Questions regarding the ADXL355

Hello everyone,

I'm looking into measuring the vibrations of a large telescope structure. My idea was to use an ADXL355 evaluation board, connect it to a microcontroller (Arduino) and have the data written to SD card. However I want to clarify/confirm a few things before I continue:

1.Resolution: I'm expecting to measure a peak acceleration in the order of 10mg with a frequency in the order of 1Hz. If i understood it correctly, the resolution is limited by noise which in turn is related to the bandwidth, so I probably want to limit my bandwidth in order to achieve higher sensitivity (from my calculation, limiting the bandwidth to 100Hz, with the given noise density of the ADXL355 results in a total noise of 0.3mg).

My question is: Is the bandwidth limit determined by an analogous low pass filter, or by some sort of digital filtering/setting? Also, how can this limit be modified?

2.Interfacing: How "easy" is it to interface the ADXL355 with a microcontroller (eg. via SPI) for someone that is new to the topic?

Thank you in advance for your help

  • QUESTION

    1.Resolution: I'm expecting to measure a peak acceleration in the order of 10mg with a frequency in the order of 1Hz. If i understood it correctly, the resolution is limited by noise which in turn is related to the bandwidth, so I probably want to limit my bandwidth in order to achieve higher sensitivity (from my calculation, limiting the bandwidth to 100Hz, with the given noise density of the ADXL355 results in a total noise of 0.3mg).

    My question is: Is the bandwidth limit determined by an analogous low pass filter, or by some sort of digital filtering/setting? Also, how can this limit be modified?

    ANSWER

    The ADXL355 contains both analog (internal) and digital filters.  The Filter register (see page 37 of the ADXL355 datasheet) provides a user-control for the digital filter.  Table 43 provides some details on the filter options that are available through the digital filter that is in the ADXL355's (internal) signal chain.

  • QUESTION

    2.Interfacing: How "easy" is it to interface the ADXL355 with a microcontroller (eg. via SPI) for someone that is new to the topic?

    ANSWER

    The ADXL355 team ( tagged for comment) is working on a reference design, but I don't think that it is ready yet. So, in the interim, here is what I would recommend to someone who is starting out:

    • You do not need an engineering education to figure this out
    • You do need to be willing to learn and you do need to take personal responsibility for the result. 
    • I would Google search "Arduino ADXL362" and/or "Arduino ADXL345" and spend some time reading through the different search results to get an idea of what it will take to connect the ADXL355 to a processor. 
      • NOTE: As I understand it, the Arduino platform was developed specifically to simplify the use of embedded processors, for non-engineers. 
      • NOTE: The ADXL345 and ADXL362 are very popular SPI-based accelerometers, so there will be tons of examples on the web.
      • NOTE: The packaging, sample rate/filter options, data resolution, ranges and some of the functions differ in the ADXL355, but these examples will provide a nice learning space for you. 
    • This blog may be useful, as it highlights the most common problem areas when paring a digital SPI sensor with an embedded processor: 
      Connecting to Smart Sensors, it Takes More Than Code