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  1. #1
    Join Date
    31st January 2009
    Posts
    5,045

    New, low cost HIGH-G 3-axis digital accelerometer breakout module

    I2C or SPI.

    12-bit representation sensitivity:

    100g mode - 0.049g/digit
    200g mode - 0.098g/digit
    400g mode - 0.195g/digit

    SparkFun Triple Axis Accelerometer Breakout - H3LIS331DL - $9.95

    https://www.sparkfun.com/products/14480

    That's less than the single piece cost ($10.90) for the IC alone:

    https://www.mouser.com/ProductDetail...qkqNUSRA%3d%3d

    IC datasheet:

    http://www.st.com/content/ccc/resour...DM00053090.pdf


    "I don't make jokes. I just watch the government and report the facts." - Will Rogers

    "If you don't read the newspaper, you're uninformed. If you read the newspaper, you're misinformed." - Mark Twain

  2. #2
    Join Date
    18th October 2016
    Posts
    624
    Sweet. I need a few of these to play with.

    TRA L2. I-class record: Vanish 29 with an I224, 14,596ft, Mach 1.92. Video here.
    New I-class record submitted: Vanish 29 with an I224, 14,762ft, Mach 2. Video here.

  3. #3
    Join Date
    22nd January 2009
    Location
    Palo Alto, CA
    Posts
    2,092
    The range and resolution are certainly nice, especially since the range is software-controllable. The power is really low. The other accuracy-related specs aren’t great, though, particularly the +/- 1G zero level. It would be nice to have the sensor be pre-calibrated but this one would clearly need a cal at least at the beginning.
    Adrian Adamson
    Featherweight Altimeters LLC
    www.featherweightaltimeters.com

  4. #4
    Join Date
    31st January 2009
    Posts
    5,045
    Quote Originally Posted by GrouchoDuke View Post
    Sweet. I need a few of these to play with.
    I bought some of these adapters a while back while planning to play with this chip, but got diverted by other projects and didn't manage to get around to it before this product popped up which is cheaper than buying a single unit quantity on Mouser (Digikey has a HUGE minimum purchase number for this accelerometer)!:

    SMD LGA16 QFN16 to DIP16 Adapter PCB Board

    https://www.ebay.com/itm/5pcs-Double...4/171243588331
    "I don't make jokes. I just watch the government and report the facts." - Will Rogers

    "If you don't read the newspaper, you're uninformed. If you read the newspaper, you're misinformed." - Mark Twain

  5. #5
    Join Date
    8th February 2009
    Location
    O'Fallon, IL
    Posts
    113
    Not bad. I have to use a 16-bit ADC with the analog ADXL377 to get these kind of specs. Costs me $40 to run that setup, and it looks like the noise at 1000Hz is even better.

    The zero-g level is pretty rough for this chip. My solution is to calibrate a more sensitive digital accelerometer, and then calibrate the the high-G accelerometer to that chip. Took about a month for me to get that bit of code working well.
    Sparky

    NAR #85720, L3
    Tripoli #12111, L3
    2017 Impulse: 86,532 N-s
    2017 Flights: 26

  6. #6
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
    Posts
    1,496
    Remember when calibrating the sensor you can take a time-averaged reading to get sub-bit resolution. Accuracy improves to the square root of the number of readings. Take 100 readings and average over time and you have improved the noise by a factor of 10. The more time you have for the cal, the better the accuracy of the result. This assumes minimal drift once calibrated, of course.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  7. #7
    Join Date
    8th February 2009
    Location
    O'Fallon, IL
    Posts
    113
    Quote Originally Posted by OverTheTop View Post
    Remember when calibrating the sensor you can take a time-averaged reading to get sub-bit resolution. Accuracy improves to the square root of the number of readings. Take 100 readings and average over time and you have improved the noise by a factor of 10. The more time you have for the cal, the better the accuracy of the result. This assumes minimal drift once calibrated, of course.
    Excellent point. Right now I take 30 samples over 30 seconds. It works well, but I have noticed some variability between successive calibrations. I'll move it up to 300 samples and see what happens.

    I also just re-read the datasheet for this sensor again. Not only is the zero-G pretty rough, but so is the resolution. At the most precise setting, its only 49 mG/LSB or 20 steps per G. For comparison, a 24-G capable LSM303 gets 12 mG/LSB (83 steps per G) and an ADXL377 - ADS1115 combo gets 9 mG/LSB (111 steps per G).
    Sparky

    NAR #85720, L3
    Tripoli #12111, L3
    2017 Impulse: 86,532 N-s
    2017 Flights: 26

  8. #8
    Join Date
    31st December 2009
    Location
    Las Cruces, NM
    Posts
    1,823
    Quote Originally Posted by OverTheTop View Post
    Remember when calibrating the sensor you can take a time-averaged reading to get sub-bit resolution. Accuracy improves to the square root of the number of readings. Take 100 readings and average over time and you have improved the noise by a factor of 10. The more time you have for the cal, the better the accuracy of the result. This assumes minimal drift once calibrated, of course.
    The sqrt improvement in noise assumes a gaussian random noise distribution and no drift in the actual signal over the averaging period. If there are other types of non-random noise sources (common in ADC's) or the sensor has drift (from clock or voltage reference, or temperature, etc), then there's a limit to the improvement from averaging. Look up "Allan Variance".

