Patent Publication Number: US-9424739-B2

Title: Self powered wireless system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/640,108, filed Apr. 30, 2013, and U.S. Provisional Application No. 61/783,202, filed Mar. 14, 2013. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     BACKGROUND 
     This invention pertains to a wireless monitoring system with a self-powered transmitter. More particularly, this invention pertains to a wireless transmitter with a single coil that is responsive to a magnet attached to a moving component. 
     DESCRIPTION OF THE RELATED ART 
     Rotating and moving machines are in widespread use. With rotating machines, rotational speed is often desired to be measured. Rotational speed provides information on how fast the machine is rotating, and depending upon the configuration, on the speed of a downstream component. With reciprocating or linear machines, such as piston operated machines and conveyors, the time between oscillations or the time the machine takes to move from one point to another provides useful information. 
     In many environments, the machine information is desired to be used at a location remote from the machine. Traditionally, a sensor or instrument is mounted on or next to the machine and wiring is needed to provide power to the sensor and/or to send a signal from the sensor to a remotely mounted monitor. In an automobile, wiring from a sensor measuring engine speed and/or tire rotational speed adds complexity and cost during manufacturing and maintenance because of the constraints inherent in a vehicle. In industrial applications, wiring from sensors on rotating, reciprocating, and linear machines adds complexity and costs because of the environment and distance between such equipment and the remote monitoring equipment. 
     Traditional sensors and instruments need a power source, either independent or as part of the signal circuit. Independent power supplies create reliability problems for the instrumentation system because the instrumentation power source is typically independent of the power source for the machine being monitored. 
     BRIEF SUMMARY 
     According to one embodiment of the present invention, a single sensor burst transmitter system is provided. The single sensor burst transmitter system is a wireless monitoring system that has no need for external wiring for a power source or sending the signal from the sensor. In this way the wireless monitoring system is self-contained without external wiring. 
     The single sensor burst transmitter system includes a magnet and a burst transmitter that is responsive to the magnet. The magnet is dimensioned and configured to be attached to a moving component of a machine. The magnet is dimensioned to be have a short interaction time compared to a dwell time where the magnet does not interact with the burst transmitter. The burst transmitter includes an inductor, a delay circuit, and a transmitter with an antenna. The magnet interacting with the inductor generates sufficient power to transmit a signal corresponding to the time that the magnet interacts with the inductor. Precise timing is insured by the inductor connected to the trigger input of the transmitter unit and the delay circuit adding a short delay of the signal applied to the trigger input with the delayed signal connected to the supply voltage connection of the transmitter. The transmitter transmits a signal upon being energized because the trigger is already at its trigger voltage when the transmitter unit is energized with enough power to transmit. The transmitter outputs a pulse to an antenna every time the magnet engages the coil. In this way, the single sensor burst transmitter system is self-powered and has a minimum number of components. 
     In one embodiment, the magnet passing by an inductor coil induces a current/voltage spike in the inductor. One end of the coil is electrically connected to a reference, common, or ground on the transmitter and to one end of an RC (resistance-capacitance) network that is also connected to the supply voltage connection of the transmitter. The other end of the coil is connected to the trigger input on the transmitter. The transmitter is powered and triggered by the magnet interacting with the coil, thereby transmitting a pulse from an antenna attached to the transmitter. In various embodiments, one or more magnets are attached to a moving part of the machine. 
     In various embodiments, the single sensor burst transmitter system senses a parameter of a vehicle or machine, such as motor or engine revolutions per minute (RPM) or the vehicle speed, and transmits data representing that parameter. In one such embodiment, the system includes a magnet positioned on a rotating or moving component of a vehicle, such as a shaft, fan belt pulley, flywheel, or drive shaft. In another embodiment, the system senses a parameter of a machine, such as a pump, a motor, or conveyor. Examples of the monitored parameter include rotational speed, rate of reciprocation, belt speed, or other cyclical motion that positions one or more magnets spatially at a fixed location with a frequency that is measured. 
     The magnet is magnetically coupled to an inductor when the magnet moves past the inductor. The magnetic coupling induces a voltage/current spike in the inductor. The inductor is connected between the reference or common and the trigger of the transmitter. The inductor is also connected to a delay, or resistor-capacitor tank circuit, that is connected to the supply voltage connection of a transmitter. The inductor supplies a trigger signal to the transmitter before the transmitter receives sufficient power from the inductor to turn on. The voltage spike from the inductor interacting with the magnet causes the transmitter to send a wireless pulse from an antenna connected to the transmitter. The transmitted pulses are sensed by a receiver that is responsive to the wireless signal. 
