System for detecting the presence and location of at least one object in a field by using a divergent radiation source and an array of opposed plural detectors which rotate together around the field

An apparatus detects the presence and location of at least one object in a field. The apparatus comprises a rotating arm which spins around the field, a position sensor for detecting the angular displacement of the rotating arm relative to a fixed point, and a processor. The rotating arm includes a transmitter and an opposing receiver array mounted thereon and fixed relative to each other. The receiver array includes a plurality of receivers located horizontally coplanar with each other. The receivers are concentrated towards one side of the receiver array which is aligned with a center region of the dartboard. The transmitter outputs a detection beam that emanates from a single point, such as a divergent beam. The detection beam overlaps the field and is simultaneously received at all times by the plurality of receivers of the receiver array. The receivers detect changes which occur in the field as a result of an object being in the field, manifested by shadows on the field. The processor receives output signals from the plurality of receivers and angular displacement data corresponding to the output signals, and determines therefrom the presence and location of an object in the field. The field may be a dartboard front surface and the detected object in the field may be a dart which lands on the dartboard front surface. The dartboard may be a Bandit.RTM. dartboard. The dartboard may be mounted in a housing wherein the front of the housing includes an outer catch ring area having a plurality of removably attachable catch ring segments made of dart-permeable and dart catching material. The processor detects when a player's turn is over by detecting removal of the darts from the dartboard, and automatically advances a scoring display to the next player.

BACKGROUND OF THE INVENTION 
Systems for detecting object presence and location in a field by using a 
radiation beam which rotates around the field are disclosed in GB 
2,196,114 (Hoare) and WO87/05688 (Fenner et al.). Both of these systems 
project radiation beams or light beams across the surface and receive the 
light at one or more opposed receivers. When an object is present in the 
field, it casts a shadow in an imaginary line between the light source and 
receiver. Both of these systems operate on the principle that if two such 
imaginary lines can be detected at different angular positions as the 
transmitter rotates around the field, then the position of the object may 
be detected from the intersection of the two lines. GB 2,196,114 (Hoare) 
discloses a dartboard implementation of the invention wherein a single 
light source and light detector rotate as a pair around the circumference 
of a dartboard surface. The scheme in this patent causes a dead area in 
the bullseye of the dartboard. No points in the dead area are detectable. 
Thus, darts that hit the bullseye are not detected. To detect objects in 
the dead area, it is necessary to physically move the scanning apparatus 
in a sideways direction. This additional step increases the complexity and 
scan time of the scanning process. WO87/05688 (Fenner et al.) also 
discloses an object detection device which may be used for locating darts 
on a dart board surface. The device uses one or more transmitters and 
receivers arranged around the edge of the surface. The preferred 
embodiment in Fenner et al. uses one or more movable transmitters which 
emit either narrow or divergent (broadcast) light beams that are received 
by stationary receivers. Alternatively, the transmitter(s) may be fixed 
and the receiver(s) may be movable. FIG. 1a of Fenner et al. shows a 
narrow light beam emitted from a single movable transmitter which is 
detected individually by a plurality of fixed receivers. FIG. 1b of Fenner 
et al. shows a divergent light beam emitted from a single movable 
transmitter which is simultaneously detected by a grouping of a plurality 
of stationary receivers. 
When using automated devices to detect objects on a surface, such as darts 
on a dartboard, position accuracy is of primary importance. Dart players 
must be able to rely upon the results of the automated scorer under a 
variety of adverse conditions. Darts may be thrown in rapid succession, 
thereby requiring the automated scorer to work quickly. Leaner darts must 
be accurately placed in the right segment. A dart which hits very close to 
a previously thrown dart must be accurately detected. Darts must be 
accurately detected anywhere on the dart surface. It is also preferred 
that the automated scorer be inexpensive, easy to manufacture, and able to 
be retrofitted to conventional dartboards. None of the prior art schemes 
meet all of these criteria. The present invention fulfills the previously 
unmet need for an object presence and location detection device which 
meets all of these criteria. 
BRIEF SUMMARY OF THE PRESENT INVENTION 
An apparatus is provided for detecting the presence and location of at 
least one object in a field. The apparatus comprises a rotating arm which 
spins around the field, a position sensor for detecting the angular 
displacement of the rotating arm relative to a fixed point, and a 
processor. The rotating arm includes a transmitter and an opposing 
receiver array mounted thereon. The receiver array includes a plurality of 
receivers located horizontally coplanar with each other. The transmitter 
and receiver array are fixed relative to each other. The transmitter 
outputs a detection beam that emanates from a single point, overlaps the 
field, and is simultaneously received at all times by the plurality of 
receivers of the receiver array. The receivers detect changes which occur 
in the field as a result of an object being in the field. The processor 
receives output signals from the plurality of receivers and angular 
displacement data corresponding to the output signals, and determines 
therefrom the presence and location of an object in the field. 
In one embodiment of the present invention, the field is a dartboard front 
surface and the detected object in the field is a dart which lands on the 
dartboard front surface. The dartboard may be a bristle dartboard having 
an inner bull and an outer bull arranged concentrically on the bristle 
dartboard, and a framework of interlocked, radial strips and 
circumferential strips mounted on the bristle dartboard to delineate 
different scoring segments, each radial strip being connected to the outer 
bull and a plurality of the radial strips being also connected to the 
inner bull. The dartboard may be mounted in a housing wherein the front of 
the housing includes an outer catch ring area having a plurality of 
removably attachable catch ring segments made of dart-permeable and dart 
catching material.

DETAILED DESCRIPTION OF THE INVENTION 
Certain terminology is used herein for convenience only and is not to be 
taken as a limitation on the present invention. In the drawings, the same 
reference numerals are employed for designating the same elements 
throughout the several figures. 
The present invention, in its most general sense, is an apparatus and 
method of detecting the presence and location of at least one object in a 
field by creating detection beams that "overlap" the field. In the context 
of the present invention, the term "overlap" is meant to be synonymous 
with "cover," encompass," or "project across." The detection beams rotate 
around the field, and an array of receivers detect changes which occur in 
the field as a result of an object being put in the field. The present 
invention operates on the principle that if two imaginary lines can be 
detected at different angular positions as the transmitter rotates around 
the field, then the position of the object may be detected from the 
intersection of the two lines. 
The "field" may be any surface, and is preferably a flat surface. It is 
envisioned that any size or shape field may be monitored by the present 
invention without departing from the invention, including two and three 
dimensional fields. In the presently disclosed embodiment of the 
invention, the field is a round dartboard surface, the object(s) is a 
dart(s), and the system detects the presence of the dart(s) on the 
dartboard surface. 
The present invention also includes a novel scheme for mounting a dartboard 
to the presence and location detection apparatus in a manner that ensures 
accurate dart detection. 
The present invention further includes a method and apparatus for detecting 
the presence of darts on the dartboard surface of a particular type of 
dartboard which forms its spider using a framework of interlocked metal 
radial strips and circumferential metal strips pressed into a bristle 
dartboard. Such a dartboard is disclosed in U.S. Pat. No. 5,417,437 
(Coppard et al.), which is incorporated herein by reference, and is 
manufactured by Puma Dart Products, Ltd., Katkati, New Zealand, and 
commercially sold as the Bandit.RTM. dartboard. The scope of the 
invention, however, includes detection apparatus that functions with other 
types of bristleboard dartboards, dartboards having other types of surface 
hitting material, and dartboards which have electronic dart detecting 
surface and use plastic-tipped darts, such as those shown and described in 
U.S. Pat. No. 4,057,251 (Jones et al.); U.S. Pat. No. 4,516,781 (DeVale et 
al.); U.S. Pat. No. 4,793,618 (Tillery et al.); U.S. Pat. No. 4,881,744 
(Hansen); U.S. Pat. No. 4,974,857 (Beall et al.); U.S. Pat. No. 5,116,063 
(Harlan et al.); and U.S. Pat. No. 5,401,033 (Lychock, Jr.), the subject 
matter of which are incorporated herein by reference. 