    Also wanted to mention: that Sparkfun board is not ready for a 100g+ environment. ;-) Considering potting it in epoxy. Also, careful how you mount it because you'll add damping and/oscillations from the fasteners, standoffs, washers, mounting brackets, board material, etc.
    -John

    NAR/TRA L3
    My LinkedIn Profile

  9. #9
    Join Date
    7th February 2009
    Location
    Arlington, TX
    Posts
    1,277
    Quote Originally Posted by SparkyVTFlyer View Post
    I also just re-read the datasheet for this sensor again. Not only is the zero-G pretty rough, but so is the resolution. At the most precise setting, its only 49 mG/LSB or 20 steps per G. For comparison, a 24-G capable LSM303 gets 12 mG/LSB (83 steps per G) and an ADXL377 - ADS1115 combo gets 9 mG/LSB (111 steps per G).
    The AltAcc2 used an 8 bit ADC and ADXL50 and still manages to do a good job controlling deployment.

  10. #10
    Join Date
    23rd January 2009
    Location
    NE Ohio
    Posts
    2,548
    Mechanically its a 400g accelerometer with all the associated tradeoffs you will get by applying it for a smaller range.

    I guess it would be a useful device for measuring av-bay ballistic impact forces into the playa.
    John Derimiggio NAR/TRA L3
    MarsaSystems

  11. #11
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
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    1,496
    Quote Originally Posted by jsdemar View Post
    The sqrt improvement in noise assumes a gaussian random noise distribution and no drift in the actual signal over the averaging period. If there are other types of non-random noise sources (common in ADC's) or the sensor has drift (from clock or voltage reference, or temperature, etc), then there's a limit to the improvement from averaging. Look up "Allan Variance".

    Also wanted to mention: that Sparkfun board is not ready for a 100g+ environment. ;-) Considering potting it in epoxy. Also, careful how you mount it because you'll add damping and/oscillations from the fasteners, standoffs, washers, mounting brackets, board material, etc.
    I did mention drift (implying that calibration was shorter than use too), and yes, Gaussian was a given. Most signal acquisition systems are unless someone hasn't designed them with sufficient headroom and they get clipping. Or if they have a non-linear signal processing chain for that matter.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  12. #12
    Join Date
    31st December 2009
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    Las Cruces, NM
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    Quote Originally Posted by OverTheTop View Post
    I did mention drift (implying that calibration was shorter than use too), and yes, Gaussian was a given. Most signal acquisition systems are unless someone hasn't designed them with sufficient headroom and they get clipping. Or if they have a non-linear signal processing chain for that matter.
    Clipping is a special case which is not really noise. Beyond that, most data acquisition systems have noise that is non-gaussian. Standard semiconductor noise, thermal noise, etc, are gaussian. But quantitizing circuits introduce noise sources that: depend on sample clock jitter, poor board layout, the input signal level, the harmonic nature of the sample frequency vs input signal frequency, and the level of noise present in the input signal itself. Much of this doesn't make sense until you've had to delve into it deeper. For example, you can improve the resolution and spurious non-gaussian noise of an ADC by *adding* gaussian noise to your input signal, about 1/2 LSB worth, or more if you can afford the extra time to average.

    In any event, there aren't many good applications for those high-g accelerometers in rocketry.
    -John

    NAR/TRA L3
    My LinkedIn Profile

  13. #13
    Join Date
    10th July 2007
    Location
    Melbourne, Australia
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    1,496
    Yes, deliberately dithering the signal is a useful technique sometimes.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  14. #14
    Join Date
    11th December 2017
    Posts
    7
    Quote Originally Posted by jsdemar View Post
    Look up "Allan Variance".


    Are you fellow time nut perhaps?

  15. #15
    Join Date
    21st April 2009
    Location
    New Jersey
    Posts
    144
    Finally they went down in price, the ADXL377 on a breakout board is something like $25.
    I worked with the ADXL78 that I soldered on a breakout board together with a cheap ADC ~ $12 to my ATmega328 or Nano, hard to calibrate though.
    I also got good results with the MMA2204KEG on a cheap breakout board ~ $10. If only the MPU6050 had at least 32G it would be great.

    -John


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