FIELD OF THE INVENTION The present invention relates to user input and control devices for use with computers, mobile phones and the like.

BACKGROUND OF THE INVENTION

Graphic displays incorporating touch screens have become an extremely convenient and popular means of human interaction with machines. In particular, the last decade has seen the popularisation of touch-activated mobile phones and tablet computers, such as the iPhone, iPad and similar Android devices.

While very simple to use and extremely flexible, touch screens suffer the limitation that it is generally necessary to look at them to use them effectively. This is obviously a huge problem for people with vision problems, and such screens are not ideal for controlling devices where it is undesirable to divert attention from another task, such as driving a car. Such displays are also not optimal for providing continuous controls. For example a volume control knob can be depicted on the screen and "turned" by finger gesture, but the operation of such controls is not highly satisfactory compared, for example, to a traditional knob which can be operated purely by feel. Knobs have many qualities desirable for certain applications, for example when used as a volume control an end-stop can provide indication to the user that the control has reached its maximum or minimum point of travel.

Touch screens have their own advantages over conventional controls, such as the ability to instantly re-label a control if its function changes.

Certain prior art systems have been developed which combine physical controls with graphic displays. For example, US patent 5,841 ,428 to Jaeger describes rotary circuit control devices with changeable graphics. In that invention, a knob is mounted in front of a display, such as an LCD panel, in such a way that rotating the knob controls circuitry which transmits the rotational activity to the system being controlled. In US patent 7,671 ,851 to Pryor, knobs are mounted on a panel comprising a projection screen, graphics are projected form the rear, and a camera detects rotation of the knob. Similar systems apply these same principles to other types of physical control devices such as pressbutton switches and sliding controls (such as faders).

Sadly, the prior art systems are complex, potentially unreliable and expensive. For use in mass-market consumer goods, there is a need for a low cost and reliable system of providing physical control devices which can be dynamically labeled by an electronic display device.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a low cost and reliable system of providing physical control devices which can be dynamically labeled by an electronic display device.

Accordingly, the present invention provides a graphic display device; at least one physical control positioned within the viewing area of said display device, said physical control comprising at least one magnet; and at least one magnetometer positioned behind said display device so that the magnetic field of said magnet can be detected by said magnetometer.

In some embodiments, the invention comprises multiple magnetometers arranged to provide sensing of the magnetic field of the magnet. Preferably, two magnetometers are arranged to sense orthogonal fields giving the invention the ability to provide unambiguous output over a large range of movement of the physical control, for example when rotating the control and hence its associated magnet through 360 degrees. In some embodiments a single multi-axis magnetometer such as those typically used in electronic compasses can be utilised with good results.

The invention can be applied to a wide variety of physical controls, including but not limited to rotary controls (knobs), sliding linear controls (faders), press-buttons, slide switches, joysticks or even three dimensional controls. DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the invention will now be described with reference to the drawings in which Fig. 1 illustrates press-button, rotary and sliding controls according to the invention.

Referring now to Fig. 1 , the realisation of press-button, rotary and sliding controls according to the invention will be described.

Press-button switch

3a/4a/5a/7a shows a plan view of the press-button switch components. 3b/4b/5b/7b and 6 is a side sectional view of the press-button switch components. In this „ embodiment, housing 4a 4b is fixed to the face of LCD 1. Switch cap 3a/3b fits movably over housing 4a/4b. Magnet 5a/5b is mounted to cap 3a/3b via standoff 6 which positions magnet 5a 5b about 2mm away from the face of LCD1. Spring 7a/7b forces switch cap 3a/3b away from LCD 1. On the back side (non-viewing side) of LCD 1 printed circuit board (PCB) 8 mounts magnetometer 9 as close as possible to magnet 5a/5b. When the user presses switch cap 3a/3b, magnet 5a/5b moves closer to magnetometer 9 which detects the increase in the magnetic flux and signals the switch depression. The associated control system preferably causes the image displayed on LCD 1 to change to indicate to the user that the switch has changed state, for example by illuminating switch cap 3a/3b with a different colour.

Sliding control

10/11 a/11 b/12a/12b illustrate a sliding control according to the invention. The operator knob 11 a/11b is retained moveably against the face of LCD 1 by baseplate 2 which is preferably a clear panel with a suitable cutout 10 in which operator knob 1 1 a/11 b slides. 12a/12b is a magnet attached to operator knob 11 a/11 b.

