Time sound generating device

A time sound generating device which generates a time announcement sound by detecting a change of time from a portion of a display element driving signal supplied to a time display element of a digital electronic clock and by driving an audio sound signal source by the detected time signal.

This invention relates to a time sound generating device of a digital clock 
which can generate a time announcement sound through a simple circuit 
construction. 
In almost all digital clocks, time is displayed by LED's, fluorescence 
display tubes, etc. Generation of such a time sound requires special IC's 
and special circuits, which are very expensive. 
According to this invention, a time sound can be generated simply by using 
conventional inexpensive clock IC's.

In FIG. 1 showing the construction of a device of this invention, 1 denotes 
an IC for a clock (time display element driving circuit) which, with an 
input of a commercial power supply of a frequency of 50 or 60 Hz, counts 
the frequency and generates display outputs of minutes and hours. Numeral 
2 denotes a time display element such as a LED, a fluorescent display 
tube, or a liquid crystal. FIG. 1 shows the situation where the time 
display element 2 is composed of six figures, i.e. an AM/PM display 
portion 2a, a time display portion for a 10-hour digit 2b which displays a 
time announcement number in the order of a 10-hour period, a time display 
portion for a 1-hour digit 2c which displays a time announcement number in 
the order of a 1-hour period, a colon for the seconds display 2d, a time 
display for a 10-minute digit 2e, and a time display portion for a 
1-minute digit 2f. Each display portion 2a to 2f has input pins (not 
shown) which correspond one to one to its segments (maximum 7 segments). 
Each input pin is connected with each output pin (not shown) of the clock 
IC 1. Numeral 3 denotes a time detection circuit which detects timing for 
generating a time sound such as at 1 hour 00 minute, 2 hour 00 minute, 
etc. Numeral 4 denotes an oscillator for producing a time sound. Numeral 
5 denotes an amplifier circuit which amplifies such a time sound signal to 
emit the time sound from a loudspeaker 6. 
When the digital clock is used in combination with a television receiver 
and a radio receiver etc., an amplifier circuit and a loudspeaker in the 
receiver can be used in place of the amplifier 5 and the speaker 6 shown 
in FIG. 1. 
FIG. 2A shows a construction example of the display portion of the 
10-minute digit 2e in FIG. 1. FIG. 2B shows the variations of a segment 
"b" of the display portion of the 10-minute digit 2e. Timing for the 
production of a time announcement sound is obtained by detecting a rise of 
the output signal applied to the segment "b". That is the time, P hour 00 
minute is detected in the following manner. Since Q-hour 00 minute follows 
P hour 59 minute, variation of "5" to "0" in the display for the 10-minute 
digit 2e should be detected. The segment "b" is at a high level when the 
numerals "1" to "4" are displayed, at a low level when the numeral "5" is 
displayed and changes to a high level when the numeral "0" is displayed. 
Therefore, the variation from a low to a high level of the segment "b" can 
be detected for a change in the hour display. 
In a time detection circuit 3 shown in FIG. 3, the output variation of the 
segment "b" is detected by a differentiation circuit comprising a resistor 
R.sub.1, a resistor of high resistance R.sub.2 and a condenser C.sub.1. In 
this figure, A denotes an input terminal connected to the segment "b". 
TR.sub.1 denotes a transistor. The differentiaion circuit is inserted 
between the base of the transistor TR.sub.1 and the input terminal A. The 
collector of the transistor TR.sub.1 is connected to a power supply 
terminal through a resistor and to a reference voltage terminal through a 
condenser C.sub.2. TR.sub.2 denotes a transistor whose base is connected 
with the collector of the transistor TR.sub.1. The collector of the 
transistor TR.sub.2 is connected to an ouput terminal C through a 
condenser C.sub.4 and to an input terminal B through a series circuit of a 
condenser C.sub.3 and a resistor R.sub.4. The input terminal B is 
connected with the output terminal of an oscillator 4. The output terminal 
C is connected to an amplifier circuit 5. 
