JPH08321887A - Interphone system - Google Patents

Abstract

PURPOSE: To transmit and receive various kinds of signals through a pair of transmission lines by allowing a slave device to detect a pretone call signal from a master device, to detect line voltage, to output its output by means of a timing circuit and to send a ring-back tone by an AND logic on conditions of its output and a hook-on output of the hand set. CONSTITUTION: The master device MQ1 is connected to plural slave devices SQ1 , etc., through a monitor camera unit KQ1 connected to a line L1 , etc., and is provided with a station selection switch 7a selecting a slave device, a power supply circuit 4b, a pretone oscillation circuit 1 and handset means 2 and 3. Each slave device is provided with a handset 34, a pretone detection circuit 23, a line voltage detection circuit 24, the timing circuit 26, and an AND logical means 27 inputting the output of the pretone detection circuit, that of the timing circuit and the hook-on output of a hook switch 29 linked with the hook-on/off of the handset. Then, a consecutive calling sound is rung by means of this means 27.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intercom system, and more particularly, to an intercom system capable of selecting a slave unit connected to a plurality of surveillance camera units star-connected via a line.

[0002]

2. Description of the Related Art Conventionally, an intercom device shown in FIG. 3 has been proposed. The intercom apparatus shown in FIG. 3 is composed of a master unit MQ ₁₁ , a plurality of surveillance camera units KA _{11 to} KA ₁₈ and slave units SQ _{11 to} SQ ₁₈ (the number of surveillance camera units and slave units is 8 for explanation). The transmission line terminals T _{51 to} T _{58 of} the master device MQ ₁₁ and the transmission line terminals T _{61 to} T ₆₈ of the surveillance camera units KA _{11 to} KA ₁₈ are connected to each other via lines L _{51 to} L ₅₈ .

The main unit MQ ₁₁ has a pretone oscillator 51, a handset 52, a communication circuit 53, a power supply circuit 54a for supplying power + V _CC to each circuit, a power supply circuit 54b for a slave unit for supplying power to the slave unit, and a dedicated monitor. The video circuit 55, the channel selection circuit 56, the channel selection switch 57a, the incoming LED 57b, and the additional monitor image demodulation circuit 58 are connected. The output side of the pretone oscillator 51 is connected to the pretone pin P ₄₁ of the channel selection circuit 56.

A call circuit 53 to which the handset 52 is connected
Is connected to the call pin P ₄₂ , the output side of the slave unit power supply circuit 54b is connected to the power supply pin P ₄₃ , the input side of the dedicated monitor video circuit 55 is connected to the video pin P _44, and is used for the dedicated monitor. The video output side of the video circuit 55 is a dedicated monitor pin P _46.
It is connected to the dedicated monitor 59 via.

The output side of the additional monitor video demodulation circuit 58 connected to the image pin P ₄₄ is connected to the additional monitor pin P ₄₇ . Output side of tuning switch 57a and incoming L
The input side of the ED 57b is connected to the control pin P ₄₅ , respectively. The surveillance camera units KA _{11 to} KA ₁₈ are provided with a parent machine line interface 61 and a child machine interface 6.
2, surveillance camera 63, receiver amplifier 64, transmitter amplifier 65
And the transmission line terminals T _{61 to} T ₆₈ connected to the lines L _{51 to} L ₅₈ , respectively, are connected to the master line interface 6
It is connected to 1.

The output side of the surveillance camera 63 has a transmission line terminal T _61.
.. to T _68, and the reception amplifier side of the parent device line interface 61 is connected to the child device interface 62 via the reception amplifier 64. The transmitter amplifier side of the slave unit interface 62 is connected to the master unit line interface 61 via the transmitter amplifier 65, and the power supply side of the master unit line interface 61 is connected to the power receiver side of the slave unit interface 62. There is.

A terminal 62a of the slave unit interface 62
It is connected to the terminal 71a of the hybrid transformer 71 provided in the slave unit SQ ₁₁ ~SQ _18. The handset SQ ₁₁ ~
The SQ ₁₈ is a hybrid transformer 71, a diode bridge 72 for non-polarity, a transmitting circuit 73, a microphone 74, a receiving circuit 75, a speaker 76, a calling circuit 77, and a calling switch 7.
8, the voice side of the hybrid transformer 71 is connected to the input side of the receiving circuit 75 via the non-polarity diode bridge 72.