FIG. 1 shows a front view of a dartboard machine 10 which uses the novel 
presence and location detection apparatus (hereafter, "object detection 
device") to detect darts 12 which hit (and remain attached to) dartboard 
14. The darts 12 may be steel-tipped darts, which are favored by most dart 
players, or they may be made of any other material which allows them to 
stick into the dartboard 14. The dartboard machine 10 shown in the figures 
includes the following major components: 
1. A conventional bristleboard dartboard 14. One preferred dartboard 14 is 
the Bandit.RTM. board discussed above. In this dartboard, a spider 16 is 
formed from a framework of interlocked metal radial strips (e.g., radial 
divider 18) and circumferential metal strips (e.g., segment divider 20) 
pressed into the bristle dartboard 14, thereby defining a plurality of 
pie-shaped target segments 22 for the different scoring areas. In FIG. 1, 
the spider 16 defines a bullseye 24, a plurality of inner pie segments 26, 
and a plurality of outer pie segments 28. In addition, as disclosed in 
U.S. Pat. No. 5,417,437 (Coppard et al.), the dartboard 14 may include a 
metal ring inside of the bullseye 24 to define an inner bullseye, the 
bullseye 24 thereby becoming an outer bullseye. The metal ring is not 
shown in FIG. 1. However, additional figures described herein include 
inner and outer bullseyes. 
One advantage of using a dartboard which has metal dividers or metal wire 
overlays, instead of painted dividers, is that metal dividers or metal 
wire prevent darts from landing between segments, thereby eliminating 
disputes regarding which segment the dart has hit. FIG. 1 shows three 
darts, 12.sub.1, 12.sub.2 and 12.sub.3. The darts 12.sub.1 and 12.sub.2 
both landed at edges of segments, but are clearly locatable in a single 
segment. 
Additional advantages are available when using a Bandit.RTM. metal 
divider-type dartboard with the present invention. The spider of the 
Bandit.RTM. dartboard projects very slightly above the dartboard surface 
(e.g., about 1.0 mm to about 1.75 mm). The combination of the metal spider 
and the use of a slightly projecting spider helps to guide darts which 
would have hit between segments into one or the other segment, thereby 
minimizing the occurrence of leaners (i.e., darts which stick into the 
board at large angles) at edges of the segments. Leaners cause significant 
detection problems in prior art dart detection schemes, such as those 
disclosed in GB 2,196,114 (Hoare) and WO87/05688 (Fenner et al.), because 
the detected location related to the shadow cast by a dart does not 
accurately represent the true location of the dart tip. The leaner problem 
is most severe when the dart hits near an edge of a segment. (Leaners 
which hit in the middle of segments present less of a problem, since even 
an inaccurate location determination may still properly place the dart in 
the right segment.) Multiple beams, offset from each other in planes 
parallel to the dartboard surface (i.e., stacked beams), are used to 
detect such leaners. Examples of such schemes are shown in FIGS. 1c and 1d 
of Fenner et al. and in FIG. 8 of U.S. application Ser. No. 08/800,301. 
The use of extra detection beams and the circuitry necessary to process 
the additional detection beam information add cost and complexity to these 
detection devices. The Bandit.RTM. dartboard minimizes the number of 
hard-to-detect leaners near segment edges, and thus eliminates the need 
for such multiple stacked beams when using the present invention. For 
example, as shown in FIG. 5, the dart 12.sub.2 is leaning only slightly, 
even though it may have initially hit the board at an extreme angle. 
The present invention further takes advantage of the characteristics of the 
Bandit.RTM. dartboard by projecting the detection beam very close to the 
surface of the dartboard 14, such as about 1.5 mm above the spider 16, or 
about 2.5 mm to about 3.25 mm above the dartboard surface, accounting for 
the spider projection of about 1.0 mm to about 1.75 mm. Distances up to 
about 2 mm above the spider 16 are also acceptable for accurate readings. 
The exposed surface plane of the spider 16 is not completely planar due to 
manufacturing and assembly tolerances. Consequently, there may be slight 
elevations in the spider 16. Also, the surface of a bristle dartboard is 
not completely smooth due to manufacturing tolerances. Furthermore, over 
time, pieces of the bristles protrude from the surface and foreign 
material becomes stuck to the surface. As a result, if the detection beam 
is projected at or extremely close to the surface, such as less than 1 mm 
above the surface, and assuming that there is no raised spider 16, the 
detection beam would likely be broken by the dartboard surface protrusions 
and erroneous detection signals would be generated. The dartboard surface 
protrusions generally do not extend beyond the raised spider 16. Thus, by 
transmitting the detection beam slightly above the raised spider 16, the 
number of erroneous detection signals caused by surface protrusions and 
elevations in the spider 16 are minimized or reduced to zero, yet the 
detection beam is still close enough to the dartboard surface so that an 
accurate determination can be made regarding which segment the dart has 
landed in. 
Referring again to the problem of leaners, the Bandit.RTM. dartboard also 
reduces the incidence of scoring inaccuracies when a dart leans across two 
adjacent segments. Consider FIGS. 9A, 9B and 9C wherein the dart 12 enters 
segment 1 of the dartboard 14 at an angle, leaning over segment 2. The 
angle of incidence (i.e., the amount of leaning) increases from FIGS. 9A 
to 9C. In FIG. 9A, the dart detection point clearly places the dart 12 in 
the correct segment (segment 1). However, as the amount that the dart 12 
leans over segment 2 increases, the dart detection point shifts to the 
right. In FIG. 9B, the dart detection point is still sufficiently within 
segment 1 to be properly scored. In FIG. 9C, the dart is leaning so much 
that the dart detection point is between segments 1 and 2, and accurate 
scoring is no longer possible. Of course, if the leaning became even more 
severe than shown in FIG. 9C, the dart detection point would move into 
segment 2, resulting in a clearly erroneous segment detection. 
When using the Bandit.RTM. dartboard, darts which hit the dartboard at 
extreme angles such as shown in FIG. 9C tend to fall out of the dartboard 
upon impact, and thus do not cause scoring errors. 
FIG. 9B further illustrates the importance of using a detection beam which 
is very close to the dartboard surface. If the hypothetical detection beam 
is used, the dart detection point shifts significantly to the right, and 
moves into segment 2, thereby causing a scoring error. 
2. A cabinet or housing 30 for mounting the dartboard 14 thereto. Front 
cover 32 of the housing 30 is visible in FIG. 1. The front of the housing 
30 includes an outer catch ring area 33 comprised of one or more, and 
preferably a plurality of, removably attachable and interchangeable catch 
ring segments 34 (shown more clearly in FIG. 4). The catch area 33 is made 
from four such catch ring segments 34. The catch ring segments 34 are made 
from any dart-permeable and dart catching material. Two suitable materials 
are rubber and high density neoprene. FIG. 1 shows the dart 12.sub.3 which 
landed dead straight into the upper catch ring segment 34. 
3. A clear lens protective ring 36 (shown more clearly in FIGS. 3 and 4) 
spaced between the outer circumferential edge of the front surface of the 
dartboard 14, and an inner circular edge of the housing 30. The protective 
ring 36 prevents stray darts and debris from entering the interior of the 
dartboard 14. 
