Accelerometers

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I want to measure static tilt using a three-axis accelerometer.

Can anyone offer guidance on what level of sensitivity I need to measure a tilt of 0.1 degrees? I'm assuming I will take two axes to keep sensitivity around the full circle.

Cheers,

Joey

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For a tilt sensing accelerometer you will only need an accelerometer with a range of +-1G (assuming the accelerometer is stationary).

Have a look at these app notes for tilt sensing using accelerometers;
http://www.freescale.com/files/s...
http://www.kionix.com/App-Notes/...

Once you have figured out what equation you need to use to calculate tilt angle from gravity, you should be able to solve it for gravity when the tilt is 0.1° degrees to find the change in gravity you need to sense.

As an example, the ADXL345 in high resolution mode (4mg/LSB) is advertised to give you a resolution of <1.0°, so that gives you an idea of the sensitivity you are looking for.

I would have a look at the BMA180 first, which is a very versitle sensor and quite cheap. It has a resolution of 0.125mg/LSB in the +-1G range. It should get you within your goals.

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Assuming x and y are level they should be at 0 Gs (1.65V?). I read the a/d, cvt to volts. subtract the 0G value, multiply by volts2Gs conversion factor, then do atan2(xGs, zGs) for pitch and atan2(yGs, zGs) for roll.

Imagecraft compiler user

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Thanks guys, some useful pointers, but more homework indicated!

Cheers,

Joey

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Just rig it up where its spitting out 4 lines of 3 values: raw a/d, volts, Gs, pitch and roll. You should be able to see the Gs go from 0 pointing sideways to 1.0 pointing up and down. Also print out magnitude sqrt(xGs^2 + yGs^2 + zGs^s). Any miniscule movement makes the magnitude go from 1.00 to 1.something. Very sensitive.

Imagecraft compiler user