Carrier modulation for ultrasound

Discussion in 'The Projects Forum' started by Ruby, May 17, 2014.

  1. Ruby

    Thread Starter New Member

    Oct 29, 2009
    6
    0
    I'm designing a general purpose ultrasonic modulator. Long ago, I built one from McGraw Hills Circuit encyclopedia, using a 555 chip. It generates an square wave carrier, and by feeding pin #5 produce PWM, and thus can Mo/Dem light to sound, though it's output is limited, plus square waves are not too pleasant to listen to. Is there any updated chip option, sine wave, with filter capabilities, and beyond 100khz? Can I get a diagram?
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Modulating pin 5 with a sinewave will produce a sinewave PWM of the output.

    The fact the output is square at ultrasonic frequencies won't matter to your ear as you can't hear th eultrasonic frequency, you will only hear the sinewave modulating the PWM.
     
    Ruby likes this.
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,647
    632
    You could try making a triangle wave generator then passing it through a shaping circuit like the one below.

    [​IMG]

    You could also drive a "sine DAC" such as this one (don't expect a high purity sine wave though).

    [​IMG]
    The Intersil ICL8038, which was replaced with the discontinued and also scarce Maxim MAX038 were both low distortion voltage controlled function generators that can generate sine waves. The newer XR-2207, which is about the same things might be easily obtainable.

    Possible web searches: Sine Shaper, Voltage Controlled Sine Wave
     
  4. Ruby

    Thread Starter New Member

    Oct 29, 2009
    6
    0
    Thank you The RB, though I have a feeling like sort of a "harsh" whisper while I'm in range. Maybe the amplifier circuit spikes, or other noises from the transducer.
     
  5. Ruby

    Thread Starter New Member

    Oct 29, 2009
    6
    0
    Thanks with my heart, mr. DickCappels. Surely don't need my glasses to this huge diagram. I happen to have a dual supply built with two LM317 connected in reverse. It does about 18+-, like at 200 mw (varies power at rising volts), though it doesn't look that much consuming. Will give it a try as soon as summer break! Now, I have used this 4018, for pulse dividing. Always thought it only is good for digital applications. It would be a surprise to see it sine waving. If memory is good, this chip is made of of flip-flops and op-amps.
     
    Last edited: May 17, 2014
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