Tangible Chess for the Compaq Tablet PC
Christopher T. Lewis
Computer Science Department
University of Saskatchewan
Saskatoon, SK., Canada
+1 306 956 7693
LewisCT@agr.gc.ca
ABSTRACT
This project will develop a prototype tangible user interface
(TUI) for playing chess on the Compaq Tablet PC
(TC1000). The project will use the TUI with existing chess
software, the GNU Chess Engine and the Winboard Chess
interface. The goal is to develop a TUI for chess which
provides a natural interface to electronic chess that is both
portable and affordable.
Keywords
Tangible User Interface, Chess, Tablet PC
INTRODUCTION
Chess is a military strategy game which pits two opponents
against one another. The objective of the game is to
capture the opposing king. Each player has 16 pieces of
varying abilities arrayed in an 8x8 grid. Traditionally, the
game is played by two opponents seated opposite each
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
used by chess engines players are unable to see hesitation
and other tells exhibited by the remote player, which
eliminates a psychological facet of the game.
Existing tangible chess projects [1,2] have focused on
moving game pieces using robotic arms with magnets or
pincers at the direction of either the computer or a player.
By contrast, this project seeks to integrate the traditional
tangible interface into electronic chess.
The initial phase of this project aims to develop a TUI
using the original game pieces as an interface to existing
electronic chess software, thereby restoring the traditional
interface to electronic chess. The second phase of the
project aims to provide the player with additional
information related to their opponent’s moves, such as
whether or not the opponent hesitated and the speed with
which the piece was moved. This is intended to allow the
player to detect their opponent’s tells and restore the
missing psychological element of the game.
Figure 1: A mockup showing how a piece would be moved
on the tablet by a physical piece with an embedded
transmitter.
SYSTEM COMPONENTS
Software
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In phase 1, the system will be tested using the WinBoard
GUI [3] and the GNUChess engine [4], though it should
work with any existing GUI and chess engine. These
programs are freely available and widely used by online
chess players. Connecting to a chess server will allow
network play using the system.
movements, which may indicate uncertainty or reveal
something of their strategy.
Communication between the GNUChess engine and the
client occurs using a coordinate based movement system
which transmits only the start and end point of the move.
The software for phase 2 has yet to be identified; however a
requirement for the software is that it must transmit either
all movement information to the remote player in real-time,
or sense the movement and transmit movement
characteristics to the remote player. This will allow the
opposing player to watch for hesitation in their opponent’s
Hardware
The TUI will consist of 32 active chess pieces with
embedded transmitters. Moving a piece will have an
equivalent effect to selecting and dragging the piece using
the TC1000’s pen. To accomplish this, each transmitter
will transmit at the same frequency as the TC1000’s pen
with the tip switch depressed.
According to the
specification filed with the Federal Communications
Commission (FCC) the pen transmits at a frequency of 482494 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
Primary dual side switch
433.8-445.4
Single Side Switch or Primary dual
side switch only
415.0-424.0
1200-1525
432 (measured)
1125-1450
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
transmitter will be inactive (power off) when the pieces
are on the playing board. Lifting the piece from the
playing surface will activate the piece. This will be
controlled by a small button on the bottom of the playing
pieces.
Using this design, it is possible that there will be problems
when capturing an opponent’s piece; at this time it is
possible that there would (briefly) be two pieces active at
the same time. Two strategies can be employed to avoid
this situation. The first possibility is the addition of a
second button to the piece, which, when depressed, would
render the transmitter inactive. This button could be
pressed on an opponent’s piece before removing it, which
would ensure that only one piece is active during the
capture. The second alternative is moving the activation
button from the bottom of the piece to another location.
Using this design the user having to press and hold the
button for the duration of their move, rather than having
the piece activate automatically when it is picked up off
the playing surface. However, this would allow an
opponent’s piece to be removed without any special
manipulations.
The digitizer used in the TC1000 only senses the pens
presence to a height of 0.5 inch above the digitizer surface
(as specified in the Fine Point Innovations Engineering
Specification). When a piece is moved beyond this
boundary, it is as if the player released the piece. This has
two undesirable consequences, 1) if the resulting move is
invalid, the piece will return to its initial starting point,
and 2) if the resulting move is valid, the piece will remain
where it was released. It is likely that neither of these is
the intended result. It may be possible to sense the zposition of the piece at the time that the signal is lost and
wait for the signal to resume if the piece has been moved
above the boundary (i.e. the z position of the piece will be
0 when the piece is placed on the board, or 0.5 inches if
the piece is lifted outside the boundary). However, while
the Tablet PC Hardware requirements specification
released by Microsoft calls for the z-coordinate to be
reported [6], it appears that existing tablet
implementations do not report it.
CLASSIFICATION WITHIN TUI FRAMEWORKS
Framework 1: Ullmer and Ishii [7], Calvillo-Gamez
et.al. [8]
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
surface is provided by the digitizer in the tablet PC which
tracks the movement of pieces over the surface. Within
the Token+Constraints framework, the pieces are tokens
associated with the corresponding virtual piece. The
movement of a piece is constrained by its movement
capabilities as well as the presence of surrounding pieces.
Framework 2: Paper 3 (Koleva et.al.) [9]
Within the Link-Coherence framework of Koleva et. al.
the chess pieces are best classified as general purpose
tools because they can be used to select and drag any item
on the screen (Table 2). This is in spite of of their
physical likeness to the pieces they are intended to move,
which may cause them to act as identifiers in the mind of
the user. The link is semi-permanent because it exists
whenever the piece is over the playing surface, but not
when the piece is on the playing surface or removed from
the game (though the user may assume that the link still
exists at this point making it a permanent link in the mind
of the user).
