Abstract:
A direction of rotation detection apparatus and method using the outputs of a single differential sequential sensor employing two matched magnetostatic elements, ie., either Hall elements or magnetoresistors (MRs), to extract direction of rotation information from the passage of a single tooth edge of a target wheel. The two matched sensing elements are spaced in close proximity to each other, preferably on the order preferably of about 1 mm to about 2 mm apart, in the circumferential direction of the target wheel and generate two identical angularly offset signals from the passage of a single tooth edge of a target wheel which are input to a signal conditioning circuit. Within the signal conditioning circuit, the two sensor signals are differentially amplified to produce a differential signal whereby the polarity of the differential signal enables one of two comparators with respective reference voltages. The output of the enabled comparator is processed and converted into a digital output signal whose voltage level indicates the direction of rotation of the target wheel.

Description:
TECHNICAL FIELD 
     The present invention relates to a method of sensing direction of crankshaft rotation and more particularly to a method and apparatus to sense direction of crankshaft rotation from the passage of single tooth edges of an encoder or target wheel with a single, currently used, differential sequential sensor employing either Hall elements or magnetoresistors. 
     BACKGROUND OF THE INVENTION 
     It is well known in the art that the resistance modulation of Hall elements or magnetoresistors can be employed in position and speed sensors with respect to moving ferromagnetic materials or objects (see for example U.S. Pat. Nos. 4,835,467; 4,926,122; and 4,939,456). 
     Increasingly more sophisticated spark timing and emission controls introduced the need for crankshaft sensors capable of providing not only precise position information, but also, during cranking, a direction of rotation signal. Currently, as shown in FIG. 1, direction of rotation, clockwise (CW)  32  or counterclockwise (CCW)  34 , is most commonly obtained from an encoder wheel  10 , also called a target wheel, having a plurality of teeth  12  and slots  14  of essentially equal length which have a spacing between adjacent teeth or a spacing between adjacent slots of P, called the tooth/slot pitch. The teeth  12  and slots  14  are sensed by SENSOR 1   16  and SENSOR 2   18  in quadrature (i.e. with spacing between sensors equal to one-quarter of the tooth/slot pitch P). Equal lengths of teeth  12  and equal lengths of slots  14  and the one-quarter pitch spacing between sensors are preferred, but not absolutely necessary. The square wave output signals from SENSOR 1   16  and SENSOR 2   18  are fed as a clock input  20  and a data input  22  into a D type FLIP-FLOP  24  whose output  26  provides a direction indication and is either high (H)  28  or low (L)  30  depending on the direction of rotation of the target wheel  10 . Due to the large P/4 distance between SENSOR 1   16  and SENSOR 2   18 , a major disadvantage of the current method is the inability to detect the change of rotational direction of the target wheel when a single tooth edge, such as tooth edge  36 , is oscillating around a single sensor, such as SENSOR 1   16 . In this case, SENSOR 1   16  would detect the back and forth oscillating single tooth edge  36  as the rising and falling edges of passing teeth  12 . Since the direction indication  26  would remain unchanged, serious position errors would be generated. For this reason, and due to the necessity of adding a second sensor, the conventional method of detecting direction of rotation is not suitable for automotive crankshaft sensors. 
     What is needed is a method and apparatus whereby the direction of rotation of an automotive crankshaft can be obtained from the passage of a single tooth edge of a target wheel. 
     SUMMARY OF THE INVENTION 
     The present invention provides detection of direction of rotation via the outputs of a differential sequential sensor employing two matched sensing elements, either Hall elements or magnetoresistors (MRs), to extract direction of rotation information from the passage of a single tooth edge of a target wheel. The two matched sensing elements are spaced in close proximity to each other, preferably on the order of about 1 mm to 2 mm apart, in the circumferential direction of the target wheel and generate two identical angularly offset signals from the passage of a single tooth edge of a target wheel which are input to a signal conditioning circuit. Within the signal conditioning circuit, the two sensor signals are differentially amplified to produce a differential signal whereby the polarity of the differential signal enables one of two comparators with respective reference voltages. The output of the enabled comparator is processed and converted into a digital output signal whose voltage level indicates the direction of rotation of the target wheel. 
