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TDC7200: Use for distance/proximity sensing above and below water

Rasmus Haase
Prodigy 20 points
Part Number: TDC7200
Other Parts Discussed in Thread: TDC1000

Hi,

I am totally new to the forum so please bear with me if this question doesn't belong here/belongs elsewhere.

I have been looking into the TDC7200 and I was wondering whether it could be used to determine close range distances (in the range of 2 - 15 cm), both in water and in air. I know that the speed of sound is radically different for water and air, but I would think this would be possible to solve with software, as long as the hardware is able to detect the measurements.

So my somewhat two-fold question is: Is it possible to use an ultrasonic transducer design for underwater usage, in air (I couldn't see why not, but I am still new to the whole piezo/ultrasonic transducer area)?

And will the signal recieved be strong enough to trigger the TDC7200 to give a measurement?

If the question is totally of, please let me know, and if possible try to steer me in the right direction.

Any help is much appreciated!

Regards

  • 0
    TI__Mastermind 31655 points
    Hello,

    To clarify, the TDC7200 is only a digital timer. It simply takes in a digital start signal, and a digital stop signal and outputs the time between those signals. It does not have an analog front end to transmit or receive ultrasonic signals. That is what the TDC1000 is for.

    Please see the TDC device FAQ which goes over some of the basics of both devices, and may answer your question about the minimum distance measurable: e2e.ti.com/.../3611.everything-you-need-to-know-for-ultrasonic-tof-liquid-coupled-collateral-tools-designs-faq

    As far as your other question, using a transducer in both air and water is very challenging. The ideal frequency (especially at such a short range) in water will be quite high compared to what will work well in air. Typical distance measurement in water will be done with 1Mhz transducers, and air can be measured with anything from 40khz to 400khz or sometimes more. I think in this case you will be limited by the short range in water, so you will need to use about a 1Mhz transducer there to minimize the ringdown time and provide good resolution in a short distance. 1Mhz will attenuate extremely quickly in air, though, so you will need to drive it with a large voltage to even have a chance of seeing a return echo.

    The TDC1000 only drives up to VDD - 0.3V (VDD max is 5.5V). So you will need some external circuitry to boost that voltage when using a transducer through air. The TDC1000-GASEVM provides a good example of this circuitry, and is described better on its page and in its user's guide which are both linked in the FAQ above.

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 20 points

    Wow, thanks!
    Thank you for the eloborate answer! 
    I will check out the FAQ you linked to in your answer. 
    And thank you for explaining about the frequencies i wasn't aware that specific frequencies are better in air and under water.

    I am considering a setup with to different transducers, wtih the air-transducer being able to withstand submerging, but if that should produce questions I will post them in a different post.

    For now I have marked this issue resolved.

    Thank you!