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Topic: Arduino Uno and Accelerometer (Read 2 times) previous topic - next topic

gkilmeedy

I'm new to the Arduino process and I have a Arduino Uno bored got along with the program for the computer.
I want to to take readings from an Accelerometer and be able to display them in a list. How do i go about setting the connection up ? Also do I have to worry about resistors etc..?  Any help really appreciated.

strykeroz

Hi, which accelerometer do you have?
"There is no problem so bad you can't make it worse"
- retired astronaut Chris Hadfield

gkilmeedy

I haven't got one yet as i unsure if certain ones will work with the uno board and leave me room if i was to add something else with it ?

groundfungus

Just about any accelerometer can be made to work with the UNO.  The easiest ones to use are probably the ones with serial output (I2C or SPI).   
I have no direct experience with the serial accelerometers as mine are analog output ones.

The ones with analog output are a bit more difficult than serial because their output at rest is biased  to some positive value so that under negative acceleration they can still output a positive voltage.  Also their full scale output isn't 5 volts.  I had to change Aref for the analog to digital converters to get better resolution.

Most of the accelerometers that are availabe for the UNO will come with a data sheet showing connections and even may have example code.

gkilmeedy

This is what I have to work with,

Measure the Vibrational characteristics of a beam that is fixed at one end and measure the resulting accelerations of the
vibrating beam and then programme a user interface that displays important results such as beam's vibrational response and frequencies.
Help please and thanks

Harristotle

Would this help?

http://forum.arduino.cc/index.php?PHPSESSID=q52f2u615b5fapc5gpe2j3vd17&topic=161649

It is basically an X,Y,Z accelerometer that records to a sd card. I have given a veroboard layout as well, so it should be quite quick to build.

I liked the MMA7260 Accelerometer - it has an analog output. Others are, I'm sure, quite fine. I think it is only a few dollars.

Cheers,
H.

groundfungus

#6
Jul 11, 2013, 05:37 pm Last Edit: Jul 11, 2013, 06:00 pm by groundfungus Reason: 1
The first thing you need to specify is the range of the accelerometer.  A beam fixed on one end and excited will vibrate in only one axis, so a tri-axis is not required.  Why waste sampling time on sensors that don't report useful data?  You will need fast sampling to reproduce the motion of the beam.  The maximum sample rate for a Uno is,ideally,  about 9KHz for one channel (you can go faster with some degradation of accuracy).  That puts the Nyquist frequency about 4.5KHz (one channel, 1.5KHz for 3) .  Will the beam vibrate at a lower frequency than 4KHz?
If so then the Arduino could be fast enough, one channel only,  if there is very little that has to happen between samples.  Where is the data going to be stored?  The Uno has 2K of SRAM.  With out any overhead from the controlling program that's 1000 samples (300 per channel for 3).
Can you specify the properties of the beam and how it will be excited?  Like material, dimensions, etc.  You going to whack it with a hammer or stress and release, or...?  You also need to look at the frequency response of the accelerometer to make sure it will be accurate at the frequency of the vibrating beam.  The MMA7260 mentioned in a prior post is 3dB down at 350Hz. 

liudr

Most accelerometer boards have low pass filters so only give you 10-100 Hz (guessing mostly 20-40Hz). If your beam vibrates too fast you can't use accelerometer, which itself is a beam.

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