Sensory chessboard and method for detecting positions of chess pieces on a chessboard and transmitting those positions to a computer or other electronic recording device

Abstract

A chess board, comprising a top layer comprising sixty-four (64) squares of alternating color arranged in eight parallel ranks and eight parallel files, and a bottom layer comprising a circuit board, the circuit board comprising sixty-four (64) radio frequency identification antennas arranged in registration with the sixty-four (64) squares of alternating color in the top layer, and an electronic circuit operatively arranged to sense positions and movement of chess pieces on the sixty-four (64) squares of the top layer and communicate the positions and movement to a computer.

Claims

1. A chessboard, comprising: a top layer comprising sixty-four (64) squares of alternating color arranged in eight parallel ranks and eight parallel files, wherein the ranks are arranged perpendicularly to the files; a bottom layer comprising a circuit board, said circuit board comprising sixty-four (64) radio frequency identification antennas arranged in registration with said sixty-four (64) squares of alternating color in said top layer; and, an electronic circuit embedded in said circuit board operatively arranged to receive a unique digital code stored in a radio frequency identification tag in each chess piece positioned atop said chessboard and to sense positions and movement of said chess pieces on said sixty-four (64) squares of said top layer, and communicate said positions and movement to a computer, wherein said circuit board includes a circuit comprising said sixty four (64) radio frequency identification antennas, wherein each antenna comprises a coil etched into said circuit board, with each coil centrally located within a square of said chess board, wherein the width of each said coil is approximately 55% of the width of each square of said chess board.

2. The chessboard recited in claim 1, wherein said radio frequency identification tag in each chess piece is positioned below a metal weight in each said chess piece, wherein a ferrite sheet is positioned between said radio frequency identification tag and said metal weight in each said chess piece.

3. The chessboard recited in claim 1 wherein said top layer is made of wood.

4. The chessboard recited in claim 1 wherein said top layer is made of vinyl.

5. The chessboard recited in claim 1 wherein said top layer is made of polyester fabric with open cell sponge rubber.

6. The chessboard recited in claim 1, wherein each antenna is tuned to have an inductance of approximately 1.92 μH.

7. The chessboard recited in claim 1 wherein said circuit further comprises a microcontroller operatively arranged to control the sixty-four radio frequency identification antennas, by scanning each square on the chessboard in sequence, to detect and identify each chess piece, if any, on each said square.

8. The chessboard recited in claim 1, wherein said each chess piece further comprises: a body having a cavity therein; a metal weight positioned within said cavity; a ferrite sheet positioned below said metal weight and in proximity thereto; and, said radio frequency identification tag is positioned below said ferrite sheet, said radio frequency identification tag is secured to said body.

9. The chessboard recited in claim 8, wherein said each chess piece further comprises a base pad fixedly secured to said radio frequency identification tag.

10. The chessboard recited in claim 8, wherein said metal weight is made of lead.

11. The chessboard recited in claim 8, wherein said body is made of wood.

12. The chessboard recited in claim 8, wherein said body is made of plastic.

13. The chessboard recited in claim 8, wherein said body is made of bone.

14. The chessboard recited in claim 8, wherein said body is made of ivory.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is described in detail below with reference to the drawings, wherein:

(2) FIG. 1 is a perspective view of a typical set-up of the sensory chess board of the present invention, in combination with the chess pieces of the invention, where the board is connected and in communication with a computer, and the moves and positions of the pieces are displayed on a monitor connected to the computer;

(3) FIG. 2 is a 2-dimensional representation of a chess board containing chess pieces in their starting positions prior to a game, illustrating the labeling of the ranks and files of the board, and identification of each square to facilitate use of Algebraic Notation to record the moves of a game, and to identify the location of pieces on the board;

(4) FIG. 3A is a schematic representation of the sixty-four (64) RFID antennas arranged within the sixty-four (64) squares of the chessboard of the invention;

