The control unit can be powered from the mains, from a battery, or from a solar cell. The battery can ^' be a replaceable battery or a rechargable battery. Desirably, however, the apparatus is powered by a combination of a solar panel and a rechargable battery. In this case, circuitry is preferably provided to ensure that the rechargable batteries are regularly discharged to a significant low level to avoid damage thereto. This can be achieved by ensuring that during day time (as sensed by a photoelectric cell or comparable sensor) the batteries are discharged via a resistor to a low level for example 10% of their capacity, such discharge ceasing at nightfall (or upon reaching said low level) to ensure that the batteries are sufficiently well charged for operation throughout the night if necessary.

-2- Preferably, the control unit is adapted to operate automatically in response to external stimuli and, optionally in a manual mode. The automatic mode can, when used in relation to blinds, be light sensitive, ie.be susceptible to the onset of night or the dawn. In these circumstances blinds can be closed when night falls and opened when day breaks. Manual control can be used during the day, for example, for sunshading or for reducing glare, for example in an office where a VDU is in use.

The slave units can conveniently be servo motors and in which case slipping clutches can be incorporated to avoid overload thereof.

The control unit can have circuitry arranged to issue pulses of a length dependent upon the value of a controllable variable in the control unit, the or each slave servo motor having a feedback potentiometer driven thereby, which potentiometer regulates the length of reference pulses, the control circuitry being adapted to sense difference between the length of said reference pulses and said pulses from the control unit and to drive the motor in a direction tending to reduce such difference.

The control circuitry preferably includes a precision servo integrated circuit, for example of the type ZN 419CE as manufactured by Ferranti Semiconductors. The remote units can be connected to

the control unit by radio or comparable links. Preferably, however the servo units are connected by wires. A number of servo units can be connected to the control unit in parallel. To enable the servo unit to operate all the servo units simultaneously, it is important that the control unit be provided with a powerful output amplifier with its output power transistors protected by appropriate heat sinks.

For opening and closing vertical blinds, that is

10 to say rotating the individual slats about their vertical axes, a unit described as above can operate using a gear wheel 20 engaging the usual chain which is normally provided for manual operation. By providing a motor in a fixed position relative to the --- ^■ chain wheel on the blind track, a loope of chain can be arranged to extend between a chain wheel on the motor shaft and the chain wheel on the track. In the case of a blind which can be drawn, that is to say the individual slats moved longitudinally of the 0 track between one or two storage positions adjacent one or both lateral edges of the opening and an operative position wherein they are arranged at regular intervals across the opening. A typical way of achieving this is to have a draw cord which is in 5 the form of a U-shaped length of cord or similar material hanging from the rail When manually operating the user pulls one or other limbs of the U

to move the slats between their two positions. It has been appreciated that the motor/servo arrangement previously described in relation to; the opening and closing of the slats can be used to effect drawing movement of the blind. Incidentally it will be appreciated that this applies to any blinds such as a Venetian blind or the like.

However, problems have been met in that various different blind manufacturers provide cords of different material and of different thicknesses and it has not proved easy to select an appropriate winch wheel which, when driven by a motor aforesaid will firmly and regularly operate the cord to draw the blind. t is an object of the invention to eliminate or reduce the above problem.

The invention further provides an actuating device for a cord operated article including a motor and a winch wheel around which the cord is arranged, wherein the winch wheel has an annular groove having axially spaced apart faces, each face being provided with projections extending towards the other face.

The two faces can be arranged to define a V-sectioned annular groove. The projections can be in the form of radial ribs. Preferably the projections on one side are offset relative to the projections on the other side so that a cord engaging the groove follows a sinuous path.

Alternatively, the annular groove can be rectangular in cross-section, the projections themselves defining a generally V-shaped entry ^' slot adjacent the periphery of the wheel. As an alternative to the ribs, projections on one or both sides of the space can be in the form of a grid of ribs projecting from the face.

Preferably, the structure is provided adjacent the winch wheel which guides the cord to the winch wheel. Such structure can include respective guides for each run of the cord, one guide being disposed on one radial side of the wheel and the other being disposed opposite the other radial side of the winch wheel. Preferably, the cord is passed through the one aperture and then crosses to engage the other side of the winch wheel, leaves the one side of the winch wheel and exits via the other of the guides.

