Rotation detecting apparatus

A first wheel mechanism and rotation detecting means for detecting rotation of the first wheel mechanism are provided within a casing. A second wheel mechanism for measurement is movable provided at the casing. The second wheel mechanism is located in a non-detecting mode at such a place as not to protrude outside the casing. When moved by a moving member, however, the second wheel mechanism partially protrudes from the casing and the rotation of the second wheel mechanism can be transmitted to the first wheel mechanism, whereby the rotation of the second wheel mechanism can be detected by the rotation detecting means.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rotation detecting apparatus for use in 
a length measuring apparatus for measuring the length of an object or 
length between two points, or a distance measure for measuring the 
distance between two points on a map. 
2. Description of the Related Art 
An apparatus is known which rotates a rotational disc along a line 
connecting two points and detects the amount of rotation of the disc to 
thereby measure the distance or length between the two points. Such a 
measuring apparatus is disclosed in, for example, Japanese Patent 
Disclosure Nos. 61-16970 and 61-149801. 
U.S. Pat. No. 3,999,298 discloses such a measuring apparatus assembled in a 
wrist watch. 
This sort of measuring apparatus is designed in a such a manner that part 
of the rotational disc disposed in a casing is exposed and, when the 
exposed part is pressed against and rolled on a map, for example, the 
disc's rotation is transmitted through a plurality of transmission gears 
to a rotational member provided within the casing. Therefore, the length 
or distance between any two points on the map can be measured by detecting 
the amount of rotation of the rotational member. 
According to such a measuring apparatus, since the rotational disc always 
engages the transmission gears, the apparatus is likely to easily function 
even when unintended, thus resulting in undesirable malfunction. In 
addition, since the rotational disc is always partially exposed from the 
casing, the disc itself may easily be damaged. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of this invention to provide a reliable 
rotation detecting apparatus which prevents a measuring disc and 
transmission gears from being damaged or malfunctioning. 
To achieve the object, there is provided a rotation detecting apparatus 
which comprises: 
a casing; 
a first wheel mechanism disposed inside the casing; rotation detecting 
means for detecting rotation of the first wheel mechanism; 
a second wheel mechanism for measurement disposed at the casing such that a 
periphery of the second wheel mechanism doe not protrude from an outer 
surface of the casing; and 
a moving member for moving the second wheel mechanism to such a location 
that rotation thereof is transmitted to the first wheel mechanism and part 
of the second wheel mechanism is exposed from the outer surface of the 
casing. 
With the above arrangement, when the second wheel mechanism, which does not 
normally protrude outside the casing, is moved to a specific position, it 
is coupled to the first wheel mechanism and partially protrudes from the 
outer surface of the casing to be ready for measurement. This can prevent 
the second wheel mechanism from being damaged or malfunctioning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of this invention as applied to an electronic wrist 
watch will now be described referring to FIGS. 1 through 10. 
FIG. 1 illustrates the front of an electronic wrist watch equipped with a 
distance measure not in use, and FIG. 2 illustrates the front of the wrist 
watch with the distance measure in use. FIG. 3 is a cross section of the 
wrist watch of FIG. 1 as taken along the line A--A illustrating the 
internal structure thereof, and FIG. 4 is a cross section of the wrist 
watch as taken along the line B--B in FIG. 2 also illustrating the 
internal structure. Referring to these diagrams, reference numeral 1 
denotes a watch casing which has a watch glass 2 mounted on the top 
thereof at the center. A rotational bezel 3 is rotatably mounted around 
the periphery of the top of the casing 1, and a back lid 5 is attached to 
the bottom thereof, with a watch module 4 disposed inside the casing 1. A 
rotation detecting apparatus 6 comprising a rotation detecting section 19, 
a gear train mechanism 18 and a measuring wheel 17 is provided over the 
region extending from inside the watch casing 1 to the outside thereof. 
The side walls of the watch casing 1 are provided with various button 
switches S.sub.1 -S.sub.4 used for mode changing, time correction, etc. A 
protecting section 8 is integrally and protrusively formed on the right 
side wall of the watch casing 1. Band attachments 9 are integrally formed 
on the front and rear walls of the watch casing 1. 