     In one embodiment, multiple single sensor burst transmitter systems are employed. Each one of the burst transmitter systems monitors a different parameter or different machine. Each one of the burst transmitter systems transmits at a different frequency or channel or with a different type of modulation. In this way, multiple parameters are monitored. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The above-mentioned features will become more clearly understood from the following detailed description read together with the drawings in which: 
         FIG. 1  is a functional block diagram of one embodiment of a single sensor burst transmitter system. 
         FIG. 2  is a schematic diagram of one embodiment of a single sensor burst transmitter system. 
         FIG. 3 a    is a diagram showing the trigger signal applied to the transmitter unit over time. 
         FIG. 3 b    is a diagram showing the Vcc voltage applied to the transmitter unit over time. 
         FIG. 3 c    is a diagram showing the pulse signal sent to the antenna over time. 
         FIG. 4  is a functional block diagram of one embodiment of a multi-sensor transmitter system. 
         FIG. 5  is a schematic diagram of one embodiment of a power supply. 
         FIG. 6  is a functional block diagram of one embodiment of a wireless tachometer system. 
         FIG. 7  is a schematic diagram for one embodiment of a signal conditioner. 
         FIG. 8  is a schematic diagram for another embodiment of a signal conditioner. 
     
    
    
     DETAILED DESCRIPTION 
     Apparatus for a single sensor burst transmitter system  10  is disclosed. The single sensor burst transmitter system  10  senses and transmits a parameter associated with a machine or device that has cyclic or reciprocating movement. 
       FIG. 1  illustrates a functional block diagram of one embodiment of a single sensor burst transmitter system  10 . The system  10  includes a magnet  102  and a burst transmitter  100 . The magnet  102 , in one embodiment, is attached to a moving object such that the magnet  102  periodically moves past the burst transmitter  100 . The burst transmitter  100  interacts with the magnet  102  and transmits a pulse  306  each time the magnet  102  passes by the burst transmitter  100 . 
     The burst transmitter  100  includes an inductor  104 , a delay  106 , and a transmitter  108  that is connected to an antenna  110 . The magnetic field  112  of the magnet  102  engages the inductor  104  when the magnet  102  moves past the inductor  104 . The magnetic field  112  of the magnet  102  interacts with the inductor  104  and induces a pulse  302  in the inductor  104 . 
     The magnet  102  is secured to a part of a machine that moves in at least one direction  114  relative to the inductor  104  in the burst transmitter  100 . The magnet  102 , through the magnetic field interaction with the burst transmitter  100 , provides the energy that powers the burst transmitter  100 . Also, the magnet  102  triggers the burst transmitter  100  to transmit the signal  306  when the magnet  102  is proximate the inductor  104 . Although the illustrated embodiment depicts the magnet  102  as moving in direction  114 , it is the relative motion between the magnet  102  and the inductor  104  that is relevant. For example, in another embodiment, the burst transmitter  100  is attached to the moving component and the magnet  102  is stationary. 
     The magnet  102  is dimensioned relative to the moving part of the machine such that the magnetic field  112  is substantially a point source that engages the inductor  104  for a shorter duration than the duration when the magnetic field  112  does not engage the inductor  104 . That is, the interaction of the magnetic field  112  with the inductor  104  occurs briefly compared to the long dwell time with no interaction by the magnetic field  112 . The interaction of the magnetic field  112  occurs during an interaction interval, which can be expressed in units of time or angular displacement. The dwell interval refers to the time or angular displacement where the magnetic field  112  does not interact with the inductor  104 . For those embodiments where a magnet  102  is attached to a moving component of a machine, the magnet  102  will be substantially smaller than the moving component in order to minimize the mass added to the moving component and to minimize any unbalancing effect from the addition of the magnet  102 . Typically, the ratio of the interaction interval to the dwell interval will be about 1:10 or less. For example, in one embodiment, the magnet  102  is cylindrical and less than ½ inch in diameter. The magnet  102  is attached to a rotating pulley that is six inches in diameter. In this example the interaction interval is approximately 10 degrees or less and the dwell interval is approximately 350 degrees or more, which results in the ratio of the interaction interval to the dwell interval of 10:350. 