4. A display 38 for communicating the player score based on detected dart 
hits, and for receiving inputs from players regarding game commands. The 
display 38 is functionally similar to conventional dartboard displays, and 
thus is not described in further detail herein. The display 38 includes a 
conventional display controller (not shown). However, a novel feature of 
the present invention is that the display 38 is detachable from the 
housing 30. Conventional dartboard displays, such as those used in the 
electronic dart patents cited above are integrated into the dartboard 
machine housing. Such machines are used with plastic-tipped darts which 
will not damage display components if hit. Since the present dartboard 14 
may be used with steel-tipped darts which may damage display components if 
hit, it is preferred that the display 38 be physically moved out of 
hitting range of the dartboard 14 to avoid damage by stray darts 12. In 
FIG. 1, the display controller of the display 38 communicates with the 
electronics inside the dartboard machine 10 via cable 40. The cable 40 may 
be replaced by any suitable wired or wireless (e.g., radio frequency (RF) 
or infrared red (IR)) transmission medium. 
5. An object detection device 42 mounted in part to the back of the 
dartboard 14, and in part to the housing 30. The object detection device 
is not visible in FIG. 1, but selective mechanical parts are visible in 
FIGS. 2, 3 and 6-8, and electrical/computer components are shown 
schematically in FIGS. 12, 13A-13G and 14. 
FIG. 2 shows the dartboard machine 10 with the front cover 32 removed, 
thereby revealing additional details of how the dartboard 14 and object 
detection device 42 are configured in, and mounted to, the housing 30. The 
object detection device 42 has three major mechanical subassemblies, (1) a 
rotating platform assembly, hereafter, "rotating arm 44", (2) a drive 
motor 46 for causing rotation of the rotating arm 44, and (3) a position 
sensor 48 for detecting the angular displacement of the rotating arm 44 
relative to a fixed point. 
In the disclosed embodiment of the present invention, the position sensor 
48 includes a transparent encoder disk 50 and an encoder sensor assembly, 
referred to herein as an "encoder read head 52". Together, the encoder 
disk 50 and read head 52 form a digital incremental encoder. The encoder 
read head 52 is fixed to the rotating arm 44, and thus rotates with the 
arm 44, and the disk 50 is stationary. Alternatively, the encoder read 
head 52 could be made stationary, and the encoder disk 50 could rotate. 
The encoder disk 50 has a series of non-transparent tick marks or marks 
53, such as 512 marks, equally spaced around its circumference. The read 
head 52 detects the marks 53 via interruptions in a light beam emitted by 
the read head 52 and generates an electrical signal in the form of a pulse 
each time it sees one of the marks 53. The read head 52 may have a light 
source and detector on opposite sides of the encoder disk 50, or it may 
use a retro-reflective beam, wherein the light source and detector are on 
one side of the encoder disk 50. Alternatively, the encoder disk 50 or a 
printed version thereof, may be fastened to, or printed directly on, the 
back of the dartboard 14, and a reflective-type read head 52 may be fixed 
to the rotating arm 44 facing the back of the dartboard 14 to detect the 
marks 53. Alternatively, the outer circumferential periphery of the 
dartboard 14 may include a plurality of evenly spaced marks, bars, or the 
like, and a reflective-type read head 52 may be fixed to the receiver 
support 82 (described below, and shown in FIGS. 3 and 8) to detect the 
marks or bars. FIG. 11 shows a read head 52 mounted on the receiver 
support 82 for implementing this alternative scheme. The encoded disk 
preferably includes a protective dust cover (not shown). 
As described in Appendix C, the 512 tick marks 53 are extrapolated to 
obtain 4096 detectable angular positions, which allows for shadow edge 
discrimination of less than 1/10 of a degree. Since the marks 53 and the 
system clock are used to obtain angular position, the rotating arm 44 need 
not be kept at a precisely constant speed. 
Other types of digital incremental encoders may be used, such as ones which 
operate on magnetic or mechanical principles. Absolute encoders or analog 
encoders may also be used, although a digital incremental encoder is 
preferred because it is believed to be the easiest and most cost-effective 
for the chosen electronics. Since the sole function of the position sensor 
48 is to detect the angular displacement of the rotating arm 44 relative 
to a fixed point, the position sensor 48 may be replaced by any suitable 
means which perform this function, such as an angular position detector 
associated with the drive motor 46, or with a direct drive mechanism 
substituted therefor. 
The drive motor 46 is fixed to the housing back or rear housing cover 54, 
which may be made of any durable, light-weight, rigid material, such as 
aluminum, plastic or wood. The drive motor 46 includes a gear reduction 
assembly 56, such as an 1850 to 120 reduction, and an output shaft 58. The 
rotating arm 44 receives power from the output shaft 58 of the drive motor 
46 via drive belt 60. The drive motor 46 may be replaced by any suitable 
means for driving the rotating arm 44, such as a direct drive mechanism. 
The drive motor 46 receives power from power supply and signal routing 
circuit board 61. A source of power, such as 120 VAC is connected to the 
power supply and signal routing circuit board 61. The circuit board 61 is 
also connected to the scoring computer, described below, and also routes 
power and the output of the scoring computer to the display controller of 
the display 38. 
The purpose of the rotating arm 44 is to spin a radiation source, also 
referred to interchangeably as a light source or radiation emitter 
(hereafter, "transmitter 64") and an array of opposed light or radiation 
detectors (hereafter, "receivers 68") around the circumference of 
dartboard surface 70. FIG. 8 shows the entire array of receivers 68, 
referred to herein in "receiver array 72." In one preferred embodiment of 
the invention, the receiver array 72 includes six receivers 68, referred 
to herein interchangeably as receivers 1-6, receivers 68.sub.1 -68.sub.6, 
or receivers TR, MR, SR, DR, CR, 6. One such receiver 68.sub.3 is visible 
in the sectional view of FIG. 3. The receivers 68 are all located in the 
same plane. The rotating arm 44 is preferably rotated about 90 to about 
140 revolutions per minute (RPM). One suitable rotation speed is about 135 
RPM (i.e., about 21/4 revolutions per second or about 810 degrees per 
second). A fast rotation speed provides faster scoring of dart hits, but 
increases audible noise. 
The rotating arm 44 and the position sensor 48 are attached to the 
dartboard 14 via center bolt 62. The center bolt 62 also goes through the 
rear housing cover 54 to draw the mounting flange 102 against the hub 94. 
See, especially, FIGS. 6 and 7. 
FIGS. 3 and 6-8 show additional components of the three major mechanical 
subassemblies and illustrate one embodiment of how the major mechanical 
subassemblies may be arranged. Reference should be made to FIGS. 2, 3 and 
6-8 in understanding the description which follows. 
The transmitter 64 receives firing signals which are detected by the 
receivers 68 of the receiver array 72. The detected signals are processed 
by a scoring engine or scoring computer 74 to determine the presence and 
location of darts 12 on the dartboard surface 70. The scoring computer 74 
is located on the receiver support 82 of the rotating arm 44. In one 
preferred embodiment of the present invention, shown in the figures 
herein, the receiver support 82 is a circuit board which has the scoring 
computer 74 and receivers 68 mounted thereon. The transmitter 64 and 
encoder read head 52 are connected to the scoring computer 74 via wires 
which run along the base of the rotating arm 44, as shown in FIG. 3. A 
slip-ring assembly, discussed below, provide the necessary power and 
communications between the scoring computer 74 and the power supply and 
signal routing circuit board 61. 
