FR2471704A1 - Pushbutton keyboard and associated printed circuit - has diode bridge connected to telephone wires providing supply to circuit having keyboard controlled variable frequency generator - Google Patents

Abstract

The signal transmission device comprises a printed circuit which is connectable to the telephone line through four terminals in an identical manner to the dial plate and mounts a diode bridge connected to the terminals to provide a rectified supply to the circuit components. The latter comprise a voltage regulator for the supply, a multifrequency generator controlled by a pushbutton keyboard and a current generator, controlled by the multifrequency generator. The current generator is connected to a terminal resistance, setting the telephone line impedance through which signals are transmitted to the line. A transistor is controlled by the multifrequency generator to short circuit the terminal resistance in the absence of any transmitted signals.

Description

The present invention relates to signaling sending devices which are intended to equip telephone sets and terminals and more particularly those which must allow the sending of frequency modulated signals.

 Indeed, this type of signaling allows data transmission and in particular numbering data in a much faster way than signaling by opening a line loop under the action of a dial which is still widely used.

 Conventionally, each station or telephone terminal has different internal or external organs which perform the functions of sending signaling with the telephone line connecting the station or terminal for receiving signaling on the line and for reciprocal conversion of the signals received from the line in sounds or information for which this station or terminal is designed and these sounds or information in signals transmissible on the line.

 Of course the use of existing telephone networks implies the use of compatible equipment and in particular of devices capable of adapting to existing equipment while being applicable to new equipment.

The present invention therefore relates to a signaling sending device adaptable on the one hand to conventional telephone sets to replace the dialing dial for these stations and on the other hand to stations and terminals intended to be connected to a telephone line.

 As stated above, this signaling sending device is intended to be associated with at least one key keyboard, associated with a multifrequency signal generator, and at least one service button generally dissociated from the keyboard, in order to allow the sending of signaling to the central office of attachment of the station or terminal via a telephone line connected to the station or terminal which comprises it.

 The device according to the invention comprises a single printed circuit, connected to the telephone line wires via four terminals in a manner identical to the telephone dial which the signaling sending device replaces, connected to the keypad via a connector so to form with this keyboard a physical unit capable of being interchanged with a possible dialing dial for a station or terminal.

According to a characteristic of the invention, the single circuit combines on the same support - a diode supply bridge connected to the line wires for
ensure the polarized supply of the rest of the circuit - a voltage regulator arrangement for the elements of the
circuit, connected at the output of the diode bridge, - a multi-frequency signal generator powered by the bridge
with diodes and controlled by the keyboard, - a current generator arrangement connected to the output of the generator
multifrequency signal generator which controls and across
of the post resistance which determines the impedance of this post
view of the line and which transmits these multifrequency signals
at the line, - an arrangement of short-circuit of the resistance of this station,
controlled by the multi-frequency signal generator.

According to another characteristic of the invention, the single circuit also combines on the same support a monostable generation of loop opening pulses, controlled by the service button of the post or terminal and connected to the line wires via a switch-off arrangement. voltage, as well as a current supply arrangement of the monostable, connected to the diode supply bridge of the circuit and to the current limitation arrangement.

The objects and characteristics of the present invention will appear more clearly on reading the following description of exemplary embodiments, said description being made in relation to the attached drawings in which
Figure I shows a diagram of a conventional telephone set
Figure 2 shows a diagram of the signaling sending device according to the invention.

FIG. I presents the diagram of a conventional telephone set, intended to be connected to the two wires Li and L2 of a telephone line responsible for supplying it and ensuring its connection with a telephone exchange of a network, both not shown.

 The line supplies the station via a set of resistors referenced here rl, r2, r3, which can be put into or out of service by straps in order to obtain the supply current necessary for the station regardless of the length of the line within a specified range. A capacitor ca3, in parallel on the aforementioned resistors, makes it possible to limit the attenuation which they introduce. A ringtone S inserted between the line wires downstream from the resistors rl, r2, r3, constitutes the call signaling reception device, it is activated by an alternating current applied to the line by the station's home office. sound system S is connected on the one hand to the output of the resistor rl by a resistor r4 and a capacitor ca2 which constitute an anti-surge device during the emission of dial pulses, and on the other hand to the wire L2.

