Pest animal repulsing apparatus

The apparatus according to the present invention is provided with two or more output systems to which transducers are connected, a source output on/off control unit that turns on/off the output from a source based upon the output from a random signal generating unit and a frequency varying unit that causes changes in the frequency of an electrical signal provided to the transducers over time at a specific rate. Every time the source output is turned off, the output of the electrical signal is stopped and the output systems are switched over, whereas when the source output is on, the electrical signal provided to the transducers on the output system to which the signal is to be provided. Since the output systems are switched over to be selected for use, it becomes possible to connect a greater number of transducers while using the same source capacity as in the prior art and noise generated from the transducers, when switching over the output systems, is eliminated.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a pest animal repulsing apparatus which 
utilizes ultrasonic waves that are generated randomly to intimidate and 
repulse pest animals such as rats and to prevent them from entering a 
designated area such as a residential building, supermarket, department 
store or the like. 
2. Description of the Related Art 
In view of the fact that pest animals such as rats dislike ultrasonic waves 
within a specific range, apparatuses in the known art that repulse rats 
and the like by emitting ultrasonic waves toward the area where the rats 
and the like live are disclosed, for instance, in Japanese Examined Patent 
Publication No. S 61-49 and Japanese Examined Patent Publication No. S 
63-16. 
The apparatus that is disclosed in the former publication, i.e., Japanese 
Examined Patent Publication No. S 61-49, creates a control signal by 
superimposing a trigger signal generated at a trigger signal generator 
upon a random signal generated at a random signal generator and provides 
this control signal to an oscillating circuit to cause random changes in 
the oscillating frequency. An intimidating signal is thereby formed that 
contains an impulsive sound component whereby changes in frequency such 
that a rapid change from a reduction to an increase in frequency occurs 
within this randomly generated oscillating frequency. The intimidating 
signal is changed by a transducer to ultrasonic waves that contain 
impulsive sound. 
In addition, in the apparatus disclosed in the latter publication, i.e., 
Japanese Examined Patent Publication No. S63-16, in which the trigger 
signal in the apparatus disclosed in the former publication is eliminated, 
a control signal corresponding to the output of a random signal generator 
is provided to an oscillating circuit to cause random changes in the 
oscillating frequency. An intimidating signal is thereby formed that 
contains an impulsive sound component whereby rapid changes from a 
reduction to an increase in frequency occur within this randomly generated 
oscillating frequency and the intimidating signal is changed to ultrasonic 
waves that contain impulsive sound by a transducer. 
However, with the apparatuses described above, which intimidate rats and 
the like by simultaneously generating random ultrasonic waves and impulse 
waves, if such apparatuses are to cover a wide range of area, a plurality 
of transducers must be connected to the oscillating circuit via the 
amplifying circuits, and this may present a problem of an insufficient 
source capacity. Thus, a wide ranging area cannot be covered unless the 
source capacity of the apparatus is increased so as to make it possible to 
increase the number of transducers which can be connected. 
In addition, while the applicant of the present invention has been 
conducting research into a method in which output systems for ultrasonic 
waves are switched in order to prevent rats and the like from becoming 
accustomed to the ultrasonic waves, there is a problem in that, when the 
output systems for the ultrasonic waves that are outputted continuously 
are switched, noise is generated at the transducers when switching the 
output systems. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a pest animal 
repulsing apparatus that is capable of driving more transducers than has 
been previously possible in the prior art using the same source capacity 
and that ensures no noise is generated from the transducers when switching 
the output systems while employing a method whereby the output systems are 
switched in order to achieve the repulsing effect on the pest animals 
imparted by ultrasonic waves. 
In order to achieve the object described above, the pest animal repulsing 
apparatus according to the present invention comprises, as shown in FIG. 