(5) FIG. 3B is an enlarged view of a schematic representation of the RFID antenna arranged under the a1 square of the chess board;

(6) FIG. 4 is a perspective, exploded, fragmentary view of the chess set of the invention, showing a white rook on the h1 square, in position above an RFID antenna in a printed circuit board under the h1 square;

(7) FIG. 5A is a cross-sectional fragmentary partially exploded view of a representative square of the chess board of the invention, and of a weighted chess piece positioned atop the square, to illustrate the electromagnetic flux lines formed as a result of the unique structure of the chess piece;

(8) FIG. 5B is a view similar to that of FIG. 5A but showing an unweighted chess piece positioned atop the square;

(9) FIG. 5C is a view similar to that of FIG. 5B but showing a weighted chess positioned atop the square, but without a ferrite layer 84 positioned above RFID tag 86;

(10) FIG. 5D is an identical, albeit smaller, view of the chess piece positioned atop the square in FIG. 5A;

(11) FIG. 6 is a schematic view of microcontroller 110 of the present invention;

(12) FIG. 7 is a partial schematic view of the control circuit of the present invention;

(13) FIG. 8 is a partial schematic view of the control circuit of the present invention;

(14) FIG. 9 is a partial schematic view of the control circuit of the present invention;

(15) FIG. 10 is a partial schematic view of the control circuit of the present invention;

(16) FIG. 11 is a partial schematic view of the control circuit of the present invention;

(17) FIG. 12 is a partial schematic view of the control circuit of the present invention;

(18) FIG. 13A is a partial schematic view of the control circuit of the present invention;

(19) FIG. 13B is a partial schematic view of the control circuit of the present invention;

(20) FIG. 13C is a partial schematic view of the control circuit of the present invention;

(21) FIG. 13D is a partial schematic view of the control circuit of the present invention; and,

(22) FIG. 13E is a partial schematic view of the control circuit of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(23) At the outset, it should be appreciated that like drawing numbers on different drawing views identify identical, or functionally similar, structural elements. It is to be understood that the claims are not limited to the disclosed aspects.

(24) Furthermore, it is understood that this disclosure is not limited to the particular methodology, materials and modifications described and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the claims.

(25) Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure pertains. It should be understood that any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the example embodiments.

(26) It should be appreciated that the term “substantially” is synonymous with terms such as “nearly,” “very nearly,” “about,” “approximately,” “around,” “bordering on,” “close to,” “essentially,” “in the neighborhood of,” “in the vicinity of,” etc., and such terms may be used interchangeably as appearing in the specification and claims. It should be appreciated that the term “proximate” is synonymous with terms such as “nearby,” “close,” “adjacent,” “neighboring,” “immediate,” “adjoining,” etc., and such terms may be used interchangeably as appearing in the specification and claims. The term “approximately” is intended to mean values within ten percent of the specified value.

(27) Adverting now to the drawings, as described above, FIG. 1 is a perspective view of the sensory chess board of the present invention shown connected to a computer/monitor via a USB cable. It should be appreciated that the board could be connected wirelessly to the computer via any wireless technology, such as by a wireless area network or by Bluetooth® connection. The board itself may be made of any suitable material, such as wood, plastic, rubber, vinyl, or the like. It may be rigid or flexible. A printed circuit board is embedded within the board. As is well known, the board itself contains sixty-four (64) squares of alternating color as shown in the drawing. Chess players refer to the squares as “black” and “white”, or “dark” and “light”, respectively, although the squares may be of any color. The files on the board are labelled “a-h” and the ranks are labelled “1-8” to facilitate recording moves using algebraic notation.

(28) In use, electronics in the circuit board (RFID antennas, etc.) sense the position and identity of each chess piece and transmit that position and identity to the computer as will be described in detail infra. The computer then displays the position of the pieces on the monitor. The moves and positions are also stored, both in an on-board memory, and also on the computer hard drive.

