R4 are current limiting resistors.

The timer circuit 5 includes a counter 51, an AND circuit 52, and a NAND circuit 53. The AND circuit 52 receives the output PR of the pay call identification circuit 3 and the clock pulse CP from a clock pulse generation circuit (not shown). , its output is counter 5
Input to count input terminal CK of No.1. Further, the output of the NAND circuit 53 is connected to the reset terminal R of the counter 51, and one input terminal of the NAND circuit 53 is connected to the reset terminal R of the counter 51.
The GS relay is grounded through the contact gs2, and a voltage V is applied through the resistor R5 so that the input becomes "H" when the contact gs2 opens, and the other input terminals are connected to the memory circuit as a reception detection signal. 4 output
ME is connected. The counter 51 counts clock pulses CP while the output of the NAND circuit 53 is "L" and the output of the paid call identification circuit 3 is "H".
When the count value reaches a predetermined value (e.g. 8), the output terminal D
One pulse "H" is outputted to the forced disconnection circuit 6 as a disconnection signal. This count value is set so that the product of the period of the clock pulse CP and this value is longer than the maximum time from when a pay call signal is received until when a charge signal is received.

The forced disconnection circuit 6 includes a flip-flop 63 consisting of NAND circuits 61 and 62, and inverters 64 and 6.
5. It is composed of a resistor R6, a transistor 66, and a GS relay. A relay operation signal GOP that outputs one pulse "L" after a certain period of time after the handset is raised is input to the NAND circuit 61, and the relay operation signal GOP is input to the NAND circuit 62. is configured so that the handset-up signal RST, which momentarily becomes "L" when the handset is raised, and the output of the timer circuit 5 via the inverter 64 are input, and the flip-flop 63 is reset by the disconnection signal from the timer circuit 5. Then, since the base current is not supplied through the resistor R6, the transistor 66 is turned off and the GS relay is restored.

Note that Z is the impedance of communication circuit 1, gs1
is the contact point of the GS relay, and when the GS relay is restored, contact gs1 opens and the communication circuit 1 is disconnected.

FIG. 3 is a time chart showing the operation of each part in the circuit of FIG. 2, and the operation of the circuit of FIG. 2 will be explained based on this chart.

FIG. 3a shows a case where the billing signal is normally received by the billing signal receiving circuit 2. In FIG.

(1) When the handset is raised, the handset-up signal RST becomes "L" momentarily, the flip-flop of the memory circuit 4 is reset, and the flip-flop 63 of the forced disconnection circuit 6 is also reset. Also the contact
Since gs2 is closed, the output of the NAND circuit 53 is "H" and the counter 51 is reset.

(2) After a certain period of time has elapsed since the handset was lifted, the relay operation signal GOP becomes "L", thereby setting the flip-flop 63 of the forced disconnection circuit 6, and the output of the NAND circuit 62 becomes "L". Therefore, the output of the inverter 65 becomes "H", a base current is supplied via the resistor R6, the transistor 66 is turned on, and the GS relay operates.
Therefore, the contact gs2 is opened, the output of the NAND circuit 53 becomes "L", and the reset state of the counter 51 is released. Also, the relay contact of communication circuit 1
gs1 is closed to form a call loop. At this time, the terminal Ta has positive polarity and the terminal Tb has negative polarity, and the phototransistor of the photocoupler PC is turned on, so that the emitter output becomes "H" and the output PR of the paid call identification circuit 3 becomes "L". Therefore, the clock pulse CP is the AND circuit 5.
3 cannot be passed, so even if the reset state of the counter 51 is released, no counting operation is performed.

(3) At time t ₁ , the polarity of the call line current is reversed in response to the called party as a paid call signal, and the terminal Ta
When the terminal Tb becomes negative polarity and the terminal Tb becomes positive polarity, the phototransistor of the photocoupler PC is turned off and the output PR of the paid call identification circuit 3 becomes "H".
Therefore, the clock pulse CP is
It passes through and is input to the counting input terminal CK. Therefore, the counting operation of the timer circuit 51 starts when the output PR from the pay call identification circuit 3 becomes "H" as a pay call signal arrival detection signal.

(4) Thereafter, when the billing signal arrives at time t ₂ within the specified time after the counting operation of the timer circuit 51 starts, and the billing signal receiving circuit 2 normally receives this, the signal processing circuit 22 sends a billing signal arrival detection signal. As a result, one pulse "L" is output to the memory circuit 4, the output ME of the memory circuit 4 becomes "L", and therefore the output of the NAND circuit 53 becomes "H" and the counter 51 is reset. Therefore, the timer circuit 5 does not output a disconnection signal and the GS relay maintains its operating state, so that the communication circuit formation is maintained.