1, two or more output systems to which transducers 1 for converting 
electrical signals to mechanical vibrations are connected with power 
supplied to the transducers 1 from a common source, a random signal 
generating unit 2 that generates random signals, a source output on/off 
control unit 3 that turns on/off the output from the source based upon the 
output from the random signal generating unit 2, a frequency varying unit 
4 that changes the frequency of the electrical signal provided to the 
transducers 1 over time at a specific rate and an output switching unit 5 
that stops the output of the electrical signal and switches over to the 
output system to which the electrical signals are to be provided each time 
the source output is turned off so that, when the source output is turned 
on, the transducers connected to the active output system receive the 
electrical signals. 
In one mode, the pest animal repulsing apparatus may comprise a set of 
speakers to which power is supplied from a common source so that 
electrical the signals can be converted to sound wave motion, a random 
signal generating unit that creates random signals by generating noise, a 
source output on/off control unit that turns the output from the source on 
and off based upon the output from the random signal generating unit, a 
frequency varying unit that creates a pulse signal in which the frequency 
sweeps at a specific rate and causes the frequency of the electrical 
signal provided to the speakers to change based upon the pulse signal, a 
source-off detection circuit that detects that the source output is in an 
off state and an output switching unit that stops the output of the 
electric signal and sequentially switches over the speakers to which the 
electric signals are to be provided every time the source output is turned 
off and, when the source output is turned on, provides the electrical 
signal to the speakers to which the switch-over has been made. 
In this structure, since the output from the source at the source output 
on/off control unit 3 is turned on/off based upon a random signal 
generated at the random signal generating unit 2, the length of time over 
which the source is on and the length of time over which the source is off 
are varied randomly. While the electrical signal created at the frequency 
varying unit 4, which changes over time at a specific rate, may be 
provided to a plurality of output systems, the output switching unit 5 
stops the output of the electrical signal each time the source output is 
turned off and, during the period of time that the source output remains 
off, switches over to the output system to which the electrical signal is 
to be provided. Then, when the source output is turned on, the electrical 
signal is provided to the transducers 1 on the newly designated output 
system to which the signal has been switched. 
Since the frequency of the electrical signal provided to the transducers 1 
changes over time at a specific rate, no impulse wave is formed due to 
rapid changes in frequency. However, the on period of the source over 
which the electrical signal is provided to the transducers 1 is dependent 
upon a random signal, thus an electrical signal created during each on 
period will include varying frequency changes and, as a result, the 
ultrasonic waves output by the transducers will also be random. Moreover, 
since the periods over which the source is turned off are also random, the 
switching cycle for the transducer will be random. 
In addition, while a plurality of transducers are provided, since the 
output systems for outputting ultrasonic waves are being switched among by 
the output switching unit, the plurality of transducers can be driven 
without increasing the source capacity over that of the prior art. 
Furthermore, since the switching of the output systems is performed while 
the source output is turned off, the problem of noise being generated by 
the transducers is eliminated. 
In a more specific structural example, the output switching unit 5 may 
include a source-off detection circuit constituted by a logic gate that 
outputs a positive logic level when the output of the source is in an off 
state, a decode counter into which the output signal from the source-off 
detection circuit is inputted and a switching element that is connected to 
an output terminal of the decode counter to interrupt the output system so 
that every time the output from the source is turned off, the output 
systems are switched sequentially. 
The frequency varying unit 4 may include a triangular wave generating 
circuit that generates triangular waves so that a pulse signal whose 
frequency changes over time can be created by changing the oscillating 
frequency in correspondence to the output voltage from the triangular wave 
generating circuit. In addition, the frequency varying unit 4 may include 
an integrating circuit that integrates the randomly changing signal that 
corresponds to the output from a random signal generating unit 2 so that a 
pulse signal, whose frequency changes over time, can be created by 
changing the oscillating frequency in correspondence to the output voltage 
from the integrating circuit. Furthermore, a pulse signal whose frequency 
changes over time may be achieved by switching between them selectively. 