     The magnet  102  is attached to a moving component that moves in a cyclical or repetitive manner such that the magnet  102  repeatedly moves proximate the inductor  104  at an interval that corresponds to some variable to be measured, such as revolutions per minute (RPM). For example, in one embodiment, the magnet  102  is attached to a shaft of a pump or motor. The magnet  102  moves in direction  114  as the shaft rotates. The rate of interactions of a single magnet  102  on the shaft with the inductor  104  provides data on the rotational speed of the shaft. One interaction between the magnet  102  and inductor  104  corresponds to one revolution of the shaft. 
     For slower moving devices, multiple magnets  102  are spaced at regular intervals and an appropriate scaling factor is applied to the sensed rate of interactions to determine the rate of movement. For example, a plurality of magnets  102  are attached to a conveyor belt at regular intervals to measure the speed of the conveyor belt. Each time a magnet  102  moves proximate the inductor  104  the burst transmitter  100  transmits a pulse  306 . Either the time difference between pulses  306  or the number of pulses  306  per unit of time are used to determine the speed of the conveyor belt. 
     The inductor  104  is responsive to the magnetic field  112  of the magnet  102 . The leads of the inductor  104  are connected to the transmitter  108 . The interaction of the magnetic field  112  of the magnet  102  with the inductor  104  causes the inductor  104  to generate a pulse  302  that sets the trigger Tr of the transmitter  108 . 
     The delay  106  is connected between the reference or ground Ref of the transmitter  108  and the supply voltage Vcc connection of the transmitter  108 . The delay  106  adds a short time delay to the pulse  302  from the inductor  104 . 
     The transmitter  108  is a device that transmits a wireless signal through an antenna  110 . In one embodiment, the transmitter unit  108  causes a wireless radio frequency (RF) signal to be sent from the antenna  110 . The transmitter unit  108  is both powered and triggered by the magnetic field  112  of the magnet  102  interacting with the inductor  104 . When multiple single sensor burst transmitter systems  10  are used within range of a single receiver, the transmitters  108  are configured to minimize or reduce interference. For example, in one embodiment, each transmitter  108  operates at a specific frequency or channel different from other transmitters  108 . 
       FIG. 2  illustrates a schematic diagram of one embodiment of a single sensor burst transmitter system  10 . The illustrated embodiment of the transmitter system  10  includes a magnet  102  and a burst transmitter  100 . The burst transmitter  100  includes an inductor  104 , a delay circuit  106 , a transmitter  108 , and an antenna  110 . 
     In one embodiment, the magnet  102  is secured to a moving part of a machine. The magnet  102  moves in a direction  114  relative to the inductor  104 . Because the magnet  102  adds mass to the moving part, the magnet  102  in one embodiment is a rare earth magnet, which ensures the size is minimized and the magnetic field generated is as strong as possible relative to the size of the magnet  102 . 
     In another embodiment, the burst transmitter  100  is secured to the moving part of the machine and the magnet  102  is stationary. 
     The inductor  104  is a coil that is responsive to the magnetic field  112  of the magnet  102 . In various embodiments, the inductor  104  is an air wound coil or a cored inductor. The inductor  104  is oriented such that the magnetic field  112  passing through the inductor  104  generates sufficient power to drive the transmitter  108 . 
     The delay  106  includes an RC circuit with a resistor  202  and capacitor  204  connected in parallel. The RC circuit  106  is connected between the reference, common, or ground Ref of the transmitter  108  and the supply voltage Vcc connection of the transmitter  108 . The delay circuit  106  adds a short delay to the voltage generated by the inductor  104  and applies that delayed signal  304  to the supply voltage Vcc connection of the transmitter unit  108 . The values for the resistor  202  and the capacitor  204  in the RC circuit  106  are selected such that the voltage across the capacitor  204  falls below the minimum required Vcc voltage  312  within the period  324  between trigger pulses  304 . That is, the time to drain the capacitor  204  is less than the period  324  being measured. 
     The transmitter  108  is a low power device with a fast response time that is operable with the amount of power generated by the magnet  102  moving relative to the inductor  104 . The transmitter  108  has a trigger input Tr that causes the transmitter  108  to output a signal from the antenna output ANT to the antenna  110  when the trigger input Tr is at or above a trigger voltage  312 . In various embodiments, the antenna  110  is an external or built-in antenna operating at the frequency of the transmitter  108 . 
