Amplifying Microcontroller Output for Ultrasonic Transducer?

Discussion in 'The Projects Forum' started by eray, Dec 27, 2012.

  1. eray

    Thread Starter New Member

    Mar 31, 2010
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    0
    hello, i am generating 40khz pulse outputs from microcontroller to send pulses with ultrasonic trandsucer. output is ttl, and i need more voltage and power for ultrasonic transducer. how can i amplify the output?
     
    Last edited: Dec 27, 2012
  2. AfdhalAtiffTan

    Active Member

    Nov 20, 2010
    117
    11
    I'm on the same page as yours, still tinkering the best way...

    What about full-bridged MOSFETs with driver?

    Any opinion guys?
     
  3. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    Yes, a full H-bridge would be a start.

    I believe ultrasonic transducers for power applications are operated with a series inductor which forms a series LC tuned circuit with the transducer's capacitance. This presents a much lower impedance to the driver (at the resonant frequency) and this allows the H-bridge to deliver much more current, and therefore much more power. The extra power is converted into a much higher voltage across the transducer.

    The tuned circuit also converts the square wave from the H-bridge into a sinewave (roughly) across the transducer. So it's a win-win-win situation. Depending on how much power you need, you may not even need a full H-bridge.

    This change will affect the starting and stopping of the ultrasonic output, because the tuned circuit will continue to resonate when the signal stops. You can reduce this effect by reducing the Q of the tuned circuit with a resistor in series with the tuned circuit (or in parallel with one of the elements).

    You also need to make sure that the transducer can handle that much power!
     
  4. AfdhalAtiffTan

    Active Member

    Nov 20, 2010
    117
    11
    I wonder if we could just program the PIC to find the resonance point...
    Hmm...
     
  5. KrisBlueNZ

    Member

    Oct 17, 2012
    111
    14
    That would be possible, but I imagine you would want the transducer to emit a specific frequency, e.g. 40 kHz, and you would tune the resonant circuit to that frequency, perhaps using an adjustable slug inside the inductor, rather than adjust the frequency to the resonant frequency of the tuned circuit.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    I'm on the road so sorry I can't copy links. If you are looking to make some sort of distance sensor you can find existing examples out there by searching out the ping))) sensor.

    The problemis basically to hit the output transducer with a 40 kHz signal and amplify the return echo to make a digital pulse the micro can grab. Either a larger drive or more amplification get you longer distances.

    Ive made such transducers in the past. We would drive the transmitter right from 5v CMOS logic by placing a few (3?) gates or pins in parallel,then use two opamps to get some 60db of gain to drive a transistor on/off to make a digital pulse. Now our sensors were contact sensors to measure liquid level so the coupling for the ultrasonic was near perfect so an open air sensor may need more drive and/or gain. One circuit I just surfed out just uses a simple transistor grounded emitter switch as drive; it places an inductor parallel to the transducer as a crude boost regulator to drive it harder.

    An h bridge and the like are overkill, just slam the transducer at the 40khz rate on and off.

    If you have a higher voltage available you can use that for the transducer section and just a simple transistor switch.
     
    Last edited: Dec 30, 2012
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