In particular, if a pulse signal obtained from an integrating circuit is 
utilized, the range over which the frequency sweeps becomes random in 
addition to achieving random output periods and random timing for 
switching the output systems, thereby making it possible to output even 
more random ultrasonic waves compared to those achieved with triangular 
waves. 
Moreover, means for adjusting the output level of an electrical signal may 
be provided in correspondence to the individual transducers. For instance, 
when the output of the source is converted by the frequency varying unit 4 
to a signal whose frequency fluctuates, to be provided to the transducers, 
the voltage level may be adjusted by the output voltage adjusters that are 
provided in correspondence to the individual output systems. By adding 
these structural features, settings such as changes in the output level 
and pauses in the output can be made freely for each output system 
depending upon the location of installation of the apparatus according to 
the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The following is an explanation of an embodiment of the present invention 
with reference to the drawings. In FIG. 2, which shows a more specific 
functional block diagram of the pest animal repulsing apparatus according 
to the present invention shown in FIG. 1, the pest animal repulsing 
apparatus comprises a low range noise generating circuit 6 that amplifies 
low range noise to convert it to a digital signal, a frequency divider 
circuit 7 that divides the frequency of the noise signal in conformance to 
the on/off of the source, a source mute circuit 8 that turns off the 
output from a variable voltage source circuit 10 based upon the signal 
from the frequency divider circuit 7 and an output voltage adjusting 
circuit 9 that adjusts the output voltage generated at the variable 
voltage source circuit 10. 
In addition, the apparatus according to the present invention is provided 
with a triangular wave generating circuit 12 that generates a triangular 
wave with a reference voltage at the center created at a reference voltage 
adjusting circuit 11, an integrating circuit 13 that integrates random 
signals output from the frequency divider circuit 7 based upon the noise 
signal while comparing it to the reference voltage, a voltage control 
oscillator (VCO) 14 that selects either the output from the triangular 
wave generating circuit 12 or the output from the integrating circuit 13 
to cause the frequency to change in correspondence to the output level, a 
rectangular wave amplifier 15 that converts the output of the source 
voltage to an electrical signal whose frequency fluctuates based upon the 
output from the VCO, a source-off detection circuit 16 that detects that 
the source voltage has been turned off and an output switching circuit 17 
that, while the source voltage is turned off, performs switching of the 
output speakers (transducers 1 shown in FIG. 1) to select the speakers 
that are to perform the outputting and causes the outputted from the 
rectangular wave amplifier 15 to be output through the speakers that have 
been selected. 
The random signal generating unit 2 in FIG. 1 corresponds to the low range 
noise generating circuit 6 and the frequency divider circuit 7 shown in 
FIG. 2, the source output on/off control unit 3 in FIG. 1 corresponds to 
the source mute circuit 8, the output voltage adjusting circuit 9 and the 
variable voltage source circuit 10 shown in FIG. 2, the frequency varying 
unit 4 in FIG. 1 corresponds to the reference voltage adjusting circuit 
11, the triangular wave generating circuit 12, the integrating circuit 13, 
the VCO 14 and the rectangular wave amplifier 15 shown in FIG. 2, and the 
output switching unit 5 in FIG. 1 corresponds to the source-off detection 
circuit 16 and the output switching circuit 17 shown in FIG. 2. 
As shown in FIG. 3, the low range noise generating circuit 6 is constituted 
with a type of A/D converter that converts noise in a semiconductor to a 
pulse signal, and random noise generated at the semiconductor is inputted 
to an inverting amplifier 19 via a buffer amplifier 18. Its output is then 
inputted to a comparator 21 via an integrating circuit 20 and by comparing 
this with the output from the buffer amplifier 18, a pulse signal that 
corresponds to the random noise is obtained. An output A from the low 
range noise generating circuit 6 is made to have the signal waveform 
indicated by A in FIG. 7, for instance, by a logic analyzer. 