     Accordingly, it is an object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth edge. 
     It is an additional object of the present invention to provide a digital output voltage for detecting direction of rotation of a target wheel at a single tooth-slot edge using two closely spaced sensing elements. 
     These, and additional objects, advantages, features, and benefits of the present invention will become apparent from the following specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a combined environmental depiction and circuit schematic of a conventional direction of rotation sensor. 
     FIG. 2 depicts an example of a preferred environment of use of the present invention. 
     FIG. 3 shows an electronic block diagram of the preferred embodiment of the present invention. 
     FIGS. 4 a  through  4   s  show the wave forms generated from FIG. 3 due to the passage of a rising edge of a tooth of a target wheel rotating in a clockwise (CW) direction. 
     FIGS. 5 a  through  5   s  show the wave forms generated from FIG. 3 due to the passage of a falling edge of a tooth of a target wheel rotating in a clockwise (CW) direction. 
     FIGS. 6 a  through  6   s  show the wave forms generated from FIG. 3 due to the passage of a rising edge of a tooth of a target wheel rotating in a counterclockwise (CCW) direction. 
     FIGS. 7 a  through  7   s  show the wave forms generated from FIG. 3 due to the passage of a falling edge of a tooth of a target wheel rotating in a counterclockwise (CCW) direction. 
     FIG. 8 is a table summarizing the results of FIGS. 4 a  through  7   s.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 2 is a schematic representation of an exemplar automotive environment of use according to the present invention, wherein a target wheel  10 ′ is rotating, such as for example in unison with a crankshaft, a drive shaft or a cam shaft, and the rotative direction thereof is to be sensed. Rotative direction of the target wheel  10 ′ is determined by sensing the passage of either a rising tooth edge  36 ′ or a falling tooth edge using a single differential sequential sensor  50 . A tooth edge  36 ′ is considered rising or falling depending upon the direction of rotation of the target wheel  10 ′ with respect to the magnetoresistive sensors MR 1  and MR 2 . The single differential sequential sensor  50  employs two matched magnetoresistor (MR) elements, MR 1  and MR 2 , which are biased by a permanent magnet  56 , wherein the magnetic flux  60  and  62  emanating therefrom is represented by the dashed arrows. The magnetic flux  60  and  62  passes from the permanent magnet  56  through the magnetoresistors MR 1  and MR 2  and through the air gaps  64  and  66  to the target wheel  10 ′. The target wheel  10 ′ is made of a magnetic material having teeth  12 ′ and spacings  14 ′ therebetween. The spacing L between MR 1  and MR 2  is between about 1 mm (or less) and about 2 mm (or more) in the circumferential direction of the target wheel  10 ′ and the target wheel is located near the single differential sequential sensor  50  as indicated in FIG.  2 . 
     Power is supplied to CURRENT SOURCE 1   72  and CURRENT SOURCE 2   74  through voltage source  70 . Power is also supplied to signal conditioning circuit  80  through voltage source  70  but is not shown. CURRENT SOURCE 1   72  supplies current to MR 1  thereby providing for an output voltage V MR1  from MRI. CURRENT SOURCE 2   74  supplies current to MR 2  thereby providing for an output voltage V MR2  from MR 2 . Output voltages V MR1  and V MR2  are input into signal conditioning circuit  80  whose output voltage V OUT  is an indication of the direction of rotation of target wheel  10 ′. It is to be understood that all voltages are measured with respect to ground unless otherwise indicated herein, and that CURRENT SOURCE 1  is matched to CURRENT SOURCE 2 . 
     FIG. 3 shows an electronic block diagram of the preferred embodiment of the present invention. It is well known in the art that the resistance of a magnetoresistor will have a larger value when the magnetoresistor is adjacent to a tooth  12 ′ of a target wheel  10 ′ of FIG. 2 than when the magnetoresistor is adjacent to a slot  14 ′ of the target wheel. Thus, when MR 1  and MR 2  are powered by constant current sources, the output voltages V MR1  and V MR2  will have higher values when the magnetoresistors MR 1  and MR 2  are adjacent a tooth  12 ′ of a target wheel  10 ′ than when MR 1  and MR 2  are adjacent a slot  14 ′ of the target wheel. The circuit of FIG. 3 functions as follows. 
