Abstract:
An electrical apparatus having at least one parametrizable function and which includes at least one potentiometer having an actuation member, cooperating with notched indexation devices demarcating several discrete positions of the actuation member. Each discrete position corresponds to a desired value of a parameter. An analogue/digital conversion and interpretation circuit receives an analogue voltage delivered by the potentiometer, dependent on the discrete position taken by the actuation member, and delivers a digital signal representative of the position of the actuation member and hence of the desired value of the parameter.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a reduced cost electrical apparatus having parametrizable function. 
     DISCUSSION OF THE BACKGROUND 
     A large number of electrical apparatuses possess a parametrizable function, this signifying that the user of the apparatus can allocate to a parameter a value chosen from among several possible values and that the apparatus takes this value into account in its operation. The apparatus then generally has one or more actuation members which the user can move in such a way as to make it take a discrete position chosen from several positions. The actuation member can be a control button with rotary or linear movement, which can be actuated manually, either directly or, for buttons of very small size, by way of a small screwdriver; the control button is accessible to the user from outside the shroud of the apparatus and the various discrete positions which it can take are labelled on the shroud of the apparatus. 
     For example, in a timer, the parametrizable functions may be the duration of the timing or an operational mode. The range of values for the timing can, for example, lie between 0.06 seconds and 30 hours. The operational mode relates to the operation of the relay or relays which the timer contains. Several operational modes exist and amongst the most widely used are delayed switch-on or the complementary thereof. In the first mode, the timing begins when the timer is switched on and the relay changes state at the end of timing and in the second mode, the relay changes state at switch-on and retains this state throughout the duration of the timing before reverting to its original state at the end of timing. 
     The allocating of a value to a parameter is achieved either by virtue of a switch with several positions, so as to define for example an operational mode or a range of values of a parameter (range of durations for a timer), or by way of a potentiometer with fine adjustment so as to define an accurate value of a parameter (adjustment of duration within the chosen range). 
     For example, one can imagine a timer with three operational modes, six ranges of durations, and fine adjustment within each range of duration. Such a timer is represented in FIG. 1 (referenced  10 ). If it were constructed according to the principles of the known technique, its front face would carry three control buttons: 
     the upper button  12  would actuate a switch with three positions making it possible to chose one of three possible modes of operation labelled by the letters A, B and C; 
     the central button  14  would actuate a switch with six positions making it possible to define six possible ranges of duration, labelled on the box by indications representing (for example) the maximum value of duration possible for each range; 
     the lower button  16  would actuate a fine-adjustment potentiometer, graduated from 1 to 10 (for example), allowing continuous adjustment of the duration within the range selected by the button  14 . 
     The orifices  18  at the base of the front face of the timer allow access to screws for binding electrical wires via which the timer can be connected to an electrical installation in which it achieves its function. 
     The switches which select the ranges of parameters or the operational modes may be expensive, especially if they must possess a considerable number of positions. They are in general devised so as to provide directly in binary form a digital signal controlling the electronic circuits which serve to establish the operation of the timer. A switch having a number of positions N which is strictly less than 2 p  provides a digital signal of p bits. The larger N is, the larger p must be and the more expensive is the switch. 
     This is all the more true if the switches have to be miniaturized. Typically, the width of the timer represented in FIG. 1 could be less than 2 centimetres, and the control buttons  12 ,  14 , and  16 , as well as the switches and potentiometer which are behind the buttons, do not exceed one centimetre in diameter. 
     On the other hand, the larger the number N of positions of the switch, the more expensive the electronic circuit (microcontroller type) which ensures the operation of the apparatus is liable to be, owing to the fact that this circuit must possess p inputs reserved for the link with the switch. 
     SUMMARY OF THE INVENTION 
     The invention aims to diminish these drawbacks while contriving matters such that the user has a practically unchanged perception of the operation of the apparatus. 
     To accomplish this, the present invention proposes an electrical apparatus having at least one parametrizable function, characterized in that it comprises at least one potentiometer having an actuation member, cooperating with notched indexation means, these indexation means demarcating several discrete positions of the actuation member, each position corresponding to a desired value of a parameter, means of analogue/digital conversion and interpretation receiving an analogue voltage delivered by the potentiometer, dependent on the discrete position taken by the actuation member and delivering a digital signal representative of the position of the actuation member and hence of the desired value of the parameter, this digital signal serving as parametrization control signal for the apparatus. 
