JP2553943B2 - Circuit for high and dry measures of public telephones - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention is an exchange that cuts off the power supply to a high and dry state after a certain period of time in the off-hook state due to forgetting to hang the handset or the like. Connected to the
The present invention also relates to a high and dry countermeasure circuit for public telephones in which loop formation is performed by relay contacts.

[Prior Art] A conventional station-powered public telephone that automatically responds to incoming calls by closing a DC loop with a latching relay has the following three states, that is, the caller-side handset is hung on the destination side. In the so-called high-and-dry state, the power supply to the public telephone in the off-hook state due to forgetting to hang up the handset is cut off when the handset is forgotten, the handset is removed in the first loop, and the handset is removed after coin insertion in the second loop. There is an exchange.

At this time, the exchange detects about 100 m in 10-second cycles in order to detect whether the public telephone is on-hook.
A contest check pulse having a time width of s is transmitted, and when the handset of the public telephone is hung up and the DC loop is opened, the station power is supplied.

[Problems to be Solved by the Invention] In the above-described conventional public telephone, when the capacitor of the power supply circuit charged by the station current exceeds a certain voltage due to this contest check pulse, the output of the loop detection circuit and the comparator output are The AND signal configured from causes the latching relay that closes the DC loop to operate, and the contact of the latching relay remains closed. After that, since power is continuously supplied to each part of the public telephone only by the output of the capacitor of the power supply circuit in the public telephone, the capacitor is eventually discharged and power cannot be supplied from the capacitor. Even if you try to open the DC loop in the control circuit by hanging up the handset in such a state, the station power supply has already been cut off, and since power can no longer be supplied from the capacitor, the control circuit cannot The contact cannot be restored. For this reason, the exchange side detects the off-hook state even though the public telephone goes on-hook, and the exchange side continues to keep the station power off. As described above, conventionally, there has been a problem that once the high and dry state is set, the public telephone cannot be used thereafter.

[Means for Solving the Problem] In order to solve such a problem, according to the present invention, the power supply is stopped after a certain period of time remains in the off-hook state due to forgetting to hang the handset or the like, and the on-hook state is changed. A loop detection circuit that is connected via a telephone line to a switch in a high-and-dry state that periodically outputs a check signal of a predetermined time period that checks the return and that detects the closing of the DC loop of the telephone line, and the telephone line A power supply circuit that inputs the power supplied from the exchange through the switch and outputs it as a power supply voltage to each part, a comparator that generates an output signal when the output voltage of the power supply circuit exceeds a certain voltage, and a DC loop of the telephone line by opening and closing the contacts. The latching relay, which opens and closes the contacts and opens the contacts when the output voltage of the power supply circuit drops to a specified value, the loop detection circuit, and the controller. In a public telephone having an AND circuit for closing the contact of the latching relay by the AND output of each output of the palator,
Latching relay contacts by delaying the first output signal of the first and second output signals output from the comparator and the loop detection circuit in accordance with the check signal output from the switchboard and applying the delayed signal to the AND circuit. Is provided with a delay circuit for maintaining the open state.

[Action]

The relay contacts do not operate even when a check signal arrives from the exchange. As a result, the station power is supplied from the exchange when the handset is set, and the public telephone can be used.

EXAMPLES Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a high and dry countermeasure circuit for a public telephone according to the present invention. In the figure, 1 is a control circuit, 2 is a communication circuit, 3 is a loop detection circuit, 4 is a comparator, 5 is a delay circuit, and 6 is an AND circuit. Then, the loop detection circuit 3 includes a photo coupler PC,
The delay circuit 5 is composed of a varistor VR and a resistor R1, and the delay circuit 5 is composed of a diode D, a capacitor C2 and resistors R2 and R3. The power supply circuit of this public telephone is composed of a constant voltage diode ZD and a capacitor C1, and its output is given to the control circuit 1. GS is a latching relay that automatically responds to incoming calls and closes the DC loop.Q1 and Q2 are transistors, DB is a diode bridge, L1 and L2 are telephone line terminals, HS is a handset contact point, and gs is a latching relay. A contact point of GS, a is an output signal of the loop detection circuit 3, b is a delayed signal output from the comparator 4 and delayed by the delay circuit 5, and c is an output signal of the AND circuit 6.

Next, FIG. 2 is a timing chart showing the timing of each part in the high and dry state described later. It is to be noted that the diagrams (a), (b) and (c) show the output signal a, the delay signal b and the AND signal of the loop detection circuit 3, respectively.
The timing of the output signal c of the circuit 6 is shown.

The operation of the high and dry countermeasure circuit of the public telephone configured as described above will be described based on this timing chart.

If the caller forgets to hang up the handset when the other party calls and the contact HS remains closed, a BT tone (busy tone) is sent from the exchange (not shown), and then the exchange is a public telephone. To stop the power supply (high and dry state).

In such a situation, the capacitor of the power circuit is still
C1 is fully charged, at which time the switch will check to see if the handset of the payphone has been hung up.
A constant check pulse (hereinafter referred to as a check signal) with a pulse width of about 100 ms is sent every 10 seconds. This check signal is detected by the photocoupler PC in the loop detection circuit 3 at the timing shown in FIG. 2 (a), and is sent to one input terminal of the AND circuit 6 as the output signal a of the loop detection circuit 3. To be done.

