Abstract:
Non-contact positions sensors are desirable because they have lower failure rates than traditional potentiometers. However, using a Hall Effect sensor as a non-contact position sensor requires a particular input polarity. In an embodiment, a polarity insensitive Hall Effect sensor includes conversion sensors configured to produce outputs responsive to an input. The sensor also includes a semiconductor rectifier arranged to power a first conversion sensor and a second conversion sensor with a given polarity regardless of whether the input has a positive or negative polarity. The sensor also includes a semiconductor multiplexer circuit arranged to direct the first output to a common output port if the input has a positive polarity and direct the second output to the common output port if the input has a negative polarity. The polarity insensitive Hall Effect sensor provides an output representing a position without requiring a input polarity.

Description:
BACKGROUND OF THE INVENTION 
     Potentiometers have a physical contact that rides on a resistive element. The physical contact of the potentiometer is a point of failure for the potentiometer. This point of failure decreases the reliability of potentiometers in relation to non-contacting sensors, such as a Hall Effect sensor. Non-contacting sensors, such as Hall Effect sensors, can replace potentiometers in many applications. 
     SUMMARY OF THE INVENTION 
     In an embodiment, a linear or rotation sensor includes a first conversion sensor configured to produce a first output responsive to a given input. The sensor further includes a second conversion sensor configured to produce a second output responsive to the given input. The sum of the first output and second outputs is constant regardless of whether the given input has a positive or negative polarity. The sensor also includes a semiconductor rectifier arranged to power the first conversion sensor and the second conversion sensor with a given polarity regardless of whether the given input has a positive or negative polarity. The sensor also includes a semiconductor multiplexer circuit arranged to direct the first output to a common output port if the given input has a positive polarity and direct the second output to the common output port if the given input has a negative polarity. 
     In an embodiment, the first conversion sensor is a hall effect sensor and the second conversion sensor is a hall effect sensor. 
     In an embodiment, the semiconductor multiplexer can include a first channel to direct the first output to the common output port. The first channel includes a first set of n-type MOSFET semiconductors connected in series and a second set of p-type MOSFET semiconductors connected in series. The first set and the second set are connected in parallel. The semiconductor multiplexer includes a second channel to direct the second output to the common output port. The second channel includes a third set of n-type MOSFET semiconductors connected in series and a fourth set of p-type MOSFET semiconductors connected in series. The third set and the fourth set are connected in parallel. 
     In an embodiment, respective sources of the MOSFETs within the respective first, second, third, and fourth sets of semiconductors are directly connected. The respective gates of the MOSFETs of the first, second, third, and fourth sets of semiconductors are directly connected. A first of the drains of the first set and a first of the drains of the second set are coupled to receive the first output. The gates of the first set and the fourth set are coupled to a first input port receiving a first signal defining a first portion of the given input. The gates of the second set and the third set are coupled to a second input port receiving a second signal defining a second portion of the given input. The first and second signals, when measured relative to each other at the same time instants, determine the polarity of the given input signal. A first of the drains of the third set and a first of the drains of the fourth set are coupled to receive the second output. A second of the drains of the first set, a second of the drains of the second set, a second of the drains of the third set, and a second of the drains of the fourth set are coupled to the common output port. 
     In an embodiment, the semiconductor rectifier includes at least four MOSFETs. Each MOSFET has a respective source, drain, and gate. A first of the MOSFETs is coupled (i) at its drain to a first port of the given input and a drain of a second of the MOSFETs, (ii) at its gate to a second port of the given input, and (iii) at its source to a the source of third of the MOSFETs and the first and second conversion sensors. The second of the MOSFETs is coupled (i) at its drain to the first port of the given input and the drain of the first of the MOSFETs, (iii) at its gate to a second port of the given input, and (iii) at its source the source of to a fourth of the MOSFETs and the first and second conversion sensors. The third of the MOSFETs is coupled (i) at its source to the source of the first of the MOSFETs, and the first and second conversion sensors, (ii) at its drain to the second port of the given input, and (iii) at its gate to the first port if the given input. The fourth of the MOSFETs is coupled (i) at its drain to the second port of the given input and the drain of the third of the MOSFETs, (ii) at its gate to the first port of the given input, and (iii) at its source to the source of the second MOSFETs and the first and second conversion sensors. 
