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how to build an ultrasonic generator

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larry_walker

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Hi friends,

I bought an ultrasonic transmitter, with no model number.
The only reference I have is : ultrasonic speaker 38mm horn.

In the specifications, I found that it works for frequencies between 9 khz and 46 khz (yes, I'm as astonished as you are).
My problem is that I do not know how to build an ultrasound generator.

I intend to build a generator, which will be powered on, each time I stop my car.
The generator should generate sin (or square) waves, between (more or less) 15 khz and 40 khz.
The frequency range should be swept every 5-10 seconds or so (in order to chase away the dogs that approach my car with dire intentions, as well as the weasels that eat up the cables, I need different frequencies, but I don't know the exact values).

Could you, please, give me some pointers to solve my problem?
Thank you in advance.
Larry.

P.S. The ultrasonic speaker needs 2.2 V (volt), 300 mW (mili-watt) and a frequency between 9 khz and 46 khz.
P.P.S. Besides the speaker, I own an Arduino Mega 2560, an Arduino Uno, and a wide range of transistors, resistors, capacitors, triac and opto-couplers, which I learn how to use (I am new to electronics, but I want to invest myself in this domain).
 

larry_walker

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Partially solved : how to build an ultrasonic generator

Hi again,

I found (on some well known commercial websites) the following circuit:
NE555 Pulse Frequency Duty Cycle Adjustable Square Wave Signal Generator HC
See img1.png

I suppose the schematics is, more or less, like in the img2.png, but for the capacitor C3, which is replaced by 4 capacitors, in order to select the frequency range.

I have, however a question : I have to change the frequency continuously, so I need to replace the variable resistors (P1 and P2) by something and I do not know what can I put in place.
I think some of the Analog Outputs of my Arduino boards, but I have no idea how to do that.

Can someone draw me a schematics?
Thanks A LOT in advance.

Larry.

P.S. It would be nice, but not mandatory, to measure the output frequency, using my Arduino boards and a digital display. Do someone know how to do that?
 

betwixt

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I intend to build a generator, which will be powered on, each time I stop my car.
This is worrying! What exactly are you trying to achieve?
Most ultrasonic transducers have a very sharp resonance at one frequency so to advise on how to drive it we need to know what you want to use it for.

Brian.
 

larry_walker

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Hi Brian,

This is worrying! What exactly are you trying to achieve?
I try to build an ultrasonic generator, with (no harmful) high frequencies.
Those frequencies are supposed to be unpleasant for animals.
Most ultrasonic transducers have a very sharp resonance at one frequency ...
The device I bought is a "Horn tweeter", thus a resonance frequency do not apply.
... so to advise on how to drive it we need to know what you want to use it for.
I will use it to protect my car against animals.
I live near a park and I've had twice the cables of my car eaten up by some animals.
Besides, all the dogs in the neighborhood mark their teritory using my car as a landmark.

Thank you in advance for an advice.

Best regards.
Larry.
 

KlausST

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Hi,

Look for a vco. A voltage controlled oscillator.

It generates a signal, the frequency depends on the input voltage.
So if you apply the correct input voltages, then it outputs frequency of 9...46kHz.

If you now use two of those VCO and give the one's output to the other's input, then you generate a frequency sweeping generator.

Klaus
 

Audioguru

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Your piezo horn tweeter sounds awful because it has a few strong resonances. It barely produces frequencies higher than about 18kHz.
If you feed it a powerful signal (MUCH more than 300mW) warbling from 25kHz to 35kHz then in might shoo away nearby animals and cause every dog in your neighbourhood to howl.
 

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larry_walker

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Look for a vco. A voltage controlled oscillator.

Thank you so much Klaus.
I think this is the solution !!!
I found an integrated circuit that looks very promising : ALD2701.
As soon as I built the device, I will provide feedback and mark it "solved" (it may take some time).
 

betwixt

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The ALD2701 doesn't look like a good choice to me. It has a maximum supply voltage of 10V and a maximum output current of 1mA, basically, it's a micropowered op-amp. What you need is a power driver producing ~1W into a low impedance and running from car battery voltage.

For a single frequency I would consider a 555 timer and a small transistor output stage, maybe with transformer matching. If you want to modulate it so the frequency rises and falls, use a second 555 or a 556 which is similar to two 555s in one package. Please keep the minimum frequency > 18KHz or it will annoy people as well as animals!

Brian.
 

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