CHI 97 Electronic Publications: Papers
"Body Coupled FingeRing": Wireless Wearable Keyboard
NTT Human Interface Laboratories
1-1 Hikari-no-oka, Yokosuka-shi, Kanagawa-ken, 239 JAPAN
NTT Human Interface Laboratories
1-1 Hikari-no-oka, Yokosuka-shi, Kanagawa-ken, 239 JAPAN
A really wearable input device "FingeRing" is developed for coming
By attaching ring shaped sensors on each finger,
many commands or characters can be input by finger-tip typing action.
"FingeRing" can be used on any typing surface such as a knee or
desk, so quick operation is realized in any situation
while standing or walking.
To improve wearability, a very small, ultra low power wireless
transmitter is developed that uses the human body as part of an
"Direct Coupling" method enables stable communication even
when body contacts any grounded surface.
A new symbol coding method that combines order and
chord typing is also proposed, and useful typing patterns are
chosen by typing speed evaluations.
Expert users of musical keyboards can input 52 different symbols
at speeds of over 200 symbols per minute by using the combination of
FingeRing and the new coding method.
wearable computer, PDA, interface device, input device, keyboard, PAN,
© Copyright ACM 1997
The main reason for carrying a PDA is immediate access to
information whenever desired.
We want to carry information not a machine.
Existing PDAs are much bigger and heavier than the information within them.
However, PDAs become smaller and lighter given the progress in
PDAs will be worn as accessories one of these days.
The question is how to operate them.
Many concepts and prototypes of wearable computers have been proposed
and partly developed.
However, small interface devices suitable for wearing have not been
Apple computer announced an image model of a wearable
Macintosh; a small wrist mounted trackball was
used as its input device.
The wearable computer project of MIT used a grip type chord
keyboard, and some PDAs use miniaturized full
or ten-digit keyboards.
These interface devices depend on the physical size of the operative organ
such as the human hand or finger.
For instance, a keyboard whose key pitch is less than
14mm has lower input speed, higher fatigue levels and higher
input error than the standard size keyboard.
Therefore, there is a trade-off between portability
In other words, it is difficult to miniaturize ordinary interface
devices without sacrificing their ease of operation.
For the coming wearable PDAs, we think that specially designed
interface devices that can be highly miniaturized are needed.
Glove or fingerstall style virtual keyboards which detect bending
or typing action of fingers by sensors mounted at joint
or tip of fingers, have been proposed
These systems seem suitable for wearable use because they do not
require a key-top or key-pad.
However, they cause trouble in daily life operation
cover the finger-tip which has the highest tactile sensitivity or
hand by sensor or glove.
A virtual keyboard for a daily use wearable PDA should not cover the
finger-tip or hand.
Considering these situations,
we described an interface device which is suitable for wearable
computers, and developed the FingeRing
which is a "ring" shaped full-time wearable keyboard
(Figure 1) .
Users can input commands and characters by finger-tip typing actions
on any support surface such as a knee or desk whenever desired.
The small sensors do not cover finger-tips, so wearing such devices
does not hinder our daily life.
FingeRing does not requires a particular space to be tapped by
fingers such as a
key-top or a key-pad,
so usability does not worsen with miniaturization.
However, the current FingeRing needs a direct electrical connection
from the sensors
on each finger to the symbol generator placed on a wrist.
Even if the sensors and symbol generator are greatly miniaturized, the
wire connection causes inconvenience in daily use.
For example, the wires are frequently twisted and become tangled.
Therefore, to realize truly wearable devices, we must
establish wireless communication between the sensors and the symbol
This paper compares several very short range,
ultra low power wireless communication methods for their
application to FingeRing.
We choose the method called "Body Coupling" which uses the human body
as an electric wire.
We discuss the problems encountered in applying the body coupling
method to FingeRing and propose "Direct Coupling" as a solution.
Figure 1: Sensor part of FingeRing (wired version).
Detecting finger-tip typing actions by accelerometer.
FingeRing is a kind of "chord" input keyboard, which makes symbols
such as command or character through combinations of simultaneously typed
Some chord keyboard systems have been proposed,
but these systems
tend to adopt useless (= hard to type) chord patterns to represent
many symbols with one stroke typing actions.
We propose a new coding method that combines of order and
chord typing actions to increase the number of representable symbols without
sacrificing input speed.
FingeRing is a prototype of a full-time wearable device for the
input of commands and characters.
A small accelerometer is worn on the base of each
finger to detect the typing shocks generated by tapping the finger
on any typing surface
such as the thigh, knee or desk (called "finger-tip typing").