     In an embodiment, the semiconductor rectifier is configured to direct a signal of a correct polarity to the first conversion sensor and the second conversion sensor based on the polarity of the given input. The semiconductor multiplexer, based on the polarity of the same given input, is configured to direct the first output or the second output to the common output port. 
     In an embodiment, the sensor also includes a programming module including three ports through which to program the first and second conversion sensors. The first and second programming module ports are coupled to the semiconductor rectifier to power the first and second conversion sensors during application of positive and negative polarity voltage levels, respectively. The third programming module port is coupled to the common output to program the first and second conversion sensors during application of the positive and negative polarity voltage levels, respectively, to the first and second conversion sensors. 
     In an embodiment, the first and second conversion sensors are configured to measure a rotation or linear position of a mechanical device being observed regardless of the polarity of the given input. 
     In an embodiment, a method of sensing linear position or rotation includes producing a first output responsive to a given input at a first conversion sensor. The method further includes producing a second output responsive to the given input at a second conversion sensor. The sum of the first output and second outputs is constant regardless of whether the given input has positive or negative polarity. The method further includes powering, at a semiconductor rectifier, the first conversion sensor and the second conversion sensor with a given polarity regardless of whether the given input has a positive or negative polarity. The method also includes directing, at a semiconductor multiplexer circuit, the first output to a common output port if the given input has a positive polarity and the second output to the common output port if the given input has a negative polarity. 
     In an embodiment, an apparatus for linear or rotation sensor includes a first conversion sensor means for producing a first output responsive to a given input. The apparatus further includes a second conversion sensor means for producing a second output responsive to the given input. The sum of the first output and second output is constant regardless of whether the given input has a positive or negative polarity. The apparatus further includes a semiconductor rectifier means for powering the first conversion sensor and the second conversion with a given polarity regardless of whether the given input has a positive or negative polarity. The apparatus also includes a semiconductor multiplexer means for directing the first output to a common output port if the given input has a positive polarity and direct the second output to the common output port if the given input has a negative polarity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIG. 1  is a block diagram illustrating an example embodiment of a polarity insensitive Hall Effect sensor employed by the present invention. 
         FIG. 2  is a block diagram illustrating an example embodiment of a traditional potentiometer. 
         FIG. 3  is a block diagram of an embodiment of a Hall Effect sensor employed to emulate a potentiometer. 
         FIG. 4  is a high level block diagram illustrating an example embodiment of the present invention. 
         FIG. 5  is a block diagram illustrating an example embodiment of the polarity insensitive Hall Effect sensor employed in an embodiment of the present invention. 
         FIG. 6A  is a block diagram illustrating an example embodiment of current paths in the polarity insensitive Hall Effect sensor in a first polarity. 
         FIG. 6B  is a block diagram illustrating an example embodiment of current paths in the polarity insensitive Hall Effect sensor in a second polarity. 
         FIG. 7  is a graph illustrating an example embodiment of percentage output of the polarity insensitive Hall Effect sensor as a function of a rotary position of a rotor in degrees. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A description of example embodiments of the invention follows. 
