CN106530909A - Beat frequency generating demonstrating instrument - Google Patents

Abstract

The invention discloses a beat frequency generating demonstration instrument, and in particular relates to the technical field of teaching demonstration appliances. The beat frequency generation demonstration instrument includes power supply, oscillator, power amplifier, speaker and connecting joints. The power supply is 5V ~ 12V DC power supply. The oscillator includes the left oscillator (O _L ) and the right oscillator (O _R ), The speaker includes the left speaker (S _L ) and the right speaker ( _SR ), the connectors include the left connector (BNC _L ) and the right connector (BNC _R ), and the oscillator generates two sets of sine waves with small frequency difference Signals, sinusoidal signals enter the power amplifier for amplification, and the amplified signals are respectively input to the speakers to generate audio, forming a clear "beat" sound. Both the left connector and the right connector are connected to the external device, and the external device will "beat" The sound is converted into a waveform output.

Description

A Beat Frequency Demonstration Instrument

technical field

The invention relates to the technical field of teaching demonstration tools, in particular to a beat frequency generation demonstration instrument.

Background technique

The "beat" (beat) phenomenon is an important physical phenomenon in higher education, and it also has important applications in academic fields such as optics and electromagnetism and in daily life (for example, the measurement of the speed of light by the photobeat method, the determination of the frequency of sound waves or radio waves , musical instrument calibration, monitoring vehicle speed, etc.). But the principle of this phenomenon is very abstract and difficult to understand.

In the teaching process, it is difficult for students to understand the principle of clapping phenomenon when they are invisible and intangible. In the past, some teachers used tuning fork resonance to demonstrate the beat phenomenon (tap two tuning forks with similar frequencies to generate sound waves, and then form the beat phenomenon), but in this process, due to the limitations of the tuning fork itself, the pitch and loudness are difficult to control , the operability is not strong, and the demonstration effect is not obvious.

Contents of the invention

The object of the present invention is to address the above-mentioned deficiencies and propose a beat frequency generation demonstrator capable of visually and intuitively demonstrating the "beat frequency" phenomenon.

The present invention specifically adopts the following technical solutions:

A beat frequency generation demonstration instrument, including a power supply, an oscillator, a power amplifier, a speaker and connecting joints, the oscillator includes a left oscillator and a right oscillator, the speaker includes a left speaker and a right speaker, and the connector includes a left Connector and right connector, the oscillator generates two sets of sinusoidal signals with a small frequency difference, the sinusoidal signals enter the power amplifier for amplification, and the amplified signals are respectively input to the speaker to generate audio, forming a clearer "beat" sound, the left side Both the connecting joint and the right connecting joint are connected with an external device, and the external device converts the "beat" sound into a waveform output.

Preferably, the power supply is provided with a main power switch, the left speaker is provided with a left speaker switch, and the right speaker is provided with a right speaker switch.

Preferably, the main power switch, the left speaker switch and the right speaker switch are all single-pole switches.

Preferably, both the left oscillator and the right oscillator are RC bridge sine wave oscillators.

Preferably, start the beat frequency generation demonstrator:

Close the main switch of the power supply, the left oscillator, the right oscillator and the power amplifier are powered on, and they are in working condition;

Close the right speaker switch, disconnect the left speaker switch, and the right speaker sends out the audio frequency corresponding to ω ₁ generated by the right oscillator;

Close the left speaker switch, disconnect the right speaker switch, and the left speaker sends out the audio frequency corresponding to _ω2 produced by the left oscillator;

Close the left speaker switch and the right speaker switch at the same time, the left speaker and the right speaker send out the audio frequency that is ω ₁ and ω ₂ superimposed by the left oscillator and the right oscillator, produce beat phenomenon;

Connect the left connector and the right connector to the X and Y channels of the oscilloscope respectively for fitting, then you can observe the shooting phenomenon through the oscilloscope for further simulation and analysis.

Preferably, the power supply is a 5V-12V DC power supply.

