Hello,

I am working on the following private project and I would like to get some advice on my thinking about it. Unfortunately, the things I am trying to make does not fall in my area of expertise, thus some help is needed

Objective: Sound generator @ 15kHz frequency.
My thinking: Since I only need one specific frequency I was thinking it would be simple to use a piezo buzzer. However, I have had hard time finding a piezo buzzer that would actually work for this frequency. Maybe someone could suggest something?
OR
Maybe I am going about this completely the wrong way? If you had to design a generator for this specific frequency how would you do it?

Some additional notes: the sound generated can be dirty, meaning that as long as i hit the 15kHz I don't really care much if there are unwanted frequencies present.

Any advice is welcome to get me started thinking in the right direction.

/R

 

Welcome to AAC!
Any decent hi-fi amplifier ought to be able to generate the frequency at a reasonable level, but what output level do you actually need? Would a tweeter be a suitable transducer?

 

Thanks!
I am looking to get at least 90dB.

 

Thanks!
I am looking to get at least 90dB.

That shouldn't be any problem for a good loudspeaker, particularly one with decent tweeters, driven by any mediocre amplifier. Just use a free tone generator app to generate the 15kHz signal.

FWIW, that frequency is not audible to most people, depending on age. Your device may make a good teenager repellant. Perhaps you already know that.

 

Thanks!
I am looking to get at least 90dB.

15 kHz at 90dB? Sounds like it will be very annoying to many, as wayneh mentioned. Just get a microcontroller and some ultrasonic sensors, and you will be able to repel most unwanted people who walk by.

 

Haha, there is no doubt that it will be annoying, but that's not the point
Hmm... thanks for the answers. Maybe I was overthinking it a little bit, but yeah. Don't really have much (or any) experience with audio...

I'm thinking if i could make it W/O MCU. so basically have an IC that would generate PWM at 15kHz, then have an amplifier and a speaker?

Would this work for the speaker: https://www.mouser.ch/ProductDetail...TkJYgZlQcSVWQ9puBTGvySwe/y3j1HgUwbactgYQmdg== ?

 

an IC that would generate PWM at 15kHz

Why PWM? Are you planning to modulate the 15kHz? If all you want is a noise, then a simple square-wave oscillator would probably suffice.

 

I'm thinking if i could make it W/O MCU. so basically have an IC that would generate PWM at 15kHz, then have an amplifier and a speaker?

I recommend a sine wave. A square wave has a lot of higher frequency information. That might all get filtered out by the amplifier or ignored by the speaker if it cannot reproduce it, and be no problem at all. But sending a whole bunch of energy at say 30-50kHz to the speaker may not be something the designers anticipated. Amps are so good these days that some can reach up to 100kHz.

 

If you use a piezo, the square wave will soon become a sinewave

 

Use a 555-timer circuit set for 15kHz. Tap off the signal from the timing capacitor. Use a simple RC low-pass filter with cut-off frequency of 20kHz.
Use audio amplifier, output to high frequency tweeter with a 3.3μF non-polar capacitor in series.

 

A 555 at 15kHz is not going to drive anything.

 

A 555 at 15kHz is not going to drive anything.

Why do you say that?

 

A 555 is only good for 100mA. 3u3 at 15kHz is 3 ohms A tweeter is 8R 11R is going to blow up the chip.
How do expect to get 90dB out of a tweeter ???

 

A 555 is only good for 100mA. 3u3 at 15kHz is 3 ohms A tweeter is 8R 11R is going to blow up the chip.
How do expect to get 90dB out of a tweeter ???

Standard LM555 is good to drive 200mA. You missed the part about "audio amplifier".

For a simple solution, use the LM555 to drive a power transistor to an LC circuit to the tweeter, all running from 12V.
I don't know about the 90dB part. TS will have to do the math.

 

Obviously you have never used a 555. Go and put one in a circuit and drive it at 15kHz and feel it before you post irrelevant information.

 

http://www.uceultrasonic.com/produc...5khz-200w-ultrasonic-power-generator-503.html

Obviously you have never used a 555. Go and put one in a circuit and drive it at 15kHz and feel it before you post irrelevant information.

A standard LM555 will drive 200mA @ 500kHz.

(Obviously I have never used a 555 and don't know what I am talking.)

 

A standard LM555 will drive 200mA @ 500kHz.

(Obviously I have never used a 555 and don't know what I am talking about)

That's right. .

 

A standard LM555 will drive 200mA @ 500kHz.

(Obviously I have never used a 555 and don't know what I am talking about)

That's right. .

With which parameter do you have a disagreement, 200mA or 500kHz?

 

With which parameter do you have a disagreement, 200mA or 500kHz?

Well, they are inter-related. Achieving both at the same time is a bigger challenge than one or the other.

 

How accurate does the 15 kHz have to be? If 5% is ok, here's my vote:

555 operating at 15 kHz, symmetrical square wave circuit with pin 3 driving the timing resistor.
Rt = R1 + R2 = 2.7K fixed + 500 ohm pot = 3.03K near the pot midpoint.
Ct = 0.01 uF.

Pick off the timing capacitor voltage to reduce the energy in the harmonic field.
Coupling capacitor Cc = 1 uF

LM383 or equivalent audio amplifier.

5 W tweeter

ak