       FIG. 1  is a block diagram  100  illustrating an example embodiment of a polarity insensitive Hall Effect sensor  110  employed by the present invention. The polarity insensitive Hall Effect sensor  110  includes a first input port  106   a  and second input port  106   b , which can be connected to a first supply port  104   a  and second supply port  104   b  of a supply device  102 , or other input device. The polarity insensitive hall effect sensor  110  is configured to receive input from the supply device  102  in any polarity. For example, when the first supply port  104   a  is coupled with the first input port  106   a  and the second supply port  104   b  is coupled with the second input port  106   b , the supply device  102  provides a first polarity path  108   a - b  to the polarity insensitive Hall Effect sensor  110 . On the other hand, if the first supply port  104   a  is coupled with the second input port  106   b  and the second supply port  104   b  is coupled with the first input port  106   a , the supply device  102  provides a second polarity path  112   a - b  to the polarity insensitive Hall Effect Sensor  110 . Reversing the connections of the input ports  106   a - b  to the supply ports  104   a - b  reverses the polarity of the polarity paths  108   a - b  and  112   a - b . For example, if the first polarity path  108   a - b  provides a voltage difference of 5V, reversing the connections reverses the polarity in the second polarity path  112   a - b , making it negative 5V. Regardless of the polarity, the polarity insensitive Hall Effect sensor  110  outputs, at its output port  114 . Like a traditional potentiometer, reversing the polarity of the input can reverse the output. For example, a potentiometer which has an output range of 0-5V and outputs 4V for the position of its rotor for one polarity outputs 1V for the same position of the rotor for a reverse polarity. The polarity insensitive Hall Effect sensor  110  performs the same way. 
       FIG. 2  is a block diagram  200  illustrating an example embodiment of a traditional potentiometer  208 . The potentiometer is connected to a first input port  202  (POWER 1 ) and a second input port  204  (POWER 2 ). The potentiometer  208  also has an output port  206 . The potentiometer  208 , based on a position of a rotor, outputs a voltage proportional to the position of the rotor between the voltage difference of the first input port  202  and second input port  204 . Some applications use potentiometers  208  as a ratiometric device (e.g., a device that produces an output proportional to its input). Inputs of power (e.g., first input port  202 ) and ground (e.g., second input port  204 ) are applied to the potentiometer  208  element. The potentiometer  208  element outputs a voltage on a wiper output (e.g., the output port  206 ) that varies between power (e.g., first input port  202 ) and ground (e.g., second input port  204 ) as the rotor is turned. In a traditional potentiometer  208 , power and ground can be applied to either end of the device because the potentiometer is a resistor, such that the first input port  202  can be either a power or a ground and the second input port  204  can be either a power of a ground. 
       FIG. 3  is a block diagram  300  of an embodiment of a Hall Effect sensor  308  employed to emulate a potentiometer. Unlike the resistance based potentiometer of  FIG. 2 , a Hall Effect sensor  308  of  FIG. 3  is an active semiconductor device and needs to have power and ground applied to specific ports. In the embodiment shown in  FIG. 3 , the Hall Effect sensor  308  has the first input port  302  (POWER 1 ), which is the power supply, connected to port  1  (V dd ) and has the second input port  304  (POWER 2 ), which is the ground, connected to port  8  (V ss ). The Hall Effect sensor  308  cannot swap the power and ground (e.g., applying power to port  8  (V ss ) and applying ground to port  1  (V dd )), however, such a swap can be performed on a traditional resistor based potentiometer, such as the potentiometer  208  of  FIG. 3 . 
       FIG. 4  is a high level block diagram  400  illustrating an example embodiment of the present invention. In an embodiment, the present invention is a polarity insensitive Hall Effect sensor which includes additional circuitry that allows power and ground to be applied in any polarity. In addition, it also changes the output voltage to mimic the output of a potentiometer. For example, suppose a user applied a 5V difference to a potentiometer which, based on the position of the rotor, output 4V. If the user then reversed the power and ground inputs to the potentiometer, the potentiometer would then output 1V (e.g., the inverse of the output with the reverse polarity based on the power scale, or 5V−4V). The polarity insensitive Hall Effect sensor modifies the output voltage to match this behavior. The present invention further provides protection for the Hall Effect Sensor against reverse polarity. Hall Effect sensors can be damaged by applying negative voltage to the power pins. The present invention provides current paths that prevent the Hall Effect sensor itself from receiving a negative voltage. 