(5) However, if the ground wire e is cut outside the public telephone, or if the ground wire e and the call lines a and b are shorted (however, the charge signal is sent between the call lines a and b and the ground wire e). case)
Or, if the billing signal does not arrive within the specified time due to reasons such as the call lines a and b being shorted (however, the billing signal is sent between the call lines a and b), or even if the billing signal does arrive, Storage circuit 4 due to failure of billing signal receiving circuit 2
If the charge signal arrival detection signal is not output to the counter 51, the counter 51 is not reset and continues to count the clock pulses CP, and when the count reaches a predetermined value (e.g. 8) at time _t3 , the D output terminal of the counter 51 outputs the clock pulse CP. As shown in FIG. 3B, the disconnection signal "H" is output, and the flip-flop 63 of the forced disconnection circuit 6 is reset. As a result, the output of the inverter 65 becomes "L" and no base current is supplied, so the transistor 66 is turned off and the GS relay is restored. Therefore, the contact gs1 is opened and the communication circuit 1 is disconnected.

(6) Note that after the polarity of the line current is reversed by the called party's response (after the counting operation of the counter 51 starts), the polarity of the instantaneous line current is restored to its original state by the called party's instantaneous hanging of the handset. Even counter 51
Since the counting contents are maintained as they are, when the polarity is changed again, the counting operation continues, so even if the called party instantly hangs up the handset, there will be no malfunction.

(7) In the case of a toll-free call, the polarity of the call line current is not reversed when the called party answers as described in (3) above, so the output PR of the paid call identification circuit 3 remains "L" until the call is completed. hold. Therefore, the clock pulse CP cannot pass through the AND circuit 53, so the counter 51 does not perform the counting operation and the timer circuit 6 does not output a disconnection signal.
GS relay remains operational. Therefore, the addition of the billing signal monitoring circuit has no effect on free calls.

(8) When the handset is hung up at the end of the call, the handset-up signal RST becomes "L" and the flip-flop 63 and memory circuit 4 are reset. Therefore, the output of the inverter 65 becomes "L" and no base current is supplied through the resistor R6, so the transistor 66 is turned off and the GS relay is restored.

In the above embodiment, a case has been described in which a photocoupler PC is used as the paid call identification circuit 3 to detect the polarity of the call line current, but it may be replaced with another device such as a relay as long as it can detect polarity reversal. Needless to say. In addition, although we have described the case where the polarity reversal of the call line current is used as the toll call signal, when an AC signal of a certain frequency is used as the toll call signal, there is a receiving circuit that extracts this signal and a memory circuit that stores the output of the receiving circuit. The toll call identification circuit may be constructed depending on the above. Furthermore, if a circuit of a different type from that described in the above embodiment is used as the billing signal, the billing signal receiving circuit may be configured accordingly. Furthermore, since the time required to monitor the arrival of a charge signal after detecting a pay call signal is determined by the product of the period of the clock pulse CP of the timer circuit 5 and the count value, it is easy to change the required time by changing these. Can be set to time.

Since the present invention is configured as described above, if the billing signal is not properly received by the public telephone due to a grounding cut, a shorting of the telephone line, a failure of the billing signal receiving circuit, etc., the telephone circuit 1 is automatically switched off. It is possible to prevent unpaid calls by disconnecting the call.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of a specific circuit configuration, and FIG. , FIG. 3b is a time chart showing the operation of each part of the circuit of FIG. 2 when no signal is received. Ta, Tb...Talking line terminal, Te...Earth terminal, a, b...Talking line, e...Earth wire, 1
...Telephone circuit, gs1...Contact, 2...Billing signal receiving circuit, 3...Paid call identification circuit, PC...Photocoupler, 4...Memory circuit, 5...Timer circuit, gs2...Contact, 51... ...Counter, 6...
Forced disconnect circuit.

Claims (1)

[Claims] 1 A toll call identification circuit that receives a toll call signal sent from the exchange and outputs a toll call signal arrival detection signal; a billing signal receiver that receives a billing signal sent from the exchange and outputs a billing signal arrival detection signal. a storage circuit that stores a charge signal arrival detection signal and outputs a reception detection signal; and a timer circuit that outputs a disconnection signal if the reception detection signal is not received within a predetermined time after receiving the charge call signal arrival detection signal. A billing signal monitoring circuit for a public telephone set, comprising; and a forced disconnection circuit that forcibly disconnects a telephone call circuit upon receiving a disconnection signal.