WO2000037964A1 - Miniature sports radar speed measuring device - Google Patents

Abstract

A speed measuring device (10) includes a Doppler sensor (12), a signal processing circuit (28), a digital circuit (143), a battery (127) and a voltage regulator (130). The Doppler sensor (12) includes a transmit/receive circuit (14) having a single transistor to generate a transmit signal at the desired transmission frequency (e.g., generally in the range of 5800 MHz +/- 75 MHz) and receive a reflected signal from a moving objet. The sensor (12) includes an antenna (20) and additional circuitry to fine tune the sensor (12) to maintain the first harmonic power within prescribed requirements (e.g., those imposed by the FCC) and to process the reflected signal to produce a signal having a frequency determined by the difference between the transmitted and received signals. The Doppler sensor (12) is powered from the output of the voltage regulator (130). The signal processing circuit (28) amplifies and filters the Doppler frequency output of the Doppler sensor (12) and produces a square wave for processing by the digital circuit. A microcontroller (144) within the digital circuit measures the frequency of the Doppler square wave provided by the signal processing circuit (28) in response to determining that the received pulses are generated from acceptable conditions for determining object speed. The square wave frequency is converted to miles per hour (MPH) or other units for display on a liquid crystal display (146).

Description

MINIATURE SPORTS RADAR SPEED MEASURING DEVICE

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of U.S. Patent Application Serial No. 09/233,556, entitled "Miniature Sports Radar Speed Measuring Device", filed on January 20, 1999, which is a continuation of U.S. Patent Application Serial No. 08/796,665, entitled "Miniature Sports Radar Speed Measuring Device", filed February 5, 1997, now U.S. Patent No. 5,864,061. In addition, this application claims priority from U.S. Provisional Patent Application Serial No. 60/113,434, entitled "Miniature Sports Radar Speed Measuring Device", filed on December 23, 1998. The disclosures of the above-referenced patent applications and patent are incorporated herein by reference in their entireties. BACKGROUND OF THE INVENTION 1. Technical Field The present invention relates generally to speed measuring devices. In particular, the present invention relates to a miniature sports radar device which measures and displays the speed of various moving objects (e.g., baseballs, softballs, tennis balls, bats, clubs, racquets, paintballs, hockey pucks or balls, punches or kicks, vehicles, etc.). 2. Discussion of Related Art Currently, continuous wave Doppler radar may be utilized to detect moving objects. This type of radar basically transmits a beam of microwave energy to produce an electromagnetic field. A moving object traversing the electromagnetic field reflects the beam, thereby producing a reflected beam having a frequency that differs from the frequency of the originally transmitted beam. The difference or Doppler shift between the transmitted and reflected beams is proportional to the velocity of the moving object. Doppler radar systems are commonly utilized within security motion sensors, industrial position sensors and police radar units. Doppler radar systems have further been utilized in sports applications to measure the velocities of sports objects. For example, U.S. Patent No. 4,276,548 (Lutz) discloses a microwave speed meter for measuring the relative velocity of an object, such as a baseball. The meter includes a diplexer for illuminating the object with a beam of microwave energy and for generating from the reflected energy a difference signal having a frequency proportional to the relative velocity of the object. A phase-locked loop synchronizes the frequency of an oscillator with that of the difference signal and generates a lock signal when synchronization is achieved. A lock detector and timer generate a reset signal from the lock signal a predetermined period after synchronization, and further generate a latch signal a subsequent period thereafter. The cycles of the oscillator generated after the reset signal are counted via a circuit until the occurrence of the latch signal to determine a sum indicating the relative velocity of the object for display. U.S. Patent No. 5,199,705 (Jenkins et al) discloses a baseball radar speed sensor and catcher's chest protector. A speed meter including a Doppler radar oscillator system is incorporated into a chest protector and measures the relative velocity of a ball thrown by a pitcher to a catcher. A transmitter transmits the speed information to remote locations. U.S. Patent No. 5,401 ,026 (Eccher et al) discloses a method and apparatus for determining a desired parameter of motion of an object. In one embodiment, the device can be used to calculate the estimated carry distance of a golf ball. A Doppler radar system is employed to illuminate the golf ball, and the reflected return signal is detected to generate difference pulses having a frequency proportional to the ball velocity. The difference pulses are processed by a microprocessor to determine if the radar has locked onto the ball. The microprocessor calculates the carry distance in response to the radar lock, and can be further programmed to calculate and display the angle of trajectory and speed of the ball and club-head speed and swing tempo. The systems described above suffer from several disadvantages. In particular, Doppler radar systems are relatively complex, thereby incurring greater costs and size requirements. Further, the systems are subject to federal or other requirements, such as those imposed by the Federal Communications Commission (FCC), especially when utilized for consumer applications. These requirements typically relate to various system characteristics (e.g., transmission frequency band, signal and harmonic power, and fundamental and first harmonic occurrence) and become increasingly difficult to achieve for low power applications. This has generally hindered the use of Doppler type systems in applications requiring extremely small size, low cost and low power. Moreover, the circuit boards and other components of the radar systems are typically constructed of special materials that are specially designed for microwave circuits, thereby increasing system costs. SUMMARY AND OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to measure the speed of a moving object via a small, low cost, low power device. It is another object of the present invention to measure the speed of a moving object via a low power device employing Doppler radar technology and complying with federal or other requirements, such as those imposed by the FCC. Yet another object of the present invention is to employ circuit boards constructed of common printed circuit board (PCB) materials within a Doppler radar speed measuring device to house RF and other circuitry. Still another object of the present invention is to selectively process detected signals within a speed measuring device to ensure accurate determination of the speed of a moving object. The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto. According to the present invention, a speed measuring device includes a Doppler sensor, a signal processing circuit, a digital circuit, a battery and a voltage regulator. The Doppler sensor includes a transmit/receive circuit having a single transistor to generate a transmit signal at the desired transmission frequency (e.g., generally in the range of 5800 MHz +/- 75 MHz ) and receive a reflected signal from a moving object. The sensor includes an antenna and additional circuitry to fine tune the sensor to maintain the first harmonic power within prescribed requirements (e.g., those imposed by the FCC) and to process the reflected signal to produce a signal having a frequency determined by the difference between the transmitted and received signals. The Doppler sensor is powered from the output of the voltage regulator. The signal processing circuit amplifies and filters the Doppler frequency output of the Doppler sensor and produces a square wave for processing by the digital circuit. A microcontroller within the digital circuit measures the frequency of the Doppler square wave provided by the signal processing circuit in response to determining that the received pulses are generated from acceptable conditions for determining object speed. The square wave frequency is converted to miles per hour (MPH) or other units for display on a liquid crystal display. The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof, particularly when taken in conjunction with the accompanying drawings wherein like reference numerals in the various figures are utilized to designate like components. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic block diagram of a sports radar speed measuring device of the present invention. Fig. 2 is an electrical schematic of a Doppler sensor of the device of Fig. 1. Fig. 3 A is an electrical schematic of a signal processing circuit of the device of Fig. 1. Fig. 3B is an electrical schematic of an exemplary low noise amplifier of the circuit of Fig. 3A. Fig. 3C is an electrical schematic of an exemplary level shifter of the circuit of Fig. 3 A. Fig. 4 is an electrical schematic of a digital circuit of the device of Fig. 1. Fig. 5 is an electrical schematic of a voltage regulator of the device of Fig. 1. Fig. 6 is a graphical illustration of an object approaching the device and a corresponding timing diagram illustrating determination of acceptable pulses. Fig. 7 is a view in perspective of the speed measuring device of Fig. 1 attached to a baseball glove for measuring the speed of a moving object employing radar reflective segments according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS A sports radar speed measuring device or system 10 according to the present invention, as illustrated in Fig. 1, includes a Doppler sensor 12, signal processing circuit 28, digital circuit 143, battery 127 and voltage regulator circuit 130. Referring to Figs. 1 and 2, it can be seen that a central part of the Doppler sensor 12 is the transmit/receive circuit 14, typically including a single NPN silicon bipolar transistor that is set to oscillate at approximately 5800 MHz (e.g., generally in the range of 5800 MHz +/- 75 MHz). The transmit signal is generated here and passes through a band stop filter 16 and phasing stub 18 to the antenna 20. A quarter wave bias stub 19 of linear configuration with a length chosen to provide high impedance at operating frequencies is connected between the transistor emitter and ground. Stub 19 grounds the transmit/receive circuit 14 at DC but is open at operating frequencies. Coarse tuning of the oscillation frequency is obtained by trimming the physical length of a tuning stub 22. In one embodiment, tuning stub 22 is preferably a 50 Ohm linear stub having an approximate length of about 0.300 inch. Fine tuning is provided by adjusting the bias resistors 24 and 26 of the transistor. Band stop filter 16 can be any type of notch filter but is preferably a spurline filter centered at approximately 1 1,600 MHz. Its purpose is to prevent the first harmonic (2fo) from exiting the circuit and causing the radiated first harmonic power to exceed FCC field strength limits. Phasing stub 18 changes the antenna impedance so that oscillation can occur in the transmit/receive circuit. Antenna 20 can have any suitable configuration but is preferably a patch antenna. Both the patch antenna and phasing stub are preferably printed on the side of the board opposite the rest of the RF circuitry, and are connected to the rest of the RF circuitry by a plated through-hole. The antenna allows the transmit signals to be launched into the air and also allows reflected signals from the target to be captured. When the transmitted signal is reflected off of the target (e.g., baseball, softball, etc.), part of the reflected signal is captured by the antenna. If the target is stationary, the reflected signal is at the same frequency as the transmitted signal or fr = ft. If the target is moving, the reflected signal frequency will be higher than the original transmitted frequency. The return signal frequency will be higher than the transmitted one by:

fd=2 fo v / c where, c=3xl 0^Λ8 m/s fo= transmit frequency Hz v= target velocity m/s

This return signal passes back through the phasing stub and band stop filter to transmit/receive circuit 14, where it is down converted to baseband. This down conversion takes place due to the non-linearities of the semiconductor material in the transistor. The result of this down conversion process is an intermediate frequency (IF) signal that has a frequency determined by the difference between the transmitted and received signals, and an amplitude determined by the degree of non-linearities in the transistor. Note that the frequency response of the Doppler Sensor extends down to 0 Hz and up to some very high frequency. The ability of the system to detect specific velocities is determined by the designed frequency response of the signal processing circuit 28. The IF output signal, fd, passes through a relatively high impedance (e.g., about 75 to 80 Ohms) transmission line 29 and a band stop filter 30 to the input 34 of the signal processing circuit 28. An optional low pass filter 32 is also shown connected between band stop filter 30 and input 34 and, if provided, may consist of a shunt capacitance and a ferrite choke or any other suitable components. Band stop filter 30 consists of two radial open circuit stubs 36 and 38 and a spurline filter 40. The radial stubs 38 and 36 are tuned to approximately 5800 MHz and 11,600 MHz, respectively. The spurline filter 40 is tuned to approximately 11,600 MHz. The purpose of these filters is to prevent the fundamental (fo) and first harmonic (2fo) from exiting the circuit and causing the radiated first harmonic power to exceed FCC field strength limits. A base shorting radial stub 42 is connected between the base of the transistor and ground to produce the impedance necessary for gain to occur in the transistor for a given frequency band. A resistor 44 is connected between radial stub 42 and band stop filter 30 to isolate RF signals from the portion of the sensor circuit dealing with the IF signal. The Doppler Sensor circuitry 12 is powered from the output 46 of voltage regulator 130 which, for example, can be +2.5 Volts. This DC voltage and current passes through bias adjust collector resistor 24, a low pass filter 51 and a band stop filter 50 to transmit/receive circuit 14. Low pass filter 51 can have any suitable configuration but preferably includes a pair of open circuit shunts 53 and 55 hanging off a transmission line 57 of relatively high impedance. Band stop filter 50 can also have any suitable configuration but preferably includes a spurline filter 52 connected between tuning stub 22 and transmission line 57, and a pair of open circuit radial stubs 54 and 56 extending from the spurline filter. The spurline and one of the radial stubs are tuned to approximately 11,600 MHz, and the other radial stub is tuned to approximately 5800 MHz. The purpose of these filters is to prevent the fundamental (fo) and first harmonic (2fo) from exiting the circuit and causing the radiated first harmonic power to exceed FCC field strength limits. A bias filter 58, shown as a pair of bias filter capacitors 60 and 62 in parallel, is connected between junction 46 and ground. The bias conditions on the transistor can be changed by changing the two bias adjust resistors 24 and 26. Signal processing circuit 28 amplifies and filters the Doppler frequency output of Doppler sensor 12. It also converts the output into a square wave for processing by a microcontroller. The filter response is band pass. Referring to Figs. 1 and 3 A - 3C, it can be seen that signal processing circuit 28 includes a 3rd order Chebychev high pass filter 64 with ldb ripple, corner frequency of approximately 400Hz, and a 3rd order Chebychev low pass filter 66 with 0.25dB ripple, corner frequency of approximately 2.5 kHz. In addition, there is additional high pass filtering provided by a coupling capacitor 68 between the filter sections which AC couples the two filtering stages to eliminate any DC offset. The overall gain of the filters is about 75.6 dB in the pass band such that a separate amplification stage is not needed. The 400 Hz high pass filter frequency was chosen low enough to pass low velocity events (e.g., a 400 Hz Doppler frequency corresponds to about 23 MPH, but since this a ldB point, the device is capable of reading velocities below this velocity, for example a low end velocity of approximately 20MPH), but high enough to reject extraneous low frequency signals and noise. These low frequency signals include real velocities, such as glove movement, (e.g., or movement of other structures supporting the device) as well as interference signals, such as those generated by power lines and fluorescent lighting. The 2.5 kHz low pass filter frequency was chosen high enough to pass higher velocity events (e.g., 2.5 kHz Doppler corresponds to about 143 MPH), but low enough to improve Signal to Noise Ratio by filtering out of band noise. The IF signal from Doppler sensor 12 is applied to the non-inverting input of an op-amp 71 in a band pass filter 70 of signal processing circuit 28. Band pass filter 70 also includes a resistor 74 and capacitor 76 connected in parallel between the output and inverting input of the op-amp, and a resistor 78 and capacitor 80 connected in series between the inverting input of the op-amp and ground. Resistor 74 and capacitor 76 form the low pass pole of the Chebychev filters. Resistor 78 and capacitor 80 form the high pass pole of the Chebychev filters. A capacitor 72 is connected between junction 46 and ground to decouple the op-amp power supply. As shown, band pass filter 70 provides approximately 41 dB of gain for the output of the Doppler sensor. It obtains its DC bias from the Doppler Sensor. The filter preferably has a high pass pole at s = -809.4, and a low pass pole at s = - 1918. These poles are the real poles of the 3rd order Chebychev filters formed by this stage and the two successive stages. The filter is shown implemented in 1/2 of a dual, low cost, op-amp but other implementations can be used. Alternatively, the IF signal from the Doppler sensor may be applied to an optional low noise amplifier 170. The low noise amplifier provides a low noise front end for the signal processing circuit (e.g., introduces less noise into the IF signal) and enhances the signal to noise (S/N) ratio of the device. By way of example only, low noise amplifier 170 (Fig. 3B) includes transistors 172, 180, biasing resistors 178, 194 and a coupling capacitor 176. The transistors are each preferably implemented by a PNP bipolar junction transistor (BJT) with the IF signal being applied to the base of transistor 172. The collector of transistor 172 is connected to ground, while the transistor emitter is coupled to the base of transistor 180. A resistor 174 is connected between the emitter of transistor 172 and a voltage terminal 190 and forms an emitter follower with transistor 172. The emitter follower provides increased input impedance to the low noise amplifier. The base of transistor 180 is coupled to the emitter of transistor 172 with coupling capacitor 176 connected between the coupled base and emitter. The coupling capacitor AC couples the amplifier stages together. Bias resistor 178 is connected between the coupled transistor emitters and the base of transistor 180, while bias resistor 194 is connected between that base and ground. The bias resistors have appropriate characteristics to bias transistor 180 in a desired fashion. A resistor 184 is connected between the collector of transistor 180 and ground, while a resistor 182 is connected between the emitter of transistor 180 and voltage terminal 190 supplying appropriate voltage for the circuit. Resistors 182, 184 and transistor 180 form a common emitter amplifier. A bypass capacitor 186 is connected between the emitter of transistor 180 and ground to bypass resistor 182 at particular frequencies, thereby