Between the guides there can be a smoothly curved sliding surface to reduce friction on the interior of the cord. The guides can be apertures entering a casing within which the motor and winch wheel are enclosed.

The invention will be described further, by way of example, with reference to the accompanying drawings wherein:-

Fig. 1 is a schematic view illustrating a preferred control apparatus of the invention;

Fig. 2 is a circuit diagram of a main control

unit of the apparatus; and

Fig. 3 is a circuit diagram of a remote unit of the apparatus.

Fig. 4 is a schematic view illustrating four different versions of modified preferred apparatus of the invention;

Fig. 5 is a more detailed circuit diagram of a transmitter of the Mark I and Mark III versions;

Fig. 6 is a similar circuit diagram of a Mark I controller;

Fig. 7 is a view of the Mark II transmitter; Fig. 8 is a circuit diagram of the Mark II receiver;

Fig, 9 is a circuit diagram showing the Mark III receiver;

Fig. 10 is a circuit diagram illustrating the several positioning circuit; and

Fig. 11 shows the switching circuit for the Mark II and IV; Fig. 12 is a schematic view illustrating a preferred blind arrangement of the invention having a facility for both slat pivoting and blind drawing;

Fig.13 is an enlarged cross-sectional view illustrating an operating box of the blind of Fig. 12; Fig.14 is a cross-section view on line 14-14 of Fig. 13

Fig.15 is a view on the direction of Arrow 15-15 in Fig. 13 ;

-7- Fig. 16 is a plan view of a winch wheel of the box shown in Fig. 13; and

Fig. 17 is a view similar to Fig. 15 but showing a possible variation in the form of the winch wheel. A first preferred control apparatus of the invention (Figs. 1 to 3) comprises a main control unit 10 and a number of remote units 11 connected to the main control unit 10 in parallel by connecting wires 12. Connecting wires 12 can be replaced by a radio or comparable remote link, but in this case each individual remote unit 11 would require its own power supply. Each remote unit 11 is mechanically connected to a blind actuating mechanism 13 which is only shown schematically and will not be described in any detail. In a typical vertical blind a shaft extends along a lower or upper end of the blind (not shown) and can be connected by a belt or gearing to an output shaft of a servo motor within the control unit. It will be appreciated that in controlling a blind between its fully closed and fully open positions a motor within the remote unit 11 will have to rotate between the extreme positions and also be able to stop intermediate those positions in order that there can be full control of the blind position. The main control unit 10 can have a solar panel 14 connected thereto or mounted on a main face thereof. The main control units can have a light sensor 15, and charge socket 16 (when rechargable batteries are

-8- used) an on/off switch 17, a manual/automatic switch

18 and a manual open/close switch 19.

Although the remote units have been described as being connected to a blind mechanism, it will be appreciated that such remote units can be connected to curtain opening devices, window controls or any other remote apparatus which needs to be adjusted.

Referring now to Fig. 2, it will be seen that the top half of the circuit diagram controls the automatic operation of the unit in response to light and darkness. The light level is sensed by the sensor 15 which activates the components of the lower half of the circuit diagram (that is to say the pulse width variator 20) to either its maximum or minimum value depending on whether the sensor has sensed the onset of night or the onset of day. When the change over switch 18 is placed on manual, the position of the potentiometer 19 influences the variator 20 to produce a chain of pulses whose width is a value dependent upon the position of the potentiometer 19. A minimum length of pulse corresponds to "blinds closed" and a maximum length pulse correspondes to "blinds open".

Turning now to Fig. 3, it will be seen that the motor 21 has a potentiometer 22 connected to a shaft driven thereby. The range of the potentiometer 22 can conveniently extend over twenty turns of the shaft which may be directly connected to the motor or to

gearing associated therewith. The value of the potentiometer 22 in accordance with associated components varies a pulse generator within an integrated circuit 23 (ZN 409CE manufactured by Ferranti Semiconductors Limited) which compares the length of pulses so generated with the control pulses being generated by the circuitry 20. The difference between the two lengths of pulse is used to generate an output current which is amplified in the circuitry indicated at 24 and fed to the motor 21 in such a sense as to drive the motor in a direction tending to reduce the difference between the two lengths of pulse. Thus, in effect, the motor follows the position of the control potentiometer 19 with a slightly amplified effect. For example, if the control potentiometer 19 is a rotatable control a single turn of the potentiometer 19 from 0 to 360° can correspond to twenty rotations of the shaft of potentiometer 22. This in turn can amount to twenty revolutions of the motor shaft or, if gearing is used twenty revolutions of an output shaft of the servo mechanism. A typical pulse separation of 18 milliseconds is appropriate and the length of pulse can vary from 1 to 2 milliseconds, the mid point being set at 1.5 milliseconds.