     In one example, the transmitter  108  is an amplitude modulated (AM) hybrid transmitter unit, such as the Model AM-RT4-315 sold by RF Solutions. The transmitter unit  108  is a complete, self-contained RF transmitter that supports a transmitted data rate up to about 4 kHz. The transmitter unit  108  requires a supply voltage (Vcc) of between 2 and 14 volts dc with a typical supply current of 4 mA at 5 Vdc. The minimum input level is 2 volts dc with a maximum equal to Vcc. The transmitter unit  108  operates at a fixed frequency of 315 MHz with a range up to 70 meters. The transmitter unit  108  has four leads: supply voltage Vcc, reference or ground Ref, trigger input Tr, and output for an external antenna Ant. The transmitter unit  108  has an equivalent circuit capacitance of 1 nF between the trigger input Tr and the supply voltage Vcc connections, and an equivalent circuit capacitance of 100 pF between the ground Ref and the trigger input Tr connections and between the ground Ref and the supply voltage Vcc connections. 
     In such an example, the supply voltage Vcc signal  304  is delayed approximately 0.6 milliseconds relative to the signal  302  applied to the trigger input Tr of the transmitter unit  108 . Such a delay is sufficient to ensure that the transmitter unit  108  transmits a signal  306  as soon as the supply voltage Vcc signal  304  is at a level sufficient to power the transmitter unit  108 . That is, with the trigger input Tr at a voltage at or above the required trigger voltage  312 , the transmitter  108  outputs a signal as soon as the Vcc voltage reaches the minimum required Vcc voltage  314 . With the transmitter unit  108  in this example, the minimum trigger input Tr and the minimum supply voltage Vcc are the same, which is 2 volts. In the tested embodiment, the magnet  102  and inductor  104  combination produce a spike of 2.8 volts, which is sufficient to operate the transmitter unit  108 . 
       FIG. 2  illustrates a simplified schematic of one embodiment of a single sensor burst transmitter system  10 . The simplified schematic does not illustrate various connections that may be required to accommodate specific components selected, for example, the transmitter unit  108  may require a crystal or other frequency selection circuitry. An antenna tuning or matching circuit may also be needed depending upon the components selected. Those skilled in the art will recognize the need for such wiring and understand how to wire such a circuit, based on the components ultimately selected for use. 
       FIG. 3 a    illustrates a diagram showing the trigger signal  302  applied to the transmitter unit  108  over time t.  FIG. 3 b    illustrates a diagram showing the Vcc voltage  304  applied to the transmitter unit  108  over time t.  FIG. 3 c    illustrates a diagram showing the output pulse signal  306  sent to the antenna  110  over time t. The output pulse  306  is a signal at the frequency of the transmitter unit  306 , which is much greater than the frequency of magnet  102 -inductor  104  interactions. The output pulse  306  is shown as a square wave because of the magnitude of the frequency difference. The diagrams also illustrate the periodic nature of the signals that correspond to the rate of interaction between the magnet  102  and the inductor  104 . In the illustrated embodiment, the period  324  between spikes or pulses  302 ,  304 ,  306  is regular. 
     The inductor  104  generates a voltage spike  302  from the interaction of the magnetic field  112  of the magnet  102  as it moves by the inductor  104 . The inductor  104  is connected between the reference or ground Ref and the trigger input Tr of the transmitter  108  such that the voltage at the trigger input Tr is positive relative to ground Ref. The trigger spike  302  has a maximum voltage that is equal to or greater than the minimum required trigger voltage  312  at the time  310  the output pulse  306  begins. The minimum required trigger voltage  312  is the voltage level required by the trigger input Tr of the transmitter  108  to send a signal. 
     The delay circuit  106  is connected between the reference or ground Ref and the supply voltage Vcc connections of the transmitter  108 . The RC circuit  106  adds a short delay to the voltage spike  302  from the inductor  104  such that the supply voltage  304  reaches a level  310  sufficient to power the transmitter  108  after the trigger input Tr has reached a sufficient level to trigger the transmitter  108  to send a pulse  306 . The minimum required Vcc level  314  is the voltage level required by the transmitter  108  to be energized and operable. 