     A semiconductor rectifier  410  is coupled to a first input port  402  and a second input port  404 , receiving voltages of V 1  and V 2 , respectively. The semiconductor rectifier  410  is coupled to output to a first conversion sensor  412  and second conversion sensor  414 , which can both be Hall Effect sensors, or other polarity sensitive sensors. The semiconductor rectifier  410  is configured to output a positive polarity to both the first conversion sensor  412  and second conversion sensor  414 , regardless of the polarity of the first input port  402  and second input port  404 . In other words, the semiconductor rectifier provides a voltage difference of |V 1 −V 2 | to both the first conversion sensor  412  and second conversion sensor  414 . Therefore, the first conversion sensor  412  and second conversion sensor  414  can output respective working signals, being Out 1  and Out 2 , respectively, to a semiconductor multiplexer circuit  416 . The semiconductor multiplexer circuit  416  is configured to determine the polarity of the first input port  402  and second input port  404  (e.g., |V 1 −V 2 |) and output either Out 1  or Out 2  at the output port  406  based on the determined polarity. 
     Therefore, the polarity insensitive Hall Effect sensor can receive a positive or negative power on either its first input port  402  or second input port  404 . An individual Hall Effect sensor, such as the Hall Effect sensor  308  shown in  FIG. 3 , can only receive positive power on its POWER 1  lead and V dd  port and negative power (or ground) on its POWER 2  lead and V ss  port. In the Hall Effect sensor of  FIG. 3 , if the voltage placed on POWER 2  is positive relative to POWER 1  (e.g., POWER 2 &gt;POWER  1 ), the Hall Effect Sensor  308  sensor does not operate. In addition, if the voltage is more than a particular amount, such as 10V, certain Hall Effect sensors can be damaged. The polarity insensitive Hall Effect sensor employed in an embodiment of the present invention solves this problem by conditioning the input signals and output signals. The polarity insensitive Hall Effect sensor, like a traditional potentiometer, has two input power leads and a single output lead to the outside world. 
       FIG. 5  is a block diagram  500  illustrating an example embodiment of the polarity insensitive Hall Effect sensor employed in an embodiment of the present invention. The polarity insensitive Hall Effect sensor employs a semiconductor rectifier  510 , first conversion sensor  512 , second conversion sensor  514 , and semiconductor multiplexer circuit  516 , corresponding to the semiconductor rectifier  410 , first conversion sensor  412 , second conversion sensor  414 , and semiconductor multiplexer circuit  416  of  FIG. 4 . The polarity insensitive Hall Effect sensor receives input from a first input port  502  (POWER 1 ), second input port  504  (POWER 2 ), corresponding to the first input port  402  and second input port  404 , respectively, of  FIG. 4 . The polarity insensitive Hall Effect sensor outputs at an output port  506 , corresponding to the output port  406  of  FIG. 4 . 
     In reference to  FIG. 5 , MOSFET transistor elements Q 1 -Q 12  are shown. Each MOSFET transistor has a respective source, drain, and gate, which are indicated in  FIG. 5  by the designations “S” for source, “D” for drain, and “G” for gate, respectively. The configuration of  FIG. 5  shows an example embodiment of the semiconductor rectifier  510  and semiconductor multiplexer circuit  516  coupled with the first and second conversion sensors  512  and  514 , but other arrangements of semiconductor elements such as the MOSFET transistor elements can be employed. An example MOSFET that can be used is the International Rectifier IRF7343 HEXFET® Power MOSFET, the details of which are available at http://www.irf.com/product-info/datasheets/data/irf7343.pdf, which is hereby incorporated by reference in its entirety. The IRF7343 houses one p-channel MOSFET and one n-channel MOSFET, however, other MOSFETs can be used. 