The beneficial effects of the present invention are: use the circuit design to replace the original sound source, analyze the beating phenomenon, integrate sound and electricity, express the "beating" signal vividly, integrate viewing and listening, and integrate learning into happy;

Adopt RC bridge oscillation circuit, the principle is simple, less components, small size, constant output voltage, small distortion, obvious "beating" phenomenon;

The demonstration instrument is small in size, low in power consumption, and not easily affected by the external environment, so it can be widely used in teaching demonstrations;

The frequency is easy to control, the operability is strong, the design is simplified, and it is easy to debug, which improves the efficiency of the experiment and realizes the stability and accuracy of the beat frequency generation;

This demonstrator can be used with oscilloscopes, multi-functional video stations and other instruments to observe the output waveforms that simulate the phenomenon of "shooting", and transform abstract concepts into visual images.

Description of drawings

Fig. 1 is that this beat frequency produces the structural block diagram of demonstrator;

Fig. 2 is the circuit schematic diagram of this beat frequency generation demonstrator;

Fig. 3 is the schematic diagram of the RC bridge sine wave oscillator circuit;

Figure 4 shows the "displacement-time" curves of two sub-vibrations.

Among them, 1 is the power supply, 2 is the oscillator, 3 is the power amplifier, 4 is the oscilloscope connector, 5 is the left oscillator, 6 is the right oscillator, 7 is the left speaker, 8 is the right speaker, 9 is the left Side connector, 10 is the right connector.

detailed description

The specific embodiment of the present invention will be further described below in conjunction with accompanying drawing and specific embodiment:

As shown in Figure 1-2, a beat frequency generation demonstration instrument includes a power supply 1, an oscillator 2, a power amplifier 3, a speaker and connecting joints. The power supply 1 is a 5V-12V DC power supply, and the oscillator includes a left oscillator 5. (O _L ) and right oscillator 6 ( _OR ), speakers include left speaker 7 (S _L ) and right speaker 8 (S _R ), connectors include left connector 9 (BNC _L ) and right Connector 10 (BNC _R ), the oscillator generates two sets of sinusoidal signals with a small frequency difference, the sinusoidal signals enter the power amplifier for amplification, and the amplified signals are respectively input to the speakers to generate audio, forming a clearer "beat" sound, left Both the connecting joint and the right connecting joint are connected with an external device, and the external device converts the "beat" sound into a waveform output.

The power supply is provided with a main power switch (S ₁ ), the left speaker is provided with a left speaker switch (S ₃ ), and the right speaker is provided with a right speaker switch (S ₂ ).

The main power switch, left speaker switch, and right speaker switch are all single-pole switches.

Both the left oscillator 5 and the right oscillator 6 are RC bridge sine wave oscillators.

Start the beat frequency generation demonstrator:

Close the main switch of the power supply, the left oscillator, the right oscillator and the power amplifier are powered on, and they are in working condition;

Close the right speaker switch, disconnect the left speaker switch, and the right speaker sends out the audio frequency corresponding to ω ₁ generated by the right oscillator;

Close the left speaker switch, disconnect the right speaker switch, and the left speaker sends out the audio frequency corresponding to _ω2 produced by the left oscillator;

Close the left speaker switch and the right speaker switch at the same time, the left speaker and the right speaker send out the audio frequency that is ω ₁ and ω ₂ superimposed by the left oscillator and the right oscillator, produce beat phenomenon;

Connect the left connector and the right connector to the X and Y channels of the oscilloscope respectively for fitting, then you can observe the shooting phenomenon through the oscilloscope for further simulation and analysis.