In FIG. 3, while the input terminal A is at low level (i.e. a display 
numeral "5" is being displayed) the, charge stored in the condenser 
C.sub.1 is substantially zero. When the input terminal A becomes a high 
level, the condenser C.sub.1 is charged with a time constant determined by 
the resistor R.sub.1 and the condenser C.sub.1. If the value of the 
resistor R.sub.1 is chosen small, the condenser C.sub.1 is charged very 
quickly. The transistor TR.sub.1 turns on substantially at the same time 
the input terminal A becomes a high level. The transistor TR.sub.1 remains 
on for the duration of a positive differentiation pulse applied in 
response to the potential change of the input terminal A. In the 
subsequent period of about 50 minutes the input terminal A is maintained 
at high level and the transistor TR.sub.1 is turned off. When the input 
terminal A changes from a high to a low level, the base potential of 
transistor TR.sub.1 changes in a minus direction but does not influence 
the switching state of transistor TR.sub.1. As described above, detection 
of P hour 00 minute condition becomes possible at the collector of the 
transistor TR.sub.1. 
The transistor TR.sub.2 forms an analog switch circuit which has a signal 
input at a terminal B from the oscillator 4 and produces an output signal 
on a terminal C. When the transistor TR.sub.2 is on, the input signal at 
the terminal B is divided by the resistor R.sub.4 and a low impedance of 
the transistor TR.sub.2 and attenuated. Almost no signal appears at the 
terminal C. When the transistor TR.sub.2 is off, the input signal at the 
terminal B appears substantially intact on the terminal C. 
Therefore, since the condenser C.sub.2 is charged through the resistor 
R.sub.3 by a positive voltage supply Vcc when the transistor TR.sub.1 is 
off, the transistor TR.sub.2 turns on and no signal appears on the 
terminal C. However, as soon as the input terminal A changes from low to 
high level, or the display number of the display part for 10-minute digit 
2e changes from "5" to "0", the transistor TR.sub.1 turns on and the 
charge in the condenser C.sub.2 is discharged instantaneously through the 
transistor TR.sub.1. At the same time, the transistor TR.sub.2 turns off 
and a signal with nearly the same amplitude as at B appears at the 
terminal C. After a time determined by the condenser C.sub.1 and the 
resistor of high resistance R.sub.2, the transistor TR.sub.1 turns off. 
The condenser C.sub.2 begins to be charged through the resistor R.sub.3. 
In accordance with the rate of charging, the transistor TR.sub.2 changes 
slowly to the on state and the output voltage at the terminal C decreases 
towards zero giving a gradually diminishing tone. If such a time 
announcement signal is amplified by the amplifier 5 to drive the 
loudspeaker 6, a soft sound having an echo is obtained. 
FIG. 4 shows the potential variations of segments "a" and "e" in the 
display portion for 1-hour digit 2C which are used for detection of time. 
FIG. 5 shows a schematic diagram of the time detection circuit. Like 
reference numerals are used to denote like elements having the same 
function. So, a detailed explanation of them is omitted. 
In FIG. 5, input terminals A.sub.1 and A.sub.2 connected with the segments 
"a" and "e" respectively are provided. One end of differentiating 
condensers C.sub.5 and C.sub.6 are connected commonly. The connection 
point is connected to a reference voltage through a bias resistor R.sub.5 
and to the base of a transistor TR.sub.3, the collector of which is 
connected to a terminal of a voltage supply through a collector resistor 
R.sub.6 and connected to the base of the transistor TR.sub.1 through the 
condenser C.sub.1. 
Change from a high to a low level or from a low to a high level of the 
segments "a" and "e" in FIG. 5 is detected by the differentiating 
condensers C.sub.5 and C.sub.6 and applied to the base of the transistor 
TR.sub.1 after being amplified and shaped by the transistor TR.sub.3. In 
this case, the two segments should be in such a relation that for a change 
from the display number "1" to "2", 2" to "3", etc. either segment changes 
its level. The operation thereafter is the same as that of FIG. 3, but the 
values of condensers C.sub.5 and C.sub.6 are different from those of FIG. 
3. They are selected to give both positive and negative pulses through 
differentiation when the waveforms on the input terminals A.sub.1 and 
A.sub.2 change. 
FIG. 6 shows the simplest example of the electrical generation of the time 
sound. In this example, the commercial power supply voltage is reduced by 
a power transformer PT and full-wave rectified by a bridge rectification 
circuit D.sub.1. A sound with a frequency twice the commercial frequency 
is taken out from a terminal D and applied to the input terminal B of FIG. 
3 or FIG. 5. In FIG. 6, R.sub.L and C.sub.L denote a resistor and a 
condenser constituting a filter circuit respectively. A d.c. voltage is 
supplied to a load 7 (a clock IC, a television receiver or a radio 
receiver). 