The watch module 4, the main part of the watch, has a circuit board 12 
provided between a top housing 10 and a bottom housing 11. Above the 
circuit board 12 is a liquid crystal display panel being electrically 
coupled to an interconnector 13a. The interconnector 13a electrically 
connects electrode terminals (not shown) of the circuit board 12 and 
electrode terminals (also not shown) of the display panel 13. An IC chip 
12a is disposed at the bottom of the circuit board 12. A battery 14 is 
disposed, pressed by a positive (+) electrode plate 15, in the bottom 
housing 11. This battery 14 is electrically coupled to the circuit board 
12 by means of the positive electrode plate 15 and a negative (-) 
electrode plate 16. The display panel 13 electro-optically displays time 
data, distance data, etc. 
The bezel 3 comprises a bezel body 3a and an attachment member 3b between 
which the measuring wheel 17 of the rotation detecting apparatus 6 (to be 
described later) is rotatably mounted. The bezel body 3a is a ring-shaped 
flat plate having an engaging section 3a.sub.1 formed at the inner wall. 
The engaging section 3a.sub.1 is rotatably engaged with an engaging 
section 1a formed at the periphery of the top section of the watch casing 
1. The attachment member 3b, serving to rotatably connect the measuring 
wheel 17 to bezel body 3a, is located where the measuring wheel 17 is 
provided, and is fixed to the bezel body 3a by ultrasonic welding, with a 
rotational shaft 17a being mounted on the wheel 17. An alignment mark 
3a.sub.2 is provided on the top of the bezel body 3a in such a manner that 
matching the mark 3a.sub.2 with the ON/OFF marks 2a and 2b printed on the 
watch glass 2 renders the watch to be usable or unusable as a map measure. 
An alignment recess 3a.sub.3 is provided at the bottom of the bezel body 
3a, and it is designed in such a manner that every time the bezel 3 
rotates 180 degrees between the ON/OFF marks 2a and 2b, the recess 
3a.sub.3 engages an alignment projection 1c with a click so as to inhibit 
the bezel 3 from rotating over 180 degrees. 
The rotation detecting apparatus 6, constituting a distance measure, 
comprises the measuring wheel 17 that rolls on a map, the gear train 
mechanism 18 that operates with the rotation of the wheel 17, and the 
rotation detecting section 19 that detects the rotation of the mechanism 
18. The measuring wheel 17, which moves together with the bezel 3, is 
integrally attached to the rotational shaft 17a that is rotatably coupled 
between the bezel body 3a and the attachment member 3b. This shaft 17a is 
attached with a drive gear 17b which rotates together with the measuring 
wheel 17. As shown in FIGS. 1 and 3, this wheel 17, partially protruding 
outside the bezel 3, is disposed, when not in use, above the protecting 
section 8 formed on the right wall of the watch casing 1 and is protected 
by the section 8 so as not to protrude farther than the periphery thereof. 
The measuring wheel 17, when in use, moves 180 degrees together with the 
bezel 3 to come to the left side of the watch casing 1, so that the wheel 
17 partially protrudes outside the watch casing 1 and the drive gear 17b 
disengageably engages an outer transmission gear 20b of the gear train 
mechanism 18 (see FIGS. 2 and 4). The wheel 17 has a circumference of 24 
mm and a diameter of 7.64 mm. 
As shown in FIGS. 4 and 5, the gear train mechanism 18 comprises a 
transmission wheel 20, an intermediate wheel 21 and a detection wheel 22, 
which are rotated by the measuring wheel 17. The transmission wheel 20, 
serving to transmit the rotation of the measuring wheel 17 into the watch 
casing 1, comprises the outer transmission gear 20b provided on the top of 
the rotational shaft 20a and an internal transmission gear 20c provided at 
the bottom of the shaft 20a, and is disposed below the bezel 3 at the left 
side of the watch casing 1. More specifically, the rotational shaft 20a is 
rotatably fitted via a water-proof ring 20d in a through hole 1b, formed 
at the left side of the watch casing 1, and it has its upper end 
protruding outside the casing 1 and its lower end extending inside the 
casing 1 and pivoted in a lower gear train rest 23. The drive gear 17b of 
the measuring wheel 17 disengageably engages the outer transmission gear 
20b, and its gear ratio is set to 1/3 (e.g., the gear 20b having 10 teeth 
with respect to the gear 17b having 30 teeth) so that the gear 20b rotates 
three times for each rotation of the gear 17b. The internal transmission 
gear 20c rotates with the outer transmission gear 20b via the shaft 20a. 