     Thus, according to the invention, the switch for selecting parameter, range of parameters, or operational mode, is physically replaced by an indexation potentiometer. This potentiometer, supplied with a voltage, delivers an analogue signal, and it is within the electronics of the apparatus that this signal is converted into a digital value (that which in the prior art was delivered by a switch) representing the index on which the actuation member of the potentiometer is positioned. Hence, the variation in the resistance of the potentiometer is harnessed in order to determine the indexed position on which the actuation member has been placed. It will be noted that the analogue/digital conversion can form part of the microcontroller which manages the entire operation of the apparatus, so that a single microcontroller input is then required to achieve the link with the potentiometer regardless of the number N of indexed positions which may be taken by the actuation member of the potentiometer. 
     The potentiometer, even when provided with notched indexation means, is less expensive than a switch once the number of indexed positions exceeds 3 or 4. 
     The user does not perceive any difference relative to the apparatuses which he customarily knows: the control buttons remain identical and the marking of the positions can remain unchanged; the sensation of turning a switch remains present by virtue of the notches of the indexation means. 
     If the potentiometer is sufficiently accurate and linear, and if it is supplied with a sufficiently accurate voltage, the means of analogue/digital conversion and interpretation may comprise a straightforward analogue/digital converter which receives the analogue voltage and which delivers directly the digital signal representative of the position of the actuation member. 
     If the potentiometer is nearer the bottom of the range, and in particular if it is not linear or not sufficiently linear (whereas one wishes to distribute the indexed positions very regularly), the means of analogue/digital conversion and interpretation may comprise not only an analogue/digital converter which receives the analogue voltage and which delivers an intermediate digital signal which directly represents the position of a slider of the potentiometer, but also a decoding device which receives this intermediate digital signal and which transposes it into a digital signal representative of one actuation member position from among N indexed positions. In this case, it will be understood that the intermediate digital signal can comprise m bits, with m greater than the number p of bits defining one from among N positions. 
     To simplify the construction, one may envisage the notched indexation means as forming part of the potentiometer. 
     To diminish the consequences of the uncertainty in the exact position of the slider with respect to the resistive track, it is possible for the resistive track to take the form of discontinuous resistive lands separated by conductive lands. 
     If the apparatus comprises several potentiometers, it is preferable to provide a multiplexer inserted between the potentiometers and the means of analogue/digital conversion and interpretation, thereby making it possible to avoid increasing the number of analogue/digital converters. 
     From the mechanical point of view, the indexation means can comprise a first indexation means integral with the actuation member and a second indexation means carried by a shroud of the apparatus. 
     In order for the switching from one discrete position to another to occur in a crisp and reliable manner, it is preferable for the cooperation between the indexation means to be of elastic type, that is to say that a certain restoring force compels the actuation member to stabilize on one of the indexed positions, without resting between two positions. 
     One of the two indexation means can comprise at least one lug and the second indexation means several notches, the lug becoming housed in one of the notches. Or conversely, there are several lugs and one notch, the notch becoming applied to one of the lugs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become apparent on reading the following description illustrated by the appended figures which represent: 
     FIG. 1, a timer in which the invention may be incorporated; 
     FIG. 2, a lateral section through the shroud of the apparatus, showing the incorporation of an indexation potentiometer in the front face of this shroud; 
     FIGS. 3 a ,  3   b ,  3   c , respectively in perspective view, in rear view (from inside the shroud), and in longitudinal section, the actuation member; 
     FIG. 4, a horizontal section showing the opening in the front wall of the apparatus, in which opening may be formed means of indexing the control of the potentiometer; 
     FIG. 5, a rear view of the front wall of the shroud of the apparatus, also showing these indexation means; 
     FIG. 6, a variant embodiment of the indexation means; 
     FIG. 7, an indexed actuation member of linear type; 
     FIG. 8, an electrical diagram explaining the electrical operation of the apparatus; 
     FIG. 9, a variant electrical diagram using a multiplexer for several indexed potentiometers; 
     FIG. 10, diagrammatically a potentiometer with resistive track formed by discontinuous resistive lands; 
     FIG. 11, a curve illustrating the relative variation in resistance as a function of the position of the slider of the potentiometer of FIG. 10; 
     FIG. 12, an exploded view of a potentiometer including the notched indexation means. 
