GB2228353A - Electrical appliances - Google Patents

Abstract

A device for indicating the disconnection of an electrical appliance from an external power supply, includes an electrical circuit 1 connectable to an external power supply (not shown) across points L and N. The circuit 1 comprises a capacitor 2 which charges up when the circuit 1 is connected to the external power supply. Upon disconnection of the circuit 1 from the external power supply, the capacitor 2 discharges, supplying power to a CMOS integrated circuit 3. The integrated circuit 3 in turn drives a piezo-electric beeper 4, which thus gives an audible indication that the external power supply has been disconnected. The device may be used to signal the automatic switch off of an electrical appliance, eg a kettle. <IMAGE>

Description

IMPROVEMENTS RELATING TO ELECTRICAL APPLIANCES This invention relates to electrical appliances and, in particular, to domestic electrical appliances of the kind which switch-off automatically at the end of a predetermined sequence of operation.

Examples of such appliances include: automatic kettles, which switch off once the water in them has boiled; toasters, which switch-off and pop-up when the toast is toasted a predetermined amount; and coffee-makers, which switch-off when the coffee is made. It is desirable that appliances of this kind be provided with means to indicate to the user that the operative sequence is complete and that the appliance has switched-off.

Known appliances of this kind are often provided with a visual indicator which alerts the user to the fact that the operational sequence has finished; for example, an automatic kettle will commonly have a light located on its handle which comes on when the water in the kettle has boiled and the heating element has switched-off.

A disadvantage of such an indicator is that the user will not see it if he is in a different room from the appliance or if he is in the same room, but not looking at the appliance.

A further disadvantage of such a visual indicator is that the light must stay on until it is noticed by the user and therefore must be provided with some means of connecting it to the external power supply, even though the appliance itself has switched-off.

It is therefore an object of the invention to provide an arrangement to overcome this disadvantage.

According to the present invention there is provided a device for indicating the disconnection of an electrical appliance from an external power supply, the device including an electrical circuit comprising: electronic means for generating an audible signal and an electrical charge storage means chargeable by connection of the appliance to said external power supply and dischargeable upon subsequent disconnection of the appliance from the external power supply; the arrangement being such that upon disconnection of the appliance from the external power supply, the discharging charge storage means provides the signal generating means with sufficient power to generate an audible signal.

Thus the present invention provides an audible indication that an electrical appliance has completed its operative sequence; an indication which can be heard by the user, not only in the room in which the appliance is situated but also in neighbouring rooms. Because it is powered by the charge stored on the charge storage means, the indicator of the present invention has the additional advantage that it will work after the appliance is switched-off, without it being necessary to provide it with a separate connection to an external power supply.

In addition, if the appliance is accidentally disconnected from its external power supply during operation by, for example, its plug being pulled out of a socket, the audible indicator will be able to alert the user to this fact, since it is not dependent on the external power supply for its operation.

In a preferred embodiment of the invention, the charge storage means is a capacitor.

In a further preferred embodiment of the invention the electronic means for generating an audible signal comprises a CMOS integrated circuit and an electro-audio transducer. It is desirable to use a CMOS integrated circuit because CMOS integrated circuits have a lower power consumption "making it possible to limit the size of the capacitor required. It is preferred that the electro-audio transducer is a piezo electric device.

Preferably the electronic means for generating an audible signal comprises means for cutting-off said audible signal after a predetermined period of time, thus enabling that signal to be cut-off before the charge storage means discharges to a point where the sound amplitude and frequency are degraded.

Preferably, the electronic means for generating an audible signal comprises means to generate an intermittent audible signal which is more likely to be heard by the user.

A specific embodiment of the invention will now be described, by way of example only, with reference to the accompanying sole drawing which shows an aerial diagram of the device of the invention.

An electrical circuit, shown generally at 1 is connected to an external power supply (not shown) across points L and N. The circuit 1 comprises a capacitor 2 which charges up when the circuit 1 is connected to an external power supply.

Upon disconnection of the circuit 1 from the external power supply the capacitor 2 discharges, supplying power to a CMOS integrated circuit 3, which in turn drives a piezo electric bleeper 4, thus giving an audible indication that the external power supply has been disconnected.