The intermediate wheel 21 serves to transmit the rotation of the internal 
transmission gear 20c to the detection wheel 22, and it always engages the 
gear 20c with its shaft 21a rotatably supported in the lower gear train 
rest 23. The detection wheel 22 is rotated by the intermediate wheel 21 
and is designed in such a manner that a driven gear 22b and a detection 
gear 22c are mounted to a rotational shaft 22a so as to rotate together 
with the shaft 22a. The rotational shaft 22a is rotatably disposed between 
the lower gear train rest 23 and an upper gear train rest 24. The driven 
gear 22b always engages the intermediate wheel 21. The detection gear 22c 
has a greater diameter than the driven gear 22b and has a plurality of 
teeth 22d (8 teeth in this embodiment) formed around its periphery. The 
detection gear 22c rotates three times for each rotation of the measuring 
wheel 17. In other words, the internal transmission gear 20c, intermediate 
wheel 21 and driven gear 22b have the same number of teeth (16 teeth in 
this embodiment). 
The rotation detection section 19, which detects the number of rotation and 
the rotating direction of the detection gear 22c, comprises a holding 
member 25 extending over the upper and lower gear train rests 23 and 24 
and having a U-shaped cross section, one light emitting diode 26 and two 
phototransistors 27 and 28. The diode 26 and phototransistors 27 and 28 
are embedded in the holding member 25, the former facing the latter, and 
these three elements are coupled by lead wires 29 to the circuit board 12 
of the time module 4. The holding member 25 is made of a synthetic resin 
such as an epoxy resin, and has a U-shaped recess 25a into which the 
detection gear 22c is partially inserted as shown in FIG. 6. Formed at the 
bottom portion of the holding member 25 is an elongated rectangular 
opening 25b (see FIG. 7) at the bottom of which the light emitting diode 
26 is embedded. As shown in FIG. 8, two slit-shaped light penetrating 
windows 25c are formed in the upper portion of the holding member 25 which 
faces the diode 26, and the phototransistors 27 and 28 are respectively 
embedded in the windows 25c. The light penetrating windows 25c, which are 
formed by mixing a visible ray dye in the epoxy resin of the holding 
member 25, absorb visible rays and pass only infrared rays. The light 
emitting diode 26 emits infrared rays in a distance measure mode 
(measuring mode). When the infrared rays pass through the opening 25b of 
the holding member 25 and pass between the teeth 22d of the detection gear 
22c, they are irradiated through the two light penetrating windows 25c 
onto the individual phototransistors 27 and 28. Upon reception of the 
infrared rays, the phototransistors 27 and 28 generate a high-level 
electric signal (electromotive force). The light emitting diode 26 and 
phototransistors 27 and 28 have the circuit configuration as shown in FIG. 
9. When a voltage is applied to electrode terminals 26a and 26b of the 
diode 26, the diode emits an infrared ray. The phototransistors 27 and 28 
have input terminals 27a and 28a coupled together and free output 
terminals, and output high-level electric signals from their output 
terminals 27b and 28b upon reception of the infrared ray. The rotation 
detecting section 19 detects the number of rotation of the detection gear 
22c by counting the pulse signals from the output terminals 27b and 28b, 
and discriminates whether the detection gear 22c are rotating in the 
forward direction or reverse direction by discriminating which pulse 
signal from the phototransistor 27 or 28 becomes a high level first. 
FIG. 10 illustrates the circuit configuration of the electronic wrist watch 
according to this embodiment. 
An oscillator 30 oscillates a reference signal (32768 Hz) and sends the 
signal to a frequency divider 31. The frequency divider 31 subjects the 
received reference signal to frequency division, and sends a 4-KHx signal 
Sb to the base of a switching transistor 32 and a 1-Hz signal Sc to a time 
counter 33 as well as one input terminal of an AND gate 53. 
The time counter 33 counts the 1-Hz signal Sc from the frequency divider 31 
to acquire present time data and date data and sends these data through a 
display switching circuit 34 to a display 35. A reset switch S.sub.1 is 
for resetting the memory content of a distance register 39 which will be 
described in a later section, and has its one terminal grounded and the 
other terminal coupled to one input of an AND gate 36. The other input 
terminal of the AND gate 36 is supplied with a mode signal M.sub.1 from a 
ternary counter 37 (which will be described later). 
The AND gate 36 sends the reset signal to a one-shot circuit 38 only upon 
reception of the signal from the reset switch S.sub.1 and the mode signal 
M.sub.1 from the ternary counter 37 simultaneously. 
