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									                   Tangible Chess for the Compaq Tablet PC
                                                Christopher T. Lewis
                                             Computer Science Department
                                              University of Saskatchewan
                                               Saskatoon, SK., Canada
                                                  +1 306 956 7693

This project will develop a prototype tangible user interface    Existing tangible chess projects [1,2] have focused on
(TUI) for playing chess on the Compaq Tablet PC                  moving game pieces using robotic arms with magnets or
(TC1000). The project will use the TUI with existing chess       pincers at the direction of either the computer or a player.
software, the GNU Chess Engine and the Winboard Chess            By contrast, this project seeks to integrate the traditional
interface. The goal is to develop a TUI for chess which          tangible interface into electronic chess.
provides a natural interface to electronic chess that is both
portable and affordable.                                         The initial phase of this project aims to develop a TUI
                                                                 using the original game pieces as an interface to existing
Keywords                                                         electronic chess software, thereby restoring the traditional
Tangible User Interface, Chess, Tablet PC                        interface to electronic chess. The second phase of the
INTRODUCTION                                                     project aims to provide the player with additional
Chess is a military strategy game which pits two opponents       information related to their opponent’s moves, such as
against one another. The objective of the game is to             whether or not the opponent hesitated and the speed with
capture the opposing king. Each player has 16 pieces of          which the piece was moved. This is intended to allow the
varying abilities arrayed in an 8x8 grid. Traditionally, the     player to detect their opponent’s tells and restore the
game is played by two opponents seated opposite each             missing psychological element of the game.
other over the game board. There are computerized
versions of the game available, which fall into two
categories: enhanced playing boards and electronic chess.
Enhanced playing boards have typically been used to allow
a single human player to play chess against the computer,
while electronic chess implementations allows a player to
play against the computer, a remote human player or to
review a past game.
Electronic chess offers a number of advantages over both
traditional chess and enhanced playing boards, for instance
the ability to record and playback a game, to track statistics
in a tournament setting, to play over a network, and to
validate moves.        However, playing electronic chess
removes the tangible pieces from the game thereby
preventing the board from being surveyed in a natural
fashion. Furthermore, due to the coordinate based moves          Figure 1: A mockup showing how a piece would be moved
used by chess engines players are unable to see hesitation       on the tablet by a physical piece with an embedded
and other tells exhibited by the remote player, which            transmitter.
eliminates a psychological facet of the game.
                                                                 SYSTEM COMPONENTS
                                                                 In phase 1, the system will be tested using the WinBoard
 LEAVE BLANK THE LAST 2.5 cm (1”) OF THE LEFT                    GUI [3] and the GNUChess engine [4], though it should
     COLUMN ON THE FIRST PAGE FOR THE                            work with any existing GUI and chess engine. These
            COPYRIGHT NOTICE.                                    programs are freely available and widely used by online
chess players. Connecting to a chess server will allow                movements, which may indicate uncertainty or reveal
network play using the system.                                        something of their strategy.
Communication between the GNUChess engine and the                     Hardware
client occurs using a coordinate based movement system                The TUI will consist of 32 active chess pieces with
which transmits only the start and end point of the move.             embedded transmitters. Moving a piece will have an
The software for phase 2 has yet to be identified; however a          equivalent effect to selecting and dragging the piece using
requirement for the software is that it must transmit either          the TC1000’s pen. To accomplish this, each transmitter
all movement information to the remote player in real-time,           will transmit at the same frequency as the TC1000’s pen
or sense the movement and transmit movement                           with the tip switch depressed.          According to the
characteristics to the remote player. This will allow the             specification filed with the Federal Communications
opposing player to watch for hesitation in their opponent’s           Commission (FCC) the pen transmits at a frequency of 482-
                                                                      494 kHz when the tip switch is depressed (Table 1) [5].

         Switch Status                           Frequency (kHz)                        Amplitude*
         Idle                                    458.0-465.0                            1250-1550
         (no switches)                           454 (measured)
         Tip switch only                         482.0-494.0                            1250-1550
                                                 476 (measured)
         Tip switch + Single Side Switch or      433.8-445.4                            1200-1525
         Primary dual side switch                432 (measured)
         Single Side Switch or Primary dual      415.0-424.0                            1125-1450
         side switch only                        416 (measured)

     Table 1: The frequencies and amplitudes for the TC1000 as specified by the manufacturer in their FCC documents as well as the
                      frequencies measured by connecting an oscilloscope to the antenna leads of the original pen.