 Two switch hook contacts CRI and CR2 or equivalent device respectively ensure the connection of the rest of the station with the wire L2 on the one hand, and the point common to the resistors rl and r4 on the other hand, when the station is used, it that is to say conventionally when the handset is lifted.

 The CRI contact is connected to a first supply terminal of a duplexer T via the idle contact for dialing the dial C when this contact is actually at rest, that is to say outside the line opening phases for creation of numbering pulses.

 The contact CR2 is connected to the other supply terminal of the duplexer T, via a resistor r5 and a balancing capacitor cal in parallel.

A microphone M is inserted between on the one hand the common point at the contact CR2, at the resistor r5 and at the capacitor cal and, on the other hand, the common point at the middle point of the primary of the differential transformer which constitutes the duplexer T.

 At least one receiving capsule R is connected to the ends of the two series receiving windings of the duplexer T.

The dial CA also includes two other contacts, the blades of which can come into contact with the blade connected to the first supply terminal of the duplexer T in order to ensure the short-circuiting of the buzzer S during the opening phases of the line by the dialing contact on the dial CA, as well as that of the induction coil T to avoid hearing the pulses via the receiving capsule R or the buzzer S.

 Conventionally, the dial CA is removable and its contacts connect respectively to four connection terminals I, II, III, IV; terminal I allows the connection between the dialing contact of the dial CA and the contact CR1, terminal II allows the connection with the first supply terminal of the duplexer T, terminal III is connected to the common point of the buzzer S and the capacitor ca2 and terminal IV is connected to the common point on contact CR2 and to the resistor r5-capacitor cal assembly.

 In the example presented in FIG. 1, the signaling sending device is essentially constituted by the dial CA and its contacts, this device is often supplemented by a service button which makes it possible for example to trigger a particular signaling. According to a conventional variant, this service button makes it possible to temporarily open the line in a manner which is not considered to be a hang up by the signaling receiver which has the charge of the line in the home telephone exchange.

 Such a service button is conventionally independent of the keyboard and appears schematically as a rest contact when the signaling is carried out by opening a line loop.

 FIG. 2 presents a signaling sending device intended to replace a telephone dial, to allow the use of a signaling keyboard in multifrequency code and the use of a service button independent of the keyboard which acts by line opening. This sending device is for example constituted by a printed circuit, referenced in FIG. 2, which is capable of connecting to the terminals I, II, III, IV, defined in relation to FIG. 1, in the same way as the would make a dial in a conventional post or telephone terminal.

For this purpose the printed circuit 1 is provided for mounting in place of a dial and for supporting a keyboard CL connected to it by a connector of the conventional type. In a variant of the invention, corresponding to a telephone set, the keyboard CL is a conventional keyboard with 12 keys comprising ten dialing keys and two additional keys. This keyboard CL is for example a magnetic recall keyboard, it is arranged in a matrix form with three columns and four lines and it therefore comprises at least one contact by line and column intersection, that is to say by key.

 In the example chosen, this keyboard CL also includes a contact element symbolized by the contact CL1 and this contact element is of the work and first actuated-last released type, consequently this contact element is activated by pressing a key on the keyboard prior to any other touch of the key and it remains activated a little longer.

The keyboard is connected by its line and column wires to a conventional multifrequency signal generator W capable of transmitting signals based on a particular combination of two frequencies when a line and a column of the keyboard CL are linked. by pressing a key.

For this purpose, the generator W is connected to a quartz oscillator Q tuned by a capacitor C in order to provide a signal at a stable base frequency. This signal at the base frequency is conventionally used by the generator to produce the different frequencies required and consequently the signals corresponding to the desired combinations.

The generator W is connected to the terminals I and II which supply it via on the one hand the diode D3 of the diode bridge D3, D4, D5, D6, D7 which serves to supply the circuit with positive potential and on the other hand the zero potential wire via transistors T8 and T5 and diode D5.

The purpose of the diode bridge D3, D4, D5, D6 is to provide a polarized supply to the electronic components of the circuit, it also comprises a double Zener diode D7 in its diagonal supplied in order to protect the electronic components supplied from overvoltages. This diode bridge is connected by its positive terminal to a voltage regulator arrangement composed of the diode
Zener D2, resistors R12 and RO and transistor T7.