The pulse width generator or variator 20 is used for driving the ZN 409CE (or ZN 7409) integrated circuit. The frame rate is generated by timer 1 and

the frequency is adjusted by VR 1 (100k) so that the time between pulses is 18 milliseconds. VR2 in conjunction with the blind control potentiometer (4.7k) is then used to control the output pulse over the range 1 to 2 milliseconds. VR3 (4.7k) is set so that the mid point of VR2 corresponds to an output pulse of 1.5 milliseconds. The servo actuator control unit uses the ZN 409CE (or ZN 7409) integrated circuit as a linear pulse width amplifier for controlling the 6 volt servo motor 21 driven through the power amplifier circuit 24 enabling the unit to be control from 4 to 6 servo actuators in parallel depending on the torque loading of the blind or other equipment to be controlled. The position of the servo is regulated by an equalising potentiometer driven from the output gear of the servo motor.

The servo units of the apparatus of the invention are modifications of conventional servo units. Each conventional servo unit comprises a motor, and a gear train having an output shaft which carries an actuator. The motor is usually low-powered and the output shaft limited to less than a single revolution. The servo unit used in the present invention has a much more powerful motor and the output shaft of the gear train is able to rotate continuously in either direction. A twenty turn potentiometer is rotatably coupled to the output shaft. This potentiometer is the 5K potentiometer

illustrated at 22 in Fig. 3. The use of the more powerful motor and the continuously movable output shaft enables that shaft to rotate through twenty turns and to have a relatively high torque up to 0.36 NM. This is quite sufficient to actuate most blind/curtain mechanisms.

As will be appreciated, this modification of a known servo unit means that there is a quite expensive potentiometer added to the relatively simple straightforward and cheap servo unit. To this end, therefore, in an installation which includes, for example, six servo units only two of those units will have the twenty turn potentiometers and these two potentiometers will be connected in parallel to give a mean value of 2.5K. The circuitry of Fig. 3 will operate perfectly well with the potentiometer 22 having a value of 5K. As all the motors are connected in parallel the two potentiometers in the aforesaid two servo units effect control of all the motors. It would be possible to operate with only a single motor provided with a potentiometer, but the use of two servos to guard against failure of that one servo unit.

For a system which was even more safe, or perhaps in a system having many relays four of the motors could be connected in series parallel to give a nett resistance of 5κ.

If any one of the servos should become stuck,

for example due to an obstruction on the blind or a very stiff mechanism its motor can overheat and burn out. However, the motors and the system are chosen so that the maximum stall current to be taken by the motor is less than the maximum current which the system can supply without overload. In the system it is preferred that the output allots one amp for each motor. With the motor selected to have a stall current of 850 mi11lamps this gives a degree of safety which enables the whole system to continue operating even if one motor should stall and burn out. In a typical industrial installation wherein 12 servos are to be operated from a common control box there will be 8 x 3 amp power transistors. Four of these transistors will drive the motor in one sense and will be equivalent to the transistors Dl. The other four will drive the motors in the opposite direction and will be the equivalent of the transistors marked D2 in Fig. 3. This arrangement gives a potential of 12 amps flowing in each direction. Thus, there is a current of 1 amp available for each unit and therefore a stalled motor places no unbearable current gain on the system. In the illustrated circuitry four power transistors gives a maximum current (in each direction) of 6 amps which is ample to drive six servo units which could accommodate most domestic blinds requirements.

Fig. 4 illustrates schematically, four practical further embodiments of the control system of the invention. These are generally designated Mark I,

Mark II, Mark III and Mark IV. In each case, the overall control principles are the same, but there is a difference in complexity and a difference in function.

Referring firstly to the Mark I system, it will be seen that this consists of a motor unit 50 which is comparable in most respects to the previously described motor unit. The motor unit 50 is connected to a control unit 51 which, in use, is mounted on a blind track adjacent the motor. The unit 51 is connected by cable 52 to a handset 53. The hand set 53 can be close to the blind, or can be remote therefrom, the cable 52 being of significant length.