providing increased gain at those frequencies. A capacitor 188 is connected in parallel to resistor 184 to provide high frequency roll-off of amplitude gain. The resulting signal from the low noise amplifier is provided at a junction 192, coupled to the collector of transistor 180, for application to band pass filter 70 described above. The low noise amplifier may be implemented by various other circuitry, and basically forms, in combination with the other amplifiers, a bandpass filter that filters out of band noise from the IF signal to enhance the S/N ratio. High pass filter 64 receives the output from band pass filter 70 and includes a pair of capacitors 84 and 86 connected in series between the output of op-amp 71 and the inverting input of an op-amp 82, a resistor 88 going to ground from the junction between the capacitors, another capacitor 90 connected between the foregoing junction and the output of op-amp 82, and a resistor 92 connected between the output and the inverting input of op-amp 82. The high pass filter illustrated provides 0 dB of gain. It typically has a pole pair located at s = 99.4 +/- J388.7. The filter is preferably implemented as a Multi Loop Feedback Filter in 1/2 of a dual, low cost, op-amp but can be implemented using any suitable configuration. DC bias is implemented using a resistor divider including a pair of resistors 94 and 96 connected in series between junction 46 of voltage regulator circuit 130 and ground, and a capacitor 98 connected between the junction between the resistors and ground, the aforementioned junction also being connected to the non-inverting input of op-amp 82. Low pass filter 66 receives the output from high pass filter 64 and includes a capacitor 68 and two resistors 100 and 102 connected in series between the output of high pass filter op-amp 82 and the inverting input of an op-amp 104 in the low pass filter stage. A capacitor 106 is connected between the junction between resistors 100 and 102 and ground. A resistor 108 is connected between the aforementioned junction and the output of op-amp 104, and a capacitor 110 is connected between the op-amp output and the inverting input of the op-amp. The low pass filter shown provides approximately 34.6 dB of gain. It typically has a pole pair located at s = 9590 +/- J2729. The filter is preferably implemented as a Multi Loop Feedback Filter in 1/2 of a dual, low cost, op- amp but can be implemented using any suitable configuration. The signal processing system 28 also includes a comparator or zero crossing detector with hysteresis 113 which receives the output from low pass filter 66 via a resistor 112 connected between the output of low pass filter op-amp 104 and the non-inverting input of an op-amp 114 of the comparator. Comparator 1 13 also includes a resistor 116 connected between the output and non- inverting input of op-amp 114, and a capacitor 118 connected from the power supply 46 to ground to decouple the op-amp from fluctuations in the power supply and to prevent the op-amp from causing fluctuations in the power supply. The zero crossing detector is preferably implemented as a comparator in 1/2 of a dual, low cost, op-amp but can be implemented in any suitable configuration. Hysteresis is preferably implemented such that the trip points of the comparator are approximately +/- 38 mV above and below the Voltage provided by the DC bias; however, other trip points can be used. The hysteresis greatly reduces the likelihood of the comparator triggering on noise. The output of the zero crossing detector when a valid Doppler signal is present is a square wave at the Doppler frequency which is provided to digital circuit 143 at junction 140. The output from the zero crossing detector may alternatively be applied to an optional level shifter or translator 120 which is shown (Fig. 3C) implemented using a single n-channel MOSFET transistor 122 with the source going to ground and a resistor 126 connected between the drain and battery terminal 128. Transistor 122 may alternatively be implemented by an NPN bipolar junction or other transistor. The level shifter shifts the output levels of the comparator op-amp to enhance compatibility with the levels needed by the microcontroller and is connected to the digital circuit 143 at junction 140. As mentioned above, the DC bias is implemented with a simple resistor divider, and, as shown, provides a DC level of 1.25 V to the high pass and low pass Chebychev filter stages, as well as the comparator. Other DC bias levels can be used. By applying DC bias directly to high- impedance inputs of the filter op-amps, no additional buffering of the reference voltage is needed, thus eliminating the need for additional op-amps and other components. Referring to Figs. 1 and 4, it can be seen that digital circuit 143 includes a microcontroller 144 receiving (via the input capture pin) the output from comparator 113 or level shifter 120, if provided, a liquid crystal display (LCD) 146 which is driven by the microcontroller, optional programming and serial port headers 158 and 160, a clock 162, a power on reset circuit 148 and a reset button 164. Microcontroller 144 measures the frequency of the Doppler square wave provided by the comparator or level shifter, converts this frequency to miles per hour (MPH) or other appropriate units of measure (e.g., kilometers per hour, etc.), then displays the result on the LCD. The microcontroller also controls the power to the Doppler Sensor and Signal Processor, as well as providing a bidirectional serial communications port for remote reporting of data. Use is made of the input capture feature of the microcontroller in order to measure the Doppler frequency. Each time an edge is detected on the input capture pin (which is connected to the output of the zero crossing detector or level shifter, if provided), the value of an internal 16 bit counter (timer 1), running at the system clock divided by four, is latched into a register, and an interrupt is generated. The measurement process is as follows (please note that words in CAPITAL LETTERS are integer algorithm constants, words in italics are microcontroller registers, and words in brackets [ ] indicate the contents of the indicated register) : After a capture cycle is initiated by pressing the RESET button, the Doppler sensor and signal processor are turned on, and an approximate 20 second transmit timer is started. (Each time the reset button is pressed while transmitting, the 20 second timer is reset.) 1. The first Doppler edge of the correct polarity generates an input capture interrupt. The interrupt service routine clears the interrupt flag, resets timer 1 , and flips the polarity of the input capture edge, so as to waste as few Doppler cycles as possible by starting measurements on the next available edge. 2. On the second interrupt, the interrupt flag is cleared, the GoodPeriod register is cleared, and the latched value of timer 1 is recorded in the Doppler waveform StartingCount register. It is also recorded in the PreviousCount register. If this count is greater than STARTTHR, a count corresponding to about 10 MPH, the present detection routine is abandoned, and restarted at step 1. Also, before exiting, the interrupt flag is checked again. If set, indicating another interrupt occurred while still processing the present interrupt, the present detection routine is abandoned, and restarted at step 1. 3. On the third interrupt, the interrupt flag is cleared, and the latched timer 1 value has the PreviousCount register subtracted from it, yielding a period count that is saved in the PresentPeriod register. The latched timerl count is then moved into the PreviousCount register. The GoodPeriod counter is then incremented by one. Before exiting, the interrupt flag is checked again. If set, indicating another interrupt occurred while still processing the present interrupt, the present detection routine is abandoned, and restarted at step 1.

