LIS3DH sensor high-pass filter question and data refresh rate consultation

yanghaii

LIS3DH sensor high-pass filter question and data refresh rate consultation [Copy link]

 

 I am currently debugging the LIS3DH three-axis acceleration sensor and have come across a few issues. I would like to ask the experts about the main application scenarios: I am going to use this sensor with a data output rate of 1HZ. I use FIFO to store data. When the data is full, an interrupt is generated to prompt the controller to read the FIFO data. I have encountered the following problems: 1. The data output rate is 1HZ. I want to know what the internal acquisition rate is. The data is output once every 1s. Is the data the average value collected by the sensor within 1s (at 1Hz, sometimes when I shake the sensor, the data output does not change, or the change is very small)? 2. After using the high-pass filter, no matter how much the output data rate is adjusted, one out of every three data is 0 for all three axes. This happens repeatedly. I don't know why (it feels like the high-pass filter has filtered out the data, but it is also a common situation when I prohibit placement); 3. What is the difference between the two high-pass filter modes HPM1 and HPM0 00 10? I don't understand the description of the 00 mode reset;

yanghaii

Push yourself up~~~

曹伟1993

Let me answer the first question: the internal acquisition rate is determined by the rate of the bus you use for acquisition, so who knows how long it takes. The second question is, do not turn on the high-pass filter. As for why, read the manual yourself. The third question is more clearly written in the manual, read it yourself.

yanghaii

Cao Wei 1993 posted on 2018-12-20 15:53 Let me answer the first question: the internal acquisition rate is determined by the rate of the bus you use for acquisition, so how often does it happen? Who knows? ...

Thank you, I would like to ask another question, can the data after passing through the high-pass filter not enter the FIFO? Now that the high-pass filter is turned on, the data coming out of the FIFO still does not filter out the DC component,

曹伟1993

yanghaii posted on 2018-12-20 16:07 Thank you, I would like to ask another question, can the data after passing through the high-pass filter not enter the FIFO? Now the high-pass filter is turned on, and the data out of the FIFO...

After turning on the high-pass filter, it can enter the FIFO mode, but it will filter out high-frequency signals. Do you think it can be used?

yanghaii

Cao Wei 1993 posted on 2018-12-20 16:35 After turning on the high-pass filter, it can enter the FIFO mode, but it will filter out high-frequency signals. Do you think it can be used?

After turning on the high-pass filter, the low-frequency signal should be filtered out, and the high-frequency signal can pass through.

littleshrimp

I haven't tested LIS3DH. Generally speaking, if you select 1Hz ODR, the sensor will sleep first, then wake up every second to measure data, output, and then sleep again. The data measured is the data from the start of measurement after wake-up to the completion of measurement. Generally speaking, it is the time corresponding to the maximum ODR of the sensor. For example, the maximum ODR of LIS3DH is 5376, so the time for each sampling is about 168us. The actual time is shorter than this time. You can use the current measurement tool to measure the current waveform of the sensor when it is working.

yanghaii

littleshrimp posted on 2018-12-20 17:41 I haven't tested LIS3DH. In general, if you choose ODR to select 1Hz, the sensor will sleep first, then wake up every second to measure data, output, and then...

littleshrimp

For details about high-pass filters, please refer to this document, page 17 LIS3DH: MEMS digital output motion sensor ultra-low-power high-performance 3-axis "nano" accelerometer AN3308.rar (1.63 MB, downloads: 23)

2018-12-20 17:49 上传

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For Chinese, please refer to the following document, page 15 LIS3DH_ MEMS 数字输出运动传感器.pdf (1.12 MB, downloads: 93)

2018-12-20 17:48 上传

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yanghaii

littleshrimp posted on 2018-12-20 17:41 I haven't tested LIS3DH. In general, if you choose ODR of 1Hz, the sensor will sleep first, then wake up every second to measure data, output, and then...

It doesn't collect data when it's sleeping, right? In other words, if it outputs at 1HZ, theoretically a large part of the acceleration situation cannot be collected? I would also like to ask, when using FIFO output, can the data from the high-pass filter not enter the FIFO? I have now measured that when the FIFO is not used and the high-pass filter is turned on, the DC data can be filtered out, and the data read out from the register (29H---2DH) has the DC component filtered out. However, when using FIFO, the data read out from the register (29H---2DH) does not have the DC component filtered out.

yanghaii

littleshrimp posted on 2018-12-20 17:49 For details about high-pass filters, please refer to this document, on page 17 LIS3DH: MEMS digital output motion sensor ultra-low-power hi ...

OK, thank you, I will study it further~~~~

曹伟1993

yanghaii posted on 2018-12-20 17:12 After turning on the high pass filter, the low frequency signal should be filtered out, and the high frequency signal can pass through.

The high pass filter filters out the high frequency, and there is also a corresponding low pass filter, which is the one that should be turned on.