the device shown comprises a structure 1 in the form of a cradle on which are mounted the various movable elements of the stop device as well as the switches and the means of control . the device comprises two lead screws 2 and 3 mounted coaxially and freely on a common axle 4 and pushed towards each of the extremities of this axle by a common helical spring 5 arranged between the lead screws . the end of the lead screw 2 opposite the spring 5 is equipped with a toothed crown wheel 6 meshing , under the thrust of the spring 5 , with the inner toothing of a crown wheel 7 fixed to the axle 4 . the thread of the lead screw 2 is elongated backwards by a part of increasing diameter in a spiral constituting a cam 8 . this cam 8 is terminated at the rear by a stop 9 . between the crown wheel 6 and the stop 9 , the body of the lead screw 2 exhibits a part in the shape of a heart - shaped cam 10 . in a similar way , the lead screw 3 exhibits a spiral cam 12 , a stop 13 , a heart - shaped cam 14 and a toothed crown wheel 15 meshing , under the thrust of the spring 5 , with the inner toothing of a toothed crown wheel 16 fixed to the axle 4 and equipped with an external toothing 17 meshing with the movable part at the output of the gear train associated with the motor to be controlled . on the structure 1 is mounted parallel to the lead screws , an axle 18 ( fig2 ) on which is mounted a rocker arm 19 which is integral in rotation , with a certain angular play , with the axle 18 . this rocker arm 19 is equipped with two transverse arms 20 and 21 supporting a cylindrical guide bar 22 on which is freely mounted a circular sliding yoke 23 equipped with a ridge 24 engaged in the thread of the lead screw 2 . the guide bar 22 is surrounded by a helical spring 25 compressed between the sliding yoke 23 and the arm 21 . the arm 20 of the rocker arm exhibits , approximately in the elongation of the bar 22 , a longitudinal arm 26 interacting with a switch 27 and on which acts a spring 28 holding , on the one hand , the sliding yoke 23 in gear with the lead screw 2 and , on the other hand , the switch 27 actuated . this switch is closed when it is actuated ( fig8 ). in addition , on the axle 18 of the rocker arm is fastened , with angular play , a radial arm 29 exhibiting on the one hand a bezel 29a and on the other hand a notch 29b . the arm 29 is positioned on the axle 18 such that when it is driven in rotation in the direction of the lead screw 2 , its bezel 29a comes to stop against the pointed edge 30 of the lead screw by acting on the latter as a cam pushing back the lead screw 2 towards the right by compressing the spring 5 and disengaging the lead screw from the crown wheel 7 . while following its travel , the arm 29 comes , by virtue of its notch 29b to actuate the heart - shaped cam 10 and to position this heart - shaped cam in a known way , for example like the zero reset hammer of a timepiece . the other lead screw 3 interacts with identical means designated by the same references accompanied by the sign &# 39 ;. these means are mounted head - to - tail relative to the first means , with the exception of the rocker arm 19 &# 39 ; and of its arms , of the spring 28 &# 39 ; and of the switch 27 &# 39 ; which are situated opposite the corresponding elements of the first means . in the upper part of fig1 a cam 31 &# 39 ; can additionally be distinguished fixed to the end of the axle 18 &# 39 ; of the rocker arm , a cam intended to actuate a switch 32 &# 39 ; which short - circuits the switch 32 &# 39 ; in actuated position . the axle 18 of the first means is equipped with a cam which is identical to the cam 31 &# 39 ;, but not visible on the drawing and actuating a shunt switch 32 shown in dots and dashes as it is not visible on the section . as can be seen in fig2 the axles 18 and 18 &# 39 ; drive the rocker arms via a profile in the form of a sector with a certain angular play . arms 29 and 29 &# 39 ; are driven in the same way with a small angular play . the role of these plays will be made clear during the description of the operation of the device . on the axles 18 and 18 &# 39 ; of the rocker arms are fixed , in addition , pinions 33 and 33 &# 39 ; ( fig5 and 7 ). the pinion 33 meshes with a rack 34 of a pusher 35 mounted in a housing at the end of the structure 1 . this pusher 35 comprises a spring 36 and it laterally exhibits a heart - shaped groove 37 in which engages the bent end of a wire spring 38 . this configuration which is well known per se provides two stable positions for the pusher 35 , i . e . a retracted position , as shown for the pusher 35 , and a non retracted position , as shown for the corresponding pusher 35 &# 39 ;. the pushers 35 and 35 &# 39 ; thus make it possible to hold the two corresponding axles 18 and 18 &# 39 ; in two defined positions . from this the necessity for angular plays in the driving of the rocker arms and the disengaging arms is evident . the electrical supply circuit of the motor is