Upon reception of the reset signal, the one-shot circuit 38 sends a reset 
signal (one-shot pulse) to the distance register 39. 
Upon reception of this reset signal from the one-shot circuit 38, the 
distance register 39 is reset to be in the initial state (no data being 
registered). The distance register 39 sends its content, distance data, to 
the display switching circuit 34, and the display 35 displays the data 
from this circuit 34. 
A scale reduction change switch S.sub.2 has one terminal grounded and the 
other terminal coupled to one input of an AND gate 41. The AND gate 41 has 
the other input terminal coupled to the output terminal of an OR gate 42 
and thus supplied with an output signal of the OR gate 42. 
The OR gate 42 has two input terminals respectively supplied with mode 
signals M.sub.1 and M.sub.2 from the ternary counter 37 (which will be 
described later). 
The AND gate 41 sends its output signal to a one-shot circuit 43 only upon 
simultaneously receiving the output signal from the OR gate 42 and the 
signal from the reduction scale change switch S.sub.2. Upon reception of 
the signal, the one-shot circuit 43 sends a scale reduction change signal 
(one-shot pulse) to a scale reduction counter 44. This counter 44, which 
is a ternary counter, sequentially counts a signal of "0," "1" or "2" upon 
each reception of the one-shot pulse (scale reduction change signal) and 
sends, to an arithmetic unit 40 and the display switching circuit 34, 
scale reduction data indicating a 1/10000 reduction for the "0" signal, a 
1/20000 reduction for the "1" signal or a 1/40000 reduction for the "2" 
signal. 
A display change switch S.sub.3 has terminal end grounded and the other 
terminal coupled to a one-shot circuit 45. When receiving a signal from 
the display change switch S.sub.3, the one-shot circuit 45 sends a display 
change signal (one-shot pulse) to the ternary counter 37, which 
sequentially outputs three kinds of display mode signals M.sub.0, M.sub.1, 
M.sub.2, M.sub.0, . . . upon each reception of the signal from the 
one-shot circuit 45. The time mode signal M.sub.0 represents a time 
display, the scale reduction mode signal M.sub.1 a scale reduction 
display, and the distance measure mode signal M.sub.2 a distance display. 
The ternary counter 37 sends the above mode signals to the display 
switching circuit 34. This circuit 34 selects the mode to cause the 
display 35 to display the time data supplied from the time counter 33 upon 
reception of the time mode signal M.sub.0 from the ternary counter 37, or 
cause the display 35 to display the scale reduction data from the scale 
reduction counter 44 upon reception of the scale reduction mode signal 
M.sub.1, or cause the display 35 to display the distance data from the 
distance register 39 upon reception of the distance measure mode signal 
M.sub.2. The ternary counter 37 also sends the scale reduction mode signal 
M.sub.1 to one input terminal of the AND gate 36 coupled to the reset 
switch S.sub.1 as well as to one input terminal of the OR gate 42. 
Further, the ternary counter 37 sends the distance measure mode signal 
M.sub.2 to one input terminal of an AND gate 46 coupled to a control 
switch S.sub.4 as well as to the other input terminal of the OR gate 42. 
The control switch S.sub.4 has one terminal grounded and the other terminal 
coupled to the other input terminal of the AND gate 46. 
The AND gate 46 has its output terminal coupled to a one-shot circuit 47 
and an input terminal T of a T flip-flop circuit (hereinafter referred to 
as T-FF circuit) 48. Upon simultaneously receiving a signal from the 
control switch S.sub.4 and the distance measure mode signal M.sub.2 from 
the ternary counter 37, the AND gate 46 sends a high-level signal the 
one-shot circuit 47 and the input terminal T of the T-FF circuit 48. 
Upon reception of this high-level signal, the one-shot circuit 47 sends a 
reset signal to a timer 41. Upon reception of the high-level signal at the 
input terminal T, the T-FF circuit 48 outputs a high-level signal from its 
output terminal Q to the gates of transfer gates 50, 51 and 52. Upon 
reception of the high-level signal, each transfer gate 50, 51 or 52 
connects its input terminal and output terminal to be electrically 
conductive. The output signal from the output terminal Q of the T-FF 
circuit 48 is supplied to one input terminal of an AND gate 53 which has 
the other input terminal supplied with the 1-Hz signal Sc from the 
frequency divider 31. While receiving the high-level signal from the 
output terminal Q of the T-FF circuit 48, the AND gate 53 keeps sending 
the Hz signal Sc to the timer 49. The timer 49 counts the 1-Hz signal Sc 
to measure the time and sends a reset signal to the reset terminal of the 
T-FF circuit 48 when a predetermined time, for example, 10 minutes, 
elapses. Upon reception of the reset signal from the timer 49, the T-FF 
circuit 48 renders the output signal at the output terminal Q to have a 
low level. 