     The Vcc voltage  304  enables the transmitter  108  to operate when the Vcc voltage  304  reaches the minimum required Vcc voltage  314  at time  310 . A first vertical line  310  shows the relationship between when the Vcc voltage  304  reaches the minimum required Vcc voltage  314  and the other signals  302 ,  306 . 
     Referring to  FIG. 3 a   , the trigger spike  302  has a voltage that is equal to or greater than the minimum required trigger voltage  312  at the time  310  the Vcc voltage  304  reaches the minimum required Vcc voltage  314 . Because these two conditions are met (trigger voltage  302  at or greater than minimum trigger voltage  312  and Vcc voltage  304  at or greater than minimum required Vcc voltage  324 ), the transmitter unit  108  sends an output pulse  306  starting at time  310 . 
     The second vertical line  320  shows the relationship between when the trigger signal  302  falls below the minimum required trigger voltage  312  and the other signals  304 ,  306 . The output pulse  306  ends at the time  320  when the trigger signal  302  falls below the minimum required trigger voltage  312  or the Vcc voltage  304  falls below the minimum required Vcc voltage  314 , whichever occurs first. In the illustrated diagrams, the output pulse  306  stop time  320  occurs when the trigger signal  302  falls below the minimum required trigger voltage  312 . The time width of the Vcc voltage signal  304  at the minimum required Vcc voltage  324 , minus the amount of time delay introduced by the RC circuit  106 , determines the width of the output pulse  306 . that is, the width of the pulse  306  is the time between the pulse start time  310  and end time  320 . 
       FIG. 4  illustrates a functional block diagram of one embodiment of a multi-sensor transmitter system  40 . The multi-sensor transmitter system  40  includes a magnet  102  that interacts with a multi-sensor transmitter  400 . The multi-sensor transmitter  400  includes an inductor  104  connected to a power supply  402  that is connected to a processor  404  and a transmitter  108 . The inductor  104 , when it interacts with the magnetic field  112  of the magnet  102 , is a power source for the power supply  402 . The power supply  402  provides power to the processor  404  and the transmitter  108 . The processor  404  has a multitude of inputs  406 , for example, inputs from sensors such as switches and transducers. The transmitter  108  has an input from the processor  404  and an output connected to an antenna  110 . 
     As with the single sensor burst transmitter system  10 , the magnet  102  moves repetitively relative to the inductor  104 . In one embodiment, the magnet  102  is attached to a machine part that reciprocates or rotates such that the magnet  102  periodically moves past the inductor  104  in direction  114 . The magnet  102  has a magnetic field  112  that periodically interacts with the inductor  104  to produce a pulse  302  in the inductor  104 . In one embodiment, multiple magnets  102  are attached to the machine such that the inductor  104  senses the magnetic field  112  at a rate greater than once per cycle or revolution. In this way the multi-sensor transmitter  400  remains functional with machines that have a low reciprocating rate or a low number of revolutions per second. 
     The magnet  102  is dimensioned relative to the moving part of the machine such that the magnetic field  112  is substantially a point source that engages the inductor  104  for a shorter duration than the duration when the magnetic field  112  does not engage the inductor  104 . That is, the interaction of the magnetic field  112  with the inductor  104  occurs briefly compared to the long dwell time with no interaction by the magnetic field  112 . The interaction of the magnetic field  112  occurs during an interaction interval, which can be expressed in units of time or angular displacement. The dwell interval refers to the time or angular displacement where the magnetic field  112  does not interact with the inductor  104 . For those embodiments where a magnet  102  is attached to a moving component of a machine, the magnet  102  will be substantially smaller than the moving component in order to minimize the mass added to the moving component and to minimize any unbalancing effect from the addition of the magnet  102 . Typically, the ratio of the interaction interval to the dwell interval will be about 1:10 or less. For example, in one embodiment, the magnet  102  is cylindrical and less than ½ inch in diameter. The magnet  102  is attached to a rotating pulley that is six inches in diameter. In this example the interaction interval is approximately 10 degrees or less and the dwell interval is approximately 350 degrees or more, which results in the ratio of the interaction interval to the dwell interval of 10:350. 
     The processor  404  includes one or more inputs  406 . The processor  404  outputs a signal to the transmitter  108  that includes an identifier and data. The identifier uniquely identifies the multi-sensor transmitter  400  for the embodiment where several transmitters  400  are used concurrently with overlapping range. In this way a receiver is able to identify the transmitter  400  and its corresponding data. The data corresponds to the inputs  406  to the processor  404 . 
