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MMA7455 acceleration values unstable — Parallax Forums

MMA7455 acceleration values unstable

FranciscoTavaresFranciscoTavares Posts: 27
edited 2012-06-04 17:54 in Accessories
I´m having a problem with acceleration values with MMA7455. The values changes too much even when the device is not moving.
I tried to adjust ofsets


Offset values FOR each axis:
'Offset values FOR each axis:
XCal CON 25 'VAR Word
YCal CON 80 'VAR word
ZCal CON 0 'VAR Word




but even so the values for XAccel changes like these ones captured from my accelerometer (see atached figure):
I´m using MMA7455 with a BS2p and with the software MMA7455L 3-Axis Accelerometer Demo (PBasic) v1.0 DEMO#1.bs2
All the axis have unstable values.
However the values seem to be coherent when you move the device. For instance, Z value is 63-69 (1 g) When you move the device you can see the values going from -63 to -69 (-1g).
Accelerometer.jpg
943 x 563 - 295K

Comments

  • kwinnkwinn Posts: 8,697
    edited 2012-06-02 16:27
    I would start by making sure the power supply is stable and noise free by using a battery as input to regulator, and measuring/scoping the output. If that is ok I would take a number of measurements with the accelerometer in each of the 3 orientations to see if the problem is in one axis for all orientations or changes with orientation.
  • FranciscoTavaresFranciscoTavares Posts: 27
    edited 2012-06-03 10:18
    The power supply are two ion lithium batteries and they are both ok. The problem happens to all 3 axis.
  • kwinnkwinn Posts: 8,697
    edited 2012-06-04 17:54
    I would think the only possible problem causes would be electrical noise, external vibration/motion, or a defective chip. Did you take several readings in each orientation?
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