    
    
     These figures merely represent exemplary embodiments of the apparatus according to the invention; other variants are conceivable without departing from the scope of the invention. These figures are not to the same scale for the sake of clarity. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For simplicity, the invention will be described with regard to a timer such as that which has been described with regard to FIG. 1, it being understood that apparatuses fulfilling other parametrizable functions may use the invention profitably. 
     The exterior appearance and the functionalities of the timer can be exactly those which have already been described with regard to FIG. 1, that is to say, in this example, three possible operational modes, six ranges of duration, and continuous adjustment of duration within a selected range. However instead of the control buttons  12  and  14  being actuation members of switches, they become control members of notched potentiometers. The control button  16  is still the actuation member of a continuous-adjustment potentiometer. 
     Before explaining the principal of electrical operation of control by notched potentiometers, a possible exemplary mechanical construction of these potentiometers will be given, such as they are incorporated into the apparatus. It will be understood that the indexation of the potentiometer can be carried out on the potentiometer itself or on its actuation member, and it is this last solution which will be described more precisely. It makes it possible to use on the one hand a fairly inexpensive potentiometer and on the other hand an indexed actuation member which could either be used for a switch (conventional solution) or for a potentiometer (solution according to the invention). 
     FIG. 2 represents a lateral section through the apparatus, together with at least one potentiometer and its indexation control member. 
     The apparatus  10  comprises a shroud  1  with a front wall  2 , a potentiometer  3  placed inside the shroud, and an actuation member  4  of the potentiometer  3 , accessible from outside the shroud  1  so that an operator can manipulate it. The actuation member  4  is situated on the front face  2  but other positions could be envisaged. It can project with respect to the front face, then accessible directly by hand, or be slightly set back behind the front face, then accessible via a screwdriver. 
     The actuation member  4  comprises a first part  40  in the shape of a cylindrical button which can be actuated from outside the shroud  1  and this first part  40  is extended via a second part  41  in the shape of a rod which projects inside the shroud  1  towards the potentiometer  3 . 
     The rod  41  terminates in an end  43  which is intended for actuating the slider  31  of the potentiometer  3 . The end  43  of the rod  41  can be cross-shaped, flat or canted and is able to penetrate into an orifice  32  of appropriate geometry of the slider  31  of the potentiometer, in such a way that the rotation of the button  40  causes the rotation of the slider. The potentiometer is not represented in detail since it may be any type of potentiometer, including a very low quality and hence very low cost potentiometer. Typically, use will be made of a straightforward potentiometer with continuous annular resistive track, on which will rub a rotationally moveable slider. 
     The shroud  1  of the apparatus possesses an opening  21 , visible in FIG. 2, for allowing through the rod  41 . Indexation means may be accommodated in this opening as will be seen. 
     The actuation member  4  which passes through the opening  21  is preferably equipped with means  42  for snap-fastening into the shroud  1 . These snap-fastening means  42  comprise, for example, one or more elastic tabs  42   a  each terminating in a projecting element  42 , for example in the shape of a flange, so as to achieve translational immobilization of the actuation member  4  when it has been inserted into the opening  21 . 
     In the example described, the snap-fastening means  42   a ,  42   b  are integral with the button  40  but it would have been possible to envisage them being integral with the rod  41 . 
     Represented in greater detail in FIGS. 3 a ,  3   b  and  3   c  are respectively in perspective, in rear view, and in longitudinal section, the construction of the actuation member  4  together with the elements already described: cylindrical button  40 , rod  41 , snap-fastening means  42 , slider actuation end  43 . Also seen therein are fixed tabs  47  of the same diameter as the inside diameter of the opening  21 , so as to ensure the retention, guidance and rotation of the button in the opening  21 . 
     The button  40  can furthermore comprise slots  44  so as to be accurately moveable with the aid of a screwdriver. In certain electrical apparatuses, the button  40  will be relatively small, for example less than a centimetre in diameter and its actuation by grasping it with the fingers is not easy. 
