Field of Invention

The invention relates to an audio communication system, for example a public address system, interphone system, home theatre system or the like, in which audio signals are transmitted between a transmitter and receiver via a mains power distribution system, for example, the mains power distribution system of a building.

Background to the Invention

A prior art public address system shown in Figure 1 comprises an amplifier (1 ) for amplifying the audio signals supplied from various audio sources such as a microphone, CD player, radio etc, one or more speakers (2), which broadcast the audio signal transmitted from the amplifier, and a cable (3) that connects the amplifier and the mentioned speaker(s). Such public address systems require the installation of cabling to connect the amplifier to speakers, which are typically in many different rooms and/or on different floors. This requires much time and expense and in some cases it may not be possible to install the required cabling.

A further problem that affects installed cables of a public address system is that when the cabling is cut or shorted, it can be very difficult to locate the short or cut, particularly if the installation is in a big building.

Additionally, for a large area public address system, a higher power amplifier may be needed to increase the power of the audio signal. In such cases, overheating and overload status on the amplifier can cause many problems.

Power line communication (PLC) is a technology for sending signals or data along power lines by carrying the signal on the AC frequency (50-60Hz) and provides a convenient and economic solution to transmitting data by using existing cabling systems.

Usually PLC is divided into two broad categories. One is to use low frequencies (under 450Khz) for low speed data transmission at around 9600bps for remote control and home automation etc. The other is to use higher frequencies (over 450KHz and up to 30MHz) for broadband internet access, home networking and high speed data transmission.

However, power lines are not designed for conducting data signals and their electromagnetic shield systems are generally not sufficiently good to ensure that the transmission of high frequency signals will not create interference problems with other electronic equipment or RF devices. Therefore, most countries have regulations prohibiting the transmission of frequencies over 450Khz by means of power lines. This has made it difficult to spread PLC technology even though PLC has several technical and economic advantages when compared with other available systems.

An object of the invention is to at least partially overcome one or more of these problems and/or to provide a convenient and cheap method of providing a public address system and/or to provide an alternative to existing products and methodology.

Summary of the Invention

The invention provides an audio signal transmitter comprising an electric plug unit connectable to a connector of an AC mains power supply, a power supply unit for

regulating and rectifying AC mains power received from the plug unit for supplying power to the audio signal transmitter, an oscillating unit for generating a particular carrier frequency according to a set clock frequency, an audio signal input unit for receiving audio signals from at least one audio source, a modulation unit for producing a modulated frequency to carry said audio signals on the particular carrier frequency generated by the oscillating unit and an RF choke unit for preventing the output of frequencies higher than the particular carrier frequency carrying the audio signal.

The invention also includes an audio signal receiver comprising an electric plug unit connectable to a connector of an AC mains power supply in a building, a power supply unit for regulating and rectifying AC mains power received from the AC mains power supply via the plug unit for supplying the audio signal receiver, a signal abstraction unit for abstracting by impedance matching a particular audio carrying signal the audio signal receiver is to receive from the AC mains power supply via the electric plug unit, a frequency amplifying unit for amplifying the audio carrying signal abstracted by the signal abstracting unit, an oscillating unit for generating a predetermined frequency the same as the frequency of the audio carrying signal the audio signal receiver, is to receive, a syntony unit for tuning the amplified audio carrying signal to the frequency generated by the oscillating unit, a signal detection unit for abstracting the audio signal from the tuned amplified audio carrying signal, an audio signal amplifying unit for amplifying the abstracted audio signal for supply to an output device and a level control unit for controlling the level of the signal supplied to the output device.

The invention also includes a public address system comprising an audio signal transmitter for transmitting an audio signal by connecting an earth terminal of a plug of the audio signal transmitter to an earth terminal of a first connector of a plurality of connectors of a power grid, the audio signal being transmitted by a carrier frequency

that carries the audio signal, and an audio signal receiver for receiving the carrier frequency carrying the audio signal by connecting an earth terminal of a plug of the audio signal receiver to an earth terminal of a second connector of said plurality of connectors.