     As used herein, the processor  404  should be broadly construed to mean any computer or component thereof that executes software. The processor  404  includes a memory medium that stores software, a processing unit that executes the software, and input/output (I/O) units for communicating with external devices. Those skilled in the art will recognize that the memory medium associated with the processor  404  can be either internal or external to the processing unit of the processor without departing from the scope and spirit of the present invention. 
     In one embodiment the processor  404  is a general purpose computer, in another embodiment, it is a specialized device for implementing the functions of the invention. Those skilled in the art will recognize that the processor  404  includes an input component, an output component, a storage component, and a processing component. The input component receives input from external devices, such as the switches, sensors, and instruments that can be connected to the inputs  406 . The output component sends output to external devices, such as the transmitter  108 . The storage component stores data and program code. In one embodiment, the storage component includes random access memory. In another embodiment, the storage component includes non-volatile memory, such as floppy disks, hard disks, and writeable optical disks. The processing component executes the instructions included in the software and routines. 
     When multiple multi-sensor transmitter systems  40  are used within range of a single receiver, the transmitters  108  are configured to minimize or reduce interference. For example, in one embodiment, each transmitter  108  operates at a specific frequency or channel different from other transmitters  108 . In another embodiment, the multiple transmitters  108  operate on the same frequency and the received signals are differentiated by the identifier sent by the transmitter  400 . Because the signal has a short duration compared to the time between transmitted signals, collisions are rare. In case of a collision of signals from two transmitters  400 , the next set of transmitted signals should not collide because the difference in the rotational speed of the magnet  102  is sufficiently different to cause the transmitters  400  to transmit at different times, assuming the transmission rate is tied to the rotational speed of the magnet  102 . 
       FIG. 5  illustrates a simplified schematic diagram of one embodiment of a power supply  402 . The power supply  402  includes an energy harvester, or voltage multiplier,  522 , a storage circuit  524 , and a voltage regulating circuit  526 . 
     The magnet  102  moves periodically in a direction  114  that causes the magnet&#39;s flux  112  to induce a current in the inductor  104 . The strength of the magnetic flux  112  and the speed of the magnet  102  as it moves past the inductor  104  influence the magnitude and shape of the induced current signal. In various embodiments, the voltage across the inductor  104  due to the induced current is selected by using a transformer or by adjusting the configuration of the inductor  104 . In one embodiment, the inductor  104  has a length parallel to the magnet direction  114  that is sufficient to produce the desired power from the interaction of the inductor  104  with the magnetic field  112  of the magnet  102 . 
     The inductor  104  is a coil that is positioned near where the magnet  102  moves. The leads of the inductor  104  are connected to the power supply  402 , which has an energy harvester  522 , a storage circuit  524 , and a voltage regulating circuit  526 . In the illustrated embodiment, the energy harvester  522  in the power supply  402  is a voltage multiplier. The voltage multiplier circuit  522  increases the voltage across the inductor  104  to a level suitable for use by the processor  404  and the transmitter  108 . The voltage multiplier circuit  522  includes a network of capacitors  502 ,  506  and diodes  504  that has an output voltage  516 ,  512  that is greater than the input voltage of the inductor  104 . The voltage multiplier circuit  522  charges the capacitor  508  in the storage circuit  524 . 
     The storage unit  524  stores the energy from the inductor  104  at the output voltage  516 ,  512  of the voltage multiplier circuit  522 . In the illustrated embodiment the storage unit  524  is a capacitor  508 . The capacitor  508  has a voltage rating sufficient to accommodate the maximum voltage from the voltage multiplier circuit  522 . The capacitor  508  has sufficient capacitance to store the energy from the periodic interactions of the magnet  102  with the inductor  104 , considering the power needs of the processor  404  and the transmitter  108 . 
     The capacitance of the capacitor  508  affects the power storage capability and the start up time before such capacity is available. A capacitor  508  with high capacitance, for example, 0.33 F, requires several minutes from a cold start before being fully charged by the interaction of the magnetic field  112  with the inductor  104 . Once charged, the capacitor  508  is able to provide power for substantial periods and/or power levels. A capacitor  508  with lower capacitance, for example, 0.022 F, is smaller in size, quicker to provide power after a cold start, and provides power for shorter periods and/or at lower power levels. 