At this time, this check signal is also sent to the comparator 4 via the capacitor C1, and as a result, the comparator 4 sends a pulse signal equivalent to this check signal. This pulse signal is delayed by the delay circuit 5 and sent to the other terminal of the AND circuit 6 as the delay signal b at the timing shown in FIG. 2 (b).
As a result, the output signal c of the AND circuit 6 is (c) in FIG.
As shown in the figure will not be delivered and therefore the transistor
Q1, Erase GS does not work, contact gs is not closed.

After that, a check signal continues to arrive from the exchange every 10 seconds, but since the handset of the public telephone is not hung up, this high and dry state is maintained. On the other hand, since the power supply capacitor C1 of the public telephone is connected to the control circuit 1 and supplies power, the electric charge is gradually discharged and the voltage is lowered. Then, when the voltage drops to a specific level, a reset signal is sent to the control circuit 1, and as a result, the control circuit 1 is initialized, and in this initialization process, if the handset is turned on, the transistor Q2
Relay GS that has been restored by driving
Make gs open.

After that, when the operator hooks the handset, the contact HS is opened. Also, at this time, unlike the conventional case, the contact gs is not closed, so that the exchange can detect the on-hook state of this public telephone by the above-mentioned check signal every 10 seconds. The station power can be supplied.

When the handset is removed in the first loop and the handset is removed in the second loop after coin insertion, a howler sound is first sent from the exchange, and then a BT sound is generated, and after a further time, the high and dry state It becomes a state.
Even in such a case, the contact gs of the latching relay GS does not operate due to the high and dry countermeasure circuit.

FIG. 3 is a timing chart showing the timing of each part when the contact point HS operates to make a call when the station power is supplied to the public telephone. In addition,
These (a), (b) and (c) diagrams show the timing of the output signal a, the delay signal b of the loop detection circuit 3 and the output signal c of the AND circuit 6, respectively. Thus, when the contact HS is closed, the output signal a of the loop detection circuit 3 is sent to one terminal of the AND circuit 6 at the timing shown in FIG. A signal equivalent to the output signal a is delayed by the delay circuit 5 to become the delayed signal b, and the AN signal is output at the timing shown in FIG.
It is sent to the other terminal of the D circuit 6. As a result, the output signal c of the AND circuit 6 is delayed and output at the timing shown in FIG. Thus, the relay GS is operated by the delayed output signal c, and the contact gs is closed.

As described above, the high and dry countermeasure circuit of this public telephone delays the check signal sent from the exchange at the time of high and dry and sends it to one input terminal of the AND circuit 6. Even if the latching relay GS does not operate due to the check signal, and therefore the high and dry state is set, the station power is supplied to the public telephone by mounting the handset, and the public telephone can be used.

The loop detection circuit 3 of the present embodiment is a photocoupler PC.
However, instead of this, a reed relay may be used, and its contact output terminal may be connected to one input terminal of the AND circuit 6.

[Effects of the Invention] As is clear from the above description, the circuit for high and dry countermeasures of the public telephone according to the present invention checks whether or not it has returned to the on-hook state by checking the switch from the high and dry state. Since the relay contact of the public telephone is not activated by delaying the signal, the power is supplied from the exchange when the handset is turned on, and as a result, the public telephone can be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a high and dry countermeasure circuit for a public telephone according to the present invention, FIG. 2 is a timing chart showing the operation of each part of the public telephone at the time of high and dry, and FIG. 6 is a timing chart showing the operation of each part of the public telephone when the loop is closed when the station power is supplied. 1 ... control circuit, 2 ... call circuit, 3 ... loop detection circuit, 4 ... comparator, 5 ... delay circuit, 6 ... AND
Circuit, GS ... Latching relay, PC ... Photocoupler VR ...
… Varistor, D …… Diode, ZD …… Voltage diode, Q1, Q2 …… Transistor, DB …… Diode bridge, C1, C2 …… Capacitor.

Claims (1)

(57) [Claims] 1. A high and low power supply that stops the power supply after a certain period of time remains in the off-hook state due to forgetting to put on the handset or the like, and periodically outputs a check signal of a predetermined time width for checking the return to the on-hook state. A loop detection circuit that is connected to the exchange in a dry state via a telephone line and detects the closing of the DC loop of the telephone line,
A power supply circuit that inputs the power supplied from the exchange through the telephone line and outputs the power supply voltage to each part, a comparator that generates an output signal when the output voltage of the power supply circuit becomes a certain voltage or more, and a contact is opened and closed. A latching relay that opens and closes the DC loop of the telephone line and opens contacts when the output voltage of the power supply circuit drops to a predetermined value, and the latching by the logical product output of the outputs of the loop detection circuit and the comparator. In a public telephone having a logical product circuit for closing a contact of a relay, among the first and second output signals output from the comparator and the loop detection circuit, respectively, according to a check signal output from the exchange. By delaying the first output signal and applying it to the AND circuit, the contact of the latching relay is opened. A high and dry countermeasure circuit for a public telephone, which has a delay circuit for maintaining a state.