(29) As described previously, FIG. 1 is a perspective view of sensory chessboard system 100, comprising sensory chessboard 10, shown connected to computer 50 via USB connector 70, where moves and the positions of the pieces on the actual board are displayed on computer monitor 60. Chessboard 10 is seen to comprise top layer 20, comprising 64 squares of alternating colors, as is well known in the art. Shown in position atop the board in their initial starting positions are white pieces 30 and black pieces 40. Each set of white and black pieces include the well-known chess pieces: King, Queen, Bishops, Knights, Rooks and Pawns. As described supra, the letters a-h are used to designate files (a row of alternating color squares oriented vertically), and the numbers 1-8 are used to designate ranks (a row of alternating color squares oriented horizontally). These rank and file designations allow unique identification of every square on the chessboard. For example, as shown in the drawing, a white Rook is positioned on square a1; another white Rook is positioned on square h1; the black Queen is positioned on square d8, and so on. Similarly, FIG. 2 is a schematic 2-dimensional drawing which illustrates the actual chessboard shown in FIG. 1, showing all the squares and the positions of the pieces. This is the type of image that would appear on a typical computer which is sensing the positions on board 10.

(30) As will be described in more detail infra, each chess piece in FIG. 1 comprises an RFID tag affixed on or at its base, and this tag contains information that uniquely identifies that chess piece. The board includes 64 RFID antennas, with one antenna located directly beneath every square. These antennas are operatively arranged to emit electromagnetic signals in the direct vicinity of its particular square, to receive a return signal if a particular chess piece is positioned on that square, and to send that piece identity and position information to the computer.

(31) FIG. 3A is a schematic circuit diagram illustrating 64 identical radio frequency identification antennas 26, where each antenna is operatively arranged to sense and identify a chess piece on an associated square 24 on printed circuit board 28, which is in registration with a single square on chessboard 10 shown in FIG. 1. The antennas are coils etched into the printed circuit board. The coils are etched into the top side of the printed circuit board, closest to where the chess pieces will be located. (The remaining electronic components are mounted on the underside of the printed circuit board in a preferred embodiment. In a preferred embodiment, the number of coil turns and separation between traces are determined in such a way as to tune each antenna to 1.92 μH. As shown in FIG. 3A, each antenna is labelled with the prefix “MUX” followed by a number. For example, antenna MUXa-8 is shown to be positioned under the a8 square; antenna MUXb-1 is shown to be positioned under the b1 square, and so on. One end of the coil of each antenna is connected to a common ground. The other end of the coil is connected to the microcontroller as each square is scanned, as will be described infra. In a preferred embodiment, the antennas are all identical, and they are all centered beneath each chessboard square.

(32) The size and spacing of the antenna coils is important. The coils cannot be so large, and so close to an adjacent coil that the antenna cannot discern the identity of a piece placed therebetween; nor should the coil be so small such that when a piece is close to the edge of a square, it won't be detected. In a preferred embodiment, with reference to FIG. 3B, the dimension X, which is the square size on the chessboard, is equal to 2.25″, and the dimension Y, which is the length and width of the coil, is equal to 1.375″, although other dimensions of both the chessboard square, and the coil are obviously possible. In the preferred embodiment described above, there is a distance of 0.438″ surrounding each coil, as measured from the outermost coil turn to the border of the square under which it is positioned. It should be noted that tournament chessboards are known to have standard size squares, such as 2.25″, 2.375″ and 2.5″.

(33) FIG. 4 is a perspective, exploded, fragmentary view of the chess set of the invention, showing a white rook on the h1 square, in position above RFID antenna 26 in a printed circuit board under the h1 square. This particular antenna is labelled MUXh-1 in FIG. 3A. This drawing shows that chessboard 10 comprises top layer 20 and bottom layer 28, where bottom layer 28 is a printed circuit board. As shown in the drawing, white square h1 is in registration with and directly aligned atop square 24 of the printed circuit board. Also shown in the drawing is white rook WR, which includes an RFID tag 86 and a base pad 88 secured to the endcap. In a preferred embodiment, the base pad may be made of felt, billiard cloth, leather, or the like. The RFID tag is in communication with a corresponding antenna beneath the square on which the white rook is perched.

