CA1226050A - Electrical appliance control - Google Patents

Abstract

ABSTRACT
A transmitter, for electrical appliance control by transmitting digital control signals on a power main, comprises two releasably connected parts, a first part comprising m actuators to initiate the generation of m control signals, and the second part containing generating means for the control signals, and a selector for selec-ting m out of n control signals. The selector is hidden by the first part when the parts are joined together and may be adjusted to select different groups of m control signals from the n possible signals. All n control sign-nals can be produced, in groups of upto m signals for each condition of the selector. Means are also provided to monitor the main to achieve transmitter queueing dep-endent upon the selector settings at the transmitters.

Description

J

BACKGROUND Ox THE INVENTION.

This invention relates to electrical appliance control and particularly concerns a transmitter or controller for the remote control of slave units.
US Patent No. 1592971 discloses a remote control system for electrical appliances. That system comprises a power main having a plurality of pyre outlets, at least one slave unit having a power input coupled to the main and operable to control the supply of power to an appliance, and a transmitter for controlling the or each slave unit, the transmitter comprising: means for generating selectively digital instruction signals at least some of which contain an address of a slave unit; and means I for modulating said digital signal onto the power main, and the or each slave unit comprising- means for de-fining the address of that unit; means for receiving the digital signal from the main and means for rev sponging to that signal when the address of the de-fining means and any address contained in the digital signal have a predetermined correspondence, Such a system will hereinafter be referred to as a "system as herein defined", Preferably the address in such a system includes an area code or address defining an area I

2.
building or home in which the system is to operate.
In one practical form, the system has various types of -transmitters such as command consoles timers and computer interfaces all of which are designed to transmit a digitally encoded 12QKHz signal onto a dour eschew or other power line. This signal is received by various types of slave units (receivers) such as lamp dimmers, Hall switch divers and appliance modules which can then turn on or off appliances an dim or brighten lamps upon receipt of the appropriate code from a transmitter.
All types of transmitters send the same code format so that a receiver will respond to codes from any type of transmitter in the system. A control system for a vehicle is disclosed in US
specification No. 1607816 (Belgian Specification No. 874722) and Rich uses digital control signals containing addresses. over, the power supply and signal path are distinct, although in one cable, so this system is not applicable directly to a domestic control system as disclosed in US Specification No. 1592971. Each trays-miller is preset to communicate only with selected local processing wits.
An object of the present invention is to provide a transmitter (or controller high can be designed for controlling thy same types of receiver as do the transmitters described in the above mentioned Patent and which has improved facilities I I

SIJMMARY OF THE INVENTION
An aspic of the invention is as follows:
A transmitter for controlling slave units by means of a digital control signal transmitted onto a 5 power main, the transmitter comprising:
means for inputting an instruction to define said digital control signals;
means for storing said instruction;
means for generating, and transmitting onto said 10 power main, said digital control signal corresponding to the stored instruction;
timing means for delaying the transmission of said digital control signal until the timing means has completed the timing of a given time;
means for monitoring the power main for detecting digital signals and noise of a given property; and means for causing the timing means to recommence its timing when the monitoring means detects signals of said given property, whereby the transmission of said 20 digital control signal is delayed until the main has been free of signals of said given property for said given time.

I OOZE
4.

For example, the given time may be eight half cycles. The given property is preferably frequency range and may be detected as the existence of more than a given number o-f cycles within a given time slot or slots in a half-cycle of the mains. The given slot or slots is or are to be chosen to coincide with possible transmit-soon time, e.g. a one millisecond slot three times each half-cycle corresponding approximately to the zero-crossings of each phase of a 3-phase system.
The design of the circuit is therefore prefer-ably such that no two transmitters will try to engage the main together. In the above example, each trays-miller continually monitors the line for signals or noise) and will not transmit until the main has been free for eight mains half cycles. Also, in the pro-furred embodiment, all transmitters waiting to engage the line will not try to do so -together. All trays-millers in such a system are synchronized by any data on the line and the "Priority" of each transmitter is set by -the above-mentioned address selector switch such that no transmitter will engage the line until it is its "turn". The effect is intended that trays-millers on the same phase will not interfere provided the selector switch settings are different, and even if two transmitters have the same setting, they will not interfere if they are on different phases. How-ever, once a transmitter has engaged the mains it by-passes the polling system and can continue to trays-mix signals without having to reengage the main each time, (unless data is keyed in at a rate slower than the transmission rate).