Magnetometer 13 is mounted behind LCD 1 and detects the field of magnet 12b. Magnetometer 13 in the preferred embodiment is a three-axis sensing device, such as MAG3100 made by Freescale Semiconductor and is mounted slightly off-axis relative to the path of magnet 12a/12b. As the slider and hence the magnet is moved, two or three axes of the magnetometer can be utilised to sense its position. A suitable algorithm combines more than one axis's data, which allows

disambiguation of position and more accurate position calculation than using a single axis sensor, in which case position would need to be deduced purely from the flux strength measured. Using this embodiment it has been found that a single multi-axis sensor can reliably measure movement over a much larger distance than using a single axis sensor. If measurement of even greater travel distance is required, the invention can be further adapted to use two or more sensors to track the magnet's position. In some embodiments of the invention, magnetometer 13 is rotated so that its sensing axes are not perpendicular or parallel to the field of magnet 12b. For example, the magnetometer can be rotated 45 degrees so that the direction of the flux cuts diagonally across the magnetometer. In some cases this provides more distinctive outputs, which are more easily processed, than if the magnet and magnetometer are aligned. Note also that the magnetometer need not be offset from the centerline of the sliding track, the preferred embodiment uses an offset to improve detection accuracy but other positioning can be used without departing from the scope of the invention.

Rotary knob control

14a/14b are plan and sectional views of the knob body of this embodiment. Flange 15a 15b retains the knob within a suitable opening in base plate 2. Magnet 16a/16b is mounted in the centre of flange 15a/15b, oriented so that the polarity of the magnetic field rotates as the knob is rotated. Magnetometer 17 is located behind LCD 1 and as close as possible to magnet 17. When the knob and hence the magnet are rotated, magnetometer 17 detects the rotation of the magnetic field. The use of at least two axes of the magnetometer enables unambiguous detection of a full 360 degree rotation, using the well-known algorithm used for compass implementation, for example. It should be noted that if a single axis magnetometer is used, only a limited range of rotation (less than 180 degrees) can be unambiguously detected.

Calibration and other refinements

Because the operation of the invention relies on magnetic fields, extraneous factors such as the earth's magnetic field or effect of other hard-iron or soft-iron

perturbations can influence the values read from the input devices of the invention. If such errors exceed the design limits of the system to which the invention is providing input, the invention can be further adapted to provide corrections, using techniques well known in the art, for example when magnetometers are used as compasses in mobile phones. In some embodiments, a reference magnetometer is used to provide nulling of the effects of ambient magnetic fields. Likewise, conventional calibration techniques can be utilised for calibrating ranges and linearity of controls.

Furthermore, in some embodiments the invention can be adapted to compensate for crosstalk between multiple input devices in close proximity.

Of course, the foregoing describe only a few of the many possible embodiments of the invention and those skilled in the art will see ample opportunity to vary the practising of the invention without departing from its scope.

For example, input devices are not limited to the ones described herein, they could be any shape or size. Although the input devices are described as having one magnet and one magnetometer, the invention can be modified to use more than one of either without departing from its scope.

Any of the control devices of the invention can be further adapted to provide different touch and feel characteristics, for example by providing detents so that movement of a knob or slider is dicky rather than smooth, or by providing lubricant or other medium to alter the feel of their movement.

Whereas the preferred embodiments of the invention are described as utilising a mounting plate to retain and position certain controls, the invention can also be usefully practiced without such a mounting plate, using controls which are fixed to the touch screen by permanent or temporary adhesive, by suction, gravity, loop-and- hook fastener, magnetism or any other method.

The controls can also be independent or interlocking. For example, controls can be adapted to that they click together in such a way that users can configure their own custom layouts.

It will also be understood that the physical controls of the invention can be transparent, translucent, opaque or any combination. If the control is transparent, images generated by the display device can be used to impart an interesting and useful image into the control device. If translucent, the display can be used to illuminate the control with colour. The invention can be practised as an assembly comprising controls, display screen and sensors, or it can be practised as an accessory comprising controls and sensors into which a display screen, such as a tablet computer, is inserted.

It will also be understood that the invention can be used with a display device which includes a touch screen, in which case areas can be left free of controls and accessible so that the touch screen can be utilized as a touch input device.