     The button  40  can also carry a label  45 , whilst the shroud  1  carries as many marks as discrete positions of the actuation member  4  and hence as desired values of the parameter selected by the button (here: operational modes or ranges of duration) . The label  45  located opposite a mark of the shroud makes it possible easily to display the selected value of the parameter. 
     The discrete positions which can be taken by the actuation member  4  make it possible to obtain a succession of discrete values of resistance of the potentiometer. These positions are obtained via notched indexation means with which the actuation member  4  cooperate [sic] . These notched indexation means  52 ,  53  are made up of a first indexation means  52  carried by the actuation member  4  (FIGS. 3 a ,  3   b  and  3   c ) and of a second indexation means  53  (FIGS. 4 and 5) which is fixed with respect to the apparatus  10 . 
     The first indexation means  52 , integral with the actuation member  4 , is represented in FIGS. 3 a ,  3   b  and  3   c  in the form of at least one lug  520  of trapezoidal shape. This lug is preferably carried by one of the elastic snap-fastening tabs  42 , but it is also possible to place it elsewhere. 
     In the example represented, the second indexation means  53 , fixed with respect to the apparatus  10 , is situated on the shroud  1  and more precisely on the rear face of the front wall  2  of the apparatus  10 . It is formed by a succession of notches or indents  51   1  to  51   n , which have substantially the same trapezoidal shape as the lug  520 . The lug  520  is intended to become housed in one of the notches  51  to  51   n  when the actuation member  4  takes one of the desired discrete positions, and to pass from notches to notches when the actuation member  4  is actuated. The notches are situated at the edge of the opening  21  of the shroud  1  as may be seen in FIGS. 4 (plan view) and  5  (rear view, that is to say viewed from the interior of the apparatus, of the front wall  2 ). 
     In the example described, the notches  51   1  to  51   n  are made on the interior face of the shroud  1  and are not visible from outside the shroud  1 . They can be moulded in the shroud  1  if the material of the shroud  1  lends itself thereto. Of course, one can envisage the notches being hollowed out on the exterior face of the shroud  1 . The choice depends on the position of the first indexation means  52 . 
     The number of notches is at least equal to the number of discrete positions  51   1 , to  51   n  desired for the actuation member  4 , and hence to the number of values desired for the parameter for adjusting the apparatus. 
     In order for the lug to pass from one notch to the next in a crisp and reliable manner, there is provision for the first indexation means  52  and/or the second indexation means  53  to be elastic. By placing the lug  520  on the elastic tabs  42   a  of the snap-fastening means  42  this condition is fulfilled. 
     The elasticity of the snap-fastening tabs, which is provided so as to allow the force-fitting insertion and then the retention of the actuation member in the opening  21 , in fact serves also to return the lug  520  towards the interior of the notches, that is to say towards the periphery of the opening  21 . The depth of the notches is smaller than the elastic deflection of the snap-fastening tabs, so that the lug can leave the notches when the control button is turned. The trapezoidal shape of the notches and of the lug makes it easier for the lug to leave a notch and for it to penetrate into another notch. Preferably, the bearing surface available between two notches is sufficiently small to prevent the lug from stabilizing outside a notch. 
     Instead of the first indexation means  52  being formed by a lug and instead of the second indexation means  53  being formed by several notches, it is possible to envisage the contrary as illustrated in FIG.  6 . 
     The second indexation means  53  now comprises a lug  532 , integral with the shroud  1  and which projects inside the shroud towards the actuation member. The first indexation means  52  comprises a succession of notches  522  carried by the rod  41  of the actuation member  4 . The lug  532  exhibits sufficient elasticity to allow its elastic retention in a notch, and to allow it to leave this notch. 
     Instead of providing at least one lug and a succession of notches, the lug passing from notch to notch, it would be possible to provide at least one notch and a succession of lugs, one of the lugs becoming housed in the notch according to the discrete position of the actuation member  4 . These lugs belong either to the first indexation means, or to the second indexation means and the notch respectively either to the second indexation means, or to the first indexation means. It is then the notch which is formed on an elastic member which returns it towards a lug. 
     In the example of the previous figures, the actuation member  4  is rotationally mobile but its movement could also be a translation as illustrated by FIG.  7 . 
