fig1 illustrates one embodiment of a baseball speed measuring device 10 , according to principles of the present invention , secured to the back of the web 12 of a baseball glove 14 on the hand 15 of the catching arm 11 of a person catching a thrown baseball 16 . the device 10 , so secured to the baseball glove 14 , is located in or within a few inches of the direct path of movement of the baseball 16 being caught . the device has a two part plastic housing that includes a forward facing housing 17 and a rearward facing housing 18 . in the illustrated embodiment of the unit 10 , the two parts of the housing 17 , 18 are secured together to form a single enclosure that contains the electronics of the unit 10 . the forward facing housing 17 is secured by a fastening element 20 , for example , a two part hook and loop fastener such as that sold under the trademark velcro , and encloses an antenna 21 ( fig2 and 3 ) with a radiation pattern having a main lobe that faces through the web 12 of the glove 14 and in the general direction of the incoming baseball 16 . the rearward facing housing 18 contains display 22 such as an lcd having , for example , two to four digits . on the rearward facing housing 18 there is also provided a plurality of user accessible control buttons 25 - 27 . one button 25 is a unit on / off switch . a second button 26 is a mode switch that permits sequential selection of the units of the display 22 , for example , in miles per hour , kilometers per hour , feet per second or meters per second . a third button 27 is a reset or start button that powers the transmitter for a predetermined amount of time , such as ten or fifteen seconds , after which the transmitter of the unit will turn off . as further illustrated in fig2 and 4 between the forward and rearward facing housings 17 and 18 is a circuit board 33 that contains the transmitting and receiving circuitry , and a signal processing circuit board 30 that contains the signal processing and logic of the unit 10 . the circuit board 30 includes a battery 31 that is replaceable through an access door 32 in the rearward facing housing 18 . the board 33 contains components and circuitry of a transmitter / oscillator circuit , which includes the strip transmission line resonator / antenna 21 . circuit board 30 contains a signal filter and processor 34 that processes the detected doppler signal that is produced in the rf circuit by the moving object , an operational amplifier - based voltage regulator chip 35 that provides filtered regulated voltage to the signal processor chip 34 at about one - half the supply voltage of the battery 31 , a microprocessor 36 that digitizes output from the signal processor 34 and interprets the detected signal as a speed reading and communicates the interpreted signal to the display 22 , and clock and delay circuits 37 and 38 , respectively , that are used by the microprocessor 36 . an alternative embodiment of the unit 10a is illustrated in fig1 a and is configured for attachment to the wrist 13 of the catching arm 11 of the person catching the baseball 16 , or at least on the catcher &# 39 ; s forearm , below the elbow , so that the unit is maintained at a constant distance from the path of the ball . with the wrist or forearm mounted unit 10a , forward and rearward facing housings 17a , 18a , respectively , are separate enclosures that are secured with a wrist or arm band 40 on opposite sides of the wrist 15 of the catcher , so that the forward facing housing 17a faces the arriving object 16 while the rearward facing housing 18a faces the catcher . the separate housings 17a , 18a are electrically interconnected through the conductors of a ribbon cable 41 contained in the band 40 . the forward facing housing 17a contains at least the antenna 21 while the rearward facing housing 18a contains at least the display 22 and the buttons 25 - 27 . the circuit board 30 and the components and devices thereon may be contained in either housing . preferably , the doppler sensor 33 and the doppler signal processor 34 are contained in the forward facing housing 17a in close proximity to the antenna 21 , while the microprocessor 36 and related circuits 37 and 38 are contained in the rearward housing 18a in close proximity to the display 22 . the electronics of the units 10 and 10a illustrated in fig3 can be fabricated utilizing readily available components . the doppler sensor circuit 33 is preferably a cw radar homodyne oscillator - detector 50 having an integral antenna circuit by which the moving object 16 is detected . the oscillator preferably operates at between 2400 - 2425 mhz , but may operate at other frequencies , typically in the 2000 to 10 , 000 mhz region . the oscillator 50 of the preferred embodiment draws about 0 . 6 milliamperes from a 2 . 5 v dc power source such as battery 31 . partially because of the location and configuration of the units 10 , 10a , less than ten microwatts need be transmitted into free - space by the oscillator resonant elements . these elements are preferably of a strip transmission line configuration that includes two electrically equivalent quarter wave micro - strip lines that form radiating elements 21a and 21b of the antenna 21 . the elements 21a and 21b , along with a transistor q1 and a coil 53 , form a negative resistance network which oscillates with a capacitor 21c at the operating carrier frequency of , for example , 2 . 4 ghz . a transmission line 51 and capacitor 49 are provided to prevent parasitic oscillations in the bias network . capacitor 52 is a bypass capacitor which creates a low impedance to ground for the carrier frequency , partially filtering the carrier signal at an outlet 54 at which the received doppler signal can be extracted . typical objects the size of a baseball or softball within a distance of about two feet from the radar produce a reflected doppler frequency signal having an amplitude in the 10 to 100 microvolt range . this signal modulates the oscillator signal at the doppler sensor output 54 of the sensor circuit 33 . a portion of the modulated oscillator signal that has been filtered within the oscillator circuit 33 and fed on outlet 54 into signal processor 34 consisting of a commercially available ac or capacitively coupled high - gain differential amplifier 55 , several stages of filters 56 and a zero crossing detector or zcd 57 . the gain of the differential amplifier 55 is preferably set at a gain of about 1000 , or 60 db . the filters 56 produce a 150 to 1200 hz passband , which covers the range of anticipated doppler frequency signals encountered in baseball and softball applications with the above oscillator frequency . the filters 56 include , for example , standard twin - tee configuration operational amplifier based 60 hz and 120 hz notch filters 56a , 56b to suppress ac power circuit interference . the filters 56 also include two second - order , multiple feedback high - pass filters 56d , 56e each having a gain of , for example , 2 . 