JPS6325792Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a public telephone that uses a noise-preventing handset or a handset for hearing-impaired persons, which is equipped with an amplifier.

Figure 1 is a circuit diagram of the main parts of a conventional example of a public telephone.
turns on, and when a coin is inserted, the coin detection contact CCL also turns on, forming a DC loop between line terminals L ₁ and L _2. Initially, line terminal L ₁ is set as the positive terminal and DC voltage from the exchanger is applied. Therefore, line terminal L ₁ - Hook switch HS - Diode D ₁ - Coin detection contact CCL - Dial pulse contact D _i - Diode of diode bridge circuit
D _a - Guide wire IND - Transmitter T - Diode of diode bridge circuit D _b - Current flows through the route of line terminal L ₂ , the exchange detects this and becomes ready to make a call, sending out a dial tone. .

When you dial after confirming this dial tone, the pulse contact D _i repeats on and off while
The shorting contact D _s of the dial remains on, a dial pulse is sent out, the exchange responds to this dial pulse, the exchange connection is completed, and when the called party answers, the polarity reversal pulse shown in Figure 2 is transmitted. A signal is sent from the exchange, and after a voltage with line terminal L ₂ as the positive electrode is applied for about 1 second, the line terminal L ₁ returns to the positive electrode state again.

Therefore, during the period of the polarization pulse signal with line terminal L ₂ as the positive polarity, line terminal L ₂ - diode D _c of the diode bridge circuit - induction wire IND - transmitter T - diode D of the diode bridge circuit. _d
- Pulse contact D _i - Coin detection contact CCL - Diode
D ₂ - Relay M - Line terminal L ₁ A current is passed through the route of L 1, and the self-holding type relay M using a permanent magnet etc. operates and holds itself, detects the called party's response, and The omitted coin storage magnet circuit is completed, and it is activated by a polarity reversal pulse signal to store the inserted and waiting coins in the storage safe.

Note that contact m ¹ is turned on by the operation of relay M, and diode D ₁ is short-circuited, so from now on,
No current flows through the relay M, and the relay M maintains its operating state until a recovery circuit (not shown in the figure) is completed due to on-hook after the end of the call.

In addition, the above-mentioned communication state is established, a conversation with the called party is carried out using the transmitter T and the receiver R, and each time a unit time determined according to the communication distance elapses, a polarity reversal pulse signal shown in FIG. 3 is generated. is sent out from the exchange machine, this activates the coin storage magnet, and each time a coin is stored, and when there are no coins waiting, this is detected by the coin detection circuit omitted in the above. Moreover, the reminder tone oscillator TG is driven, a reminder tone of an audible frequency is sent from the oscillator TG, and the capacitor C ₁
By applying the signal to the telephone receiver R via the signal, a notification indicating that there are no coins remaining in response to the handling tone is performed.

However, as shown in FIGS. 2 and 3, each polarity inversion pulse signal is provided with a cutoff period of about 0.5 seconds or several tens of milliseconds in order to prevent the generation of noise such as clicks, and during this period, For the purpose of supplying talking current to the transmitter T, the guide wire IND,
A large-capacity capacitor _C2 is connected in parallel with a communication circuit consisting of a transmitter T and a receiver R.

However, due to the internal resistance of the communication current supply circuit in the exchange and the resistance component of the line connecting the exchange and line terminals L ₁ and L ₂ , the capacitor
The time constant when charging C ₂ is large,
As shown in FIG. 4, after the DC loop is constructed, the terminal voltage V _c2 of the capacitor C ₂ gradually increases.

Therefore, the talking current of the transmitter T does not quickly reach the specified value, and this is not a particular problem in general handsets, but in the handset for the hearing-impaired and the noise prevention type handset, the talking current of the transmitter T does not reach the specified value quickly. If you use a handset with an amplifier in the handset/receiver circuit, the operating status of the amplifier will not quickly return to the normal operating state, and the exchange It takes some time before the tone emitted from the device becomes audible, which is inconvenient for the operator.

The purpose of this invention is to eliminate all of these drawbacks of the conventional technology at once. By connecting a resistor in parallel with the coin detection contact, the amplifier in the handset circuit can be brought into normal operating condition quickly. It provides a highly effective public telephone.

Hereinafter, the present invention will be explained in detail with reference to FIG. 5 and subsequent figures showing embodiments.

FIG. 5 is a circuit diagram of the main parts similar to FIG. 1,
A resistor R _c is connected in parallel with a coin detection contact CCL inserted in series with the communication circuit and capacitor C ₂ via a diode bridge circuit consisting of diodes D _a to D _d . The resistance value of R _c is determined so that the current for precharging the capacitor C ₂ can pass within a range in which the exchange does not respond, and is approximately 10 KΩ, for example.