     The voltage regulating circuit  526  in the illustrated embodiment includes a series of light emitting diodes (LEDs)  410 . The LEDs  410 , across the storage capacitor  508 , serve to regulate the voltage output of the power supply  402 . Red LEDs have a forward voltage of between 1.6 and 2.0 volts, depending upon the doping of the LED. For example, an output voltage of approximately 5 volts can be obtained with three LEDs between the ground  516  and the second output  512 . An output voltage of approximately 3.2 volts can be obtained with two LEDs between the ground  516  and the first output  514 . Until the output capacitor  508  is charged, the output voltages  512 ,  514  will be less than the voltage drop across the LEDs  510 . The forward current through the LEDs  510  is limited because the current from the inductor  104  and the voltage multiplier circuit is limited. Another embodiment of the voltage regulating circuit  526  uses a Zener diode to control the output voltage  512 ,  514 . In various embodiments, one or both of the outputs  512 ,  514  are used, based on the needs of the processor  404  and transmitter  108 . 
     Upon first starting up, the power supply  402  has a zero output voltage. As the magnet  102  interacts with the inductor  104 , the voltage multiplier circuit  522  charges the capacitor  508  in the storage unit  524  to the sum of the forward voltages of the diodes  510  in the voltage regulator circuit  526 . The voltage regulator circuit  526  maintains a relatively constant voltage until current is drawn through the power supply  402 . The voltage output  512 ,  514  remains somewhat constant until the output current level increases to the level where the capacity of the inductor  104  and voltage multiplier circuit  522  to keep the storage unit  524  charged is exceeded. The output voltage  512 ,  514  then falls. With an increasing load, that is, with a decreasing load impedance, when the output current level reaches a level where the magnet-inductor  102 ,  104  interaction cannot supply the full energy requirement, the output voltage  512 ,  514  drops, as does the current. The output voltage  512 ,  514  recovers only when the load decreases, that is, when the load impedance increases. 
       FIG. 5  illustrates a simplified schematic of one embodiment of a power supply  402 . The simplified schematic does not illustrate various connections and components that may be required to accommodate specific components selected and/or desired circuit specifications. For example, the number of capacitors  502 ,  506  and diodes  504  in the voltage multiplier circuit  522  depend upon the desired output voltage and power desired at the output  512 ,  514 . In another example, the size of the capacitor  508  in the storage unit  524  will vary depending upon the desired start time (larger capacitance requires a greater charging time upon startup) and the power desired for the transmitter  108  (larger capacitance allows for greater energy storage). 
       FIG. 6  illustrates a functional block diagram of one embodiment of a wireless tachometer system  60 . The wireless tachometer system  60  includes a tachometer receiver circuit  600  and a conventional tachometer  608 . The tachometer receiver circuit  600  is responsive to a wireless signal from a transmitter  108  that sends pulses corresponding to a rotational speed of a device. In various embodiments, the transmitter  108  is one in a single sensor burst transmitter system  10 , a multi-sensor transmitter system  40 , a wireless system such as described in U.S. Pat. No. 8,035,498 (hereby incorporated by reference), or another wireless system that monitors a rotating device. 
     The tachometer receiver circuit  600  includes an antenna  602 , a receiver  604 , and a signal conditioner  606 . The antenna  602  and receiver  604  detect the pulses corresponding to the rotational speed of a device desired to be monitored. The signal conditioner  606  is a circuit that converts the output of the receiver  604  into a signal that is compatible with a conventional tachometer  608 . The wireless tachometer  60  monitors engine speed in a vehicle with a wireless connection between the sending unit and the wireless tachometer  60 . 
     Typically, vehicles operate with a voltage of 12 Vdc. Wireless receivers  604  provide an analog output signal at half the supply voltage because the receiver output is an ac signal that, at most, fluctuates peak-to-peak between −6 and +6 volts, which is a range of 12 volts but with a maximum voltage of half of the operating voltage. The nominal maximum output of 6 volts for the receiver  604  is reduced further because of the level of the wireless signal fluctuates under normal conditions and receivers  608  are not intended to be operated at maximum gain for long term use. Accordingly, the conventional receiver  604  operating at a 12 volt rail voltage has an output substantially less than 6 volts. For example, a 10 db reduction from maximum, which is not normally considered a substantial reduction, results in an output level of 0.6 volts, which is insufficient to drive a conventional tachometer  608 . 
