GB2075304A

GB2075304A - Telephone receiving equipment

Info

Publication number: GB2075304A
Application number: GB8014228A
Authority: GB
Original assignee: TRILTRONICS UK Ltd
Current assignee: TRILTRONICS UK Ltd
Priority date: 1980-04-30
Filing date: 1980-04-30
Publication date: 1981-11-11
Also published as: GB2075304B

Abstract

A telephone receiver handset (14) has, in addition to a speaker (13) and a switch (17), a separate loudspeaker (35) in controlled by the switch (17) so that in one position of the switch (17) the separate loudspeaker (35) alone is operative whereas in the other position of the switch (17) both the speaker (13) and the microphone (15) of the handset (14) are operative. <IMAGE>

Description

SPECIFICATION Telephone receiving equipment This invention relates to telephone receiving equipment.

According to this invention there is described telephone receiving equipment comprising a handset including a microphone and a speaker and a separate loudspeaker, a switch being carried by the handset and being connected to control switching circuitry connected to the microphone speaker and the separate loudspeaker so that in one position of the switch the microphone and the speaker of the handset are operative and the separate loudspeaker is inoperative and in the other position of the switch, only the loudspeaker is operative.

The arrangement that when the loudspeaker is operative the microphone is inoperative limits the possibility of acoustic feedback, which is very annoying.

Preferably, the switching circuitry comprises a relay the coil of which is connected for energisation under the control of the switch.

Preferably, the relay has contacts which, when the loudspeaker is energized, disconnect the microphone and/or are arranged to short circuit the transmit lines to which the receiving equipment is connected in use.

Preferably, the relay includes a changeover contact operative to change over between the handset speaker and the loudspeaker.

An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawing which is a circuit diagram of a subscribertelephone receiver circuit.

Referring to the drawing, as is conventional there are two receive lines 1 and 2 and two transmit lines 3 and 4. The receive line 1 is connected to a movable contact 5 movable between two fixed contacts 6 and 7, being part of the relay whose coil is indicated at 8.

The transmit line 3 is connected to a further movable contact 9 of the relay which is movable between fixed contacts 10 and 11, line 4 being connected to fixed contact 10 through a resistor 12. In the event that the relay coil 8 is not energised, the movable coritacts 5 and 9 are in engagement with the fixed contacts 6 and 10 respectively as shown but when the relay coil 8 is energised movable contacts 5 and 9 are brought into engagement with fixed contacts 7 and 11 respectively. Fixed contact 7 and line 2 are connected to the speaker 13 of a handset 14 whereas fixed contact 11 and line 4 are connected to the microphone 15 of the handset 14. Line 2 is connected to a line 16 which is the negative supply line.The handset 14 includes a toggle pushbutton switch 17 one contact of which is connected through the relay coil 8 and a resistor 18 to the positive supply line 19 and the other contact of which is connected to a negative supply line 16 so that on closure of the switch 17, the relay coil 8 is energised.

Fixed contact 6 is connected by a D.C. blocking capacitor 20, a variable resistor 21 and a fixed resistor 22 to one input of a differential amplifier 23 of a preamplifier. Associated with the preamplifier are bias resistors 24 and 25 connected in series between a voltage line 26 and the line 16 with their junction connected to the other input of the differential amplifier 23.

The line 26 is connected to the line 19 through a resistor 27 and to line 16 through a capacitor 28 so that line 26 is at a stabilised voltage.

The output of the differential amplifier 23 is connected to its input through resistors 29 and 30 provid ing feedback, the junction of the resistors 29 and 30 being connected to line 16 through a capacitor 31 and a variable resistor 32 connected in series. The wiper of the resistor 32 is connected to one input of a power amplifier 33, the other input of which is connected to the line 16. The output of the power amplifier 33 is connected through a capacitor 34 to a loudspeaker 35.

The line 19 is energised through an isolating transformer36 and a double pole switch 37 from the mains, rectification being provided by a single diode 38. Light emitting diode 39 for indicating that the supply has been switched on is connected in series with a resistor 40 between the lines 19 and 16.

In use, in the eventthatthe switch 17 is not closed and the contacts of the relay are in the positions shown an input signal between the lines 1 and 2 passes through the contacts 5 and 6 which are connected to each other and is applied to the preamplifier including the differential amplifier 23. The output of the preamplifier 23 is connected to the input of the power amplifier 33 and energises the loudspeaker 35 at a level controlled by the setting of the variable resistor 32. Underthese conditions, since movable contact 9 is not in engagement with the fixed contact 11 but is instead in engagement with the fixed contact 10, the microphone 15 is not operative and moreover the transmit lines 3 and 4 are short circuited so that there can be no acoustic feedback between the loudspeaker 35 and the microphone 15.When the push-button switch 17 is closed, the relay coil 8 is energized bringing the contacts 5 and 9 into engagement with the contacts 7 and 11 respectively. As a result no signal can now reach the preamplifier23 orthe loudspeaker35 but instead a received signal is supplied via contacts 5 and 7 to the handset speaker 13. Moreover, since contact 9 is in engagement with contact 11, the microphone in the handset is operative and speech received by the microphone 15 will be transmitted on lines 3 and 4.

The transformer 36 may be double wound for protection and is shown as fused.

1. Telephone receiving equipment comprising a handset including a microphone and a speaker and a separate loudspeaker, a switch being carried by the handset and being connected to control switching circuitry connected to the microphone speaker and the separate loudspeaker so that in one position of the switch the microphone and the speaker of the handset are operative and the separate loudspeaker is inoperative and in the other position of the switch, only the loudspeaker is operative.