Resistors 5 and 6 are mains dropping resistors which limit current to a zener regulating circuit comprising diodes 7 and 8, capacitor 9 and zener diode 10 and in which half wave rectification is used to provide a d.c. supply of 15V. The capacitor 2 is prevented from discharging its power to anywhere other than the CMOS integrated circuit 3, on removal of the external power supply, by the diode 8.

The external power supply is applied to the master reset of the CMOS integrated circuit 3 across resistor 11 and capacitor 9 via diode 12. The values of resistor 11 and capacitor 9 are chosen such that sufficient voltage to the master reset of the CMOS integrated circuit 3 is maintained when the external power supply is applied, but this rapidly falls to zero upon removal of the external power supply.

When the external power supply is removed counting at the CMOS integrated circuit 3 begins, with the circuit 3 deriving its power from the charge stored on the capacitor 2. The integrated circuit 3 includes a master oscillator (not shown) which drives the piezo electric bleeper 4. The fundamental frequency of the integrated circuit 3 is determined by resistors 13, 14 and capacitor 15 and values of these are chosen so that the piezo electric bleeper is driven at a frequency of 4kHz.

It is intended that the device of the invention be incorporated inconspicuously into the body of the appliance with which it is intended to be used, for example in the handle of a jug kettle. For this reason, it is important that the number of components in the overall circuit, and their size, be kept to a minimum. It is for this reason that a CMOS integrated circuit is preferred. CMOS integrated circuits operate at very low powers and therefore the use of one in the invention makes it possible to limit the size of the capacitor 2 and thus the device, although any integrated circuit which achieves this could be used.

In order to prevent a deterioration in the amplitude and frequency of the bleeper 4, as the capacitor 2 discharges, the counter of the CMOS integrated circuit 3 is chosen to have an output corresponding to a count of 8192. This count rate ensures that the bleeper is cut off after an interval of 2 seconds and before capacitor 2 discharges to the point where bleep amplitude and frequency are degraded.

The bleeper 4 in circuit 1 is arranged to have an intermittent tone, which is more noticable than a continuous tone, particularly at low sound intensities. This is done by using a further output 16 from the integrated circuit 3 and connecting the output 16 to the bases of transistors 17 and 18 via diode 19.

Output oscillations are fed from pin 20 via base current limit resistor 21 to transistors 17 and 18. A single transistor could be used, but this would require the use of a discharge resistor to discharge the piezo element during each off period of the oscillation and this would affect the sound intensity of the bleeper.

The circuit 1 could be arranged on a printed circuit board to minimize its size or alternatively the physical size of the circuit could be reduced still further by use of surface mount components or thick film technology.

The device of the invention could be used to provide an indication of the operational sequence in a wide variety of appliances in addition to those already mentioned, for example: deep fat fryers, sandwich toasters, tumber dryers, washing machines or any appliance in which it is required that an audible indication be given to a user that the power supply has been cut-off.

Claims (8)

1. A device for indicating the disconnection of an electrical appliance from an external power supply, the device including an electrical circuit comprising: electronic means for generating an audible signal and an electrical charge storage means chargeable by connection of the appliance to said external power supply and dischargeable upon subsequent disconnection of the appliance from the external power supply; the circuit being arranged such that upon disconnection of the appliance from the external power supply, the discharging charge storage means provides the signal generating means with sufficient power to generate an audible signal.

2. A device as claimed in claim 1, wherein the charge storage means is a capacitor.

3. A device as claimed in claim 1 or 2, wherein the electronic means for generating an audible signal comprises a CMOS integrated circuit and an electro-audio transducer.

4. A device as claimed in claim 3, wherein the electro-audio transducer is a piezo electric device.

5. A device as claimed in any preceding claim, wherein the electronic means for generating an audible signal includes means for terminating said audible signal after a predetermined period of time, thereby enabling the signal to be discontinued before the charge storage means discharges to a point where the sound amplitude and frequency are degraded.

6. A device as claimed in preceding claim, wherein the electronic means for generating an audible signal includes means to generate an intermittent audible signal.

7. A device for indicating the disconnection of an electrical appliance from an external power supply, said device being substantially as herein described with reference to the accompanying drawing.

8. An electrical appliance including a device, as claimed in any preceding claim, for indicating the disconnection of the appliance from an external power supply.