Abstract:
Apparatus for dispensing paper from rolls which feeds continuously, roll to roll, and does not require extra procedure to bring stub roll into position. The apparatus has means for holding and positioning at least first and second rolls of paper with respect to each other; means for dispensing paper from the first roll; means for dispensing paper from the first and second rolls simultaneously when the first roll reduces to a predetermined diameter of paper, means for positioning the depleted first roll for replacement without the necessity of removing the second roll; and means for dispensing from the second and replacement rolls simultaneously when the second roll reduces to a predetermined diameter of paper. The apparatus also has a proximity sensor, which senses when a hand is placed near the dispenser, and thereupon dispenses a set amount of towel. The proximity sensor incorporates “static” and noise immunity circuitry.

Description:
PRIORITY  
       [0001]     This file is a Continuation-in-Part of Ser. No. 09/780,733, filed Feb. 9, 2001. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to the field of paper roll dispensers. In particular it relates to a carousel dispensing system for paper towels adapted to dispense paper from a plurality of rolls. This invention relates to the field of proximity sensors. In particular it relates to the field of phase-balance proximity sensors. It relates to spurious noise-immune proximity sensors.  
         [0004]     2. Background  
         [0005]     As is readily apparent, a long-standing problem is to keep paper towels available in a dispenser and at the same time use up each roll as completely as possible to avoid paper waste. As part of this system, one ought to keep in mind the person who refills the towel dispenser. An optimal solution would make it as easy as possible and as “fool-proof” as possible to operate the towel refill system and have it operate in such a manner as the least amount of waste of paper towel occurs. This waste may take the form of “stub” rolls of paper towel not being used up.  
         [0006]     Transfer devices are used on some roll towel dispensers as a means of reducing waste and decreasing operating costs. These transfer devices work in a variety of ways. The more efficient of these devices automatically begin feeding from a reserve roll once the initial roll is exhausted. These devices eliminate the waste caused by a maintenance person when replacing small rolls with fresh rolls in an effort to prevent the dispenser from running out of paper. These transfer devices, however, tend to be difficult to load and/or to operate. Consequently, these transfer devices are less frequently used, even though they are present.  
         [0007]     The current transfer bar mechanisms tend to require the maintenance person to remove any unwanted core tube(s), remove the initial partial roll from the reserve position, and position the initial partial roll into the now vacant stub roll position. This procedure is relatively long and difficult, partly because the stub roll positions in these current paper towel dispensers tend to be cramped and difficult to get to.  
         [0008]     In order to keep a roll available in the dispenser, it is necessary to provide for a refill before the roll is used up. This factor generally requires that a “refill” be done before the current paper towel roll is used up. If the person refilling the dispenser comes too late, the paper towel roll will be used up. If the refill occurs too soon, the amount of paper towel in the almost used-up roll, the “stub” roll, will be wasted unless there is a method and a mechanism for using up the stub roll even though the dispenser has been refilled. Another issue exists, as to the ease in which the new refill roll is added to the paper towel dispenser. The goal is to bring “on-stream” the new refill roll as the last of the stub roll towel is being used up. If it is a task easily done by the person replenishing the dispensers, then a higher probability exists that the stub roll paper towel will actually be used up and also that a refill roll be placed into service before the stub roll has entirely been used up. It would be extremely desirable to have a paper towel dispenser which tended to minimize paper wastage by operating in a nearly “fool proof” manner with respect to refilling and using up the stub roll.  
         [0009]     As an enhancement and further development of a system for delivering paper towel to the end user in as cost effective manner and in a user-friendly manner as possible, an automatic means for dispensing the paper towel is desirable, making it unnecessary for a user to physically touch a knob or a lever.  
         [0010]     It has long been known that the insertion of an object with a dielectric constant into a volume with an electrostatic field will tend to modify the properties which the electrostatic field sees. For example, sometimes it is noticed that placing one hand near some radios will change the tuning of that radio. In these cases, the property of the hand, a dielectric constant close to that of water, is enough to alter the net capacitance of a tuned circuit within the radio, where that circuit affects the tuning of the RF signal being demodulated by that radio. In 1973 Riechmann (U.S. Pat. No. 3,743,865) described a circuit which used two antenna structures to detect an intrusion in the effective space of the antennae. Frequency and amplitude of a relaxation oscillator were affected by affecting the value of its timing capacitor.  
         [0011]     The capacity (C) is defined as the charge (Q) stored on separated conductors with a voltage (V) difference between the conductors: 
 
C=QN. 
 
         [0012]     For two infinite conductive planes with a charge per unit area of a, a separation of d, with a dielectric constant ε of the material between the infinite conductors, the capacitance of an area A is given by: 
 
 C=εAσ/d  
 
         [0013]     Thus, where part of the separating material has a dielectric constant ε 1  and part of the material has the dielectric constant ε 2 , the net capacity is: 
 
 C=ε   1   A   1   σ/d+ε   2   A   2   σ/d  
 
         [0014]     The human body is about 70% water. The dielectric constant of water is 7.18×10 −10  farads/meter compared to the dielectric constant of air (STP): 8.85×10 −12  farads/meter. The dielectric constant of water is over 80 times the dielectric constant of air. For a hand thrust into one part of space between the capacitor plates, occupying, for example, a hundredth of a detection region between large, but finite parallel conducting plates, a desirable detection ability in terms of the change in capacity is about 10 −4 . About 10 −2  is contributed by the difference in the dielectric constants and about 10 −32  is contributed by the “area” difference.  
         [0015]     Besides Riechmann (1973), other circuits have been used for, or could be used for proximity sensing.  
         [0016]     An important aspect of a proximity detector circuit of this type is that it be inexpensive, reliable, and easy to manufacture. A circuit made of a few parts tends to help with reliability, cost and ease of manufacture. Another desirable characteristic for electronic circuits of this type is that they have a high degree of noise immunity, i.e., they work well in an environment where there may be electromagnetic noise and interference. Consequently a more noise-immune circuit will perform better and it will have acceptable performance in more areas of application.  
       SUMMARY OF THE INVENTION  
       [0017]     The invention comprises to a carousel-based dispensing system for paper towels, in particular, which acts to minimize actual wastage of paper towels. The invention comprises means for holding and positioning at least first and second rolls of paper with respect to each other, means for dispensing paper from the first roll, means for dispensing paper from the first and second rolls simultaneously when the first roll reduces to a predetermined diameter of paper, means for positioning the depleted first roll for replacement without the necessity of removing the second roll and means for dispensing from the second and replacement rolls simultaneously when the second roll reduces to a predetermined diameter of paper.  