As shown in Figure 3, the schematic diagram of the RC bridge sine wave oscillator circuit,

The main function of the RC oscillating circuit is to generate two simple harmonic vibrations with similar vibration frequencies, equal amplitudes, and identical phases, paving the way for the synthesis of beat phenomena. The frequency adjustment of the RC series-parallel oscillator is convenient, and the adjustment range is also wide. It is a positive feedback oscillator, and the frequency selection circuit composed of R ₁ , C ₁ , R ₂ , and C ₂ , for the convenience of analysis, take R ₁ ＝R ₂ ＝R, C ₁ ＝C ₂ ＝C, R ₁ , C ₁ series impedance Z ₁ ＝R ₁ +1/jωC ₁ , R ₂ , C ₂ parallel impedance Z ₂ ＝R ₂ /(1+jωR2C2 ), the transmission coefficient Fu in the frequency selective network:

Fu＝U _F /U ₀ ＝Z ₂ /(Z ₁ +Z ₂ )

=1/[(1+R ₁ /R ₂ +C ₁ /C ₂ )+j(ωR ₁ C ₂ −1/ωR ₂ C ₁ )] (1)

When ω ₀ ＝1/RC, ω＝ω ₀ , the specific values of transmission coefficient Fu and phase angle φF can be deduced from the above formula:

Fu＝1/sqrt[(9-j(ω/ω ₀ -ω ₀ /ω))]＝1/3 (2)

φF＝-arctan[(ω/ω ₀ -ω ₀ /ω)/3]＝0 (3)

At this time, the RC series-parallel oscillation output frequency f ₀ =1/2πRC, by changing the values of R and C in the RC feedback loop, different frequency output signals can be obtained.

The RC series-parallel circuit maintains self-oscillating conditions:

(1) Amplitude condition: AF=1 means that the magnitude of the feedback signal is equal to that of the input signal.

(2) Phase condition: ψ=2nπ (n is an integer), indicating that the feedback signal is in phase with the input signal.

When the circuit starts to oscillate, the excitation signal is very weak. At this time, the circuit needs positive feedback, that is, AF>1, and the circuit can start to oscillate. After the vibration starts, the amplitude of the output signal increases gradually. When it reaches the set value, AF=1 must be set to stabilize the output signal amplitude. In the main oscillator circuit, set C ₁ =C ₂ =C, R ₁ is a constant, R ₂ =R ₂ x, change the output signal frequency by adjusting Rx, the output frequency is:

f ₀ =1/[2πC sqrt(R ₁ R ₂ x)] (4)

Assuming R _X >>R ₁ , Fu=1/(2+R ₁ /R _2X )≈1/2 can be obtained from formula (1), and A=1+( R _T +R _P )/R>2, that is, the circuit can start to oscillate if R _T +R _P >R is satisfied. When the output reaches the set value after the vibration starts, let R _T + R _P = R to stabilize the amplitude. In the circuit, R _T is connected in parallel with two diodes, one forward and one reverse. The resistance value decreases, and the two diodes make the circuit automatically play the role of shaking and stabilizing the amplitude.

The main function of the power amplifier circuit is to amplify the signal generated by the RC oscillator circuit, which is the premise of the beat phenomenon. Since the signal output by the RC oscillator circuit is not enough to drive the speaker, its power needs to be amplified to drive the speaker to realize the synthesis and generation of the beating phenomenon.

The 8002A is an audio power amplifier with shutdown mode. 8002A features:

(1) No output coupling capacitors or external snubber circuits are required.

(2) Stable gain output.

(3) External gain setting.

When working at 5V input voltage, the average power on the load (3Ω) is 3W, and the distortion does not exceed 5%. For portable devices, when VDD acts on the shutdown terminal, the 8002A will enter the shutdown mode, and the power consumption at this time is extremely low, and the _IQ is only 0.6uA. 8002A is an audio power amplifier specially designed for high-power, high-fidelity applications. The required external components are few, and it can work under the input voltage of 2.0V ~ 5.5V.

In this beat frequency generation demonstrator,

Set R ₂ , R ₃ , R ₅ , R ₆ , and R ₇ as fixed value resistors;

R ₂ =10KΩ, R ₃ =15KΩ, R ₅ =2.4KΩ, R ₆ =10KΩ, R ₇ =10KΩ;

R ₁ and R ₄ are variable resistors: R ₁ ＝0～100KΩ, R ₄ ＝0～100KΩ;

C ₁ is a variable capacitor: C ₁ =0.01～0.10uF; C ₂ is a fixed value capacitor: C ₂ =0.01uF.