I

GRIEF DESCRIPTION OF THE DRAWINGS.
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:
Figure 1 is a perspective and partially cut-away view of a plug-in keyboard for an appliance control transmitter;
Figure 2 is a perspective view of the main body of the transmitter;
Figure 3 is a circuit diagram of a first circuit within the main body;
Figure 4 is a circuit diagram of a second air-cult within the main body; and Figure 5 Audi spa show a block diagram of an integrated circuit within the main body.

I

DESCRIPTION OF A PREFERRED E.~lBODI~lE~T.
One practical form of the transmitter or con-troller discussed in said US Patent 1,592,971 is designed to control up to sixteen receiver modules (slave units) by pressing any of the sixteen numb bier (or Dress keys, to create a nurser (address) code, follotved by a junction key, (e.g. On, Off, Bright to create a function.
The transmitter described hereinbelow and chutney in Figures 1 and 2 has four rocker type switches 1 and its circuitry is designed such that pressing one side of a rocker twill send a number (address) code, automatically followed by the 'ON' code, and pressing the other side of the rocker will send a no or (address) code, automatically followed by the 'OFF' code.
Receiver modules can thus be turned 'ON' or 'OFF' with a single key operation, which is a convenience to the user. As shown in the drawings, the trays-miller is designed for use on 120V domestic mains in the United States of America, but can easily be adapted for other circumstances.
The transmitter is extremely compact, being designed to fit into a standard wall outlet, no-placing an existing wall switch. For this reason, it only has four address ON~OFF"rocker switches. It is still possible to control up to sixteen receiver modules, however, as it has a 16-position selector switch 2 (Figure 2) which allows the user to set which group of receiver modules is to be controlled, i.e. it the selector switch is set in one position, the four rocker switches can turn on and off mod-vies having addresses 1, 2, 3 and 4. If it is set to the next position, the rocker switches will control modules 2, 3, 4 and 5 If set to the fourteenth position, modules 14, 15, 16 and 1 can be controlled, and so on, Thus, any sequence of four successive module addresses can be controlled, the selector switch 2 setting the start address of the sequence.
The switches 1 are carried by a keyboard section 3 (Figure 1) which is plugged into a main body (Fig-use 2), several versions of keyboard section being available so as to give options such as Bright-Dim rocker switch, or an All Lights On All Off rocker switch, Looking at the keyboard section in more detail it includes a simple printed circuit board from which project eight pins 6. The outer two pins connect to zero and negative power lines respectively~ithin body and to respective sides of the rocker switches.
In detail, the outer pins connect to printed circuit strips 7 which extend below the respective sides of the rocker switches and carry domed switching mom-biers 8 to be actuated by the rockers to make a con-section between one or other of strips 7 and Dyne of four lines associated with respective switches. These four lines are connected to four of the remaining six pins 6, depending upon the function desired for each rocker switch.
Before considering the circuitry of the trays-miller various features will be described.
One feature is an option which can be selected to give momentary On or momentary Off control, ire.
a module will turn 'ON' when the key is pressed, and turn 'OFF' when the key is released, or vice versa.
This feature is particularly useful when interfacing to a remote sensor when designe~-to ye plunge into the socket 12.
which the keyboard section normally plugs into, i.e.
it can be arranged that the transmitter sends the code to turn on a heater when a thermostat (which is plugged into the micro-controller) closes and sends I
8.
the code to -turn off the heater when the thermostat opens.
US Patent l,59~,971 describes trays-millers which send a one millisecond burst of data immediately after each zero crossing, for use in 3-phase circuit. It can be shown, however, that there is a 30 phase difference between 120V and 208V and between 120V and 277V in the USE, There-Gore a one millisecond burst of data coupled from the 120V line to the 208V or 277V line will not over-lap the zero crossing of the 208V or 277V line. 208V
and 277V slave units or receivers, therefore, cannot be controlled from existing transmitters without using a repeater/coupler which is designed to receive a signal from the 120V phases and retransmit it onto the 208V or 277V phases, retimed so as to coincide with the correct zero crossing.
The present embodiment, however, contains an option which allows it to send data over the full half cycle of the mains (instead of a one millisecond burst). The signal will therefore overlap the zero crossing points of the 208V or 277V lines. This, therefore, eliminates the need fox a repeater in systems which only use such transmitters, The present embodiment also allows the user to press keys simultaneously and if keys 1-ON, 2-ON,