     As the passage of a tooth edge  36 ′ is sensed by MR 1  and MR 2 , the two sensor signals V MR1  and V MR2  are input into a differential amplifier  90  to produce a differential signal pulse V D , which in this case V D  is taken to be V MR1 −V MR2.  V D  could also be taken as V MR2 −V MR1  within the scope of the present invention. During the time that the polarity of V D  is positive and greater than the reference voltages +ΔV, which is applied to the negative input of comparator C 1 , the output of comparator C 1 , V C1 , will be high and the output of comparator C 2 , V C2 , will be low. Further, during the time that the polarity of V D  is negative and less than the reference voltage −ΔV, which is applied to the positive input of comparator C 2 , the output of comparator C 2 , V C2 , will be high and the output of comparator C 1 , V C1 , will be low. Hence, the output of C 1 , will be a square wave with a positive voltage level or value for V C2 , for V D  having positive values greater than +ΔV, whereas the output of C 2  will be a square wave with a positive voltage level or value for V C2  for VD having negative values less than −ΔV. 
     The square wave output of either C 1  or C 2  appears at the output of OR gate G 3  as a square wave with a positive voltage for V G3  which is input into the FALLING EDGE SINGLE SHOT block  92 . FALLING EDGE SINGLE SHOT block  92  outputs a pulse with a positive voltage for V SS  whose falling edge is used as the clock input into FLIP-FLOP  94  to latch the output voltage V OUT  of the FLIP-FLOP to the value of the input voltage V C3  to the FLIP-FLOP. The value of V C3  is determined as follows. 
     If C 1  outputs a square wave, as previously described, then DUAL SINGLE SHOT 1   96  will output a pulse on the rising and falling edges of the square wave. The rising edge pulse from DUAL SINGLE SHOT 1   96  latches the output voltage, V SH1 , of SAMPLE &amp; HOLD 1   98  to the value of V MR1  at this time. The falling edge pulse from DUAL SINGLE SHOT 1   96  latches the output voltage, V SH2 , of SAMPLE &amp; HOLD 2   100  to the value of V MR1  at this time. 
     On the other hand, if C 2  outputs a square wave, as previously described, then DUAL SINGLE SHOT 2   102  will output a pulse on the rising and falling edges of the square wave. The rising edge pulse from DUAL SINGLE SHOT 2   102  latches the output voltage, V SH2 , of SAMPLE &amp; HOLD 2   100  to the value of V MR1  at this time. The falling edge pulse from DUAL SINGLE SHOT 2   102  latches the output voltage, V SH1 , of SAMPLE &amp; HOLD 1   98  to the value of V MR1  at this time. 
     Within the scope of the present invention, V MR2  could be the sampled voltage of SAMPLE &amp; HOLD 1   98  and SAMPLE &amp; HOLD 2   100  instead of V MR1 . V SH1  is one input into comparator C 3  and V SH2  is another input into comparator C 3 . If V SH2  is larger than V SH1  then the output of C 3 , V C3 , will be a high voltage which will appear as V OUT  when a clock pulse is input to FLIP-FLOP  94  as previously described. If V SH1  is larger than V SH2  then the output of C 3 , V C3 , will be a low voltage which will appear as V OUT  when a clock pulse is input to FLIP-FLOP  94  as previously described. As will be explained in FIGS. 4a through 7s, the value of VOUT is indicative of the direction of rotation of the target wheel. With V D  taken to be V MR1 −V MR2  and V MR1  being the sampled voltage of SAMPLE &amp; HOLD 1   98  and SAMPLE &amp; HOLD 2   100 , a high voltage for V OUT  indicates a CW rotation of the target wheel  10 ′ of FIG. 2 whereas a low voltage for Vout indicates a CCW rotation of the target wheel. 