Commands and characters are generated from combinations of finger-tip
Each accelerometer is small and the finger-tip is not covered so they can be
worn continuously in everyday life without trouble.
In addition, no take-up action is needed for use, so immediate
start of operation is possible.
Detection of finger-tip typing
Acceleration by finger-tip typing conveys from the finger tip
to the sensor which is mounted on the base of typed finger.
The acceleration is called "Self typing".
However, the acceleration of the other fingers is also received by
the same sensor; this is
a type of cross-talk.
Therefore, it is necessary to isolate the intended typing
acceleration from the others.
Figure 2 shows the frequency
distribution of accelerometer
Five subjects ( 154cm to 190cm in height ) mounted accelerometers
on the bases of their five fingers, and made finger-tip typing actions on a
desk ( reflects "Hard" typing surface ) and on a thigh ( reflects
"Soft" surface ).
Figure 2 indicates that the self-typing and
cross-talk signals have
an amplitude difference of about 10 to 15 dB in the frequency
area around 90Hz.
Thus, a sharply carved Band Pass Filter (BPF),
which passes only frequencies around 90Hz, can be used to eliminate
the cross-talk regardless of typing surface stiffness.
The example of BPF (24dB/Oct) setting is also shown in
To be accurate, the filter property should different for each finger,
but a simple resonance type BPF which has center frequency of 90Hz and
Q (Quality factor: Sharpness of resonator) = 6 can be applied
to all fingers.
Figure 2: Frequency spectrum of typing acceleration.
Self-typing and cross-talk signal can be separated by difference
in frequency distribution.
FingeRing can be highly miniaturized without sacrificing ease of operation.
However, the current FingeRing needs a wired connection from each
sensor to the symbol generator.
These connections cause many troubles such as
catching on objects, even if the wires are extremely short.
Therefore, to realize a truly wearable device, we must establish
wireless communication between the sensors and symbol generator module.
Wireless link methods
The wireless communication method for FingeRing must have the
The characteristics of several communication methods are shown
in Table 1.
Optical communication realizes high-speed links, but requires a
Moreover, at least 1mA of current is needed to drive an LED.
Radiowaves (air wave) allow non line-of-sight
communication when the distance is very short, but the electric power
consumption is high.
Sound wave are suitable for non line-of-sight communication,
but electric-to-sound transducers are hard to miniaturize, and the
efficiency of energy conversion is poor.
Nevertheless, non-electric power operation can be realized if a
mechanical sound generator is constructed by micro machining
BPFs for the detection of self-typing will also be unnecessary if the
mechanical sound generator has frequency selectivity.
Communication by magnetic coupling is feasible with less
electric power consumption when the communication distance is short
such as between finger and wrist.
However, coils of many turns are needed which can not be easily miniaturized.
Moreover, the permeability of the human body is almost the same as that
of the atmosphere and
the effect of magnetic flux concentration can not be anticipated.
- Easy miniaturization:
Miniature transmitters (TX) are especially required.
(target size of TX: less than 10mm in diameter, less than 10mm high,
few grams in weight)
- Low power consumption:
One day operation with one time charging is desired.
(target of TX: less than 1mA in current consumption,
3 to 5 volt power supply)
No battery operation is best if possible.
- Non line-of-sight communication:
Line-of-sight communication cannot be established
between the transmitter (TX) mounted on the base of finger and
the receiver (RX) mounted on the wrist when the hand is bent inward.
- Multi channel communication:
It is necessary to separate the signals of each finger (typically five).
Table 1: Methods of wireless communication.
Body coupling is suitable for wireless link between ring and wrist.
Fortunately, the human body has good conductivity.
Therefore, by using human body as a signal route (= electric wire),
seemingly wireless communication can be realized.
For these reasons, we selected the communication method
called "Body Coupling" which uses the human body as an electric wire.
The human body has some electrical
conductivity at comparatively high frequencies.
Body coupling is a communication method that transmits electric
signals via the human body.
It is dangerous to pass excessive current through the
human body, and limits have been set by many countries.
For example, the current limitation on the skin surface as specified in
Japan (JIS T1001-1992) is 10microA at DC-1KHz, 100microA at
10kHz, 1mA at 100kHz and 10mA at over 1MHz.
As the signal frequency increases, the current limit is
Thus, it is effective to use high frequency signals, over dozens of
Khz, when transmitting electric signals through the human body.