The frequency divider circuit 7 is constituted by connecting two "74HC74" 
elements, which are known in the prior art as CMOS D-type Hi speed 
flipflop ICs (22, 23). The output from the low range noise generating 
circuit 6 is inputted to a clock input terminal CP of the D-FF (22) at the 
first stage. This first stage D-FF (22) constitutes a T-FF, which is 
engaged in an up-edge operation and at the D-FF (23) at the second stage, 
the output from the first stage D-FF (22) is inputted to a CP terminal, so 
that an output H from the source-off detection circuit 16, which is to be 
detailed later, is inputted to a D terminal and a signal that achieved by 
inverting this is input to a preset terminal (PR) during a rise of the 
output H. In addition, a signal whose logical level is set to Low during 
the rise of the output D, which is to be detailed later, is inputted to a 
CLR terminal at the second stage D-FF (23). Consequently, the signal 
indicated by B in FIG. 7 is obtained in correspondence to the random 
signal from the low range noise generating circuit 6 that is indicated by 
A in FIG. 7. 
Synchronization with the on/off of the source output is achieved as well as 
synchronization with the noise signal in this manner to ensure that, since 
noise will be generated unless the speakers are switched over when the 
source is turned off, frequency division for the noise signal is not 
performed during a source off period, as will be described in more detail 
later. Because of this, even when there is a request for a random output, 
the noise signal is not admitted at the second stage D-FF (23) during a 
source off period and the signal is admitted only after the source is 
turned on. 
An output B from the frequency divider circuit 7 (output from a Q-bar 
terminal at the second stage D-FF) is inputted to the source mute circuit 
8. As shown in FIG. 4, the source mute circuit 8 is provided with a 
transistor 24 which constitutes a switching element and is emitter 
grounded. The output from the frequency divider circuit 7 is inputted to a 
base terminal of the transistor 24 with its connector terminal 
constituting an output terminal. Thus, the collector voltage is turned 
on/off as the base voltage shifts and the waveform achieved by inverting 
the output from the frequency divider circuit 7 is outputted from the 
source mute circuit 8. 
The output terminal of the source mute circuit 8 is connected to the output 
voltage adjusting circuit 9, which is provided with transmission gates 25 
and voltage adjustment variable resistors 26, which are assigned to 
individual output terminals of the output switching circuit 17. The 
transmission gate 25, corresponding to the output terminal to which the 
signal is output from the output switching circuit 17, is turned on and 
continuity is achieved between the output side of the source mute circuit 
8 and the voltage adjustment variable resistor 26, which varies the 
divided voltage of a source voltage Vcc. The transmission gates 25 are 
sequentially closed by the output switching circuit 17, which is to be 
detailed later, and the voltage at the output side of the source mute 
circuit 8 when the transmission gates 25 are closed can be varied by 
operating the voltage adjustment variable resistors 26. As a result, the 
waveform of the output from the source mute circuit 8 (or the output 
voltage adjusting circuit 9) when the signal indicated by B in FIG. 7 is 
inputted is as indicated by C in FIG. 7, the amplitude of which is 
determined by setting the voltage adjustment variable resistors 26. 
In the variable voltage source circuit 10, a connection point N1 of the 
source mute circuit 8 and the output voltage adjusting circuit 9 is 
connected with a non-inverting terminal of an operational amplifier 27 and 
a source output line is connected with an inverting terminal, 
respectively, and the output terminal of the operational amplifier 27 is 
connected between two light emitting diodes (D1 and D2) that are connected 
in series relative to the constant voltage source. As a result, only the 
light emitting diode D1 emits light when the applied voltage at a 
non-inverting input terminal of the operational amplifier 27 has dropped 
to the ground level due to the closing of the transistor 24 at the source 
mute circuit 8, or when the applied voltage at the non-inverting input 
terminal becomes lower than the applied voltage at the inverting input 
terminal due to an adjustment made at the voltage adjustment variable 
resistors 26 while the transistor 24 remains open. In contrast, only the 
light emitting diode D2 emits light when the applied voltage at the 
non-inverting input terminal is higher than the applied voltage at the 
inverting input terminal. 