Therefore, the off-hook causes the off-hook to switch.
When HS is turned on, line terminal L ₁ - hook switch HS - diode D ₁ - resistor R _c - pulse contact D _i
−Diode D _a −Capacitor C ₂ −Diode D _b
- Since capacitor C ₂ is immediately pre-charged by the route of line terminal L ₂ , coin detection contact CCL is turned on by inserting a coin, resistor R _c is short-circuited, and capacitor C ₂
As shown in Figure 6, the terminal voltage _Vc2 of the capacitor _C2 quickly reaches the specified value, and the current flowing to the terminal of the transmitter T also reaches the specified value, and the caller There shall be no period during which hearing is impossible.

However, when using a handset for the hearing-impaired, the terminal voltage of capacitor C ₂ will fluctuate if the short-circuit contact D _s turns on and off in the middle of sending dial pulses for each digit. As a result, the amplifier in the handset/receiver circuit becomes unstable, generating abnormal sound, which may cause discomfort to the operator.

FIG. 7 is a circuit diagram of the main part of an embodiment in which measures are taken against the generation of abnormal noise mentioned above, in which the capacitor C ₂
The contact ^m2 of relay M is inserted in series with , and the capacitor _C2 is disconnected from the circuit until the sending of dial pulses is completed.When the polarity reversal pulse signal shown in Fig. 2 arrives due to the called party's response, It is assumed that capacitor _C2 is connected only after relay M is activated.

In addition, a diode D ₃ as a directional element is connected to this added contact m ² in parallel and in the forward direction with respect to the charging and flowing direction of the capacitor C ₂ . Terminal L ₁ −Hook switch HS−
Precharging of the capacitor _C 2 was carried out by the route of diode D ₁ - resistor R _c - pulse contact D _i - diode D _a - capacitor C ₂ - diode D ₃ - diode D _b - line terminal L ₂ . up,
While contact m ² is off, diode D ₃ prevents capacitor C ₂ from discharging.

The dial pulse is sent after the coin detection contact CCL is turned on by inserting a coin, and after the exchange connection, when the polarity reversal pulse signal shown in Fig. 2 is given by the called party's response, the line terminal L ₂ - Diode D _c - Capacitor C ₂ - Diode D ₃ - Diode D _d - Pulse contact D _i - Coin detection contact CCL - Diode D ₂ - Relay M - Line terminal L The capacitor C ₂ is charged by the route of ₁ . Even if some discharge occurs due to the self-discharge of capacitor C ₂ and the reverse leakage current of diode D ₃ , the terminal voltage of capacitor C ₂ hardly decreases.

Therefore, after the relay M is activated and self-maintained by the polarity reversal pulse signal, the terminal voltage _Vc2 of the capacitor _C2 quickly reaches the specified value, and the contact ^m2 is turned on, as shown in Figure 6. This completes the discharge circuit of capacitor _C2 .

Therefore, capacitor _C2 is not connected to the circuit at first, thereby preventing the delayed flow of the communication current, and the dial tone is immediately heard.
The generation of abnormal sounds when dial pulses are sent out is also prevented.

Further, immediately after the relay M is activated, a normal communication current is passed to the terminal of the transmitter T, and the amplifier in the handset/receiver circuit quickly returns to the normal operating state.
The call can be made immediately upon the called party's response.

Note that the resistance value of the resistor R _c may be determined according to the loop current detection characteristics of the exchange, but a directional element such as a metal rectifier or a transistor may be used as the diode D ₃ , and a directional element such as a metal rectifier or a transistor may be used as the contact m ² . teeth,
The same effect can be achieved by using contacts of other relays that operate in the same way as relay M, and various modifications are possible.

As is clear from the above explanation, according to the present invention, only by adding a resistor, the communication current immediately reaches the specified value, preventing the caller from being unable to hear in the initial state, and preventing the called party from responding. Since the handset circuit immediately returns to its normal operating state, it is highly effective in public telephones that use a handset equipped with an amplifier that operates on talking current, such as handsets for hearing-impaired people and noise-preventing handsets.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the main part showing a conventional example, Figures 2 and 3 are waveform diagrams of a polarity reversal pulse signal, Figure 4 is a diagram showing changes in capacitor terminal voltage, and Figure 5 is an implementation of the present invention. Main part circuit diagram showing an example, Figure 6 is a diagram showing the terminal voltage change of the capacitor in Figure 5, Figure 7 is a diagram showing the terminal voltage change of the capacitor in Figure 5.
The figure is a main part circuit diagram showing another embodiment. IND...Induction wire ring, T...Telephone, R...Telephone receiver, _C2 ...Capacitor, D _a ~ D _d ...Diode (diode bridge circuit), CCL...Coin detection contact, R _c ... …Resistor.

Claims (1)

[Scope of utility model registration request] A public telephone comprising a capacitor connected in parallel with a speech circuit in order to supply a speech current during a disconnection period of a polarity inversion pulse signal, and further comprising an amplifier operated by the speech current in a handset circuit, wherein the telephone circuit and the capacitor are provided. A resistor is connected in parallel to the coin detection contact inserted in series via a diode bridge circuit, and has a resistance value that allows a current to precharge the capacitor to pass within a range where the exchange does not respond. public telephones.