For example, current flow at the skin surface is a maximum of 160microA when
a 100KHz, 50Vp-p sine wave signal is injected into the skin via 10pF
In this case, flow current is 6 times smaller than the limit and there is no
deleterious effect on the human body.
In addition, the metallic parts of the electrodes do not contact
the human body directly.
"Personal Area Networks (PAN)"
is another communication method that uses the
human body as an electric circuit.
TX and RX electrodes are placed near the human body to
establish a data link by using spread spectrum (SS) modulation
with carrier frequencies of 100kHz to 1MHz.
The coupling model of PAN is shown in Figure 3-a.
In a PAN system, TX and RX electrodes capacitively couple to the human body.
It is necessary for establishment of a electric circuit to make an
PAN uses the human body as one (signal) side of the loop,
and "earth ground" as the other (return) side.
In this case, circuit efficiency is greatly exhibited
when the signal side electrode is placed near the human body and the
return side is placed near the earth ground.
The paper states that a shoe insert is the best
location for the TX and RX electrodes.
The paper also described examples of PAN devices such as a
wrist watch and eye glasses.
However, we think that extremely small PAN devices cannot work properly.
Figure 3-bshows the coupling model of a small (ring) TX
mounted on the base of the finger for FingeRing application.
In this case, the coupling between signal side electrode and human
body is strong enough, but the return side electrode is so small and the
distance from the earth ground is so far that coupling ('p' in the figure)
is weak and the effective communication distance becomes too short.
Moreover, when the finger is typed on the human body such as the
knee or the thigh,
the TX is surrounded by the body which is used for signal side path,
and the coupling between the return side electrode and the earth ground
becomes too weak.
(a) Coupling model of PAN
Figure 3: Coupling models.
Another problem occurs if the body contacts a grounded surface
The paper states that the sensitivity of the RX is
reduced by about 20dB when the body (signal side) contacts the earth
ground (return side).
In FingeRing, finger-tip typing may be taken on desk-top or wall surfaces,
which can be regarded as the earth ground in many cases.
Thus, the data link from TX to RX is cut when the finger tip contacts the
desk or wall for typing.
Therefore, it is hard to directly apply the PAN method to FingeRing.
Figure 3(b): Coupling model of PAN (Small size TX)
(b)(c): PAN's coupling become weak when transmitter is small,
or human body contacts the earth ground.
Figure 3(c): Coupling model of PAN (Desk top typing)
In FingeRing, the communication distance is about 15cm, finger base to wrist.
Thus, the TX and RX return side electrodes can be directly coupled via air,
without using the earth ground (Figure 3-d).
In this case, couplings between the earth ground and both TX and
RX return side electrodes are weaker than the direct coupling
between both return side electrodes.
Therefore, TX - RX coupling is not influenced by the nearness of
the earth ground, and problems related with the earth ground can be
solved; for example, finger-tip typing on the knee or the thigh
(the earth ground is so far), and that on the desk or the wall
(the earth ground contacts the body).
In this "Direct Coupling" method, sensitivity is still reduced
when the human body contacts or comes very near to the TX or RX return
However, this problem can be solved by placing the return side
electrode of TX on the back of the finger, and that of RX on
the upper side of wrist.
Consequently, the human body does not contact either return side
electrode in ordinary use.
Thus, we chose the direct coupling method to realize a wireless
Figure 3(d): Direct Coupling between ring-TX and wrist-RX
Direct coupling can be work well, even if TX is small
(ring) size and human body contacts a grounded surface.
Ring style TX of FingeRing must meet the following requirements.
Frequency modulation (FM) offers several good advantages.
It requires few parts (= low power consumption)
and can easily support multiple communication channels.
In the wireless FingeRing, the output of each accelerometer is directly
transmitted as an analog FM signal, so the TX circuit is simple.
Carrier frequencies of the five fingers are set as 50k, 58k, 67k, 78k
and 91kHz to avoid interference from higher harmonics.
- Extra low power consumption
- Multiple channel communication
The output voltage of the FM modulator swings at 3 to 5 volts, and
amplification is needed to enhance the communication distance.
Wireless FingeRing uses a combination of a choke coil and an LC resonator
to boost output voltage.
By using this combination, output voltage is easily boosted with low current
consumption; for example, 42 Vp-p output signal is generated in
180microA of current consumption.
The ring shaped TX uses its "ring" part as the signal side electrode,
and the housing of the TX is used as the return side electrode to maximize
Each electrode is molded within an insulator, and the metallic part of the
electrode does not directly contact the human body.
An electric double layer capacitor is used as the power source,
as it has the good characteristics of fast and easy charging.