The invention also includes a method of providing an audio communication system, the method comprising connecting an electrical connector of an audio signal transmitter to any one of a plurality of electrical connectors of an electrical power supply system in a building and connecting an electrical connector of an audio signal receiver to any other one of said plurality of electrical connectors of the electrical power supply system, said audio signal transmitter being arranged to transmit a carrier frequency carrying an audio signal along a line of said electrical power supply system and said audio signal receiver being arranged to receive said carrier frequency from said line and separate said audio signal for supply to an output device.

Brief Description of the Drawings

In order that the invention may be well understood, an embodiment thereof, which is given by way of example only, will be described with reference to the drawings, in which:

Figure 1 is brief block diagram of a prior art public address system;

Figure 2 illustrates a prior art electrical connector of a mains power distribution system;

Figure 3 is a block diagram of an audio signal transmitter;

Figure 4 is a block diagram of an audio signal; and

Figure 5 is a block diagram illustrating a public address system comprising the transmitter of Figure 3 and receiver of Figure 4.

Detailed Description of the Embodiment

The embodiment comprises audio signal transmitting and receiving devices for a public address system that use power line communication technology to transmit audio signals along power lines, abstract the audio signal transmitted by the transmitter and supply the audio signal to at least one speaker without installing dedicated cabling to connect the audio source and speaker(s).

Generally speaking, public address systems are installed in factories, shops, office buildings, schools, hospitals, railway and bus stations etc to broadcast information or background music.

Referring to Figure 2, a mains electricity power line, which may, for example, be installed in a school or factory is provided with connectors (30), which are typically fixed in or on a wall of the building, to provide a connection to AC power grid. The connectors (30) have two terminals (A) (B) to supply AC power and one ground, or earth, terminal (C) to be commonly connected to one point in a building.

Figure 3 shows an audio signal transmitter (10) comprising a power supply unit (11 ), an oscillating unit (12), an audio signal input unit (13), a modulation unit (14), a level control unit (15), a RF choke unit (16) and an electric plug unit (10A).

The power supply unit (1 1 ) supplies the required power to various elements of the transmitter (10A) after regulating and rectifying the AC power that is received from terminals (a) and (b) of the plug unit.

The power supply unit (11 ) comprises a transformer that steps the AC power down according to the turn ratio of its primary and secondary windings, a bridge diode to rectify the AC power received from the transformer, regulators to change the voltage to for example, l2Vdc, 5Vdc, GND and 8Vdc, to supply the required power to elements of the audio signal transmitter.

The oscillating unit (12) generates a particular frequency under the instruction of set clock frequency, for example 21.4MHz for supply to the modulation unit (14).

The audio signal input unit (13) receives audio signals from various audio sources, such as an audio amplifier, microphone, CD player or the like.

The modulation unit (14) modulates the audio signal on the particular frequency generated by the oscillating unit (12) as a data carrier.

The level controlling unit (15) controls the level and output power during modulation of the audio signal on the carrier frequency by the modulation unit (14).

The RF choke unit (16) prevents the generation of unnecessary frequencies higher than the particular frequency produced by the modulation unit (14) and to output the carrier frequency through the earth terminal (c) of the plug (10A)

In use, when the plug unit (10A) of the audio signal transmitter (10) is connected to a connector (30) in a building, terminals (a) and (b) of the plug unit are connected to terminals (A) and (B) of the connector (30), and terminal (c) of the plug unit (10A) is connected to terminal (C) of the connector (30). The power supply unit (11 ) receives,

reduces and regulates the AC power supplied from the plug (1OA) and supplies the needed power to elements of the audio signal transmitter (10).

When power is supplied to elements of the audio signal transmitter (10), the oscillating unit (12) generates the particular frequency according to an instructed frequency, for example 500KHz and outputs it to the modulation unit (14).

When an audio signal is received via the audio input unit (13), it is interfaced to the modulation unit (14) and the modulation unit produces and sends the modulated frequency carrying the audio signal as carrier data to the RF choke unit (16).

The RF choke unit (16) prevents the generation of unnecessary frequencies higher than the frequency output by the modulation unit (14) and supplies the carrier frequency through the earth terminal (c) of the plug unit (10A) to the terminal (C) of the connector (30).