Referring particularly to FIGS. 3 and 8, the rotating arm 44 is 
approximately rectangular in shape, although the exact shape and size is 
not critical, as long as it rotates the transmitter 64 and receiver array 
72 around the area to be detected. The rotating arm 44 may be made of any 
durable, lightweight, rigid material such as aluminum, plastic or wood, 
although aluminum is preferred. Three of the four sides of the rotating 
arm 44 (excluding the receiver mounting side) are bent or turned up to 
form lips 78 for rigidity. The transmitter 64 is mounted on a support 80 
extending upwards from one side of the rotating arm 44, and the receiver 
array 72 is mounted on a support 82 (which is the scoring computer circuit 
board in the illustrated embodiment) extending upwards from the other side 
of the rotating arm 44. The transmitter 64 is further extended from the 
rotating arm 44 by a mount 84. As discussed in detail below, the receivers 
68 are preferably not spaced equally from each other, but instead are 
arranged so that particular detection beams 76 (76.sub.1 -76.sub.6) pass 
through specific areas of the dartboard 14. FIG. 11 is a mid-section side 
view of the dartboard machine 10 and shows a more detailed view of the 
placement of the receivers 68 on the support 82 (which is also the scoring 
computer circuit board). The receiver support 82 is attached to the 
rotating arm 44 via tab supports 85. The transmitter 64 outputs a 
divergent beam which is simultaneously received at all times by each 
receiver 68. Each detection beam 76 is thus defined by an imaginary line 
drawn between the transmitter 64 and the respective receiver 68. 
FIGS. 3, 6 and 7 show a slip ring assembly 86 comprised of rotating 
conductive slip rings 88 (three are shown) and non-rotating contact 
brushes 90 (three are shown). The slip rings 88 are located on the outer 
circumference of a rotor 92 which rotates around a stationary hub 94. The 
three slip rings 88 and their respective contact brushes 90 are used for 
power, ground and bidirectional communication (including dart location 
data), respectively. A wire is soldered to the inside surface of each slip 
ring 88, and the wires are routed through a groove 95 in the rotor 92 up 
to the rotating arm 44, and along the rotating arm 44 to the scoring 
computer 74. The contact brushes 90 are electrically connected to the 
power supply and signal routing circuit board 61. An additional set of 
contact brushes 90 may be used for redundancy, or to provide additional 
power and/or communication lines. FIG. 6 further shows a ball bearing 
assembly for permitting rotation of the rotor 92 around the hub 94. The 
ball bearing assembly includes upper and lower bearing mounts 96 with 
inner and outer races, and ball bearings 98 mounted therein. The rotor 92 
is fixed to the rotating arm 44. The drive belt 60, via drive belt pulley 
100, thus causes rotation of the rotor 92/rotating arm 44 assembly. 
The non-rotating components are fixed to the dartboard 14 via mounting 
flange 102 (shown in two parts in FIG. 6, but which may be a unitary part) 
which is screwed into the back of the dartboard 14 and the center bolt 62 
which extends through the hub 94 and screws into a captive mounting nut 
104 embedded either fully or partially into the dead center of the back of 
the dartboard 14. The captive nut 104 preferably extends partially out of 
the back of the dartboard 14, as shown in FIGS. 6 and 7, to allow for 
precise centering of the rotating arm 44 and position sensor 48 mounted 
thereto. The opening of the mounting flange 102 facing the captive nut 
104, labeled in FIG. 7 as opening 106, is sized slightly greater than the 
outer diameter of the captive nut 104 to receive the extending portion of 
the captive nut 104. 
Additional components of the mounting apparatus include an encoder disk 
support 108 and an encoder disk collar (not shown) for attaching the 
encoder disk 50 to the encoder disk support 108. Attachment screws for the 
collar are visible in FIG. 6. The encoder disk support 108 is fixed to the 
hub 94, and may alternatively be formed as a unitary part of the hub 94. 
Appendix A is a detailed parts list of the mechanical components of the 
present invention described above, and includes additional components not 
described above. 
The mounting scheme described herein also allows the dartboard 14 to be 
rotated with respect to the housing 30 without having to remove any of the 
parts behind the dartboard 14. To rotate the dartboard 14, it is only 
necessary to loosen the center bolt 62, while it remains attached to the 
captive nut 104. When the new position is reached, the center bolt 62 is 
tightened to re-lock together all of the mounting components. Rotation of 
the dartboard 14 evens out wear on the dartboard 14 since not all segments 
are hit equally over time. 
The dart location data is output by the scoring computer 74, and 
transmitted through the slip ring assembly 86 to the circuit board 61, 
which routes the data to the display controller of the display 38. The 
data is preferably transmitted in a serial stream to minimize the number 
of transmission channels (e.g., slip ring circuits required). 
Other means may be used to communicate between the scoring computer 74 and 
the circuit board 61 and to power the scoring computer 74, thereby 
eliminating the need for the slip ring assembly 86. For example, batteries 
may be mounted to the scoring computer 74, and RF or IR devices may be 
used for communication. 
As discussed above, the preferred embodiment of the present invention in a 
dartboard environment uses a dartboard with a raised metal spider. In such 
an embodiment, the detection beams 76 are preferably emitted about 1.5 mm 
to about 2 mm above the spider. Alternatively, the dartboard may have a 
spider which is flush or near flush to the surface, or which is embedded 
in the spider. When using a flush or embedded spider, the detection beams 
76 should be emitted as close to the dartboard surface as possible, but 
not so close that surface protrusions of the dartboard interfere with the 
beam. 
The present invention detects darts by looking for detection beam shadows 
cast by a dart in the path of the beam. A dart shadow persists for a 
predetermined angular displacement of the rotating arm 44. FIG. 10 shows a 
modulated detection beam emitted by the transmitter 64 (signal 1). If no 
dart or other obstruction is in the path of any of the opposed receivers 
68 at a given instance in time during rotation of the transmitter 64 and 
receivers 68, then each receiver 68 outputs a corresponding signal (signal 
2). However, if a dart is detected in the path of the detection beam, the 
receiver signal becomes a logic "0" for a predetermined number of pulses 
(signal 3) until the transmitter beam no longer casts a shadow on the 
dart. In the example of FIG. 10, which is shown solely to illustrate the 
principle of the detection scheme, the logic state of "0" persists for 
about eight transmitter pulses. Since noise or sporadic interfering matter 
may cause the receiver 68 output signal to occasionally go low when no 
dart is present, the detection circuitry should ignore low signals unless 
they persist for a predetermined number of pulses. For example, the 
receiver signal 4 is a logic low for only one transmitter pulse, and is 
thus ignored. To minimize the number of false signals, the frequency of 
the transmitter 64 is sufficiently high so that when the arm 44 is 
rotating at speeds of about 90 to about 140 revolutions per minute (RPM), 
there are a sufficient number of transmitter pulses for each pass by a 
dart to generate a clear dart detection signal. 
FIGS. 12, 13A-13G, 14A and 14B show a detailed schematic diagram of the 
hardware of the scoring computer 74. FIG. 12 shows the hardware of the 
transmitter 64 with overlaid functional blocks. FIG. 13A shows exemplary 
receiver TR (receiver 68.sub.1) with overlaid functional blocks. FIGS. 
13B-13G show each of the six receivers TR, MR, SR, DR, CR, 6 (receiver 
68.sub.1 -68.sub.6) without overlaid functional blocks. FIGS. 14A and 
1413, taken together, shows the processing components, including the 
necessary microprocessor. Appendix B is a detailed parts list of the 
individual components of the schematic diagrams. The operation of the 
scoring computer 74 hardware is self-explanatory from these figures and 
the parts list. Accordingly, the circuits are not described in detail 
herein, other than to highlight particular features, as follows. 
FIG. 12 shows transmitter 64 which includes, in sequence, a reference 
generator, an LED driver and a light emitter. The LED emits primarily in 
the non-visible infrared region. The LED emits a single, divergent 
(broadcast) light beam which is simultaneously received at all times by 
each of the receivers 68, thereby simulating a plurality of individual 
transmitter/receiver pairs. The transmitter 64 may optionally be a laser 
beam. However, a laser beam embodiment is significantly more costly than 
an LED embodiment. The transmitter may also optionally be comprised of a 
six individual narrow beams which project from the same point and are 
aimed at the individual receivers 68. However, this scheme would be costly 
and difficult to implement. 