The transfer gate 50 has its input terminal coupled to the emitter terminal 
of the switching transistor 32, its output terminal coupled through a 
resistor r.sub.1 to a negative power source V.sub.SS and its gate coupled 
to the output terminal Q of the T-FF circuit 48. 
The switching transistor 32 has its base supplied with the 4-KHz signal Sb 
from the frequency divider 31, and its collector coupled to the cathode 
terminal of the light emitting diode 26 whose anode terminal is grounded. 
The transfer gates 51 and 52 have their input terminals coupled to the 
emitters of the respective phototransistors 27 and 28 and input terminals 
of the arithmetic unit 40; the collectors of these phototransistors are 
grounded. The transfer gates 51 and 52 have their output terminals coupled 
through respective resistors r.sub.2 and r.sub.3 to the negative power 
source V.sub.SS and their gates coupled to the output terminal Q of the 
T-FF circuit 48. 
The phototransistors 27 and 28 send high-level signals to the arithmetic 
unit 40 while receiving the light from the light emitting diode 26 and 
low-level signals to the unit 40 while not receiving this light. 
Based on pulse signals sent from the phototransistors 27 and 28 when the 
phototransistors intermittently receive the light from the diode 26, the 
arithmetic unit 40 computes distance data from the scale reduction data 
supplied from the scale reduction counter 44 and sends the computed data 
to the distance register 39. 
A description will be given of how to use the electronic wrist watch having 
the above arrangement. 
In a case where the wrist watch is used as a watch, the alignment mark 
3a.sub.2 provided on the top surface of the bezel 3 is aligned with the 
OFF mark 2b printed on the watch glass 2 as shown in FIG. 1, and in this 
state the display change switch S.sub.3 is operated to set the mode to the 
time mode. As a result, the present time, day of a week, month, day, year, 
etc. are displayed on the liquid crystal display panel 13 of the display 
35 as shown in FIG. 1 so that this watch can be used as an ordinary wrist 
watch. In this case, since the measuring wheel 17 is not engaged with the 
transmission wheel 20 of the gear train mechanism 18, the wheel 17 is 
prevented from functioning on its own. Since the measuring wheel 17 is 
located above the protecting section 8 formed at the watch casing 1 and 
does not protrude from this section 8 as shown in FIG. 3, the wheel can be 
protected against damage by the section 8. Therefore, the watch can well 
serve as a wrist watch. 
In a case where the watch is used as a map measure, the bezel 3 is rotated 
180 degrees so that the alignment mark 3a.sub.2 on the bezel 3 is aligned 
with the ON mark 2a printed on the watch glass 2. Consequently, the drive 
gear 17b of the measuring wheel 17 is engaged with the outer transmission 
gear 20b of the transmission wheel 20 and the wheel 17 partially protrudes 
from the watch casing 1. Thereafter, the scale reduction data is set, 
followed by the distance measuring operation. 
To set the scale reduction data from the time display mode, first, the 
display change switch S.sub.3 is operated once. This switch operation 
causes the one shot circuit 45 to send the display change signal (one-shot 
pulse) to the ternary counter 37. In the time display mode, the ternary 
counter 37 sends the time mode signal M.sub.0 to the display switching 
circuit 34 so that this circuit 34 selects the time display mode. When the 
one-shot pulse is sent once to the ternary counter 37, however, this 
counter sends the scale reduction mode signal M.sub.1 to the display 
switching circuit 34 so that this circuit 34 selects the scale reduction 
data from the scale reduction counter 44 and causes the display 35 to 
display the selected data. 