The output side of the reception circuit 75 is connected to the speaker 76, and the transmission side of the non-polarity diode bridge 72 is connected to the output side of the transmission circuit 73 to which the output side of the microphone 74 is connected. The calling side of the hybrid transformer 71 is connected to the output side of a calling circuit 77 to which a calling switch 78 is connected.

With such an intercom device, when the tuning switch 57a of the master device MQ ₁₁ shown in FIG. 3 is pressed to select the surveillance camera unit KA ₁₁ , for example, the pretone pin P
₄₁ , the call pin P ₄₂ , the power supply pin P _43, and the video pin P ₄₄ are connected to the channel selection pin P ₅₁ . The power supply pin P ₄₃ of the parent device MQ ₁₁ is connected to the transmission line terminal T ₆₁ of the surveillance camera unit KA ₁₁ through the channel selection pin P ₅₁ , the transmission line terminal T _51, and the line L _51, and the power supply circuit 54b for the child device is connected. Power is supplied to the surveillance camera unit KA ₁₁ via the power supply pin P ₄₃ .

Due to this power supply, the surveillance camera 63 connected to the transmission line terminal T ₆₁ becomes active, and the video pin P via the channel selection pin P ₅₁ of the channel selection circuit 56 provided in the master device MQ _11.
The video signal is sent to ₄₄ . Further, the reception circuit 75 provided in the slave unit SQ ₁₁ supplies power via the master-machine line interface 61, the slave-unit interface 62, the hybrid transformer 71, and the non-polarity diode bridge 72 of the surveillance camera unit KA ₁₁ . And become active.

At the same time, when the pretone pin P ₄₁ is connected to the channel selection pin P ₅₁ , the single ringing tone generated by the pretone oscillator 51, for example, "Pong", is sent to the surveillance camera unit K.
Vs. master unit line interface 61 of the A _11, the reception amplifier 6
4. The data is sent to the child device SQ ₁₁ via the child device interface 62, and the speaker 76 is sounded via the hybrid transformer 71 of the child device SQ ₁₁ and the receiving circuit 75.

Here, the slave unit SQ ₁₁ side is a voice call using the speaker 76 and the microphone 74. As a usage example, for example, the slave unit SQ ₁₁ side is a karaoke box and the master unit MQ ₁₁ side is a karaoke box management side. There is. In this state, the handset 52 can talk with the handset SQ ₁₁ while watching the dedicated monitor 59 on the handset MQ ₁₁ .

[0013] If you call the parent machine MQ ₁₁ from the slave unit SQ ₁₁ presses the call switch 78. Pressing the call switch 78, the control call signal and tuning pins P ₅₁ of the channel selection circuit 56 provided in the base unit MQ ₁₁ are sent to the base unit MQ ₁₁ pins P ₄₅
The incoming call LED 57b lights up via. When the tuning switch 57a corresponding to the illuminated incoming LED 57b is pressed, the handset 52 can talk with the handset SQ ₁₁ while watching the dedicated monitor 59 on the base device MQ ₁₁ .

[0014]

Since the conventional intercom system is constructed as described above, the slave unit SQ ₁₁ has the master unit M.
A single ring tone generated by the pre-tone oscillator 51 of Q ₁₁ ,
For example, there is a difficulty in missing the call because it is only listening to "pon". Further, if a conventional intercom device is used to output a continuous ringing tone, a complicated circuit for superimposing or multiplexing the continuous ringing tone on a voice signal, a video signal or a ringing signal is required. However, there is a problem in that it is necessary to provide a large number of transmission lines for transmitting respective signals to the master device MQ ₁₁ and the slave device SQ ₁₁ when sending out.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem and does not provide a complicated circuit for superposing or multiplexing a voice signal, a video signal and a calling signal on a master unit and a slave unit. Another object of the present invention is to provide an intercom device capable of transmitting and receiving a continuous ringing tone and various signals through a pair of transmission paths.

