JPS6276354A - Hook-off detection circuit - Google Patents

Abstract

PURPOSE:To attain the detection of an off-hook signal without being affected by a ringer signal or a dial signal by providing a means that detects the peak value of a current in a telephone circuit that flows in both a forward direction and a backward direction and a means that obtains the exclusive OR of each detection output value. CONSTITUTION:By a current flow on the telephone circuit by the off-hooking of a telephone set, a phototransistor 2-2 is made on when the current flow is from a terminal L1, to L2, and another phototransistor 3-2 is made on when the current flow is from the L2 to the L1. The peak value of the current waveform in each direction is detected with peak value circuits 4-6 and 8-10, and is waveform-shaped at buffer circuits 7 and 11. Two waveform outputs (e) and (f) on which waveform shapings are appied, are outputted after logical operations are applied on them by an exclusive OR circuit 12. Thereby, the off-hook signal that is not affected by the dial signal or the ringer tone, etc. can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a network control circuit for connecting input/output devices for transmitting information over a 'M telephone line, and in particular to hook-off of telephones connected to a 'C telephone line. This relates to a detection circuit.

BACKGROUND OF THE INVENTION Conventionally, an example of this type of network control circuit is shown in FIG. i! The hook-off detection circuit 20 of the telephone connected to Lx and L2 and the telephone connection terminal T1eT2 and the connection terminal 19-1.19-2 of the input/output device via the transformer 18 are connected to the telephone line L1°L2. and a control unit (not shown) that receives the output 16 of the hook-off detection circuit 20 after detecting the hook-off of the telephone and enables the switching relay 17 to switch. This hook-off detection circuit 20, as shown in FIG.
1 and 3-1, and a telephone line connection section in which a capacitor 28 for passing sound is connected in parallel, and phototransistors 2-2 and 3-1 forming a photocoupler corresponding to these light emitting diodes 2-1 and 3-1. 3-2 and the logical sum of the outputs of phototransistors 2-2 and 3-2.
An R circuit 29, a peak value holding circuit 30 that holds the peak value of the output of this logic 10, and a peak value holding circuit 30 that holds this peak value at the output terminal 1.
6, and a buffer 31 for outputting to 6.

Next, to explain this operation, in FIG. 4, the communication line L1. L2 is relay contact 17-1.1 of switching relay 17
It is connected to the telephone connection terminal T1° T2 side from the front connection terminal 7-2. Terminal T 1. After calling the other party using the telephone connected to T2, when transmitting to or receiving from an external device connected to branch 19-1. The unit monitors the state of the terminal 16, and when the hook-off detection circuit 20 confirms that the handset has hooked off, the relay contact 17-
1.17-2 must be switched to the DC loop holding transformer 18 side, and transmission or reception must be performed via the DC loop holding transformer 18. Therefore, the hook-off detection circuit 20
It is necessary that the operation is performed reliably and there should be no malfunction.

However, conventional hook-off detection circuits have a problem in that malfunctions occur due to interruptions in the direct current loop of the telephone line due to dialing from the telephone set, and changes in current in the telephone line due to ringer signals (calling signals).

The problem of causing this malfunction will be explained in a little more detail. If the capacitance of the capacitor 28 that forms part of the telephone line connection section in FIG. 5 is small, the hook-off detection output is normal and does not turn off as shown in FIG. When receiving, Figure 6B
As shown in FIG. 2, the hook-off detection output turns on due to malfunction, so there is a drawback that the ringer signal cannot be detected. Next, increase the capacitance of the capacitor 28 sufficiently,
If the ringer signal prevents the hook-off detection from turning on normally (as shown in Figure 6), the hook-off detection output malfunctions and turns off when the dial pulse is sent, as shown in Figure 6C. Therefore, there was a drawback that the ringer signal detection circuit was turned on by the dial pulse, resulting in an automatic call receiving state. In this case, the reason why the hook-off detection output is turned off is that the sending of dial pulses causes the current flowing through the line to turn on and off, reducing the average current charged in the capacitor 28, and as a result, the photocoupler turns off.

Problems to be Solved by the Invention It is an object of the present invention to provide a hook-off detection circuit which solves the above-mentioned drawback, that is, the problem of malfunction caused by a ringer signal or a dial signal.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention connects the telephone to the telephone line in the initial state, disconnects the input/output device, and connects the telephone to the telephone line after detecting hook-off of the telephone. In a network control circuit that connects input/output devices and controls telephones to disconnect, there is a telephone line connection section that detects current in both the forward and reverse directions of the telephone line, and a A configuration is adopted that includes means for obtaining the peak value of detected currents in both the reverse directions, means for obtaining the exclusive OR of these detected currents in the forward and reverse directions, and an output terminal that outputs this output to the control section of the network control circuit. It is something to do.

