GB2062414A

GB2062414A - Portable radio receiver

Info

Publication number: GB2062414A
Application number: GB7931274A
Authority: GB
Original assignee: Filtrona PLC
Current assignee: Essentra PLC
Priority date: 1979-09-10
Filing date: 1979-09-10
Publication date: 1981-05-20

Abstract

A portable radio receiver is enabled by a signal picked up from an inductive loop. The receiver output is supplied to loudspeakers 38 and 62 housed in a hearing protector set for use in a factory environment. The components of the receiver are housed in the protectors 81 and 82. A touch sensitive switch gives control over energisation of the amplifier 14 and the loudspeaker unit 13, which control can be cancelled by the absence of output of an inductive loop pick-up unit coupled to supply a control signal to either a time switch, or a tone controlled switch, located in series between the tuner and the touch sensitive switch. The time switch is closed for a set time initiated by the reception of a control signal by the pick-up unit 15. The tone controlled switch is held closed for the duration of reception of the control signal. A low pass audio frequency filter, coupling the pick-up unit 15 to the amplifier 14, may be provided to enable communications transmitted inductively to be fed from the pick-up unit 15 to the loudspeakers. <IMAGE>

Description

SPECIFICATION Portable radio receiver This invention relates to a portable radio receiver.

It is an object of the present invention to provide a portable radio receiver which is especially suitable for use by a worker in a factory environment in that the receiver can be subjected to such control over its functioning that theft of the receiver is discouraged.

According to the present invention there is provided a portable radio receiver comprising means for receiving, selecting and demodulating radio broadcasts and producing in response thereto an electrical audio frequency signal, electrical audio frequency amplifying means arranged to receive and amplify electrical audio frequency signals produced by the receiving, selecting and democ ulating means, means for transducing amplified audio frequency signals produced by the amplifying means into sound, inductive pick-up means for receiving an induction field control signal, controlled switching means arranged to control operation of the receiving, selecting and demodulating means and adapted to be controlled in a manner dependent upon reception by the inductive pick-up means of the induction field control signal, and manually controllable switching means arranged to control operation of the said controlled switching means.

The controlled switching means is adapted to be controlled in a manner dependent upon reception by the inductive pick-up means of the induction field control signal in one embodiment by a timing unit which, for the duration of a timing signal initiated by reception by the pick-up means of the said control signal, holds the controlled switching means in one state thereof in response to which the receiving, selecting and demodulating means is rendered operative. At times other than during a timing cycle, the timing unit holds the controlled switching means in another state thereof in response to which the receiving, selecting and demodulating means is rendered inoperative.

In another embodiment the inductive pick-up means is coupled to the controlled switching means by a filter which passes the induction field control signal to the controlled switching means so as to hold the controlled switching means in one state thereof in response to which the receiving, selecting and demodulating means is rendered operative, the controlled switching means rendering the receiving, selecting and demodulating means inoperative in the absence of the reception of the induction field control signal by the pick-up means.The pick-up means may be coupled to the audio frequency amplifying means by a further filter which rejects the induction field ,control signal but passes a predetermined band of audio frequency signals so that when audio frequency induction field signals in the said predetermined frequency band are received by the pick-up means in the absence of the induction field control signal, corresponding amplified audio frequency signals are transduced into sound by the transducing means.

Preferably the manually controllable switching means controls the operative states of the amplifying means and the transducing means.

An embodiment of the invention is preferably housed in a pair of hearing protectors mechanically coupled to form a hearing protector set and each hearing protector each adapted to operate as an earphone, the two earphones constituting the said transucing means. The receiving selecting and demodulating means may include a variable capacitor provided with a manually operable varying member accessible at the outside of one hearing protector, and the manually controllable switching means may include a pair of contacts so mounted in one of the hearing protectors as to be electrically couplable together by bridging manual contact. Each hearing protector preferably has a hard cup-like shell of plastics material containing acoustic damping material in addition to the transducing means and electrical circuits.Where elements of the receiver apparatus exit from the hearing protectors such elements preferably do so through acoustically sealed apertures in the hard shells. The rim of each shell may be provided with a cushioning acoustic seal.

A hearing protector set embodying the invention may have the appearance of a set of stereo earphones without a connecting cable.

Thus a worker can wear such a hearing protector set in a factory and be able to move freely about machinery without the danger, encumbrance and restriction which would arise if the hearing protectors required a connecting cable. An inductive loop system can be installed in, for example, the roof over a factory shop floor where workers are supplied with hearing protectors embodying the present invention. If the embodiment has two filters as described hereinbefore, information and instructions can be transmitted by the inductive loop system.