A synchronous detection scheme is used to minimize the presence of 
erroneous detection signals caused by noise or stray receiver signals. In 
this scheme, the receiver signals are gated to the transmitter 64 so that 
signals from the receivers 68 are collected only when a transmitter pulse 
occurs. Accordingly, any signals detected by the receivers 68 between 
transmitter pulses are ignored by the processing circuitry. 
FIG. 13A shows exemplary receiver TR (receiver 68.sub.1), which includes, 
in sequence, a light detector, a high gain AC-coupled amplifier, a 
synchronous rectifier, a lowpass filter and DC amplifier, and a 
comparator. 
FIGS. 14A and 14B, taken together, shows one example of processing 
circuitry which uses four chips: (1) microprocessor U9, (2) a so-called 
"glue logic" chip U10; (3) EPROM U11; and (4) RAM U12 which functions as 
scratch memory for the microprocessor U9. In a low cost embodiment of the 
present invention, one suitable microprocessor U9 is a Phillips P80C32EBAA 
microprocessor, or equivalent. This microprocessor has no onboard ROM, and 
thus an external ROM must be used for storing the scoring computer 
program. In FIGS. 14A and 14B, taken together, the scoring computer 
program is stored in the EPROM U11. This embodiment is vulnerable to 
illegal copying because the contents of the EPROM may be read directly 
from the chip. In a higher cost, but more secure embodiment of the present 
invention, a suitable microprocessor U9 is a Phillips P87C52EBAA 
microprocessor, an Integrated Silicon Solution, Inc. IS89C52-20PL 
microprocessor, or equivalents thereto. These microprocessors have 8K of 
onboard memory which may be used to store the scoring computer program. If 
one of these microprocessors is used, EPROM U11 is omitted from the 
circuit. These microprocessors have security provisions to prevent the 
program from being read. 
The six receiver outputs are input into pins 4-9 of the microprocessor U9. 
The microprocessor U9 also receives signals from the read head 52. In one 
embodiment of the invention, the microprocessor U9 samples signals from 
the read head 52 to detect tick marks 53. In addition, the microprocessor 
U9 samples signals from the read head 52 to detect the number of 
revolutions made by the dartboard 14, as determined by a revolution 
counting scheme. The two circuits for sampling the read head signals are 
shown in the lower middle portion of FIG. 14 (see 1/REV and TICKS signal 
lines). 
FIGS. 15A and 15B show two alternative revolution detection schemes. In the 
first scheme, shown in FIG. 15A, which is used in the presently disclosed 
embodiment, there are 510 tick marks 53, and one index mark. The index 
mark has the width of two marks 53 and thus is readily detectable by the 
encoder read head 52. In an alternative scheme, shown in FIG. 15B, there 
are two encoder disks 50, or two concentric circles defined on a single 
encoder disk 50. One circle has a predetermined number of equally spaced 
tick marks 52 (e.g., 512 tick marks) and an encoder read head 52, and the 
other circle has a single index mark and a corresponding index mark 
encoder read head. In either embodiment, the index mark is used during a 
calibration routine to obtain a reference point, such as to indicate that 
the rotating arm 44 is at zero degrees. The tick marks 52 are then used to 
determine the angular rotation in respect to the reference point. 
The circuit in the upper left-hand corner of FIG. 14A is entirely optional 
and provides no functional capabilities. This circuit provides a visual 
"fun light" effect. The infrared light emitted by the transmitter 64 of 
FIG. 12 is not visible because the emitting frequency is outside of the 
range of visible light. The "fun light" circuit emits a steady glow that 
bathes the dartboard 14 in red light. The light functions to entertain the 
players and to indicate to the players that the scoring computer 74 is on. 
The jumper J4 at the very bottom of FIG. 14B is also optional and provides 
test points for the six receivers 68. 
Appendix C is a functional flowchart of the scoring computer program, and 
includes an explanation of each major function. This flowchart is 
self-explanatory and thus is not described in detail herein. 
Appendix D, in conjunction with FIGS. 19A-19C, show the steps and geometric 
considerations of a dartboard calibration procedure. (A preferred 
calibration procedure is described below with respect to FIGS. 21A, 21B 
and 22.) The specific sequence of display buttons which are hit will 
depend upon the programming logic of the specific dartboard display and 
scoring computer. 
FIG. 20 shows geometrically one example of how to detect the position of a 
dart after two shadow center lines are determined from two different 
angular positions of the rotating arm 44. In this example, signals from 
receiver MR (also known as receiver 5 or receiver 68.sub.2) are used for 
both shadow center lines. No information from any of the other receivers 
is used. One advantage of using the same receivers for both shadow center 
lines is that it simplifies the geometry, since the resultant triangles 
are equal. This speeds up the scoring process, since the calculations are 
less complex. If different receiver signals are used (e.g., one shadow 
center line determined from receiver 5, and another shadow center line 
determined from receiver 6) to find the intersecting point, then geometry 
must be adjusted because the resultant triangles in FIG. 20 will not be 
equal. This will cause an additional delay in the scoring process due to 
the extra calculations. 
The following notes should be used in conjunction with FIG. 20: 
EQU .beta.=(.theta..sub.2 -.theta..sub.1)/2 
EQU l=R/cos .beta. 
Assuming two shadows from one detector R are known, input: 
2 encoder readings ("angles") 
EQU .beta.=abs(.theta..sub.2 -.theta..sub.1)/2 which is always &lt;.pi./2 
EQU .varies.=(.theta..sub.1 +.theta..sub.2)/2 
If the two angles are on opposite sides of the origin, the results must be 
adjusted by .pi. 
EQU .beta.=.pi.-abs(.theta..sub.2 -.theta..sub.1)/2 
EQU .varies.=.pi.-(.theta..sub.1 +.theta..sub.2)/2 
Depending on where the scan is started, .theta..sub.1 is not necessarily 
&lt;.theta..sub.2, hence use the abs (). 
End Notes 
In sum, the simplest geometry results from the use of the intersection of 
two shadow center lines obtained from the same receiver 68. A more complex 
scheme, but equally feasible scheme, is to use the intersection of two 
shadow center lines obtained from different receivers 68. A still more 
complex, but also feasible scheme, is to perform a least squares 
calculation using the shadow center lines obtained from all unobstructed 
receivers. 
As discussed in more detail below, it is not necessary to use the same 
receiver signal to obtain both shadow center lines which are used to 
determine the dart location. In many instances, it is not even desirable 
to use the same receiver signals. 
Some considerations that determine which receiver signals should be used 
and how receivers should be arranged are as follows: 
1. Detection signals from receivers which do not clearly indicate that a 
dart is detected (e.g., noisy signals or signals such as signal 4 in FIG. 
10) should not be used to form shadow center lines. 
2. The accuracy of the received signal improves as the detection beam moves 
away from the center of the dartboard 14. This is due to the fact that the 
longest shadows are cast by the darts which are closest to the dartboard 
center. A shadow may be in the range of 180 degrees or greater for 
detection beams defined by receivers CR and 6 which pass at or near the 
center of the dartboard for a dart that lands at or near the dartboard 
center. If a dart hits dead center, the dart will cast a 360 degree shadow 
(i.e., there will be a shadow at all points in the rotation) for a 
detection beam which passes directly through the center. In contrast, the 
shadow may be in the range of few degrees for darts which land at edges of 
the dartboard and which are hit by detection beams defined by receivers MR 
and TR. 
Overlapping shadows cause accuracy problems because an estimation must be 
made to find the center line of the shadow. Thus, receiver TR provides the 
most accurate signal, since it receives detection beams which are furthest 
away from the center of the dartboard 14. Consequently, receivers CR and 6 
provide the least accurate signals since they receive detection beams 
which are closest to the center of the dartboard 14. 
