fredfmah
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Dear experts,
I'm trying to get an equation for tilt angle into a MPU. This is no problem if you can find the equation.
The ADXL103 data sheet is indeed mysterious in that it is about a chip that measures acceleration. and yet gives no formula for the relation between input signal and the output signal. i.e. Input g and output delta mV
I can see that when the chip is flat on the Earth's surface the output is zero , referenced to half of the supply voltage .
This is the information, the useful starting information:
PAGE3
-------
So the DC output is 2.500 V at 0g
The next part of the specification gives SENSITIVITY "typical" as 1000mV/g
PAGES 6 to 8
--------------
Great load of graphs on statistical information which shows sources of error. Great, but this is later when the beast is functioning.
PAGE9
-------
The theory of operation, but still no equation o/p = function(i/p)
PAGE10
---------
All good basic theory on filtering and responses, fine if we know the o/p we are filtering.
Self test mentions that 750mg change in output produces a delta of 750mV, (typical I suppose )
PAGE11
---------
There is a slight whiff of an equation. Just looking at the x-axis response.
"When the accelerometer is perpendicular to gravity, its output changes
nearly 17.5 mg per degree of tilt. At 45°, its output changes at
only 12.2 mg per degree, and resolution declines. "
Going back to PAGE3
'SENSITIVITY "typical" as 1000mV/g'
Taking a mean for my small range of 0º to 15º ; (17.5+12.2)/2 =15mg per degree
So if for example my tilt is 5º then the acceleration, Ax = 75mg
Wait a minute, this is putting the cart before the horse, because
I need to calculate Ax and then I can get the degrees from...
PITCH = ASIN(Ax/1 g)
If anyone can see the relation between tilt_angle and the DC output of this chip, I would be most grateful.
Other wise I'll just have to put it on a wooden table. Tweak the orientation for exactly 2.5000V
Then carefully change the angle with respect to the table in 3 steps of 5º Measure the change in DC output
and interpolate to get the 1degree steps from 0 to 15º
Cheers
Fred
I'm trying to get an equation for tilt angle into a MPU. This is no problem if you can find the equation.
The ADXL103 data sheet is indeed mysterious in that it is about a chip that measures acceleration. and yet gives no formula for the relation between input signal and the output signal. i.e. Input g and output delta mV
I can see that when the chip is flat on the Earth's surface the output is zero , referenced to half of the supply voltage .
This is the information, the useful starting information:
PAGE3
-------
So the DC output is 2.500 V at 0g
The next part of the specification gives SENSITIVITY "typical" as 1000mV/g
PAGES 6 to 8
--------------
Great load of graphs on statistical information which shows sources of error. Great, but this is later when the beast is functioning.
PAGE9
-------
The theory of operation, but still no equation o/p = function(i/p)
PAGE10
---------
All good basic theory on filtering and responses, fine if we know the o/p we are filtering.
Self test mentions that 750mg change in output produces a delta of 750mV, (typical I suppose )
PAGE11
---------
There is a slight whiff of an equation. Just looking at the x-axis response.
"When the accelerometer is perpendicular to gravity, its output changes
nearly 17.5 mg per degree of tilt. At 45°, its output changes at
only 12.2 mg per degree, and resolution declines. "
Going back to PAGE3
'SENSITIVITY "typical" as 1000mV/g'
Taking a mean for my small range of 0º to 15º ; (17.5+12.2)/2 =15mg per degree
So if for example my tilt is 5º then the acceleration, Ax = 75mg
Wait a minute, this is putting the cart before the horse, because
I need to calculate Ax and then I can get the degrees from...
PITCH = ASIN(Ax/1 g)
If anyone can see the relation between tilt_angle and the DC output of this chip, I would be most grateful.
Other wise I'll just have to put it on a wooden table. Tweak the orientation for exactly 2.5000V
Then carefully change the angle with respect to the table in 3 steps of 5º Measure the change in DC output
and interpolate to get the 1degree steps from 0 to 15º
Cheers
Fred