3-ON, 4-ON were pressed, the digital control signal code actually sent would define:- 1, 2, 3, 4, ON.
This cuts down transmission time and allows group dimming. The reason why group dimming is possible is that all receiver modules (slave units) will remain addressed until reset by any number which follows a function or command. Thus, signals 2, 3, 4, ON
would switch on units 1 to 4 and if that signal is then followed by a command 'DOW', any dimming circuits in units 1 to 4 would operate.
A further feature of this new transmitter is its ability to continuously monitor the power main for digital control signals (or noise) and hold back any transmissions until the main is free. Even if several such transmitters have had keys pressed while another was transmitting, and are therefore waiting to transmit, they will not all try to trays-mix together. All such transmitters are synchrony iced by any data on the line, and contain a self polling system (determined by the selector switch 2), so that no two transmitters with different selector switch settings on any one phase will inter-lore with each other, and even transmitters with the same selector switch setting will not interfere if on different phases.
This self synchronizing interrupt facility Sian important feature for any control system which has multiple controllers accessing data onto a single wire pair, and has applications outside domestic electrical appliance control systems.
Returning now to details of construction of the transmitter, Figure 2 shows that the main body 4 includes a further rotary selector switch 9 by which one can set a specific house code, corresponding to the house code set at the slave units.
Within the main body 4 are two printed air-cult boards Andy Asian in Figures 3 and 4.
The board 10 carries the fixed contacts of house code and switch code selectors 2 and 3, an eight way connector 12 for pins 6, components C7, C8, C9 and RFC2 ion use in generating the 120KHz carrier and an integrated circuit 11 (shown in Figure 5). Options mentioned above are selected by links Lo, Lo and Lo.

10 .
The board l~aprovides diodes DO, Do end Do for creating the supply voltages ODD (-Ye) and VSS
(Ox) for -the circuitry. Also provided are coupon-ens, including transistors Try and TRY and transform-or TCl, or injecting 120KHz digital control signals from circuit 11 onto the mains and for receiving signals from the mains at Lo, Lo. From mains line Lo is obtained a voltage TRIG fed to circuit 11 for the detection of mains zero-crossings.
Turning now to Figure 5, seven key sensing blocks A to G are provided, connected to key con-sections Al to I Clue, KF2 and KID. In the example shown in Figure 3, KF2 is left unconnected and is thus unused in this example, but could be connected so that its block F replaces one other of the blocks.
Of the six blocks then available four are used at any one time ! depending upon which keyboard section is plugged into the main body.
Blocks Al to K4 are all used for entering Number On/Number Off functions, i.e. for issuing codes comprising addresses together with an 'ON' or 'OF' commando Block Al is used for entering the ON/OFF command for the first device number in a sequence of four K2 is used for the second device number and so on for K3 and K4. The blocks A to are identical, so only block A is shown in detail.
Referring to block A, the key connection or input Al normally sits at a voltage of VDD/2, This volt-age is too low to turn on OR gate 57 via its high threshold path Hit, and too high to urn off the OR
gate via its low -threshold path Lot, A switch closure to either supply rail will give a '1' from OR gate 57 which is then denounced by denounce logic 30 and provides a pulse (TIC) - another pulse, TED
is produced when Al is OPENED, but assume for the ~%~