FIG. 7 shows a mechanical time sound generator comprising an electromagnet 
L.sub.1, a rotatably supported hammer 8, an iron piece 9 fixed to the 
hammer, and vibration piece 10 such as a tuning fork or a plurality of 
bars and pipes. In FIG. 7, the collector of transistor TR.sub.2 of FIG. 3 
or FIG. 5 is connected with a terminal E so that, while the transistor 
TR.sub.2 is on, the electromagnet L.sub.1 is driven to pull the iron piece 
9 and separate it from the vibration piece 10. When the transistor 
TR.sub.2 becomes off, the vibration piece 10 is struck by the hammer 8. 
FIG. 8 shows another example of a time detection circuit 3. Like reference 
numerals are used to denote like elements having the same function as that 
of the elements of FIG. 3. 
In FIG. 8, in addition to the circuit of FIG. 3, a diode D.sub.1 is 
inserted between the resistor R.sub.1 and the condenser C.sub.1 with the 
cathode on the side of condenser C.sub.1, and a resistor R.sub.5 is 
inserted between a connection point of the diode D.sub.1 and the condenser 
C.sub.1 and a reference voltage. 
Next, consider how a time adjustment is performed in the clock IC 1 as 
shown in FIG. 1. Usually, time adjustment is accomplished by sequentially 
increasing the display time, i.e. P hour 00 minute, P hour 01 minute, P 
hour 02 minute, . . . , Q hour 00 minute. As a result, the time sound 
generating circuit using the time detection circuit shown in FIG. 3 is 
inconvenient because, at every X hour 00 minute, a time sound is 
generated. In a clock IC capable of displaying X minute .DELTA..DELTA. 
second by the same display segments by utilizing a switch (not shown), a 
similar inconvenience arises at every X minute 00 seconds. 
The circuit shown in FIG. 8 solves this problem in a simple way. 
Explanation of the circuit will be made next. 
In the FIG. 8 circuit, the fact that the condenser C.sub.1 discharges only 
when the input terminal A is at low level, or when the display number is 
"5", is utilized. By insertion of the diode D.sub.1 which is cut off when 
the input terminal A is at low level, the condenser discharges through the 
resistors R.sub.2 and R.sub.5. Thus, if the resistance of the resistor 
R.sub.5 is made high enough to keep the discharge time of the condenser 
C.sub.1 longer than 1 minute, the time detection circuit does not operate 
unless the display number keeps the state "5" for more than 1 minute. This 
means that, when the time display is varied for the purpose of adjusting 
the time, quick feed from P hour 50 minute to Q hour 00 minute may be done 
within 1 minute and that quick feed from P hour 00 minute to Q hour 00 
minute may be done within 6 minutes. Practically, it is unreal to spend 6 
minutes for a 1 hour time adjustment. Usually, a 1 hour quick feed is 
done by a fast and rough time adjustment taking a time period of 1 second 
or the like, while a 1 minute quick feed is done by a fine time adjustment 
also taking a time period of 1 second or the like. Therefore, for 1 minute 
quick feed taking one second, the period of display number "5" is only 10 
seconds so that the problem of unnecessarily generating the sound at each 
time adjustment can be completely avoided. 
In FIG. 8, when the input terminal is at high level the diode D.sub.1 is 
conducting. Since charging of condenser C.sub.1 is done rapidly, timing 
for generating such a time sound is not influenced. 
A similar explanation holds for the inconvenience arising for a display of 
a second. The period of display number "5" occurs only for 10 seconds from 
P minute 50 second to Q minute 00 second so that the inconvenience of 
generating the unnecessary time sound can be completely avoided. 
Although in the above explanation the discharge time of condenser C.sub.1 
is made larger than 1 minute by increasing the value of the resistor 
R.sub.5, it is needless to say that the same effect can be obtained 
practically by a discharging time of the order of 10 seconds. The 
discharge time of this order can be simply obtained by usual resistors and 
condensers without using special elements. 
The circuit of FIG. 8 has the additional advantage of preventing a negative 
pulse from appearing at the base of the transistor TR.sub.1 when input 
terminal A changes from a high to a low level. Without the diode D.sub.1, 
the negative pulse caused by a level change at terminal A could destroy 
the emitter junction of transistor TR.sub.1. This problem can be 
completely avoided by the FIG. 8 circuit. 