A block diagram of the TX is shown in Figure 4.
The RX electrode is mounted on the wrist.
The signal electrode is placed on the skin side of the wrist band,
and the return electrode is placed on the outer side of the wrist band
near the back of the hand.
In order to improve RX sensitivity, it is necessary to keep the
return side electrode far from the human body.
A block diagram of the RX is also shown in Figure 5.
Figure 4: Block diagram of FingeRing (TX).
Frequency modurated sensor signal is boosted by choke coil
and LC resonator.
Figure 5: Block diagram of FingeRing (RX).
Symbol is generated from combination of demodulated typing actions.
Power consumption of the prototype TX, which includes sensor driver,
is 1.75mW (5V, 0.35mA) per channel,
and operation time with electric double layer capacitor (5V, 0.22F)
is about 30 minutes per charge (takes 2 minutes).
Maximum communication distance is 20cm for the combination of ring
style TX and disc (3cm in diameter) shaped RX electrode.
In addition, the attenuation is 3.7dB when the hand is placed on the
body, and 4.2dB when the hand contacts any grounded surface,
in comparison with the reference condition when the hand is
stretched out in the air.
Communication can be stably established in all conditions, and the effectivity
of direct coupling method has been confirmed.
The prototype of wireless FingeRing (TX and the electrode part of RX)
is shown in Figure 6.
Size of the prototype TX is 20mm of diameter and 20mm of height,
because it uses conventional DIP package ICs.
With the use of specially manufactured ICs, TX will be able to
miniaturized toward the ideal size ( less than 10mm in diameter, 10mm in
Figure 6: Wireless FingeRing (prototype).
Size of TX will be reduced by the use of specially manufactured IC chip.
TX battery charging
The prototype TX is charged by direct connection to the
However, TX and RX housings must be fully molded and the charging process
must be a non-contact type for waterproofing.
Electromagnetic induction can supply comparatively large power,
but it does not suit miniaturization because
it is coupled by AC and requires a large capacitor to reduce
ripples in the AC to DC converting
stage; (The electric double layer capacitor can not absorb ripples).
Solar batteries can generate DC power with no additional parts.
However, existing single crystal photocells about 10mm in diameter
generate only 10microW (4V, 2.5microA) indoors (500lux).
About 2mW (4V, 0.54mA) of electric power can be achieved with
a "charging stand" which has a strong light of about 110,000lux
(same as solar rays in midsummer).
Therefore, charging stands will become practical when the ability of the
solar cell is increased about 10 times, but charging under indoor
operation will remain difficult.
The prototype TX continuously transmits a carrier signal and wastes
electric power needlessly.
It would be better if the TX transmitted only during typing,
but this method has problems; the boot-up stage of oscillation
is unstable and the detection of typing is somewhat delayed.
The current modulation circuit uses a CR oscillator, and channel number
are limited to about 20.
Thus, there is the fear of interference when many users operate
at the same time.
Expanding the carrier range causes interference from higher harmonics
and beat signals from multiple carriers.
Moreover, it is difficult to enhancing the channel number by narrowing
the carrier interval, because the CR oscillator can not yield stable carrier frequencies.
In addition, it is hard to re-program channels when the channels are set
up by the parameters of C, R and X'tals.
In FingeRing, the local TXs are close to the local RX, while other
TXs are further away.
In this case, interference from other TXs can be ignored by the masking
effect of frequency modulation ("The law of the jungle") when the
local TX is active.
However, interference appears when the local TX is quiescent.
This interference can be avoided without excessively increasing channel
number by assigning a unique ID to a group of TXs and RX for one user.
The ID number transmitted with the sensor signal is compared in the
RX, and only the signal with valid ID number is accepted.
A method for programming and transmitting IDs with little additional
circuit is needed.
Orderly typing chord input
FingeRing is a kind of "chord" input keyboard, which represent symbols
such as commands or characters by combinations of simultaneously typed
Many chord keyboards represent symbols by one-stroke typing actions.
Therefore, useless (= hard to type) chord patterns are sometimes used
to represent many kind of symbols with few fingers (typically five).
FingeRing combines chord input with order input, which
means that the typing actions that has slight time lag each other, for
represent many kind of symbols without using hard typing actions.
Notation of this method is shown in
Figure 7 and
example of chord sequence determination is also shown in
An outline of the combination input method
(named "orderly typing chord input" )
is given below.
- Define one-stroke chord as a combination of
typed fingers where the period between the actions is
less than a pre-determined interval time named "simultaneous
typing interval: T1".