In the variable voltage source circuit 10, a phototransistor PT1, which 
achieves continuity upon receiving light emitted by the light emitting 
diode D1, and a phototransistor PT2, which achieves continuity upon 
receiving light emitted by the light emitting diode D2, are connected in 
parallel via resistors and diodes so that their directions of electrical 
continuity are the reverse of each other. Moreover, an inverter 28 is 
provided in parallel with the emitter of the phototransistor PT2 connected 
to the ground via a capacitor 29 and the emitter of the phototransistor 
PT1 connected to the gate of a FET 32, which constitutes a snubber circuit 
in a rectifying smoothing unit 31. 
In this structure, the light emitting diodes D1 and D2 are made to emit 
light selectively based upon the signal generated by the source mute 
circuit 8 and the output voltage adjusting circuit 9. When the 
phototransistor PT1 receives light, continuity at the FET 32 is 
interrupted and the output from the source circuit is set to Hi (ON). If, 
on the other hand, the phototransistor PT2 receives light, continuity is 
achieved at the FET 32 and the output from the source circuit is set to 
Low (OFF). For instance, if a signal with the waveform indicated with C in 
FIG. 7 is input to the variable voltage source circuit 10, the output from 
this circuit will be as indicated by D in FIG. 7. 
The reference voltage adjusting circuit 11 may be, for instance, the one 
shown in FIG. 5, in which a divided voltage, which is set by a variable 
resistor 34, is inputted to a non-inverting input terminal of a voltage 
follower 33 and the output from the voltage follower 33 can be varied 
depending upon the setting at the variable resistor 34 so that the 
reference voltage at the operational amplifier, which is to be detailed 
later, can be adjusted. 
The triangular wave generating circuit 12 generates a triangular wave by 
integrating, for instance, a square wave. It employs an operational 
amplifier 35 as a comparator and the output voltage from the voltage 
follower 33 is inputted to an inverting input terminal of the operational 
amplifier 35, a saturation voltage node N2 of the operational amplifier 35 
and the output terminal of an operational amplifier 36 are connected 
through resistors R1 and R2 and the voltage at the connection point N3 of 
the resistors R1 and R2 is input to a non-inverting terminal of the 
operational amplifier 35 to compare it with the output from the reference 
voltage adjusting circuit 11. In addition, the operational amplifier 36, 
together with a resistor R4 and a capacitor C1 constitutes an integrating 
circuit. As a result, the saturation voltage at the operational amplifier 
35 forms a square wave and the output voltage from the operational 
amplifier 36 forms a triangular wave which is determined by the time 
constant of C1, R4. In FIG. 7, E represents an example the output waveform 
from the triangular wave generating circuit 12. 
The integrating circuit 13 is constituted by inputting the output from the 
first stage D-FF(22), constituting the frequency divider circuit 7, to an 
inverting input terminal of an operational amplifier 37 and inputting the 
output from the reference voltage adjusting circuit 11 to its 
non-inverting terminal. Thus, the output from the first stage D-FF, 
constituting the frequency divider circuit 7, becomes a random pulse 
signal achieved by performing A/D conversion on noise and, consequently, 
the output from the integrating circuit 13, too, becomes a voltage with a 
waveform that fluctuates over a random amplitude. It is to be noted that 
the time constant at the integrating circuit 13 is set in such a manner 
that the speed at which the output from the integrating circuit changes is 
approximately equal to the speed at which the output from the triangular 
wave generating circuit 12 changes. 