         [0018]     A proximity sensor embodiment comprises a circuit according to a balanced bridge principle where detection is based on detecting a phase difference, which depends upon the amount of detected capacitance difference or change of capacitance in a region of detection.  
         [0019]     A second embodiment of this invention comprises a second electronic proximity sensor. The second detector circuit is a miniaturized, micro-powered, capacitance-based proximity sensor designed to detect the approach of a hand to a towel dispenser. It features stable operation and a three-position sensitivity selector. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0021]      FIG. 1  is a side elevation of the dispenser with the cover closed, with no internal mechanisms visible;  
         [0022]      FIG. 2  is a perspective view of the dispenser with the cover closed, with no internal mechanisms visible;  
         [0023]      FIG. 3  shows a view of the carousel support, the locking bar and the transfer bar;  
         [0024]      FIG. 4A  is a perspective view of the of the dispenser with the carousel and transfer bar, fully loaded with a main roll and a stub roll;  
         [0025]      FIG. 4B  is a side view of the locking bar showing the placement of the compression springs;  
         [0026]      FIG. 4C  shows the locking mechanism where the locking bar closest to the rear of the casing is adapted to fit into a mating structure in the rear casing;  
         [0027]      FIG. 5  is a perspective, exploded view of the carousel assembly;  
         [0028]      FIG. 6A  is a side elevation view of the paper feeding from the stub roll while the tail of the main roll is positioned beneath the transfer bar;  
         [0029]      FIG. 6B  is a side elevation view of the stub roll is completely exhausted, so that the transfer bar tucks the tail of the main roll into the feed mechanism;  
         [0030]      FIG. 7A  is a side elevation view of the carousel ready for loading when the main roll reaches a specific diameter;  
         [0031]      FIG. 7B  is a side elevation view of the locking bar being pulled forwardly to allow the carousel to rotate 180°, placing the main roll in the previous stub roll position;  
         [0032]      FIG. 7C  shows the extension springs which tend to maintain the transfer bar legs in contact with the stub roll;  
         [0033]      FIG. 7D  shows the cleanable floor of the dispenser;  
         [0034]      FIG. 8A  shows a schematic of the proximity circuit;  
         [0035]      FIG. 8B  (prior art) shows the schematic for the National Semiconductor dual comparator LM393;  
         [0036]      FIG. 9A  shows the square wave output at U1A, pin  1 ;  
         [0037]      FIG. 9B  shows the RC exponential waveforms at pins  5 ;  
         [0038]      FIG. 9C  shows the RC exponential waveforms at pin  6 ;  
         [0039]      FIG. 10  shows a schematic of a second proximity switch;  
         [0040]      FIG. 10A  shows the asymmetric oscillator and the first static protection circuit;  
         [0041]      FIG. 10B  shows the antenna, the antenna reset circuit, a second static protection circuit, the antenna buffer unity follower circuit, and the peak detector circuit; and a peak detector circuit;  
         [0042]      FIG. 10C  shows the low pass filter for rejecting 50/60 Hz, the amplifier circuit, and the test points for adjusting VR 1  to 3.0 V with all eternal capacitance-like loads in place;  
         [0043]      FIG. 10D  shows the auto-compensate capacitor, the 50/60 Hz reject capacitor, and the output comparator which will produce an output pulse for signals which have passed all the rejection tests; these tests designed to prevent spurious signals from setting off an output pulse; and  
         [0044]      FIG. 10E  shows a sensitivity select switch and circuit.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0045]     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is merely made for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.  
         [0046]     An embodiment of the invention comprises a carousel-based dispensing system with a transfer bar for paper towels, which acts to minimize actual wastage of paper towels. As an enhancement and further development of a system for delivering paper towel to the end user in a cost effective manner and in as user-friendly manner as possible, an automatic means for dispensing the paper towel is desirable, making it unnecessary for a user to physically touch a knob or a lever. An electronic proximity sensor is included as part of the paper towel dispenser. A person can approach the paper towel dispenser, extend his or her hand, and have the proximity sensor detect the presence of the hand. The embodiment of the invention as shown here, is a system, which advantageously uses a minimal number of parts for both the mechanical structure and for the electronic unit. It has, therefore, an enhanced reliability and maintainability, both of which contribute to cost effectiveness.  
         [0047]     An embodiment of the invention comprises a carousel-based dispensing system with a transfer bar for paper towels, which acts to minimize actual wastage of paper towels. The transfer bar coupled with the carousel system is easy to load by a service person; consequently it will tend to be used, allowing stub rolls to be fully utilized. In summary, the carousel assembly-transfer bar comprises two components, a carousel assembly and a transfer bar. The carousel rotates a used-up stub roll to an up position where it can easily be replaced with a full roll. At the same time the former main roll which has been used up such that its diameter is less than some p inches, where p is a rational number, is rotated down into the stub roll position. The tail of the new main roll in the upper position is tucked under the “bar” part of the transfer bar. As the stub roll is used up, the transfer bar moves down under spring loading until the tail of the main roll is engaged between the feed roller and the nib roller. The carousel assembly is symmetrical about a horizontal axis. A locking bar is pulled out to unlock the carousel assembly and allow it-to rotate about its axis, and is then released under its spring loading to again lock the carousel assembly in place.  
         [0048]     A side view,  FIG. 1 , of the dispenser  20  with the cover  22  in place shows an upper circular bulge  24 , providing room for a full roll of paper towel, installed in the upper position of the carousel. The shape of the dispenser is such that the front cover tapers inwardly towards the bottom to provide a smaller dispenser volume at the bottom where there is a smaller stub roll of paper towel. The shape tends to minimize the overall size of the dispenser.  FIG. 2  shows a perspective view of the dispenser  20  with cover  22  in place and the circular (cylindrical) bulge  24 , together with the sunrise-like setback  26  on the cover  22 , which tends to visually guide a hand toward the pseudo-button  28 , leading to activation of a proximity sensor (not shown). A light emitting diode (LED)  130  is located centrally to the pseudo-button  28 . The LED  130  ( FIG. 3 ) serves as an indication that the dispenser  20  is on, and dispensing towel. The LED  130  may be off while the dispenser is not dispensing. Alternatively, the LED  130  may be lit (on), and when the dispenser  20  is operating, the LED  130  might flash. The LED  130  might show green when the dispenser  20  is ready to dispense, and flashing green, or orange, when the dispenser  20  is operating to dispense. Any similar combination may be used. The least power consumption occurs when the LED  130  only lights during a dispensing duty cycle. The sunrise-like setback  26  ( FIG. 2 ) allows a hand to come more closely to the proximity sensor (not shown).  