(34) There are major technical problems associated with sensing a chess piece atop a chess board, regardless of the method of detection used. One of these problems is caused by the traditional weighting of chess pieces by metal slugs, such as lead. The problem is the generation of eddy currents about the surface of the weighting slugs, and subsequent interference with communication between the piece and the board electronics as a result of disturbance of the electromagnetic field. FIGS. 5A-5D illustrate this problem and the unique solution provided by the chess pieces of the present invention. FIG. 5A is a cross-sectional fragmentary partially exploded view of square h1 shown in FIG. 4, and of white rook WR positioned atop the square, taken generally along line 5-5 in FIG. 4. This view shows the weighted chess piece and its components, and the unique electromagnetic flux fields produced by the combination of RFID antenna 26 in combination with the chess piece. As seen in the drawing, WR includes body 80, and lead weight 82 positioned in a cavity in the body. Although a lead slug is used to weight the piece in a preferred embodiment, other types and compositions could be used—such as metal and the like. The body of the chess piece may be made of wood, plastic, ivory, resin, bone, marble, ceramic or any other suitable material. Ferrite layer 84 is placed below weight 82. In a preferred embodiment, ferrite layer 84 is made from a flexible sintered ferrite sheet, such as MHLL5040-000 ferrite sheet available from Laird in Earth City, Mo. The ferrite layer acts as a reflective barrier for the electromagnetic flux emitted by the chess board antennae. This layer prevents the flux from reaching the metal weight in the chess piece. RFID tag 86 is fixedly secured to the bottom of the chess piece, after the tag has been programmed to uniquely identify the piece. In a preferred embodiment, the tag is an ISO15693 RFID tag. In a preferred embodiment, both the antenna in the board and the antenna in the RFID tag are tuned to a center frequency of 13.56 MHz. Finally, base pad 88 is secured to the chess piece below the RFID tag. In less expensive chess sets the base pad is made of felt; in more expensive sets the base pad is made of billiard cloth or leather.

(35) FIG. 5B illustrates a scenario where an unweighted chess piece 89 is used with the sensory chessboard of the invention. In this scenario, with no metal present in the chess piece, there is no interference of the electromagnetic flux produced by the antenna in the board. The antenna in RFID tag 86 should easily receive the signal transmitted by the antenna since both antennae are tuned to a center frequency of 13.56 MHz, which is the main carrier frequency of the RFID module.

(36) FIG. 5C illustrates the scenario where chess piece 80 includes lead slug 82 as a weight, and this slug interferes with the electromagnetic flux produced by the chessboard antenna. Some of this flux is absorbed by the lead slug, and the flux creates Eddy currents on the surface of the slug which, in turn, creates a secondary electromagnetic field. The net result of the Eddy currents and the secondary electromagnetic field is a detuning of the antennae in the board and in the RFID tag, making them unusable.

(37) Finally, FIG. 5D is a view similar to that of FIG. 5A, where the above problems have been uniquely solved by the placement of ferrite layer 84 between lead slug 82 and RFID tag 86. The ferrite layer reflects the electromagnetic flux and avoids interference caused by Eddy currents and secondary electromagnetic fields. It should be appreciated that ferrite layer 84, RFID tag 86, and base pad 88 may be affixed to the chess piece, and to each other, in any suitable way, such as by adhesive.

(38) It should be appreciated that, although the RFID tag and the ferrite layer may be two separate elements, that these elements could be combined as a single unit, and are known in the art as RFID anti-metal tags, RFID tags for metal, anti-metal RFID labels, and metal adhesive RFID labels. They are typically made of special rubber magnetic sticky film in combination with an electronic tag on a back side. This type of tag technically successfully solves the issue of eliminating electromagnetic interference in reading an RFID tag when it is attached to a metal surface.

