JPH0314860Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an incoming call detection circuit applied to a front-loop type public telephone.

[Prior art]

In front-loop public telephones, the DC loop circuit is closed only by the off-hook, and calls can be made. Therefore, the off-hook alone prevents transmission and reception, and the blocking state is released when the conditions for allowing calls are met. However, in the case of an incoming call, it is necessary to be able to make a call immediately by simply going off-hook, and for the purpose of controlling this, incoming calls are generally detected using an incoming relay that maintains operation when a ringing signal arrives. It has become something to do.

However, a latching type must be used for the incoming call relay, which is expensive and requires a large space to accommodate, creating drawbacks that impede the reduction in price and size of public telephones.

[Summary of the idea]

The purpose of the present invention is to eliminate such drawbacks of the conventional methods at once.The capacitor is charged by the arrival of a calling signal, the light emitting element is caused to emit light by this charge, and this emitted light is received by the light receiving element. The control unit, which comes into operation in response to
In the case of incoming call detection, it is configured to cancel the transmitting/receiving blocking state by the relay contact, and is extremely effective.
This provides an incoming call detection circuit for public telephones.

〔Example〕

Hereinafter, details of the present invention will be explained with reference to figures showing embodiments.

The figure is a circuit diagram, in which a capacitor C ₁ and a diode bridge are connected via a switch HS ¹ to a line terminal L ₁ to which the positive line of the telephone line is connected, and to a line terminal L 2 to _which the negative line is connected. circuit
The series circuits of DB and Bell B are connected in a bridge manner, and a constant voltage diode ZD ₁ is connected in parallel between the positive terminal and negative terminal of the diode bridge circuit DB. A diode D ₁ and a capacitor C ₂ are connected to the capacitor C ₂ in the forward direction, and a light emitting diode of a photocoupler PC is connected in parallel in the forward direction as a light emitting element to the capacitor C 2 via a resistor R ₁ .

In addition, a diode is connected between the line terminals L ₁ and L ₂ and the communication circuit TKC via a switch HS ¹ .
A bridge circuit consisting of D ₂ to _{D 5} , a switch SW using switching elements such as transistors, and a constant voltage diode ZD ₂ are inserted, and a DC loop circuit is closed in response to off-hook, and a loop current is passed to these. As the loop current, which has a constant polarity due to the bridge circuit, passes through the constant voltage diode ZD ₂ , regardless of the polarity of the line voltage, a constant voltage is inserted as a direction to generate a Zener voltage with respect to the loop current. Due to the Zener voltage of the voltage diode ZD ₂ , the diode for reverse current blocking
The capacitor _C3 is charged via _D6 , and the terminal voltage of the capacitor C3 is supplied as a local power supply, so that the control unit CNT performs control operations.

However, contact ss ¹ of a magnetic latching type blocking relay SS is connected in parallel to the communication circuit TKC, and this is initially turned on to block transmission and reception. As a result, it is impossible to make a call, and the control unit CNT, which is composed of a processor such as a microprocessor and a memory, determines whether the call permission conditions such as coin insertion are satisfied through a route not shown in the diagram, and then activates the blocking relay SS.
When the operating winding F is driven, the relay SS maintains the operation, and the contact SS ¹ is turned off, making it possible to talk.

In addition, the recovery winding R of the blocking relay SS is driven in response to the turning on of the switch ^HS2 due to the on-hook, while the charge in the capacitor _C3 is not discharged, thereby restoring the relay SS. It is becoming.

In addition, the control unit CNT initializes in response to the voltage rise of the local signal and then starts the control operation. During this initialization, the control unit CNT determines the state of the photodetector transistor of the photocoupler PC as a photodetector. However, if this is in the ON state, an incoming call is detected, and the operation winding F of the blocking relay SS is immediately driven to release the blocked state of transmitting and receiving calls.

That is, when a call arrives, the incoming call signal passes through the diode bridge circuit DB and the bell B,
As a result, bell B rings, and the calling signal is rectified by diode bridge circuit DB.
Capacitor through diode D ₁ for backflow blocking
_C2 is charged, and its charge is discharged through the resistor _R1 and the light-emitting diode of the photocoupler PC, so the light-emitting diode emits light for a certain period of time even after off-hook, and this light is received by the light-receiving transistor, and its impedance decreases to turn on, and the collector voltage applied from the local signal via the resistor _R2 becomes "L" (low level).

Therefore, during initialization, the control unit CNT determines that if the collector voltage of the light-receiving transistor is "L", it is an incoming call, and conversely, if it is "H" (high level), it is an outgoing call, and as described above, controls in response to the incoming call. ,
Alternatively, control can be performed in response to the call.

In addition, the control unit CNT monitors the dialed number through a route not shown in the diagram, checks whether or not there are coins inserted during a call, and monitors the coin storage status, etc., to prevent calls from prohibited numbers or lack of coins inserted. , if it detects that the coins are not properly stored, the switch will be activated.
The switch is turned off, the exchange is restored, and the call is forcibly disconnected.

Note that the values of capacitor C ₁ and resistor R ₁ are:
Until the battery is sufficiently charged in response to the arrival of intermittent call signals about two times and the control unit CNT completes initialization in response to off-hook.
It may be determined as a discharge time constant that allows the light emitting diode to emit light.

However, in some cases, a constant voltage diode
ZD ₁ and diode D ₁ may be omitted, or the same effect can be obtained by connecting the diode bridge circuit DB in parallel with the bell B and inserting a current-limiting resistor, etc. in series with the bridge circuit DB. , the connection part of contact ss ¹ can be selected arbitrarily as long as it can block transmission and reception, and depending on the situation, make type or transfer type may be used for contact ss ¹ , and the operation of blocking relay SS and recovery can also be in the opposite relationship.

In addition, the blocking relay SS may be one that maintains operation using a permanent magnet, or one that maintains operation mechanically.
In particular, various modifications are possible, such as using a dedicated one constructed from a combination of various logic circuits without using a processor.

[Effect of idea]

As is clear from the above explanation, according to the present invention, incoming calls can be reliably detected without using an incoming call relay, and the cost can be reduced and the size can be easily reduced, so it is highly effective in front-loop public telephones. is obtained.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the present invention. L ₁ , L ₂ ... Line terminal, HS ¹ , HS ² ... Hook switch, TKC ... Communication circuit, C ₁ - C ₃ ... Capacitor, DB ... Diode bridge circuit, D ₁ - D ₆
...Diode, R ₁ , R ₂ ...Resistor, ZD ₁ , ZD ₂
... Constant voltage diode, PC ... Photocoupler,
CNT...control unit.

Claims (1)

[Scope of Claim for Utility Model Registration] In a pre-loop type public telephone, a capacitor that is charged when a calling signal arrives, a light emitting element that emits light due to the charge of the capacitor, and a light receiving element that receives light emitted from the light emitting element. a control unit that is activated in accordance with the flow of loop current due to off-hook and determines an incoming call when the light-receiving element is in a light-receiving state; and a relay contact for releasing the light, and the charge of the capacitor has a value sufficient to cause the light receiving element to emit light until the control unit determines the light receiving state. Incoming call detection circuit.