GB2084368A - Sound-operated Switching Circuit - Google Patents

Abstract

A sound-operated switching circuit comprises a microphone (1) connected to a pulse generating circuit (7) which generates an initiating pulse in response to receipt of a sound input by the microphone. An output device (33), such as a vibrator, produces an audible sound when energised via an output switch (30) which is turned on by a delay circuit (22) in response to the initiating pulse. The delay circuit maintains the output switch in the on condition for a predetermined period of time after the onset of the sound input. <IMAGE>

Description

SPECIFICATION Sound-Operated Switching Circuit This invention relates to a sound-operated switching circuit, and particularly to such a circuit which causes energisation of a vibrator or like audible device in response to the receipt of sound by the circuit.

It is an object of the invention to provide a switching circuit which will cause energisation of an output device for a predetermined period following the receipt of a sound input and which will then de-energise the output device unless a further sound input is received at the deenergisation time.

According to the invention, a switching circuit comprises a microphone; a pulse generating circuit operative to generate an initiating pulse in response to receipt of a sound input by the microphone; an output device which when energised produces an audible sound; an output switch switchable to an ON condition to energise the output device; and a delay circuit responsive to the initiating pulse to set the output switch in the ON condition and to maintain it in that condition for a predetermined period of time.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying circuit diagram.

Refering to the diagram, a microphone 1 is connected across a d.c. supply 2 via a resistor 3.

Electric signals produced by the microphone in response to sounds received thereby are fed via a capacitor 4 to a potentiometer 5 which acts as a sensitivity control.

The output of the potentiometer 5 is fed via a coupling capacitor 6 to a pulse generating circuit 7 which comprises two transistors 8 and 9 connected in a switching mode. The base electrode of the transistor 8 is connected to the d.c. supply line 2 via a resistor 10. The emitter is connected to a ground line 11 via a resistor 12.

The collector of the transistor 8 is directly connected to the base electrode of the transistor 9. The collector of the transistor 9 is connected to the supply line 2 via a resistor 13, and its emitter is connected to ground via a resistor 14 which is decoupled by a capacitor 1 5. Feedback from the emitter of the transistor 9 to the base electrode of the transistor 8 is provided by a resistor 1 6.

The output pulse from the collector of the transistor 9 is fed via a capacitor 1 7 to the base electrode of an amplifier transistor 18, the bias condition of which is set by resistors 19 and 20 connected in series between the d.c. supply line 2 and ground 1 The collector of the transistor 18 is connected to the line 2 via a resistor 21, and the emitter is connected to ground.

An integrated circuit delay device 22 receives the amplified pulse from the collector of the transistor 18 and produces a d.c. level at a terminal 23 which is fed to the base electrode of an output transistor 24 via a resistor 25. A decoupled power supply for the device 22 is derived from a resistor 26 and a capacitor 27. The d.c. level at the terminal 23 is maintained for a predetermined period, say 3 seconds, as determined by a capacitor 29.

The collector circuit of the transistor 24 includes an operating coil 29 of a relay 30, shunted by a reverse-connected diode 31.

Normally-open contacts 32 of the relay 30 are connected between a vibrator 33 and a 3 volt battery supply 34. The coil 29 is connected via a switch 35 to a 9 volt battery 36. The switch 35 may, if desired, be ganged with the potentiometer 5. The supply 2 is also derived from the battery 36 via a decoupling circuit comprising a resistor 37 and a capacitor 38.

In operation of the sound-operated switching circuit of the present invention, when a sound of sufficiently high intensity is received by the microphone 1 , the circuit 7 produces an initiating pulse which is fed to the delay circuit 22. The circuit 22 immediately feeds a positive d.c.

potential to the base electrode of the transistor 24, thereby causing the transistor to conduct. The relay 30 is thereby energised, causing operation of the vibrator 33. The d.c. potential remains at that level for a predetermined period and then, in the absence of further sound input to the microphone 1, falls to a level at which the transistor 24 cuts off and the relay 30 is deenergised. If a sound input is still present at the end of the predetermined period, however, a further pulse is fed to the delay circuit 22, and the d.c. potential fed to the base of the transistor 24 is maintained for a second period at the high level.