3. The receiver TR has the least amount of range, whereas the receivers CR 
and 6 have the most amount of range. That is, darts which land on outer 
parts of dart segments are detected by more receivers than darts which 
land on inner parts of dart segments. Thus, for example, darts which fall 
near the center of the dartboard 14 do not cast any shadows that can be 
detected by the receiver TR at any point throughout rotation of the arm 
44, whereas almost all darts which land near the center of the dartboard 
14 will cast shadows detectable by receivers CR or 6 at two points 
throughout rotation of the arm 44. 
In view of these considerations, one approach to maximizing accuracy is to 
use the furthest most receivers possible which receive clear detection 
signals. Another approach, which is preferred and is used in the present 
embodiment of the invention, is to use a voting and weighting scheme, as 
follows: 
(a) Obtain the dart position (i.e., ring and segment), as determined from 
each of the six receivers, or from as many receivers as is possible. 
(b) Cast a vote for each receiver of the dart position. 
(c) Weight the votes by giving greater weight to receivers farthest from 
the center (and which provide the most accurate shadow center lines, as 
discussed above), and receivers which have unobstructed, clear views 
(i.e., receivers which do not have to estimate the shadow center line due 
to overlapping shadows). 
4. Appendix C explains how to determine the center line of the shadow 
(i.e., the estimated line where the tip of the dart entered the dartboard 
14) when there are overlapping shadows. To further explain this process, 
consider FIG. 16. In FIG. 16, a previously thrown dart 1 and a newly 
thrown dart 2 casts a single shadow S.sub.1+2, having a width of X-Y, and 
which is detected by receiver MR as the transmitter traverses through arc 
P.sub.1. The shadow center line associated with arc P.sub.1 may be 
determined as follows: 
(i) Obtain a non-overlapping shadow detected at receiver CR for the new 
dart 2 at another transmitter arc (i.e., other than transmitter arc 
P.sub.1), such as arc P.sub.2. The scoring computer stores all previously 
determined shadows, so if no previous shadow was detected for receiver CR 
through arc P.sub.2, then it is presumed that the new shadow is the result 
of the new dart. 
(ii) Determine the width of the non-overlapping shadow. 
(iii) Take the new edge of the overlapping shadow S.sub.1+2 and subtract 
the width of the non-overlapping shadow obtained in step (ii) to determine 
where the other edge for dart 2 falls along the line X-Y. 
(iv) Now that both edges are known, take the midpoint between the two edges 
and obtain the center line. 
5. Referring to FIG. 8, the receivers 68 are concentrated towards one side 
of the receiver array 72 which is aligned with the center region of the 
dartboard to improve detection accuracy of darts which land close to the 
center and in the bullseye region. As discussed above, accuracy decreases 
for such center darts (due to larger shadows). The extra receivers 68 
improve the prospect for obtaining receiver signals which do not require 
shadow estimations. One preferred arrangement of receivers 3-6 (SR, DR, 
CR, 6) is shown in FIG. 8, and is illustrated more clearly in FIG. 17, and 
described as follows: 
receiver 3 (SR)--tangent to the single bullseye 
receiver 4 (DR)--tangent to the double bullseye 
receiver 5 (CR)--very close to, or directly through the center of the 
double bullseye 
receiver 6 (6)--close to, but not directly through the double bullseye 
This scheme allows for the scoring computer 74 to infer whether a dart is 
in the double bullseye or single bullseye from the presence or absence of 
signals from particular receivers. For example, if the receivers 5 and 6 
both detect a shadow, a position may be computable in the normal manner. 
However, if this is not possible, then the scoring computer 74 may examine 
receiver 4. If receiver 4 does not detect a shadow, but receivers 5 and 6 
both detect shadows, then the dart must be in the double bullseye region. 
Likewise, if receiver 4 detects a shadow, but receiver 3 does not detect a 
shadow, then the dart must be in the single bullseye region. Additional 
details regarding dart scoring in the bullseye regions are given in the 
"Score dart" section of Appendix C. 
FIG. 21A shows a preferred calibration tool 110 for use with a preferred 
calibration procedure described below. The calibration tool 110 has a 
four-prong or two-prong tip 112. FIG. 21B shows an end view of a 
four-prong tip 112. 
FIG. 22 shows the calibration tool 110 as it appears when placed on the 
dartboard 14 in preparation for the preferred calibration procedure. The 
preferred calibration procedure is as follows: 
1. The player presses the calibrate button on the display controller. 
2. The display controller sends the calibrate command to the scoring 
computer 74. 
3. The scoring computer 74 sends an acknowledgement to the display 
controller. 
4. The display controller indicates that the calibration tool 110 should be 
placed over the intersection of the outer triple ring and the divider 
between the 18 and 4 segments. 
5. The player places the calibration tool 110 and presses enter on the 
display controller. 
6. The display controller sends a command to the scoring computer 74 to 
tell it to take the first reading. 
7. The scoring computer 74 takes a reading and sends an acknowledgement to 
the display controller. 
8. The display controller display indicates that the calibration tool 110 
should be placed over the intersection of the outer triple ring and the 
divider between the 16 and 7 segments. 
9. The player places the calibration tool 110 and presses enter on the 
display controller. 
10. The display controller sends a command to the scoring computer 74 to 
tell it to take the second reading and perform the calibration 
computations. 
11. The scoring computer 74 takes a reading, performs the calibration 
computations and sends an acknowledgement to the display controller. 
12. The scoring computer saves the calibration results. 
The two point calibration helps to adjust for variations in the shape and 
position of the spider 16 and the mounting of the dartboard 14. 
Calibration is necessary to adjust for variations in the placement of 
detectors (i.e., receivers 68) on the scoring computer 74 and rotation of 
the dartboard 14. 
The scoring computer 74 locates the center of an object over the dartboard 
14 by using the position that corresponds to the middle of the shadow. For 
calibration, this information is used to locate specific points on the 
dartboard 14 by placing the calibration tool 110 or a dart 12 at the point 
of interest. Using a dart 12, the calibration function is actually 
locating the center of the dart 12, not the intersection of two dividers 
of the spider where the dart 12 is placed. Since the dart 12 is adjacent 
to and not directly over the desired calibration point, the calibration 
function must adjust the computed location to take into consideration the 
radius of the dart 12. The radius of darts can vary from manufacturer to 
manufacturer, introducing an error into the calibration results. 
The calibration tool 110 is designed to fit over the spider intersection, 
thus precisely locating the center of the tool over the calibration 
point(s). The width of the calibration tool 110 is not significant since 
the scoring engine inherently locates the centerline of the object over 
the dartboard 14. 
The scope of the present invention is not limited to the particular 
arrangement of receivers 68, but includes other arrangements which provide 
sufficient scoring accuracy. A fast and inexpensive scoring computer 
should minimize the use of complex receiver processing methods, since 
program storage requirements and score detection time increases rapidly 
with complexity. 
Additional features may be added to improve the dart detection 
capabilities. For example, FIG. 18 shows a sonic detection circuit 200 for 
detecting when a dart has struck the dartboard 14. When a steel-tipped 
dart hits a bristleboard dartboard, an audible thump is generated. The 
circuit 200 includes a microphone 202 disposed against, in, or near the 
dartboard 14 and a dart hit detector 204 programmed to detect a frequency 
or frequencies associated with the thump. The dart hit detector 204 
outputs either a high or low signal which is gated to the dart 
microprocessor U9 shown in FIG. 14A. A high signal indicates that a dart 
was detected, and the microprocessor should look at the signals from the 
receivers 68. A low signal indicates that no dart was detected, and the 
microprocessor should not process any receiver signals. This scheme 
minimizes false scoring from darts which momentarily land on the dartboard 
14 but do not stick to the dartboard 14. 