4. In subsequent interrupts, the interrupt flag is cleared, the PresentPeriod register is moved into the PreviousPeriod register, and the latched timerl value has the PreviousCount register subtracted from it, yielding a period count that is saved in the PresentPeriod register. The latched timerl count is then moved into the PreviousCount register. The difference between the PresentPeriod register and the PreviousPeriod register is then taken. If the absolute value of this difference is less than or equal to ( 1/2 )^PT0L • smaller of [PresentPeriod] or [PreviousPeriod], where PTOL is the period tolerance constant, then the period is a valid period, and the contents of the GoodPeriod register are incremented by one. In addition, if this is the INITVNUM good period, the latched timerl value is also stored in the IntVCount register. The above continues until either 255 good periods are measured, a period is encountered which is not valid, timerl overflows, another input capture interrupt occurs while processing the present interrupt, or the 20 second transmit counter times out. If any of these conditions are met, the number of valid periods recorded in the GoodPeriod register is compared against the NALIDPERIOD threshold. If there are enough good periods (e.g., preferably nine, but may be any desired value in the approximate range of 0 - 255), the microcontroller proceeds to turn off the Doppler sensor and signal processor, and then calculates a velocity based on the value in the StartingCount register, the IntVCount register, the GoodPeriod register, and the count at the end of the last good period (which will be in the PreviousCount register.) If there are not enough good periods, the detection process starts over at step 1 , unless the transmit timer has timed out, in which case a velocity of "00" MPH is displayed on the LCD, and the Doppler sensor and signal processor are turned off. If enough good periods were obtained, a velocity is calculated based on the following algorithm, which may include a correction for the cosine effect, the phenomenon by where the Doppler sensor is only measuring the component of projectile velocity in the direction of the sensor. (If the projectile is not aimed directly at the sensor, as it approaches the radar the angle between it and the radar increases, and thus the radar reports lower and lower Doppler frequencies as the distance between it and the projectile decreases.) The microcontroller first calculates a base velocity over the first INITVNUM of periods, (e.g., preferably four, but may be any desired value in the approximate range of 0 - 255), DOPPLERCALCONSTANT , V_BASE = UnitVCountλ - \ StartinεCount] • TIMERDELTA INITVNUM where DOPPLERCALCONSTANT is in units of MPH per Doppler frequency, and TIMERDELTA is in units of seconds per Timerl count. This, in itself, provides improved accuracy over averaging of all valid Doppler cycles, as the first cycles will be farthest from the radar, where the cosine affect is the smallest. And, since INITVNUM is defined to be smaller than the number of good periods required for a valid measurement (VALIDPERIOD), it will be certain that the measurements for the base velocity are always taken at least a certain distance from the radar. This distance is equal to _c • (INITVNUM - VALIDPERIOD), 2/₀ where c = speed of light, ₀ = radar transmit frequency, INITVNUM = number of periods over which the base velocity is calculated, and VALIDPERIOD = number of valid periods required for a valid measurement. The assumption is then made that the last good period detected was near to the point where the projectile made its closest approach to the radar. This is a valid assumption, since if the projectile hits the radar, the Doppler cycles will end. Even if the projectile passes by the radar, and the Doppler cycles do not end, there will still be a missing or stretched out Doppler cycle as the projectile makes its closest approach to the radar, since its velocity in the direction of the radar goes to zero at this point. This stretched out or missing Doppler cycle will not meet the valid period criteria, so the assumption that the last valid period occurred in the area of the closest approach is valid. The calculated base velocity may be displayed as the measured speed of the projectile. However, an angle correction for the cosine effect may be enabled that facilitates the microcontroller providing an enhanced measurement of the speed. In particular, the general approach of the ball to the radar is assumed as shown in Figure 6. Point P2 is taken as the point where the ball made its closest approach to the radar, and has zero velocity component in the direction of the radar. At P2 a line drawn from the radar to the projectile is perpendicular to the actual velocity vector of the projectile. Point PI is taken as the point where the base velocity was calculated; at this point the ball has a velocity component in the direction of the radar equal to the base velocity. From PI to P2 the ball has moved a distance Rl - R2 = = (c / 2f₀) « N closer to the radar, where Ν = Number of Doppler cycles between P 1 and P2. Now, there is some ambiguity as to the number of Doppler cycles between PI and P2, since P 1 is only defined as the point where the projectile has a velocity component in the direction of the radar equal to the base velocity, and this velocity was calculated by averaging over INITVNUM number of periods, or Doppler cycles. Therefore, the total number of Doppler cycles between PI and P2 is defined as N≡ [GoodPeriod] - INITVNUM. 2 thus locating P 1 at a radius from the radar midway between the radius where the first valid transition (Timer 1= [StartingCount]) occurred, and the radius where the INITVNUM valid period occurred. Given the above, from the geometry of Figure 6 an enhanced estimate of the actual projectile velocity can be made. From the figure, cos (Θ) = (VACTUAL • AT). Rl where V _CTU_AL is the actual ball velocity, AT is the time it took the projectile to move from PI to P2, and Rl is the distance from the radar to point P 1. The time at which the projectile reaches P2 is given by the timerl count at the last good period (which is in the PreviousCount register) multiplied by the TIMERDELTA constant. The time at which the projectile reaches P 1 is defined as (StartinsCountλ + \ IntVCount] • TIMERDELTA. 2 As long as the component of the projectile's velocity in the direction of the radar does not change too much over the first INITVNUM of periods, this definition places the time at P 1 at approximately the time when the projectile was at a radius from the radar midway between the radius where the first valid transition (Timerl Count = StartingCount) occurred, and the radius where the INITVNUM valid period occurred. Now, also from Figure 6, VBASE = V ACTUAL • Cos (Θ),

