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BOOSTXL-PGA460: Minimizing dead zone

Part Number: BOOSTXL-PGA460
Other Parts Discussed in Thread: PGA460-Q1, PGA460,

Hello,

I am trying to get 3 - 100 Cm distance measurement, with a Beam angle of at least 30 degrees, with a Bi-Static configuration using the transformer method to drive the transducer.

I can get reasonable distance results with  200 kHz Steminc SMATR200H19XDA transducers but the beam angle is too narrow for my Application. I can not find an "off the shelf" 200 Khz transducer with wide beam angle.

when using lower frequency transducers, for example the supplied Murata MA58MF14-7N,  I have noticed that the actual ringing time of the transducer as measured with oscilloscope is much shorter than the ringing time as observed on TI PGA460-Q1 software, I measured 300 micro seconds with oscilloscope and 1000 micro seconds with PGA460 software.

even if I disconnect the receiving transducer I still get long ringing time. I wonder why this happens and how can this be solved.

I have read previous posts in E2E forums regarding this issue and applied all the suggestions with no success, including tuning capacitors, damping resistors and lowering the TVG to a minimum at the ringing time.

I also know that theoretically it is possible and there are also cheap sensors like HC-S04 and equivalents with closed top transducers that measure 3 Cm to 2.5 meter with 40 Khz transducers.

So I wonder, is this due to receiving transducer ringing time or some EM coupling somewhere in the system.

I have 3 action courses in mind:

1. to damp the receiving transducer/circuit

2. to use 2 PGA460 one for bursting and one for listening and synchronizing the 2 PGA460 somehow

3. ask for a custom transducer solution from a transducer manufacturer. 

Do you have any experience and success  with these action courses.

If option 2 is possible what will be the best and fastest method to test it? can I stack two PGA460 on the same MSP-EXP430 Launchpad? how can I synchronize the two PGA460?

Thanks,

Assaf

  • Hi Assaf,

    Thanks for your detailed problem statement. In a bi-static mode on the PGA460, there may still be some internal coupling from the driver block onto the AFE receiver path, even when these two paths are disconnected externally. However, the true ultrasonic energy at the receiving transducer from a return echo should produce a stronger amplitude than the internally coupled driver noise.

    Considering you have done you due-diligence, here my advanced recommendations/debug tips:

    1. Minimize the time varying gain during the burst and decay even though you are using a bi-static mode. This will reduce the false positive created by the internal driver block.
    2. Place a damping resistor in parallel on both the transmitting-transducer and receiving-transducer.
    3. Most high-frequency transducers have very narrow field--of-view patterns as you've noted. You will need to use a low-frequency bi-static transducer with wave-guides to achieve the range and medium field-of-view required. See PGA460 FAQ #4.4.9 ( http://www.ti.com/lit/an/slaa733/slaa733.pdf ) for details on a transducer wave-guide / horn to reduce a transducer's field-of-view.

    Your proposed option 2 could be used as the best case means of driver and receiver isolation, but will require a lot more work. I have been able to see downwards of 3cm in a low frequency bi-static solution using a single device, so I suggest saving your option 2 as a last resort.

    Option 2 comments: I discuss using separate transmitter and receiver PGA460's devices in the PGA460 Array of Ultrasonic Transducers for Triangulation and Tracking app note. You can use one LaunchPad, but you will need another PGA460 board/device to jumper wire to the UART pins. You could technically stack the two PGA460 devices, but you should use an external power supply for both, and ensure the UART_ADDR of both devices are different before attempting to communicate with them. I have some example code for the triangulation and tracking example here: PGA460 Energia Library and Code Example. You don't need the triangulation algorithm aspect of this code; you only need to refer to the broadcast commands to enable parallel burst/listen operation between multiple PGA460 devices.

  • Hello Akeem,

    Thank you for your advise.

    I have now good short distance results, I have built my own custom "daughter card" and the the short distance results are now good..

    I have 2 boostxl-pga460  and in both of them the results were not good and similar with the original daughter cards , so it seems that it is not an issue of just one faulty daughter card but at least a batch or I did something wrong with them  (I desoldered the R36 resistor and Installed the receiver sense transducer element to J14). it is interesting to understand why and if there is some design problem but I did not test it any further.