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Electronics => Electronics => Topic started by: Pierre20 on April 13, 2009, 12:59:51 PM

Title: accelerometer
Post by: Pierre20 on April 13, 2009, 12:59:51 PM

HI

I want use an accelerator to know the gravity in an ambulance.

I don't know how the accelerometer works.

 I have an DE-ACCM3D +/- 3g tri-axis accelerometer. With that, I have an Atom pro 24 and the LCD is SerLCD V2.5

For X axis, the output with a volmeter is 1.67 volt. On the LCD , it is written 359.

I don't understand why I get 359.  What does this number mean ? If the accelerometer doesn't move, I should have 0 gravity for x axis.

How can I get the gravity on the LCD



volts var word
main
adin 0,volts
serout 1,i9600,[254,1, "x = ", DEC volts]
pause 100
goto main

Thanks

Pierre

Title: Re: accelerometer
Post by: TrickyNekro on April 13, 2009, 01:06:20 PM

an accelerometer also shows incline... So the value you get means X is flat....
To measure accelerations such as gravity you need to find the difference on the axis... not the value...
For example... an incline can produce accelerations to a system cause it means that a dynamic energy is stored to the system...
Basically....
Without any motion, when the X axis is vertical it means 1g, and when horizontal 0g....
I don;t really know if all these help you
but I gotta make a try

Title: Re: accelerometer
Post by: paulstreats on April 13, 2009, 06:12:08 PM

well the gravity in an ambulance would be ~ 9.8ms s the same as anywhere else...

what is it you specifically want?

Quote

For X axis, the output with a volmeter is 1.67 volt. On the LCD , it is written 359.

which way up do you have the accelerometer? is the accelerometer moving when you take this reading?

Title: Re: accelerometer
Post by: Pierre20 on April 14, 2009, 04:18:50 PM

Hi

When the accelerometer doesn't move, I get

X axis = 0.02 (ok)
Y axis = 0.02 (ok)
z axis  = 0.98 ???
                                           

Title: Re: accelerometer
Post by: TrickyNekro on April 16, 2009, 05:00:26 PM

Of course!!!

0.98 is earth gravity acceleration...
What's wrong....

Title: Re: accelerometer
Post by: SmAsH on April 16, 2009, 05:15:17 PM

pirre20, your z-axis will always have 9.8 whatever they measure this stuff in. so you will have to make your microcontroller think that that is the normal 'still' position. the easiest way to do this would be with calibration when you turn the bot on.

Title: Re: accelerometer
Post by: Razor Concepts on April 16, 2009, 08:16:10 PM

That must be one nice accelerometer, the Earths standard gravitational force is 9.8 m/s and it looks like yours is spot on.