     FIG. 8 represents the principle of electrical operation of the apparatus. 
     The potentiometer  3  is shown diagrammatically by a resistor  33 . Its slider  31  is moved and takes the various discrete positions  51   i  under the control of its actuation member  4 . The potentiometer is for example quite simply supplied with a voltage V so that a fraction of this voltage, which can vary discretely, appears on its slider. The potentiometer could also be mounted in a resistor bridge. 
     The analogue voltage Ve present on the slider is applied to the input of the electronic circuits which allow the apparatus to execute the parametrizable functions for which it is provided. These circuits essentially comprise a processing device  7  which consists in practice of a programmed microcontroller. For the embodiment of the invention, the electronic circuits must comprise means of analogue/digital conversion and interpretation  6 , which are preferably integrated into the microcontroller. These means of analogue/digital conversion and interpretation  6  establish a digital signal of p bits, representing one of the N possible discrete positions of the indexation potentiometer, and therefore representing one of the desired values of the parameter adjusted by this potentiometer. This digital signal of p bits replaces the signal of p bits which would have been provided in the prior art by a switch with p bits. It is used directly by the processing device  7  in order to operate the apparatus with the value of selected parameter. 
     In the simplest case, the means of analogue/digital conversion and interpretation-comprise a straightforward analogue/digital converter of p bits. However, this presupposes that the potentiometer is very accurate, and very linear, so that there is a one-to-one correspondence, for each discrete position of the slider, between the geometrical position of the slider and the signal of p bits which results therefrom. If one wishes to use a low-cost potentiometer, of may be [sic] considerable scatter, supplied with a voltage which is not necessarily very accurate, possibly subjected to considerable climatic, thermal and mechanical constraints, the one-to-one correspondence will be difficult to obtain via a straightforward analogue/digital converter of p bits. 
     One therefore prefers to use an analogue/digital converter of higher resolution, for example of p+m bits and decoding means, the converter and the decoding means together constituting the means of conversion and interpretation  6  mentioned hereinabove. The decoding means then match the various possible values of the analogue voltage, which are digitally coded on p+m bits, with a single digital value coded on p bits which represents a discrete position to which this analogue voltage value is assumed to correspond. There is moreover no need for the single value coded on p bits to correspond precisely to the p highest order bits of the digital value coded on p+m bits, the decoding table being arbitrary. In particular, this correspondence will not in general exist if the potentiometer is not sufficiently linear. 
     The decoding means can be integrated, just like the analogue/digital converter, into a microcontroller constituting the nub of the circuits  7 . These decoding means can consist of an electrically programmable read-only memory. Any defects in the potentiometers, or the adapting of the apparatus to another potentiometer, or changes in supply voltage, can be taken into account by having a read-only memory with several different areas, or even by changing the content of the read-only memory. 
     A single link is required between a specified indexation potentiometer and the microcontroller. 
     If the apparatus possesses several potentiometers  3 , it is possible to use the same analogue/digital converter for all the potentiometers, on condition that a multiplexer is interposed between the potentiometers and this converter. The multiplexer  8  can form part of the microcontroller, in which case the microcontroller must posses as many inputs as potentiometers. It can also be outside the microcontroller and placed upstream of the latter, in which case a single analogue link is required between the output of the multiplexer and the microcontroller, the various potentiometers being linked to the various inputs of the multiplexer  8  as is represented in FIG.  9 . The analogue/digital converter is designated by reference  61  in FIG. 9, and it is followed by a decoding means  62 . 
     If moreover there is in the apparatus a potentiometer with continuous, non-indexed, adjustment, as is the case for the timer represented in FIG. 1 which possesses continuous adjustment of timing duration within a range of selected durations, this continuous-adjustment potentiometer can be connected across the multiplexer to the same microcontroller (and in practice to the same analogue/digital converter). The resulting signal is utilized by the apparatus to define the end of duration adjustment. 
     FIG. 10 diagrammatically represents a particular embodiment of the invention, in which the resistive track of the potentiometer, on which the slider of the potentiometer (represented by symbolic arrow  70 ) moves, takes the form of discontinuous resistive lands R 0  to R 4 , separated by conductive lands P 0  to P 5  (hatched). 