(39) FIG. 6 is a schematic view of microcontroller 110 of the present invention. In a preferred embodiment, microcontroller 110 is model PIC18F4550, manufactured by Microchip Technology Inc. Quartz crystal oscillator is configured with capacitors C.sub.1 and C.sub.2 to provide a 4 MHz signal to the microcontroller via pins 13 and 14, as is well known in the art. The microcontroller is arranged to constantly communicate with RFID module 150 shown in FIG. 12. In a preferred embodiment, RFID module 150 is a model DLP-RFID2 SMT Module manufactured by DLP Design, Inc. The module is a low-cost, compact module for reading from and writing to high frequency RFID transponder tags via an internal or external antenna. It has the ability to both read and write data in addition to reading the unique identifier (UID). All of the electronics on this module reside on a single, compact printed circuit board, and all operational power is taken from one 3.0 to 5.0 volt power supply.

(40) The microcontroller also communicates with EEPROM 135, shown in FIG. 10. The microcontroller only writes to the EEPROM when there is a change in position on the board. The purpose of the EEPROM is to record the moves in each game, and to record a number of games played on the board. In a preferred embodiment the EEPROM is 512 KB. This size memory permits recording of approximately 13,000 games, where each game is approximately 40 moves in length (where one move is defined to be one move by white and one move by black). In a preferred embodiment, EEPROM 135 is a model 24FC512, manufactured by Microchip Technology, Inc., or equivalent.

(41) The microcontroller is also operatively arranged to communicate with WiFi module 140, shown in FIG. 11. Module 140 can function as a WiFi host or as a WiFi adapter (slave), communicating with a router in an existing WiFi network. This module, in combination with the microcontroller, can transmit moves of games being played on the chessboard over a WiFi network, for reception by a computer, or for communication and broadcast over the Internet. In a preferred embodiment, module 140 is a model ESP8266EX manufactured by Espressif Systems. This module provides a complete, self-contained WiFi networking solution. When hosting an application, the module boots up directly from an external flash. It has an integrated cache to improve the performance of the system in this application. Alternatively, when serving as a WiFi adapter, the module provides wireless internet access to the microcontroller. One of the advantages of this module also being capable of serving as a host is the ability of someone to locate and communicate with the sensory board of the present invention from a laptop, smart phone, or similar device, and download the games stored in that board, or watch a game in progress live. For example, in a strong tournament, a spectator or even a competitor may wish to download, view and then study all the games played on Board 1 (traditionally the highest rated player begins the tournament on Board 1, and then the players who perform the best in that tournament plays on Board 1). Often, the most interesting, or at least the highest level, games are played on Board 1.

(42) Microcontroller 110 is also operatively arranged to connect via a serial connection to an external chess clock, such as a digital chess clock. This connection allows the clock time display for each player to be communicated to a computer and displayed on the computer monitor. It also permits the times of each move to be recorded in EEPROM 135. It is also envisioned that the clock times could be communicated from the clock to the system wirelessly via WiFi module 140.

(43) Voltage regulator 130 converts the 5V USB bus voltage supplied by USB connector 125 to 3V. Most of the circuit components of the invention operate at 3V. In a preferred embodiment, voltage regulator 130 is Model TC1185 manufactured by Microchip Technology Inc.

(44) LED assembly 115 includes LED.sub.1 and resistor R.sub.1. In a preferred embodiment, LED.sub.1 is green. If this LED is active, the user knows that everything is operating normally. LED assembly 120 includes LED.sub.2 and resistor R.sub.2. In a preferred embodiment LED.sub.2 is red. If there is an issue with the board, the circuit, or the software, LED.sub.2 will light red.