Figure 4 shows an audio signal receiver (20) comprising an electric plug unit (20A), a power supply unit (21 ), a signal abstraction unit (22), a signal amplifying unit (23), a syntony unit 24, an oscillating unit (25), a detection unit (26), an amplifying unit (27) and a level control unit (28).

The power supply unit (21 ) comprises a transformer that steps the AC power down according to the turn ratio of its primary winding and secondary windings, a bridge diode to rectify the AC power output by the transformer and regulators to change the voltage to, for example, 12Vdc, 5Vdc, GND and 8Vdc, to supply the required power to elements of the audio signal receiver.

The signal abstraction unit (22) abstracts the particular signal (the carrier frequency carrying the audio signal) by impedance matching the signals received through the earth terminal (c1 ) of the plug unit (20A), which is connected to the neutral line of the AC power grid.

The signal amplifying unit (23) amplifies and outputs the frequency delivered from the signal abstraction unit (22).

The syntony (24) unit tunes the frequency of the signal received from the amplifying unit (23) to a frequency generated by the oscillating unit (25). The syntony unit (24) tunes into components of the RF signal received from the signal amplifying units 23 which have the same frequency or phase as that of the oscillating unit 25 and passes only those components to the signal detecting unit 26. The syntony unit (24) preferably has more than one tuning unit to increase reliability and stability. The oscillating unit (25) generates a particular frequency according to a set clock frequency, for example and preferably, 500KHz.

The signal detection unit (26) abstracts the audio signal from the tuned frequency received from the syntony unit (24).

The audio signal amplifying unit (27) amplifies the audio signal abstracted by the detection unit (26) and supplies it to an output device such as a speaker or earphone jack (not shown). The level control unit (28) controls the level of the audio signal output from the audio signal amplifying unit (27).

In use, when the plug unit (20A) of the audio signal receiver (20) is connected to any connector (30) in a building, terminals (a1 ) and (b1 ) of the plug unit are connected to

terminals (A) and (B) of the connector (30), and terminal (d ) of the plug unit is connected to C terminal of the connector (30).

The power supply unit (21 ) reduces and regulates the AC power supplied through terminals (a1 ) and (b>1 ) of the plug unit (20A) and supplies the required power to elements of the audio signal receiver (20). When power is supplied to the audio signal receiver, the signal abstraction unit (22) abstracts the particular frequency supplied through terminal (c1 ) of the plug unit (20A) by impedance matching and supplies it to the signal amplifying unit (23).

The amplifying unit (23) delivers the amplified abstracted frequency to the syntony unit (24) and the syntony unit (24) tunes the amplified abstracted frequency to the frequency generated by the oscillating unit (25) The tuned frequency is supplied to the signal detection unit (26). The signal detection unit (26) abstracts the audio signal carried as carrier data from the frequency tuned by the syntony unit (24) and delivers it to the audio signal amplifying unit (27).

The audio signal amplifying unit (27) amplifies the audio signal to a level controlled by the level control unit (28) and outputs the audio signal to the speaker or an earphone jack (not shown).

Referring to Figure 5, when a public address system is to be installed in a building, the plug unit (10A) of an audio signal transmitter (10) is connected to any connector (30) of the power grid of the building and the plug unit (20A) of an audio signal receiver (20) is connected to any other connector (30) of the power grid thereby simply and easily providing the public address system. Specifically, to install the transmitting unit, the terminals (a) and (b) of the electric plug unit (10A) of the audio signal transmitter (10)

are simply connected respective to terminals (A) and (B) of any connector (30) of the power grid in the building and the earth terminal (c) of the plug unit is connected to earth terminal (C) of the connector.

Similarly, to install the receiving unit of the public address system, terminals (a1 ) and (b1 ) of the electric plug unit (20A) of the audio signal receiver (20) are respectively connected to terminals (A) and (B) of any connector (30) and the earth terminal (c1 ) of the plug unit is connected to the earth terminal (C) of the connector.

The public address system can readily be modified by disconnecting the electric plug unit (20A) of the audio signal receiver (20) from one connector (30) and connecting to any other connector (30) in the building.