if .
moment that input OVA is floating so that TED is not enabled and will be ignored. use after PI
D-type bistable circuit 58 is clocked via delay circuit 51 and if K1 was closed to OVA the output Q of D-type bistable circuit 53 will be a '1'; this will allow TIC to set an 'ON' bistable circuit 5 (via guts Andy). If K1 was closed to ODD, the Q output of circuit 58 would be '0', setting 'OFF' bistable 62 (via gates 63 and I). Block A therefore recognizes a switch closure to OX to represent, ON"
(ire, address number 1 and command ON and a switch closure to ODD to represent "1, OFF". Similarly block B reeognises a switch closure to OX to repro-sent "2, ON" and a switch closure to ODD to repros-en "2, OFF". Likewise or blocks C and D tire.
ON, OFF functions for keys K3 and K4).
Blocks E, F and G are provided to issue commands only, ire, corl~ands which apply to all, or groups of, slave units designed to respond to those commands (assuming, as always, that the house code associated with the command is the correct one Block E gives an "All lights on" command for a closure to OX and an "All units off" command for a closure to ODD.
Block F gives an "All lights on" command for an OX
I closure and an "All lights off" command for a ODD
closure.
Now, if OVA pin is tied to OVA TED is enabled and so therefore are gates Andy 66. This has the effect that the bistable circuit 59 or 62 clocked on opening switch K1, is the opposite to that docked on closing K1, i.e. if closing K1 to OX represents "1, ON", opening K1 from OX represents "1, OFF", And if closing K1 to ODD represents "1, OFF", open-in K1 from ODD represents "1, ON". Similarly blocks B, C and D give momentary 'ON' control when closing 1 '. .
and opening K2, K3 or K4 -to and from OX, and moment-cry 'OFF' control when closing and opening K2, K3 or K4 to and from ODD. Block E will signal "All lights on" for closure to OX and "All units of"
when KFl is opened from OVA and "All units off" for closure to ODD and "All lights on" when opened from ODD. Block F will signal "All lights on" when KF2 is closed to OX and "All lights off" when KF2 is opened from OVA and "All lights off" for closure to ODD and "All lights on" when opened from ODD.
Input KID, block 'G' and its associated de-bounce circuitry signals a closure to OX to provide a 'Bright' command and a closure to ODD to provide a 'Dim' command. This circuitry is unaffected by OPAL
The fourteen possible "number, ON/OFF" out-puts and function outputs (All lights on, All units off, All lights off, Bright and Dim), are fed to fourteen (only six shown) 3-input gates I whose outlets go to a 14-input OR gate 6?, which enables gate 53 which passes a clock signal to a 14-bit recirculating shift register 19 (Fig. pa). This register has a '1' circulating through it, a '1' being fed back in-to it by gate I
when all its outputs To to To are 'O'. The outputs of the register serve to enable each input AND
gate 52 in turn (looking to see if any key has been pressed). Signals "OFF EN " (Off enable), IRON EN"
(On enable), and "FUNCTION EN" (Function enable) are all at '1' at this time, enabling the RAND gates 52.
Therefore, if any key is pressed, the output of the gate I goes high and stops the clock to the register 19, with one of the outputs To to T14 then being a '1'. If one of outputs To to To (associated with blocks A to D) is a '1', this is decoded by OR gates 13, 14, 15 and 16, whose outputs address a 1 of I
13.
block decoder 54 This block decoder 54, together with a 1 of 16 decoder 55 address a 256 bit rum 56.
This 1 o-f 16 decoder is addressed by the 4 bits of the address selector switch 2 of Figure 2. The out-puts of gates 13, 14, 15 and 16 represent K1 ('ON' or 'OFF'), Cowan' or 'Off'), K3 and K4 etc., rest pectively, and the contents of the 256 bit rum are such that if the selector switch is set to the binary equivalent of decimal 1, the output of the block decoder will be the binary equivalent of deal-met 1 for To, decimal 2 for To, 3 for To and 4 for To (i.e. keys K1 to K4 correspond to numbers 1 to 4).
If the selector switch is set to the binary equip-alert of decimal 2, then the outputs of the block decoder will correspond to 2, 3, and 5 for To, To, To and To and so on, ire the selector switch and the 256 bit rum allow the four input keys to select any of 16 codes in groups of 4 consecutive numbers, dependent on the setting of the selector switch.
It, however, one of the outputs To to T14 is a '1' (instead of To to To) this represents a lung-lion only ("all lights on", "All lights off", "All units off", "Bright or "Dim"), and is decoded by a function decoder 26. The outputs of the function decoder are "Orbed" with the outputs of the block decoder and applied to five of the preset inputs of a 9-stage recirculating shift register 20, (the other four inputs are connected to the house code selector switch). The code representing the key pressed, together with the selected House Code, is loaded into the shift register by a signal (To +
TO) from a gate 17. Gate 18 will generate a TO
signal when signal COOK from gate 67 is obtained (i.e. a key has been pressed) together with signal BUSY being a '1' (not transmitting) and together 1'1 .
with signal TON being a '1' no other transmitter is transmitting). If the key that was pressed was a function (To to T14), then this function will be loaded into the 9-bit shift register, TO will no-set whichever input logic (blocks A to F) had generated Coequal arc as more than one key may have been pressed, the recirculating register 19 may now continue to look for another coincidence.
If the next coincidence found indicates that a "number, ON OF key was pressed, (To to T8j, then the number will be loaded into register 20 by TO, and one of the inputs to gates 21 and 22 will be a '1'. If a "Number, ON" key was pressed (To, To, To, To), gate 21 will reset a bistable circuit 23, This will make "OFF EN" and "FUNCTION EN" a 'O';
