JPH03823B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION There are various conditions for a telephone answering device to operate correctly and efficiently. The first condition must identify incoming call signals and outgoing dial pulses from the telephone to which the device is connected. This discrimination must be such that the device responds when an actual ringing signal is present, but not when an outgoing dial pulse is present.

Another condition for efficient operation of a telephone answering device is if the calling party hangs up before the end of the device's normal operating cycle, or if the called party picks up the telephone before the end of the normal operating cycle of the device. In this case, the device must immediately stop working and return to its original auto-response position.

The circuit and device of the invention provide a simple and economical means of meeting all of the above conditions. The circuit and apparatus of this invention are generally of the same type as described in US Pat. No. 4,074,081.
However, the circuit and apparatus of the present invention achieve the results achieved by this patent in a different manner and using a simpler circuit.

The circuit shown in the drawing is a series of amplifiers Z1A, Z1B,
Including Z1C and Z1D. Both of these may be housed in an LM324 type integrated circuit. Amplifier Z1A is 1
connected as an input attenuating amplifier with a gain less than . For example, the gain of amplifier Z1A is
It may be about 0.025. Amplifiers Z1B and Z1C are connected as absolute value amplifiers, and may have a gain of, for example, about 3.7. Amplifier Z1D is connected as a comparator.

A pair of resistors R, each with a value of 22 megohms
1 and R3 to connect the inverting and non-inverting input terminals of amplifier Z1A to the telephone line. These resistors provide a high impedance coupling of the telephone answering equipment to the telephone line as recognized by the Federal Communications Commission of the United States and the British Postal Service of the British Empire.

The output of amplifier Z1A is 560 kilohm resistor R2
is connected to the input via the non-inverting input terminal.
Voltage conductor V _REF through 560 kilohm resistor R4
It is connected to the. Conductor V _REF is connected to the common point of a pair of 1 kilohm resistors R14, R15 connected between the positive terminal of a 12 volt voltage source and ground. Therefore, a reference voltage of 6 volts is supplied to conductor V _REF .

Amplifier Z1A is connected as an input attenuation amplifier with a gain of 0.025, as previously described. Thus, if the telephone line voltage varies, for example between ±40 volts, amplifier Z1A will produce an output of ±1 volt. This amplifier allows telephone line voltages up to, for example, 240 volts to be measured without distortion and without damaging the equipment.

The output of amplifier Z1A is connected to the inverting input terminal of amplifier Z1B through a 10 kilohm resistor R6, and the output of amplifier Z1A is connected to the inverting input terminal of amplifier Z1B through a 10 kilohm resistor R5.
Connected to the inverting input terminal of Z1C. Amplifier Z1B,
The non-inverting input terminal of Z1C is connected to the voltage reference conductor V _REF .

The output of amplifier Z1B is a pair of diodes D1, D
Connected to 2. These diodes are connected to the inverting input terminal of amplifier Z1B along with a 10 kOhm resistor R7 and a 5.1 kOhm resistor R.
8 to the inverting input terminal of amplifier Z1C. The output of amplifier Z1C is 39 kilohm resistor R9
is connected to the non-inverting input terminal via.

Amplifier Z1B, Z1C and diodes D1, D2
constitutes a double wave rectifier circuit, for example 3.7
It acts as an absolute value amplifier with a gain of . These amplifiers are independent of the polarity of the voltage appearing on the telephone line, and therefore the ±
When there is an output of 1 volt, the amplifier circuit Z1B, Z1C
produces an output of ±3.7 volts.

The output of the attenuation amplifier Z1A is connected to the NPN transistor Q via a 0.1 microfarad capacitor C2.
It is also connected to the base of 2. The emitter of this transistor is connected to ground. The capacitor is connected to the base through a 22 kilohm resistor R15, which in turn is connected to a 10 kilohm ground resistor R14 and to a 47 kilohm ground resistor R16. Capacitor C2
The connection point of the resistor R12 is also connected to the ground diode D3.

A circuit of transistor Q2 responds to the output of amplifier Z1A to generate a ringing signal for the telephone answering device.

The output of amplifier Z1C is connected through a Zener diode _Z01 to a 4.7 kilohm ground resistor R12. The junction between the Zener diode and resistor R12 is connected to the base of a common emitter NPN transistor Q1 through a 4.7 kilohm resistor R13. Transistor Q1 is normally conductive. However, when the telephone line voltage drops below, say, 20 volts, transistor Q1 becomes non-conducting;
Its output voltage rises rapidly.