[0016]

In order to achieve such an object, in an intercom apparatus according to the present invention, a master unit is connected to a plurality of slave units via a surveillance camera unit connected to each line of a plurality of slave units. However, the master unit has a tuning switch that selects each slave unit, a power supply circuit that supplies power to the corresponding line when the tuning switch is closed, and a pretone oscillation circuit that generates a pretone ringing signal to the slave unit. , A handset for communicating with the handset, a handset for communicating with the handset's handset, a pretone detection circuit for detecting a pretone ringing signal, a line voltage for detecting the line voltage supplied to the line A detection circuit, a time circuit which outputs the line voltage detected by the line voltage detection circuit for a predetermined time,
AND logic means to which the output of the pretone detection circuit, the output of the time limit circuit, and the hook-on output of the hook switch interlocking with hook-on / off of the handset are input, and a continuous ringing tone oscillating means for oscillating a continuous ringing tone by the output of the AND logic , Has a ringing means for ringing a continuous ringing tone.

[0017]

When the tuning switch provided on the master unit is pressed, the selected slave unit is supplied with power from the power supply circuit via the respective lines. At the same time, the pretone calling signal oscillated by the pretone oscillation circuit is sent to the slave unit.

The selected slave unit detects the pretone call signal transmitted from the master unit by the pretone detection circuit, and
The line voltage supplied to the line is detected by the line voltage detection circuit. The output of the line voltage detection circuit is output by the time circuit for a predetermined time. The AND logic operates based on the output of the pretone detection circuit, the output of the time limit circuit, and the hook-on output of the hook switch that is linked to the hook-on / off of the handset, and the continuous ringing tone oscillates the continuous ringing tone according to the AND logic. To do.

The continuous ringing tone generated by the continuous ringing tone oscillating means sounds the ringing means.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the intercom system of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, the intercom apparatus according to the present invention is a surveillance camera unit K in which a base unit MQ ₁ is connected to respective lines L ₁ , L ₂ ...
Q _1, KQ ₂ ... connected to a plurality of slave unit SQ _1, SQ ₂ ... via the master unit is tuning switch 7 to the station each election the handset
a, a power supply circuit 4b that supplies power to the corresponding line when the tuning switch is closed, a pretone oscillation circuit 1 that generates a pretone ringing signal to the slave unit, and transmission / reception circuits 2 and 3 that communicate with the slave unit. The slave unit has a handset 34 for communicating with the transmitter / receiver circuit of the master unit, a pretone detection circuit 23 for detecting a pretone ringing signal, a line voltage detection circuit 24 for detecting the line voltage supplied to the line, and a line voltage detection circuit. A time limit circuit 26 for outputting the line voltage detected by the output for a predetermined time, an AND logic circuit 27 to which the output of the pre-tone detection circuit and the output of the time limit circuit and the hook-on output of the hook switch 29 interlocking with hook-on / off of the handset are input, A continuous ringing tone oscillation circuit 31 that oscillates a continuous ringing tone by the output of the AND logic circuit 27, and a ringing circuit 32 that rings a continuous ringing tone. It is equipped with a 33.

As shown in FIG. 1, the intercom apparatus according to the present invention includes a base unit MQ ₁ and a plurality of surveillance camera units KQ _1.
To KQ ₈ and slaves SQ _{1 to} SQ ₈ (for the sake of explanation, the number of surveillance camera units and slaves is ₈ ), the master MQ
₁ transmission line terminals T _{1 to} T ₈ and surveillance camera units KQ _{1 to} K
The transmission line terminals T _{11 to} T ₁₈ of Q ₈ are connected to each other via lines L _{1 to} L ₈ .

The main unit MQ ₁ is a pretone oscillator 1, a handset 2, a communication circuit 3, a power supply circuit 4a for supplying a power supply V _CC to each circuit, a power supply circuit 4b for a slave unit for supplying power to a slave unit, and a dedicated monitor. Video circuit 5, tuning circuit 6, tuning switch 7a,
It is composed of an incoming call LED 7b and an additional monitor video demodulation circuit 8, and the output side of the pretone oscillator 1 is connected to the pretone pin P ₂₁ of the channel selection circuit 6.

The call circuit 3 to which the handset 2 is connected is connected to the call pin P _22, and the output side of the slave unit power supply circuit 4b is connected to the power supply pin P ₂₃ . The input side is connected to the video pin P _24, and the video output side of the dedicated monitor video circuit 5 is connected to the dedicated monitor 9 via the dedicated monitor pin P ₂₆ .