There are three types of scale reduction data in this embodiment, which 
respectively indicate 1/10000 reduction, 1/20000 reduction and 1/40000 
reduction and one of which is displayed on the display 35 by operating the 
scale reduction change switch S.sub.2 (the display of the scale reduction 
data being not illustrated). While viewing the display 35, an operator 
operates the switch S.sub.2 to select the proper scale reduction data for 
the reduced scale of a map to be measured. When the desired scale 
reduction data, for example, 1/20000, is displayed on the display 35, the 
operator operates the reset switch S.sub.1 once to reset the content of 
the distance register 31, and then operates the display change switch 
S.sub.3 again to proceed to the distance measuring operation. When the 
switch S.sub.3 is operated once, the one-shot circuit 45 sends the display 
change signal (one-shot pulse) to the ternary counter 37 which in turn 
sends the distance measure mode signal M.sub.2 to the display switching 
circuit 34. As a result, the circuit 34 causes the display 35 to display 
the data from the distance register 39. At this time, since the distance 
data in the register 39 is reset, "00.00" will be displayed on the lower 
right portion of the display panel 13 though not illustrated. 
When the operator operates the control switch S.sub.4 in the above state, 
the AND gate 46 outputs a high-level signal since the distance measure 
mode signal M.sub.2 has already been supplied to one of the input 
terminals of the AND gate 46, and sends this high-level signal to the 
one-shot circuit 47 and the input terminal T of the T-FF circuit 48. Upon 
reception of the high-level signal from the AND gate 46, the one-shot 
circuit 47 sends a one-shot pulse to the timer 49 to reset it. Upon 
reception of the high-level signal from the AND gate 46 at the input 
terminal T, the T-FF circuit 48 sends a high-level signal from the output 
terminal Q to the gate terminals of the transfer gates 50-52 and one of 
the input terminals of the AND gate 53. Upon reception of the high-level 
signal from the output terminal Q of the T-FF circuit 48, each transfer 
gate 50, 51 or 52 connects its own input terminal and output terminal. 
Accordingly, the transfer gate 50 supplies power to the light emitting 
diode 26 through the switching transistor 32, and the transfer gates 51 
and 52 supply power to the phototransistors 27 and 28. Consequently, the 
diode 26 and phototransistors 27 and 28 start functioning. 
Under the above condition, with the watch casing 1 set upright, the 
measuring wheel 17 partially protruding from the casing 1 is directly 
pressed against the map and is rolled thereon. The rotation of the 
measuring wheel 17 rotates the drive gear 17b, thereby rotating the outer 
transmission gear 20b of the transmission wheel 20. In this case, since 
the gear ratio of the outer transmission gear 20b to the gear 17b is 1/3, 
the gear 20b rotates three times for each rotation of the measuring wheel 
17. In this manner, the rotation of the outer transmission gear 20b is 
transmitted via the rotational shaft 20a of the transmission wheel 20 to 
the internal transmission gear 20c within the watch casing 1 and the 
rotation of the gear 20c is transmitted via the intermediate wheel 21 to 
the driven gear 22b of the detection wheel 22c, thus rotating the 
detection gear 22c. Since the internal transmission gear 20c of the 
transmission wheel 20, the intermediate wheel 21 and the driven gear 22b 
of the detection wheel 22 have the same number of teeth, the detection 
gear 22c rotates three times for each rotation of the measuring wheel 17. 
As the detection gear 22c rotates, the infrared rays emitted from the 
light emitting diode 26, which are irradiated on the gear 22c through the 
opening 25b, are irradiated on the phototransistors 27 and 28 through the 
light penetrating windows 25c above when the intervals between the teeth 
22d of the gear 22c come above the phototransistors 27 and 28. Upon 
reception of the infrared rays, the phototransistors 27 and 28 output 
high-level signals. Accordingly, while the detection gear 22c is rotating, 
the phototransistors 27 and 28 output pulse signals which are counted by 
the arithmetic unit 40. 
Consequently, the number of rotation of the detection gear 22c is detected 
and the number of rotation of the measuring wheel 17 can be found on the 
basis of the detected number of rotation. More specifically, when the 
numbers of the pulses from the phototransistors 27 and 28 counted are 
equal to a predetermined number (the number of teeth 22d of the detection 
gear 22c; eight in this embodiment), it is detected that the detection 
gear 22c has rotated once, from which it is found that the measuring wheel 
17 has made 1/3 of its rotation. The arithmetic unit 40 acquires distance 
data from the numbers of the counted pulses from the phototransistors 27 
and 28 and the scale reduction data from the scale reduction counter 44, 
and stores the acquired data in the distance register 39. The distance 
data in this register 39 is displayed on the display panel 13 of the 
display 35. (The displayed distance data is "6.21 km" in FIG. 2.) In this 
case, the forward rotation or reverse rotation of the detection wheel 22 
is discriminated depending on which pulse signal from the phototransistor 
27 or 28 becomes a high level first. Therefore, when the measuring wheel 
17 is rolled beyond a specific position on the map and is then returned to 
the position, for example, this event is discriminated by the 
phototransistors 27 and 28 and the number of counts corresponding to the 
amount of the returned distance is subtracted from the actual number of 
counts for compensation for the over rolling of the wheel 17. 