     FIGS. 4 a  through  4   s  show the wave forms generated from FIG. 3 due to the passage of a rising edge  36 ′ of a tooth  12 ′ of a target wheel  10 ′ rotating in a clockwise (CW) direction. The sensors MR 1  and MR 2  are initially adjacent to a slot  14 ′ of the target wheel  10 ′ which is rotating in a CW direction as shown in FIG. 4 a  and V MR1  and V MR2  have a low value as depicted in (a) of FIG. 4 d.  As the target wheel  10 ′ rotates CW, MR 1  becomes adjacent to a tooth  12 ′ of the target wheel whereas MR 2  is still adjacent to a slot  14 ′ but is approaching the tooth as shown in FIG. 4 b.  During this time V MR1 , rises quickly to a high level whereas V MR2  starts to rise as MR 2  approaches the tooth  12 ′ as shown in (b) of FIG. 4 d.  As the target wheel  10 ′ continues to rotate CW, both MR 1  and MR 2  become adjacent to a tooth  12 ′ and V MR1  and V MR2  are at a high level as shown in (c) of FIG. 4 d.    
     FIG. 4 e  depicts the differential voltage pulse V D,  which is positive in this case, thereby, producing a square wave output, V C1 , from comparator C 1  of FIG. 3, as shown in FIG. 4 f,  which is then input to DUAL SINGLE SHOT 1   96  of FIG.  3 . The DUAL SINGLE SHOT 1  of FIG. 3 outputs a pulse V DSS1  (R) of FIG. 4 j  on the rising edge of V C1  as well as a pulse V DSS1  (F) of FIG. 4 k  on the falling edge of V C1 . 
     V DSS1  (R) is input to OR gate G 1 , of FIG.  3  and the output of OR gate G 1 , V G1 , shown in FIG. 4 n  is input to SAMPLE &amp; HOLD 1   98  of FIG.  3 . The output of SAMPLE &amp; HOLD 1   98  of FIG. 3, V SH1 , is denoted as V 1 , and is depicted in FIGS. 4 d  and  4   q.  V 1 , in FIG. 4 d,  is the value of V MR1  at the rising edge of V C1 , of FIG. 4 f  and is applied to the negative input of comparator C 3  of FIG.  3 . 
     V DSS1  (F) is input to OR gate G 2  of FIG.  3  and the output of OR gate G 2 , V G2 , shown in FIG. 4 o  is input to SAMPLE &amp; HOLD 2   100  of FIG.  3 . The output of SAMPLE &amp; HOLD 2   100  of FIG. 3, V SH2 , is denoted as V 2  and is depicted in FIGS. 4 d  and  4   p.  V 2 , in FIG. 4 d,  is the value of V MR1  at the falling edge of V C1  of FIG. 4 f  and is applied to the positive input of comparator C 3  of FIG.  3 . 
     As can be seen in FIG. 4 d  and by comparing FIG. 4 p  to FIG. 4 q,  V 2  is greater than V 1 . Thus the output of comparator C 3  of FIG. 3, V C3 , will have a high value as shown in FIG. 4 r.  V C3  in FIG. 3 is input to FLIP-FLOP  94  and is transferred to the output of the FLIP-FLOP where it appears as Vout upon reception of the falling edge of a clock pulse, V SS , to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT  92 . 
     The clock pulse, V SS , is shown in FIG. 4 i.  V SS  is the output of FALLING EDGE SINGLE SHOT  92  of FIG.  3 . The FALLING EDGE SINGLE SHOT  92  of FIG. 3 generates the pulse V SS  upon the falling edge of V G3  of FIG. 4 h  which is obtained from the falling edge of V C1 , via OR gate G 3  of FIG.  3 . Thus, when the clock pulse, V SS , is input to FLIP-FLOP  94  of FIG. 3, V OUT  will have a high value as depicted in FIG. 4 s  indicating, in this case, a CW rotation of the target wheel  10 ′ of FIG.  3 . 