The relay 30 therefore remains energised, and the vibrator 33 continues to operate. This will be repeated for as long as a sound input is present at the end of each timing period. The diode 31 helps to maintain the coil 20 energised whilst the delay circuit 22 is resetting under these conditions.

Although the device 33 is specified above as a vibrator, alternative kinds of output device could be used to produce an audible sound output. For example, the device could be a siren or an electric bell. Clearly, by providing an a.c. supply in place of the battery 34 an a.c.-powered output device 33 could be used. The device 33 and/or its power supply can be either in the same unit as the switching circuit or remote therefrom. Similarly, the battery 35 and/or the microphone 1 may be located remotely from the switching circuit unit.

The battery 34 and/or the battery 36 may be replaced by a mains-operated power supply.

The transistor 24 and the relay 30 may be replaced by an alternative switching device, such as power transistor which is connected in series with the device 33 across a d.c. supply, There are many uses for the switching circuit of the present invention. For example, the microphone could be located adjacent the bell of a telephone, and the device 33 could be located remotely, for example in another room, to give to persons in that room, and unable to hear the telephone bell, a warning that the bell is ringing.

The device 33 will continue to operate as long as the bell is ringing. Alternatively, the microphone could be affixed to a door so that the unit transforms a single knock on the door into a longer audible summoning signal. In another alternative use, the circuit could act as a baby alarm. The microphone would be located close to the baby and the device 33 could be located in another room. A short noise from the baby would result in only a single alarm output burst from the device 33, whereas prolonged noise, such as crying, would produce a continuous alarm output.

in fact, the circuit might be used in any application in which an output device is to be energised for a pre-determined period following the sensing of an input sound.

Furthermore, if the device 33 is located close to the microphone 1, a sound detected by the microphone will initiate operation of the circuit, and then the sound from the device 33 will maintain the circuit in operation. Hence, following an initial sound of sufficient intensity to cause operation of the device 33, the device will continue to operate until the circuit is switched off by means of the switch 35. This would be very useful as an intruder alarm, for example.

Claims (7)

Claims

1. A sound-operated switching circuit, comprising a microphone; a pulse generating circuit operative to generate an initiating pulse in response to receipt of a sound input by the microphone; an output device which when energised produces an audible sound; an output switch switchable to an ON condition to energise the output device: and a delay circuit responsive to the initiating pulse to set the output switch in the ON condition and to maintain it in that condition for a predetermined period of time.

2. A circuit as claimed in Claim 1, wherein the pulse generating circuit includes two transistors connected in a switching mode.

3. A circuit as claimed in Claim 1 or Claim 2, wherein the output switch comprises a relay and a transistor which controls energising current for the relay.

4. A circuit as claimed in Claim 1 or Claim 2, wherein the output switch comprises a power transistor.

5. A circuit as claimed in any preceding claim, wherein the delay circuit comprises an integrated circuit.

6. A circuit as claimed in any preceding claim, wherein the output device is located in such position relative to the microphone that feedack from the output device to the microphone causes continual setting of the output switch in the ON condition.

7. A circuit as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying circuit diagram.

7. A circuit as claimed in any preceding claim, wherein the output device comprises a vibrator.

8. A circuit as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying diagram.

New Claims or Amendments to Claims filed on 11th September 1981 Superseded claims 1-8 New or Amended Claims: 7

1. A sound-operated switching circuit, comprising a microphone; a pulse generating circuit operative to generate an initiating pulse in response to receipt of a second input by the microphone; a vibrator; an output switch switchable to an ON condition to energise the vibrator; and a delay circuit responsive to the initiating pulse to set the output switch in the ON condition, to maintain it in that condition for a predetermined period of time, and then to reset it to de-energise the vibrator.

2. A circuit as claimed in Claim 1, wherein the pulse generating circuit includes two transistors connected in a switching mode.

3. A circuit as claimed in Claim 1 or Claim 2, wherein the output switch comprises a relay and a transistor which controls energising current for the relay.

4. A circuit as claimed in Claim 1 or Claim 2, wherein the output switch comprises a power transistor.

5. A circuit as claimed in any preceding claim, wherein the delay circuit comprises an integrated circuit.

6. A circuit as claimed in any preceding claim, wherein the vibrator is located in such position relative to the microphone that feedback from the vibrator to the microphone causes continual setting of the output switch in the ON condition.