(45) RFID module 150, shown in FIG. 12, controls the transmission of signals from the RFID antenna array, and the processing of the received signals from the RFID tags on the pieces. It does this by controlling a plurality of RF multiplexer switches shown in FIGS. 13A-13E, as described infra. The RFID module, of course, in in turn controlled by microcontroller 110. Voltage monitor 160 monitors the voltage supplied to the RFID module, to prevent corruption of firmware in the RFID module. The RFID module is very sensitive to low voltages. In a preferred embodiment, if the voltage drops below a preset level (e.g., 3V), monitor 160 shuts down the RFID module to prevent corruption. In a preferred embodiment, monitor 160 is model TLV803 manufactured by Texas Instruments.

(46) Optoisolator 145 is a switch which controls relay 155 which, in turn, communicates the multiplexing signals between RFID module 150 and the first multiplexing switch RS.sub.1, in the system. Any solid state switch could be used in lieu of optoisolator 145, as is well known in the art. In a preferred embodiment optoisolator model LCA110L by IXYS Integrated Circuits Division is used in the multiplexing circuit of the invention. Relay 155 is a standard relay well known in the art, and is only necessary if the first switch/multiplexer RS.sub.1 in the array needs the RFID signal to be off before changing its on/off state. In a preferred embodiment, relay 155 is Model 9007 by Coto Technology, Inc.

(47) Relay 155 controls RF switch RS.sub.3, the first in a line of identical RF switches, as will be discussed infra. The microcontroller also controls switch RS.sub.1 via control lines CNTL-5 and CNTL-6. In a preferred embodiment, these switches, which include RS.sub.1 through RS.sub.21, are all identical, and are all Model 42440, manufactured by Peregrine Semiconductor Corp. All of the switches are controlled by the microcontroller via control lines. The four outputs C, D, E and F of RS.sub.1 become the inputs for RF switches RS.sub.2, RS.sub.3, RS.sub.4, and RS.sub.5, as shown in FIG. 13A. These four switches, in turn, provide outputs G, H, I, J; K, L, M, N; O, P, Q, R; and S, T, U, V, respectively, which all become the inputs for switches RS.sub.6-RS.sub.21, respectively, as shown in FIGS. 13B-13E. As shown in the drawings, switches RS.sub.6-RS.sub.21 control multiplexing of the individual antennas under each square of the chessboard. For example, as shown in FIG. 13B, it is seen that RS.sub.6 controls the antennas MUXg-8, MUXg-7, MUX g-6, and MUXg-5.

Circuit Operation

(48) To begin operation, a user would connect the board via a USB port in a computer. The computer in combination with the board, will sense the initial position of the pieces and know that a new game is about to begin. Upon connection of the board to the computer the microcontroller will control a complete fresh scan of all 64 squares on the board. In a preferred embodiment, the microcontroller is programmed to scan all 64 squares in order from a-1 to a-8, from b-1 to b-8, from c-1 to c-8 . . . to h-1 to h-8, although the order of scanning all the squares on the board can obviously be changed. In a preferred embodiment, the scanning is done at a rate of approximately 5 ms per square, which is equivalent to approximately three scans of the entire board every second. Each time a square is scanned the result of the scan is transmitted to the microcontroller where it is stored in RAM memory, and also transmitted immediately to the computer via the USB connection. It is important to note that only one antenna is active at any time. So, only one square is being queried at any given time. All 64 squares are scanned in a rapid succession. If there is no response when querying one particular antenna, then the board electronic circuit assumes that there is not a chess piece or token at that square and it moves to the next square. When a change in the state of any square is detected (because a piece has left the square, or been placed on the square, etc.) this change of state is also communicated to the EEPROM, since this indicates that a move has been made, and the electronics of the invention records all moves made during a game.

(49) The end of a game can be indicated and sensed in any number of ways. For example, a “White Wins” token can tell the computer that the player with white pieces was the winner of the game. Also, tokens like “Black Wins” or “Draw” can tell the computer that black won or the game was drawn respectively. Alternatively, certain pieces, such as Kings, can be placed on certain squares on the board to indicate game result. For example, placing the Kings on e4 and d5, two white squares, might indicate that White has won the game, while placing the Kings on d4 and e5, two black squares, would indicate that Black has won the game. Placing one King on a white square and one King on a black square might be used to indicate that the game has ended in a draw.