To conserve power and reduce wear of moving mechanical parts, the 
microprocessor may optionally start a timer after each dart detection and 
to turn off the drive motor 46 if no subsequent dart hits are detected 
after a predetermined period of time. 
The microprocessor may also optionally keep a running total of the number 
of times that a dart hits each dartboard segment and output a signal 
indicating that the dartboard 14 should be rotated after a segment has 
been hit a predetermined number of times. The microprocessor may also 
optionally keep a running total of the number of times that a dart hits 
the dartboard 14 and output a signal indicating that the dartboard 14 
should be replaced after the dartboard 14 has been hit a predetermined 
number of times. 
The scoring computer 74 may also be used to automatically advance the 
display 38 to the next player by detecting the removal of darts from the 
dartboard front surface. During game play, the object detection device 42 
and the scoring computer 74 work together to constantly scan the dartboard 
14 for darts and to score any detected hits. When a player's turn is over, 
the player removes all of the darts from the dartboard 14 before the next 
player throws any darts. Thus, the scoring computer 74 may determine when 
all of the darts have been removed from the dartboard 14 and may send a 
signal to the display controller of the display 38 to automatically 
advance the display to the next player. In this manner, the player does 
not need to manually press the player advance button which is provided on 
conventional displays. In an alternative embodiment of this automatic 
advancing feature, the display may advance to the next player upon 
detecting the removal of less than all of the darts, rather than waiting 
until all of the darts have been removed. 
To minimize crosstalk between the receivers 68, the receivers 68 may be 
selected to operate at different bandwidths, and the transmitter 64 may be 
selected to output a broad range of frequencies, including each of the 
different bandwidths. 
Although the present invention is described in a dartboard embodiment, the 
principles set forth above are equally applicable to other types of 
surfaces, and the scope of the invention includes object detection systems 
for other types of objects and surfaces. 
It will be appreciated by those skilled in the art that changes could be 
made to the embodiments described above without departing from the broad 
inventive concept thereof. It is understood, therefore, that this 
invention is not limited to the particular embodiments disclosed, but it 
is intended to cover modifications within the spirit and scope of the 
present invention as defined by the appended claims. 
__________________________________________________________________________ 
APPENDIX A 
TS LIST OF MECHANICAL COMPONENTS 
DESCRIPTION QTY. 
MFG. PROCESS 
COMMENTS 
__________________________________________________________________________ 
Front Cover 1 Injection Molded 
Rear Cover 1 Injection Molded 
Motor Plate, Lower 
1 Metal Stamping 
Convert to Molded Part 
Rotor 1 Injection Molded 
Support Hub (Shaft) 
1 Injection Molded 
Flange, Hub Support 
1 Injection Molded 
Retainer (Lock Sleeve) 
1 Injection Molded 
Drive Shaft 1 Screw Machine 
Drum 1 Injection Molded 
Convert From Pulley 
Slip Ring 3 Screw Machine 
Slip Ring Spacer 3 Injection Molded 
Collar, Encoded Disk 
1 Injection Molded 
Core 1 Injection Molded 
Adaptor 1 Screw Machine 
Rotating Arm 1 Stamping 
Brush Spring Assy 
6 Special 
Brush Holder 2 Injection Molded 
Emitter Support 1 Injection Molded 
Emitter Mount 1 Injection Molded 
Spacer 1 2 Injection Molded 
Pulley 1 Injection Molded 
Crowned Pulley 1 Injection Molded 
Spacer 3 4 Injection Molded 
Bushing 1 4 Injection Molded 
Bearing Mount 1 Injection Molded 
Spacer 4 2 Injection Molded 
Pulley 1 Injection Molded 
Design as Molded Part 
Stretch Belt, .080 Pitch, 85T, .12W 
1 Purchased 
Stretch Belt, .03 .times. .31 .times. 27.25 LG. 
1 Purchased 
Ball Bearing (50 ID .times. 72 OD .times. 12 W) 
2 Purchased 
Ball Bearing (6 ID .times. 13 OD .times. 3.5 W) 
2 Purchased 
Motor 1 Purchased, Special 
Power Supply PCB 1 Purchased, Special 
Scoring Engine PCB 
1 Purchased, Special 
Sound Isolation Bushings 
4 Purchased 
Encoder Disk 1 Purchased, Special 
Encoder Dust Cover 
1 Injection Molded 
Encoder Sensor Assy 
1 Purchased, Special 
Emitter Assembly 1 Purchased, Special 
Dart Board 1 Purchased, Special 
Display Panel Assembly 
1 Purchased, Special 
Display Panel Cord (Phone Cord) 
1 Purchased, Special 
External Transformer 
1 Purchased, Special 
__________________________________________________________________________ 
__________________________________________________________________________ 
APPENDIX B 
TS LIST OF HARDWARE COMPONENTS IN FIGS. 12, 13A-13G AND 14 
VALUE SIZE QTY. 
DESIGNATOR MANUFACTURER 
T NO. 
__________________________________________________________________________ 
10R 5% 1206 1 R201 Panasonic 
ERJ-8GEYJ 
22R 1W 5% 
Axial0.6 
1 R123 Yageo 22E MO-1 W-B 5% 
56R 5% 1210 3 R104, R105, R106 
Panasonic 
ERJ-14Y 
100R 1% 
1206 4 R110, R111, R112 (*10K), 
Panasonic 
ERJ-8ENF 
R113 (*10K) 
200R 1% 
0805 6 R7, R24, R41, R58, R75, R92 
Panasonic 
ERJ-6ENF 
1.00k 1% 
0805 26 R3, R8, R9, R10, R20, R25, 
Panasonic 
ERJ-6ENF 
R26, R27, R37, R42, R43, R44, 
R54, R59, R60, R61, R71, R76, 
R77, R78, R88, R93, R94, R95, 
R107, R108 
4.02k 1% 
0805 6 R4, R21, R38, R55, R72, R89 
Panasonic 
ERJ-6ENF 
4.7k 5% 
0805 1 R103 Panasonic 
ERJ-6RSJ 
6.8k 5% 
0805 6 R11, R28, R45, R62, R79, R96 
Panasonic 
ERJ-6RSJ 
10.0K 1% 
0805 34 R1, R5, R12, R14, R16, R18, R22 
Panasonic 
ERJ-6ENF 
R29, R31, R33, R35, R39, R46, 
R48, R50, R52, R56, R63, R65, 
R67, R69, R73, R80, R82, R84, 
R86, R90, R97, R99, R101, R109 
R114, R118, R122 
21.5K 1% 
0805 6 R15, R32, R49, R66, R83, R100 
Panasonic 
ERJ-6ENF 
49.9K 1% 
0805 2 R116, R120 Panasonic 
ERJ-6ENF 
100k 1% 
0805 18 R2, R6, R17, R19, R23, R34, R36 
Panasonic 
ERJ-6ENF 
R40, R51, R53, R57, R68, R70, 
R74, R85, R87, R91, R102 
1.00M 1% 
0805 8 R13, R30, R47, R64, R81, R98, 
Panasonic 
ERJ-6ENF 
R117, R121 
S.I.T. 0805 1 R115 Panasonic 
ERJ-6ENF 
S.I.T. 0805 1 R119 Panasonic 
ERJ-6ENF 
27p NPO 
0805 2 C32, C33 Panasonic 
ECU-V1H 
1000p NPO 
0805 6 C1, C6, C11, C16, C21, C26 
Panasonic 
ECU-V1H 
1800p NPO 
0805 1 C41 Panasonic 
ECU-V1H 
0.022u Z5U 
0805 6 C2, C7, C12, C17, C22, C27 
Murata Erie 
GRM-40 
0.047u Z5U 
0805 6 C4, C9, C14, C19, C24, C29 
Murata Erie 
GRM-40 
0.1u Z5U 
0805 2 C36, C42 Murata Erie 
GRM-40 
0.1u Z5U 
1206 4 C34, C35, C37, C38 
Murata Erie 
GRM-40 
0.22u Z5U 
0805 6 C3, C8, C13, C18, C23, C28 
Murata Erie 
GRM-40 
10u 6.3V 
1206 7 CS, C10, C15, C20, C25, 
Panasonic 
ECS-T0JY106R 
C30, C31 
470u 6.3V 
F-size 
9 C39, C40, C43, C44, C45, C46 
Panasonic 
ECE-V0JA471P 
C47, C48, C49 
2N3904 SOT-23 
20 Q1, Q3, Q4, Q5, Q7, Q8, Q9, 
Zetex FMMT3904 
Q11, Q12, Q13, Q15, Q16, Q17, 
Q19, Q20, Q21, Q23, Q24, 
Q28, Q29 
2N3906 SOT-23 
6 Q2, Q6, Q10, Q14, Q18, Q22 
Zetex FMMT3906 
IRLZ14 TO-220 
1 Q30 International 
IRLZ14 
Rectifier 
LMC662 SO-8 7 U2, U3, U5, U6, U7, U8, U13 
National E 
CD4066 SO-14 2 U1, U4 Harris 
PDI-E801 
T-13/4 
1 LED4 Photonic Detectors, 
PDI-E801 
Inc. 