or cos (Θ) = VBASE V ACTUAL where V_BASE is equal to the base velocity . Equating this value for cos (Θ) with the value from above yields VBASE = VACTUAL • AT (1) VACTUAL Rl where, by the Pythagorean theorem, Rl² = R2² + (V_ACTUAL • AT)², substituting R2 = Rl -X and solving for Rl yields Rl =X+ (VACTUAL • AT)² (2) 2 2X Thus, an enhanced measurement of the actual velocity of the projectile can be determined from equations (1) and (2) above to be { (V_BASE • X²) I (2 C AT - V_BASE • AT²) Ϋ'\ where, as stated before, X= c • N. 2 fo Besides measuring and calculating velocities, the microcontroller provides a firmware implemented 1200 baud, N,8, 1 , serial interface for data I/O between the unit and a PC or other serial capable device, and also controls the user interface. The user interface includes the LCD and the single RESET button on the device. The LCD is direct drive, with output lines of the microcontroller providing the common and segment drivers for the LCD. The LCD waveforms are generated in firmware via a timer interrupt routine. The reset button, when pushed, sets a flag that is checked periodically by the microcontroller. At power on, the unit briefly lights all segments of the LCD, then displays "00". At this point, the Doppler sensor and the signal processor circuitry are off, and the unit draws about 200 uA from the battery. If the RESET button is not depressed within approximately one minute, the microcontroller will turn off the display and go to sleep. In sleep mode, the unit draws under 1 uA of current. Once asleep, the RESET button must be pressed in order to wake the unit up. When the microcontroller awakens, it will place on the display the same value that was being displayed when it went to sleep. Once awake, the microcontroller waits approximately one minute for the RESET button to be pressed again. If it is not pressed within this time, the unit will go back to sleep. If it is pressed, the microcontroller will turn on the Doppler sensor and the signal processor and wait for a valid Doppler signal. While the Doppler sensor is on, the display flashes "00" at about a 1 Hz rate, indicating the unit is transmitting. While transmitting, the unit draws approximately 3mA - 4mA. Once the microcontroller obtains a valid Doppler signal, it calculates a velocity and displays it on the LCD. At this time, the microcontroller also turns off the Doppler sensor and the signal processor, and waits for RESET to be pressed again. If it is not pressed within approximately one minute, the unit goes to sleep. If no valid Doppler cycle occurs within approximately 20 seconds of the RESET button being pressed, the microcontroller turns off the Doppler sensor and the signal processor, displays "00" on the LCD, and waits for RESET to be pressed again. If it is not pressed within approximately one minute, the unit goes to sleep. LCD 146 is preferably direct drive with one common and 15 segment drivers but can have any suitable configuration. The power on reset 148 is an RC circuit that holds the microcontroller reset line low until after power comes up fully. Power on reset circuit 148 is shown in Fig. 4 having a voltage detector 150 connected to the reset line of microcontroller 144 via a resistor 152, with a capacitor 154 going to ground from the junction between the resistor and the voltage detector and a resistor 156 being connected between the junction and battery terminal 128. The programming header 158 brings out the lines needed to program the microcontroller in- circuit, and may be utilized to adjust the thresholds and constants (e.g., the device tolerances) described above for measuring the projectile speed. In addition, the programming head may be utilized to enable or disable the angle correction feature. Data entered via the programming header is maintained by the microcontroller despite power loss (i.e., non-volatile). The serial port header 160 brings out the serial in, serial out, and ground lines to support serial communications. This header may also be utilized to program the microcontroller, however, data programmed via the serial header is not retained upon loss of power (i.e., volatile). The clock 162 is shown in Fig. 4 formed of a 1.0 MHz ceramic resonator and two capacitors that form the frequency determining elements of a Pierce oscillator internal to the microcontroller. The voltage regulator circuit 130 is shown in Fig. 5 having a low dropout, low noise, linear regulator 132, such as a model TC1014-2.5VCT regulator, with digital on/off control. The purpose of the regulator is to provide a constant, low noise, voltage to the Doppler sensor and signal processor. The low drop out voltage extends battery life, as does the on/off control. Battery voltage is applied to the input line of linear regulator 132 at junction 128, with a capacitor 136 going to ground from the input line. Another capacitor 134 is connected between the output line of the linear regulator and ground. A pull down resistor 138 is connected between the enable line of the linear regulator and ground so that the regulator output 46 goes to zero volts when the battery starts to lose power and the microcontroller goes to reset and floats the enable line. The enable line of linear regulator 132 is connected to an input/output (I/O) line of microcontroller 144 at junction 142. The speed measuring device of the present invention may be utilized to measure the speed of various types of moving objects. For example, the device may be mounted on a baseball glove or supported in some other fashion to measure the speed of a baseball or softball. Similarly, the device may be mounted on a hockey goalie or glove or supported in some other fashion to measure the speed of a hockey puck. Further, the device may be disposed within a baseball tee to measure the velocity of a bat swing. The device may be utilized to similarly measure the swing velocity in other sports, such as golf or tennis. Moreover, the device may be mounted on various martial arts type impact pads or bags to measure the velocity of strikes (e.g., punches, kicks, elbows, knees, etc.). The device may further be mounted on or in the proximity of a paint ball gun to measure the velocity of the paintballs. The device housing may be constructed in any fashion to accommodate a particular application and/or withstand impact forces of the moving object on a receiving or other structure. It is to be understood that the device is not limited to the disclosed applications, but may be utilized to measure the speed of any moving object for sporting (e.g., baseball, softball, golf, tennis, hockey, lacrosse, football, etc.) or other purposes (e.g., measure speed of vehicles, runners, etc.). Various types of training/practice baseballs and softballs are designed to minimize injury to players. However, the construction of these types of objects provides poor radar reflecting properties. In order to enhance radar visibility, the objects may include strips or segments of radar reflective material as illustrated, by way or example only, in Fig. 7. Specifically, a ball 198 (e.g., baseball or softball) is propelled toward a baseball glove 196 having speed measuring device 10 mounted thereon to measure the ball speed as described above. A series of reflective strips or segments 199 are affixed to ball 198 via adhesives or other