Fig. 1 shows, in the form of a simplified block diagram, a first embodiment of the invention in which a touch-sensitive switch 11 is connected between a ground terminal 12 and a loudspeaker unit 13, an audio amplifier 14, a pick-up unit 15, and, through a time switch 16, a tuner unit 17. A positive supply terminal (not shown in Fig. 1) is connected to the units 13, 1 5 and 17 and to the amplifier 14, and a timer unit 18 is permanently connected to the ground terminal 12 (by a connection not shown in Fig. 1) and to the positive supply terminal (not shown).

The pick-up unit 15, the amplifier 14 and the loudspeaker unit 1 3 are operative whenever the touch-sensitive switch 11 is closed. The timer unit 1 8 is triggered into a timing cycle by the pick-up unit 1 5 whenever the pick-up unit 1 5 receives a 20 kilohertz signal from an inductive loop (not shown) and the timer unit 1 8 is not undergoing a timing cycle. Throughout each timing cycle, the timer unit 1 8 produces an output signal which holds the time switch 1 6 closed and, provided the touch-sensitive switch 11 is closed, the tuner unit 1 7 is then provided with a connection to the ground terminal 12 through the time switch 1 6 and the touch-sensitive switch 11.If the touchsensitive switch 11 is turned off during a timing cycle of the timer unit 18, the tuner unit 17, the amplifier 14 and the loudspeaker unit 13 are all turned off, but can be turned on again by subsequent closure of the touch-sensitive switch 11 during the timing cycle of the timer unit 18.

The tuner unit 17 is designed in this example to receive medium wave radio broadcasts and to supply the amplifier 14 with a demodulated audio frequency signal which is amplified by the amplifier and supplied to the loudspeaker unit.

It is arranged that the signal produced by the pick-up unit 1 5 cannot reset the timer unit 1 8 to the beginning of its timing cycle but can only -trigger a new timing cycle after the timer unit 18 has reset itself automatically in response to the ending of the previous timing cycle.

Fig. 2 shows, again in the form of a simplified block diagram, a second embodiment of the invention in which a touch-sensitive switch 11 is connected between a ground terminal 12 and a loudspeaker unit 13, an audio amplifier 14, a pick up unit 15, and, through a control switch 19, a tuner unit 1 7. A positive supply terminal (not shown in Fig. 2) is connected to the units 13, 15 and 17 and to the amplifier 14.

The pick-up unit 15, the amplifier 14 and the loudspeaker unit 13 are operative whenever the touch-sensitive switch 11 is closed. Whenever and for as long as the pick-up unit 1 5 receives a 20 kilohertz signal from an inductive loop (not shown), this 20 kilohertz signal is passed through a control filter 20 to the control switch 1 9 which is thereby held closed. While the control switch 19 is closed, the tuner unit 17, the audio amplifier 14 and the loudspeaker unit 13 can be switched on and off by closing and opening respectively of the touch-sensitive switch 11.

If audio frequency signals, below 10 kilohertz, are received by the pick-up unit 1 5 instead of the 20 kilohertz signal, and the touch-sensitive switch 11 is in its closed state, the audio amplifier 14 receives these audio signals through a low pass filter 21 which couples signals below 10 kilohertz from the pick-up unit 1 5 to the input of the amplifier 14.

Thus, provided the touch-sensitive switch 11 is in its closed state, reception of a radio broadcast can be interrupted by an audio frequency communication below 10 kilohertz transmitted from the inductive loop (not shown) to the pick-up unit 15.

The tuner unit 17 of the two embodiments of Figs. 1 and 2 is shown in detail in Fig. 3. The unit 1 7 includes a ferrite rod aerial 22 tunable to receive medium wave radio broadcasts. Three transistors 23, 24 and 25 provide amplification and are coupled as shown by a medium wave radio frequency coil 26 and three intermediate frequency coils 27, 28 and 29.

The output of the final intermediate frequency coil 29 is rectified by a diode 30 and an audio frequency output is provided at an output terminal 31. The tuner unit 1 7 includes a positive rail 32 coupled as shown to a positive supply input terminal 33, and a ground rail 34 connected directly to a ground connection terminal 35.

Tuning of the unit 17 can be effected by means of a pair of ganged variable capacitors 36 and 37.