 The role of the transistor T7 is to regulate the voltage applied by the bridge to the electronic components; this transistor T7 therefore has its emitter connected to the zero potential wire and its collector connected to the positive potential wire. The Zener diode D2 is a precision diode enabling the multi-frequency signal generator W to be supplied at its minimum voltage in order to comply with the conditions of insertion of the device on the line.

 The voltage regulator arrangement composed of the diode D2 and the transistor T7 provides a constant supply voltage to the multifrequency signal generator W in order to obtain a constancy of the output level of this generator.

 The output of generator W is connected to a second order filter consisting of resistors R8, R9, R10, R11 and capacitors C3, C4 in order to cut the frequencies emitted by generator W outside the frequency band accepted by the lines telephone and eliminate the parasitic harmonics produced by this generator W. The output of this filter, here constituted by the point common to the resistor R10 and to the capacitor C3, is connected to a current generator arrangement constituted essentially by the transistor T6, resistors R7, R17 and capacitor C5. The output signals from the multifrequency signal generator W are applied to the base of transistor T6, via the filter, and are applied to the terminals of a resistor R14, called line impedance, which has an alternating current impedance equal to that which the station must present on the line during the keyboard operating phases.

Resistor R14 is then connected on the one hand by one of its terminals to terminal I via diode D3, the positive potential wire of the circuit, transistor T7 and a separation diode D10 and on the other hand by its other terminal to terminal II via a transistor
T5 and diode D5.

 The generator W comprises a field effect transistor (not shown here), which is inserted between its terminals 11 and 16, these are themselves connected one to the base of a control transistor T4, the another to the positive potential wire of the circuit, so as to block T4, when the generator W transmits.

The transistor T4 is itself connected by its collector to the base of a short-circuit transistor T8 responsible for short-circuiting the resistor R14 outside of the signaling periods.

 Pressing a keyboard key firstly switches off the communication devices such as microphone and receiving capsule by closing the common contact element which connects the terminals II and IV which supply them.

A resistance R13 of low value is then inserted between II and IV to eliminate any parasitic microphonic currents and to let circulate a weak signaling return current towards the receiving capsule when sending signaling to inform the sender. Similarly, a set of Zener diodes D8, D9 mounted head to tail between terminals III and IV makes it possible to short-circuit the ringtone S during signaling - by the button BP. Pressing a keyboard key then produces the connection of a column wire and a keyboard line wire, this connection is detected by the multifrequency signal generator W. Terminals 16 and 11 of this generator are connected by an internal transistor not shown here, this blocks the transistor T4, the base of which is connected to the terminal 16 of the generator W, as well as the short-circuit transistor T8 of the resistor R14, the latter is therefore presented on the line.

 The multi-frequency signal generator W supplies a line modulation current via the transistor T6 and a dual-frequency signal applied to the terminals of the resistor R14 and consequently to the wires of the telephone line concerned.

At the end of transmission of dual-frequency signals, the release of the last key causes the communication devices to be switched on again when the contact element CL1 is opened and the station resistance R14 is short-circuited by the transistor T8 itself controlled by the generator W via the transistor T4.

 From the moment when a multifrequency signaling is used and when it is desired to use in addition a service button during communication it is possible to group on the same signaling sending circuit all the necessary components.

 According to the invention, the station is provided with a BP signaling button comprising a rest type contact connected on the one hand to the positive potential wire of the circuit and on the other to the point common to the diodes D4 and D5, via a resistor R1 . The standby contact of the BP button activates an arrangement composed of a current generator and a monostable R2C1 which produces a current pulse on the line.

For this purpose the current generator has a mounting
Darlington of two transistors T2, T3 connected on the one hand to the positive potential wire of the circuit and on the other hand to the base of a line supply voltage switch transistor T5 connected by its collector to the point common to the resistor R14 and to the transistor T8 and by its emitter at the point common to the diodes D4, D5.