shown in fig8 . the motor m is a direct current motor supplied by a source of current of 12 v via an invertor switch which is not shown . the switches 27 and 27 &# 39 ; are shown in actuated position and the switches 32 and 32 &# 39 ; in nonactuated position . the positions correspond to intermediate positions of the sliding yokes 23 and 23 &# 39 ;. the switches 27 and 32 are mounted in series with a diode d1 and a relay r1 , while the switches 27 &# 39 ; and 32 &# 39 ; are mounted in parallel , in series with a diode d3 and a relay r2 . the diodes d1 , d3 are opposite and parallel . between the terminals of the windings of each of the relays r1 , r2 are mounted , opposite and parallel , free - wheel diodes d2 and d4 . the relays r1 and r2 are equipped with an invertor contact r1 , respectively r2 shown at rest and whose common points c are connected respectively to each of the terminals of the motor m . in parallel with the contact r1 is connected a diode d6 permitting the passage of current in the motor when the contact r1 is in rest position as shown in the drawing . in the same way , a diode d5 is connected in parallel to the contact r2 . when the circuit is supplied with the polarity shown in the drawing , the current passes through the switch 27 &# 39 ;, the diode d3 and the relay r2 which is then excited . the contact r2 passes to the position b and the current can pass through the motor m through the contact r2 and the diode d6 . for the other direction of rotation of the motor m , it is the relay r1 which is excited and the motor is supplied through the contact r1 on terminal b and diode d5 . assume first of all that the sliding yokes 23 and 23 &# 39 ; are in any position , for example the position shown in fig1 . when the motor turns , the two sliding yokes are each driven by their lead screw in opposite directions . assume that the sliding yokes move in the direction of their cam 8 and 8 &# 39 ;. the first sliding yoke which mounts onto its cam , for example the sliding yoke 23 drives the rocker arm 19 which can rock freely on its axle 18 by reason of the angular play provided for this purpose . the arm 26 ceases to actuate the contact 27 which opens bringing about the stopping of the motor ( fig3 and 4 ). the setting of the high and low stopping points of a blind will be described by means of fig5 and 6 . the two pushers 35 and 35 &# 39 ; are retracted into their second position . the two rocker arms 19 and 19 &# 39 ; are thus moved away from the lead screws and the sliding yokes 23 and 23 &# 39 ; are instantaneously brought into their initial position by their springs 25 and 25 &# 39 ;, that is to say abutting against the stops 9 and 13 as shown in fig5 for the sliding yoke 23 and the pusher 35 . the retraction of the pusher 35 has the additional effect , at the end of a certain travel determined by the play of the arm 29 on the axle 18 , of driving the arm 29 which successively disengages the lead screw 2 and positions this lead screw in angular position via its heart - shaped cam 10 . it is the same for the lead screw 3 . simultaneously , the shunt contacts 32 and 32 , are closed making it possible to supply the motor . as a result , it is possible to supply the motor and to bring the windable element into a first stop position , for example that determined by the sliding yoke 23 . it is then sufficient to again press on the push - button 35 in order to bring the rocker arm into its rest position shown in fig1 . the lead screw 2 is again engaged and the sliding yoke 23 is engaged with it . the setting - up of the first stopping point is thus terminated . a reverse voltage is next applied to the motor in order to drive it in the other direction and the setting - up of the other stopping point is carried out in the same manner by means of the pusher 35 &# 39 ;. the setting - up of the two stopping points is thus carried out very rapidly , by the use of simple operations without risk of error and with very great precision given the setting to zero of the lead screws by means of the heart - shaped cams . in one simplified version , it would , needless to say , be possible to do without the heart - shaped cams , a precise angular initial position of the lead screws not being necessary in every case . as already mentioned in the introduction , the end of travel switches could be actuated in a direction parallel to the axis of the lead screws . in this case , the cams 8 and 8 &# 39 ; are not necessary . according to a simplified embodiment , the disengagement of the lead screws could also be dispensed with . according to another simplified embodiment of the invention , the bistable means of positioning the rocker arms , constituted by the pushers 35 and 35 &# 39 ;, could be removed and the rocker arms held away by another means . the actuating cams of the sliding yokes could have another shape . if only one stopping point is desired , the device could comprise a single lead screw and a single sliding yoke .