2. Telephone receiving equipment as claimed in claim 1 wherein the switching circuitry comprises a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Telephone receiving equipment This invention relates to telephone receiving equipment. According to this invention there is described telephone receiving equipment comprising a handset including a microphone and a speaker and a separate loudspeaker, a switch being carried by the handset and being connected to control switching circuitry connected to the microphone speaker and the separate loudspeaker so that in one position of the switch the microphone and the speaker of the handset are operative and the separate loudspeaker is inoperative and in the other position of the switch, only the loudspeaker is operative. The arrangement that when the loudspeaker is operative the microphone is inoperative limits the possibility of acoustic feedback, which is very annoying. Preferably, the switching circuitry comprises a relay the coil of which is connected for energisation under the control of the switch. Preferably, the relay has contacts which, when the loudspeaker is energized, disconnect the microphone and/or are arranged to short circuit the transmit lines to which the receiving equipment is connected in use. Preferably, the relay includes a changeover contact operative to change over between the handset speaker and the loudspeaker. An embodiment of this invention will now be described, by way of example, with reference to the accompanying drawing which is a circuit diagram of a subscribertelephone receiver circuit. Referring to the drawing, as is conventional there are two receive lines 1 and 2 and two transmit lines 3 and 4. The receive line 1 is connected to a movable contact 5 movable between two fixed contacts 6 and 7, being part of the relay whose coil is indicated at 8. The transmit line 3 is connected to a further movable contact 9 of the relay which is movable between fixed contacts 10 and 11, line 4 being connected to fixed contact 10 through a resistor 12. In the event that the relay coil 8 is not energised, the movable coritacts 5 and 9 are in engagement with the fixed contacts 6 and 10 respectively as shown but when the relay coil 8 is energised movable contacts 5 and 9 are brought into engagement with fixed contacts 7 and 11 respectively. Fixed contact 7 and line 2 are connected to the speaker 13 of a handset 14 whereas fixed contact 11 and line 4 are connected to the microphone 15 of the handset 14. Line 2 is connected to a line 16 which is the negative supply line.The handset 14 includes a toggle pushbutton switch 17 one contact of which is connected through the relay coil 8 and a resistor 18 to the positive supply line 19 and the other contact of which is connected to a negative supply line 16 so that on closure of the switch 17, the relay coil 8 is energised. Fixed contact 6 is connected by a D.C. blocking capacitor 20, a variable resistor 21 and a fixed resistor 22 to one input of a differential amplifier 23 of a preamplifier. Associated with the preamplifier are bias resistors 24 and 25 connected in series between a voltage line 26 and the line 16 with their junction connected to the other input of the differential amplifier 23. The line 26 is connected to the line 19 through a resistor 27 and to line 16 through a capacitor 28 so that line 26 is at a stabilised voltage. The output of the differential amplifier 23 is connected to its input through resistors 29 and 30 provid ing feedback, the junction of the resistors 29 and 30 being connected to line 16 through a capacitor 31 and a variable resistor 32 connected in series. The wiper of the resistor 32 is connected to one input of a power amplifier 33, the other input of which is connected to the line 16. The output of the power amplifier 33 is connected through a capacitor 34 to a loudspeaker 35. The line 19 is energised through an isolating transformer36 and a double pole switch 37 from the mains, rectification being provided by a single diode 38. Light emitting diode 39 for indicating that the supply has been switched on is connected in series with a resistor 40 between the lines 19 and 16. In use, in the eventthatthe switch 17 is not closed and the contacts of the relay are in the positions shown an input signal between the lines 1 and 2 passes through the contacts 5 and 6 which are connected to each other and is applied to the preamplifier including the differential amplifier 23. The output of the preamplifier 23 is connected to the input of the power amplifier 33 and energises the loudspeaker 35 at a level controlled by the setting of the variable resistor 32. Underthese conditions, since movable contact 9 is not in engagement with the fixed contact 11 but is instead in engagement with the fixed contact 10, the microphone 15 is not operative and moreover the transmit lines 3 and 4 are short circuited so that there can be no acoustic feedback between the loudspeaker 35 and the microphone 15.When the push-button switch 17 is closed, the relay coil 8 is energized bringing the contacts 5 and 9 into engagement with the contacts 7 and 11 respectively. As a result no signal can now reach the preamplifier23 orthe loudspeaker35 but instead a received signal is supplied via contacts 5 and 7 to the handset speaker 13. Moreover, since contact 9 is in engagement with contact 11, the microphone in the handset is operative and speech received by the microphone 15 will be transmitted on lines 3 and 4. The transformer 36 may be double wound for protection and is shown as fused. CLAIMS

2. Telephone receiving equipment as claimed in claim 1 wherein the switching circuitry comprises a relay the coil of which is connected for energisation underthe control of the switch.

3. Telephone receiving equipment as claimed in claim 2 wherein the relay has contacts which. when the loudspeaker is energised, disconnect the microphone andlor are arranged to short circuit the transmit lines to which the receiving equipment is connected in use.

4. Telephone receiving equipment as claimed in claim 2 or claim 3 wherein the relay includes a changeover contact operative to change over between the handset speaker and the loudspeaker.

5. Telephone receiving equipment as claimed in any preceding claim wherein the switch is a pushbutton switch.

6. Telephone receiving equipment substantially as hereinbefore described with reference to the accompanying drawing.