The Mark I system is adapted to control a single blind or like structure, and in essentially the same manner as described in relation to Figs. 1 to 3. Indeed, the control from the control unit 51 to the motor 50 is essentially identical to that described in relation to the aforesaid figures.. The Mark I system is adapted only to effect control of the blind between two positions. In the case of a vertical blind this will be rotation of its slats about a vertical axis. For the sake of brevity such a control of a blind is referred to as "tilt". It should be appreciated that in relation to horizontal

blinds or roller blinds a similar consideration applies, that is to say there is only a single movement between a closed and an open position under the "tilt" control. In the Mark I configuration the handset, or controller 53 has two push buttons 54 and 55 which can be designated "open" and "closed" respectivel .

In the Mark II configuration, a motor 56 is controlled from a control unit 57 connected to a handset 58. The control unit is also connected to a unit 59 which can be integral part of the control unit 57, but, as the control unit 57 is normally arranged at the top of a blind at a high level can be in the form of a secondary control unit or "pendant" at a convenient operating level, for example below or adjacent the window or comparable aperture to be controlled by the blind in question. In the Mark II version the handset 58 is connected to the control unit 57 by means of an infra-red transmitter/receiver system and the handset 58 has a single operating button 60. The system incorporated within the control unit 57 can be such as to allow the motor 56 to be controlled according to ambient light (a "automatic" system) or to be controlled manually (i.e. via the pendant 59) or remotely as by the handset 58. Pendant 59 has switches 61 which allow transfer between these various conditions. Circuitry appropriate to this arrangement is shown in Fig.11.

In the Mark III system the motor 62 is regulated by a control unit 63 connected to a handset 64. The motor and control unit will be mounted on a track of a blind or like article to be controlled, whilst the handset can be adjacent or remote therefrom connected by the line 65. The Mark III system is a simple doubling-up of the Mark I system and therefore the handset has four press buttons arranged in two pairs 66 and 67. The button 66 serves exacetly the same purpose as the buttons 54,55. The buttons 67 serve to control a "park" function of the blind control. In the Mark III embodiment there is, as well as the motor 62, a supplementary motor 68 whose function is ^* to move the blind between a closed and a withdrawn position. This sort of control is most appropriate to a vertical blind, but is also applicable to a Venetian type horizontal blind. Thus, whilst the earlier control of "open and closed" relates to the attitude of the slats in relation to their own axis, the "park" facility relates to the withdrawal of the slats from their disposed to a storage position. This facility allows a vertical blind to be completely withdrawn for open access to or open light from a window or the like, or allows a Venetian blind to be raised above its window or comparative opening.

The Mark IV system is comparable in many ways to the Mark II system in that it applies that system to both types of control, that is to say the tilt control

and the "park" control. To this end, the Mark IV includes a motor 70 for the tilt system and a motor 71 for the "park" system. The motors 70,71 are controlled from a controller 72 which is connected firstly to a handset 73 via an infra-red link 74 and to a switch unit 75. The switch unit 75 is comparable to the pendant 59 and enables the Mark IV system to be switched between the various modes. As in the Mark II system, the controller 72 will have automatic, (i.e. solar cell) control, remote control, in the handset 73, or local control via the unit 75. The handset 73 has a tilt switch 76 and a park switch 77.

The following circuit diagrams illustrate the various systems in rather more detail as follows. In each of the transmitters and receivers an encoder/decoder chip is used which offers several thousand different codes which can be selectable by the various imputs. Control in this manner is not illustrated, but this type of control can be used if several blinds or other items have to be controlled in a room or the like. Blind selection will be effected by, for example, a numeric or alphanumeric keyboard. Each blind would be allocated a code and the encoder/decoder chips, accommodated one within the handset and one within the controller of each system respectively would ensure that when the code for a particular blind or other item was inserted caused operation of that blind via its appropriate

controller. The various control units 57 and 72 include the IR receivers which are in turn connected to additional control circuity which passes on signals to the appropriate motors. Although not shown, each of the control units 57 or 72 can control additional motors. Similar features can be incorporated in the Mark I and III embodiment.