fastening techniques. Alternatively, ball 198 may be constructed to have the segments integrally formed into the ball. The segments are substantially rectangular and are preferably constructed of copper foil tape. However, the segments may be of any shape or size, and may be constructed of any suitable reflective materials. Three segments 199 are preferably positioned on ball 198 and are spaced around the ball such that at least one segment may be visible from any angle. The segments are typically placed to avoid coincidence with the ball seams, and are generally pressed to remove wrinkles therein and provide a smooth reflective surface. Additional segments may be applied to the ball to enhance radar detection, however, any quantity of segments may be employed and positioned on the ball in any fashion. The segments basically enhance reflection of signals emitted by device 10 (e.g., increase intensity of reflected signals), thereby providing increased visibility of ball 198 by the device (e.g., even with the ball constructed of materials having virtually no radar reflecting properties). The device enables speed measurements of the practice balls to monitor throwing improvements by players. It is to be understood that the segments may utilized in conjunction with any object in substantially the same manner described above to enhance radar visibility of that object. While a particular embodiment of the sports radar device has been described and shown, it will be appreciated that various changes and modifications can be made in accordance with the present invention. Some other embodiments of the basic design include: Implementing the Doppler Sensor using a monolithic microwave integrated circuit (MMIC), a dielectrically stable oscillator (DSO), or a cavity oscillator. Implementing the Doppler Sensor with separate transmit and receive sections. Using technologies other than silicon for the Doppler Sensor (e.g., Gallium Arsenide). Using frequencies other than 5.8GHz for the Doppler Sensor; however, by using a relatively high frequency such as 5.8 GHz , smaller components can be used and intermediate frequencies above common noise sources are generated thereby eliminating the need for additional filters. Combining the Signal Processor and the microcontroller in an ASIC. Implementing entire design in hardware, discretely, or in an ASIC. Implementing the signal processing as switched capacitor filters. Implementing the signal processing digitally in a complex programmable logic device (CPLD), gate array, or digital signal processing (DSP) chip. Adjusting the band pass and other filter cutoff frequencies for other velocity ranges. Adjusting the microcontroller operating frequency for other velocity ranges. Using the sensor remotely via the serial communications link. The link may be wired or wireless for remote display of the speed. Adjusting serial communications link to other baud rates or formats. Running the device at other voltage levels to take advantage of lower power or less noisy components. The sports radar device can be implemented using a single transistor transmit receive circuit as shown, or with other types of homodyne, heterodyne or superheterodyne circuits and with continuous or modulated signals. In a single transistor design, the intermediate frequency can be taken from the emitter, collector or base. The filters in the signal processing circuit of the device can be implemented as multiloop feedback filters as shown or in other configurations such as, for example, switched capacitor filters. Further, the various filters of the device may be implemented by any type of filters providing the desired signal filtering described above. The band pass, low pass and high pass filters may be configured to filter signals for any desired frequencies. The gain of the device filters may be adjusted in any desired fashion, while the signal processing circuit filters may further be adjusted in any manner to accommodate the gain of the low noise amplifier. The various stubs in the Doppler sensor can be open or shorted (i.e., connected to ground), radial (i.e., fan shaped), or rectangular or have any other suitable configuration. When a base stub is used, the size of the base stub can be used alone or in combination with the size of the tuning stub to adjust the frequency of the transmit/receive circuit. The antenna is preferably a patch antenna as described above but can be a dipole or any other type of suitable antenna. A patch antenna is preferred since it can be attached to the transmit/receive circuit at a single junction thereby allowing harmonic and other filters to be inserted. The transmission lines in the Doppler sensor can be configured in numerous ways including, but not limited to, coaxial, stripline, and coplanar waveguide configurations. The device according to the present invention can be implemented on one or more circuit boards and enclosed within a housing for attachment to a glove or other support in any manner to measure and display the speed of an object. The circuitry components may be implemented by individual or any combination of conventional or other components having any desired characteristics and arranged in any fashion to perform the functions described above. Further, the transmit/receive circuit may include any quantity of any type of transistor (e.g., BJT, MOSFET, etc.). The moving object may include any quantity of segments of any shape or size disposed at any locations on the object. The segments may be constructed of any suitable reflective material to enhance radar visibility of the object. The microcontroller may be implemented by any processor or circuitry capable of performing the above described functions. The parameters and thresholds within the microcontroller may be adjusted in any fashion to set the device at desired tolerances. Further, the microcontroller may be programmed to ignore a predetermined amount of consecutive bad or invalid periods (e.g., when the low noise amplifier is employed), thereby providing increased tolerance. The device may determine the speed in any desired units of measurement (e.g., MPH, kilometers per hour, etc.). The transmit and sleep intervals may be set to any desired intervals. The display may be implemented by an LCD, LED or any other type of display. The device circuit boards may be constructed of any suitable materials, but is preferably constructed of materials commonly used for printed circuit boards (e.g., epoxy fiberglass). The clock may be implemented by any conventional or other clock having any desired frequency. The voltage regulator may be implemented by any conventional regulator or other device providing any desired voltage. The microcontroller may include software and/or firmware with the software being implemented in any suitable computing languages. From the foregoing description it will be appreciated that the invention makes available a novel miniature sports radar speed measuring device wherein a Doppler type sensor and associated circuitry measure the speed of various moving objects. Having described preferred embodiments of a new and improved miniature sports radar speed measuring device, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the teachings set forth herein. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by the appended claims.