FIG. 9 shows another embodiment of the time detection circuit 3. This 
embodiment prevents an erroneous operation of the time detection circuit 
which may happen when the brightness of the time display element is 
adjustable. 
If the brightness of the display element is required to be adjustable, 
usual methods currently employed are to vary the high level voltage of 
each output pin of the clock IC 1 by insertion of a variable resistor for 
brightness adjustment or to switch a plurality of resistors with different 
resistances in circuit with a switch. However, if the high level voltage 
is varied by a variable resistor, the voltage at the terminal A fluctuates 
around the high level in addition to changing from a low to a high level. 
This may cause an erroneous operation of the time sound generating 
circuit. 
Now, if we assume that the high level of the terminal A is varied between 
H.sub.L and H.sub.H by a brightness adjusting variable resistor with a 
relation H.sub.H -H.sub.L .gtoreq.H-L, then it is considered that a time 
sound generating circuit with the time detection circuit of FIG. 3 may 
generate a time sound due to a rapid change of the variable resistor. In 
the FIG. 9 embodiment, a relationship H.sub.H -H.sub.L &lt;&lt;H-L is obtained 
by a diode D.sub.2 and resistors R.sub.6 and R.sub.7. 
According to this embodiment, in addition to the circuit of FIG. 3, a 
series circuit of a resistor R.sub.6 and a resistor R.sub.7 is inserted 
between a voltage supply terminal and a reference voltage, and a diode 
D.sub.2 is inserted between a connection point of the resistor R.sub.1 and 
the condenser C.sub.1 and a connection point of the resistors R.sub.6 
R.sub.7. 
If the values of resistors R.sub.6 and R.sub.7 are selected such that the 
potential V.sub.b at the point b satisfies V.sub.b .ltoreq.H.sub.L, the 
potential V.sub.a at the point a is fixed V.sub.a =V.sub.b +V.sub.D2 when 
the input terminal A is at a high level (where V.sub.D2 denotes a voltage 
drop in the forward direction of diode D.sub.2) so that a variation 
between H.sub.H and H.sub.L does not appear at the point a. When the input 
terminal A is at a low level, the diode D.sub.2 is cut off and the circuit 
condition is the same as that of FIG. 3. Thus the charging of the 
condenser C.sub.1 is rapidly done as in FIG. 3 when the terminal A 
switches to a high level. 
Therefore, in the circuit shown in FIG. 9, even if the terminal A varies 
from L (low level), through H.sub.L to H.sub.H, the potential at the point 
a varies only from L to V.sub.b +V.sub.D2. Thus, the inconvenience of 
generating a time sound which could arise by a rapid change of the 
brightness adjusting variable resistor at each brightness adjustment can 
be avoided. 
If the value of the resistor R.sub.7 is large, the potential at the point a 
varies a little. This problem can be solved by using a Zener diode D.sub.3 
as shown in a circuit .alpha. instead of the circuit .alpha.. In this 
case, it is necessary that V.sub.b =V.sub.z (V.sub.z is the Zener voltage 
of the Zener diode D.sub.3). 
FIG. 10 shows a further embodiment of the time detection circuit 3. This 
embodiment combines the circuit constructions of FIGS. 8 and 9. The anode 
of the diode D.sub.2 is connected with the anode of the diode D.sub.1. 
FIG. 10 obtains the merits of both FIGS. 8 and 9. 
Although the foregoing embodiments are adapted to produce the time 
announcement sound when the second switching transistor is maintained off, 
alternative circuit arrangements may be possible to produce the sound when 
such a transistor is maintained on. 
FIG. 11 shows another embodiment, in which both a time detection circuit 3 
and an oscillator circuit 4 are shown. A differential amplifier is used in 
place of the transistor TR.sub.2 of the time detection circuit of FIG. 3, 
while a CR oscillator circuit is used for the oscillator 4. 
In this figure, the functions of resistors R.sub.1, R.sub.5, R.sub.6 and 
R.sub.7, diodes D.sub.1 and D.sub.2, a condenser C.sub.1 and a transistor 
TR.sub.1 are the same as those of like elements in FIGS. 9 and 10. R.sub.9 
and R.sub.11 denote bias resistors which make a condenser C.sub.5 
discharge rapidly when the transistor TR.sub.1 is turned on and fixes the 
base potential V.sub.B1 of a transistor TR.sub.3 at a constant value 
(V.sub.N1(MIN) =V.sub.E +V.sub.CE(SAT) TR.sub.1, where V.sub.CE(SAT) 
TR.sub.1 is the collector-emitter voltage of the transistor TR.sub.1 when 
TR.sub.1 is on). If a relation V.sub.B1(MIN) &lt;&lt;V.sub.B2 is satisfied, a 
time sound with a maximum amplitude appears at a terminal C, where 
V.sub.B2 denotes the base (reference) voltage of a transistor TR.sub.4 
which constitutes a differential amplifier. 
