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PGA460: Some questions for PGA460

Sungkon Jin
Prodigy 130 points
Part Number: PGA460

Hi,

I would like to use the PGA460 to detect vehicles entering the parking lot.I would like to ask a question below.

1.When a vehicle with ultrasonic parking assistance system enters the parking lot,
   1) Can the error occur if the frequency of the ultrasonic system detecting the vehicle entry is the same as the ultrasonic frequency of the parking assistance system of the entering vehicle?

   2) How can I avoid the error in this situation?

2. Change the internal register value of the PGA460 to change the operating frequency of the ultrasonic transducer from one frequency to another through UART command depending on the situation, for example, 30KHz, 45KHz, 58KHz, 180KHz, 300KHz, 380KHz. Is it possible?

2-1) How long does it take to change to another frequency while operating at one frequency?
2-2) Is it possible without changing circuit components?

3. Is the distance from the detected object to the maximum amplitude of the echo signal? Or is it where you cross the threshold level for the first time?

4. How does the PGA460 measure the width of an object?

5. Can the PGA460 measure the width of the detected object even when the object to be detected is not moving?

Thank you.

  • 0
    TI__Mastermind 27950 points

    Hi Sungkon,

    Responding to your questions:

    1.1) If the center frequency of the parking lot ultrasonic sensor is identical to the vehicle entering the lot, then it is possible to experience interference.

    1.2) To avoid this problem, it is best to randomize the time delta between each burst-and-listen command cycle, or use a high-frequency transducer (+100kHz) since most automotive park assist systems use ultrasonic transducers at <80kHz.

    2.1) Yes, it is possible to update the center frequency of the PGA460 to a value between 30-80kHz or 180-480kHz on the fly through a UART command. The UART interface can be set to a speed of 2.4-115.kBaud. A single register command to update the FREQUENCY register is five frames, where each frame contains a single stop bit, eight data bits, and 2 stop bits (11 bits total per frame).

    2.2) Transducers are high-Q single resonant frequency systems. For example, a tranducer specified for opration at 40kHz will only work at 40kHz, so there is no need to change the frequency value on the fly, unless you have devised a transducer multiplexing system to switch between two different transducers which operate at frequencies.

    3) The first instance of the threshold crossing determines the time of flight value reported by the ultrasonic measurement result command. The PGA460 can report up to eight threshold crossing instances per burst-and-listen command.

    4) Echo width is measured by the duration of how long the echo envelope exceeds the threshold level. The maximum width that can be reported is ~4000us.

    5) Object width is different than echo width. Ultrasonic sensors do not have the built in intelligence to calculate an object's width or size. In general, a large object will return a stronger peak and wider echo width than a small object. When an object is moving, the bigger concern is Doppler shift, which is a shift in frequency. You should set the PGA460 DSP bandwidth to 8kHz, and select a transducer with a wide bandwidth (i.e. +/-2kHz).