         [0049]      FIG. 3  shows the main elements of the carousel assembly  30 . The carousel arms  32  have friction reducing rotating paper towel roll hubs  34 , which are disposed into the holes of a paper towel roll ( 66 ,  68 ,  FIG. 4A ). The locking bar  36  serves to lock and to release the carousel for rotation about its axis  38 . The locking bar  36  rides on one of the corresponding bars  40 . The two corresponding bars  40  serve as support bars. Cross-members  42  serve as stiffeners for the carousel assembly  30 , and also serve as paper guides for the paper to be drawn over and down to the feed roller  50  and out the dispenser  20 . These cross members are attached in a rigid fashion to the corresponding bars  40  and in this embodiment do not rotate.  
         [0050]     The legs  46  of the transfer bar  44  do not rest against the friction reducing rotating paper towel roll hubs  34  when there is no stub roll  68  present but are disposed inward of the roll hubs  34 . The bar part  88  of the transfer bar  44  will rest against a structure of the dispenser, for example, the top of modular electronics unit  132 , when no stub roll  68  is present. The bar part  88  of the transfer bar  44  acts to bring the tail of a new main roll of paper towel  66  ( FIG. 4A ) down to the feed roller  50  which includes intermediate bosses  146  ( FIG. 3 ) and shaft  144 . The carousel assembly is disposed within the fixed casing  48 . The cover is not shown.  
         [0051]     Feed roller  50  serves to feed the paper towels  66 ,  68  ( FIG. 4A ) being dispensed onto the curved dispensing ribs  52 . The curved dispensing ribs  52  are curved and have a low area of contact with the paper towel dispensed (not shown). If the dispenser  20  gets wet, the curved dispensing ribs  52  help in dispensing the paper towel to get dispensed by providing low friction and by holding the dispensing towel off of the wet surfaces it would otherwise contact.  
         [0052]     The feed roller  50  is typically as wide as the paper roll, and includes drive rollers  142  and intermediate bosses  146  on the drive shaft  144 . The working drive rollers or drive bosses  142  ( FIG. 3 ) are typically an inch or less in width, with intermediate bosses  146  ( FIG. 3 ) located between them. Intermediate bosses  146  are slightly less in diameter than the drive rollers or drive bosses  142 , having a diameter 0.015 to 0.045 inches less than the drive rollers or drive bosses  142 . In this embodiment, the diameter of the intermediate bosses  146  is 0.030 inches less than the drive roller  142 . This configuration of drive rollers or drive bosses  142  and intermediate bosses  146  tends to prevent the dispensing paper towel from becoming wrinkled as it passes through the drive mechanism and reduces friction, requiring less power to operate the feed roller  50 .  
         [0053]     A control unit  54  operates a motor  56 . Batteries  58  supply power to the motor  56 . A motor  56  may be positioned next to the batteries  58 . A light  60 , for example, a light-emitting diode (LED), may be incorporated into a low battery warning such that the light  60  turns on when the battery voltage is lower than a predetermined level.  
         [0054]     The cover  22  of the dispenser is preferably transparent so that the amount of the main roll used (see below) may be inspected, but also so that the battery low light  60  may easily be seen. Otherwise an individual window on an opaque cover  22  would need to be provided to view the low battery light  60 . Another approach might be to lead out the light by way of a fiber optic light pipe to a transparent window in the cover  22 .  
         [0055]     In a waterproof version of the dispenser, a thin piece of foam rubber rope is disposed within a u-shaped groove of the tongue-in-groove mating surfaces of the cover  22  and the casing  48 . The dispensing shelf  62  is a modular component, which is removable from the dispenser  20 . In the waterproof version of the dispenser  20 , the dispensing shelf  62  with the molded turning ribs  52  is removed. By removing the modular component, dispensing shelf  62 , there is less likelihood of water being diverted into the dispenser  20  by the dispensing shelf  62 , acting as a funnel or chute should a water hose or spray be directed at the dispenser  20 , by the shelf and wetting-the paper towel. The paper towel is dispensed straight downward. A most likely need for a waterproof version of the dispenser is where a dispenser is located in an area subject to being cleaned by being hosed down. The dispenser  20  has an on-off switch which goes to an off state when the cover  22  is pivoted downwardly. The actual switch is located on the lower face of the module  54  and is not shown.  
         [0056]     In one embodiment, the user may actuate the dispensing of a paper towel by placing a hand in the dispenser&#39;s field of sensitivity. There can be adjustable delay lengths between activations of the sensor.  
         [0057]     There is another aspect of the presence of water on or near the dispenser  20 . A proximity sensor (not visible) is more fully discussed below, including the details of its operation. However, as can be appreciated, the sensor detects changes of capacitance such as are caused by the introduction of an object with a high dielectric constant relative to air, such as water, as well as a hand which is about  70 % water. An on-off switch  140  is provided which may be turned off before hosing down and may be turned on manually, afterwards. The switch  140  may also work such that it turns itself back on after a period of time, automatically. The switch  140  may operate in both modes, according to mode(s) chosen by the user.  
         [0058]     A separate “jog” off-on switch  64  is provided so that a maintenance person can thread the paper towel  66  by holding a spring loaded jog switch  64  which provides a temporary movement of the feed roller  50 .  
         [0059]      FIG. 4A  shows the dispenser case  48  with the carousel assembly  30  and transfer bar  44 . The carousel assembly  30  is fully loaded with a main roll  66  and a stub roll  68 , both mounted on the carousel arms  32  and rotate on the rotating reduced friction paper towel roll hubs  34  (only shown from the back of the carousel arms  32 ). In the carousel assembly  30 , the two carousel arms  32 , joined by corresponding bars  40  and cross members  42 , rotate in carousel fashion about a horizontal axis defined by the carousel assembly rotation hubs  38 . The locking bar  36  is supported, or carried, by a corresponding bar  40 . The corresponding bar  40  provides structural rigidity and support. The locking bar  36  principally serves as a locking mechanism. Each paper towel roll  66 ,  68  has an inner cardboard tube which acts as a central winding core element, and which provides in a hole in paper towel roll  66 ,  68  at each end for engaging the hubs  34 .  
         [0060]      FIG. 5  shows the carousel assembly  30  in exploded, perspective view. The number of parts comprising this assembly is small. From a reliability point of view, the reliability is increased. From a manufacturing point of view, the ease of manufacture is thereby increased and the cost of manufacture is reduced. The material of manufacture is not limited except as to the requirements of cost, ease of manufacture, reliability, strength and other requirements imposed by the maker, demand.  