The nominal line voltage of telephone lines is typically greater than 20 volts, for example around 50 volts for most telephone equipment. Therefore, under normal conditions, transistor Q1 is conductive. When a ring signal is generated, the ring signal is detected by the circuit of transistor Q2 and the ring signal from transistor Q2 is used to activate the telephone answering device.

However, when the home telephone is off-hook, the telephone line voltage drops below 20 volts and transistor Q1 becomes non-conducting. In this condition, the signal on the telephone line may be a dialing pulse from the home telephone, and in any case, the telephone answering equipment cannot answer the telephone because the home telephone is off-hook. Must not be. Appropriate circuitry within the telephone answering device examines the output voltage from transistor Q1 immediately after the occurrence of what appears to be a line ringing signal. This circuit allows the ringing signal output from transistor Q2 to activate the telephone answering device only when the voltage output from transistor Q1 is at a low value, and when the voltage output from transistor Q1 is at a high level. For example, make sure that the telephone answering device does not respond.

Thus, the telephone answering device only responds when a true ringing signal is present and does not respond to outgoing dial pulses that occur when the local telephone is off-hook.

The output of amplifier Z1C is connected to the non-inverting input of comparator Z1D and the 6.2 kilohm resistor R10
to the inverting input terminal of the comparator. The inverting input terminal is also connected to a grounded capacitor C1 of 10 microfarads;
It is shunted by a kiloohm resistor R11. These elements form a self-biasing circuit for the comparator, with the inverting input being approximately equal to the non-inverting input.
Biased towards 94%. Therefore, the comparator responds to voltage differences on the telephone line and not to the absolute level of the voltage.

Comparator Z1D generates an output when a voltage difference that exceeds a predetermined value occurs, for example. For example, when a genuine ringing signal appears on a telephone line, a telephone answering device responds, thereby reducing the voltage on the telephone line to a level on the order of, for example, 10 volts.

If the called party then picks up the phone during the announcement time (T1) or the normal message recording time (T2), a further drop in line voltage occurs to a level on the order of 6 volts. Comparator Z1D detects the 4 volt voltage difference and generates a supervisory signal. This supervisory signal causes the device to switch between normal T1 and/or T1.
Immediately hang up without completing two cycles.

Similarly, if the calling party hangs up after the device answers, this also causes a drop in line voltage, and comparator Z1D again responds to the resulting voltage difference to generate a supervisory signal.

Therefore, this device is suitable for the announcement period and/or
or if the called party picks up the phone during the message recording time, or if the calling party hangs up during the same period, it will generate a supervisory signal and immediately disconnect the device from the phone and take appropriate measures to return to the initial state. A circuit is provided.

Accordingly, the present invention provides an improved system operative to identify ringing signals and dial pulses on a telephone line and to detect situations in which the calling party hangs up or the called party picks up the telephone. A simple circuit and device were provided.

Although specific embodiments of the apparatus of the invention have been illustrated and described, it will be understood that many modifications may be made. It is intended that the following claims encompass all such modifications.

[Brief explanation of the drawing]

The figure is a circuit diagram of a preferred embodiment of the circuit and apparatus of the present invention.

Claims (1)

Claims: 1. In a monitoring device for controlling the operation of a telephone answering device responsive to a difference in direct current voltage on a telephone line, independent of the actual direct voltage level of the telephone line,
an input circuit connected to the telephone line and including circuit means for generating an output voltage representative of the actual DC voltage level of the telephone line; a first input terminal connected to the output of the input circuit;
a second input terminal of the comparator for biasing the second input terminal to a voltage representing a predetermined percentage of the voltage applied to the first input terminal; a self-biasing circuit connected to an input terminal; the telephone answering device is adapted to generate an output signal when a difference in DC voltage generated after being energized by a ringing signal received on the telephone line exceeds a predetermined minimum value. Monitoring equipment for telephone answering equipment. 2 In the device described in claim 1,
The input circuit includes an input attenuating amplifier circuit with a gain less than unity that produces an output voltage that is a fraction of the telephone line voltage; and an absolute value amplifier circuit with a gain greater than unity, which produces a single polarity output in response to polarity outputs. 3 In the device described in claim 2,
A monitoring device for a telephone answering device, wherein the input attenuating amplifier circuit includes a high impedance element that couples the device directly to a telephone line. 4 In the device described in claim 1,
A telephone answering equipment monitoring device, wherein said output circuit includes time delay means for causing said output circuit to generate an output signal only when the voltage difference exceeds a predetermined minimum time interval.