To avoid having 32 active pieces at one time, the                       The digitizer used in the TC1000 only senses the pens
transmitter will be inactive (power off) when the pieces                presence to a height of 0.5 inch above the digitizer surface
are on the playing board. Lifting the piece from the                    (as specified in the Fine Point Innovations Engineering
playing surface will activate the piece. This will be                   Specification). When a piece is moved beyond this
controlled by a small button on the bottom of the playing               boundary, it is as if the player released the piece. This has
pieces.                                                                 two undesirable consequences, 1) if the resulting move is
Using this design, it is possible that there will be problems           invalid, the piece will return to its initial starting point,
when capturing an opponent’s piece; at this time it is                  and 2) if the resulting move is valid, the piece will remain
possible that there would (briefly) be two pieces active at             where it was released. It is likely that neither of these is
the same time. Two strategies can be employed to avoid                  the intended result. It may be possible to sense the z-
this situation. The first possibility is the addition of a              position of the piece at the time that the signal is lost and
second button to the piece, which, when depressed, would                wait for the signal to resume if the piece has been moved
render the transmitter inactive. This button could be                   above the boundary (i.e. the z position of the piece will be
pressed on an opponent’s piece before removing it, which                0 when the piece is placed on the board, or 0.5 inches if
would ensure that only one piece is active during the                   the piece is lifted outside the boundary). However, while
capture. The second alternative is moving the activation                the Tablet PC Hardware requirements specification
button from the bottom of the piece to another location.                released by Microsoft calls for the z-coordinate to be
Using this design the user having to press and hold the                 reported [6], it appears that existing tablet
button for the duration of their move, rather than having               implementations do not report it.
the piece activate automatically when it is picked up off               CLASSIFICATION WITHIN TUI FRAMEWORKS
the playing surface. However, this would allow an                       Framework 1: Ullmer and Ishii [7], Calvillo-Gamez
opponent’s piece to be removed without any special             [8]
manipulations.                                                          Within the classifications of Ullmer and Ishii this TUI is
                                                                        best classified as an Interactive Surface, though it overlaps
the Token+Constraints framework.            The interactive              tools because they can be used to select and drag any item
surface is provided by the digitizer in the tablet PC which              on the screen (Table 2). This is in spite of of their
tracks the movement of pieces over the surface. Within                   physical likeness to the pieces they are intended to move,
the Token+Constraints framework, the pieces are tokens                   which may cause them to act as identifiers in the mind of
associated with the corresponding virtual piece. The                     the user. The link is semi-permanent because it exists
movement of a piece is constrained by its movement                       whenever the piece is over the playing surface, but not
capabilities as well as the presence of surrounding pieces.              when the piece is on the playing surface or removed from
                                                                         the game (though the user may assume that the link still
Framework 2: Paper 3 (Koleva [9]
                                                                         exists at this point making it a permanent link in the mind
Within the Link-Coherence framework of Koleva et. al.
                                                                         of the user).
the chess pieces are best classified as general purpose

          Category     Ex.       Trans.       Scope                                     Conf.     Lifetime      Autonomy
          General      Chess     Literal      Lifting piece, Setting piece down,        Fixed     Semi-         Autonomous
          Purpose      Piece                  translation parallel to surface                     permanent
 Table 2: Classification of the chess pieces within the Link-Coherence Framework of Koleva et. al. Note that the Chess pieces have been
              classified as General Purpose Tools despite their physical resemblance to the piece they are intended to move.

          Action          Time             Location       Direction        Dynamics             Modality        Expression
          Move Piece      Yes              Yes            Yes              Yes                  Yes             Yes
          Opponent        Phase 1: No      No             Phase 1: No      Phase 1: No          Phase 1: No     Phase 1: No
          Moves           Phase 2: Yes                    Phase 2: Yes     Phase 2: Yes         Phase 2: Yes    Phase 2: Yes
          Capture         Yes              Yes            Yes              Yes                  Yes             Yes
          Opponent        Phase 1: No      No             No               No                   Yes             No
          Captures        Phase 2: Yes
      Table 3: Classification of the actions in the tangible chess game within the Interaction Frogger Framework of Wensvenn