         [0061]     When the main roll,  66  ( FIG. 4A ) and the stub roll  68 , ( FIG. 4A ) are in place, the carousel arms  32  are connected by these rolls  66  and  68  ( FIG. 4A ). Placing cross-members  42  to connect the carousel arms  32  with the locking  36  and corresponding  40  bar results in better structural stability, with racking prevented. The locking bar  36 , which was shown as a single unit locking bar  36  in the previous figures, acts as a locking bar  36  to lock the carousel assembly  30  in the proper orientation. It acts also as the release bar, which when released, allows the carousel assembly  30  to rotate. Two compression springs  70 ,  72  are utilized to center the locking bar  36 .  
         [0062]      FIG. 4B  is a side view of the locking bar showing the placement of the compression springs. The compression springs  70 ,  72  also tend to resist the release of the locking bar  36 , insuring that a required force is needed to unlock the locking bar  36 . The required force is typically between 0.5 lbf and 3.0 lbf, or more. In this embodiment, the force is 2.0 lbf when the spring in a fully compressed position, and 1.1 lbf when the spring is in the rest position. In the rest position, the forces of the opposing springs offset each other.  
         [0063]     The actual locking occurs as shown in  FIG. 4C . The locking bar  36  closest to the rear of the casing  48  is adapted to fit into a generally u-shaped mating structure  118  which is adapted to hold the locking bar  36  and prevent it and the carousel assembly  30  from rotating. When the locking bar  36  is pulled away from the rear of the casing  48 , the locking bar  36  is disengaged from the mating structure  118 . The mating structure has an upper “high” side  120  and a lower “low” side  122 , where the low side has a “ramp”  124  on its lower side. As the locking bar  36  is pulled out to clear the high side  120 , the carousel assembly  30  is free to rotate such that the top of the carousel assembly  30  rotates up and away from the back of the casing  48 . As the carousel assembly  30  begins to rotate, the user releases the locking bar  36  which, under the influence of symmetrically placed compression springs  70 ,  72  returns to its rest position. As the carousel assembly rotates, the end of the symmetrical locking bar  36  which originally was disposed toward the user now rotates and contacts the ramp  124 . A locking bar spring, e.g.,  70  or  72 , is compressed as the end of the locking bar  36  contacting the ramp  124  now moves up the ramp  124 . The end of the locking bar  36  is pressed into the space between the low side  122  and the high side  120 , as the end of the locking bar  36  slides past the low side  122 . A locked position for the carousel assembly  30  is now reestablished.  
         [0064]      FIG. 5  shows the carousel arms  32  adapted to receive the loading of a new roll of towel  66  ( FIG. 4A ). The arms  32  are slightly flexible and bent outward a small amount when inserting a paper towel roll  66  ( FIG. 4A ) between two opposite carousel arms  32 . A friction reducing rotating paper towel roll hub  34  is inserted into a hole of a paper towel roll  66  ( FIG. 4A ), such that one roll hub  34  is inserted into a hole on each side of the paper towel roll  66  ( FIG. 4A ). Also shown in  FIG. 5  are the tamper resistant fasteners  74 , which attach the friction-reducing rotating paper towel roll hubs  34  to the carousel arms  32 .  
         [0065]      FIG. 5  shows the surface  76  of the roll hubs  34  and the surface  78  of the carousel arms  66 , which contact each other. These contact surfaces  76 ,  78  may be made of a more frictionless material than that of which the carousel arms  32  and the roll hubs  34  are made. For example, a plastic such as polytetrafluoroethylene (PTFE), e.g., TEFLON®, may be used, as a thin layer on each of the contacting surfaces. The paper towel dispenser  20  and its components may be made of, including but not limited to, plastic, metal, an organic material which may include but is not limited to wood, cardboard, treated or untreated, a combination of these materials, and other materials for batteries, paint, if any, and waterproofing.  
         [0066]      FIG. 6A  shows the paper  80  feeding from the stub roll  68  while the tail  82  of the main roll  66  is positioned beneath the transfer bar  44 . The legs (visible leg  46 , other leg not shown) of the transfer bar  44  rests against the stub roll. When the diameter of the stub roll  68  is larger by a number of winds of paper towel than the inner roll  84 , the legs  46  of the transfer bar  44  dispose the bar  88  of the transfer bar  44  to be rotated upward from the feed roller  50 .  
         [0067]      FIG. 6B  shows the situation where the stub roll  68  is exhausted, so that the transfer bar  44  tucks the tail  82  of the main roll  66  into the feed mechanism  86 .  FIG. 6B  shows the stub roll  68  position empty, as the stub roll has been used up. The stub roll core  84  is still in place. As the stub roll  68  is used up, the legs  46  of the transfer bar  44  move up toward the stub roll core (inner roll)  84 , and the bar  88  of the transfer bar is disposed downward toward the feed roller  50  and toward the top of a structural unit of the dispenser  20  ( FIG. 2 ), such as the top of the electronics module  132  ( FIG. 3 ). Initially the main roll  66  is in reserve, and its tail  82  in an “idling” position such that it is under the transfer bar  44 . The main roll  66  and its tail  82  are not initially in a “drive” position. However, as the stub roll  68  is used up, the downward motion of the bar transfer bar,  44  driven by its spring loading, brings the bar  88  of the transfer bar  44  down to engage the main roll tail  82  with the feed roller  50 .  
         [0068]      FIG. 7A  shows the carousel assembly  30  ready for loading when the main roll  66  reaches a specific diameter. The diameter of the main roll  66  may be measured by comparison of that diameter with the widened “ear” shape  122  ( FIG. 4A ) on each end of the carousel arms  32 . That part of each carousel arm  32  is made to measure a critical diameter of a main roll  66 . The carousel assembly  30  is tilted forward when it is locked. The carousel assembly  30  may rotate unassisted after the locking bar  36  is released, due to the top-heavy nature of the top roll. That is, the torque produced by the gravitational pull on the main-roll  66  is larger than that needed to overcome friction and the counter-torque produced by the now empty stub roll  68 .  
         [0069]      FIG. 7B  shows the process of loading where the service person pulls the locking bar  36  and allows the carousel to rotate  1800 , placing the main roll  66  in the previous stub roll  68  position. Now a new full sized roll  66  can be loaded onto the main roll  66  position. The transfer bar  44  automatically resets itself. The transfer bar  44  is spring loaded so as to be disposed with the transfer bar legs  46  pressed upward against the stub roll  68  or the stub roll core  84 . The transfer bar legs  46  are adapted to be disposed inward of the roll hubs  34  so the bar  88  of the transfer bar  44  will have a positive stop at a more rigid location, in this case, the top of the electronics module  132  ( FIG. 2 ).  