The current generator also includes a transistor T1 for regulating the current of the Darlington circuit by reducing the base current of the transistors T2, T3 as a function of the voltage across the terminals of the resistor R4. A blocking diode D1 is inserted between the collector of transistor T1 and the base of transistor T2 which is itself connected to the negative terminal of the polarized capacitor Ci and to a first terminal of the resistor R2 of the monostable R2C1. The second terminal of the resistor R2 is connected to the point common to the diodes D4, D5 of the bridge via a resistor R3, a Zener diode D11 is connected on the one hand to the positive potential wire of the circuit and on the other to the point common to the resistors R2 and R3.

 The Zener diode D11 ensures the limitation of the potential applied between the point common to the resistors R2, R3 and the positive potential wire to a limited value whatever the supply voltage applied to the station and therefore to the circuit.

 The depressing of the push button BP led to the opening of the rest contact, the capacitor C1 charges in reverse through Ri, the positive terminal of the capacitor Ci previously at the positive potential via the contact 2 changes to a zero potential. When the button is released, the positive terminal of the capacitor Ci suddenly goes back to the positive potential, this positive variation is transmitted by the capacitor C1 which then discharges with a time constant defined by the values of the resistor R2 and the capacitor C1.

The transistor T5 is blocked under the action of the Darlington circuit and opens the loop between points I and II as long as the monostable has not returned to its normal state.

 Of course, it should be understood that the device according to the invention makes it possible to equip any telephone set or terminal with multifrequency signaling from the moment when it is possible to have access to terminals I, II, III, IV or in equivalent points.

Claims (7)

1. Device for sending signaling for telephone sets or terminals comprising at least one keypad with keys, associated with a multi-frequency signal generator and a service button generally dissociated from the keyboard in order to allow the sending of signaling to the home telephone exchange of the post or terminal via a telephone line connected to this post or terminal, characterized in that it comprises a single circuit connected to the telephone line wires via four terminals in a manner identical to the telephone dial to which the signaling sending device replaces itself, said circuit grouping together on a same support a diode supply bridge, connected to the wires of the telephone line, in order to provide the polarized supply necessary for the other components of the circuit, a voltage regulator arrangement which is connected in output of the diode bridge, a multi-frequency signal generator powered by the diode bridge and controlled by the keyboard, a fixture ent current generator connected to the output of the multifrequency signal generator which controls it and across a station resistor which determines the impedance of the station seen from the telephone line and which transmits the signals to this telephone line, an arrangement of substation resistance short-circuit controlled by the multi-frequency signal generator.  2. sending signaling device according to claim 1, characterized in that the single circuit also includes on the same support a monostable generation of loop opening pulse controlled by the service button and connected to the line son via a voltage switch arrangement, as well as a current supply arrangement for the monostable connected to the diode supply bridge of the circuit and to the current limitation arrangement.  3. device for sending signaling according to claim 1, characterized in that it comprises an insertable resistor between the line wires via the diode bridge and a short-circuit transistor of this resistor connected to the terminals of this resistance and controlled by the multi-frequency signal generator via an intermediate transistor.  4. signaling sending device according to claim 3, characterized in that the monostable generation of loop opening consists of a polarized capacitor and a resistor for determining the time constant, the polarized capacitor having its positive terminal connected on the one hand to the positive potential wire via an idle contact of the service button and to the threshold potential wire via a resistor, the resistance for determining the time constant being connected by a terminal to the second terminal of the capacitor and to the arrangement for supplying the monostable with current and by a second terminal to the negative potential line wire via a limiting resistor, a Zener diode for fixing the potential being inserted between this second determination resistance terminal and the wire positive potential of the circuit. 5. Device for sending signaling according to claim 3, characterized in that the current supply arrangement is constituted by a Darlington circuit of two transistors controlled by a regulation transistor acting on the basis of the first of them , via a blocking diode; the collectors of the Darlington circuit transistors being connected to the base of a voltage switch transistor inserted between the negative potential line wire and the circuit zero potential wire, the base of the first transistor of the circuit Darlington being connected to the common point of the resistance and the capacitor of the monostable of the loop opening pulse generator.  6. Telephone set characterized in that it comprises a device for sending signaling according to one of claims 1 to 5.  7. Telephone terminal characterized in that it comprises a device for sending signaling according to one of claims 1 to 5.