Fig. 3 also shows part of the loudspeaker unit 13, namely one loudspeaker 38 connected in series with an adjustable resistor 39, a fixed resistor and a capacitor between two terminals 40 and 41.

Fig. 4 shows the remaining circuitry of the first embodiment (Fig. 1) in detail.

The touch-sensitive switch 11 consists of two metal contacts 42 and 43 coupled by a bistable circuit 44 to a switching transistor 45 having its emitter connected to the ground terminal 12, which is the negative terminal of a battery 46, and its collector connected to the emitter of another switching transistor 47 which, together with a base resistor 48, constitutes the time switch 1 6.

The collector of the time switch transistor 47 is connected to the ground connection terminal 35 of the tuner unit 1 7, the positive supply input terminal 33 of which is connected to the positive terminal of the battery 46.

The bistable circuit 44 includes a capacitor 49 which is either in a charged state or a discharged state depending upon the state of two NAND gates 50 and 51 of the bistable circuit 44.

The capacitor 49 is in its charged state when the NAND gate 50 has a logic 1 output, and in its discharged state when the NAND gate 50 has a logic 0 output. The output of the NAND gate 51 is the logical opposite of that of the NAND gate 50.

A resistor 52 couples the NAND gate 51 to the base of the transistor 45, and a resistor 53 couples the NAND gate 50 to the capacitor 49 and to the contact 42, so that if the capacitor 49 is charged and the transistor 45 is off, provision of a conducting path between the contacts 42 and 43 by the touch of a finger discharges the capacitor 49 and switches on the transistor 45. A subsequent touching of the contacts 42 and 43 switches the transistor 45 off and recharges the capacitor 49.

The pick-up unit 1 5 has a coil 54 sharply tuned to respond selectively to 20 kilohertz. The response of the coil 54 is amplified in the unit 15 by an amplifier 55 capacitively coupled to the input stage 56 of the timer unit 1 8. The input stage 56 is formed by two NAND gates arranged to provide an all or nothing response to the output of the pick-up unit 1 5, and is capacitively coupled to a bistable latch 57 which is set by an output from the input stage 56 indicative of reception of a 20 kilohertz signal by the coil 54, and can only be reset by "full" signal from a counter 58.The timer unit 18 includes an oscillator 59 which oscillates so as to supply one pulse per 1.76 seconds to the clock input terminal of the counter 58 which produced the "full" signal at a count of 16,384(=2'4). This arrangement provides a timing cycle from setting of the bistable latch 57 to generation of the "full" signal of approximately eight hours. The oscillator 59 runs only during the set state of the latch 57, and the latch 57 is so coupled to the time switch transistor 47 that the time switch transistor 47 conducts only while the latch is in its set state.

The amplifier 14 is formed by two operational amplifiers 60 and 61 in series and an automatic gain control circuit operating on the operational amplifier 60. The output terminal 31 of the tuner unit 1 7 is coupled to the input terminal of the operational amplifier 60, and the output terminal of the operational amplifier 61 is connected to the input terminal 41 of the loudspeaker unit which includes, in addition to the loudspeaker 38 shown in Fig. 3, a loudspeaker 62 connected to the collector of the touch switch transistor 45. The automa tic gain control circuit includes another operational amplifier 63, and the power connections to the four amplifiers 55, 60, 61 and 63 are represented by connections to a block 64 between the positive terminal of the battery 46 and the collector of the touch switch transistor 45.

The remainder of the circuitry of the second embodiment (Fig. 2) is shown in Fig. 5 where items corresponding to the same in Fig. 4 are given corresponding reference numerals.

In Fig. 5, the pick-up unit 1 5 includes two transistors 65 and 66 providing amplification for signals of frequencies up to and including 20 kilohertz. Frequencies above 10 kilohertz are blocked by the filter 20 which consists of two capacitors 67 and 68 and two resistors 69 and 70, and are passed by the filter 21 which includes two capacitors 71 and 72 and a resistor 73, an amplifier circuit including an operational amplifier 74, and a rectifying circuit including a transistor 75 of which the collector is coupled to the switching transistor 47 of the control switch 1 9.

Fig. 6 shows, partly in section, a physical structure incorporating either the embodiment of Figs. 1, 3 and 4 or of Figs. 2, 3 and 5. The physical structure of Fig. 6 comprises two hearing protectors 81 and 82 connected by a headband 83. The hearing protector 81 contains the tuner unit 1 7 and the loudspeaker 38, and the protector 82 contains the loudspeaker 62 and other circuitry. Both protectors 81 and 82 have an outer shell 84 with a mounting plate 85 secured therein.