     MOSFET transistor elements Q 1 , Q 2 , Q 3  and Q 4  rectify the POWER 1  and POWER 2  signals. In an embodiment, Q 1  and Q 3  are N-channel MOSFETs and Q 2  and Q 4  are P-channel MOSFETs. The semiconductor rectifier  510  is coupled to provide a correct polarity to the first conversion sensor  512  and second conversion sensor  514  at their V dd1  and V ss1  and V dd2  and V ss2  ports, respectively. A capacitor C 1  maintains a voltage difference between the two outputs of the semiconductor rectifier  510 . Capacitors C 2  and C 3  further maintain a voltage difference between one of the outputs of the semiconductor rectifiers and the first conversion sensor  512  and second conversion sensor  514 . 
     The first conversion sensor  512  provides an output to the semiconductor multiplexer circuit  516  and the second conversion sensor  514  provides an output to the semiconductor multiplexer circuit  516 . The semiconductor multiplexer circuit  516  also accepts POWER 1  and POWER 2  as inputs. Based on the relationship of POWER 1  and POWER 2 , the semiconductor multiplexer circuit  516  outputs either the output of the first conversion sensor  512  or the output of the second multiplexer circuit  516  at the output port  506 . 
       FIG. 6A  is a block diagram  600  illustrating an example embodiment of current paths in the polarity insensitive Hall Effect sensor in a first polarity. If the voltage of POWER 1  is greater than POWER 2  (POWER 1 &gt;POWER 2 ), Q 2  and Q 3  turn on and conduct, and Q 1  and Q 4  turn off and do not conduct. POWER 1  Current Path  610   a - b  therefore conducts through Q 2  to V dd1  of the first conversion sensor  512 . The POWER 1  current path  610   b  continues at V ss1  of the first conversion sensor  512 , conducting through Q 3  to the second input port  604 . The POWER 1  current path  610   a  also conducts to V dd2  of the second conversion sensor  514 . The POWER 1  current path  610   b  also continues at V ss2  of the second conversion sensor  514 , conducting through Q 3  to the second input port  604 . 
       FIG. 6B  is a block diagram  620  illustrating an example embodiment of current paths in the polarity insensitive Hall Effect sensor in a second polarity. If POWER 2  is greater than POWER 1  (POWER 1 &lt;POWER 2 ), Q 1  and Q 4  turn on and conduct and Q 2  and Q 3  turn off and do not conduct. The POWER 2  current path  630   b  therefore conducts from POWER 2  through Q 4  to V dd2  of the second conversion sensor  514 . The POWER 2  current path  630   b  also continues at V ss2  of the second conversion sensor  514 , conducting through Q 1  to the first input port  602 . The POWER 2  current path  630   a  also conducts to V dd1  of the first conversion sensor  512 . The POWER 2  current path  630   b  also continues at V ss1  of the first conversion sensor  512 , conducting through Q 1  to the first input port  602 . 
     Q 1 , Q 2 , Q 3 , and Q 4  are selected so that the sum of gate threshold voltages of the N and P channel MOSFETs is less than the applied voltage. The Q 1 , Q 2 , Q 3 , and Q 4  MOSFETs of the semiconductor rectifier  510  route the positive voltage applied to the V dd1  and V dd2  pins of the first conversion sensor  512  and second conversion sensor  514  (e.g., Hall Effect sensors), respectively. The Q 1 , Q 2 , Q 3 , and Q 4  MOSFETs of the semiconductor rectifier  510  route the negative voltage to the V ss1  and V ss2  pins of the first conversion sensor  512  and second conversion sensor  514 , respectively. 