Claims

What is Claimed is: L A device for measuring the speed of a moving object comprising: a motion sensor for detecting said object and generating signals proportional to the object velocity, said sensor including: an antenna for emitting a transmit signal having a first frequency and receiving a return signal reflected by said moving object and having a second frequency; a transmit/receive circuit for generating said transmit signal and converting said return signal to a velocity signal having a third frequency determined by the difference between said first and second frequencies of said transmit and return signals; and harmonic filter circuitry for limiting power of transmit signal harmonics radiated by said device by suppressing said transmit signal harmonics; a signal processing circuit to receive said velocity signal and produce a pulsed signal having a fourth frequency proportional to said third frequency of said velocity signal; and a processor circuit to selectively process portions of said pulsed signal and determine said object speed for display based on said fourth frequency of said pulsed signal.

2. The device of claim 1 wherein said transmit/receive circuit includes a single oscillating transistor to produce said transmit signal.

3. The device of claim 2 further including: a timing stub to facilitate coarse tuning of said transistor to produce said transmit signal at said first frequency; and bias resistors to bias and facilitate fine tuning of said transistor to produce said transmit signal at said first frequency.

4. The device of claim 2 further including: a phasing stub to adjust antenna impedance and facilitate transistor oscillation to produce said transmit signal at said first frequency; and a bias stub connected between said transmit/receive circuit and ground to provide high impedance at frequencies within an operating range of said device.

5. The device of claim 1 wherein said signal processing circuit includes: velocity signal filter circuitry to amplify and reduce noise within said velocity signal and to produce a filtered signal having information related to said object speed; and a detector to receive said filtered signal and generate said pulsed signal based on the frequency of said filtered signal.

6. The device of claim 5 wherein said signal processing circuit further includes: a low noise amplifier to receive said velocity signal from said motion sensor and increase a signal to noise ratio of said device.