The output side of the additional monitor video demodulation circuit 8 connected to the image pin P ₂₄ is connected to the additional monitor pin P ₂₇ . Output side of tuning switch 7a and LED for incoming call
Input side of 7b is connected to the respective control pins P _25. The surveillance camera units KQ _{1 to} KQ ₈ are composed of a parent device line interface 11, a child device interface 12, a surveillance camera 13, a reception amplifier 14, and a transmission amplifier 15, and the lines L _{1 to} L ₈ are connected to each other. The transmission line terminals T _{11 to} T ₁₈ are connected to the master-machine line interface 11.

The output side of the surveillance camera 13 has a transmission line terminal T ₁₁
To T ₁₈ , respectively, and the receiver amplifier side of the master-machine line interface 11 is connected to the slave unit interface 12 via the receiver amplifier 14. The transmitter amplifier side of the slave unit interface 12 is connected to the master unit line interface 11 via the transmitter amplifier 15, and the power supply side of the master unit line interface 11 is connected to the power receiver side of the slave unit interface 12. There is.

The terminal 12a of the slave unit interface 12
It is connected to the monitoring camera unit side of the hybrid transformer 21 through a line L ₁₁ ~L ₁₈ connected to the terminal 21a of the handset SQ ₁ ~SQ _8. Handset SQ _1- SQ
Reference numeral ₈ designates a hybrid transformer 21, a non-polarity diode bridge 22, a pretone detection circuit 23, a line voltage detection circuit 24, a time circuit 26, a logic circuit 27, a transmission mute circuit 28, a hook switch 29, a power source on / off circuit 30, Continuous ringing tone oscillator 31, amplifier 32, speaker 3
3, handset 34, transmitter circuit 35a, receiver circuit 35
b, the calling circuit 37, and a power supply circuit 38 for supplying power supply + V _CC to each circuit, the hybrid transformer 21 to which the terminal 21a is connected is connected to the non-polarity diode bridge 22, and the non-polarity diode bridge 22 is a logic. Circuit 2
7 are connected to the line voltage pin P ₃₁ , the pretone detection circuit 23, and the line voltage detection circuit 24, respectively.

The output side of the pretone detection circuit 23 is connected to the pretone pin P _32, and the output side of the line voltage detection circuit 24 is connected to the timed line voltage pin P _{33 of} the logic circuit 27 via the timed circuit 26. Hook switch 29
The output side of is connected to the pretone stop pin P ₃₆ of the pretone detection circuit 23, the transmission mute release pin P _{35 of the} transmission mute circuit 28, and the logic circuit 27.

The hook switch pin P ₃₄ of the logic circuit 27 is connected to the calling circuit side of the hybrid transformer 21 via the calling circuit 37. The receiver side of the hybrid transformer 21 is connected to the receiver of the handset 34 through the receiver circuit 35b, and the transmitter of the handset 34 passes through the transmitter mute circuit 28 and the transmitter circuit 35a and is connected to the diode bridge 22 for non-polarity. It is connected to the sender.

The power supply side of the power supply circuit 38 for supplying power to each circuit is connected to the power supply on / off circuit 30 to which the logic output side of the logic circuit 27 is connected. The output side of the power on / off circuit 30 is connected via a continuous ringing oscillator 31
It is connected to the amplifier 32, and the output side of the amplifier 32 is connected to the speaker 33. As shown in FIG. 2, the logic circuit 27 includes NAND circuits Q ₁ , Q ₂ , Q ₃ , Q ₄ , resistors R _{31 ,} R ₃₂ ,
And a noise prevention capacitor C ₃₁ and a NAND circuit Q
_The line voltage pin P ₃₁ is connected to _one input side of ₁ , and the output side of the NAND circuit Q ₁ is connected to the input side of the power supply ON / OFF circuit 30.

The pretone pin P ₃₂ is provided on one input side of the NAND circuit Q ₄ , and the timed line voltage pin P is provided on the other input side.
₃₃ are connected to each other, and a reference potential point is connected to one input side of the NAND circuit Q ₄ via a resistor R ₃₁ . The output side of the NAND circuit Q ₄ are, is connected to one input of the NAND circuit Q _2, the output side of the NAND circuit Q ₃ is connected to the other input side.

