Note: Descriptions are shown in the official language in which they were submitted.
1318017
This invention relates to a sound responsive
switching device, particularly suitable for responding to the
clapping of hands and other sudden noises.
Devices are commonly used in discotheques and the
like for modulating light intensity in response to sound
level. Such devices generally employ complex circuitry and
vary the light level continuously in response to the
intensity of sound.
An object of the present invention is to provide a
simple sound-responsive switching device device that has
particularly pleasing characteristics.
According to the present invention there is
provided a sound-responsive switching device comprising a
transducer for generating a signal representative of sound
intensity, a primary operational amplifier with positive
feedback provided by a high resistance sensitive to small
currents and a capacitor for ensuring the stability of a
logic state of the operational amplifier said primary
operational amplifier having first and second inputs, said
first input being connected to receive said signal and said
second input being connected to receive a reference voltage,
a secondary operational amplifier acting as a voltage
follower to said main operational amplifier, and switching
means for an external power circuit having stable on and off
status, said switching means being driven by said secondary
operational amplifier into an on or off state in response to
the intensity of ambient sound.
In a preferred embodiment the transducer is piezo-
electric transducer connected such that the state of the
operational amplifier is directly sensitive to the peak
voltage produced by the transducer.
Preferably, the switching device includes two
variable resistances to permit the thresholds for switching
on and the thresholds for switching off to be set at
different levels. The secondary operational amplifier is
conveniently optically coupled to the switching device to
isolate the operational amplifiers from the power circuit.
13180t7
The device is extremely simple in construction
since the operational amplifier serves as a detector, signal
shaper and controller.
The response characteristics of the device are such
that it is particularly pleasing for dance occasions. It
will respond either to hand clapping or to music with a
staccato rhythm. It will also respond to the intensity of
continuous sound, above a certain threshold, by an
oscillation with ~he frequency roughly proportional to the
logarithm of the power of the continuous sound. For music,
the device responds sometimes to rhythm, sometimes to
intensity, in a varied and entertaining manner.
The device can be used to turn off a reading lamp
at night. It can be set so that a loud noise, such as might
be generated by snapping a book shut, will turn off the light
and that sounds of similar intensity will not turn the light
back on.
The device can also be set so that a light can be
switched on and off at a certain rate even in the absence of
sound with a duty cycle determined by the settings of the
variable resistances. For this purpose, the device can, for
example, be used to switch on and off Christmas tree lights
with a more artistic effect than can be obtained with
conventional bimetallic strips.
In the free oscillation mode, the piezo-electric
transducer emits a brief sound each time the device switches
state. This permits the device to serve as a metronome.
The invention will now be described in more detail,
by way of example only, with reference to the accompanying
drawings, in which the single figure is a circuit diagram of
a sound-responsive switching device in accordance with the
invention.
0 1 7
The device shown in the single figure comprisès a
power suppiy stage 1, a control stage 2, and a switching
stage 3.
The power stage 1 comprises input terminals A and B
between which is connected the primary winding of a
transformer 4, the secondary winding of which is connected to
a diode rectifier bridge 5, supplying a voltage stabilizer 6,
provided b~ an integrated circuit no. 7805 manufactured by
National Semiconductors. A smoothing 1000 micro-farad
capacitor is connected across the diode bridge 5. A steady
DC voltage is available at the output of the power supplying
circuit 1.
The control stage comprises a voltage divider 7,
provided by two 180 ohm resistors, a main operational
amplifier 8 (no. 1/4LM324 manufactured by National
Semiconductors) and a secondary operational amplifier 9 (no.
1/4LM324 manufactured by National Semiconductors) acting as a
voltage follower to the main operational amplifier 8.
A piezo-electric transducer 10 is responsive to
ambient sound. Positive feedback for the main operational
amplifier 8 is provided by a variable ~0 meg- ohm resistor 11
in parallel with 0.1 micro-farad stabilizing capacitor 12.
The capacitor 12 ensures that the operational amplifier 8
remains in a stable state for a certain period of time after
switching state.
The inverting input of the operational amplifier 8
is connected to the centre-point of the voltage divider 7,
and the non-inverting input is connected to the piezo-
electric transducer 10, and to the resistor 11 - capacitor 12
combination. The non-inverting input is also connected
through a 10 meg-ohm resistor 13 to the centre-point of a 50
K ohm variable resistor 14 to vary the bias level of the non-
inverting input. A 330 K ohm resistor is connected between
the two inputs of the operational amplifier 8.
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1318017
The secondary operational amplifier 9, acting as
voltage follower, has its non-inverting input connected to
the output of the operational amplifier 8, and an inverting
input connected directly to its output. The output of the
voltage follower operational amplifier 9 is connected through
an LED 15 and a 150 ohm resistor 16 to the supply line of the
power supply stage 1. The light emitting diode 15 no. MOC
3010 is optically coupled to a photo sensitive diode 16
connected through resistor 17 to the gate of triac 18.
1~ Elements 15 and 16 are provided by no. MOC3010 manufactured
by Motorola. The triac 18 connects a power output C, D to
the main power input A, B.
In operation, the peak voltage of the signal
produced by the piezo-electric transducer 10 directly
determines if there will be a change of state of the
operational amplifier 8. This results in the device having a
rapid response to brief sounds, such as hand clapping.
The variable resistor 11 controls the sound level
at which the required sound intensity for switching occurs.
~0 The variable resistance 14 controls the spread between the
switching into the on and off states. For example, switching
can be made to occur such that the device will switch on at a
lower level than off, and vice versa.
The device is particularly desirable and pleasing
on dance occasions. If the two variable resistors are
adjusted so as to have a high threshold for a transition to
the on stage, and a low threshold for the transition to the
off stage, the device is ideal for controlling a night
reading light. A person in bed merely has to close his book
suddenly to switch off the light, which will not come on
again unless he makes a louder noise. A low level noise
occurring in the night will not switch on the light and cause
him to wake up. The control of the sensitivity of the
variable resistor 11 can be such that the device will switch,
and if connected to a lamp the lamp will come on and off, at
-- 4 --
1318017
a certain rate even in the absence of noise~ In this
configuration, the device can be used to control Christmas
tree lights with a certain duty cycle, the resistor 14
controlling the duty cycle and the resistor 11 controlling
the repetition rate, to permit a desired artistic effect to
be produced.
Since the piezo-electric transducer gives off a
brief sound each time the device switches, the device can be
made to serve, for example, as a metronome.
Since the inputs of the operational amplifier are
sensitive to very small currents, the lamp can be switched on
and off by touching these inputs because of the voltages
induced by the stray fields when the person touches.
Continuous touching has an effect equivalent to a continuous
sound (oscillations), while a short touch has an effect
similar to hand clapping (switching on and off). In this
embodiment, the negative feedback input is connected by a
wire to an easy-to-touch metal surface so that the device can
be operated, if necessary, without any sound by touching the
metal surface.