7 and a 3 db cutoff frequency of 160 hz . next , the filters 56 include a single order passive low - pass filter 56e having , for example , a 3 db cutoff frequency of 1200 hz . the passband can be tailored to fulfill specific needs by selection of the corresponding low and high pass filter component values which establish the corner frequencies . the amplified and filtered signal from the filtering stages 56 is fed to the zero - crossing detector ( zcd ) 57 , which is a standard schmitt trigger that uses a commercial comparator , with positive feedback to create hysteresis . the zcd produces a square - wave which is output and applied to the input of an eight - bit microprocessor 36 . the microprocessor 36 is connected to external clock circuit 37 which provides a time reference to the microprocessor 36 . the microprocessor 36 is programmed to verify the validity of the received signal , for example , by requiring at least four consecutive doppler frequency cycles , which causes it to recognize the received signal as a valid doppler signal reading . when a reading is determined to be a valid doppler signal reading , the microprocessor calculates the corresponding velocity . the microprocessor 36 has an output 61 that communicates a signal representative of the calculated doppler speed measurement through appropriate drivers ( not shown ) to liquid crystal display ( lcd ) 22 for display . the calculation is made by detecting successive negative edge zero crossings following the depression of the reset button 27 , which trigger a microprocessor interrupt that samples the clock 37 to cause the times of each crossing to be stored and so the intervals between them can be calculated . the sampling is terminated after 26 successive negative transitions are stored , or there has been a dead time of at least 1 / 6 second since the last transition , indicating that the object or target is no longer moving . once the data has been captured , the differences between transition times are calculated from which the doppler frequency is determined . in making the calculations , the microprocessor 36 enhances the speed reading validity by starting with the difference between the first two recorded time readings and then looking for a sequence of at least three consecutive periods that are within 25 % of each other . if none is found , the process is started over and additional readings are stored . when three consecutive readings within 25 % of each other are found , the data is scanned until three consecutive readings are not within 25 % of each other , whereupon the calculations are averaged . the averaged calculated doppler frequency value is then converted to the selected units and displayed . velocity can be displayed in miles - per - hour , kilometers per hour or meters per second in the preferred embodiment , selectable by the user by way of the mode switch 26 , which is a pushbutton switch which , when depressed , sequentially steps the display 22 through the various units , as is convenient for the user . the electronics are powered by a power supply formed of the battery 31 which is connected / disconnected by the on / off switch 25 , which controls signal power to the microprocessor 36 , the signal processor 34 and display 22 . however , the oscillator transmitter circuit power is controlled by the ready , or reset switch 27 through the microprocessor 36 when the battery power switch 25 in &# 34 ; on &# 34 ;. activation of the reset switch 27 causes the microprocessor 36 to close transmitter power switch 60 which applies electrical power to the transmitter / doppler sensor circuit 33 for a prescribed time interval ( e . g . 10 - 15 seconds ) controlled by the time delay circuit 38 , or until a object velocity signal is calculated as controlled by the microprocessor 36 , whichever occurs first , after which the transmitter 33 and signal processor circuit 34 are deactivated as the microprocessor causes the switch 60 to turn &# 34 ; off &# 34 ;. activation of the reset switch 26 causes the microprocessor 36 to reset the lcd 22 , which is holding the previously calculated velocity value , and to re - apply power to the transmitter 33 and signal processor 34 for performing the next detection and velocity measurement . in this manner , the transmitter radiated output is limited to just the period of time of actual measurement usage , and battery power is also conserved . a single transistor oscillator - detector - antenna circuit 33 , signal processor 34 with the doppler bandpass amplifier and the zero - cross detector , eight - bit microprocessor velocity calculator and transmitter controller 36 , liquid crystal display 22 , single - cell battery power supply 31 and on / off and reset switches 26 and 27 can easily be packaged in a volume of about 1 - 3 cubic . for example , the specific embodiment described above can be packaged in a volume of less than two cubic inches using discrete circuit components , and , with appropriate utilization of a custom application - specific integrated circuit ( asic ) and at a frequency of about 5 ghz , the device can be packaged in a volume of approximately one half cubic inch . at higher frequencies of 10 or 20 ghz , which can be used , the package size will be essentially the preferred size of the display . those skilled in the art will appreciate that the application of the present invention herein are varied , and that the invention is described in preferred embodiments accordingly , additions and modifications can be made without departing from the principles of the invention . accordingly , the following is claimed :
a sensor is provided for measuring the speed of a moving sports object , for example a ball such as a baseball or softball . the sensor is operable over a short range and is preferably mounted in close proximity to the path of the moving object . for measuring the speed of a ball , the sensor is preferably mounted on or in a ball glove or is otherwise mounted on the forearm of a person catching or otherwise receiving or interacting with the ball , for example , by wearing the sensor on such person &# 39 ; s wrist . the sensor measures the speed of a ball about to be caught , for example , and displays the speed of the ball to the catching player . the sensor of the preferred embodiment utilizes cw doppler radar in the form of a microwave radio frequency transmitter and receiver that has a single - transistor integrated antenna / oscillator . a simple , low cost unit having a low radiation and low energy consumption transmitter , receiver and signal processor , is provided .