Category
Ex.
Trans.
Scope
Conf.
Lifetime
Autonomy
General
Purpose
Tool
Chess
Piece
Literal
Lifting piece, Setting piece down,
translation parallel to surface
Fixed
Semipermanent
Autonomous
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
Moves
Piece
Phase 1: No
No
Phase 1: No
Phase 1: No
Phase 1: No
Phase 1: No
Phase 2: Yes
Phase 2: Yes
Phase 2: Yes
Phase 2: Yes
Capture
Piece
Yes
Yes
Yes
Yes
Yes
Yes
Opponent
Captures
Piece
Phase 1: No
No
No
No
Yes
No
Phase 2: Yes
Phase 2: Yes
Table 3: Classification of the actions in the tangible chess game within the Interaction Frogger Framework of Wensvenn et.al.
Framework 3: Paper 4 (Wensveen et.al.) [10]
All actions which are performed on the remote system will
experience a slight delay before occurring on the local
system, this delay is introduced when the coordinates are
processed by the chess server, and can be eliminated (as
much as possible given current technologies) by moving
to a peer-to-peer implementation in phase 2 of the project.
The reaction for all actions which occur on the local tablet
will appear in the same location, and a moment later the
same reaction will occur on the remote tablet. The change
to a real-time, peer-to-peer system in phase 2 will not
change this behavior, except that the reaction on the
remote tablet might occur marginally faster.
On the local system, the direction of movement is coupled
to the direction of the reaction. On the remote system, the
direction of movement is not coupled to the reaction on
the remote system because there is no path information
transmitted using coordinate based moves in phase 1.
However, when the path of movement is transmitted to the
remote computer in phase 2, the direction of reaction will
be coupled with the direction of action.
Because captured pieces disappear, the reaction to
capturing a piece cannot be coupled to the physical action
of removing the piece on the remote tablet. There are no
plans to change this behavior in phase 2 of the project.
Similarly, there is no way to show dynamics or expression
on the remote tablet when capturing a piece.
When moving a piece on the local tablet, the dynamics of
the action are coupled to the dynamics of the reaction.
However, due to the coordinate based moves used in
phase 1, it is impossible for this coupling to occur on the
remote computer. However, it will be possible to display
this coupling in phase 2 of the project.
Similarly, when moving a piece on the local tablet, the
expression of the action is reflected in the reaction on the
local tablet. However, again, due to the coordinate based
moves used in phase 1, it is impossible for this coupling to
occur on the remote computer. However, once again, it
will be possible to display this coupling in phase 2 of the
project.
DESIGN CONSTRAINTS
The goals of portability and affordability introduce weak
constraints on piece design in that the pieces must be
small enough to travel well, solid enough to withstand
minimal abuse while traveling and priced such that the
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.
subsequent analysis of the waveform produced by the pen
revealed that it was producing a sine wave. The fact that
the pen produces a sine wave was not known when we set
out to build the circuit based on the NE555 because we
did not initially have access to an oscilloscope.
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
piece.
The intent is to use 1.4V hearing aid batteries, such as the
Energizer AC312. Such batteries are available in spools
of 16 for approximately 20$ (Can) or $1.25 a piece,
though online retailers sell larger quantities at a lower per
unit cost. The dimensions of the AC312 are 0.311”
(width) x 0.142” (height), which means that the AC312
should easily fit inside a chess piece. Two batteries
operating in parallel should produce 2.8V of power for
approximately 1000 hours; so any parts we use must be
able to operate at or below 2.8 V Vcc.
IMPLEMENTATION
The pieces used in this project must be able to produce a
frequency within the range specified for the pen with the
tip switch depressed (482-494 KHz). There have been
two attempts to produce this frequency, one based on an
NE555 timer and a second attempt using a dual
operational amplifier (op amp). Unfortunately both
attempts failed.
NE555 Timer
The schematic for the circuit based on the NE555 timer is
shown in Figure 2 [11]. Using this circuit, the 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
Figure 2: This figure shows the circuit used with the
NE555 timer in an attempt to produce the 488 KHz
frequency used in the tablet pen.
Dual Operational Amplifier
The schematic for the single supply wein bridge using a
dual op amp is shown in Figure 3 [12]. Using this circuit
the frequency is calculated using the forumula:
f=1/2πRC
To achieve the desired 488 KHz frequency we used
C=100pF and R=3261KOhms. However at this frequency
the dual op amp used failed to oscillate. By adjusting the
RC values we were able to successfully produce a 200
KHz wave, though the output frequency deviated
substantially from the theoretical frequency for the RC
values used. Further investigation revealed that this
attempt failed because the gain bandwidth (1MHz) of the
dual op amp used (LMV982MA) is too low to produce a
488 KHz frequency. According the theory, the gain
bandwidth must be at least 3 times the output frequency.
ACKNOWLEDGMENTS
Thank you to Merlin Hansen for his assistance building
and troubleshooting the circuits used in this
implementation.
REFERENCES
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Chess.
Available
at
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?page=Chess
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T.
XBoard.
Available
http://savannah.gnu.org/projects/xboard/
at
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FCC ID
Search
Page.
Available
at
http://www.fcc.gov/oet/fccid/ (search for product
NEJNT2).
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Available
at
http://www.microsoft.com/windowsxp/tabletpc/develo
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