I'd still like to hear why you couldn't use a smartphone with an app before I'd build a tone generator.

 

This whole thing is normally done with a flyback or feedback oscillator with inductor and a single transistor.

 

This whole thing is normally done with a flyback or feedback oscillator with inductor and a single transistor.

What "whole thing"?

 

I'd still like to hear why you couldn't use a smartphone with an app before I'd build a tone generator.

I don't think a phone can drive an external speaker to 90 dB SPL.

ak

 

This whole thing is normally done with a flyback or feedback oscillator with inductor and piezo diaphragm and a single transistor.
What "whole thing"?

The requirement for 15kHz and 90dB.

 

This whole thing is normally done with a flyback or feedback oscillator with inductor and piezo diaphragm and a single transistor.
What "whole thing"?

The requirement for 15kHz and 90dB.

Now that I see what you are talking about - the hard part is finding a 3-lead piezo element that resonates at 15 kHz.

ak

 

I don't think a phone can drive an external speaker to 90 dB SPL.

ak

I had earlier recommended a standard audio amp for the power. I see no reason to build anything if you string together a function generator, an amp and a tweeter.

 

Agree, that is more than good enough to get a handle on exactly what is needed for the final whatever.

ak

 

standard audio amp for the power. I see no reason to build anything if you string together a function generator, an amp and a tweeter.

Why don't you add a CRAY computer to your string of absurdities.

 

standard audio amp for the power. I see no reason to build anything if you string together a function generator, an amp and a tweeter.

Why don't you add a CRAY computer to your string of absurdities.

The TS says he wants 15kHz at >90dB. I could do that in about 20 seconds by walking upstairs and connecting my iPhone to my home theater, and setting a free function generator app to give me a sine wave at 15kHz.

Do tell why you want to make it more complicated.

 

You are assuming the original poster has a staircase he can walk up.

 

You are assuming the original poster has a staircase he can walk up.

I'm assuming that someone able to get on the internet and join an electronics forum probably has both a smartphone and an audio amp. If not, fine. He's probably got several constraints we haven't heard yet, because that's typical of threads here. We don't learn the real goals until 20 posts in. You've anticipated that he wants a standalone, compact solution and you may be right.

 

How are you going to get an audio amp to drive a piezo tweeter?

It needs about 80v.

Maybe an LM386 will do the job.

 

Hello,

@Colin55 , How can you say that a LM386 can give the 80 Volts?
It has a maximum supply voltage of 15 or 22 Volts depending on the model.
Just have a look at the datasheet.

Bertus

 

Bertus, that was Colin's attempt as sarcasm. He is a regular participant on other fora, one of the things that makes AAC better.

And, he's Australian.

ak

 

To debunk any short comings of the 555-timer as alluded to by detractors, I tested an NE555 timer chip at 5V supply.

For the rated 200mA output, you should be able to drive a 25Ω load.
Running in astable mode at 1MHz, 50% duty cycle with a 15Ω load on output pin-3, the output voltage measured on an oscilloscope was 3.5V.
With 15Ω load, that is 233mA output drive.

There was no appreciable increase in chip temperature using a finger test.

 

There was no appreciable increase in chip temperature using a finger test.

Wow, that changes my understanding of what the 555 is capable of. Impressive.

 

For the rated 200mA output, you should be able to drive a 25Ω load.
Running in astable mode at 1MHz, 50% duty cycle with a 15Ω load on output pin-3, the output voltage measured on an oscilloscope was 3.5V.
With 15Ω load, that is 233mA output drive.

How square was the output?

ak

 

How square is square?

1MHz output


15kHz output


15kHz timing capacitor

 

What use is an output voltage of 3.5v ? You could only use it to power the motor on an electric bike at 20mph.
Test the chip at 12v and 15kHz and feel the heat. At 120mA you can just keep your finger on it and 200mA "blows you away."