     Conventional tachometers  608  require an input signal of 12 Vdc pulses because the conventional tachometer  608  is configured to be connected directly to the vehicle&#39;s coil or a tach output on an electronic ignition. The output of conventional receivers  604  are not compatible with the input of conventional tachometers  608 . To correct the mismatch of voltage levels, a signal conditioner  606  matches the output of the conventional receiver  604  to the input of the conventional tachometer  608 . Without the signal conditioner  606 , the conventional tachometer  608  cannot provide a reliable indication with only the output of the conventional receiver  604 . 
     In one embodiment, the wireless tachometer system  60  functions with a wireless input corresponding to a signal with two pulses per revolution and with the conventional automotive tachometer  608  configured with a setting corresponding to a 6 cylinder engine. The two pulses received for the wireless input correspond to a wireless transmitter sensing two magnets on the rotating member for one revolution. For those conventional automotive tachometers  608  that include a pulse per revolution (PPR) setting, the tachometer PPR setting is adjusted to correspond to the number of magnets  102  used. 
       FIG. 7  illustrates a schematic diagram for one embodiment of a signal conditioner  606 -A for a wireless tachometer system  60 . In the illustrated embodiment, an operational amplifier (op amp)  702  conditions the output signal  708  from the receiver  604  into a signal that is compatible with the tachometer  608 . The capacitor  704  and variable resistor  706  are connected across the gain connections of the op amp  702  to control the level of the output  710 . 
     In one such embodiment, the op amp  702  is an LM386, the capacitor  704  is 10 μF, and the resistor  706  is 10K ohms. In another embodiment, the op amp  702  is an LM4861 and the resistor  706  is not used. The input  708  to the signal conditioner  606 -A is the low voltage output of the receiver  604 . That is, the input  708  to the signal conditioner  606 -A is at a nominal maximum of 6 volts. The gain of the signal conditioner  606 -A is such that the output  710  is at a nominal 12 Vdc, which is sufficient to trigger the conventional automotive tachometer  608  reliably. In one such embodiment, the operational amplifier functions as a comparator with the gain set to minimize overdriving the operational amplifier while avoiding saturation. 
       FIG. 8  illustrates a schematic diagram for another embodiment of a signal conditioner  606 -B. In the illustrated embodiment, a step up transformer  802  is used to convert the input  708  to the output  710 . In one such embodiment, the transformer  802  is a step up transformer with a turns ratio of 3:1 or greater. In one such embodiment, the transformer  802  has a turns ratio of at least 5:1. 
     The input  708  to the signal conditioner  606 -B is the low voltage output of the receiver  604 , which is at a nominal maximum of 6 volts. The ratio of the transformer  802  is such that the output  710  is at a nominal 12 Vdc, which is sufficient to trigger the conventional automotive tachometer  608  reliably. 
     The output of the conventional receiver  604  is an alternating current (ac) signal. The transformer  802  steps up the receiver output voltage to a level that ensures reliable operation of the conventional tachometer  608 . In one such embodiment, the gain of the receiver  604  is set or adjusted so that the output of the transformer  802  is at or near the operating voltage of the vehicle. In another such embodiment, the turns ratio of the transformer  802  is selected such that the output of the transformer  802  is at or near the operating voltage of the vehicle considering the output of the receiver  604 . For installations where the transmitted signal strength is fixed and with a receiver  604  having a fixed gain, the transformer ratio is selected to provide an output that is greater than the minimum voltage requirement of the tachometer  608  and less than the saturation or maximum voltage of the tachometer  608 . 
       FIGS. 7 and 8  illustrate a simplified schematics of the signal conditioners  606 . The simplified schematics do not illustrate various connections that may be required to accommodate specific components selected. 
     The single sensor burst transmitter system  10  includes various functions. The function of generating power and a trigger signal is implemented, in one embodiment, by the inductor  104 , which interacts with the magnet  102 . 
     The function of ensuring the transmitted pulse  306  is transmitted at a specific time is implemented, in one embodiment, by the delay  106 , which ensure the trigger input Tr is at a voltage sufficient to trigger the transmitter unit  108  before the transmitter unit  108  has sufficient power to be energized. 
     From the foregoing description, it will be recognized by those skilled in the art that a self-powered, single sensor burst wireless transmitter system  10  has been provided. The wireless transmitter system  10  has a minimal parts count, requires no external wiring, and has a low cost of installation and maintenance. 
     While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.