7. The device of claim 5 wherein said signal processing circuit further includes a level shifter to receive said pulsed signal and adjust levels of said pulsed signal for compatibility with said processor circuit.

8. The device of claim 1 wherein said processor circuit includes: signal evaluation means for measuring said fourth frequency of a portion of said pulsed signal and verifying said pulsed signal portion has said fourth frequency proportional to said object speed; a counter incremented in response to said signal evaluation means to maintain a quantity of verified pulsed signal portions; threshold means for comparing said counter to a predetermined threshold of verified pulsed signal portions for determining said object speed; and velocity means for determining said object speed from said measured fourth frequencies of verified pulsed signal portions in response to said threshold means determining a sufficient quantity of pulsed signal portions have been verified.

9. The device of claim 1 wherein said processor circuit includes: correction means for adjusting said determined object speed to compensate for deviations in said determined object speed due to angular offsets produced as said moving object approaches said device.

10. The device of claim 1 wherein said fourth frequency of said pulsed signal is equal to said third frequency of said velocity signal.

11. A system for measuring the speed of an object propelled toward an intended target comprising: a receptacle serving as said intended target for capturing said moving object and absorbing forces generated by said moving object impacting said receptacle; a Doppler radar speed sensing device for transmitting and receiving energy waves and measuring said speed of said moving object based on received energy waves reflected by said moving object; and a fastener to secure said speed sensing device to said receptacle to measure said object speed.

12. The system of claim 11 further including reflective material selectively affixed to said moving object to increase intensity of said reflected energy waves and enhance visibility of said moving object by said speed sensing device.

13. In a speed measuring device including a motion sensor to detect a moving object, a signal processing circuit and a processor circuit, a method of measuring the speed of a moving object comprising the steps of: (a) generating a transmit signal having a first frequency via said motion sensor and emitting said transmit signal via a motion sensor antenna; (b) receiving, via said antenna, a return signal reflected by said moving object and having a second frequency; (c) converting, via said motion sensor, said return signal to a velocity signal having a third frequency determined by the difference between said first and second frequencies of said transmit and return signals; (d) limiting power of transmit signal harmonics radiated by said device by suppressing said transmit signal harmonics via said motion sensor; (e) receiving said velocity signal within said signal processing circuit and producing a pulsed signal having a fourth frequency proportional to said third frequency of said velocity signal; and (f) selectively processing portions of said pulsed signal, via said processor circuit, and determining said object speed for display based on said fourth frequency of said pulsed signal.

14. The method of claim 13 wherein said step (a) further includes: (a.l) producing said transmit signal via a single oscillating transistor.

15. The method of claim 14 wherein step (a.l) further includes: (a.1.1) coarse tuning said transistor via a tuning stub to produce said transmit signal at said first frequency; and (a.1.2) biasing and fine tuning said transistor to produce said transmit signal at said first frequency via biasing resistors.

16. The method of claim 14 wherein step (a) further includes: (a.2) adjusting antenna impedance via a phasing stub for facilitating transistor oscillation to produce said transmit signal at said first frequency; and (a.3) establishing high impedance at frequencies within an operating range of said device via a bias stub connected between said motion sensor and ground.

17. The method of claim 13 wherein step (e) further includes: (e.l) amplifying and reducing noise within said velocity signal and producing a filtered signal having information related to said object speed; and (e.2) generating said pulsed signal based on the frequency of said filtered signal.

18. The method of claim 17 wherein step (e.l) further includes: (e.1.1) receiving said velocity signal from said motion sensor via a low noise amplifier to increase a signal to noise ratio of said device.

19. The method of claim 17 wherein step (e) further includes: (e.3) adjusting levels of said pulsed signal for compatibility with said processor circuit.

20. The method of claim 13 wherein step (f) further includes: (f.l) measuring said fourth frequency of a portion of said pulsed signal and verifying said pulsed signal portion has said fourth frequency proportional to said object speed; (f.2) incrementing a counter in response to verification of said pulsed signal portion to maintain a quantity of verified pulsed signal portions; (f.3) comparing said counter to a predetermined threshold of verified pulsed signal portions for determining said object speed; and (f.4) determining said object speed from said measured fourth frequencies of verified pulsed signal portions in response to said determination that a sufficient quantity of pulsed signal portions have been verified.

21. The method of 13 wherein step (f) further includes: (f.l) adjusting said determined object speed to compensate for deviations in said determined object speed due to angular offsets produced as said moving object approaches said device.

22. The method of claim 13 wherein step (e) further includes: (e.1) producing said pulsed signal having said fourth frequency equal to said third frequency of said velocity signal.

23. A method for measuring the speed of an object propelled toward an intended target comprising the steps of: (a) securing a Doppler speed sensing device to a receptacle serving as said intended target to measure said object speed, said receptacle capturing said moving object and absorbing forces generated by said moving object impacting said receptacle; and (b) transmitting and receiving energy waves, via said speed sensing device, and measuring said speed of said moving object based on received energy waves reflected by said moving object as said object moves toward said receptacle.

24. The method of claim 23 wherein step (a) further includes: (a.l) selectively affixing reflective material to said moving object to increase intensity of said reflected energy waves and enhance visibility of said moving object by said speed sensing device.

25. In a speed measuring device emitting energy waves and processing received waves reflected from a moving object to produce a velocity signal having a frequency proportional to a speed of the object, a method for determining object speed from the velocity signal comprising the steps of: (a) measuring said frequency of a portion of said velocity signal and verifying said velocity signal portion has said frequency proportional to said object speed; (b) incrementing a counter in response to verification of said velocity signal portion to maintain a quantity of verified velocity signal portions; (c) comparing said counter to a predetermined threshold of verified velocity signal portions for determining said object speed; and (d) determining said object speed from said measured frequencies of verified velocity signal portions in response to said determination that a sufficient quantity of velocity signal portions have been verified.

26. The method of 24 wherein step (d) further includes: (d.1) adjusting said determined object speed to compensate for deviations in said determined object speed due to angular offsets produced as said moving object approaches said device.