In the voltage control oscillator (VCO) 14, which is constituted by 
utilizing an astable multi-vibrator, when the output from an inverter 38 
is set to Hi, a capacitor C2 is electrically charged and during the 
initial period of the charge, a voltage is generated at a connection point 
N4 of resistors R5 and R7. This voltage is then applied to an inverter 39 
via the resistor R7, thereby setting the output from the inverter 39 to 
Low. The capacitor C2 is further electrically charged and the potential at 
the connection point N4 goes down gradually until it is at Low, thereby 
causing the output from the inverter 39 to become reversed to Hi and 
setting the output from the inverter 38 to Low so that the capacitor C2 
becomes electrically charged in the reverse direction. As this charge in 
the reverse direction progresses, the potential at the connection point N4 
gradually increases until it is at Hi, to reverse the output from the 
inverter 39 to Low and set the output from the inverter 38 to Hi so that 
the capacitor C2 is electrically charged in the forward direction again. 
While oscillation is achieved by repeating this process, the waveform from 
the triangular wave generating circuit 12 or the integrating circuit 13 is 
inputted between the inverters so that the cycle of the output waveform is 
gradually changed in correspondence to the input voltage. In other words, 
as the voltage input between the inverters gradually increases, the charge 
period for the capacitor becomes reduced resulting in the cycle becoming 
gradually shortened, whereas as the voltage becomes gradually reduced, the 
cycle of the output waveform becomes lengthened. As a result, when the 
triangular wave indicated by E in FIG. 7 is inputted to the VCO 14, the 
output from the inverter 38 taken out via T-FF, which is constituted by a 
D-FF (40), will produce the waveform indicated with F in FIG. 7. 
As shown in FIG. 6, in the rectangular wave amplifier 15, a P- MOSFET (41) 
and an N- MOSFET (42) are connected in series to the output line from the 
variable voltage source circuit to input the output from the VCO 14 to the 
gate of the N- MOSFET (42) via an inverter 43 and also to the base of a 
transistor 44. In addition, the output from the variable voltage source 
circuit is inputted to the gate of the P- MOSFET (41) via inverters 45 and 
46. 
If the output from the VCO 14 is at Hi, the output from the inverter 43 is 
at Low and the N- MOSFET (42) is in a discontinuous state (OFF). At the 
same time, the transistor 44 enters a continuous state (ON) and while the 
output from the inverter 45 is at Hi, the output from the inverter 46 is 
set to Low and the P- MOSFET (41) is set in a continuous state (ON). 
Consequently, in this state, the output from the rectangular wave 
amplifier is at Hi as long as the output from the output voltage waveform 
source circuit is at Hi and is at Low as long as the output from the 
output voltage waveform source circuit is at Low. 
Next, when the output from the VCO 14 is set to Low, the output from the 
inverter 43 is set to Hi and the N- MOSFET (42) enters a continuous state 
(ON). At the same time, since the transistor 44 enters a discontinuous 
state (OFF), setting the output from the inverter 45 to Low and the output 
from the inverter 46 to Hi, the P- MOSFET (41) enters a discontinuous 
state (OFF). As a result, in this state, the output terminal of the 
rectangular wave amplifier remains at Low even when the output from the 
variable voltage source circuit is at Hi. 
It is to be noted that R8, C3 and D3 constitute a circuit in which a delay 
occurs only at a fall and R9, C4 and D4 constitute a circuit in which a 
delay occurs only at a rise, so that a time lag is created to ensure that 
the N- MOSFET (42) is turned off before the P- MOSFET (41) is turned on 
when the output from the VCO is set to Hi and that the N- MOSFET (42) is 
turned on after the P- MOSFET (41) is turned off when the output from the 
VCO is set to Low. 
Thus, since the frequency in the output F from the VCO 14 fluctuates as 
indicated in FIG. 7, switching occurs between the FETs (41 and 42) in 
conformance to the fluctuations, and the output from the rectangular wave 
amplifier 15 is set to Hi only when the output from the variable voltage 
source circuit 10 is at Hi and the output from the VCO 14 is at Hi. As a 
result, when a signal by the waveform indicated with F in FIG. 7 is 
inputted to the rectangular wave amplifier, the waveform indicated by G in 
FIG. 7 is produced. 