         [0070]      FIG. 7C  shows the extension springs  126 ,  128  which tend to maintain the transfer bar legs  46  in contact with the stub roll  68  or stub roll core  84 . The transfer bar  44  contains the two extension springs  126 ,  128 . The spring forces are typically 0.05 lbf to 0.5 lbf in the bar  44  lowered position and 0.2 lbf to 1.0 lbf in the bar  44  raised position. In this embodiment, the spring forces are 0.2 lbf in the lowered position an 0.43 lbf in the raised position. The force of the two springs  126 ,  128  is additive so that the transfer bar  44  is subject to a total spring force of 0.4 lbf in the lowered position and 0.86 lbf in the raised position.  
         [0071]     While modular units ( FIG. 7D ) such as the electronics module  132 , the motor  56  module, and the battery case  150 , are removable, they fit, or “snap” together so that the top of the electronics unit  132 , the top of the motor  56  module and remaining elements of the “floor”  148  of the dispensing unit  20  form a smooth, cleanable surface. Paper dust and debris tend to accumulate on the floor  148  of the dispenser  20 . It is important that the dispenser  20  is able to be easily cleaned as part of the maintenance procedure. A quick wiping with a damp cloth will sweep out and pick up any undesirable accumulation. The removable modular dispensing shelf  64  may be removed for rinsing or wiping.  
         [0072]     The feed roller  50  may be driven by a motor  56  which in turn may be driven by a battery or batteries  58 , driven off a 100 or 220V AC hookup, or driven off a transformer which is run off an AC circuit. The batteries may be non-rechargeable or rechargeable. Rechargeable batteries may include, but not be limited to, lithium ion, metal hydride, metal-air, nonmetal-air. The rechargeable batteries may be recharged by, but not limited to, AC electromagnetic induction or light energy using photocells.  
         [0073]     A feed roller  50  serves to feed the paper towel being dispensed onto the curved dispensing ribs  52 . A gear train (not visible) may be placed under housing  86 , ( FIG. 3 ) for driving the feed roller. A control unit  54  ( FIG. 3 ) for a motor  56  ( FIG. 3 ) may be utilized. A proximity sensor (not shown) or a hand-operated switch  64  may serve to turn the motor  56  on and off.  
         [0074]     As an enhancement and further development of a system for delivering paper towel to the end user in as cost effective manner and user-friendly manner as possible, an automatic means for dispensing the paper towel is desirable, making it unnecessary for a user to physically touch a knob or a lever. Therefore, a more hygienic dispenser is present. This dispenser will contribute to less transfer of matter, whether dirt or bacteria, from one user to the next. The results of washing ones hands will tend to be preserved and hygiene increased.  
         [0075]     An electronic proximity sensor is included as part of the paper towel dispenser. A person can approach the paper towel dispenser, extend his or her hand, and have the proximity sensor detect the presence of the hand. Upon detection of the hand, a motor is energized which dispenses the paper towel. It has long been known that the insertion of an object with a dielectric constant into a volume with an electromagnetic field will tend to modify the properties, which the electromagnetic field sees. The property of the hand, a dielectric constant close to that of water, is enough to alter the net capacitance of a suitable detector circuit.  
         [0076]     An embodiment of the invention comprises a balanced bridge circuit. See  FIG. 8A . The component U1A  90  is a comparator (TLC3702 158) configured as an oscillator. The frequency of oscillation of this component, U1A  90 , of the circuit may be considered arbitrary and non-critical, as far as the operation of the circuit is concerned. The period of the oscillator is set by the elements C ref    92 , R hys    94 , the trim resistance, R trim    96 , where the trim resistance may be varied and the range resistors R range    152  are fixed. The resistors R range    152  allow limits to be placed on the range of adjustment, resulting in an easier adjustment. The adjustment band is narrowed, since only part of the total resistance there can be varied. Consequently a single potentiometer may be used, simplifying the adjustment of R trim    96 . A value for R range    152  for the schematic shown in  FIG. 8A  might be 100 k.Ω. R trim    96  might have an adjustment range of 10 kΩ to 50 kΩ. The output signal at pin  1   98  of component U1A  90  is a square wave, as shown in  FIG. 9A . C ref    92  is charged by the output along with ANT  100 , both sustaining the oscillation and measuring the capacitance of the adjacent free space. The signals resulting from the charging action are applied to a second comparator, U1B  102 , at pin  5   104  and pin  6   106  ( FIG. 8A ). These signals appear as exponential waveforms, as shown in  FIG. 9B  and  FIG. 9C .  
         [0077]     The simplest form of a comparator is a high-gain differential amplifier, made either with transistors or with an op-amp. The op-amp goes into positive or negative saturation according to the difference of the input voltages because the voltage gain is typically larger than 100,000, the inputs will have to be equal to within a fraction of a millivolt in order for the output not to be completely saturated. Although an ordinary op-amp can be used as comparator, there are special integrated circuits intended for this use. These include the LM306, LM311, LM393  154  ( FIG. 8A ), LM393V, NE627 and TLC3702  158 . The LM393V is a lower voltage derivative of the LM393  154 . The LM393  154  is an integrated circuit containing two comparators. The TLC3702  158  is a micropower dual comparator with CMOS push-pull  156  outputs.  FIG. 8B  (prior art) is a schematic which shows the different output structures for the LM393 and the TLC3702. The dedicated comparators are much faster than the ordinary op-amps.  
         [0078]     The output signal at pin  1   98  of component U1A  90 , e.g., a TL3702  158 , is a square wave, as shown in  FIG. 2A . Two waveforms are generated at the inputs of the second comparator, U2B  102 . The first comparator  90  is running as an oscillator producing a square-wave clocking signal, which is input, to the clock input of the flip-flop U2A  108 , which may be, for example, a Motorola D flip-flop, No. 14013.  
         [0079]     Running the first comparator as a Schmitt trigger oscillator, the first comparator U1A  90  is setup to have positive feedback to the non-inverting input, terminal  3   110 . The positive feedback insures a rapid output transition, regardless of the speed of the input waveform. R hys    94  is chosen to produce the required hysteresis, together with the bias resistors R bias1    112  and R bias2    114 . When these two bias resistors, R bias1    112 , R bias2    114  and the hysteresis resistor, R hys    94 , are equal, the resulting threshold levels are ⅓ V+ and ⅔ V+, where V+158 is the supply voltage. The actual values are not especially critical, except that the three resistors R bias1    112 , R bias2    114  and R hys    94 , should be equal, for proper balance. The value of 294 kΩ maybe used for these three resistors, in the schematic shown in  FIG. 8A .  