     The first conversion sensor  512  outputs a signal at Out 1  (Port  15 ) as Power 1  Output Path  612  and the second conversion sensor  514  outputs a signal at Out 2  (port  7 ) as Power 2  Output Path  632 . The semiconductor multiplexer circuit  516  (e.g., a switch matrix) routes one of the two outputs, Out 1  and Out 2  of the first conversion sensor  512  and second conversion sensor  514 , respectively, to the output port  606 . The semiconductor multiplexer circuit  516  is comprised of MOSFETs Q 5 , Q 6 , Q 7 , Q 8 , Q 9 , Q 10 , Q 11  and Q 12 . In an embodiment, the MOSFETs Q 5 -Q 12  are MOSFET pair IRF7343 devices, however other MOSFETs can be used. When positive voltage is applied to POWER 1  and relative negative power to POWER 2 , Q 5 , Q 6 , Q 7 , and Q 8  (a first channel) are turned on while Q 9 , Q 10 , Q 11  and Q 12  (a second channel) are in cutoff. The current runs through Q 5 , Q 6 , Q 7 , and Q 8  (the first channel) to output port  606  along Power 1  Output Path  612 . Even though both the first conversion sensor  512  and second conversion sensor  514  are powered by the POWER 1  current path  610   b , only Out 1  of the first conversion sensor  512  is outputted at the output port  606 . 
     When a positive voltage is applied to POWER 2  relative to POWER 1 , MOSFETs Q 9 , Q 10 , Q 11  and Q 12  (the second channel) are turned on and Q 5 , Q 6 , Q 7  and Q 8  (the first channel) are turned off/in cutoff. The current runs through Q 9 , Q 10 , Q 11  and Q 12  (the second channel) to output port  606  along Power 2  Output Path  632 . Even though both the first conversion sensor  512  and second conversion sensor  514  are powered by the POWER 2  current path  630   a , only Out 2  of the second conversion sensor  514  is outputted at the output port  606 . 
     A person of ordinary skill in the art can recognize that regardless of the polarity of POWER 1  and POWER 2 , that POWER 1  current path  610   a - b  and POWER 2  current path  630   a - b  flow through V dd1 , V ss1  and V dd2 , V ss2  simultaneously, respectively. However,  FIGS. 6A-B  show the current paths powering the respective conversion sensor that is outputting to the output port  606  to clearly show the role of the semiconductor rectifier and semiconductor multiplexer, even though both conversion sensors are simultaneously powered. 
     Pairs of MOSFETs Q 5  and Q 6 , Q 7  and Q 8 , (the first channel) Q 9  and Q 10 , and Q 11  and Q 12  (the second channel) are coupled at each pair&#39;s respective MOSFET source port such that the body diode of the opposing channel MOSFET does not conduct current. Further, each channel needs a set of N-channel MOSFETs and a set of P-channel MOSFETs because neither an N-channel MOSFET nor a P-channel MOSFET alone can conduct over the full range of output voltages for the polarity insensitive Hall Effect sensor. For example, when POWER 1  is positive (e.g., 5V) relative to POWER 2 , the gates of Q 5  and Q 6  are at 5V, and Q 5  and Q 6  are turned on for output voltages from 0 to about 4V. Above 4V, there is no longer sufficient gate-source voltage to keep the MOSFET on. Likewise, P-channel MOSFETs Q 7  and Q 8  are turned on when the output voltage is between 1V and 5V, but for voltages below 1V, there is insufficient gate-source voltage to keep them on. For much of the range, both the N-channel and P-channel MOSFETs pairs are active but at the extremes of the range, only one or the other is turned on. Likewise, the combined output at the Output Port  606  is the combination of the current through MOSFET pairs Q 5  and Q 6  and Q 7  and Q 8 . Although the output impedance varies, typical current draw in most applications is small, so the voltage drop in the semiconductor multiplex has a minimal variance in the voltage drop. 
     The resistance at saturation (Rds) of the MOSFETS determines the voltage drop through the MOSFETs. One example MOSFET that can be used is the IRF7343, which has 50 mΩ and 105 mΩ Rds for the N- and P-channel MOSFETs, respectively. These Hall Effect sensors consume current of approximately 16 milliamps (mA), which causes a voltage drop through the MOSFETS of about 2.48 mV. The voltage applied powers two Hall Effect sensors, for example an MLX90316, which houses two separate Hall Effect sensor dies in one package. 