     FIG. 5 shows the wave forms generated from FIG. 3 due to the passage of a falling edge  36 ′ of a tooth  12 ′ of a target wheel  10 ′ rotating in a clockwise (CW) direction. The sensors MR 1  and MR 2  are initially adjacent to a tooth  12 ′ of the target wheel  10 ′ which is rotating in a CW direction as shown in FIG. 5 a  and V MR1  and V MR2  have a high value as depicted in (a) of FIG. 5 d.  As the target wheel  10 ′ rotates CW, MR 1  becomes adjacent to a slot  14 ′ of the target wheel whereas MR 2  is still adjacent to a tooth  12 ′ but is approaching the slot as shown in FIG. 5 b.  During this time V MR1  falls quickly to a low level whereas V MR2  starts to fall as MR 2  approaches the slot  14 ′ as shown in (b) of FIG. 5 d.  As the target wheel  10 ′ continues to rotate CW, both MR 1  and MR 2  become adjacent to a slot  14 ′ and V MR1  and V MR2  are at a low level as shown in (c) of FIG. 5 d.    
     FIG. 5 e  depicts the differential voltage pulse V D , which is negative in this case, thereby, producing a square wave output, V C2 , from comparator C 2  of FIG. 3, as shown in FIG. 5 g,  which is then input to DUAL SINGLE SHOT 2   102  of FIG.  3 . The DUAL SINGLE SHOT 2   102  of FIG. 3 outputs a pulse V DSS2  (R) of FIG. 51 on the rising edge of V C2  as well as a pulse V DSS2  (F) of FIG. 5 o  on the falling edge of V C2 . 
     V DSS2  (R) is input to OR gate G 2  of FIG.  3  and the output of OR gate G 2 , V G2 , shown in FIG. 5 o  is input to SAMPLE &amp; HOLD 2   100  of FIG.  3 . The output of SAMPLE &amp; HOLD 2   100  of FIG. 3, V SH2 , is denoted as V 1 , and is depicted in FIGS. 5 d  and  5   p.  V 1 , in FIG. 5 d,  is the value of V MR1  at the rising edge of V C2  of FIG. 5 g  and is applied to the positive input of comparator C 3  of FIG.  3 . 
     V DSS2  (F) is input to OR gate G 1  of FIG.  3  and the output of OR gate G 1 , V G1 , shown in FIG. 5 n  is input to SAMPLE &amp; HOLD 1   98  of FIG.  3 . The output of SAMPLE &amp; HOLD 1   98  of FIG. 3, V SH1 , is denoted as V 2  and is depicted in FIGS. 5 d  and  5   q.  V 2 , in FIG. 5 d,  is the value of V MR1  at the falling edge of V C2  of FIG. 5 g  and is applied to the negative input of comparator C 3  of FIG.  3 . 
     As can be seen in FIG. 5 d  and by comparing FIG. 5 p  to FIG. 5 q,  V 1 , is greater than V 2 . Thus the output of comparator C 3  of FIG. 3, V C3 , will have a high value as shown in FIG. 5 r.  V C3  in FIG. 3 is input to FLIP-FLOP  94  and is transferred to the output of the FLIP-FLOP where it appears as V OUT  upon reception of the falling edge of a clock pulse, V SS , to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT  92 . 
     The clock pulse, V ss , is shown in FIG. 5 i.  V SS  is the output of FALLING EDGE SINGLE SHOT  92  of FIG.  3 . The FALLING EDGE SINGLE SHOT  92  of FIG. 3 generates the pulse V SS  upon the falling edge of V G3  of FIG. 5 h  which is obtained from the falling edge of V C2  via OR gate G 3  of FIG.  3 . Thus, when the clock pulse, V SS , is input to FLIP-FLOP  94  of FIG. 3, V OUT  will have a high value as depicted in FIG. 5 s  indicating, in this case, a CW rotation of the target wheel  10 ′ of FIG.  3 . 