therefore the recirculating register 19 will only look for further "Number, On" key presses, (keys may be pressed simultaneously so there may be up to four "Number-On" coincidences. Each such number code is shifted into and then out from register 20 in turn and transmitted in the same fashion as desk cried in the above-mentioned patent.
If a "Number, Off" key was pressed, gate 22 will reset bistable circuit Sue that recirculating register 19 will only look for further "Number-Off"
key presses. Aster transmitting all "Number-On"
numbers or all "Number-Off" numbers, it is required to transmit "ON" or "OFF". Yen bistable 23 or 24 was reset, "FUNCTION EN" went to a '0' and one input of gate 25 went to a '1'; therefore when all numbers have been transmitted (Conical and BUSY), TO is pro-duped and the junction decode block 26 applies either the "ON" or the "OFF" code to register 20 and this is loaded by TO (via gate 17).
It is therefore evident that if keys "l-ON", "2-ON", "3-ON" and "4-ON" are pressed simultaneously (or within 200 milliseconds of each other the codes actually transmitted will be "1, I, 3, 4, ON", This cuts down transmission time and allows "Group Dimming"
5 as all four slave units will remain addressed once so activated, The transmission circuitry has been discussed in the above-mentioned patent, In summary, a state counter 27 controls when the data is shifted out from register 20 (gate 28), ire, no 'Clock' signal in States 0-3 and State 4 (Start Code Insertion) and no 'Clock' signals in even states, ire, 2 (complement data). In States O - 3, 120 HUT is grated to the serial output (gate 29) and in State the output is disabled (gate 30); therefore code 1110 is produced (start code) in States 0 to I, In Odd states (2j true data is grated to the output (gate 31) and in even states 2, complement data is grated through gates 32 and 33, The output signal envelope is gent crated by a timing decoder 34 with option input OPB1 (at gate 35) selecting either three one millisecond bursts (as with the above-mentioned patent, or one burst encompassing a full half cycle, If option input OPB2 is held at a '1', Q32 of the state counter 27 will be held at a '1' and as this so applied to bit stable circuit 36, a-t the end of State 22 (decoded by gate 37), END will be set which will stop the trays-mission (gate 30), ire, only one complete code is sent, If, however, OPB2 is a '0', the sixth stage of the state counter will have Q = 'O' which will prevent END from being set; therefore the whole code will be transmitted again, The second time round, however, the sixth stage of -the state counter will have toggled and so END will be set, stopping the transmission, Codes are thus transmitted Tess, 16.
BUSY is not reset until State 6 (bistable 38) which has the effect of inserting zero's in the first six mains half cycles following the end of a transmission, These options are chosen using links Lo and Lo at instate input OPB1 and 2 (Figure 3). with no links, a single message with 3 one millisecond bursts is produced; with link Lo, a double transmission is produced with 3 one millisecond bursts; and with link Lo, a single message is produced for one half-cycle, A six stage binary counter 39 monitors the mains during signal envelope time, looking for signals from other transmitters or noise of a frequency which could lock out a transmission. For this purpose the recurrent one millisecond envelope signal EN
is used. A one millisecond burst of signal is recog-nosed by a decode of 63 which sets bistable 40 and I removes transmit enable (THEN) from gate 18 prevent-in any transmission while a signal from another transmitter is on the line. All transmitters in a system therefore will be prevented from transmitting whilst another transmitter has the line. A decode of 63 means that a signal (or noise) is detected with a frequency of at least 64KHz. The transmitter which has the line, however, has "BUSY" set, which sets bistable circuit 41 to produce "ENGAGED" and locks out 'DECODE 63' and prevents bistable circuit 40 I from being set, At the end of transmission, the state counter 27 will be at State 22. All other transmitters in the system, however, vowel have had their state counter set to 31 by "DECODE 63". There-fore, on the next state, all transmitters in a system will have their state counters synchronized a-t State 1. On State 8, bistable 40 is reset taking signal Lo to a 'O', but if several transmitters had been waiting to transmit it would not be desirable for them all to try to transmit at State 1. Therefore, each trays-I miller in a system will not get a signal "THEN" until the output of the state counter coincides with the setting of the selector switch (signal "oOINC2"), ire, at the end of transmission all 17.
other transmitters are at State 31. All trays-millers are synchronized and when State 8 is reached bistable circuit 40 is reset on all transmitters, The state counter keeps counting and if on a paretic-ular transmitter the-selector switch is set Tess, 3, the state counter will count 9, lo, if, 12, 13, 14, 15,l, 2, 3, at which time "KINK" will go to a 'l', giving a 'l' at the output of gate 42 which will produce a TOTS resetting the state counter to lo State l and starting the transmission, This trays-mission will reset all other transmitters to State 31 again, and at the end of this transmission if another transmitter has its selector switch set to say 5, then its state counter will count to State 5 at which time "KINK" will be produced and the transmitter will be able to take the line.
Finally, it is noted that there is a zero crossing detector 57 for producing a signal TRIG' at the mains zero crossings for controlling the timing of various of the functions set out above.