       FIG. 7  is a graph  700  illustrating an example embodiment of percentage output of the polarity insensitive Hall Effect sensor as a function of a rotary position of a rotor in degrees. The polarity insensitive Hall Effect sensor has two output curves, Output 1   702  and Output 2   704 , representing a respective polarity of the input signal. When the voltage polarity is switched, the output polarity of the Hall Effect sensor is inversed to mimic the output of a traditional potentiometer. When the wiper of a potentiometer is offset from center and the polarity of the input voltage is reversed, the output voltage follows the input. When the input switches polarity, the semiconductor multiplexer circuit, or output multiplexer, switches from the output of one Hall Effect sensor to the other Hall Effect Sensor. 
     Potentiometers and their Hall Effect sensor equivalents can change their output linearly as the rotational position they are detecting changes. Output 1   702  shows the output of the polarity insensitive Hall Effect sensor in a first polarity. Output 2   704 , the complimentary output to Output 1   702 , should therefore an increase in voltage from the negative supply that is the same as the voltage decrease that Output 1   702  has from the positive supply. For example, if the input shaft of the hall sensor is at 90°, Output 1   702  produces a signal representing 25% of the positive supply, and Output 2   704  produces a signal representing 75% of the positive supply, or 25% away from the negative supply. 
     In an embodiment, the invention also solves a problem created when using the two Hall Effect sensors. Each Hall Effect sensor is programmed, for example by a Melexis PTC-04 programming box. Programming a Hall Effect sensor is performed by connecting to three wires of the sensor. However, two Hall Effect sensors share the three wires. The circuit of the present invention solves this problem. To program the first hall sensor, the three programming wires are connected to the polarity insensitive Hall Effect Sensor. To program the second sensor, the power and ground wires are reversed and a second sensor can then be programmed. The programming box can access only one of the two sensors at a time because the switching elements behave different depending on how power is applied. The polarity insensitive Hall Effect sensor allows power reversal and therefore provides a way of programming two Hall sensors through a single wire interface. 
     Other structures of the polarity insensitive Hall Effect circuit can be designed by a variety of electrical devices and connections. 
     “Polarity protection implemented with a MOSFET” by Jokinen, U.S. Pat. No. 7,126,801 (hereinafter “Jokinen”) shows an N-channel MOSFET in series with a negative lead to disconnect in case of reverse polarity. “Input Power Protected Ratiometric Output Sensor Circuit” by Lin, U.S. Pat. No. 7,453,268 shows a system for a ratiometric sensor using both high side and low side MOSFET switches. “Reverse Voltage Protection Circuit” by Zhang, U.S. Pub. No. 2011/0195744 (hereinafter “Zhang”) and “Integrated overvoltage and reverse voltage protection circuit” by Laraia, U.S. Pub. No. 2004/0052022 (hereinafter “Laraia”) show similar methods. However, Jokinen, Lin, Zhang and Laraia do not suggest operation while reverse voltage is applied. 
     “Polarity Detection Circuit” by Terasaki, Japanese Pat. No. JP02148955 (hereinafter “Terasaki”) shows a system for detecting reverse polarity, but employs a diode bridge for rectification, which results in an undesirable high voltage drop across the diode bridge. The present invention avoids such a voltage drop. 
     The above patents and patent applications are hereby incorporated by reference in their entirety. 
     In another embodiment, instead of using two separate Hall Effect sensors, the polarity insensitive Hall Effect sensor can couple an amplifier to a single Hall Effect sensor to provide an inversed output graph with a negative transformation (e.g., the relationship of V out =V supply −V in  when polarity is reversed). Using only one Hall Effect sensor reduces cost and requires programming of only one Hall Effect sensor. However, the output when the polarity is reversed may have a larger error because the amplifier&#39;s error is added to the Hall Effect error. When using two Hall Effect sensors, only one sensor is active at a time so only the error from one sensor is present. 
     Other elements could be used as substitutes for the MOSFET transistors (e.g., relays or other devices) as long as they have high off state resistance and low voltage drop in the on state. 
     The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.