The other end of the hook switch pin P ₃₄ of the NAND circuit Q while the input side of the noise preventing capacitor C ₃₁ having one end connected to a reference potential point of ₃ is connected, the hook switch pin P ₃₄ has one end Is connected to the other end of a resistor R ₃₂ connected to the power source + V _CC . The hook switch pin P ₃₄ of the logic circuit 27 is connected to the calling circuit 37.

When the channel selection switch 7a of the base unit MQ ₁ shown in FIG. 1 is pressed with such an intercom device and the surveillance camera unit KQ ₁ , for example, is tuned in, the pretone pin P ₂₁ , the communication pin P ₂₂ , The power supply pin P ₂₃ and the video pin P ₂₄ are connected to the tuning pin P ₁ . When feeding pin P ₂₃ of the main unit MQ ₁ is connected to the transmission line terminal T ₁₁ of the monitoring camera unit KQ ₁ via the channel selection pin P _1, transmission line terminals T ₁ and line L _1, handset power circuit Power is supplied from 4b to the surveillance camera 13 of the surveillance camera unit KQ ₁ via the power feeding pin P ₂₃ .

By this power supply, the surveillance camera 13 becomes active, and a video signal is sent to the video pin P ₂₄ through the tuning pin P ₁ of the tuning circuit 6 provided in the master device MQ ₁ . Also, the terminal 21a of the slave unit SQ _1, is powered via the terminal 12a of the monitoring camera unit KQ ₁ pair base unit line interface 11 and-child machine interface 12.

At the same time, when the pretone pin P ₂₁ is connected to the channel selection pin P ₁ , the pretone of the single ringing tone generated by the pretone oscillator 1 is sent to the handset SQ ₁ , and the hybrid transformer 21 and the diode bridge 22 for non-polarity are used.
To the pre-tone detection circuit 23 via. The pretone detection circuit 23 sets the line voltage pin P ₃₂ of the logic circuit 27 to the H level while detecting the pretone.

The non-polarizing diode bridge 22 to which the pretone is input sets the pretone pin P ₃₁ to the H level. The line voltage detection circuit 24 detects the line voltage,
A predetermined time in the timing circuit 26, a timed line voltage pin P ₃₃ to H level. In this state, the hook switch 29 brings the hook switch pin P ₃₄ of the logic circuit 27 to the H level. Therefore, as shown in FIG. 2, one input side and the other input side of the NAND circuit Q ₄ provided in the logic circuit 27 are both at H level for a predetermined time, and the output side of the NAND circuit Q ₄ is at L level. It is at a level.

Since one input side of the NAND circuit Q ₂ to which the output side of the NAND circuit Q ₄ is connected is at L level, the output side of the NAND circuit Q ₂ becomes at H level. When the output side of the NAND circuit Q ₂ becomes H level, _{one and} the other input sides of the NAND circuit Q ₁ both become H level. When _{one and} the other input sides of the NAND circuit Q ₁ both become H level, the output side of the NAND circuit Q ₁ becomes L level.

When the output side of the NAND circuit Q ₁ becomes L level, the power-on / off circuit 30 is turned on and the continuous ringing tone oscillator 31 starts oscillating. When the continuous ringing tone oscillator 31 starts oscillating, a continuous ringing tone is sent to the speaker 33 via the amplifier 32. At the time when the continuous ringing tone is sent from the speaker 33, a fixed time has elapsed, the outputs of the pretone detection circuit 23 and the time limit circuit 26 are at L level, and the output of the NAND circuit Q ₄ is at H level.

When the handset 34 is off-hooked, the hook switch 29 operates to set the hook switch pin P ₃₄ of the logic circuit 27 to the L level. Hook switch pin P
When ₃₄ becomes L level, the output side is at the H level of the NAND circuit Q _3, the other input side is the H level of the NAND circuit Q _2, the output side of the NAND circuit Q ₄ are from the L level H level, the NAND circuit Q ₂ The output side changes from H level to L level.