When the public address system is installed in a building, the audio signal input from an audio source, such as a microphone, CD player, audio amplifier and/or radio is transmitted the power lines in a bundle by the carrier frequency carrying the audio signal to be received by the or each audio signal receiver (20) connected to a/the connector(s) (30) of the power grid.

The audio signal receiver(s) (20) connected to the power grid receive the carrier frequency carrying the audio signal and supply the audio signal to an output device, such as a speaker or earphone jack, by employing the above described processes of abstraction, syntony, and detection.

As described above, the embodiment has the advantage that it saves cable installation expenses and provides a convenient means of providing a public address system by using existing power lines to transmit the audio signal from the audio signal transmitter

to the audio signal receiver(s) by simply connecting the plug units of the transmitter and the receiver(s) to any connector of the power grid without installing additional cables and purchasing an expensive high power amplifier.

The audio signal transmitter and the audio signal receiver can be moved easily to any place in a building by connecting the plugs of the transmitter and the receiver to any connector of the power grid in a building. Because the transmitter and receiver can simply be unplugged and reconnected at different locations where there are suitable connectors, a flexible and mobile public address system can be provided.

In the described embodiment, power lines are used to transmit audio signals produced by an audio source such as a CD player or audio amplifier, from the transmitter to a speaker via power lines and an audio signal receiver. The audio signal transmitter has an electric plug unit that is connected to power lines of the power grid of a building. A power supply unit supplies the required power to various components of the audio signal transmitter after regulating the AC Power received from the electric plug unit. An oscillating unit generates a particular frequency according to a set clock frequency, an audio signal input unit receives the audio signal from the audio source, a modulation unit produces the modulated frequency carrying the audio signal on the carrier frequency generated by the oscillating unit and a RF choke unit outputs the particular carrier frequency carrying the audio signal into the power system via the transmitter's plug unit. An audio signal receiver power grid in the building by an electric plug unit is used to collect the audio signal. The audio signal receiver includes a power supply unit for supplying the required power to various components of the audio signal receiver after regulating the AC power supplied from the plug unit, a signal abstraction unit for abstracting the particular signal by impedance matching, a frequency amplifying unit for amplifying the signal abstracted by the signal abstracting unit, an oscillating unit for

generating the same frequency as is transmitted by the transmitter, a syntony unit for tuning the amplified frequency to the frequency generated by the oscillating unit, a signal detection unit for abstracting the audio signal carried by the carrier frequency from the tuned frequency, an audio signal amplifying unit for amplifying the audio signal abstracted from the carrier frequency for supply to a speaker and a level control unit for controlling the sound level supplied to the speaker.

The embodiment provides a convenient and cheap apparatus from which a public address system or interphone can be constructed by simply connecting the plug unit of the transmitter to any suitable electrical connector in a building and connecting the plug of one or more receivers to other such electric connectors in the same building.

It will be appreciated that the connectors used to connect the transmitter and receiver to the AC power supply may be of any suitable form for connecting to a power supply system, for example a mains power system, and permit access to the audio signal transmitted along the power lines. Typically, the connector will be an electrical power socket and the electrical plug unit of the transmitter and receiver will be arranged to be plugged into such sockets. Usually, the connectors will be fixed to a building or similar such structure.

The embodiment provides a public address system using the audio signal transmitter (10) and receiver (22) to transmit and receive the audio signal through the respective earth terminals of the plug units of the transmitter and the receiver by simply connecting into any electric connector in a building. The system uses the audio signal transmitter to transmit the audio signal with a modulation system to send the audio signal modulated on the particular carrier frequency and the audio signal receiver to receive the audio signal from the transmitter through the earth terminal of the plugs of

the transmitter and the receiver and to supply the amplified audio signal to the speaker. Thus, a public address system can be installed by simply connecting the plugs of the transmitter and the receiver into any connector of the power grid in a building with the audio signal being delivered through the earth lines of AC power grid.

It will be understood that the earth line/terminals mentioned herein may be referred to in some parts of the world as a ground line/terminals and the terms are to be taken as having the same meaning.

While the invention has been described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.