We have now devised a digital controller which is of simple construction but which is effective in use to control a computer via its analogue joystick port.

In accordance with this invention there is provided an electrical switch assembly in the form of a digital controller, comprising actuating means and switching means controlled by the actuating means, the actuating means having first, second and third conditions in which the switching means connects a supply rail of the assembly to an output terminal of the assembly through respective paths of different resistance values. Typically the first, second and third conditions of the actuating means represent, respectively, a centre position and positions displaced from said centre position in opposite directions along an axis.

The switch assembly may be in the form of a joystick, which can be connected to the analogue port of a computer: it then simulates the action of a potentiometer but in low resolution as the resistance value is sampled at three points only, as compared with the full range sweep that a potentiometer would provide. Embodiments of this invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of an electrical switch assembly in accordance with this invention; and FIGURE 2 is a circuit diagram of a digital joystick controller in accordance with the invention.

Referring to Figure 1, an electrical switch assembly in accordance with this invention comprises a switching means 10 and an actuating means 20 controlling the switching means. The actuating means 20 has first, second and third conditions, in which the switching means 10 connects a supply rail SR to an output terminal OPl through respective paths 21,22,23 of different resistance values. The actuating means 20 also has

fourth, fifth and sixth conditions, in which the switching means 10 connects the supply rail SR to a second output terminal OP2 through respective paths 24,25,26 of different resistance values. In the example schematically illustrated in Figure 1, the actuating means comprises two pairs of push¬ buttons 31,32 and 33,34 arranged on orthogonal axes. Depression of push-button 31 or 32 represents movement up or down, whilst depression of neither button represents a central position along the vertical axis (respectively ^" the second, third and first conditions of the actuating means) . Depression of push-button 33 or 34 represents movement to the left or right, whilst depression of neither button represents a central position along the horizontal axis (respectively the fifth, sixth and fourth conditions of the actuating means) . Alternatively, instead of four push-buttons operated by individual fingers of the user, the actuating means may comprise four microswitches arranged at 90° intervals around a joystick control lever, and operated according to the direction in which the lever is moved. Figure 2 is a circuit diagram should the two pairs of push-button switches or microswitches SW1, SW2 and S 3, S 4. A first output terminal OPl is connected by switch SW2 to a positive rail +ve, and is also connected to this rail by resistors Rl . and R5 in series. A switch device UIC is connected across resistor R5 and has its control terminal connected to the positive rail by a resistor R2 and to ground by the switch SW1. Similarly, a second output terminal 0P2 is connected by switch SW4 to the positive rail, and is also connected to this rail by resistors R6 and R3 in series. A switch device UlA is connected across resistor R6 and has its control terminal connected to the positive rail by a resistor R4 and to ground by switch S 3.

It will be appreciated that the controller is, in use, connected to a computer by a cable, which has one wire connected to a positive supply in the computer, another connected to ground in the computer and another two (the signal inputs from OPl and OP2) connected by shunt resistors to ground in the computer but providing the digital input signals to the computer.

For example in the case of a joystick controller, in the central position of the joystick control lever, the switches SW1 to SW4 are all open. Considering one axis of movement, with switches SW1 and SW2 both open, output terminal OPl is connected to the positive rail through resistor Rl only (the control terminal of switch U1C being high so that this switch is closed to short-circuit resistor R5) . If the control lever is moved in one direction to close switch SW1, then switch U1C is opened and terminal OPl is connected to the positive rail through both resistors R5 and Rl. If the control lever is moved in the opposite direction, thus opening switch SW1 and closing switch SW2, then terminal OPl is connected directly to the positive rail. Thus in the centre position of the control lever, the output terminal OPl is connected to the positive rail by a path of first resistance value Rl, whilst if the lever is moved in one direction terminal OPl is connected to the positive rail by a path of higher resistance value Rl plus R5, and if the lever is moved in the opposite direction terminal OPl is connected to the positive rail by a path of lower resistance value (substantially zero) . The output terminal OP2 provides similar digital output signals in response to movement of the control lever along the perpendicular axis.