     FIG. 6 shows the wave forms generated from FIG. 3 due to the passage of a rising edge  36 ′ of a tooth  12 ′ of a target wheel  10 ′ rotating in a counterclockwise (CCW) direction. The sensors MR 1  and MR 2  are initially adjacent to a slot  14 ′ of the target wheel  10 ′ which is rotating in a CCW direction as shown in FIG. 6 a  and V MR1  and V MR2  have a low value as depicted in (a) of FIG. 6 d.  As the target wheel  10 ′ rotates CCW, MR 2  becomes adjacent to a tooth  12 ′ of the target wheel whereas MR 1  is still adjacent to a slot  14 ′ but is approaching the tooth as shown in FIG. 6 b.  During this time V MR2  rises quickly to a high level whereas V MR1  starts to rise as MR 1  approaches the tooth  12 ′ as shown in (b) of FIG. 6 d.  As the target wheel  10 ′ continues to rotate CCW, both MR 1  and MR 2  become adjacent to a tooth  12 ′ and V MR1  and V MR2  are at a high level as shown in (c) of FIG. 6 d.    
     FIG. 6 e  depicts the differential voltage pulse V D,  which is negative in this case, thereby, producing a square wave output, V C2 , from comparator C 2  of FIG. 3, as shown in FIG. 6 g,  which is then input to DUAL SINGLE SHOT 2   102  of FIG.  3 . The DUAL SINGLE SHOT 2   102  of FIG. 3 outputs a pulse V DSS2  (R) of FIG. 61 on the rising edge of V C2  as well as a pulse V DSS2  (F) of FIG. 6 m  on the falling edge of V C2 . 
     V DSS2  (R) is input to OR gate G 2  of FIG.  3  and the output of OR gate G 2 , V G2 , shown in FIG. 60 is input to SAMPLE &amp; HOLD 2   100  of FIG.  3 . The output of SAMPLE &amp; HOLD 2   100  of FIG. 3, V SH2 , is denoted as V 1 , and is depicted in FIGS. 6 d  and  6   p.  V 1 , in FIG. 6 d,  is the value of V MR1  at the rising edge of V C2  of FIG. 6 g  and is applied to the positive input of comparator C 3  of FIG.  3 . 
     V DSS2  (F) is input to OR gate G 1 , of FIG.  3  and the output of OR gate G 1 , V G1 , shown in FIG. 6 n  is input to SAMPLE &amp; HOLD 1   98  of FIG.  3 . The output of SAMPLE &amp; HOLD 1   98  of FIG. 3, V SH1 , is denoted as V 2  and is depicted in FIGS. 6 d  and  6   q.  V 2 , in FIG. 6 d,  is the value of V MR1  at the falling edge of V C2  of FIG. 6 g  and is applied to the negative input of comparator C 3  of FIG.  3 . 
     As can be seen in FIG. 6 d  and by comparing FIG. 6 p  to FIG. 6 q,  V 2  is greater than V 1 . Thus the output of comparator C 3  of FIG. 3, V C3 , will have a low value as shown in FIG. 6 r.  V C3  in FIG. 3 is input to FLIP-FLOP  94  and is transferred to the output of the FLIP-FLOP where it appears as V OUT  upon reception of the falling edge of a clock pulse, V SS , to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT  92 . 
     The clock pulse, V SS , is shown in FIG. 6 i.  V SS  is the output of FALLING EDGE SINGLE SHOT  92  of FIG.  3 . The FALLING EDGE SINGLE SHOT  92  of FIG. 3 generates the pulse V SS  upon the falling edge of V G3  of FIG. 6 h  which is obtained from the falling edge of V C2  via OR gate G 3  of FIG.  3 . Thus, when the clock pulse, V SS , is input to FLIP-FLOP  94  of FIG. 3, V OUT  will have a low value as depicted in FIG. 6 s  indicating, in this case, a CCW rotation of the target wheel  10 ′ of FIG.  3 . 
     FIG. 7 shows the wave forms generated from FIG. 3 due to the passage of a falling edge  36 ′ of a tooth  12 ′ of a target wheel  10 ′ rotating in a counterclockwise (CCW) direction. The sensors MR 1  and MR 2  are initially adjacent to a tooth  12 ′ of the target wheel  10 ′ which is rotating in a CCW direction as shown in FIG. 7 a  and V MR1  and V MR2  have a high value as depicted in (a) of FIG. 7 d.  As the target wheel  10 ′ rotates CCW, MR 2  becomes adjacent to a slot  14 ′ of the target wheel whereas MR 1  is still adjacent to a tooth  12 ′ but is approaching the slot as shown in FIG. 7 b.  During this time V MR2  falls quickly to a low level whereas V MR1  starts to fall as MR 1  approaches the slot  14 ′ as shown in (b) of FIG. 7 d.  As the target wheel  10 ′ continues to rotate CCW, both MR 1  and MR 2  become adjacent to a slot  14 ′ and V MR1  and V MR2  are at a low level as shown in (c) of FIG. 7 d.    