         [0080]     An external pull-up resistor, R pullup1    116 , which may have a value, for example, of 470 Ω, is only necessary if an open collector, comparator such as an LM393  154  is used. That comparator  154  acts as an open-collector output with a ground-coupled emitter. For low power consumption, better performance is achieved with a CMOS comparator, e.g., TLC3702, which utilizes a CMOS push-pull output  156 . The signal at terminal  3   110  of U1A charges a capacitor C ref    92  and also charges an ANT sensor  100  with a capacitance which C ref    92  is designed to approximate. A value for C ref  for the schematic of  FIG. 8A , for the most current board design, upon which it depends, is about 10 pF. As the clocking square wave is effectively integrated by C ref    92  and the capacitance of ANT  100 , two exponential signals appear at terminals  5   104  and  6   106  of the second comparator U1B, through the R protect    160  static protection resistors. R protect    160  resistors provide limiting resistance which enhances the inherent static protection of a comparator input lines, particularly for the case of pin  5   104  of U1B  102 . In the schematic shown in  FIG. 8A , a typical value for R protect    160  might be 2 kΩ. One of the two exponential waveforms will be greater, depending upon the settings of the adjustable resistance R trim    96 , C ref    92 , and ANT  100 . The comparator U1B  102  resolves small differences, reporting logic levels at its output, pin  7   118 . As the waveforms may initially be set up, based on a capacitance at ANT  100  of a given amount. However, upon the intrusion of a hand, for example, into the detection field of the antenna ANT  100 , the capacitance of ANT  100  is increased significantly and the prior relationship of the waveforms, which were set with ANT  100  with a lower capacitance, are switched over. Therefore, the logic level output at pin  7   118  is changed and the d flip-flop  108  state is changed via the input on pin  5  of the D flip-flop  108 .  
         [0081]     The second comparator  102  provides a digital quality signal to the D flip-flop  108 . The D flip-flop, U2A  108 , latches and holds the output of the comparator U1B  90 . In this manner, the second comparator is really doing analog-to-digital conversion. A suitable D flip-flop is a Motorola 14013.  
         [0082]     The presence, and then the absence, of a hand can be used to start a motorized mechanism on a paper towel dispenser, for example. An embodiment of the proximity detector uses a single wire or a combination of wire and copper foil tape that is shaped to form a detection field. This system is very tolerant of non-conductive items, such as paper towels, placed in the field. A hand is conductive and attached to a much larger conductor to free space. Bringing a hand near the antenna serves to increase the antenna&#39;s apparent capacitance to free space, forcing detection.  
         [0083]     The shape and placement of the proximity detector&#39;s antenna ( FIG. 8A, 100 ) turns out to be of some importance in making the proximity sensor work correctly. Experimentation showed that a suitable location was toward the lower front of the dispenser unit. The antenna ( FIG. 8A, 100 ) was run about two-thirds the length of the dispensing unit, in a modular, replaceable unit above the removable dispensing shelf  62  ( FIG. 3 ). This modular unit would be denoted on  FIG. 3  as  120 .  
         [0084]     A detection by the proximity detection circuit ( FIG. 8A ) in the module  120  sets up a motor control flip flop so that the removal of the hand will trigger the start of the motor cycle. The end of the cycle is detected by means of a limit switch which, when closed, causes a reset of the flip-flop and stops the motor. A cycle may also be initiated by closing a manual switch.  
         [0085]     A wide range of sensitivity can be obtained by varying the geometry of the antenna and coordinating the reference capacitor. Small antennae have short ranges suitable for non-contact pushbuttons. A large antenna could be disposed as a doorway-sized people detector. Another factor in sensitivity is the element applied as R trim . If R trim    96  is replaced by an adjustable inductor, the exponential signals become resonant signals with phase characteristics very strongly influenced by capacitive changes. Accordingly, trimming with inductors may be used to increase range and sensitivity. Finally, circuitry may be added to the antenna  100  to improve range and directionality. As a class, these circuits are termed “guards” or “guarding electrodes,” old in the art, a type of shield driven at equal potential to the antenna. Equal potential insures no charge exchange, effectively blinding the guarded area of the antenna rendering it directional.  
         [0086]     The antenna design and trimming arrangement for-the paper towel dispenser application is chosen for adequate range and minimum cost. The advantages of using a guarded antenna and an adjustable inductor are that the sensing unit to be made smaller.  
         [0087]     From a safety standpoint, the circuit is designed so that a detection will hold the motor control flip-flop in reset, thereby stopping the mechanism. The cycle can then begin again after detection ends.  
         [0088]     The dispenser has additional switches on the control module  54 .  FIG. 3  shows a “length-of-towel-to-dispense-at-one-time” (“length”)switch  134 . This switch  134 , is important in controlling how long a length of paper towel is dispensed, for each dispensation of towel. It is an important setting for the owner of the dispenser on a day-to-day basis in determining cost (to the owner) versus the comfort (to the user) of getting a large piece of paper towel at one time.  
         [0089]     A somewhat similar second switch  136  is “time-delay-before-can-activate-the-dispensing-of another-paper-towel” (“time-delay”) switch  136 . The longer the time delay is set, the less likely a user will wait for many multiple towels to dispense. This tends to save costs to the owner. Shortening the delay tends to be more comfortable to a user.  
         [0090]     A third switch  138  is the sensitivity setting for the detection circuit. This sensitivity setting varies the resistance of R trim    96  ( FIG. 8A ). Once an effective antenna  100  ( FIG. 8A ) configuration is set up, the distance from the dispenser may be varied. Typical actual use may require a sensitivity out to one or two inches, rather than four or six inches. This is to avoid unwanted dispensing of paper towel. In a hospital setting, or physician&#39;s office, the sensitivity setting might be made fairly low so as to avoid unwanted paper towel dispensing. At a particular work location, on the other hand, the sensitivity might be set fairly high, so that paper towel will be dispensed very easily.  
         [0091]     While it is well known in the art how to make these switches according to the desired functionalities, this switch triad may increase the usefulness of the embodiment of this invention. The system, as shown in the embodiment herein, has properties of lowering costs, improving hygiene, improving ease of operation and ease of maintenance. This embodiment of the invention is designed to consume low power, compatible with a battery or battery pack operation. In this embodiment, a 6 volt DC supply is utilized. A battery eliminator may be use for continuous operation in a fixed location. There is a passive battery supply monitor that will turn on an LED indicator if the input voltage falls below a specified voltage.  
