Hi,

I've received a new accelerometer with a scale factor declared as: 800 mV/g @ 1.5g. I googled and searched the forum but still can't fully be sure I understand the accelerometer and its functioning, so please correct me where I'm wrong:

One thing that very helped me to get some understanding, was this post:

http://tom.pycke.be/mav/69/accelerometer-to-attitude

where you see this:

giving the calculation of:

accelerometer = cos (theta) * gravity

theta = acos (accelerometer / gravity)

Formula is easy and beautiful, and this is my first question please:

what 'gravity' means there? Suppose the robot owning this accelerometer is on Earth surface, then this 'gravity' means 9.8m/s^2?

Next how to relate this to my accelerometer board output please?

I apply a 5V to its board and it has a 10bit ADC, so if I receive:

x(LSB) * 5(V)/1024(LSB)

now to get rid of V dimension I use the scale factor:

x(LSB) * 5(V)/1024(LSB) * (1/{800mV/g})

get rid of 'm':

x(LSB) * 5(V)/1024(LSB) * (1000/{800V/g})

or

x(LSB) * 5(V)/1024(LSB) * (10/{8V/g})

finally:

x*(25/4096)g

questions:

- but this finall scale factor is a very small number! seems wrong
- in data sheet the scale factor is declared: 800 mV/g @ 1.5g

how to take to account the 1.5g? I can imagine when the vertical upward is 1g and vertical downward is -1g, but can't imagine 1.5g. - Am I right with the g unit there? As long as I know, this is an embedded number like 9.8m/s^2 on Earth surface. So finally, having 'g' in both accelerometer and gravity in this formula:

theta = acos (accelerometer / gravity)

we remain with a scalar number and everything stands good at the end of the story, correct?!

Please help to make this clear!