How the left and right oscillators work:

The circular frequencies of the two harmonic vibrations are ω ₁ and ω ₂ respectively, and ω ₁ >ω ₂ , for simplicity, set the amplitude A ₁ =A ₂ =A, and the initial phase φ ₁ =φ ₂ =0. Then the vibration equations are:

y ₁ =Acosω ₁ t (5)

y ₂ =Acosω ₂ t (6)

Combined vibration is

In the above formula It can be regarded as the amplitude of the combined vibration, which changes periodically with time; and the latter in part with Simple harmonic vibration of circular frequency.

Through analysis, it can be seen that the shooting phenomenon has the following characteristics:

(1) The amplitude changes periodically with time, and the cycle is constant, and one change in strength is one beat.

(2) The time of each shot (that is, the cycle of the shot) is:

(3) The circular frequency of combined vibration is:

As shown in Figure 4, a and b respectively represent the "displacement-time" curves of the two sub-vibrations. It can be seen from the figure that at the time _t1 , the phases of the two sub-vibrations are the same; at the time _t2 , the phases of the two sub-vibrations are opposite , the combined amplitude is the smallest; at time t ₃ , the phases of the two vibrations are the same again, and the combined amplitude is the largest again. In c, the dotted line indicates that the amplitude of the combined vibration changes slowly periodically with time, that is, the "beat" phenomenon.

Of course, the above descriptions are not intended to limit the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or replacements made by those skilled in the art within the scope of the present invention shall also belong to the present invention. protection scope of the invention.

Claims (6)

1. A beat frequency produces a demonstrator, characterized in that it includes a power supply, an oscillator, a power amplifier, a speaker and a connecting joint, the oscillator includes a left oscillator and a right oscillator, and the speaker includes a left speaker and a right speaker The connectors include the left connector and the right connector. The oscillator generates two sets of sinusoidal signals with small frequency difference. The sinusoidal signals enter the power amplifier for amplification, and the amplified signals are respectively input into the speakers to generate audio, forming a clearer "" "beat" sound, both the left connector and the right connector are connected to the external device, and the external device converts the "beat" sound into a waveform output. 2. A kind of beat frequency generation demonstrator as claimed in claim 1, is characterized in that, described power supply is provided with main power switch, left side speaker switch is provided with on left side speaker, and right side speaker is provided with right side Speaker switch. 3. A kind of beat frequency generating demonstrator as claimed in claim 2, characterized in that, the main power switch, the left speaker switch and the right speaker switch are all single-pole switches. 4. A beat frequency generation demonstrator as claimed in claim 1, characterized in that, the left side oscillator and the right side oscillator are both RC bridge sine wave oscillators. 5. A kind of beat frequency as claimed in claim 1 produces demonstration instrument, is characterized in that, starts beat frequency and produces demonstration instrument: Close the main switch of the power supply, the left oscillator, the right oscillator and the power amplifier are powered on, and they are in working condition; Close the right speaker switch, disconnect the left speaker switch, and the right speaker sends out the audio frequency corresponding to ω ₁ generated by the right oscillator; Close the left speaker switch, disconnect the right speaker switch, and the left speaker sends out the audio frequency corresponding to _ω2 produced by the left oscillator; Close the left speaker switch and the right speaker switch at the same time, the left speaker and the right speaker send out the audio frequency that is ω ₁ and ω ₂ superimposed by the left oscillator and the right oscillator, produce beat phenomenon; Connect the left connector and the right connector to the X and Y channels of the oscilloscope respectively for fitting, then you can observe the shooting phenomenon through the oscilloscope for further simulation and analysis. 6. A beat frequency generation demonstration instrument as claimed in claim 1, wherein the power supply is a 5V-12V DC power supply.