I2C and SPI

Automation and Control Sensors Transducers
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1

i bought ADXL 313. while connected to the microcontroller, i see the signal is low compared to my hypotheisis.
I would like your support. The sensor only is connected using SPI and I2C. Thank you so much.

2

Welcome to the forum.

I’ve never worked with an accelerometer so can’t help directly but I saw that SparkFun has a page with a lot of information that may help. SparkFun Qwiic 3-Axis Accelerometer (ADXL313) Hookup Guide - learn.sparkfun.com

3

Can you elaborate a bit more on what you mean by “the signal is low compared to my hypothesis”?

If you are reading lower “g” values than you expected, a simple test is to orient the sensor such that one of the 3 axes are oriented in the vertical direction. Then, with the sensor held static (no motion), you should measure 1g due to the force of gravity. If you do not read 1g, then you are probably not calculating the data correctly.

4

The signal is low compared to my hypothesis : I am reading the vibration of the muscle while flexing my leg. Is there any means to amplify this signal? My signal of interest is 5-50Hz sampled at 1600 Hz ( Both I2C and SPI connection) .
However, i failed to implement the band pass and fixed sampling frequency.
I am reading exactly 1g (9.8 m/s^2) as you said as the sensor is oriented in either direction (x, y, z) and held static.
Thank you.

5

Amplification of data in digitized form is done by multiplying the data by the desired gain factor.

If you are correctly reading the acceleration of gravity, that suggests that the accelerometer and your system for reading its data are working properly. If the accelerations you are measuring with it have an amplitude smaller than you are expecting, a few possible explanations seem likely:

  1. The accelerations being measured simply are smaller than you are expecting.
  2. The added mass of the accelerometer and other components is reducing the acceleration caused by a given force, according to the equation F=M*A
  3. There is a poor mechanical connection between the vibration source and the accelerometer, that is absorbing the vibration and causing measured acceleration values to be lower than expected.
6

Okay, How to fix the sample rate (Data Rate??)

Thank you for the above explanation.

7

The sampling rate for the device is controlled by the data written to the BW_RATE register, described on pages 8 and 19 of the datasheet.