The source-off detection circuit 16 is constituted by connecting an 
inverter 47 to the output line from the variable voltage source circuit 
10. In other words, when the output from the variable voltage source 
circuit 10 is set to Low, the logic level of the output from the inverter 
47 becomes positive. 
In the output switching circuit 17, the output from the source-off 
detection circuit 16 is inputted to a decode counter 48 and every time the 
source-off detection circuit 16 detects that the source is off, output 
terminals (Q0.about.Q3) at the decode counter 48 are sequentially switched 
to Hi. These output terminals (Q0.about.Q3) of the decode counter 48 are 
connected to the output line from the rectangular wave amplifier 15 via 
FETs (49) and amplifiers 50. 
Thus, when one of the output terminals (Q0.about.Q3) of the decode counter 
48 is set to Hi, its output is inputted to the gate terminal of the 
corresponding FET (49) via the corresponding amplifier 50 and it becomes 
possible to provide the output signal from the rectangular wave amplifier 
15 only to the speakers in the corresponding output system. Then, when the 
output from the variable voltage source circuit 10 is turned off and the 
next output terminal at the decode counter 48 is switched to Hi, it 
becomes possible to provide the output signal from the rectangular wave 
amplifier 15 to the speakers of the newly switched output system. In this 
manner, the output from the rectangular wave amplifier 15 can be provided 
to different speakers sequentially with the switching at the decode 
counter 48, and when the output from the variable voltage source circuit 
10 is turned on, the electrical signal indicated by G in FIG. 7 is 
provided only to the speakers that have been switched to one of the 
outputs (1.about.4) only during the period of time over which the output 
from the variable voltage source circuit is in the ON state to be 
converted to a sound wave motion that includes mechanical vibration, i.e., 
ultrasonic waves. 
In the structure described above, a signal for turning on/off the source is 
generated at the frequency divider circuit 7 from a random pulse generated 
at the low range noise generating circuit 6 and, with this signal, the 
source mute circuit 8 is operated to turn on/off the output voltage from 
the variable voltage source circuit 10. The triangular wave generated at 
the triangular wave generating circuit 12 is converted by the VCO 14 to a 
pulse signal which sweeps without rapidly deviating from a specific 
frequency range, and the rectangular waves amplifier 15 converts the 
output from the variable voltage source circuit 10 during an on period to 
an electrical signal with the same frequency changes, based upon the pulse 
signal from the VCO. In addition, during a period over which the output 
from the variable voltage source circuit 10 is off, the off state is 
detected by the source-off detection circuit 16 and the speaker to which 
the output from the rectangular wave amplifier 15 is to be provided is 
selected by the output switching circuit 17. 
Consequently, the frequency of the electrical signal provided to the 
individual speakers is achieved by extracting a portion of a frequency 
that sweeps within a specific frequency range in a stable manner, and 
while the frequency is not changed rapidly, since the timing with which 
the speakers are switched over and the period over which that portion of 
the frequency is extracted depend upon the low range noise, ultrasonic 
waves with random frequencies are generated within these restrictions to 
prevent the pest animals, such as rats, from becoming accustomed to the 
sound. 
Moreover, since the switching over of the output terminals of the speakers 
is performed during the period of time over which the source remains off, 
noise that would otherwise be generated from the speakers, when switching 
between the output systems, is eliminated. Also, since a plurality of 
speakers are employed to be sequentially selected in correspondence to 
individual output systems, it becomes possible to drive a number of 
speakers with the same source capacity as that in the prior art. As 
measures against noise, it is also conceivable to employ a method in which 
the output signal is muted simply by using an analog amplifier. This 
method, however, is not suited for driving a plurality of speakers since 
an analog amplifier provides inferior power conversion efficiency. In 
addition, if the frequency is simply caused to sweep and a rectangular 
wave amplifier is employed, it is not possible to drive a plurality of 
speakers in the method in the prior art in which ultrasonic waves are 
continuously outputted. This structure is characterized in that a 
plurality of speakers can be driven as well as achieving prevention of 
noise in view of those factors described above. 