- Define one symbol as a sequence of chords where
the period between the actions is less than a pre-determined
interval time named "orderly typing interval: T2".
- The consecutive typing of same finger is not contained in one
- Only the chord sequences that can be input quickly are selected
Figure 7: Notation of orderly typing chord input method.
Corresponding finger is typed as the order of chord number
(same numbered finger is typed simultaneously).
In this method, the number of representable symbols can be increased
by increasing the number of maximum strokes.
But excessive stroke number deteriorates input speed, and some
combination of diffrent strokes disturb the input rhythm.
Therefore, FingeRing uses two-stroke chord sequences which
can be input as quickly as one-stroke chord patterns.
In addition, chord sequences of more than three strokes
can be used for key-macros, special commands and passwords.
Figure 8: Example of chord sequence determination.
Simultaneous and orderly typing is separated by two time
constants T1 and T2.
Typing speed evaluation
Experiments were conducted to select the usable chord sequences by using a
wired version of FingeRing.
Subjects typed displayed chord sequences as quickly as possible.
One chord sequence was displayed in each trial.
In order to remove reading and understanding time of each
sequence, and to maintain a constant finger placement at the start of
each trial, the time between start chord
() typed by
subject and the end of displayed chord sequence, was measured with a
resolution of 1msec.
212 chord sequences were tested to each subject; the set contained
all the 31 patterns that can be represented by one-stroke
combinations, and all the
181 patterns that can be represented by two-stroke combinations
where the same finger is not used consecutively.
The chord sequences were displayed at random, and the trials
iterated until at least one correct typing sequence was obtained for
each of the 212 chord sequences.
Data was collected only for trials resulting in correct
typing, which means the order of the finger-tip typing agreed
with the displayed chord sequence.
The finger-tip typing surface used in the experiment was a desk covered
with a thin urethane sheet (5mm); this stiffness is intermediate
between "Hard" and "Soft" surface as previously described.
Total number of subjects was 10 and all had experience in
QWERTY style computer keyboard operation.
As a result of a brief experiment,
a significant difference was observed between
subjects who have experience in playing musical keyboards (piano
group) and those who have no experience (non-piano group).
Therefore, collected data was split into
two groups; piano and non-piano group.
Figure 9 shows the average input time for each chord
sequence for the non-piano group.
It is seen from the slope of the curve that the chord sequence set can be
divided into 3 categories.
The categories are numbered 1, 2, and 3 starting with the shorter input time.
Input time of a chord sequence is considered to reflect the
difficulty of typing that sequence.
In other words, category 1 offers easiest typing.
Table 2 shows the chord sequences
and average input times for categories 1 and 2.
One-stroke chord patterns belonging to category 3
are also shown in Table 2.
In selecting the chord sequences to be used, category 1 is used
If there are still more symbols are needed, category 2 chord
sequences are assigned.
Chord sequences of category 3 should be avoided even if one-stroke
typing is used.
In the non-piano group, only 2 orderly typing sequences appear in category 2
(indicated by bold-face characters).
Figure 9: Distribution of typing speed (non-piano group).
Chord sequences can be divided into 3 categories.
Figure 10 shows the average input time of
the piano group for each chord sequence.
The chord sequences can be divided into 3 categories, as in the non-piano
Table 3 shows the chord sequences in
category 1 and 2, together with the corresponding average input time.
The one-stroke chord patterns belonging to category 3
are also shown in Table 3.
It is seen from the table that a large number of orderly typing sequences
are included in categories 1 and 2 (indicated by bold-face characters).
Table 2: Chord sequences and average input time
The effectiveness of orderly typing is less for the non-piano group.
Figure 10: Distribution of typing speed (piano group).
Input speed is collectively faster than non-piano group.
Table 3: Chord sequences and average input time (piano group).
Many two stroke chord sequences can be input as a same time of
one stroke chord.
Efficiency of the coding method
The result of finger-tip typing experiment is shown below.
Table 4 shows the number of representable symbols and the
average input time when the chord sequences of category 1 or both of
category 1 and 2 are used, for non-piano and piano groups.
It is thought that the proposed input method will be effective for
trained user of chord keyboard, if the skill needed to operate a
chord keyboard is equivalent that needed to operate a musical keyboard.
- Input speed of the piano group was about 1.5 times
faster than that of the non-piano group.
- The effect of orderly typing is less for the subjects of non-piano group.
- The orderly typing chord input method was most effective for
The number of representable symbols is doubled by the
same input speed as that of the one stroke chord input method.