         [0092]     A second embodiment of this invention comprises a second electronic proximity sensor. The second detector circuit is a miniaturized, micro-powered, capacitance-based proximity sensor designed to detect the approach of a hand to a towel dispenser. It features stable operation and a three-position sensitivity selector.  
         [0093]      FIG. 10  shows the whole proximity detector circuit. In order to examine the circuit more carefully,  FIG. 10  is broken out into sections  10 A through  10 E. These component circuits are shown separately as  FIGS. 10A through 10E , corresponding to the breakout shown in  FIG. 10 .  
         [0094]     At the heart of the proximity detector is an adjustable asymmetric rectangular wave oscillator running in a range of 24 kHz to 40 kHz, as shown in FOG.  10 A. Once an initial adjustment has been set it is not readjusted during operation, normally. The asymmetrical feature of having a longer on-time and shorter off-time allows for more useable signal, i.e., on-time. This 24 kHz to 40 kHz oscillation range provides a basis for a high rate of sampling of the environment to detect capacitance changes, as detailed below. As shown, a fast comparator, XU2A  200 , has positive feedback through XR18  202  from the output terminal  1   204  (XU2A) to the positive input terminal  3   206  (XU2A). The comparator operates as a Schmitt trigger oscillator with positive feedback to the non-inverting input, terminal. The positive feedback insures a rapid output transition, regardless of the speed of the input waveform. As the capacitor XC 6   208  is charged up, the terminal  3   206  of the XU2A  200  comparator reaches ⅔ XV DD . This voltage ⅔ XV DD  is maintained on terminal  3   206  by the voltage dividing network XR 17   212  and XR 20   214 , and the positive feedback resistor XR 18   202  that is in parallel with XR 17   212 , where XR 17   212  and XR 20   214  and XR 18   202  are all equal resistances. The simplest form of a comparator is a high-gain differential amplifier, made either with transistors or with an op-amp. The op-amp goes into positive or negative saturation according to the difference of the input voltages because the voltage gain is typically larger than 100,000, the inputs will have to be equal to within a fraction of a millivolt in order for the output not to be completely saturated. Although an ordinary op-amp can be used as comparator, there are special integrated circuits intended for this use. For low power consumption, better performance is achieved with a CMOS comparator, such as a TEXAS INSTRUMENT® TLC3702CD  158  ( FIG. 8B ). The TLC 3702  158  is a micropower dual comparator with CMOS push-pull  156  ( FIG. 8B ) outputs. These dedicated comparators are much faster than the ordinary op-amps.  
         [0095]     As the transition occurs, the output, at the output terminal  1   204 , goes relatively negative, XD 5   216  is then in a forward conducting state, and the capacitor XC 6   208  is preferentially discharged through the resistance XR 15   218  (100 kΩ) and the diode XD 5   216 .  
         [0096]     The time constant for charging the capacitor XC 6   208  is determined by resistors XVR 1   220 , XR 13   222  and XR 15   218 . The resistor XR 15   218  and the diode XD 5   216  determine the time constant for discharge of the capacitor XC 6   208 .  
         [0097]     The reset time is fixed at 9 μs by XD 5   216  and XR 15   218 . The rectangular wave source supplying the exponential to the antenna, however, can be varied from 16 to 32 μs, utilizing the variable resistance XVR 1   220  and the resistors XR 13   222  and XR 15   218 . Once set up for operational the variable resistance is not changed. The asymmetric oscillator can produce more signal (16 μs to 32 μs, as compared to the reset time. The reset time is not especially important, but the reset level is both crucial and consistent. The exponential waveform always begins one “diode voltage drop” (vbe) above the negative rail due to the forward biased diode voltage drop of XD 2   224  ( FIG. 10B ). One “diode voltage drop” (vbe) is typically in the range 0.5 V to 0.8 V, or typically about 0.6 V.  
         [0098]     The dual diode XD 4   226  ( FIG. 10A ) provides protection from static electricity. Terminal  1   228  of XD 4   226  will conduct when terminal  3   230  is at least one diode voltage drop below the ground, or negative rail. Terminal  2   232  will conduct when terminal  3   230  is at least one diode voltage drop above V DD    234 . Therefore, the signal level at terminal  3   230  is limited to the range −vbe to VDD+vbe, thereby eliminating voltage spikes characteristic of “static”, which may be induced by lightening or the operation of electrical motors, for example. The static is primarily built up by the internal mechanisms of the towel dispenser and the movement of the paper and is discharged by bringing a waving hand near the sensor.  
         [0099]     The asymmetric square wave charges the antenna  236  ( FIG. 10B ) through the resistors XR 9   238  and XR 4   240 . The sum resistance, XR, is equal to XR 9   238  plus XR 4   240 , or 1.7 MΩ, for the example values shown in  FIGS. 10 and 10 B. The antenna  236  forms one conducting side of a capacitor, while the atmosphere and other materials form a dielectric between the antenna as one conducting element and other conductive materials including buildings and the actual earth as a second conductive element. The capacitance C of the antenna  236  relative to “free space” is approximately 7 pF to 8 pF, as determined by experiment, yielding a time constant τ, where τ is equal to RC. Thus, the time constant, for the exemplary values, is about 13 μs.  
         [0100]     If a hand of a person is placed in proximity to the antenna of the circuit, the capacitance of the antenna to free space may double to about 15 pF with a resultant longer time constant and lower amplitude exponential waveform. The time constant T is increased to about 26 μs. While it is possible to directly compare the signals, it is also desirable to have as stable an operating circuit as possible while retaining a high sensitivity and minimizing false positives and false negatives with respect to detection. To aid in achieving these goals, the signal is conditioned or processed first.  
         [0101]     Looking at the operational amplifier XU1A  242 , the (signal) waveform sees very high impedance, since operational amplifiers have high input impedance. The impedance on the antenna  236  side of the operational amplifier  242 , in the form of resistance, is about 1.9 MΩ. The impedance on the other side of the operational amplifier is of the order of 5 kΩ. In order to provide an impedance buffer the signal the operational amplifier UX1A  242  is set up as a unity follower with a voltage gain of 1.0, that is, the gain given by V out /V in  equals one. The unity follower has an input-side (of the operational amplifier) resistance of about 1.0 TΩ (10 13  Ω). The (operational amplifier&#39;s) output impedance is in a range about 40 to 600 to several thousand ohms. Consequently, this unity follower configuration serves to isolate or buffer the upstream high-impedance circuit from the downstream low impedance circuit.  