Referring to the Mark I system, it should be mentioned that this is the simplest system. The handset 53 has two buttons 54 and 55, one for open and one for closed. The handset 53 is connected by cables 52 to the controller 51 which in turn regulates the motor 50. The open and closed positions of the blinds are set using circuitry described in relation to Figs. 1 to 3 associated with the control unit 51. If the user wishes to close the blinds he presses button 55 and the blinds move towards their closed position. If the user wishes to open the blinds button 54 is pressed and the blind moves towards its open position. in both the Mark I and the Mark III embodiment

(circuit diagrams in Figs 5 and 6 and 9, individual switches are used to control the opening and closing movements.

The difference between the Mark III system and the Mark I system is that in the Mark III system there is a motor 62 for the tilt function and a motor 68 for the. "park" system. Each movement being essentially controlled by a pair of buttons.

Fig. 7 illustrates a circuitry for the pendant 59 and 75 of the Mark II and Mark IV systems. The circuitry is essentially a collection of four switches which allow the controller 57/72 to operate in an appropriate mode.

In the Mark IV system there is one button 76 for the tilt function and one button 77 for the "park" function. The circuitry is such that once the button 76 has been depressed the blind moves towards its other position. That is to say if it is closed it goes towards an open and if it is open it goes towards closed. Button 77 controls the "park" facility in a comparable manner. Interlocks between the buttons and the motors ensure that once the button has been pressed it is not possible to override the control by repressing the button. The blind must move fully to the extent of its movement before operation of the button again has any effect thereon.

In each of the control units, the or each motor is associated with a potentiometer and that potentiometer is connected into the control circuitry. The control circuitry, as described in relation to the embodiment of Figs. I to 3 has circuitry generating a reference frequency, and a further circuit including that rotatable potentiometer (or, indeed, any other movable electric component could be used of course) which generates a signal having a different frequency. The arrangement is such that the motor is driven in a

direction which reduces the difference in frequency between said signals. Once the signals are equal then the power to the motor is cut off.

In the Mark I and Mark III transmitter there is incorporated a 32 command pulse modulation transmitter. Four commands are used depending on whether or not the tilt or draw modes are both present. The transmitter actuates an infra-red transmitting diode. in the tilt mode a select line is made which effectively brings a logic one onto the output pins which is smoothed and balanced by a resistor network. Tuning is effective via a potentiometer. The signal is then fed to an RC network which supplies the base current to a pre-amplifier transistor. When this transistor switch is on, voltage at its emitter via the collector is then connected to the base of the power output transistor. Current from the power output transistor is then fed to the IR transmitter diode and the pulse of radiation is transmitted at a set frequency. Separate individual lines are selected to give required logic depending upon modes selected. Using this type of circuit an effective range can be up to 40 feet giving ample distance to activate receiver via user command.

The Mark I/III controller uses a high gain pre-amplifier which is designed to process infra-red signals. The signals are received via a diode coupled

to the pre-amplifier. The receiver is tuned to the transmitter using the Rl.

In the output stage two outputs are used to drive a switching transistor which in turn drive the gates of the power output mosfet bridge. The mosfets are used to supply the current to the servo motor. The mosfet bridge operates in a manner comparable to the previously described circuitry allowing power to be distributed to several motors simultaneously, but allowing power overload to be achieved without danger. If the mosfets are overloaded they simply cease to conduct without suffering damage. Once the overloadis removed the mosfets regain their function. The switching transistor is effectively used to switch individual signals simultaneously but not together. When two signals are applied at the same time the switching transistor prevents any high current draw across the mosfet therefore protecting the motor servo system. The Mark II/IV transmitter system uses a circuit which includes a pair of input AND gates driving an emitter diode giving only a singleOperation on the ouput pulse, that is open or closed or park or deploy. The handset is one pushed to make switch handling both operations.

Voltage to the switch is clamped by a Zener diode operating at 5.1 volts. This is the integrator circuit operating voltage. When the switch is made,

voltage is applied via a resistor network to the IR remitting diode and to the collector of switching transistor when a logic level of one appears at pin 4, switching on transistor 1. Depressing the switch a second time alters the logic level of pin 4, switching off transistor 1 and switches on transistor 2. The indicator diode 2 is connected to pin 2 of the integrator circuit with a logic one constantly when the switch is pressed giving better a voltage indication. Tuning of the circuit is achieved by a variable resistor 1 capacitor combination connected to the output pin 4 of the integrator circuit, thus setting the frequency of the transmission.