After a lapse of time determined by the time constant of the 
differentiation circuit just after the voltage of the input terminal A 
changes from a low to a high level, the transistor TR.sub.1 is turned off 
and the condenser C.sub.5 is charged gradually through a resistor 
R.sub.10. In accordance with this, the base voltage V.sub.B1 of a 
transistor TR.sub.3 increases and approaches the potential V.sub.B2. 
Through differential operation of the transistors TR.sub.3 and TR.sub.4, 
the potential V.sub.B1 rises, whereby the time sound signal from the 
terminal C diminishes gradually. 
When V.sub.B1 &gt;&gt;V.sub.B2, the transistor TR.sub.4 is cut off and the time 
sound output from the terminal C is zero. R.sub.12 is a resistor which 
suppresses the maximum voltage V.sub.B1(MAX) and hence a voltage applied 
on the condenser C.sub.5 while reducing the reverse voltage applied 
between the base and the emitter of the transistor TR.sub.4. R.sub.13 and 
R.sub.14 are emitter resistors of the differential amplifier which extend 
the dynamic range of the amplifier. R.sub.15 is a load resistor of the 
transistor TR.sub.4. R.sub.16 and R.sub.17 are base bias resistors of the 
transistor TR.sub.4. TR.sub.5 denotes a constant current cource 
transistor, to the base of which a signal from a time sound oscillator 
circuit 4 is supplied. The signal is amplified by the differential 
amplifier and modulated by the voltage V.sub.B1, and an output signal is 
obtained from the collector of the transistor TR.sub.4. R.sub.18 is an 
emitter resistor of the constant current transistor TR.sub.5 and C.sub.6 
is a condenser for cutting the d.c. current. In the oscillator circuit 4, 
TR.sub.6 is a transistor for generating a time sound signal. Oscillation 
having a sinusoidal waveform is obtained at a frequency determined by a 
phase shift circuit formed by resistors R.sub.27 and R.sub.28 and 
condensers C.sub.8, C.sub.9 and C.sub.10. R.sub.22 is a load resistor. 
R.sub.25 and R.sub.26 are base bias resistors. R.sub.23 is an emitter 
resistor for current feedback. R.sub.24 is an emitter resistor and C.sub.7 
is a bypass condenser. R.sub.19, R.sub.20 and R.sub.21 are bias resistors 
for the constant current transistor TR.sub.5. 
As described above, according to this invention, an error action of a time 
sound generator circuit is avoided by a very simple method, and a time 
sound generating circuit with a reliable operation can be obtained. 
(A specific value of each element in FIG. 11 is shown below for reference.) 
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R.sub.1 
6.8K R.sub.17 
4.7K D.sub.2 
MA150 
R.sub.3 
5.6K R.sub.18 
1K C.sub.1 
4.7.mu. 16V 
R.sub.5 
18M R.sub.19 
33K C.sub.5 
4.7.mu. 16V 
R.sub.6 
1K R.sub.20 
2.2K C.sub.6 
10.mu. 25V 
R.sub.7 
390 R.sub.21 
33K C.sub.7 
47.mu. 10V 
R.sub.9 
1K R.sub.22 
6.8K C.sub.8 
0.0047.mu. 50V 
R.sub.10 
470K R.sub.23 
27 C.sub.9 
0.0047.mu. 50V 
R.sub.11 
3.9K R.sub.24 
1K C.sub.10 
0.0047.mu. 50V 
R.sub.12 
270K R.sub.25 
120K TR.sub.1 
C1685 
R.sub.13 
100 R.sub.26 
15K TR.sub.3 
C1685 
R.sub.14 
100 R.sub.27 
15K TR.sub.4 
C1685 
R.sub.15 
5.6K R.sub.28 
15K TR.sub.5 
C1685 
R.sub.16 
15K D.sub.1 MA150 TR.sub.6 
C1685 
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