Table 4: Number of representable symbols and average input time.
Proposed chord input method is suitable for untrained (non-piano)
user with command input operation, and for trained (piano) user
with command + character input operation.
Separation of simultaneous and orderly typings
When orderly typing is used with simultaneous typing, it is necessary
to separate both typing styles by using the interval between typing actions.
Based on the timing data of the finger-tip typing of each finger obtained by
the above experiment, two time constants (T1: simultaneous typing
interval, and T2: orderly typing interval), were estimated.
The data was collected from the piano group because orderly typing
was efficient in this group.
The distribution of time intervals of simultaneous typing, and that of
orderly typing are shown in Figure 11.
The total number of collected intervals was 1705 for
simultaneous typing and 910 for orderly typing.
In Figure 11, the distribution of
the orderly typing interval
for the chord sequence belonging to category 1 and 2 is shown as
heavily hatched plot.
This figure shows that simultaneous and orderly typing
can be separated, by setting T1 as 15msec.
It is also seen that quick input can be enabled by setting T2 as
120msec, when only chord sequences belonging to category 1 and 2 are used.
Moreover, the distribution of the simultaneous typing interval of the
non-piano group was similarly collected; T1 of this group was
estimated to be 20msec.
Figure 11: Distribution of simultaneous and orderly typing
intervals (piano group).
1) Simultaneous and orderly typing can be separated properly
by setting T1 as 15msec.
2) Chord sequences of category 1 and 2 have shorter orderly
Symbol table assignment
This experiment evaluated the combinations of finger actions that
can be typed quickly, for collecting fundamental data for symbol
However, effective assignment of symbol table such as commands or
characters is strongly depended on each application.
Moreover, it is necessary to modify the symbol table for each user
to suit the individual's characteristics, for example, one finger
may be rather stiff.
Therefore, the symbol table should be assigned not for general purpose use
but for application and user specific.
Evaluating the learning curve of this method is a remaining problem.
From the view-point of the ease of training and
ease in recalling forgotten patterns, it is necessary to assign
"patterns that can easily be recalled", even if the input speed
deteriorates to some extent.
In orderly typing, for example, some chord sequence pairs are
"reverse order" and assigning them to mirror reversed symbols
seems most efficient, for example parenthsis '(' and ')'.
Combinations of symmetrical chord sequence pairs which can be
typed easily, are shown in Table 5.
In the above experiments the error rate was not collected, because separating
human and machine (FingeRing) error is difficult.
Moreover, human input error tend to occur between specific chord
sequences, thus "fault tolerant"
symbol table might need to be considered.
For example, if chord sequence 'A' is often mis-typed as
sequence 'B', critical commands should not assigned to chord
sequence 'A' and 'B', or the same command assigned to both chord
Table 5: Symmetrical chord sequence pairs.
Symmetrical chord sequences are suitable for symmetirical
such as '(' and ')'.
This paper has described a wireless communication method that links the sensors
and the symbol generator module of FingeRing, a command and character
input device developed for wearable PDAs.
We showed that body coupling, which uses the human body as an electric
conductor, is effective for very short range, ultra low power communication.
Moreover, the direct coupling method which does not contains the earth
ground in its transmission route is also effective even when the return side
electrode of TX is very small.
The direct coupling method also offers stable communication
when the human body contacts a grounded surface.
A prototype TX was introduced that has a power consumption of 1.75mW
and about 30 minute operating time per 2 minute charge; the maximum
communication distance is 20cm.
This paper also described a symbol coding method for FingeRing,
named the orderly typing chord input.
For the untrained user (with no experience in musical keyboards),
the effectiveness of the orderly typing is less.
Up to 27 symbols can be typed easily using one hand, and the
average input speed is approximately 130 symbols/min.
On the other hand, the proposed method is effective for the trained
user (with experience in musical keyboards).
Up to 52 symbols can be typed easily, and the average input speed is
approximately 210 symbols/min.
Consequently, when this method is used for the input interface, the
untrained user should concentrate on cursor motion and simple
The trained user can quickly input not only various commands but also the
We are testing menu structures, suitable assignment of symbol table,
and a feedback method by testing a prototype "Walking PDA"
which uses FingeRing
as the input device and a text-to-speech synthesizer as the feedback device.
Application to musical use such as piano and drums is also being
We are planning to enhance the operation time, communication distance,
channel number, and non-contact charging method to realize a
"full-time" wearable FingeRing.
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CHI 97 Electronic Publications: Papers