The control unit of the Mark II/IV system uses a receiver diode which receives and detects the signal, the signal is then smoothed and filtered and fed to the base of a transistor. This transistor switches on and feeds a smooth signal to the input of an operational amplifier which in turn provides an output at one of its pins. Further amplification occurs in the operational amplifier. The output signal is then fed to the input of 358A and uses the threshold detector, then being rectified and smoothed and fed via the collector of transistor 2 and then to pi 3 of a bistaple, that is to say the clock input. When the switch on the handset is depressed the signal appears at the clock input which in turn supplies the required logic at the output to drive

the servo. The direction of drive of the servo is determined by the circuitry i.e. whether or not BC109 is switched on or off.

Referring now to Fig. 12 it will be seen that a blind arrangement 25 is of the vertical type and includes a rail 26 and a plurality of hanging slats 27. Rotation of the slats about their vertical axes is effected by the means of a chain 28 and lateral movement over the slats between their storage and their operative position, that is to say a "drawing" movement is effected by means of a U-shaped length of cord 29. For operating both the chain 28 and the cord 29 a control box 30 is provided secured to structure adjacent the blind opening. Figs. 13 and 14 illustrate the box 30 in more detail. It will be seen that the box contains a motor and servo 31 which operates a chain wheel 32 to drive the chain 28. Operation of this servo is in precisely the same manner as has been previously described. The box also contains a second motor 33 which drives a winch wheel 34. Winch wheel 34 (see Figs. 15 and 16) is made from plastics material and has an annular groove 35 which is engaged by the cord 29. In order to allow the wheel 34 to accommodate different types of cord and different thicknesses of cord the groove 35 is provided with formations which create a generally V-shaped entry to the groove so that a thinner cord can go further towards the centre

and a thicker cord remain further from the centre. In the preferred embodiment this is achieved by the surfaces of the groove defining a generally V-shaped annular opening and each surface having inwardly extending radial ribs 36, 37. Looking at Fig. E it will be seen that the ribs 36 and 37 on each side of the groove are offset so as to constrain the cord to a somewhat sinesoidal configuration. This increases the winch wheels' grip on the cord and discourages slippage.

Figs. 17 and 18 illustrate alternative forms which the formations on the winch wheel can take. Fig. 17 shows how instead of the ribs 36,37 a grid of upstanding ribs 38 can be provided on each face of the winch wheel. By having the two grids offset the cord entering the groove between this is caused to take up a sinezoidal configuration for the reasons mentioned aforesaid.

Fig. 18 shows how the groove 35 in the winch wheel 34 can be rectangular, but ribs 39 can be provided whose outer parts 40 are tapered to create an inwardly pointing wedge-shaped entry which forms the gripping function on cords of various diameters. Fig. 14 illustrates a further advantageous arrangement which ensures a good wrap of the cord 29 around the winch wheel 34. Here it will be seen that the top of the box 30 has two guides in the form of apertures 41,42. Aperture 41 is (in the drawing)

above one radial edge of the wheel 34 and aperture 42 is above the diametrically opposite edge of the wheel. The cord entering via aperture 41 crosses and enters the winch wheel on the side below aperture 42 then passes around the wheel and leaves the wheel from its edge below aperture 41, crosses back and exits via aperture 42. This crossing of the cord between the inlet guide apertures and the wheel forms a greater wrap of the cord around the wheel and reduces the possibility of slippage. In order to reduce friction between the inner edges of the two limbs of the cord as they past through the guide apertures 41, 42 is smoothly rounded guide body 43 is provided between the apertures 41 and 42. In operation, the box is firmly fixed and the cord 29 is arranged to be relatively tensioned between the rail 26 and the box 30. In this condition operation of the motor servo 33 is sufficient to cause the winch wheel 34 to operate the cords in order to draw the blind slats between their two positions. As mentioned elsewhere in the specification such control can be in response to signals from a hand held control unit controlling the motor via wire or by an infrared remote control or the like. The invention is not limited to the precise details of the foregoing and variations may be made thereto, for example the number of turns available from the servo motor can be varied widely depending

upon the apparatus or installation which needs to be remotely actuated. For example, the number of turns can vary from a high number, wherein a motor is required, for example to open or close a door, or can be a fraction of a turn when using, for example, a pivoted arm to control a window or the like.

The links between the control unit and the remote unit can be by radio or other remote transmission means provided that such remote units have their own power supply.

The power of the output amplifier 25 can be varied to suit the number of remote units which are to be operated simultaneously in a wired system. Many other variations are possible.