Four different ear seals are illustrated, namely, a long vane flexible seal 86, a flexible cushion seal 87, a short vane cushion seal 88, and an absorbent, PVC foam filled seal 89.

The headband 83 has a spring 90 surrounded by a foam filling 91 within a PVC cover 92. The spring 90 is anchored at a swivel, e.g. 93, on each shell 84.

An electric cable 94 connects circuitry in the two protectors 81 and 82.

A turning knob 95 is provided for the tuner unit 17 and is mounted in the shell 84 of the protector 81.

The contacts 42 and 43 are mounted in the shell 84 of the protector 82 which also contains a battery charging socket 96.

Interior spaces in the shells 84 are substantially filled with acoustic foam rubber.

Where the cable 94, a shaft for the knob 95, and the contacts 42 and 43 pass through or are mounted in either of the shells 84, acoustic sealing is provided to prevent entry of noise into the shell by way of the apertures in which the cable, shaft and contacts are located.

Claims

1. A portable radio receiver comprising means for receiving, selecting and demodulating radio broadcasts and producing in response thereto an electrical audio frequency signal, electrical audio frequency amplifying means arranged to receive and amplify electrical audio frequency signals produced by the receiving, selecting and demodulating means, means for transducing amplified audio frequency signals produced by the amplifying into sound, inductive pick-up means for receiving an induction field control signal, controlled switching means arranged to control operation of the receiving, selecting and demodulating means and adapted to be controlled in a manner dependent upon reception by the inductive pick-up means of the induction field control signal, and manually controllable switching means arranged to control operation of the said controlled switching means.

2. A receiver according to claim 1, wherein the controlled switching means is adapted to be controlled in a manner dependent upon reception by the inductive pick-up means of the induction field control signal by a timing unit which, for the duration of a timing signal initiated by reception by the pick-up means of the said control signal, holds the controlled switching means in one state thereof in response to which the receiving, selecting and demodulating means is rendered operative, the timing unit at times other than during a timing cycle holding the controlled switching means in another state thereof in response to which the receiving, selecting and demodulating means is rendered inoperative.

3. A receiver according to claim 1, wherein the inductive pick-up means is coupled to the controlled switching means by a filter which passes the induction field cdntroi signal to the controlled switching means so as to hold the controlled switching means in one state thereof in response to which the receiving, selecting and demodulating means is rendered operative, the controlled switching means rendering the receiving, selecting and demodulating means inoperative in the absence of the reception of the induction field control signal by the pick-up means.

4. A receiver according to claim 3, wherein the pick-up means is coupled to the audio frequency amplifying means by a further filter which rejects the induction field control signal but passes a predetermined band of audio frequency signals so that when audio frequency induction field signals in the said predetermined frequency band are received by the pick-up means in the absence of the induction field control signal, corresponding amplified audio frequency signals are transduced into sound by the transducing means.

5. A receiver according to any preceding claim, wherein the manually controllable switching means controls the operative states of the amplifying means and the transducing means.

6. A receiver according to any preceding claim, wherein the receiver is housed in a pair of hearing protectors mechanically coupled to form a hearing protector set and each hearing protector is adapted to operate as an earphone, the two earphones constituting the said transducing means.

7. A receiver according to claim 6, wherein the receiving, selecting and demodulating means includes a variable capacitor provided with a manually operable varying member accessible at the outside of one hearing protector.

8. A receiver according to claim 6 or 7, wherein the manually controllable switching means includes a pair of contacts so mounted in one of the hearing protectors as to be electrically couplable together by bridging manual contact.

9. A receiver according to any one of claims 6 to 8, wherein each hearing protector has a hard cup-like shell of plastics material containing acoustic damping material in addition to the transducing means and electrical circuits, and where elements of the receiver exit from the hearing protectors such elements do so through acoustically sealed apertures in the hard shells.

10. A receiver according to any one of claims 6 to 9, wherein the rim of each sheet is provided with a cushioning acoustic seal.

11. A portable radio receiver substantially as described hereinbefore with reference to Figs.1,3 and 4, or to Figs. 2, 3 and 5 of the accompanyin'g drawings.

12. A portable radio receiver according to claim 11 and substantially as described hereinbefore with reference to Fig. 6 of the accompanying drawings.