Framework 3: Paper 4 (Wensveen [10]                              Because captured pieces disappear, the reaction to
All actions which are performed on the remote system will                capturing a piece cannot be coupled to the physical action
experience a slight delay before occurring on the local                  of removing the piece on the remote tablet. There are no
system, this delay is introduced when the coordinates are                plans to change this behavior in phase 2 of the project.
processed by the chess server, and can be eliminated (as                 Similarly, there is no way to show dynamics or expression
much as possible given current technologies) by moving                   on the remote tablet when capturing a piece.
to a peer-to-peer implementation in phase 2 of the project.              When moving a piece on the local tablet, the dynamics of
The reaction for all actions which occur on the local tablet             the action are coupled to the dynamics of the reaction.
will appear in the same location, and a moment later the                 However, due to the coordinate based moves used in
same reaction will occur on the remote tablet. The change                phase 1, it is impossible for this coupling to occur on the
to a real-time, peer-to-peer system in phase 2 will not                  remote computer. However, it will be possible to display
change this behavior, except that the reaction on the                    this coupling in phase 2 of the project.
remote tablet might occur marginally faster.                             Similarly, when moving a piece on the local tablet, the
On the local system, the direction of movement is coupled                expression of the action is reflected in the reaction on the
to the direction of the reaction. On the remote system, the              local tablet. However, again, due to the coordinate based
direction of movement is not coupled to the reaction on                  moves used in phase 1, it is impossible for this coupling to
the remote system because there is no path information                   occur on the remote computer. However, once again, it
transmitted using coordinate based moves in phase 1.                     will be possible to display this coupling in phase 2 of the
However, when the path of movement is transmitted to the                 project.
remote computer in phase 2, the direction of reaction will
be coupled with the direction of action.
DESIGN CONSTRAINTS                                              subsequent analysis of the waveform produced by the pen
The goals of portability and affordability introduce weak       revealed that it was producing a sine wave. The fact that
constraints on piece design in that the pieces must be          the pen produces a sine wave was not known when we set
small enough to travel well, solid enough to withstand          out to build the circuit based on the NE555 because we
minimal abuse while traveling and priced such that the          did not initially have access to an oscilloscope.
average user can purchase a set. The selection of the
Tablet PC as the playing surface imposes an additional
strong design constraint in that it offers a relatively small
playing area requiring that each piece be no more than 3/4
of an inch in diameter in order to fit within the squares of
the chess board.
Assembling the pieces from common electronics
components will help to ensure a minimal production cost.
However, the choice of components is restricted to those
having low voltage requirements as each piece will be
battery powered. The selection of a battery is another
important design consideration, and the output voltage
will further constrain the components used in the chess
The intent is to use 1.4V hearing aid batteries, such as the
Energizer AC312. Such batteries are available in spools
                                                                  Figure 2: This figure shows the circuit used with the
of 16 for approximately 20$ (Can) or $1.25 a piece,
                                                                  NE555 timer in an attempt to produce the 488 KHz
though online retailers sell larger quantities at a lower per
                                                                            frequency used in the tablet pen.
unit cost. The dimensions of the AC312 are 0.311”
(width) x 0.142” (height), which means that the AC312           Dual Operational Amplifier
should easily fit inside a chess piece. Two batteries           The schematic for the single supply wein bridge using a
operating in parallel should produce 2.8V of power for          dual op amp is shown in Figure 3 [12]. Using this circuit
approximately 1000 hours; so any parts we use must be           the frequency is calculated using the forumula:
able to operate at or below 2.8 V Vcc.                                                  f=1/2πRC
IMPLEMENTATION                                                  To achieve the desired 488 KHz frequency we used
The pieces used in this project must be able to produce a       C=100pF and R=3261KOhms. However at this frequency
frequency within the range specified for the pen with the       the dual op amp used failed to oscillate. By adjusting the
tip switch depressed (482-494 KHz). There have been             RC values we were able to successfully produce a 200
two attempts to produce this frequency, one based on an         KHz wave, though the output frequency deviated
NE555 timer and a second attempt using a dual                   substantially from the theoretical frequency for the RC
operational amplifier (op amp). Unfortunately both              values used. Further investigation revealed that this
attempts failed.                                                attempt failed because the gain bandwidth (1MHz) of the
NE555 Timer                                                     dual op amp used (LMV982MA) is too low to produce a
The schematic for the circuit based on the NE555 timer is       488 KHz frequency. According the theory, the gain
shown in Figure 2 [11]. Using this circuit, the frequency       bandwidth must be at least 3 times the output frequency.
is determined by altering the values of R1, R2, and C
according to the following formula:
             f = 1 / (.693 * C * (R1 + 2 * R2))
This to achieve the desired 488 KHz frequency, we
arbitrarily selected a capacitor value (C) of 0.0022 µF
then selected R1 = 430 Ohms and R2 = 457 Ohms.
This attempt failed for two reasons. First, we were only
able to achieve an output frequency of 300 KHz without
clipping; clipping occurs when the maximum output
frequency that the integrate circuit is able to produce has
been exceeded, and it causes the resulting waveform to be
distorted. For example, clipping may be occurring in your
amp if your music sounds distorted at high volume.
Second, the NE555 produces a square wave, while
ACKNOWLEDGMENTS                                              7. Ullmer, B. and Ishii, H. (2003), Emerging Frameworks
Thank you to Merlin Hansen for his assistance building          for Tangible User Interfaces. In Human-Computer
and troubleshooting the circuits used in this                   Interactions in the New Millennium.
implementation.                                              8. Calvillo Gamez, E.H., Leland, N, Shaer, O. Jacob,
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   Computerized       Chess.            Available    at         CLIHC 2003 Latin American Conference On Human-                 Computer Interaction, 2003.
   spr03/student/dmeppeli/project2/chesster.pdf              9. Koleva, B., Benford, S., Ng, K.H., & Rodden, T. A
2. Clapham, A. Chess. Andy’s LEGO Mindsotrms Page.              framework for tangible user interfaces, Physical
   Available at      Interaction 2003 Workshop on Real World User
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5. Federal Communications Commission.          FCC ID            Feedforward. DIS 2004.
   Search      Page.                   Available    at (search for product         11. Van Roon, T. 555 Timer Tutorial. Available at
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   Requirements.                 Available          at           OSCILLATOR.                       Available         at  
   per/hdwreq.asp                                                dge.htm

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