Tilt Sensor (Part 3)

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It is possible to run the accelerometer “out of the box”, but the results will be difficult to use without some adjustments and interpretation. Here is a flow diagram of how the accelerometer can be used as a tilt sensor, or, in other words, how to convert the chip position versus gravitational force in degrees.

Run once:

  • Set anolog to digital converters (mV/adc counts)
  • Calibrate offsets (mV)
  • Calibrate sensitivity (mV/Deg)

and for each measurement:

  • Acquire raw adc values
  • Convert raw adc values in mV
  • Subtract offsets
  • Compute accelerations
  • Normalize accelerations
  • Compute tilt angles
  • Display results

Note: Calibration might be quite complex, so that the next coming posts will describe the simplest way of calibrating the accelerometer: the default factory settings shall be used, as per the description from Analog Devices data sheet. Offset shall be equal to half VSS and sensitivity shall be set to 300 mV/G.
Note: These values shall be corrected because of the divider bridge that we are using in order to match the 0 to 1.1 V adc setting.

These fixed calibration parameters will work for the most simple applications; however, manual tuning or automatic tuning will help producing more accurate results for advanced use. These questions shall be described later on.

In addition to the basic tilt angle measurement, we may refine the system by adding:

  • Min/max tilt angle records
  • Alarm and number of tilts (based on fixed threshold)
  • etc.

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