         [0102]     The resistor XR 2   244  acts as a current limitor, since the current i is equal to V/XR 2  at XR 2   244 . Further protection against static is provided by the diode pair XD 3   246  in the same way as diode pair XD 4   226  ( FIG. 1A ). Terminal  1   248  of XD 3   246  will conduct when terminal  3   250  is at least one diode voltage drop below the ground, or negative rail. Terminal  2   252  will conduct when terminal  3   250  is at least one diode voltage drop above V DD . Therefore, the signal level at terminal  3   250  is limited to the range −vbe to V DD +vbe, so that voltage spikes characteristic of “static” are eliminated.  
         [0103]     Asymmetric oscillator pulses, after detecting capacitance which either includes or does not include a proximate dielectric equivalent to that of a proximate hand, act on the positive (non-inverting) input terminal  254  of the unity follower operational amplifier  242  to produce a linear output at its output terminal  256 . The state of the output terminal is determined by first, the length of the asymmetric on pulse, and within the time of the “on” pulse, the time taken to charge up the antenna  236  (as capacitor) and the time to discharge through XR 2   244  to the non-inverting input terminal  254 . The time-constant-to-charge is 13 μs to 26 μs. The time-constant-to-discharge is 0.8 to 1.6 μs. To charge the antenna  236  to a certain charge, Q, for a capacitance based on a dielectric constant for “free space” of ε 0 , i.e., Cε 0 , a voltage of V=Q/Cε 0  is required. For the case of a capacitance, i.e., Cε 0 +ε, which includes a detectable hand in “free space,” the voltage required to store charge Q is Q/Cε 0 +ε. However, Cε 0 +ε is about twice Cε 0 , so that the voltage peak for the detected hand is about half of the no-hand-present case.  
         [0104]     The diode XD 1   258  allows positive forward conduction but cuts off the negative backward conduction of a varying signal pulse. The forward current, or positive peak of the current, tends to charge the capacitor XC 5   260 . The diode XD 1   258 , the resistor XR 8   262 , the capacitor XC 5   260  and the bleed resistor XR 10   264  comprise a peak detector network. XD 1   258  and XC 5   260  capture the positive peak of the exponential waveform. XR 8   262  prevents oscillation of XU1A  242 . XR 8   262  limits the charging time constant to 5 ms, where XR 8   262  is 4.99 kΩ and XC 5   260  is 0.1 μF. This has an averaging effect on the peak detection and prevents noise spikes from pumping up the detector. The resistor XR 10   264  discharges the detector at a half-second time constant.  
         [0105]     When the hand is detected, the stored charge on XC 8   260  is such that the voltage is sufficient to raise the input to the non-inverting terminal  266  of operational amplifier XU1B  268  above ½XV DD , so as to drive that operational amplifier output to a usable linear voltage range.  
         [0106]     The combination of the resistor XR 1   270  (e.g., 499 kΩ) and the capacitor XC 1   272  (e.g., 0.1 μF) comprise a low pass filter with a corner frequency of 1/XR 1 ●XC 1  (e.g., 20 Hz), which corresponds to a time constant of XR 1 ●XC 1  (e.g., 50 ms). This filter is for rejection of large 50 Hz or 60 Hz noise. These “high” frequencies are effectively shorted to ground. It is particularly helpful when the towel dispenser proximity detector is powered from an AC-coupled supply. The ubiquitousness of the AC power frequency, however, makes this protection desirable, regardless.  
         [0107]     The signal is next amplified by an operational amplifier XU1B  268 , which has a gain of 22. The resistor XR 5   277  serves as a feedback resistor to the negative (inverting) input terminal  279  of the operational amplifier  268 . There is a ½ XV DD  offset provided by the voltage divider network of XR 3   274  and XR 11   276 . The output rests against the negative rail until a peak exceeds ½ XV DD ; The charge time adjustment XVR 1  becomes a very simple and sensitive way to adjust to this threshold. A setting of 3 V between test points XTP 1   278  and XTP 2   280  is recommended. This adjustment is made with all external capacitive loads (i.e., plastic and metal components) in place.  
         [0108]     The output comparator  282  ( FIG.10D ) is connected to the signal processing from the operational amplifier  268  ( FIG. 10C ) by the auto-compensate capacitor XC 3   284  ( FIG. 10D ). This makes the circuit insensitive to DC levels of signal, but sensitive to transients, e.g., a waving hand. As long as the charge-time adjustment function remains in a linear range, the sensitivity to a moving hand will be stable.  
         [0109]     The capacitor XC 4   286  allows the reference level (REF)  288  to track with approximately 50 Hz or 60 Hz noise on the SIGNAL  290  and not cause erroneous output pulses, since the AC noise will also track on the REF  288  (non-inverting) input to the comparator  282 .  
         [0110]     The output stage of the proximity detector is implemented as a variable threshold comparator, XU2B  282 . The signal is set up with an offset voltage, where the resistors XR 7   292  and XR 12   294  are equal and divide the V DD  voltage into two ½ V DD  segments. Three sensitivity settings are provided by SW 1   296 , high, medium, and low. These settings include where the reference voltage is the voltage drop across XR 6   298  (499 kΩ) with the remainder of the voltage divider equal to XR 19   300  (453 kΩ) plus XR 16   302  (20 kΩ) plus XR 14   304  (10 kΩ). This is the high setting, since the base reference voltage (V DD ●499/[499+483]} is greater than, but almost equal to the base signal value (V DD ●499/[499+499]}. The signal must overcome, i.e., become smaller than the reference voltage (since the input is an inverting input), in order to swing the output  306  of the comparator XU2B  282  high and activate, say, a motor-control latch (not shown in  FIG. 10D ). The medium sensitivity setting, in  FIG. 1E , of switch XSW 1   296  (bypassing XR 14 ,  304  10 kΩ, by way of switch XSW 1   296 ) widens the difference between the signal and reference levels. The low sensitivity setting (bypassing XR 14   304 , 10 kΩ, and XR 16   302 , 20 kΩ, by way of switch XSW 1   296 ), widens that difference between the signal and reference levels even more. Consequently, a larger difference between the signal and the reference voltage must be overcome to activate the motor by way of the comparator XU2B  282  and the motor-control latch (not shown in  FIG. 10D ).  
         [0111]     The entire sensor circuit runs continuously on approximately 300 μA at a supply voltage (XV DD    234 ) of 5 V.  
         [0112]     Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.-Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.