Which accelerometer should i use?

[DatsAbk]

I have the following specifications to be fulfilled accurately:

-0.2mg/LSB-------->Sensitivity
-SPI--------------->Serial interface
-0.02 degrees of accuracy

Most important....I need tutorials or e-docs for understanding how to fetch the data.;-)

 

[MirekCz]

Hi DatsAbk,

You didn't write what range of acceleration you need?
For this kind of operation the only precise and cheap accelerometer I know is the BMA180. You will get this sensitivity with a +/- 1.5g range.
I have got a shop - www.robodudes.com - and I have got both the chips and a ready to use module with a soldered in BMA180 for easy interfacing available atm. I can send you over a simple source code how to start with this chip (althrought using I2C, but the commands to send/receive data will be the same).
If you need more info feel free to PM or email me.

 

[DatsAbk]

Hello MirekCz,

Well a +-10 degree application of tilt sensing is my requirement henceforth even a small g range would do....

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Hello MirekCz,

Well a +-10 degree application of tilt sensing is my requirement henceforth even a small g range would do....

 

[MirekCz]

So this accelerometer will work fine and it's quite easy to interface (just set few registers and then keep reading out the data )
I'm a bit doubtfull if you will achieve 0.02degree accuracy even with very good calibration...

 

[DatsAbk]

Well,could you be kind enough to help me understand coding of MMA9550LT using SPI interface with PIC18......??

There are two user manuals available and i'm messed up as both show different technique for the same

 

[MirekCz]

I saw your other question...
At least the datasheet you provided doesn't show what data should be sent over SPI. It only shows the general singal constrains like transmit speed etc.
You should search for a datasheet with list of registers and their functions, so you can do something like:
Control register 0/1/... - send appropriate settings (like set device for +/-2g, 100Hz continous output etc. - this is usually done only once at the beggining of program)
Data registers x/y/z - read acceleration data from those registers, usually in U2 format.
Without knowing those registers addresses and exact meaning you won't be able to go any further - so search for the appropriate datasheet first.

PS. Please take notice that the accelerometer you selected has got an CPU inside and there are 4 versions with different firmware saved to the CPU so obviously reading out data from those 4 chips might be different. Be sure to get the proper datasheet for your model/firmware.