PN334PA 
0.1" 6 PIN1, PIN2, PIN3, PIN4, PIN5, 
Panasonic 
PN334PA 
PIN6 
ZVN3306 
SOT-23 
3 Q25, Q26, Q27 Zetex ZVN3306F 
80C52 PLCC44 
1 U9 Phillips P80C32EBAA (low 
cost option) 
P87C52EBAA 
(secure option) 
Integrated Silicon 
IS89C52-20PL 
Solution, Inc. 
(secure alternate) 
16K .times. 8 
PLCC32 
1 U11 AMD AM27C128 
EPROM 
8K .times. 8 
SOP-28 
1 U12 Mosel Vitelic 
MS6264L-100FC 
SRAM Integrated Silicon 
1S62C64-100U 
Solution, Inc. 
(alternate) 
12MHz HC-49 1 Y1 ECS, Inc. 
ECS-120-32-4 
74HC14 SO-14 1 U14 Harris 
74HC373 
SOL-20 
1 U10 Harris 
Super bright 
T-13/4 
3 LED1, LED2, LED3 
Toshiba TLSH180P 
LED 
32-pin socket 
PLCC 1 (for U11) Aries 
44-pin socket 
PLCC 1 (for U9) Aries 
3-pin 0.1" header 
4 J1, J2, J3, J5 
connector 
Circuit Board ISD971105-1 
__________________________________________________________________________ 
APPENDIX C 
Scoring Engine Program Flow 
The following sequence is repeated continuously: 
Tick for tick--Collect samples for 1 revolution 
If the number of sample changes=2 and darts thrown this round&gt;0 
All darts have been removed, reset values for the next player else if 
current samples&gt;previous samples 
if darts thrown&lt;3 
n=0 
do 
n=n+1 
prepare the detectors for scoring 
Tick for tick--Collect samples for 1 revolution 
Shadow capture--extract the shadow edges for each detector from the 
samples 
Find darts--compute the dart position for each detector 
Score dart--consolidate the results of the detectors while the number of 
results&gt;n 
if a satisfactory result was found send the result to the front panel save 
the edge information for the next dart 
else check for calibration mode 
Calibrate--calibrate the unit 
The following is a description of individual functions: 
Tick for Tick 
There are 512 encoder ticks per revolution. The program samples the 
detector and encoder information repeatedly looking for changes. When a 
change occurs, the program stores the number of ticks before the change, 
the time since the last tick and the data. When the next tick occurs, the 
program divides the time into eighths and computes which eighth the change 
occurred in and stores this along with the other data. This is repeated 
until all 512 encoder ticks have been seen. 
Dividing the 512 encoder ticks into eight intervals give an effective 
sampling interval of 1 in 4096. 
Shadow Capture 
This function extracts the rising and falling edge pairs for each detector 
from the data collected in Tick for tick. Subsequent processing is done 
for each detector independent of the others. 
Find Darts 
This function first attempts to find the center of the shadows 
corresponding to a new dart. This is done by matching the current edges 
against the previous edges. If both edges of a pair do not match any 
previous edges, it is considered a new shadow. If one edges matches and 
the other doesn't, it is considered a hidden shadow. Edge pairs that match 
previous edges are ignored in subsequent processing. Previous edge pairs 
that can no longer be accounted for may indicate a dart that has fallen 
out. 
If at least one new shadow and one hidden shadow have been found, the 
program tries to find the centers of the shadows. This is done by finding 
the value exactly between the two edges. For hidden shadows, it is 
necessary to find the "hidden" edge by subtracting the width of the new 
shadow from the new edge of the hidden shadow. The centers of the shadows 
correspond directly to the angle of the PC board when the detector is 
centered on the dart. 
If the function is able to find two angles, it can compute the distance (r) 
and angle (theta) of the dart using similar triangles. 
theta=(angle.sub.1 +angle.sub.2)/2-calibrated angle offset 
r=calibrated detector radius /cos (theta) 
The r and theta values are converted to a ring and segment of the dart 
board which are returned from the function. If the function is unable to 
find two angles, no ring and segment are returned and the detector is not 
used in scoring the dart. 
Score Dart 
This function takes the ring and segment results from each of the detectors 
and resolves any discrepancies using a priority weighting system. In 
general, the detector farthest from the center of the board without any 
hidden edges is given the most weight. 
In cases near the center of the board where the dart position measurement 
is less reliable because the shadows are larger, and in/out test is used 
to verify results. Two detectors are placed such that they are tangent to 
the single bull and double bull rings. If a center detector "sees" a 
shadow and the double bull detector does not see it, a double bull is 
scored. Likewise, if a center detector or the double bull detector "sees" 
a shadow and the single bull detector does not, a single bull is scored. 
The result of the function is the scoring weight (single, double, triple) 
and the segment of the dart scored. The number of different results is 
also available to judge the quality of the result. 
Calibrate 
This function is used to compensate for variations in the position of the 
detectors and the rotation of the board. A measurement is taken of one or 
more darts in known positions. The difference between the known location 
and the measured position is stored for each detector. These values of r 
and theta are then used to correct the computed positions of the darts 
during normal scoring. 
APPENDIX D 
Dart Board Calibration Procedure 
To perform a calibration: 
1. Throw 3 darts 
2. Press any player button to reset dart counter 
3. Place your fist on the board, the LED's will come on 
4. Remove your fist and place it back on the board, the LED's go off and 
the unit beeps and displays a 1 
5. Remove fist and all darts 
6. Place a dart in the triple 4 in the corner closest to 18 and the outer 
edge of the board 
7. The unit beeps and displays a 2 
8. Remove the dart, wait briefly and place the dart in the comer of the 
single 18 near the outer triple ring and the 4 (i.e., in the diagonally 
opposite corner of the intersection of the 4-18 segment divider and the 
outer triple divider) 
9. The unit should beep and display 3 or 6 
10. Remove the dart, the board is calibrated 
Notes 
If the LED's come on during game play, remove all darts and wait 10 
seconds. If the LED's do not go off, turn the unit off and back on. The 
calibration will not be affected. 
If the second or third beep above does not happen within 5 seconds after 
placing the dart, remove the dart, wait 5 seconds and replace it. 
If any problems occur, turn unit off and back on to reset it.