Since the high-level signal from the output terminal Q of the T-FF circuit 
48 is supplied to one input terminal of the AND gate 53 and when 1-Hz 
signal Sc is supplied to the other input terminal thereof, the AND gate 53 
sends this signal Sc to the timer 49. 
Upon reception of the 1-Hz signal, the timer 49 counts this signal and 
sends a reset signal to the reset terminal R of the T-FF circuit 48 when 
the count coincides with the preset value stored in the timer 49. When 
receiving the reset signal at its reset terminal R, the T-FF circuit 48 
renders the output signal from the output terminal Q to have a low level. 
When the low-level signal is supplied to the transfer gates 50-52 and AND 
gate 53, each transfer gate disconnects the connection between its input 
terminal and output terminal. As the transfer gate 50 makes the 
disconnection, the supply of power from the negative power source V.sub.SS 
through the resistor r.sub.1, transfer gate 50 and switching transistor 32 
is stopped and the light emitting diode stops the light emission. When the 
transfer gates 51 and 52 similarly each make the disconnection between the 
input terminal and output terminal, the supply of power from the power 
source V.sub.SS through the resistor r.sub.2 and the transfer gate 51 and 
through the resistor r.sub.3 and the transfer gate 52 is stopped. This 
stops the operation of the phototransistors 27 and 28. Further, since the 
low-level signal is supplied to one input terminal of the AND gate 53, the 
output signal of the gate 53 becomes a low-level signal and the timer 49 
stops the counting operation. 
When the control switch S.sub.4 is operated during the counting operation 
of the timer 49, the AND gate 46 sends its high-level output signal to the 
input terminal T of the T-FF circuit 48 and the one-shot circuit 47. When 
receiving the high-level signal at its input terminal T at this point, the 
T-FF circuit 48 renders its output at the output terminal Q to be a 
low-level signal and sends the signal to the transfer gates 50-52 and one 
input terminal of the AND gate 53. As a result, each transfer gate 50, 51 
or 52 disconnects the electric connection between its input terminal and 
output terminal, so that the light emitting diode 26 and phototransistors 
27 and 28 stop functioning. Upon reception of the high-level signal from 
the AND gate 46, the one-shot circuit 47 sends the one-shot pulse to the 
timer 49 to reset it. 
In short, when the control switch S.sub.4 is operation during the counting 
operation of the timer 49, the operations of the diode 26 and 
phototransistors 27 and 28 are stopped. 
When the control switch S.sub.4 is operated after the timer 49 has 
completed the counting operation and the diode 26 and phototransistors 27 
and 28 has stopped their operations, the high-level signal is supplied 
through the AND gate 46 to the input terminal T of the T-FF circuit 48. 
Since the low-level signal is output from the output terminal Q of the 
T-FF circuit 48 at this time, the high-level signal being supplied to the 
input terminal T renders the output of the output terminal Q to be a 
high-level signal so that the timer 49, light emitting diode 26 and 
phototransistors 27 and 28 start operating as described earlier. 
Although, according to the above embodiment, the protecting section 8 is 
provided at the right side of the watch casing 1 to protect the measuring 
wheel 17, this design may be modified such that the band attachments 9 
formed at the front and rear sections of the watch casing 1 serve as the 
protecting section. 
The measuring wheel 17 is provided on the bezel 3 to be able to move in arc 
according to the above embodiment. This invention is not, however, 
restricted to such arrangement, but may be modified so that when the 
measuring wheel 17 linearly slides to come to the position where it can be 
used as a distance measure, the wheel 17 partially protrudes from the 
casing 1 and can drive transmission wheel 20, etc. of the gear train 
mechanism 18. 
Although the foregoing description of this embodiment has been given with 
reference to the present invention being applied to an electronic wrist 
watch, this invention is in no way restricted to this particular case but 
may be applied to other electronic devices such as a travel watch and a 
card type radio. 
The application of the present rotation detecting apparatus is not limited 
to a distance measure for measuring the distance between two points on a 
map, but the apparatus may be modified to measure the moving speed, 
rotational speed, the number of rotation, etc.