Operation Since the present invention is configured as described above, each of the forward and reverse currents of the telephone line is detected at the telephone line connection part, and is coupled to the telephone line connection part 1, which has a time constant larger than the period of the dial signal and the ringer signal. By shaping the peak value by a peak value detection means and passing the two through a means for obtaining an exclusive OR, it is possible to prevent the hook-off circuit from malfunctioning due to the dial signal after the hook-off, or to prevent the arrival of a ringer signal from being detected when the telephone is hook-off. This eliminates the possibility of mistaken recognition.

EXAMPLES Next, examples of the present invention will be explained with reference to the drawings. Referring to FIG. 1, which shows a block diagram of an embodiment of the present invention, the footer-off detection circuit of the present invention includes a sensing current setting resistor 1, and a photocoupler 2-1 that detects the W current flowing from terminal L1 to L2. and 2-2, photocouplers 3-1 and 3-2 that detect the current flowing from terminal L2 to Ll, and resistor 4°5, 8. 9 and 13, capacitors 6, 10 and 14, and buffer circuit 7, which has hysteresis characteristics to prevent chatter from occurring due to gradual rises and falls of input signals, and exclusive OR of 11 and 15. It consists of a circuit 12 and an output terminal 16 of a hook-off detection circuit, 17-1 and 17-2.
．． 18.19-1 and 19-2゜Ll and ri,,T
l and Tt are the same as those with the same symbols in FIG.

Further, the capacitor 28 in parallel with the sensing current setting resistor l shown in FIG. 4 is omitted because its value is negligible with respect to the ringer signal and the dial signal. Furthermore, the light emitting diodes 2-1 and 3-1 on the input side of the photocoupler normally operate at a voltage of 1.0 to 1.5 V or more, and current flows and the light emitting diodes 2-1 and 3 begin to emit light.
-1 by connecting resistor l in parallel to resistor 1
The voltage drop caused by the current flowing through is 1.0 to 1.5 V.
In the following, the light emitting diodes 2-1 and 3-1 are turned off, but when the voltage drop exceeds 10 to 1.5 cm, the light emitting diode 2-1 or 3-1 is turned on. The resistor 1 is set to operate at the minimum value of the DC loop current when the telephone hooks off, thereby preventing malfunctions due to small currents below the minimum value.

Capacitor 6 is charged through resistor 5 when phototransistor 2-2 is turned on, and discharged through resistors 4 and 5 when phototransistor 2-2 is turned off. Here, the time constants of capacitor 6 and resistors 4 and 5 are set to 1 of the ringer signal.
The period is set to one period or more of one pulse of the dial pulse of the telephone, and the resistor 5 is set to one-fifth or less of the resistor 4, and the configuration of the capacitor 6 and resistors 4 and 5 operates as a peak value detection circuit. I'll do what I do. capacitor 10
The same applies to resistors 8 and 9.

Further, the capacitor 14 and the resistor 13 are provided at the output end of the exclusive OR circuit 12 to remove noise caused by a difference in timing of input signals.

Next, the operation of the hook-off detection circuit will be explained with reference to FIGS. 1 and 2. In Figure 2, the waveform a %
i corresponds to the waveform at the a% i point shown in Figure 1. L-121 is the telephone hook-on state, 22 is the telephone hook-off state, 23 is the telephone dialing state, 24 is the state waiting for a response from the other party after dialing, and 25 is the other party's response state. Indicates the connection status with,! Additionally, the 1's and 0's on the left side of the waveform indicate the fidget on and off states.

When the hook-off of the telephone causes a current exceeding the value set by the current setting resistor 1 to flow in the telephone line, the light emitting diode 2-1 or 3-1 emits light, and the phototransistor 2-2 or fC becomes 3. -2 turns on.

First, it is assumed that a voltage of positive polarity bL2 and negative polarity is applied to the telephone port #connection terminal L1. Waveforms a and b show the current waveforms flowing through the phototransistor 2-2.3-2, and waveform a corresponding to the current flowing from terminal L1 to L2 is in the 0 state when the telephone is hooked on, in the 1 state when the telephone is hooked off, and during dialing. repeats the state of 0 and l. When the other party answers and the other party forms a DC loop, the polarity of the telephone line is reversed and
The waveform a changes from the O state to the 1 state, and the waveform corresponding to the current flowing from the terminal L2 to Ll changes from the O state to the 1 state. Then, when the communication is completed and hook-on is performed, both waveforms a and b return to the O state.

The peak value of waveform a is detected by resistors 4 and 5 and capacitor 6, and waveform C is obtained. Waveform C is further waveform-shaped by buffer circuit 7 to obtain waveform e. Similarly, a waveform f is obtained from the waveform. When the exclusive OR circuit 12 performs exclusive OR of waveform e and waveform f, waveform g is obtained.

i anti-13 for waveform g. When noise is removed by the capacitor 14, a waveform is obtained. The waveform is buffer circuit 1
5, the waveform is shaped to obtain waveform i.