Claims (12)

CLAIMS:

1. A transmitter for controlling slave units by means of a digital control signal transmitted onto a power main, the transmitter comprising:
means for inputting an instruction to define said digital control signals;
means for storing said instruction;
means for generating, and transmitting onto said power main, said digital control signal corresponding to the stored instruction;
timing means for delaying the transmission of said digital control signal until the timing means has completed the timing of a given time;
means for monitoring the power main for detecting digital signals and noise of a given property; and means for causing the timing means to recommence its timing when the monitoring means detects signals of said given property, whereby the transmission of said digital control signal is delayed until the main has been free of signals of said given property for said given time.

2. A transmitter according to Claim 1, and comprising means for defining said time as a given number of mains half-cycles.

3. A transmitter according to Claim 2, wherein the monitoring means is operable to detect frequency range as said given property.

4. A transmitter according to Claim 1, wherein the monitoring means comprises means for counting the number of cycles modulated on the main within at least one given time slot in each cycle of the main to determine that the main its free when the count is less than a given value.

5. A transmitter according to Claim 4, wherein said at least one time slot substantially coincides with a time slot in which said digital control signal is transmitted relative to the main.

6. A transmitter according to Claim 1, wherein the timing means comprises a counter, the causing means is means coupled to the monitoring means for resetting the counter each time said signal or noise of said given property is detected, the transmitter comprising means for causing said counter to count when said digital control signal is ready for transmission, and adjustable means for determining the count to be reached by said counter before transmission occurs, whereby the priority of the transmitter to transmit is determined by said adjustable means.

7. A transmitter according to Claim 1, wherein the inputting means comprise:
m actuating means for selecting m slaves; and storage means for storing substantially simultaneous actuations of the actuating means for generating said digital control signal in a form which has a portion comprising the addresses of all slave units for which a given command has been entered by the actuating means but excluding the command itself, and a second portion consisting of said given command as a single command.

8. A transmitter according to Claim 7, wherein two different commands can be entered by said actuating means, and comprising means for organizing the storage of the actuations in the storage means according to the different commands so as to be operable to produce from a group of actuations two digital control signals, one comprising one command with the associated selected addresses and the other comprising the other command with the associated selected addresses.

9. A transmitter according to Claim 1 and comprising:
a transmission option selectable either to emit a digital control signal in three bursts within a half-cycle of the main (to couple with all phases of a three-phase system), or to emit a digital control signal in a burst existing for substantially the whole of one half-cycle of the main.

10. A transmitter according to Claim 1 for controlling at least m slave units, the transmitter comprising:
a first part comprising m actuating means and;
a second part releasable connectable to said first part and comprising digital control signal generating means having x (>m) input means so as to be responsive to the operation of x distinct actuating means; and coupling means for coupling said m actuating means to m of said x input means for generating said digital control signal with a form depending upon which of the m actuators has been operated, wherein the first part can be removed and replaced by another first part with m actuating means and with coupling means for coupling to a different m of said x input means, whereby the second part will generate digital control signals that depend upon the coupling means of first part.

11. A transmitter according to Claim 10, wherein said second part includes selector means for selectively altering the functioning of the transmitter, the selector means being hidden by the first part in normal use but being accessible when the first part is removed.

12. A transmitter according to Claim 11, wherein the selector means comprises means for selecting an area code to be incorporated into the digital control signal for activating only slave units able to recognize that area code.