While, in reference to the example described above, a structure in which 
the input terminal of the VCO 14 and the output terminal of the triangular 
wave generating circuit 12 are connected to each other via a changeover 
switch 51 is presented, by connecting the integrating circuit 13 and the 
VCO 14, the output F from the VCO is caused to sweep with a random 
frequency period, thereby making it possible to further promote the 
generation of ultrasonic waves with random frequencies. 
Namely, the output voltage from the integrating circuit 13, which changes 
randomly in correspondence to the output from the low range noise 
generating circuit 6, as indicated by E in FIG. 8, for instance, and the 
VCO 14 forms a waveform such as indicated by F in FIG. 8 by randomly 
changing the oscillating frequency with this voltage waveform. 
Subsequently, the same processing as that described above is performed and 
ultrasonic waves with randomly sweeping frequencies are outputted while 
the output systems are sequentially switched over. 
In such a structure, since the frequency is caused to change over time at 
the same rate as that in the case of the triangular wave, no rapid change 
in the frequency occurs just as in the case of the triangular wave, which 
means that no impulse wave results. However, since the frequency variable 
range changes randomly, the frequency in the electrical signal becomes 
dependent upon noise and is set more randomly compared to the case of the 
triangular wave and, as a result, an even greater effect in intimidating 
and repulsing pest animals such as rats is achieved. 
Moreover, since the level of the electrical signal provided to the speakers 
can be adjusted at the voltage adjustment variable resistor 26 for each 
output terminal, regardless of whether a triangular wave or an integrated 
waveform is employed, the outputs of the speakers and the number of 
speakers that are driven can be adjusted in correspondence to the 
particularities of the location where the apparatus according to the 
present invention is installed. Such adjustment includes freely selecting 
the speakers at which the output of the ultrasonic waves is to be halted. 
It is to be noted that, while in the structural example described above, 
four output systems are provided and one transducer 1 is connected to each 
output system so that the four of them can be switched sequentially, 
theoretically there are no restriction imposed upon the number of output 
systems to be provided as long as there are two or more. The number of 
transducers to be connected to each output system, too, may be two or more 
as long as the capacity of the source supports that number of transducers. 
In practical use, it is desirable to provide 2.about.4 transducers at each 
output system. Furthermore, as long as the capacity of the source permits, 
two or more output systems may be switched over at the same time instead 
of switching among a plurality of output systems one system at a time. 
As has been explained, according to the present invention, since a 
plurality of transducers to which power is supplied from a common source 
are selected with random cycles in units of output systems and an 
electrical signal with a frequency that changes randomly can be provided 
to the transducers for a random output period, an advantage of effectively 
intimidating and repulsing pest animals such as rats can be achieved while 
preventing them from becoming accustomed to the ultrasonic waves, as 
happens with the prior art. In addition, since the transducers to which 
the electrical signal is provided are selected by switching over the 
output systems, a greater number of transducers can be driven while 
employing the same source capacity as that in the prior art. Moreover, 
since the switching of the output systems is performed during source 
output off periods, noise that would otherwise be generated from the 
transducers, when the output systems are switched, is eliminated. 
In addition, since the frequency of the electrical signal provided to the 
transducers is made to change over time at a specific rate, transducers 
with lower frequency response characteristics can be employed as long as 
they are of the type that are normally used in the ultrasonic wave range. 
This contributes to a reduction in cost when installing the apparatus 
according to the present invention together with the fact that a large 
number of transducers can be supported with a common source. 
Furthermore, if a means for adjusting the output level of the electrical 
signal is provided in correspondence to each output system, it is possible 
to make free settings such as the change in the output level and the pause 
in the output at each output system depending upon the installation 
location, thereby achieving a pest animal repulsing apparatus with a 
higher degree of versatility.