As a result, the waveform i corresponding to the output signal of the hook-off detection circuit remains on during sections 22 to 25 regardless of the dialing of the telephone, and the hook-off detection circuit does not cause any malfunction due to dialing of the telephone.

Next, referring to FIG. 3, the operation when receiving a ringer signal will be explained. In Fig. 3, waveforms a' to i
' corresponds to the waveform at point a-i shown in Figure 1, and 2
6 indicates a state in which a ringer signal has arrived but 7 has not, and 27 indicates a state in which a ringer signal has arrived.

When a ringer signal is applied between the telephone line connection terminals Ll and L2, the telephone connection terminals T1. A ringer signal current flows through the telephone connected to T2.

When a current exceeding the value set by the current setting resistor 1 flows through the telephone line, the light emitting diode 2-1''! or 3-1
Light is emitted, and the phototransistor 2-2 straddle 3-2 is turned on. When this current flows from terminal L1 to L2, a current flows to light emitting diode 2-1, and when it flows from terminal L2 to L1, a current flows to light emitting diode 3-1, which emits light. As a result, phototransistors 2-2 and 3 -2 current waveforms a' and b' are obtained.

Waveforms a/ and b' are converted into waveform e by a peak value detection circuit and a buffer circuit each consisting of a resistor and a capacitor.
' and f' are obtained. Waveform g' is obtained as the exclusive OR of waveform e' and waveform f'. Waveform i' is obtained by removing noise from waveform g' and further shaping the waveform. Waveform 1' shows the output signal of the hook-off detection circuit,
The hook-off detection circuit remains off regardless of the arrival of the ringer signal, and the hook-off detection circuit does not malfunction when receiving the ringer signal.

Effects of the Invention As explained above, according to the present invention, there is provided a means for detecting current flowing in a telephone line in both forward and reverse directions and obtaining a peak value;
By providing means for obtaining the exclusive OR of the respective current detection output signals, it is possible to obtain a stable and inexpensive hook-off detection circuit that is not affected by the dial of the telephone and the ringer signal coming from the telephone line. There is.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing an embodiment of the present invention, Figure 2 is a waveform diagram showing the operation of the hook-off detection circuit, and Figure 3 is a ringer diagram.
4 and 5 are respectively a connection block diagram and a hook-off detection circuit diagram of a conventional example, and FIG. 6 is a waveform diagram of FIG. 4, showing the operation when receiving a signal. 1... Resistor for setting the moving current, 2-1.3-1
...... Light emitting diode, 2-2.3-2...
...Phototransistor, 4. 5. 8. 9 and 13...Resistor, 6.10 and 14...
...Capacitor, 7, 11° and 15...
Buffer circuit with hysteresis characteristics, 12...
...Exclusive OR circuit, 16...Output signal of hook-off detection circuit, 17...Switching relay, 17
-1 and 17-2...continuous contact,
18... DC loop holding transformer, 19-1 and 19-2... Input/output terminal for connecting external equipment, 20... Hook-off detection circuit, 21...・
...Telephone hook-on state, 22...Telephone hook-off state, 23...Telephone dialing state, 24...Telephone telephone response waiting state after completion of dialing, 25...・Connecting with the other party, 26...
...Status in which no ringer signal has arrived, 27...
... Ringer signal arrival state, 28 ... Audio passing capacitor, 29 ... OR circuit, 3o ...
...Peak value holding circuit, 31...Buffer circuit, Ll and L2...Telephone line connection terminal, T
1 and T2...Telephone connection terminal, G...
...Grounding, 10V...Power supply voltage, a-i...
...Waveforms of various parts of the hook-off detection circuit at the time of telephone hook-off and telephone dialing at~i'... Waveforms of various parts of the hook-off detection circuit when receiving a ringer signal, A...
...When dialing capacitor 28 small, B...
・When receiving the ringer signal of capacitor 28 small, C...
...When dialing capacitor 28, D...When receiving ringer signal of capacitor 28, k~n...
・Waveforms of various parts of the conventional hook-off detection circuit. Agent Benchoushi Kuri 1) Yu Haru 26 27 ;z6chi''
3 te top ￥-4 pu [■ [ 茅5＠1fu

Claims (1)

[Claims] A hook-off detection circuit that connects to a telephone line and detects current in both forward and reverse directions of the telephone line to detect hook-off of the telephone; and a switching relay that switches and connects the telephone and input/output device to the telephone line. and a control unit that enables the switching relay to be switched after the hook-off detection circuit detects the hook-off; A hook-off detection circuit comprising means for obtaining an exclusive OR of the peak value outputs of these detection means.