JPS5834841Y2 - Off-hook detection device - Google Patents

Description

[Detailed description of the invention] This invention is an off-hook detection device that detects when the handset of a telephone is lifted (off-hook) in a data transmission system using a subscriber telephone line and disconnects the data terminal from the subscriber telephone line. Regarding.

A so-called automatic meter reading system is being considered in which a data terminal device is installed on a subscriber telephone line to collect consumption data from consumer meters for water, gas, electricity, etc. when the telephone is not in use.

In this system, even if data is being transmitted, if the telephone goes off-hook, it is necessary to stop data transmission and give priority to the telephone.

A conventional device of this type is shown in FIG.

That is, relay contacts al and a2 are provided between the connection terminals L1 and L2 with the exchange and the data terminal DTE, and data transmission is performed via these contacts al and a; i' when the telephone is not in use, and when the telephone is off-hook. The direct current loop current flowing through the device operates relay A, turns off contacts al and a2, and disconnects data terminal DTE from the telephone line.

By the way, when the DC loop is closed, a voltage drop occurs due to the line resistance of the telephone line.

This voltage drop varies depending on the length of each telephone line, and increases as the line becomes longer.

Therefore, the longer the line, the smaller the current flowing through relay A, and the relay A needs to have a smaller current.

In reality, relays are limited to small currents that can be satisfied with any line length, making them expensive and limiting their use.

Furthermore, the use of relays itself has drawbacks that are inherently unfavorable to miniaturization and integration of devices.

The present invention provides such an improvement, and provides an off-hook detection device that performs off-hook detection using an optical coupling element, and is capable of reliably disconnecting a data terminal when off-hook, without being affected by the line length of the telephone line. .

An embodiment of the present invention will be described with reference to underground drawings.

In Fig. 2, Ll and L2 are connection terminals to the telephone line,
LAl, Li2 are connection terminals to the telephone, 1 is the telephone, 2
is the main device of the data terminal.

Note that the connection terminals Ll and L2 are connected to the exchange via a telephone line, and under normal conditions Ll is 10-chi, L2 or 1-4.
8v, L during calls and operation of data terminal equipment
Power is supplied so that 2 is 148V and L1 is 148V.

Connection terminal LA1 is connected to connection terminal L1, and connection terminal L
A photodiode portion of a photocoupler 3 and a resistor 4 are inserted and connected in series between A2 and the connection terminal L2.

A varistor 5 and a capacitor 6 are connected in parallel to both ends of a series circuit consisting of the photodiode section of the photocoupler 3 and the resistor 4, respectively.

Further, the collector and emitter of an npn transistor 7 are connected to the connection terminal L2 and one terminal of the main device, respectively.

A self-biasing resistor 8 is connected between the collector and base of this transistor I, and a phototransistor portion of the photocoupler 3 and a diode 9 are connected between the base and emitter of this transistor 7 in forward and reverse directions, respectively. connected in parallel in the direction.

A diode 10 and a thyristor 11 are connected in series between the connection terminal L1 and the other terminal of the main device 2, and a diode 12 is connected between the connection point of the diode 10 and the thyristor 11 and the emitter of the transistor 7. The starting signal detection circuit 1”3 is connected in parallel with this diode 12.
is provided.

The thyristor 11 is triggered by the output of the activation signal detection circuit 13.

In the above configuration, the resistor 4 is used to bypass the photocoupler 3 to the varistor 5 side so that the forward current in the photodiode portion of the photocoupler 3 does not exceed a predetermined value when the line length of the telephone line is the shortest. Similarly, the varistor 5 protects the reverse withstand voltage of the photodiode section, the diode 9 protects the reverse withstand voltage of the phototransistor section of the photocoupler 3 and the transistor 7, and the diode 12 protects the main device 2.

Assume that the handset of telephone 1 is currently on-hook, and that the data terminal device is called in this state.

At this time, the polarity of the exchange power supply is reversed, and 10-48 V appears at the connecting terminal L2 and -48 V appears at the connecting terminal L1.

As a result, a small bias current sufficient to make the transistor 7 conductive flows through the path of the resistor 8, the activation signal detection circuit 13, and the diode 10, and the transistor 7 becomes conductive.

Subsequently, when a specific activation signal (tone signal) for data collection is sent, this signal is received and detected by the activation signal detection circuit.

The detection output from the starting signal detection circuit 13 is the thyristor 11
, the thyristor 11 is triggered to conduct.

As a result, a first DC loop is formed by the route of the connection terminal L2 transistor 7, the main device 2, the thyristor 11, the diode 10, and the connection terminal L1, and sufficient current is supplied to the main device 2 for its operation.

In this state, data is transmitted from the main device 2 to the exchange side.

When the handset of telephone 1 is lifted up (off-hook) during this data transmission (collection), a second DC current flows through the route of connection terminal L2, resistor 4, photodiode section of photocoupler 3, telephone 1, and connection terminal L1. A loop is formed and the photodiode section becomes conductive.

Therefore, the phototransistor portion, which is the secondary side of the photocoupler 3, becomes conductive.

Therefore, the base current to the transistor I that had been supplied through the resistor 8 bypasses the phototransistor portion of the photocoupler 3 and flows, and the transistor 7 is not biased and becomes non-conductive.

Even if this transistor 7 becomes non-conductive, a route for the resistor 8, the phototransistor portion of the photocoupler 3, and the main device 2 is formed, and there is a possibility that current will flow into the thyristor 11.

However, as the transistor 7 is cut off, the bypass current flowing through the route becomes lower than the holding current of the thyristor 11, so the thyristor 11 is turned off and the bypass current is blocked.

Therefore, the main device 2 is completely disconnected from the telephone line.

In order to satisfy the turn-off condition of the thyristor 11, the value of the resistor 8 is set so as to be equal to or less than the holding current of the thyristor 11.

The present invention is not limited to the above embodiments, and can be applied in various modifications. For example, the secondary side of the photocoupler 3 is not limited to a phototransistor, but may also be a switching element such as a photothyristor, and the transistor 7 may be a switching element such as a photothyristor. A switching element such as a Darlington type transistor, a field effect transistor, or a phototransistor may be used.

As described above, according to the present invention, off-hook detection is performed using an optical coupling device and switching control of a semiconductor switching device is performed, so it is not affected by the line length of the telephone line like a relay, and responds with a weak current. The data terminal can be disconnected reliably, and compared to the use of relays, it is effective in reducing costs and downsizing and integrating the device.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing a conventional off-hook detection device;
The figure is a wiring diagram showing an off-hook detection device according to an embodiment of the present invention. 1... Telephone, 2... Main device, 3... Photocoupler (optical coupling element), 4... Resistor, 5... Varistor,
6... Capacitor, 7... Transistor, 8...
Resistor, 9°10.12...Diode, 11...Thyristor, 13...Start signal detection circuit.

Claims (1)

[Scope of utility model registration request] In a terminal device in which a main device is connected in parallel with a telephone set to a subscriber telephone line and data is transmitted via the subscriber telephone line, the first switching element has a control pole that is brought into conduction by a self-bias by an exchange power supply; A start signal detection circuit connected to the exchange side via a switching element to receive and detect the start signal; and a start signal detection circuit that is triggered by the output of this start signal detection circuit and connected to the exchange side and the main device via the first switching element. The primary side is connected in series between a second switching element constituting a DC loop, the telephone set and the exchange side, and the secondary side is connected to the control pole of the first switching element, and is operated when the telephone set is off-hook. and an optical coupling element that turns off the first switching element.