     FIG. 7 e  depicts the differential voltage pulse V D , which is positive in this case, thereby, producing a square wave output, V C1 , from comparator C 1  of FIG. 3, as shown in FIG. 7 f,  which is then input to DUAL SINGLE SHOT 1   96  of FIG.  3 . The DUAL SINGLE SHOT 1  of FIG. 3 outputs a pulse V DSS1  (R) of FIG. 7 j  on the rising edge of V C1  as well as a pulse V DSS1  (F) of FIG. 7 k  on the falling edge of V C1 . 
     V DSS1  (R) is input to OR gate G 1  of FIG.  3  and the output of OR gate G 1 , V G1 , shown in FIG. 7 n  is input to SAMPLE &amp; HOLD 1   98  of FIG.  3 . The output of SAMPLE &amp; HOLD 1   98  of FIG. 3, V SH1 , is denoted as V 1 , and is depicted in FIGS. 7 d  and  7   q.  V 1 , in FIG. 7 d,  is the value of V MR1  at the rising edge of V C1 , of FIG. 7 f  and is applied to the negative input of comparator C 3  of FIG.  3 . 
     V DSS1  (F) is input to OR gate G 2  of FIG.  3  and the output of OR gate G 2 , V G2 , shown in FIG. 7 o  is input to SAMPLE &amp; HOLD 2   100  of FIG.  3 . The output of SAMPLE &amp; HOLD 2   100  of FIG. 3, V SH2 , is denoted as V 2  and is depicted in FIGS. 7 d  and  7   p.  V 2 , in FIG. 7 d,  is the value of V MR1  at the falling edge of V C1 , of FIG. 7 f  and is applied to the positive input of comparator C 3  of FIG.  3 . 
     As can be seen in FIG. 7 d  and by comparing FIG. 7 p  to FIG. 7 q,  V 1 , is greater than V 2 . Thus the output of comparator C 3  of FIG. 3, V C3 , will have a low value as shown in FIG. 7 r.  V C3  in FIG. 3 is input to FLIP-FLOP  94  and is transferred to the output of the FLIP-FLOP where it appears as V OUT  upon reception of the falling edge of a clock pulse, V SS , to the FLIP-FLOP from the output of FALLING EDGE SINGLE SHOT  92 . 
     The clock pulse, V SS , is shown in FIG. 7 i.  V SS  is the output of FALLING EDGE SINGLE SHOT  92  of FIG.  3 . The FALLING EDGE SINGLE SHOT  92  of FIG. 3 generates the pulse V SS  upon the falling edge of V G3  of FIG. 7 h  which is obtained from the falling edge of V C1  via OR gate G 3  of FIG.  3 . Thus, when the clock pulse, V SS , is input to FLIP-FLOP  94  of FIG. 3, V OUT  will have a low value as depicted in FIG. 7 s  indicating, in this case, a CCW rotation of the target wheel  10 ′ of FIG.  3 . 
     The Table of FIG. 8 summarizes how the direction of rotation is obtained from a single tooth edge  36 ′ from a knowledge of the polarity of the differential signal pulse, V D , and whether the output signal, in this example, V MR1 , is rising or falling within the differential pulse interval. It is understood by those knowledgeable in the art that V MR2  or a combination of V MR1  and V MR2  could also be used as the output signal within the differential pulse interval within the scope of the present invention. 
     It is to be understood that while magnetoresistors (MRs) were exemplified in the foregoing detailed description of a preferred embodiment of the present invention, other analogous sensing elements, such as hall elements my be utilized, the class of such sensors being inclusively denoted as magnetostatic elements. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.