How to output an Ultrasonic Square wave?

Discussion in 'The Projects Forum' started by Electronicsrookie, Aug 14, 2012.

  1. Electronicsrookie

    Thread Starter New Member

    Nov 28, 2010
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    Hi all,
    I am currently working on a circuit which aims at producing an ultrasonic sound wave(square) as output. Basically, I (will)use a 555 to produce the wave and amplify(LM358) it to my speaker.
    Before purchasing components, I've tried to output such a wave(from an Arduino Uno) to a piezo element. The problem is I hear it(technically not possible).
    After consulting the data sheet of the piezo element, I've learnt that it outputs from 1khz to 10khz, so I presume it was emitting on this limit.
    My problem is how to output the sound; a real speaker or a tweeter? I plan on using a 9v battery. What component can I use, bearing in mind that the power supply?

    Your help is much appreciated,
    The Rookie xD
     
  2. wayneh

    Expert

    Sep 9, 2010
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    How do you expect anyone to answer when you haven't given the frequency? :rolleyes:

    The LM358 is almost certainly too slow.
     
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  3. BMorse

    Senior Member

    Sep 26, 2009
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    Using a piezo element on this will not work in ultrasonic frequencies, you will need an ultrasonic transducer to accomplish this.... and also, to increase the "output" power of the transducer, drive it with an RS232 to TTL converter IC, have the signal going into one of the TTL TX pins, then connect the Transducer to the RS232 side of the IC.
     
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  4. Electronicsrookie

    Thread Starter New Member

    Nov 28, 2010
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    @Wayneh Sorry. I was thinking about 22khz maximum.
    @BMorse. Ok. But could working at 22khz not have alternative devices? I've seen circuits where people mention the piezo buzzer. Thanks for your help.
     
    Last edited: Aug 14, 2012
  5. crutschow

    Expert

    Mar 14, 2008
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    A high frequency tweeter should readily work for 22kHz. Just make sure you don't exceed its power rating. Parts Express, among others, sells them.
     
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  6. wayneh

    Expert

    Sep 9, 2010
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    The so-called "cool mist" humidifiers use an ultrasonic circuit to atomize the water. It must deliver a fair amount of power to accomplish that. I don't know what you're doing, but maybe that's of interest. They're pretty cheap.
     
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  7. Electronicsrookie

    Thread Starter New Member

    Nov 28, 2010
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    @Wayneh Actually I'm in the brainstorming phase of a very simple project. I want to build a circuit that outputs a sinewave of 22khz through a speaker. You might have guessed it's use(insects repeller. ;)) Thanks for your kind advice. I've been looking at options for generating the wave, wien, maybe even a PIC(waste :/). Could you suggest alternatives based on the fact that I intend to power it from a 9v battery? Thanks again.
    @crutshow Thanks for the advice. I've looked it up and came up with the 1/2" dome tweeter element. Can I send my wave directly to it, or do I need a driver? And will it work based on my 9v supply(battery)? Your help is much appreciated. :)
     
  8. wayneh

    Expert

    Sep 9, 2010
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    Ooh, I was afraid of that. Pretty sure that technology doesn't work. Might keep dogs and cats away, though.
     
  9. crutschow

    Expert

    Mar 14, 2008
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    Depends upon the output power you want. Driving an 8 ohm speaker directly from a 555 (through a large series capacitor to eliminate DC bias) operating from a 9V supply will generate a few hundred milliwatts into the speaker. If you want more than that you will need a driver and perhaps a higher voltage supply (depending upon the power needed).
     
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