Therefore, one input side of the NAND circuit Q ₁ changes to H level and the other input side changes from H level to L level. When other input of the NAND circuit Q ₁ is at the L level output of the NAND circuit Q ₁ is at the H level. When the output side of the NAND circuit Q ₁ goes high, the power is turned on.
The off circuit 30 is turned off, and the continuous ringing oscillator 31 stops oscillating.

[0040] When calling the base unit MQ ₁ from the slave unit SQ _1, calling circuit 37 operates when the handset 34 is off-hook, the master unit M as if conventional call switch is pressed
Call for LED7b is lit, which is provided in Q _1.

[0041]

As is apparent from the above description, according to the intercom apparatus of the present invention, a plurality of slave units are connected via the surveillance camera unit connected to each line, and the master unit is , A tuning switch that selects each slave unit, a power supply circuit that supplies power to the corresponding line when the tuning switch is closed, a pretone oscillation circuit that generates a pretone ringing signal to the slave unit, and a call with the slave unit The handset has a handset that communicates with the handset transmitter / receiver circuit, a pretone detection circuit that detects a pretone ringing signal, a line voltage detection circuit that detects the line voltage supplied to the line, and a line voltage. A timed circuit that outputs the line voltage detected by the detection circuit for a predetermined time, the output of the pretone detection circuit and the output of the timed circuit, and the hook-on of the handset.
Since the AND logic circuit to which the hook-on output of the hook switch linked with OFF is input, the continuous ringing tone oscillation circuit that oscillates the continuous ringing tone by the output of the AND logic circuit, and the ringing circuit that rings the continuous ringing tone, It is possible to send and receive a continuous ringing tone and various signals through a pair of transmission lines without providing a complicated circuit such as superimposing or multiplexing voice signals, video signals and ringing signals on the master unit and the slave unit.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an intercom apparatus according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a logic circuit used in the intercom apparatus according to the present invention.

FIG. 3 is a block diagram of a conventional intercom device.

[Explanation of symbols]

1 ・ ・ Pre-tone oscillator circuit 2 ・ ・ Handset (transmission / reception means) 3 ・ ・ ・ ・ Talking circuit (transmission / reception means) 4b ・ ・ ・ ・ ・ ・ Power supply circuit for handset (Power supply circuit) 23 .... Pretone detection circuit 24..Line voltage detection circuit 26..Timer circuit 27..AND logic circuit (means) 29 ..・ ・ ・ ・ Hook switch 31 ・ ・ ・ ・ ・ ・ Continuous ringing circuit (means) 32 ・ ・ Amplifier (ring means) 33 ・ ・ Speaker (ring means) 34 ・ ・ ・ ・・ ・ Handset MQ ₁・ ・ ・ ・ ・ ・ Main unit SQ ₁ , SQ ₂・ ・ ・ ・ ・ ・ Slave unit L ₁ , L ₂・ ・ ・ ・ ・ Line 7a ・ ・ ・ ・ ・ Channel selection switch KQ ₁ , KQ ₂ ... Surveillance camera unit

Claims (1)

[Claims] 1. A master unit (MQ ₁ ) is connected to each line (L ₁ ,
Monitoring camera unit connected to _{L 2 ...) (KQ 1,} KQ
₂ ...) to a plurality of slave units (SQ ₁ , SQ ₂ ...) and the master unit selects a tuning switch (7a) for selecting each of the slave units, and the tuning switch is closed. A power supply circuit (4b) for supplying power to the corresponding line, a pretone oscillation circuit (1) for generating a pretone calling signal to the slave unit, and a transmitting / receiving means (2, 3) for talking with the slave unit. Then, the slave unit has a handset (34) for communicating with the transmitter / receiver of the master unit, a pretone detection circuit (23) for detecting the pretone call signal, and a line voltage detection for detecting the line voltage supplied to the line. Circuit (24),
A time limit circuit (26) that outputs the line voltage detected by the line voltage detection circuit for a predetermined time, and a hook switch (29) that interlocks with the output of the pretone detection circuit, the output of the time limit circuit, and the hook on / off of the handset. AND logic means (27) to which the hook-on output is inputted,
An intercom device comprising: a continuous ringing tone oscillating unit (31) for oscillating a continuous ringing tone and a ringing unit (32, 33) for ringing the continuous ringing tone according to the output of the AND logic unit.