(50) It should also be appreciated that, although in a preferred embodiment, a USB connection is established between the board and a computer, and the chessboard position is transmitted to the computer via this connection, that this information can also be transmitted using a Bluetooth or WiFi connection. A module is used to implement these two wireless connections. The WiFi connection can connect to a WiFi network's router or a smart cell phone. A chess game can thus be watched live in a website by using any of the three available connections.

(51) Thus, it is seen that the objects of the present invention are efficiently obtained, although modifications and changes to the invention should be readily apparent to those having ordinary skill in the art, which modifications are intended to be within the spirit and scope of the invention as claimed. It also is understood that the foregoing description is illustrative of the present invention and should not be considered as limiting. Therefore, other embodiments of the present invention are possible without departing from the spirit and scope of the present invention.

LIST OF REFERENCE NUMERALS

(52) 10 sensory chessboard 20 top layer of chessboard 24 square on printed circuit board 26 radio frequency identification antenna(s) 28 printed circuit board 30 white chess pieces 40 black chess pieces 50 computer 60 computer monitor 70 USB connector 80 body of white Rook WR 82 lead weight in white Rook WR 84 ferrite layer 86 RFID tag 88 felt, billiard cloth or leather base pad 89 unweighted chess piece 100 sensory chessboard system 110 microcontroller 135 EEPROM 140 WiFi module C.sub.1 22 μF capacitor C.sub.2 22 μF capacitor C.sub.3 470 nF capacitor C.sub.4 10 μF capacitor C.sub.5 10 μF capacitor C.sub.6 56 pF capacitor C.sub.7 56 pF capacitor C.sub.8 56 pF capacitor C.sub.9 56 pF capacitor C.sub.10 56 pF capacitor C.sub.11 56 pF capacitor C.sub.12 56 pF capacitor C.sub.13 56 pF capacitor C.sub.14 56 pF capacitor C.sub.15 56 pF capacitor C.sub.16 56 pF capacitor C.sub.17 56 pF capacitor C.sub.18 56 pF capacitor C.sub.29 56 pF capacitor C.sub.20 56 pF capacitor C.sub.21 56 pF capacitor C.sub.22 56 pF capacitor C.sub.23 56 pF capacitor C.sub.24 56 pF capacitor C.sub.25 56 pF capacitor C.sub.26 56 pF capacitor C.sub.27 56 pF capacitor C.sub.28 56 pF capacitor C.sub.29 56 pF capacitor C.sub.30 56 pF capacitor C.sub.31 56 pF capacitor C.sub.32 56 pF capacitor C.sub.33 56 pF capacitor C.sub.34 56 pF capacitor C.sub.35 56 pF capacitor C.sub.36 56 pF capacitor C.sub.37 56 pF capacitor R.sub.1 300Ω resistor R.sub.2 300Ω resistor R.sub.3 4.7 kΩ resistor R.sub.4 4.7 kΩ resistor R.sub.5 1 kΩ resistor R.sub.6 4.7 kΩ resistor R.sub.7 100 kΩ resistor R.sub.8 100 kΩ resistor R.sub.9 1 kΩ resistor R.sub.10 1 kΩ resistor R.sub.11 1 kΩ resistor R.sub.12 1 kΩ resistor R.sub.13 1 kΩ resistor R.sub.14 1 kΩ resistor R.sub.15 1 kΩ resistor R.sub.16 1 kΩ resistor R.sub.17 1 kΩ resistor R.sub.18 1 kΩ resistor R.sub.19 1 kΩ resistor R.sub.20 1 kΩ resistor R.sub.21 1 kΩ resistor R.sub.22 1 kΩ resistor R.sub.23 1 kΩ resistor R.sub.24 1 kΩ resistor WR white Rook X.sub.1 4 MHz quartz crystal oscillator