     Each conductive land is situated at the site of a respective discrete position of the slider as defined by the notched indexation means (which are not represented in FIG.  10 ). 
     This particular arrangement is aimed at diminishing the consequences of the uncertainty in the exact position of the slider with respect to the resistive track when the slider is on an indexed position, given the manufacturing scatter from one apparatus to another. 
     In practice, the resistive track is a track which is continuous over the entire extent of movement of the slider, but it is covered locally, at the site of the lands P 0  to P 5 , by a conductive layer which locally short-circuits the resistive track and which therefore endows it with a discontinuous configuration. Silver paste can be used for the conductive layer. 
     The graph of the relative variation in the resistance of the potentiometer versus the variation in the position of the slider is then that of FIG.  11 : the resistance varies stepwise. 
     The use of conductive lands which overall have a length (along the track) substantially equal to the total length of the resistive lands, or even twice this length, seems to be a satisfactory compromise. 
     It will be noted that if the value of the total resistance of the potentiometer (slider at end of track) is imposed, it is necessary to increase the resistance of the track per unit length with respect to what it would be in the absence of conductive lands. For example, a potentiometer envisaged for 200 kilohms in total will have to be constructed from a resistive layer correspond [sic] theoretically to a potentiometer of around 500 kilohms. 
     FIG. 12 represents an exploded view of a practical exemplary embodiment in which the notched indexation means  71 ,  72  form part of the potentiometer  3  itself and in which the resistive track R is rendered discontinuous by the use of conductive lands P which locally cover the resistive track at the site of the indexed positions of the slider  70 . 
     The potentiometer represented comprises three parts  80 ,  81 ,  82 . Part  80 , on the right in the figure, is a box which contains in the bottom thereof the resistive track  73  formed by discontinuous resistive lands R separated by conductive lands P. With a view to the electrical supply of the potentiometer the two ends of the resistive track  73  are each linked to a conductive tab  83  which leaves the box. In the example of FIG. 12, the ends of the track  73  are situated at the level of conductive lands P. 
     The rotationally moveable middle part  81  becomes housed in the box. 
     It comprises a conductive ring  86  provided with a relief part  70  which forms the slider and which comes into contact with the resistive track  73  when the middle part  81  is mounted in the box  80 . The relief part  70  is V shaped in the example described. 
     This conductive ring  86  is mounted around an insulating spindle  85  which serves in the rotational actuation of the slider  70 . During mounting, the insulating spindle  85  comes to bear on one side at the bottom of the box. On the other, the spindle  85  can be accessed from outside the box so as to allow the actuation of the ring and hence of the slider  70 . In FIG. 12 the spindle  85  is hollow and can be rotated with the aid of a screwdriver so as to move the slider  70 . 
     The last part  82  is a cover which is secured to the box  80  in order to close it. 
     The cover  82  comprises an opening  87  for allowing through the insulating spindle  85 . The notched indexation means  71 ,  72  consist simply of bosses cooperating with one another. The first indexation means  71  is formed by at least one boss, carried by the ring  86 , in relief towards the cover  82  in the example described. 
     The second indexation means  72  is formed by several bosses, carried by the cover  82 , sunken towards the ring  86 . A boss  71  carried by the ring  86  in relief towards the cover  82  becomes housed in one of the bosses  72  carried by the cover. When the ring  86  is rotated the boss  71  passes from boss  72  to boss  72  and the slider  70  from conductive lands to conductive lands. 
     In the example, the number of bosses  72  corresponds to the number of discrete positions desired by the actuation member. It is of course possible to employ a boss  71  sunken towards the cover  82  and bosses  72  in relief towards the ring  86 . 
     In order for the switch from one discrete position to the next to occur in a crisp and reliable manner, the ring  86  carrying the boss  71  possesses a certain elasticity given by a slot  88  situated level with the slider  70 . 
     The cover  82  is conductive and possesses a conductive tab  89  which makes it possible to gather the voltage present at the level of the slider  70 . In order to correctly position the cover  82  with respect to the box  80  and prevent it from turning, provision may be made for the cover  82  to comprise at least one tongue  91  which becomes housed in an indent  90  of the box  80 .